As in glaucoma and other optic neuropathies cellular dysfunction often precedes cell death, sensitive assessment of retinal ganglion cell (RGC) function represents a key outcome measure for neuroprotective strategies aimed at targeting distressed but still viable cells. Here we offer a conceptual framework to identify progressive stages of RGC dysfunction leading to cell death in mouse models of glaucoma and other optic neuropathies based on non-invasive pattern electroretinogram (PERG), to differentiate phenotypic and altered RGC response dynamics, to assess susceptibility to stressors and to assess reversible dysfunction.

Leber’s hereditary optic neuropathy (LHON) is a common mitochondrial genetic disease, causing irreversible blindness in young individuals. Current treatments are inadequate, and there is no definitive cure. This study evaluates the effectiveness of delivering wildtype human NADH ubiquinone oxidoreductase subunit 4 (hND4) gene using mito-targeted AAV(MTSAAV) to rescue LHOH mice. We observed declining pattern electroretinograms amplitudes as mice aged across all groups (P< 0.001), with significant differences among groups (P = 0.023, Control vs. LHON, P = 0.008; Control vs. Rescue, P = 0.228). Inner retinal thickness and intraocular pressure do not change significantly with age or groups. Compared to LHON mice, those rescued with wildtype hND4 exhibit improved retinal visual acuity (0.29± 0.1 cy/deg vs.0.15 ± 0.1 cy/deg) and increased functional hyperemia response (effect of flicker, P<0.001, effect of Group, P=0.004; Interaction Flicker x Group, P<0.001). Postmortem analysis shows a marked reduction in retinal ganglion cell density in the LHON group compared to the other groups (Effect of Group, P<0.001, Control vs. LHON, P<0.001, Control vs. Rescue, P=0.106). These results suggest that MTSAAV-delivered wildtype hND4 gene rescues, at least in part, visual impairment in an LHON mouse model and has the therapeutic potential to treat this disease.

Dysfunction and selective loss of retinal ganglion cells (RGCs) is a known cause of vision loss in glaucoma and other neuropathies where ocular hypertension (OHT) is the major risk factor. We investigated the impact of transient non-ischemic OHT spikes (spOHT) on RGC function and viability in vivo to identify cellular pathways linking low-grade repetitive mechanical stress to RGC pathology. We found that repetitive spOHT had an unexpectedly high impact on intraocular homeostasis and RGC viability, while exposure to steady OHT (stOHT) of similar intensity and duration failed to induce pathology. The repetitive spOHT induced a rapid activation of the inflammasome, marked by the upregulation of NLRP1, NLRP3, AIM2, caspases -1, -3/7, -8, gasdermin D (GsdmD) and the release of interleukin-1β (IL-1β) and other cytokines into the vitreous. Similar effects were also detected after 5 weeks of exposure to chronic OHT in an induced glaucoma model. The onset of these immune responses in both spOHT and glaucoma models preceded a 50% deficit in pattern electroretinograms (PERG) amplitude, and significant loss of RGCs at 7 days post-injury. Inactivation of inflammasome complexes in NLRP1-/- , Casp1-/- and GsdmD-/- knockout animals, significantly suppressed the spOHT induced inflammatory response and protected RGCs. Our results demonstrate that mechanical stress produced by acute repetitive spOHT or chronic OHT is mechanistically linked to inflammasome activation, which leads to RGC dysfunction and death.