Dioxins in Food Chain Linked to Breastfeeding Ills
Week Ending FRIDAY June 12, 2009---------------------------News Archive/Return to Today's News Alerts
How Cocaine and Heroin Harm Placenta
Cocaine and heroin increase permeability of the placenta. Researchers writing in BioMed Central's open access journal Reproductive Biology and Endocrinology have shown that exposure to the drugs causes an increase in the passage of some chemicals into the fetus
Antoine Malek led a team of researchers from Zurich University Hospital's Department of Obstetrics, who used a perfusion technique to study human placental tissue function in the lab. They found that exposure to cocaine and/or heroin in the presence of methadone increased transfer of a test chemical called antipyrine across the organ.
"As the consumption of illegal drugs, especially cocaine, is increasing in many countries, our results concerning cocaine and heroin causing an increased antipyrine transfer may improve the practical management in monitoring pregnant women" says Malek.
As complete abstinence is impossible for many people addicted to drugs who become pregnant, maintenance treatment with methadone is often used to limit damage to the developing child.
However, methadone itself can also be dangerous, too much fetal exposure leading to harmful withdrawal symptoms in the newborn. Malek and his colleagues sought to investigate the effects cocaine and heroin on the placenta. They found that while the narcotics didn't increase transfer of methadone, they did allow transfer of other test substances. This suggests the barrier function of the placenta may be compromised.
According to Malek "More toxic substances or bacteria and viruses may cross the placenta and harm the fetus. Previous studies have reported increased prevalence of infectious diagnoses in cocaine-exposed infants".
These results emphasise the fact that pregnant drug users who can't abstain completely must attempt to exclusively use methadone. Combining it with other drugs could cause extra harm to their child.
How Mutations Extend Life Span
In the sense that organisms existing today are connected through a chain of life through their parents, grandparents, and other ancestors almost a billion years back to the first animals of the pre-Cambrian era, an animal’s reproductive cells can be considered to be immortal
These germline cells generate their offspring’s somatic cells other cells involved in all aspects of growth, metabolism, and behavior, which have a set life span and new germline cells that continue on, generation after generation.
Now, in a dramatic finding, researchers from the Massachusetts General Hospital (MGH) Department of Molecular Biology have found that certain genetic mutations known to extend the life span of the C. elegans roundworm induce “mortal” somatic cells to express some of the genes that allow the “immortality” of reproductive germline cells. Their report will appear in the journal Nature and is receiving advance online release.
“C. elegans mutants with extreme longevity accomplish this feat, in part, by adopting genetic programs normally restricted to the germline into somatic cells,” says Sean Curran, research fellow in genetics at MGH Molecular Biology and the study’s lead author. “We know that germline cells are more stable than somatic cells they live longer and are more resistant to stresses that damage other cells and understanding the molecular pathways involved in that stability may someday allow us to devise therapies protective against age-related decline in other tissues.”
Curran is a research fellow in the laboratory of MGH investigator Gary Ruvkun, whose work focuses on the development, longevity, and metabolism of C. elegans, a tiny worm broadly used as a model for studying basic biological systems. Ruvkun and other researchers discovered that simple mutations in genetic pathways conserved throughout evolution can double or triple the life span of C. elegans, and that similar mutations in the corresponding pathways also dramatically extend mammalian life span.
Longevity-associated mutations have been shown to lead to enhanced immune response including increased control of gene expression through RNA interference (RNAi) in somatic cells. Since it is known that RNAi is among the mechanisms underlying germline cells’ enhanced resistance to pathogens and other stresses, the researchers examined whether the reactivation of germline genetic programs was involved in the extended life span of C. elegans mutants.
A series of experiments demonstrated that worms with increased longevity induced by mutations in the insulin-like signaling pathway did exhibit somatic cell expression of genes usually active only in germline cells. The mutant worms also were protected from stresses that damaged the DNA of nonmutant worms.
The researchers also found that inactivating germline-expressed genes in the mutant worms eliminated the increased life span and that longevity-associated mutations in two genes from a different metabolic pathway one involved with detoxification and stress response also increased the expression of germline markers.
“The idea that somatic cells can reacquire genetic pathways usually restricted to germline cells is fascinating, and since germline protection is seen across species, the activity of these genes may play a role in controlling mammalian life span,” says Ruvkun, senior author of the Nature paper. “Understanding the mechanisms involved in this transformation could help us develop new ways to repair and even regenerate key cells and tissues.”
Why Smoking Increases Risk of Heart Disease and Strokes
Researchers at Charles Drew University of Medicine and Science in Los Angeles and Western University of Health Sciences in Pomona have discovered a reason why smoking increases the risk of heart disease and strokes
The study, which will be presented Thursday, June 11 at The Endocrine Society's 91st annual meeting in Washington, D.C., found that nicotine in cigarettes promotes insulin resistance, a pre-diabetic condition that raises blood sugar levels higher than normal. People with pre-diabetes are at greater risk of developing cardiovascular disease.
Theodore Friedman, MD, Ph.D., chief of the endocrinology division at Charles Drew University, said the findings help explain a "paradox" that links smoking to heart disease.
Smokers experience a high degree of cardiovascular deaths, Friedman said. "This is surprising considering both smoking and nicotine may cause weight loss and weight loss should protect against cardiovascular disease."
The researchers studied the effects of twice-daily injections of nicotine on 24 adult mice over two weeks. The nicotine-injected mice ate less food, lost weight and had less fat than control mice that received injections without nicotine.
"Our results in mice show that nicotine administration leads to both weight loss and decreased food intake," Friedman said. "Mice exposed to nicotine have less fat. In spite of this, mice have abnormal glucose tolerance and are insulin resistant (pre-diabetes)."
Studies have shown that smokers who are pre-diabetic have blood glucose levels higher than normal, but not high enough for diabetes, a known risk factor for heart disease. Smokers also have higher rates of diabetes, but it is not directly clear whether smoking is the cause, because there could be other risk factors, Friedman said.
In the tests, however, the mice receiving nicotine developed pre-diabetes and also had high levels of the stress hormone cortisol, which increases blood pressure and blood sugar. The study's authors were able to partially reverse the harmful effects of pre-diabetes by treating the mice with a drug that blunts the action of nicotine.
"Our results suggest that decreasing insulin resistance may reduce the heart disease seen in smokers," Friedman said. "We anticipate that in the future there will be drugs to specifically block the effect of nicotine on insulin resistance."
New drugs are needed because those that are currently available are not specific enough to completely block nicotine's effects or they have bothersome side effects, said Friedman, whose study is one of 34 being featured at The Endocrine Society's 91st annual meeting.
Stress DOES Make Your Hair Go Gray
Those pesky graying hairs that tend to crop up with age really are signs of stress, reveals a new report in the June 12 issue of Cell, a Cell Press publication
Researchers have discovered that the kind of "genotoxic stress" that does damage to DNA depletes the melanocyte stem cells (MSCs) within hair follicles that are responsible for making those pigment-producing cells. Rather than dying off, when the going gets tough, those precious stem cells differentiate, forming fully mature melanocytes themselves. Anything that can limit the stress might stop the graying from happening, the researchers said.
"The DNA in cells is under constant attack by exogenously- and endogenously-arising DNA-damaging agents such as mutagenic chemicals, ultraviolet light and ionizing radiation," said Emi Nishimura of Tokyo Medical and Dental University. "It is estimated that a single cell in mammals can encounter approximately 100,000 DNA damaging events per day."
Consequently, she explained, cells have elaborate ways to repair damaged DNA and prevent the lesions from being passed on to their daughter cells.
"Once stem cells are damaged irreversibly, the damaged stem cells need to be eliminated to maintain the quality of the stem cell pools," Nishimura continued. "We found that excessive genotoxic stress triggers differentiation of melanocyte stem cells." She says that differentiation might be a more sophisticated way to get rid of those cells than stimulating their death.
Nishimura's group earlier traced the loss of hair color to the gradual dying off of the stem cells that maintain a continuous supply of new melanocytes, giving hair its youthful color. Those specialized stem cells are not only lost, they also turn into fully committed pigment cells and in the wrong place.
Now, they show in mice that irreparable DNA damage, as caused by ionizing radiation, is responsible. They further found that the "caretaker gene" known as ATM (for ataxia telangiectasia mutated) serves as a so-called stemness checkpoint, protecting against MSCs differentiation. That's why people with Ataxia-telangiectasia, an aging syndrome caused by a mutation in the ATM gene, go gray prematurely.
The findings lend support to the notion that genome instability is a significant factor underlying aging in general, the researchers said. They also support the "stem cell aging hypothesis," which proposes that DNA damage to long-lived stem cells can be a major cause for the symptoms that come with age.
In addition to the aging-associated stem cell depletion typically seen in melanocyte stem cells, qualitative and quantitative changes to other body stem cells have been reported in blood stem cells, cardiac muscle, and skeletal muscle, the researchers said. Stresses on stem cell pools and genome maintenance failures have also been implicated in the decline of tissue renewal capacity and the accelerated appearance of aging-related characteristics.
"In this study, we discovered that hair graying, the most obvious aging phenotype, can be caused by the genomic damage response through stem cell differentiation, which suggests that physiological hair graying can be triggered by the accumulation of unavoidable DNA damage and DNA-damage response associated with aging through MSC differentiation," they wrote.
THURSDAY June 11, 2009---------------------------News Archive/Return to Today's News Alerts
Pre-pregnancy Depression May Increase Premature Birth
Researchers trying to uncover why premature birth is a growing problem in the United States and one that disproportionately affects black women have found that pre-pregnancy depressive mood appears to be a risk factor in preterm birth among both blacks and whites.
Black women, however, have nearly two times the odds of having a preterm birth compared to white women, according to Amelia Gavin, a University of Washington assistant professor of social work and lead author of a new study that appears online in the June issue of the Journal of Women's Health.
"Preterm births are one of the most significant health disparities in the United States and the overall number of these births increased from 10.6 percent in 2000 to 12.8 percent in 2005," she said.
While there appears to be some sort of link between giving birth prematurely and depressed mood, the study found no cause and effect, said Gavin, who studies health disparities. She believes the higher preterm birth rate among blacks may be the result of declining health over time among black women.
For this study, premature birth referred to any child born after less than 37 weeks of gestation. Normal gestation ranges from 38 to 42 weeks.
Data for the study was drawn from a larger longitudinal investigation looking at the risks for cardiovascular disease among more than 5,000 young adults in four metropolitan areas. The Coronary Artery Risk Development in Young Adults Study also collected information about mental health and pregnancy outcomes. Between 1990 and 1996, 555 women in the larger study gave birth. These women were the subjects in the depression-premature birth study.
"At this point we can't say that pre-pregnancy depressive mood is a cause of preterm birth or how race effects this association," said Gavin. "But it seems to be a risk factor in giving birth prematurely and higher pre-pregnancy depressive mood among black women compared to white women may indirectly contribute to the greater odds of preterm birth found among black women."
In the study 18.1 percent of the black women had a preterm birth compared to 8.5 percent of the white women.
This difference may be the result of what she calls "weathering," or accelerated declines in health due to repeated socioeconomic and political factors.
"What some people experience by being black takes a toll on the physiological system, and over time wear and tear that occurs across neural, neuroendocrine and immune systems as a result of chronic exposure to stressors lead to health disparities for blacks. Some of this may manifest itself in premature birth and low-birth weight," Gavin said.
The study did not look at depressive mood or depression during pregnancy because the larger research project did not collect that data. She hopes to replicate and expand her findings by analyzing data from another study to look at depressive mood prior to pregnancy and childhood poverty to see if those two factors in part explain the black and white difference in preterm delivery. That study also will look at the role antidepressive medication plays in preterm birth.
"My ultimate goal is to incorporate a life course health development framework to examine disparities in birth outcomes," she said. "You have to look at the context of health across the life course of a woman, not just during pregnancy."
The consequences of higher preterm delivery are a growing burden on the health care system and parents. Studies have shown that preterm babies have higher morbidity rates and U.S. preterm birth rates are creeping up with no good explanation.
In the U.S. the population at greatest risk for major depression is women of childbearing age and the onset and course of depression are often intertwined with reproductive events.
A recent national study reported that 8.4 percent of pregnant women in the past year experienced major depression and only slightly more than 14 percent of those women sought treatment for any mood disorder.
Hormone Therapy, Physical Activity Reduce Belly Fat & Body Fat Percentage After Menopause
Older women who take hormone therapy to relieve menopausal symptoms may get the added benefit of reduced body fat if they are physically active, according to a new study
The results were presented at The Endocrine Society's 91st Annual Meeting in Washington, D.C.
The study provides new information on the health benefits of any type of physical activity, not just exercise, said the presenting author Poli Mara Spritzer, MD, PhD, a professor at the Federal University of Rio Grande do Sul in Porto Alegre, Brazil, and chief of the Gynecological Endocrinology Unit at the university's Hospital de Clinicas de Porto Alegre.
After menopause, a woman's percentage of body fat tends to increase and redistribute to the abdomen, Spritzer said. Excess belly fat is a risk factor for diabetes and heart disease.
Postmenopausal women who exercise have a lower percentage of body fat than sedentary women, past research shows. However, Spritzer said less is known about the influence on body fat composition of physical activity in women receiving hormone replacement therapy, or HRT. Some data suggest that estrogen treatment may add to the effect of exercise in reducing fat.
Spritzer and her colleagues studied 34 healthy women who had an average age of 51 years, had experienced menopause for less than 3 years and sought HRT to relieve hot flashes, night sweats and vaginal dryness. They evaluated the women's cholesterol levels, body mass index (BMI), waist circumference (a measure of abdominal fat) and percentage of body fat before and after 4 months of HRT.
The women received estrogen plus progesterone therapy in either non-oral (nasal and vaginal) or low-dose oral preparations. For 6 consecutive days before starting HRT and 6 days at the end of HRT, women wore a pedometer to estimate their level of physical activity. The device measured the steps they took, including walking, working, and doing house chores and leisure activities. They were instructed to not change their usual activities.
Most of the women did not play sports or do any structured physical exercise, according to Spritzer.
Results showed that 24 of the women were physically active - defined as taking 6,000 steps or more per day - and 10 were inactive (less than 6,000 steps a day). For a woman who has a step, or stride, length of 2 feet (60 cm), 6,000 steps would be around 2.25 miles (3.6 km), Spritzer estimated. For active women, the higher the number of steps they took, the lower was their waist measurement and the better their level of "good" (high-density-lipoprotein, or HDL) cholesterol, the authors reported.
The inactive women did not have any changes in body fat or cholesterol. However, when all 34 women were considered in the analysis, body fat still declined significantly after HRT.
"Data from our study suggest that active women could benefit from hormone therapy beyond the relief of menopausal symptoms - by preserving a good body fat percentage and distribution," Spritzer said. "Further studies with a larger number of subjects are needed in order to answer whether a specific physical activity is better than others."
Bisphenol A (BPA) Exposure in Pregnant Mice Permanently Changes DNA of Offspring
Exposure during pregnancy to the chemical bisphenol A, or BPA, found in many common plastic household items, is known to cause a fertility defect in the mother's offspring in animal studies, and now researchers have found how the defect occurs
The results of the new study will be presented Saturday at The Endocrine Society's 91st Annual Meeting in Washington, D.C.
The study, funded partly by the National Institutes of Health, joins a growing body of animal research showing the toxic health effects of BPA, including reproductive and developmental problems. Last August the U.S. Food and Drug Administration found BPA to be safe as currently used but later said more research on its safety is needed.
BPA is used to make hard polycarbonate plastic, such as for baby bottles, refillable water bottles and food containers, as well as to make the linings of metal food cans.
BPA has estrogen-like properties and in pregnant animals has been linked to female infertility.
"The big mystery is how does exposure to this estrogen-like substance during a brief period in pregnancy lead to a change in uterine function," said study co-author Hugh Taylor, MD, professor and chief of the reproductive endocrinology section at Yale University School of Medicine.
To find the answer to that question, Taylor and his co-workers at Yale injected pregnant mice with a low dose of BPA on pregnancy days 9 to 16. After the mice gave birth, the scientists analyzed the uterus of female offspring and extracted DNA.
They found that BPA exposure during pregnancy had a lasting effect on one of the genes that is responsible for uterine development and subsequent fertility in both mice and humans (HOXA10). Furthermore, these changes in the offspring's uterine DNA resulted in a permanent increase in estrogen sensitivity. The authors believe that this process causes the overexpression of the HOXA10 gene in adult mice that they found in previous studies.
The permanent DNA changes in the BPA-exposed offspring were not apparent in the offspring of mice that did not receive BPA injection (the controls). This finding demonstrates that the fetus is sensitive to BPA in mice and likely also in humans, Taylor said.
"We don't know what a safe level of BPA is, so pregnant women should avoid BPA exposure," Taylor said. "There is nothing to lose by avoiding items made with BPAand maybe a lot to gain."
BPA May Cause Heart Disease in Women, Research Shows
New research by a team of scientists at the University of Cincinnati (UC) shows that bisphenol A (BPA) may be harmful for the heart, particularly in women
Results of several studies are being presented in Washington, D.C., at ENDO 09, the Endocrine Society's annual meeting, June 10-13.
A research team lead by Scott Belcher, PhD, Hong Sheng Wang, PhD, and Jo El Schultz, PhD, in the department of pharmacology and cell biophysics, found that exposure to BPA and/or estrogen causes abnormal activity in hearts of female rats and mice.
In addition, these researchers found that estrogen receptors are responsible for this affect in heart muscle cells.
"There is broad exposure to bisphenol A, despite recognition that BPA can have harmful effects," Belcher says. "We had reason to believe that harmful cardiovascular affects can be added to the list."
BPA, an environmental pollutant with estrogen activity, is used to make hard, clear plastic and is common in many food product containers. It has been linked to neurological defects, diabetes and breast and prostate cancer.
Using live cultures of cells isolated from rat or mouse hearts, researchers briefly exposed the cardiac cells to BPA and/or estrogen. Both compounds caused striking changes in the activity of cardiac muscle cells from females but not males. Additional studies revealed that these cellular changes in activity caused improperly controlled beating in the female heart.
"Low doses of BPA markedly increased the frequency of arrhythmic events," Belcher says. "The effect of BPA on these cardiac arrhythmias was amplified when exposed to estradiol, the major estrogen hormone in humans."
The mechanism underlying this harmful effect was investigated using cellular imaging techniques.
"BPA and/or estrogen rapidly stimulated contraction by altering control of the concentrations of free calcium inside the heart cell but only in heart muscle cells from females, showing that these effects were sex-specific," Belcher says. "BPA's presence increased the frequency of calcium 'sparks' from the sarcoplasmic reticulumthe part of the cardiac muscle that stores and releases calcium ionsindicating spontaneous release or 'leak' that's likely causing the heart arrhythmias and may have other harmful actions, especially following heart attack."
Belcher and colleagues also investigated the nature of the mechanisms that mediated the responses of the cardiac muscle cells to estrogen and BPA.
"Pharmacological studies using selective estrogen receptor drugs and animal models lacking estrogen receptors were used to investigate the role of each estrogen receptor in mediating the rapid sex-specific function effects of E2 and BPA in cells," he says. "Our findings suggest that estrogen has opposing actions in cardiac cells.
"In female cardiac muscle cells, the blocking or genetic removal of estrogen receptor beta completely blocked the contractile effects of BPA and estrogen, while in males, blockade of the effects of estrogen receptor alpha caused the male heart to become more 'female-like' and become responsive to estrogen and BPA.
"These studies have identified new and important potential cardiac risks associated with BPA exposure that may be especially important for women's heart health," he says.
The Placental Origin of Blood Stem Cells - HSCs
Hematopoietic stem cells (HSCs) are generated in the placenta, before the circulatory system is fully operational, researchers report is this week's issue of Cell Stem Cell. The finding offers researchers a better shot at defining the microenvironment required to grow HSCs in vitro
Researchers have known that the placenta holds a reserve of HSCs, and had observed that when placental HSCs decline in number, the liver's reserve expands.
Katrin Rhodes at the University of California, Los Angeles (UCLA) and colleagues, showed that the placenta produces HSCs de novo, rather than simply acting as a "HSC kindergarten," said Hanna Mikkola from UCLA, the principal investigator of the study.
In the past, it had been difficult to determine the exact location of HSC generation, because blood circulation begins at the same stage of development that HSCs appear.
The researchers used a knockout mouse that lacks a heart beat and the ability to circulate blood in order to capture HSC formation before blood flow confused the picture. They then stained for surface molecules of developing HSCs, which revealed two different HSC areas in the placenta, one that generated HSCs de novo, and another where HSCs replicated.
These results have important implications for patients, because appropriate bone marrow donors are hard to find, and the alternative, cord blood, yields a relatively low number of HSCs.
Only fetal HSCs replicate into more HSCs, whereas adult HSCs differentiate into the different blood cell lineages.
By learning more about the microenvironments that nurture different stages of the HSC life-cycle, researchers hope to reproduce the signals that push HSCs into a self-regenerating program for therapy.
WEDNESDAY June 10, 2009---------------------------News Archive/Return to Today's News Alerts
Too Few Women in Clinical Trials?
Do cancer-drug studies fail to reflect true incidence of disease in the population? Nature magazine asks the question
It appears that women are under-represented in cancer studies. A survey of clinical research suggests that women are not getting fair access to experimental drugs. The reasons run from women's practical limitations as mothers with low paying incomes dropping out of trials - to ingrained 'old boy's club' preferences in medicine.
Reshma Jagsi is an oncologist at the University of Michigan Medical School who specializes in breast cancer. She led this survey on clinical trials for other types of cancer, to find whether a fair proportion of women are represented in the often several year process of testing cancer medications.
After reviewing a sample of hundreds of studies, covering more than half a million participants, Jagsi's research found that 75% of the studies under-represented women. In studies on seven different cancer types, six under-represented women often by as much as a third. Given that 45% of lung-cancer affects women, but about 31% of lung-cancer study participants were women - drug trial results were not fully representing women's cancer response to the drug. Research results are published in the journal Cancer1.
Male and female physiology can affect drug responses radically. The anti-cancer drug erlotinib (Tarceva) works better in women than in men. But why is not fully understood. The reasons for the under-representation are similarly unclear. The sensitivity of eggs in the ovary and the possibility of pregnancy during a trial exclude women of child bearing age from some studies. But, Jagsi notes. "By protecting them from research, we're excluding them" which could also mean these women won't have equal access to new drugs potentially capable of saving their lives.
It has been found that women with childcare responsibilities cannot afford to pay the additional costs of babysitters and transportation to participate in clinical trials. Some suggest this population should be compensated for their time to improve their representation. However, clinical trials already have the burden of skewing results towards the largest population responding. If a new population responds for financial reward, won't the results be similarly skewed in that direction? Similar problems affect pediatrics as many drugs are tested entirely on adults, leaving issues of dosing, side effects and efficacy of these drugs in children unstudied and children without access to potentially life saving, or enhancing, medications.
The US National Institutes of Health (NIH) instigated an act in 1993 intending to balance the numbers of women and enable independent gender-linked results for analysis. Jagsi's study notes that "It has been [more than] 15 years [since the act] and we're still seeing a persistent problem."
Super-Resolution Microscopy Captures Molecules in Motion
A new twist on a sophisticated light microscopy technique is enabling researchers to capture short videos of fast-moving cellular processes while delivering super high resolution images of whole cells
The new microscopy technique, developed by scientists at the Howard Hughes Medical Institute’s Janelia Farm Research Campus, captures up to 11 images per second. It is reported in the May 2009 issue of the journal Nature Methods.
Optical microscopesthe kind that use light and glass lenseshave been around since the late 1500s. Although ideal for looking at live samples, these scopes all run up against the same wall: they cannot distinguish objects that are closer to each other than about 200-nanometersone-500th of the width of a human hair. That may sound small, but the complicated molecular machinery inside cells is even smaller.
The basic problem is something called the “diffraction limit.” Light is a wave and the microscope runs into trouble when the distance between objects of interest is less than half the wavelength of the light. Until the 1990s, the diffraction limit was considered a law of nature. Once scientists realized they could in effect break the law, the field of super-resolution light microscopy took off.
One HHMI researcher leading the charge is Mats Gustafsson, who is now a group leader at Janelia Farm. In 2000, while at the University of California, San Francisco (UCSF), Gustafsson introduced structured-illumination microscopy or SIM. The technology takes advantage of moiré patterns, which are produced by overlaying one pattern with another. Two rows of chain-link fencing seen from a distance can produce a moiré pattern, as can overlapping layers of gauzy curtains.
In structured-illumination microscopy, the sample under the lens is observed while it is illuminated by a pattern of light (more like a bar code than the light from a lamp). Several different light patterns are applied, and the resulting moiré patterns are captured each time by a digital camera. Computer software then extracts the information in the moiré images and translates it into a three-dimensional, high-resolution reconstruction. The basic idea has been around since the 1960s, but wasn't fully realized until recently.
At UCSF, Gustafsson used SIM to visualize the molecular scaffolding that holds the shape of cells, with two-fold better resolution than a conventional microscope. Since then, his group has improved its resolution and also introduced three-dimensional SIM, making it possible to see parts of cells that go undetected using most light microscopes.
Until now, SIM was too slow to image living cells, whose inner parts are constantly in motion. “I’ve given talks on structured illumination microscopy as a means of generating high resolution images of fixed cells for several years,” says Gustafsson. “The first question after my talks is always, ‘Can you do this live?’ We wanted to answer that question with ‘Yes.’”
Now he can, thanks in part to the addition of a liquid crystal spatial light modulator, a half-inch-sized mirror-like device that generates patterns of light using thousands of pixels that the researchers can control individually. Spatial light modulators are similar to liquid crystal displays in televisions and laptops, except that Gustafsson used a version with a much faster (sub-millisecond) response time. “That is precisely what we needed,” Gustafsson says. With this part in place, a microscope can generate new patterns of light about 1,000 times faster than the original SIM equipment.
After adding the spatial light modulator to their microscope, they used it to visualize microtubuleslong, thin filaments that provide structure and support to cells in living fruit fly cells. They could see individual microtubules moving as the cell’s skeleton reorganized itself to prepare for cell division. At 100-nanometer resolution, SIM revealed much more detailed images than could be obtained by traditional methods for live cell imaging.
To see if they could capture a faster moving target, Gustafsson’s team tried live SIM on kinesins, proteins that carry cellular supplies along microtubule “tracks” at a blistering pace of about a micron per second. Microtubules and kinesins also help get cells ready to divide.
By setting the light intensity and exposure frequency just right, the researchers could see the kinesin zipping over the microtubule. They recorded the event by capturing images from the microscope at 11 frames per second for several hundred frames. “I was excited to see that we could image moving kinesin, which is one of the most rapidly moving processes in a living cell,” Gustafsson says. “If we can image kinesin, we should be able to image most other cell processes.”
In recent years, other groups have tweaked super-resolution methods, each of which has unique advantages, Gustafsson says. For example, researchers who developed Stimulated Emission Depletion (STED) microscopy have made it possible to take videos of live cellular processes with 60 nanometer resolution. Unlike SIM, however, STED is limited to a small field of view. “We think this technique fits a niche where you want to simultaneously have high frame rates and large imaging areas,” he says.
The technique can be adjusted to fit individual researchers’ needs. Gustafsson has started collaborations with researchers who plan to use SIM to see how cells migrate toward or away from chemical targets. And although the research reported in Nature Methods used 2D-SIM, 3D-SIM is also on the horizon. Gustafsson says this will require making adjustments to the hardware and taking more images per frame.
Gustafsson acknowledges that the technical details of his new technique may be a bit obscure, but the point, he says, is not: “Look, this technique gives you twice the resolution of the normal microscope, looking at a whole cell at 10 frames per second, and that’s just plain cool.
Exposure to dioxins during pregnancy harms the cells in rapidly-changing breast tissue, which may explain why some women have trouble breastfeeding or don’t produce enough milk, according to a University of Rochester Medical Center study
Researchers believe their findings, although only demonstrated in mice at this point, begin to address an area of health that impacts millions of women but has received little attention in the laboratory, said corresponding author B. Paige Lawrence, Ph.D., associate professor of Environmental Medicine and of Microbiology and Immunology at URMC.
“Estimates are that three to six million mothers worldwide are either unable to initiate breastfeeding or are unable to produce enough milk to nourish their infants,” Lawrence said. “But the cause of this problem is unclear, though it has been suggested that environmental contaminants might play a role. We showed definitively that a known and abundant pollutant has an adverse effect on the way mammary glands develop during pregnancy.”
Dioxins are generated mostly by the incineration of municipal and medical waste, especially certain plastics. Most people are exposed through diet. Dioxins get into the food supply when air emissions settle on farm fields and where livestock graze. Fish also ingest dioxins and related pollutants from contaminated waters. When humans take in dioxin most often through meat, dairy products, fish and shellfish the toxin settles in fatty tissues; natural elimination takes place very slowly. The typical human exposure is a daily low dose, which has been linked to possible impairment of the immune system and developing organs.
In 2004 Lawrence’s laboratory made the novel discovery that dioxin impairs the normal development of mammary glands during pregnancy. However, the underlying mechanisms were unclear, as was the extent of injury and whether exposure during certain stages of pregnancy had more or less of an impact on milk production.
This week, in an online report in Toxicological Sciences, researchers showed that dioxin has a profound effect on breast tissue by causing mammary cells to stop their natural cycle of proliferation as early as six days into pregnancy, and lasting through mid-pregnancy. In tissue samples from mice, exposure to dioxin caused a 50-percent decrease in new epithelial cells. This is important, Lawrence said, because mammary glands have a high rate of cell proliferation, especially during early to mid-pregnancy when the most rapid development of the mammary gland occurs.
Researchers also found that dioxin altered the induction of milk-producing genes, which occurs around the ninth day of pregnancy, and decreased the number of ductal branches and mature lobules in the mammary tissue.
The timing of dioxin exposure also seemed to be significant, the study noted. For example, when exposure occurs very early in pregnancy but not later, lab experiments showed that sometimes the mammary glands can partially recover from the cellular injury. However, although it is important to understand timing of exposure for research purposes, it is irrelevant for humans, who cannot really control their exposure to dioxins, Lawrence said.
“Our goal is not to find a safe window of exposure for humans, but to better understand how dioxins affect our health,” she said. “The best thing people who are concerned about this can do is think about what you eat and where your food comes from. We’re not suggesting that we all become vegans - but we hope this study raises awareness about how our food sources can increase the burden of pollutants in the body. Unfortunately, we have very little control over this, except perhaps through the legislative process.”
Much of Lawrence’s research focuses on a transcription factor known as aryl hydrocarbon receptor, or AhR.When pollutants enter the body they bind to AhR, which then turns on certain genes responsible for detoxification. By using dioxin to activate AhR, researchers have learned that dioxin impairs the ability to fight off infection. The link between dioxin and the immune system is still being studied, but meanwhile researchers looked further at the mammary tissue after observing coincidentally that cells involved in milk production were sustaining so much damage that rodents could not nourish their offspring.
The next step is to understand what controls the differentiation process. An important question to answer, Lawrence said, is whether the toxic harm is occurring directly in the breast, or if it occurs throughout the entire body but has a unique manifestation in the fatty mammary tissue.
Embryology Study Offers Clues to Limb Birth Defects
The study showed that retinoic acid controls the development (or budding) of forelimbs, but not hindlimbs, and that retinoic acid is not responsible for patterning (or differentiation of the parts) of limbs
Gregg Duester, Ph.D., professor of developmental biology at Burnham Institute for Medical Research (Burnham), along with Xianling Zhao, Ph.D., and colleagues, have clarified the role that retinoic acid plays in limb development. Their research corrects longstanding misconceptions about limb development and provides new insights into congenital limb defects. The study was published online in the journal Current Biology on May 21.
In studies of mice and zebrafish, the team found that retinoic acid suppresses the gene fibroblast growth factor 8 (Fgf8) during the period when forelimb budding occurs, creating a suitable environment for the creation of forelimb buds.
“For decades, it was thought that retinoic acid controlled limb patterning, such as defining the thumb as being different from the little finger,” said Dr. Duester. “However, we have demonstrated in mice that retinoic acid is not required for limb patterning, but rather is necessary to initiate the limb budding process. We also found that retinoic acid was unnecessary for hindlimb (leg) budding, but was needed for forelimb (arm) budding.”
Congenital birth defects of the arms, legs, hands or feet result from improper development of limb bud tissues during embryogenesis. These processes are regulated by signaling molecules that control the growth and differentiation of progenitor cells by regulating specific genes.
One of these signaling molecules is retinoic acid, a metabolite produced from vitamin A (retinol), which plays a key role in the development of limbs and other organs. Dr. Duester's lab was instrumental in identifying Raldh2 and Raldh3, the genes responsible for retinoic acid synthesis, and has shown that retinoic acid is only produced by certain cells at precise stages of development.
In the study, the team of scientists showed that mice missing the Raldh2 and Raldh3 genes, which normally die early and do not develop limbs, could be rescued by treatment with a small dose of retinoic acid. However, forelimb development was stunted, suggesting that retinoic acid is required for forelimb but not hindlimb development. In zebrafish, the forelimb (pectoral fin) is also missing in retinoic acid-deficient embryos, but they were able to rescue fin development by treating such embryos with a drug that reduces fibroblast growth factor activity, thus supporting the hypothesis that retinoic acid normally reduces this activity.
By providing a more complete understanding of the molecular mechanisms involved in normal limb development, these findings may lead to new therapeutic or preventative measures to combat congenital limb defects, such as Holt-Oram syndrome, a birth defect characterized by upper limb and heart defects.
TUESDAY June 9, 2009---------------------------News Archive/Return to Today's News Alerts
Women May Not Be So Picky After All About Choosing a Mate
Men and women may not be from two different planets after all when it comes to choosiness in mate selection, according to new research from Northwestern University.
When women were assigned to the traditionally male role of approaching potential romantic partners, they were not any pickier than men in choosing that special someone to date, according to the speed dating study
That finding, of course, is contrary to well-established evolutionary explanations about mate selection. An abundance of such research suggests that women are influenced by higher reproductive costs (bearing and raising children) than men and thus are much choosier when it comes to love interests.
The new study is the latest research of two Northwestern psychologists whose well-reported work on speed dating offers unparalleled opportunities for studying romantic attraction in action.
Deviating from standard speed-dating experiments - and from the typical conventions at professional speed-dating events - women in the study were required to go from man to man during their four-minute speed dates half the time, rather than always staying put. In most speed-dating events the women stay in one place as the men circulate.
“The mere act of physically approaching a potential partner, versus being approached, seemed to increase desire for that partner,” said Eli Finkel, associate professor of psychology in the Weinberg College of Arts and Sciences at Northwestern and co-investigator of the study.
Regardless of gender, those who rotated experienced greater romantic desire for their partners, compared to those who sat throughout the event. The rotators, compared to the sitters, tended to have a greater interest in seeing their speed-dating partners again.
“Given that men generally are expected - and sometimes required - to approach a potential love interest, the implications are intriguing,” Finkel said.
“Let’s face it, even today, there is a huge difference in terms of who is expected to walk across the bar to say ‘hi,’” added Northwestern’s Paul Eastwick, the study’s other co-investigator.
The study is forthcoming in Psychological Science, a journal of the Association for Psychological Science.
Three-hundred-fifty undergraduates were recruited for the study’s speed-dating events. In half of the events, the men rotated while the women sat. In the remaining events, the women rotated. Following each four-minute “date,” the participants indicated their romantic desire in that partner and how self-confident they felt. Following the event, the students indicated on a Web site whether they would or would not be interested in seeing each partner again.
When the men rotated, the results supported the long-held notion of men being less selective. When the women rotated, this robust sex difference disappeared.
The study draws upon embodiment research that suggests that physical actions alter perception. In one such study, for example, participants who were told to pull an unrelated object toward themselves while evaluating Chinese ideographs rated them as prettier than participants who pushed an unrelated object away from themselves while viewing the symbols.
“The embodiment research shows that our physical activity and psychological processes interface in ways that are outside our conscious awareness,” Finkel said. “In conjunction with this previous embodiment research, our speed-dating results strongly suggest that the mere act of approaching a potential love interest can boost desire.”
The researchers suggest that confidence also may have affected the results. Approaching a potential date increases confidence, which in turn makes the approacher less selective.
The study presents a clear example of how inconspicuous gender norms (having men rotate and women sit) can not only affect the outcome of a study, but also skew the chances of a speed dater walking away with a potential match.
“Our society is structured in gendered ways that can be subtle but very powerful,” Eastwick concluded. The study has implications both for companies that capitalize on the business of dating and for researchers concerned with how social norms may affect research.
How Cells Tell Time
The fuzzy pale mold that lines the glass tubes in Dr. Yi Liu’s lab doesn’t look much like a clock
But this fungus has an internal, cell-based timekeeper nearly as sophisticated as a human’s, allowing UT Southwestern Medical Center physiologists to study easily the biochemistry and genetics of body clocks, or circadian rhythms.
In a new study appearing online this week in the Proceedings of the National Academy of Sciences, Dr. Liu and his co-workers have found that this mold, which uses a protein called FRQ as the main gear of its clock, marks time by a sequence of changes in the protein’s chemical structure.
Dr. Yi Liu is studying mold that uses a protein called FRQ as the main gear of its biological clock. His research team had found that a sequence of changes in the protein’s chemical structure is used to mark time, a finding that might someday help develop treatments for human sleep disorders.
Dr. Liu said the new finding might someday help researchers develop treatments for human sleep disorders and other problems associated with a faulty biological clock.
“This timekeeping protein is really the core component of the circadian clock,” said Dr. Liu, professor of physiology at UT Southwestern and senior author of the study.
Despite the evolutionary distance from mold to man, mechanisms controlling their circadian clocks are very similar. In both, circadian rhythms control many biological processes, including cell division, hormonal release, sleep/wake cycles, body temperature and brain activity.
The researchers employed a fungus called Neurospora, an organism frequently used in studies on genetics and cell processes, especially circadian rhythms. It reproduces in the dark and rests in the light.
A decade ago, Dr. Liu discovered that FRQ controlled the cellular clock in Neurospora by chemical changes of its protein structure. As the day goes on, the cell adds chemical bits called phosphates to the protein. Each new phosphate acts like a clock’s ticking, letting the cell know that more time has passed.
When the number of phosphates added to FRQ reaches a certain threshold, the cell breaks it down, ready to start the cycle again.
The researchers, however, did not know where the phosphates attached to FRQ, how many got added throughout a day, or how they affected the protein’s ability to “tell” time.
In the current study, the researchers used purified FRQ to analyze the specific sites where phosphate groups attach. In all, the researchers found 76 phosphate docking sites.
“This is an extremely high number,” Dr. Liu said. “Most proteins are controlled by only a handful of phosphate sites.”
They also studied how these phosphates are added to FRQ daily and found that two enzymes are responsible for adding most of the phosphate groups in Neurospora. They also found that the total number of phosphates oscillates robustly day by day.
In addition, the researchers created a series of mutations in many of the phosphate docking sites, creating strains of mold that had abnormally short or long daily clocks.
Chemotherapy Drug Triggers Fatal Allergic Reactions
A chemotherapy drug that is supposed to help save cancer patients' lives, instead resulted in life-threatening and sometimes fatal allergic reactions
A new study from the Research on Adverse Drug Events and Reports (RADAR) pharmacovigilance program at Northwestern University Feinberg School of Medicine identified 287 unique cases of hypersensitivity reactions submitted to the FDA's Adverse Event Report System between 1997 and 2007 with 109 (38 percent) deaths in patients who received Cremophor-based paclitaxel, a solvent-administered taxane chemotherapy.
Adverse event reports generally only represent from 1 to 10 percent of actual incidence, so the number of hypersensitivity reactions and deaths is likely significantly higher. The severe allergic reactions are believed to be caused by Cremophor, the chemical solvent - a derivative of castor oil - that is used to dissolve some insoluble drugs before they can be injected into the blood stream.
Two patients who died from an allergic reaction had early-stage breast cancer, which had been surgically removed, and were being treated with Cremophor-containing paclitaxel to prevent the cancer from coming back. Both of these patients had received medications before the chemotherapy to reduce the risk of hypersensitivity reactions.
The study was led by Charles Bennett, M.D., RADAR program coordinator and a professor of hematology/oncology at Northwestern's Feinberg School, and Dennis Raisch, a professor of pharmacy at the University of New Mexico.
"The deaths of women with early-stage breast cancer are particularly disturbing because without the adverse reaction, they could have likely had 40 years of life ahead of them," Bennett said.
RADAR investigators also found that 22 percent of all fatalities occurred in patients despite patients having received premedication to prevent hypersensitivity reactions, while another 15 percent of such patients experienced life-threatening respiratory arrest.
The report was presented at the 45th Annual Meeting of the American Society of Clinical Oncology held recently in Orlando, Fla.
Cremophor-containing paclitaxel has been associated with hypersensitivity reactions, with responses ranging from mild skin conditions to more severe effects, including anaphylaxis and cardiac collapse. Current U.S. product labeling for Cremophor containing paclitaxel includes a black-box warning alerting physicians and patients of potential toxicity and recommending the use of corticosteroids and other medications before chemotherapy administration to reduce the risk of hypersensitivity reactions.
"The results of our review suggest that physicians should be vigilant in monitoring the safety of their patients undergoing chemotherapy treatment," said Bennett, who also is the A.C. Buehler Professor in Economics and Aging at the Feinberg School and a member of the Robert H. Lurie Comprehensive Cancer Center of Northwestern University.
"Patients receiving Cremophor-based paclitaxel should be given medications to prevent hypersensitivity reactions, but what is sobering, as the study has shown and as the black-box warning indicates, women suffer anaphylaxis despite receiving steroid premedication," Bennett said. "Physicians should be diligent in reporting adverse events to regulatory agencies to better monitor the impact of Cremophor on patient safety. Physicians may also want to consider exploring other alternative chemotherapy options that do not include Cremophor."
In addition to the two women with early-stage breast cancer who died after treatment with the Cremophor-based paclitaxel, four other women with early-stage breast cancer experienced life-threatening anaphylaxis reactions. Each of them had received prior medications to prevent the reactions.
"The fatal outcomes observed in patients with early-stage breast cancer were particularly striking as this is a patient population with a good prognosis that is generally treated with curative intent," said Raisch.
For the report, Bennett and Raisch reviewed adverse event reports submitted to regulatory agencies in the U.S., Europe and Japan. The most common cancer diagnosis for these patients with allergic reactions was lung cancer followed by breast cancer and ovarian cancer.
Multivitamins in Pregnancy Reduce Risk of Low Birth Weights
Prenatal multivitamin supplements are associated with a significantly reduced risk of babies with a low birth weight compared with prenatal iron-folic acid supplementation, found a new study in the Canadian Medical Association Journal (CMAJ)
The World Health Organization currently recommends iron-folic acid supplements for all pregnant women. Previous studies have not shown an advantage from prenatal multimicronutrient supplementation over iron-folic acid supplementation.
"Low birth weight and related complications are considered the most common cause of global infant mortality under the age of 5 years," write Dr. Prakash Shah and study coauthors from Mount Sinai Hospital in Toronto. "With the possibility of reducing low birth weight rates by 17%, micronutrients supplementation to pregnant women, we believe, offers the highest possible return for the investment. These results are synthesized findings from 15 studies published worldwide."
It is estimated that of the total 133 million births worldwide per year, 15.5% are low birth weight babies. The authors suggest that approximately 1.5 million babies born with a low birth weight could be avoided each year globally, if all mothers receive prenatal multimicronutrient supplementation.
The research is limited by variability among the included studies, including timing, duration, composition of micronutrients, and characteristics of the study populations.
In a related commentary http://www.cmaj.ca/press/pg1188.pdf, Dr. Zulfiqar Bhutta and Dr. Batool Azra Haider of the Aga Khan University in Karachi, Pakistan recommend that multimicronutrient supplementation during pregnancy replace iron and folate supplements in susceptible populations if it is proven safe and effective. They note that multiple interventions in developing countries may be necessary to improve maternal nutrition and fetal status such as fortified food supplements, interventions that address specific nutrient deficiencies, and measures to reduce the burden of HIV, malaria and other diseases.
MONDAY June 8, 2009---------------------------News Archive/Return to Today's News Alerts
Chromosomal Instability, Centrosome Defects and Cancer
In a new study, Dana-Farber Cancer Institute scientists disprove a century-old theory about why cancer cells often have too many or too few chromosomes, and show that the actual reason may hold the key to a novel approach to cancer therapy
Since the late 19th century, scientists have attributed the surplus or shortage of intact chromosomes in cancer cells to a kind of fragmentation in cell division: instead of dividing neatly into two identical daughter cells, as normal cells do, cancer cells were thought to frequently split into three or four cells, each with a motley assortment of chromosomes. This explosive division was thought to occur because many cancer cells have extra centrosomes, tiny circular structures that help pairs of chromosomes line up in preparation for cell division.
When study lead author Neil Ganem, PhD, of Dana-Farber used newly developed microscope equipment to watch living cancer cells for a week or more, he found that not only were such abnormal divisions quite rare, but the resulting daughter cells were so discombobulated by their chromosomal quirks, they generally survived for only a few days far too briefly to deliver abnormal chromosome content to a tumor.
The way that extra centrosomes do cause chromosome instability, Ganem and his colleagues have discovered, is by setting up a tug-of-war for chromosomes that are eventually caught between newly forming daughter cells of a dividing cancer cell. In normal cells, which have two centrosomes, division occurs as the pairs of chromosomes split neatly apart, like halves of a zipper, each set moving into one of the daughter cells. The extra centrosomes in cancer cells exert an unequal pull on some chromosomes, causing the daughter cells to inherit an irregular number of them explaining, in part, why tumors are often filled with cells of varying quantities of chromosomes.
Their findings are reported in the journal Nature as an advanced online publication.
"Chromosome instability is a hallmark of most cancer cells, arising when chromosomes are missegregated into daughter cells during division," said Ganem, who led the study with senior author David Pellman, MD, and co-author Susana Godinho, PhD, of Dana-Farber. "Such instability may be a double-edged sword. It may confer a survival benefit on cancer cells by enabling them to adapt to a stressful environment in the body or by helping them become resistant to chemotherapy drugs. But it may also have deleterious effects that could make tumor cells susceptible to therapeutic attack."
"Although centrosome defects have been recognized in tumors for a long time," Pellman said, "it has been a tough problem to rigorously study. Neil and Susana have made a significant advance by developing useful methods to create comparable cells that carry or don't carry extra centrosomes."
In the early stages of division, cells make duplicate copies of their chromosomes, enabling their daughter cells to each receive an identical set. The centrosomes' role is to construct the mitotic spindle, the axis along which the chromosome pairs position themselves as division proceeds.
In normal cells, the two centrosomes serve as the polar ends of the spindle, the chromosomes arrayed between them like ranks of twin soldiers. Cells with more than two centrosomes enter a "multipolar" phase with several axes along which division may take place. Under a microscope, such cells look briefly like a sliced pizza ready to be pulled into three or four pieces.
But cancer cells usually avoid this fate by clustering extra centrosomes in a rough line, allowing a single spindle to form and division to proceed somewhat normally. In a study last year, researchers from Pellman's lab used genome-wide approaches to discover how this clustering occurs. In the current study, the investigators found that when cancer cells with extra centrosomes enter "anaphase" the stage of cell division when chromosomes move toward the poles of the spindle before being drawn into the new daughter cells a few chromosomes lagged behind the others. As a result, some of those chromosomes became homeless left out of the daughter cell they were destined for, and marooned in the other daughter cell, where they inhabit a kind of island outside the nucleus where the other chromosomes congregate.
"We showed that even though most cancer cells with extra centrosomes form a single mitotic spindle, they pass through a brief 'multipolar spindle' stage," Ganem said. "The presence of this unique spindle configuration causes a few chromosomes to attach improperly to the eventual two-ended spindle. That, in turn, disrupts the normally orderly process by which chromosomes are pulled into the daughter cells."
According to Pellman, chromosomal instability, it turns out, "is actually a side effect of the cells' ability to cluster their excess centrosomes. From the standpoint of the tumor cell, it is a trade-off: the cell survives because it can correct for the surplus centrosomes, but the correction process creates other problems that result in chromosomal instability."
While the new study demonstrates that extra centrosomes are major actors but likely not the only ones in chromosome instability, it is an open question as to what causes some cells to have those extra centrosomes. That will be a future area of research for the Dana-Farber team.
Leptin’s Role in Restoring Blood-Sugar Control
By influencing a tiny group of neurons, hormone restores blood-sugar control
In investigating the complex neurocircuitry behind weight gain and glucose control, scientists have known that the hormone leptin plays a key role in the process. But within the myriad twists and turns of the brain’s intricate landscape, the exact pathways that the hormone travels to exert its influence have remained a mystery.
Now, a study led by Harvard investigators at Beth Israel Deaconess Medical Center (BIDMC) sheds further light on the subject. Reported in the journal Cell Metabolism, the findings demonstrate that when leptin sensitivity is restored to a tiny area of neurons in the brain’s hypothalamus, a group of mice deficient in the leptin receptor are cured of severe diabetes and also spontaneously double their activity levels independent of any change in weight or eating habits.
“This discovery suggests a new therapeutic pathway for drugs to treat insulin-resistant diabetes in humans with severe obesity, and possibly even to stimulate their urge to exercise,” explains Christian Bjorbaek, an investigator in the Division of Endocrinology, Diabetes and Metabolism at BIDMC and associate professor of medicine at Harvard Medical School. “We know that the majority of humans with type 2 diabetes are obese and that weight loss can often ameliorate the disease. However, in many cases, it’s difficult for these individuals to lose weight and keep weight off. If, as these findings suggest, there is a system in the brain that can control blood glucose directly, it offers hope for the identification of novel anti-diabetic drug targets.”
First identified in 1994 as an appetite and weight-regulation hormone, leptin plays a key role in energy homeostasis through its effects on the central nervous system. Over the years, investigators have pinpointed a region of the brain’s hypothalamus known as the arcuate nucleus (ARC) as one key area where leptin exerts its influence. Within the ARC, they have identified two types of leptin-responsive neurons, the Agouti-related peptide (AgRP) neurons, which stimulate appetite, and the pro-opiomelanocortin (POMC) neurons, which curb appetite.
“Still other studies had indicated that, by way of the ARC, leptin also had a function in both blood-sugar control and in activity levels” notes Bjorbaek. “We hypothesized that, in both cases, the POMC neurons were involved.”
To test their hypothesis, the scientists studied a group of leptin-receptor-deficient laboratory mice. “The animals were severely obese and profoundly diabetic,” Bjorbaek explains. “Using Cre-Lox technology we were able to genetically and selectively re-express leptin receptors only in the POMC neurons. When leptin receptor activity was restored to just this very small group of neurons, the mice began eating about 30 percent fewer calories and lost a modest amount of weight.”
More dramatically, the animals’ blood-sugar levels returned to normal, independent of any change in weight or eating habits, and their activity levels spontaneously doubled.
While more research is needed to explain the mechanisms at play, it may be that the POMC neurons reduce blood glucose by regulating key organs such as the liver or muscle tissue.
“Normally, the liver is critical for increasing glucose production between meals in order to provide fuel for the brain, while skeletal muscle is important for the removal of glucose from the blood immediately after a meal,” he notes.
In this case, however, the POMC neurons may be decreasing glucose release into the blood by the liver and/or increasing glucose uptake from the blood into muscle.
“The fact that normal glucose levels were restored independent of food or weight changes is important because it suggests that it is possible to normalize blood glucose even without weight loss,” explains Bjorbaek. “Furthermore, our finding that the mice had greatly increased activity levels despite still being highly overweight provides hope that POMC neurons and downstream neuronal systems might eventually be tapped to develop drugs that increase the will to voluntarily exercise in individuals who are overweight or obese.”
Researchers Solve 'Bloodcurdling' Mystery
Team uncovers the molecular basis for the regulation of blood clotting
By applying cutting-edge techniques in single-molecule manipulation, researchers at Harvard University have uncovered a fundamental feedback mechanism that the body uses to regulate the clotting of blood. The finding, which could lead to a new physical, quantitative, and predictive model of how the body works to respond to injury, has implications for the treatment of bleeding disorders.
A team, co-led by Timothy A. Springer, Latham Family Professor of Pathology at Harvard Medical School and Children's Hospital Boston, and Wesley P. Wong, Rowland Junior Fellow and a Principal Investigator at the Rowland Institute at Harvard, reported its discovery about the molecular basis for the feedback loop responsible for hemostasis in the June 5th issue of Science.
"The human body has an incredible ability to heal from life's scrapes and bruises," explains Wong. "A central aspect of this response to damage is the ability to bring bleeding to end, a process known as hemostasis. Yet regulating hemostasis is a complex balancing act."
Too much hemostatic activity can lead to an excess of blood clots, resulting in a potentially deadly condition known as thrombosis. If too little hemostatic activity occurs in the body, a person may bleed to death.
To achieve the proper balance, the body relies on a largely mechanical feedback system that relies on the miniscule forces applied by the circulation system on a molecular "force sensor" known as the A2 domain of the blood clotting protein von Willebrand factor (VWF).
By manipulating single molecules of this A2 domain, the researchers found that the A2 domain acts as a highly sensitive force sensor, responding to very weak tensile forces by unfolding, and losing much of its complex three-dimensional organization. This unfolding event allows the cutting of the molecule by an enzyme known as ADAMTS13.
"In the body, these cutting events decrease hemostatic potential and also enable blood clots to be trimmed in size. The system is so finely tuned that the A2 shear sensor is able to regulate the size of VWF within the blood stream, maintaining the optimal size for responding properly to traumas," says Wong.
To make the discovery, the team relied upon an "optical tweezers" system developed in Wong's lab. The tweezers are capable of applying miniscule forces to individual molecules while observing nanoscale changes in their length. Such manipulations enabled the researchers to characterize both the unfolding and refolding rates of single A2 molecules under force, as well as their interaction with the enzyme.
The molecular construct was created in Dr. Springer's lab, and consisted of an A2 domain connected to two DNA handles for manipulation. This elegant molecular system allowed the VWF "shear sensor" to be carefully studied and tested in isolation.
Ultimately, this work enhances the understanding of how the body is able to regulate the formation of blood clots, and is step towards a physical, quantitative, and predictive model of how the body responds to injury. It also gives insight into how bleeding disorders, such as type 2A von Willebrand disease, disrupt this regulation system, potentially leading to new avenues for treatment and diagnosis.
A New Lead for Autoimmune Disease
A drug derived from the hydrangea root, used for centuries in traditional Chinese medicine, shows promise in treating autoimmune disorders, report researchers from the Program in Cellular and Molecular Medicine and the Immune Disease Institute at Children's Hospital Boston (PCMM/IDI), along with the Harvard School of Dental Medicine
In the June 5 edition of Science, they show that a small-molecule compound known as halofuginone inhibits the development of Th17 cells, immune cells recently recognized as important players in autoimmune disease, without altering other kinds of T cells involved in normal immune function. They further demonstrate that halofuginone reduces disease pathology in a mouse model of autoimmunity.
Currently there is no good treatment for autoimmune disorders; the challenge has been suppressing inflammatory attacks by the immune system on body tissues without generally suppressing immune function (thereby increasing risk of infections). The main treatment is antibodies that neutralize cytokines, chemical messengers produced by T cells that regulate immune function and inflammatory responses. However, antibodies are expensive, must be given intravenously and don't address the root cause of disease, simply sopping up cytokines rather than stopping their production; patients must therefore receive frequent intravenous infusions to keep inflammation in check. Powerful immune-suppressing drugs are sometimes used as a last resort, but patients are left at risk for life-threatening infections and other serious side effects.
Through a series of experiments, the researchers show that halofuginone prevents the development of Th17 cells in both mice and humans, halts the disease process they trigger, and is selective in its effects. It also has the potential to be taken orally. "This is really the first description of a small molecule that interferes with autoimmune pathology but is not a general immune suppressant," says Mark Sundrud, PhD, of the PCMM/IDI, the study's first author.
Recognized only since 2006, Th17 cells have been implicated in a variety of autoimmune disorders including inflammatory bowel disease, rheumatoid arthritis, multiple sclerosis, type 1 diabetes, eczema and psoriasis. They are genetically distinct from the other major categories of T-cells (Th1, Th2 and T-regulatory cells).
Th17 cells normally differentiate from "naïve" CD4+ T cells, but when Sundrud and colleagues cultured mouse CD4+ T-cells along with cytokines that normally induce Th17 development, there was a pronounced decrease in Th17 cells - but not in Th1, Th2 or T regulatory cells - when halofuginone was added. Similarly, in cultured human CD4+ T-cells, halofuginone selectively suppressed production of IL-17, the principal cytokine made by Th17 cells.
And in mice with experimental autoimmune encephalitis (EAE), an artificially-induced immune disease resembling multiple sclerosis in humans, and marked by infiltration of Th17 cells into the central nervous system, low-dose halofuginone treatment significantly reduced both the development of EAE and its severity. (In mice with another form of EAE that doesn't involve Th17 cells, halofuginone had no effect.)
Wondering how halofuginone works, the researchers did microarray studies of the halofuginone-treated cells to examine patterns of gene expression in response to the drug. Unexpectedly, many genes involved in stress responses were turned on. Eventually, they found that halofuginone acts by activating a biochemical pathway known as the "amino acid starvation response," or AAR, which typically protects cells when amino acids, essential building blocks of proteins, are in short supply. When excess amino acids were added to cultured T-cells exposed to halofuginone, the AAR didn't switch on, and Th17 cells were able to develop. Conversely, the researchers were able to inhibit Th17 differentiation simply by depleting amino acids, thereby inducing the AAR.
Why would the AAR prevent Th17 cells from forming? The researchers propose that the AAR has an energy-saving function, slowing down a cell's building activities to conserve amino acids. "When a cell senses amino acid deprivation, it tries to conserve amino acids by preventing specific types of responses that are energetically expensive," says Sundrud. "In inflamed tissues, a lot of cells are producing a lot of protein, so it would make sense that a cell with amino acid deprivation would want to block signals that promote inflammation."
Halofuginine is one of the 50 fundamental herbs of traditional Chinese medicine, and has been used as an antimalarial agent. Decades ago, the U.S. Army tried to improve upon its antimalarial properties, without success. It has been in clinical trials for scleroderma, but because it is now in the public domain, the pharmaceutical industry has not shown interest in further developing it therapeutically.
But halofuginone, or some yet-to-be developed derivative compound, could potentially be used to address any autoimmune or inflammatory disease related to Th17 cells by activating the AAR, the researchers say.
"Remarkably, halofuginone evokes the AAR in all cells but selectively inhibits T-cell inflammatory responses," says Anjana Rao, PhD, of the PCMM/IDI, a senior investigator on the study. "This recalls the actions of cyclosporin A and FK506, two other immunosuppressive drugs that block the activity of calcineurin. Calcineurin is present in all cells, but selectively prevents the rejection of heart, lung, liver and bone marrow transplants when given to patients. These drugs revolutionized transplant medicine when they were introduced over 20 years ago, and halofuginone may herald a revolution in the treatment of certain types of autoimmune/inflammatory diseases."