Project Summary/Abstract Glaucoma, the leading cause of irreversible vision loss characterized by the degeneration of retinal ganglion cells (RGCs) and their axons, will affect an estimated 100 million people worldwide by the year 2040. Sensitivity to intraocular pressure (IOP) is the only modifiable risk factor in glaucoma. IOP can be reduced by a number of hypotensive therapies, which often slow progression, but many patients continue to lose vision despite significant pressure control. IOP-related stress is conveyed by mechanisms that pique RGC axons within the optic nerve head. Thus, the first cellular responders to stress likely reside in the optic nerve head and represent primary targets for neuroprotective treatment. In this region, axons are located in close proximity to astrocytes. Astrocytes are intimately involved in the response to neurodegenerative stress and have become an attractive target for the development of neuroprotective therapies. Astrocytes are densely interconnected by gap junctions, primarily composed of the protein connexin-43 (Cx43), and can function as a broader network of cells. Such networks are capable of enhancing astrocyte homeostatic capacities, including metabolite distribution and extracellular ionic buffering, but their role in neurodegenerative disease is an emerging field. Early glaucomatous degeneration is characterized in part by enhanced RGC excitability and a reduction in axon function. Interestingly, a subset of RGCs which produce sustained responses at light offset (αOFF-S) appear to be more vulnerable to IOP-related stress. Astrocytic networks play key roles at this early stage of glaucoma. Work in the Calkins lab demonstrated that astrocyte-specific deletion of Cx43 grossly accelerates degenerative changes in a mouse model of glaucoma. Preliminary experiments indicate that astrocytic Cx43 deletion preferentially alters the firing properties of αOFF-S RGCs. This proposal expands upon these findings, aiming to illuminate the mechanisms underlying the differential susceptibility of RGC types and to explore the importance of astrocyte networks in enhancing one neuroprotective function – buffering the contents of the extracellular environment. Electrophysiologic, pharmacologic, and cell imaging techniques, alongside a mouse model of glaucoma, will be employed to accomplish these aims. These studies will provide important insight into the early physiologic events in glaucomatous neurodegeneration and establish a framework for future neuroprotective therapies targeting astrocytes. The training plan outlined in this proposal is strengthened by an abundance of resources and expertise, as well as strong mentorship and a commitment to training an independent physician scientist.