Imaging technology captures how neurons communicate with new clarity

For the first time, scientists from The Hospital for Sick Children (SickKids) used advanced imaging technology at the SickKids Nanoscale Biomedical Imaging Facility to reveal the atomic structure of an enzyme that neurons use to communicate.

All brain activity – from memory and emotion to learning and motor control – is made possible by communication through synapses, the connections between neurons. When this communication fails, various conditions can occur, such as epilepsy.

A neuron is a type of cell that specializes in communicating with other cells by sending chemical signals called neurotransmitters to synapses. In the brain there are 100 trillion synapses between neurons.

The way neurons communicate has been studied for decades, but research published in Science shows models derived from hundreds of thousands of high-resolution images that reveal synaptic function with new clarity.

Led by Dr. John Rubinstein, senior scientist in the Molecular Medicine program, and Dr. Claire Coupland, first author and postdoctoral researcher in the Rubinstein Lab, the research team hopes that by capturing images and modeling how chemicals are released from neurons could potentially provide new therapeutic targets that will help improve care for children with epilepsy and other neurological disorders.

In publishing these findings, Rubinstein shares how his team captured the images and what their findings could mean for patients in the future.

What has your research revealed about the way neurons communicate?

When communicating, neurons release neurotransmitters into a synapse to be delivered to a receiving neuron. These neurotransmitters are released from small packets called synaptic vesicles. Once a message is received, the neurotransmitters must be reabsorbed and repackaged into new synaptic vesicles to clear the synapse and make room for the next signal.

To facilitate this process, an enzyme called the vesicular ATPase (V-ATPase) acts as a pump to drive neurotransmitters into synaptic vesicles. V-ATPase also regulates the release of neurotransmitters from the vesicles.

In our research, we learned that the way V-ATPase controls the process of neurotransmitter release from synaptic vesicles is by spontaneously disassembling after the vesicles are loaded. We found that when we filled the synaptic vesicles with neurotransmitters, the V-ATPases split into two parts, releasing the neurotransmitter.

How did you capture images of this process?

Using novel biochemical methods and new imaging methods, supported by the SickKids Nanoscale Biomedical Imaging Facility, we were able to isolate and image synaptic vesicles. From there, we developed new computational approaches to analyze the images to display the V-ATPase in the vesicles at high resolution – something that has not been done before.

We created 3D models of the V-ATPase from images we captured using cryogenic electron microscopy (cryo-EM), a method that images samples at –196°C. Our team saw that V-ATPase interacts with several components of the synaptic vesicle, which contains many proteins and lipids involved in neurotransmitter release.

Most surprisingly, we learned that the V-ATPase interacts with a protein called synaptophysin. By weight, synaptophysin is the most abundant synaptic vesicle protein. Until now, its function in neurons was not understood. What we found shows that synaptophysin could help recruit V-ATPase into synaptic vesicles as they initially form.

What are the next steps for this research?

Now that we have discovered that V-ATPase interacts with synaptophysin in synaptic vesicles, we are working with Dr. Lu-Yang Wang, a senior scientist in the Neurosciences & Mental Health Program, to understand the role of this interaction in the brain. We also want to understand how vesicle loading causes the V-ATPase to disassemble, and how this process regulates the release of neurotransmitters from neurons.

In the future, this process could be a therapeutic target for many health problems, including some forms of epilepsy.