Metabolic capacity regulates retinal ganglion cell survival in neurodegeneration

Abstract

Purpose : Retinal ganglion cell (RGC) death underlies vision loss during glaucoma. RGCs exhibit differential resilience to glaucomatous neurodegeneration, but it is unclear what cellular characteristics underlie this heterogeneous survival. Since survival in degenerative conditions likely requires high energy expenditure, we set out to test whether metabolic fitness influences survival of resilient RGC subsets.

Methods : We measured cellular ATP by 2-photon in vivo imaging of the FRET biosensor ATeam1.03 expressed specifically in RGCs. This method allows us to assess variance in ATP levels across the RGC population at the resolution of individual cells. We examined ATP dynamics in RGCs following pharmacologic challenge, correlating their differential response to survival following axon injury by optic nerve crush.

Results : At baseline, mouse RGCs maintain normally distributed cellular ATP levels. Intravitreal injection of sodium azide (NaN₃), a mitochondrial respiration inhibitor, revealed three RGC populations with distinct energetic behavior: a population resistant to ATP decline; a susceptible population with early decline and prolonged ATP depletion; and an intermediate population exhibiting delayed onset of ATP decrease followed quickly by recovery. Individual ATP responses in RGCs were reproducible across repeat NaN₃ challenge injections. Further, NaN₃ was not toxic as no RGC loss was observed up to 8 weeks after injection, allowing correlation of ATP dynamics with survival after optic nerve injury. Preliminary analysis suggests that the ATP-stable population have increased survival 14 days after optic nerve crush (32% survival) compared to RGCs that exhibited transient or prolonged ATP decline (17% survival).

Conclusions : We can directly examine energetic characteristics of individual RGCs in vivo and match energetic signatures with survival potential. We have found three cohorts of RGCs differentiated by their susceptibility to mitochondrial inhibition. Our preliminary data suggest that this heterogeneity in the ability to sustain cellular ATP may influence RGC survival after axotomy. Future experiments will examine other energetic pathways using appropriate pharmacologic inhibitors, in addition to more relevant glaucoma models.

This is a 2021 ARVO Annual Meeting abstract.