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Home | Pregnancy Timeline | News Alerts |News Archive Sep 5, 2013

 

This super resolution image shows the nucleus of a cell from a rat brain.
Each red spot is a individual nuclear pore complex, cellular structures found
on the envelope surrounding the nucleus, which are crucial to communications between the nucleus and the rest of the cell. The Salk scientists studied long lived proteins that serve as important structural components of these complexes.

Credit: Courtesy Brandon Toyama, Waitt Advanced Biophotonics Center

The study is the first comprehensive and unbiased identification of extremely
long-lived proteins (ELLPs), under a given set of environmental conditions.







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The 'weakest link' is the aging protein

Salk Institute and The Scripps Research Institute find long-lived proteins lead to understanding the molecular basis of cell aging.

Proteins are the chief actors in cells, carrying out functions encoded in our genes. Most proteins live two days or less, ensuring that damaged proteins are replaced frequently with new functional copies.

But in a study published August 29 in Cell led by the Salk Institute for Biological Studies and The Scripps Research Institute (TSRI), scientits identified a small subset of proteins in the brain that persist for more than a year before being replaced.


"Protein longevity can be a major contributor to cell aging. Simply identifying all long-lived proteins allows us to focus our studies on what may be the weakest link in the aging proteome."

Martin Hetzer, professor in Salk's Molecular and Cell Biology Laboratory, holder of the Jesse and Caryl Philips Foundation Chair, and senior author of the study along with TSRI Professor John Yates.


The study is the first comprehensive and unbiased identification of extremely long-lived proteins (ELLPs), under a given set of environmental conditions. In a 2012 study published in Science, Hetzer and colleagues identified long-lived proteins in the cell nuclei of the rat brain, stating in the abstract: "The longevity of these proteins would be expected to expose them to potentially harmful metabolites, putting them at risk of accumulating damage over extended periods of time. Thus, it is possible that failure to maintain proper levels and functional integrity of ELLPs in nonproliferative cells might contribute to age-related deterioration in cell and tissue function."

The new study takes the Science findings one step further by providing a system-wide identification of proteins with long lifespans. So far they have found that long-lived proteins include those involved in gene expression, neural communication, enzymatic processes, as well as members of the nuclear pore complex (NPC) – which is responsible for all traffic into and out of a cell nucleus.

They discovered the nuclear pore complex undergoes slow, contiuous turnover to clear the inevitable accumulation of damaged components. "This can be thought of as similar to maintaining a car, where you replace components as they break down," says lead study author Brandon Toyama, a postdoctoral fellow in Hetzer's laboratory. Hetzer and colleagues had previously identified nuclear pore complex deterioration to be a sign of an aging mechanism leading to age-related defects in nuclear function. Other laboratories have also linked protein instability to declining cell function and disease.


The new findings reveal cellular components that are at increased risk for accumulated damage, linking long-term protein persistence to the process of cell aging.


"Now that we have identified these long-lived proteins, we can begin to examine how they may be affected in aging and what the cell does to compensate for inevitable damage," says Toyama.

Hetzer's team is now identifying targets that are involved in aging and potential pathways to address this. Hetzer: "We're starting to think about how to get functionality back to that younger version of the protein."

Highlights
Metabolic pulse-chase labeling of rats identified long-lived proteins in rats
Long-lived proteins include nucleoporins, histone variants, and enzymes
Long-lived proteins cannot be replaced despite their robust translation
Nuclear pores are maintained over the lifespan of the organism

Summary
Intracellular proteins with long lifespans have recently been linked to age-dependent defects, ranging from decreased fertility to the functional decline of neurons. Why long-lived proteins exist in metabolically active cellular environments and how they are maintained over time remains poorly understood. Here, we provide a system-wide identification of proteins with exceptional lifespans in the rat brain. These proteins are inefficiently replenished despite being translated robustly throughout adulthood. Using nucleoporins as a paradigm for long-term protein persistence, we found that nuclear pore complexes (NPCs) are maintained over a cell’s life through slow but finite exchange of even its most stable subcomplexes. This maintenance is limited, however, as some nucleoporin levels decrease during aging, providing a rationale for the previously observed age-dependent deterioration of NPC function. Our identification of a long-lived proteome reveals cellular components that are at increased risk for damage accumulation, linking long-term protein persistence to the cellular aging process.

Other researchers on the study were Jeffery N. Savas, Sung Kyu Park and John R. Yates of TSRI and Michael S. Harris and Nicholas T. Ingolia of the Carnegie Institute for Science.

The work was supported by the National Institutes of Health, the Hewitt Foundation, the Glenn Foundation for Medical Research, the American Cancer Society, the Ellison Medical Foundation, and the Searle Scholars Program.

About the Salk Institute for Biological Studies:

The Salk Institute for Biological Studies is one of the world's preeminent basic research institutions, where internationally renowned faculty probe fundamental life science questions in a unique, collaborative, and creative environment. Focused both on discovery and on mentoring future generations of researchers, Salk scientists make groundbreaking contributions to our understanding of cancer, aging, Alzheimer's, diabetes and infectious diseases by studying neuroscience, genetics, cell and plant biology, and related disciplines.

Faculty achievements have been recognized with numerous honors, including Nobel Prizes and memberships in the National Academy of Sciences. Founded in 1960 by polio vaccine pioneer Jonas Salk, M.D., the Institute is an independent nonprofit organization and architectural landmark.

Original press release: http://www.salk.edu/news/pressrelease.html