Measuring Synapse Between Neurons, Muscle Cells
In an effort to identify the underlying causes of neurological disorders that impair motor functions such as walking and breathing, UCLA researchers have developed a new system to measure communication between stem cell-derived motor neurons and muscle cells
The study provides an important proof of principle that functional motor circuits can be created outside of the body using stem cell-derived neurons and muscle cells. And, that the level of communication/synaptic activity - between the cells can be accurately measured by stimulating motor neurons with an electrode to measure the transfer of electrical activity between muscle cells and connected motor neurons.
When motor neurons are stimulated, they release neurotransmitters that depolarize the membranes of muscle cells, allowing the entry of calcium and other ions that cause muscel cells to contract. By measuring the strength of this activity, a good estimate of overall motor neuron health can be made.
That estimation could shed light on a variety of neurodegenerative diseases such as spinal muscular atrophy and amyotrophic lateral sclerosis - Lou Gehrig's disease - in which the communication between motor neurons and muscle cells is thought to unravel, according to senior author Bennett G. Novitch (assistant professor of neurobiology and a scientist with the Eli and Edythe Broad Center of Regenerative Medicine and Stem Cell Research at UCLA).
The findings of the study appear May 4, 2012 in PLoS ONE, a peer-reviewed journal of the Public Library of Science.
Novitch: "Now that we have this method to measure the strength of the communications between motor neurons and muscle cells, we may be able to begin exploring what happens in the earliest stages of motor neuron disease, before neuronal death becomes prevalent. This can help us pinpoint where things begin to go wrong and provide us with new clues into therapeutic interventions that could improve synaptic communication and promote neuronal survival."
Novitch said the synaptic communication activity his team was able to create and measure using mouse embryo derived motor neurons and muscle cells looks very similar to what is seen in a mouse, validating that their model is a realistic representation of what is happening in a living organism.
"That gives us a good starting point to try to model what happens in cells that harbor genetic mutations that are associated with neurodegenerative diseases,. To do that, we had to first define an activity profile of normal synaptic communication," he said.
"Some research suggests that a breakdown in this communication can be an early indication of disease progression or possibly an initiating event. Neurons that cannot effectively transmit information to muscle cells will eventually withdraw their contacts, causing both the neurons and muscle cells to degenerate over time. Hopefully, we can now create disease models that will allow us to study what is happening."
In this study, Novitch and his team, led by Joy Umbach (associate professor of molecular and medical pharmacology) used mouse embryonic stem cells to create the motor neurons and previously established lines of muscle precursors to produce muscle fibers.
They put both cells together in a Petri dish, cultured to encourage communication. Novitch said the team wanted to see if they could naturally form synaptic contacts, and whether or not neural transmission between them occured. In less than a week, the neurons had reached out to the muscle cells and assembled the protein networks needed for synaptic communication.
To measure the connections between the cells, the scientists used a technique called dual patch clamp recording.
Pipettes containing stimulating and recording electrodes are inserted into the membranes of the motor neurons and muscle cells, being careful not to injure them. With this method, they were able send an electrical current into the motor neurons and measure responses in the muscle cells, as well as visualize the muscular contractions.
"The in vitro system developed here might accordingly be expanded to assess the underlying cellular and molecular mechanisms that contribute to this decline in synaptic input to motor neurons," the study states.
Looking forward, Novitch and his team hope to recreate and confirm the work using human stem cell-derived motor neurons and muscle cells and measure the synaptic communications with newly developed optical recording methods, which are less invasive than the patch clamp techniques used in this study.
The study was funded by the California Institute of Regenerative Medicine, UCLA Broad Stem Cell Research Center, the Muscular Dystrophy Association, UCLA Cellular and Molecular Biology Training Program and the Ruth L. Kirschstein National Research Service Award.
The stem cell center was launched in 2005 with a UCLA commitment of $20 million over five years. A $20 million gift from the Eli and Edythe Broad Foundation in 2007 resulted in the renaming of the center. With more than 200 members, the Eli and Edythe Broad Center of Regenerative Medicine and Stem Cell Research is committed to a multi-disciplinary, integrated collaboration of scientific, academic and medical disciplines for the purpose of understanding adult and human embryonic stem cells. The center supports innovation, excellence and the highest ethical standards focused on stem cell research with the intent of facilitating basic scientific inquiry directed towards future clinical applications to treat disease. The center is a collaboration of the David Geffen School of Medicine, UCLA's Jonsson Cancer Center, the Henry Samueli School of Engineering and Applied Science and the UCLA College of Letters and Science. To learn more about the center, visit our web site athttp://www.stemcell.ucla.edu. To learn more about the center, visit our web site athttp://www.stemcell.ucla.edu.
Original article: http://www.eurekalert.org/pub_releases/2012-05/uoc--usm050212.php