The discovery of natural and engineered light-sensitive proteins has developed a versatile and easy-to-use method in neuroscience called optogenetics that uses a light stimulus to precisely regulate neural activity in time and space, and has had an immense impact on understanding neural networks, neuronal function, and signaling pathways.
Scientists at the Ruhr-University Bochum, Germany, have now discovered a new optogenetic tool and demonstrated its potential in epilepsy research. This tool, a member of a family of proteins called opsins found in the brain and eyes in zebrafish, continuously activates an important intracellular signaling pathway called the Gi/o pathway.
Unlike other optogenetic proteins that are turned on when light is shone on them, this protein (Opn7b) is turned off by blue or green light. Characterization of Opn7b that the scientists reported in an article in Nature Communications, “Reverse optogenetics of G protein signaling by zebrafish non-visual opsin Opn7b for synchronization of neuronal networks,” will allow researchers to interrupt the continuously active Gi/o signaling pathway transiently, by shining blue or green light on Opn7b.
The teams, led by Melanie Mark, PhD, scientist at the behavioral neurobiology research group and Stefan Herlitze, PhD, professor and scientist at the department of general zoology and neurobiology, showed that shining light on Opn7b deactivates the permanently active Gi/o pathway that normally opens specific ion channels resulting in an influx of ions into the cell and downstream steps in the signaling process. Raziye Karapinar, PhD, Ida Siveke, PhD, and Dennis Eickelbeck, PhD, characterized the function of Opn7b in detail and identified that the receptor protein is deactivated by light.
“This suggests that light acts as an inverse agonist for Opn7b and can be used as an optogenetic tool to inhibit neuronal networks in the dark and interrupt constitutive inhibition in the light,” the authors noted.
Little research has so far been conducted on G protein-coupled receptors that are activated without stimulation, although it is presumed that they play a role in various neuropsychiatric conditions, night blindness, and the development of virally induced cancers. Opn7b, the researchers believe, will be important in gaining further insights into the function of G protein-coupled receptors that are continuously active and obtain new knowledge on their role in the development of diseases by examining receptors in a time-controlled manner in specific cell types.
“So far in all seizure models, seizure induction is time-consuming and demands long-lasting light activation protocols with unreliable onset of seizures,” the authors noted. To demonstrate the application of Opn7b as a tool in epilepsy research, the Bochum researchers Jan Claudius Schwitalla, PhD, and Johanna Pakusch, PhD, engineered cells called pyramidal cells, in the cerebral cortex of mice to express the zebrafish receptor protein, Opn7b. When Opn7b is deactivated by light, the researchers showed, it triggers seizures in the animals that can be specifically controlled with light. The researchers hope it will be possible to use this optogenetic tool to better understand the underlying mechanisms and timeline of the development of epileptic seizures.