Summary: Researchers have developed a new protein-based tool that can modify brain activity and memory in targeted ways without using drugs or chemicals.
Source: USC.
GFE3 may help researchers map the brain’s connections and control neural activity.
Scientists at the University of Southern California (USC) have created a novel protein tool that can selectively alter neuronal activity and memory by targeting inhibitory synapses, without relying on pharmacological agents.
The protein, called GFE3, is designed to help researchers map neuronal connections and better understand how inhibitory synapses influence brain function, said lead author Don Arnold, a professor of biological sciences at the USC Dornsife College of Letters, Arts and Sciences. Arnold also noted that GFE3 could enable precise manipulation of neural activity, with potential implications for studying conditions ranging from schizophrenia to cocaine addiction.
GFE3 functions like a molecular “off switch” for specific synaptic proteins in chosen cells. When encoded into an animal’s genome, the protein prompts the targeted removal of the molecular scaffolding that maintains inhibitory synapses. With those synapses disabled, the affected neurons increase their electrical activity.
“GFE3 harnesses a little-known and remarkable property of proteins within the brain,” Arnold said.
Hijacking the brain’s recycling system
GFE3 exploits a natural cellular process: the continuous cycle of degrading and replacing proteins. Many neuronal proteins are short-lived and are regularly broken down and renewed. GFE3 directs that degradation machinery specifically to proteins that anchor inhibitory synapses, causing those synaptic structures to disassemble.
“Rather than a cell deciding when a protein needs to be degraded, we sort of hijack the process,” Arnold said.
In experiments reported in the journal Nature Methods, the research team tested GFE3 in mice and zebrafish. They observed that expression of the protein caused neurons on the two sides of the spinal cord to act in opposition, producing uncoordinated movements — a clear demonstration that disabling inhibitory synapses alters circuit behavior in predictable ways.
Traditional drugs that reduce inhibitory signaling, such as benzodiazepines, act broadly on many cells within a brain region and cannot distinguish among neighboring neurons with different, even opposite functions. That nonspecific action makes it difficult to interpret how particular circuits contribute to behavior. Encoding GFE3 genetically allows researchers to modulate inhibitory synapses only in selected cell types, leaving nearby cells and circuits intact.
“Unfortunately, cells that have very different, even opposite functions tend to be right next to each other in the brain,” Arnold said. “Thus, pharmacological experiments are especially difficult to interpret. By encoding GFE3 within the genome, we can target and modulate the inhibitory synapses of specific cells without affecting other cells that have different functions.”
The study’s co-authors include Garrett Gross, William Dempsey and Jason Junge of USC Dornsife; Scott Fraser of USC Dornsife and the USC Viterbi School of Engineering; Christoph Straub and Bernardo Sabatini of Harvard Medical School; and Jimena Perez Sanchez, Yves De Koninck and Paul De Koninck of Université Laval in Canada.
Funding: The research was supported by a National Institutes of Health grant (NS-081687).
Source: Emily Gersema – USC
Image credit: Don Arnold.
Original research: Abstract for “An E3-ligase-based method for ablating inhibitory synapses,” published in Nature Methods (online June 6, 2016). DOI: 10.1038/nmeth.3894.
USC. “New Protein Can Modify Brain Function and Memory.” NeuroscienceNews. Published June 23, 2016.
Abstract
An E3-ligase-based method for ablating inhibitory synapses
Current techniques can modulate neuronal activity, but few allow precise control over neuronal connectivity. The authors introduce GFE3, a tool that mediates the rapid, specific and reversible elimination of inhibitory synaptic inputs onto genetically specified neurons. GFE3 is a fusion between an E3 ubiquitin ligase, which targets proteins for degradation, and a recombinant antibody-like protein (FingR) that binds to gephyrin, a key scaffolding protein at inhibitory synapses. Expression of GFE3 causes a strong and specific reduction of gephyrin both in culture and in vivo, leading to a significant decrease in phasic inhibition in cells expressing GFE3. Temporary expression of GFE3 allows inhibitory synapses to regrow after ablation, demonstrating that this method is reversible. Together, these results present a straightforward and reversible approach to modulate inhibitory synaptic input onto genetically defined cells.
Authors: Garrett G. Gross, Christoph Straub, Jimena Perez-Sanchez, William P. Dempsey, Jason A. Junge, Richard W. Roberts, Le A. Trinh, Scott E. Fraser, Yves De Koninck, Paul De Koninck, Bernardo L. Sabatini, and Don B. Arnold. Published in Nature Methods, June 6, 2016. DOI: 10.1038/nmeth.3894.