Abstract
<jats:p>Retinal ganglion cells (RGCs) degenerate in optic neuropathies like glaucoma and traumatic optic nerve injury leading to irreversible vision loss. Higher levels of homeostatic Ca2+ and canonical Ca2+ regulated signaling promote RGC survival in animal models of glaucoma and optic nerve injury. Mitochondrial dysfunction is also a hallmark of degenerating neurons, including RGCs. Here, we investigate the intersection of mitochondrial function, Ca2+ homeostasis, and cellular resilience by performing an optic nerve crush model of RGC degeneration while monitoring and manipulating mitochondrial Ca2+ levels (mito-Ca2+). We find that mito-Ca2+ is predicative of RGC survival in that surviving RGCs are enriched for higher homeostatic mito-Ca2+ levels. Mitochondrial dysfunction was observed where mito-Ca2+ was reduced in RGCs after injury, regardless of survival. We then examined the importance of higher mito-Ca2+ in surviving RGCs by altering mito-Ca2+ levels and Ca2+ transit using pharmacological and AAV-mediated approaches. Paradoxically, treatment to decrease mito-Ca2+ increased survival to ONC. We then manipulated mito-Ca2+ permeability by altering the expression levels of the mitochondrial calcium uniporter (MCU) pore forming subunit that allows Ca2+ to enter mitochondria from the cytoplasm. Overexpressing MCU reduced RGC survival to injury, while shRNA knockdown of MCU increased RGC survival. These results reveal a complex relationship between mito-Ca2+ and RGC degeneration and suggest that well-surviving RGCs may be under chronic mitochondrial stress due to higher homeostatic mito-Ca2+ levels.</jats:p>