The cell-specific role of cGMP in striatum and hippocampus

• Applicants: Shiqiang Gao, Ph.D.; Christine Elizabeth Gee, Ph.D.
• Subject Area: Molecular Biology and Physiology of Neurons and Glial Cells ; Cognitive, Systems and Behavioural Neurobiology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 538090107

Dysregulated cGMP signaling is associated with many neurological diseases, indicating the importance of cGMP-related pathways in the brain. We have observed that cGMP, and the enzymes controlling it, play different roles in different brain regions and cell types, e.g. in setting the strength of neuronal synapses. These differences, and in particular the implications for overall circuit and brain function, are poorly understood. One reason for this lack of understanding has been the absence of suitable methods to visualize and manipulate cGMP in select cell types. Collaborating within a team of neuroscientists and protein engineers, we have developed light-activated guanylyl cyclases that we use to manipulate cGMP in genetically targeted subtypes of cells in the brain and elsewhere. A healthy, fertile conditional transgenic mouse expressing one of our published light-activated guanylyl cyclases has also been produced to support our further endeavors. The overarching goal of this proposal is to understand the cell type-specific roles of cGMP in brain function and its impact on behavior and synaptic function. We will take a three-pronged approach to achieve this goal. To measure cGMP levels in behaving mice and test the hypothesis that dynamic changes in cGMP underlie and are critical for motor learning and other behaviors, we will use fiber photometry. Second, we will manipulate cGMP levels in specific brain areas (hippocampus, striatum) and neuronal populations (pre- or postsynaptic) to assess behavioral effects in vivo. Also, we will dissect in detail the role of cGMP on synaptic and circuit function using slice electrophysiology. Third, we will study the photoregulation mechanism of light-activated cyclases and phosphodiesterases and use the knowledge gained to further improve specificity and enable bidirectional control of cGMP in genetically targeted cells. Despite natural occurrences of light-activated phosphodiesterases, their characteristics, such as dark activity and suboptimal light activation efficacy, render them less than ideal for optogenetic use. Our focus will be on deciphering their light regulation mechanism and concurrently refining them into effective optogenetic tools. These newly developed optogenetic tools will be immediately applied to determine the extent to which cell-specific cGMP signaling contributes to brain circuit function and behavioral performance. We will also create tools with subcellular targeting to delve into the cGMP signaling heterogeneity within individual cells, known as subcellular compartmentalization or microdomains. In summary, our project will take advantage of novel and existing optogenetic tools to unravel the role of cGMP in behavior with a precision heretofore impossible.

• DFG Programme: Research Grants