Restoration of mitochondrial axonal transport by adaptor supplementation prevents neurodegeneration and rescues visual function in glaucoma

Abstract

Purpose : Mitochondria distribution in retinal ganglion cells (RGC) is crucial for homeostasis and neurotransmission. Here, we tested the hypotheses that: i) mitochondrial axonal transport deficits contribute to energetic imbalance and RGC damage in glaucoma, and ii) supplementation of the adaptor protein Disc1 (Disrupted in Schizophrenia 1) restores mitochondrial mobility, prevents energy decline, and rescues RGC function

Methods : Ocular hypertension (OHT) was induced by intracameral injection of magnetic microbeads in Thy1-CFP-MitoS mice. RGC-specific Disc1 levels were increased using recombinant adeno-asociated virus (AAV.Disc1). Two-photon laser scanning microscopy was used to i) record mitochondrial movement along RGC axons followed by kymograph analysis, and ii) measure axonal ATP levels using the sensor Ateam. Mitochondrial volume in single RGC axons was quantified using confocal microscopy and Imaris software. RGC density was quantified in RBPMS-stained retinas using a stereological approach. RGC function was assessed by measuring light-evoked positive scotopic threshold responses (pSTR) and using the optomotor reflex assay for visual acuity.

Results : Live imaging of mitochondrial mobility along RGC axons showed a reduction of anterograde transport in glaucomatous eyes (OHT-2 weeks: 40% decrease, t-test p<0.001, n=14/grp). Transport deficits were accompanied by a decrease in mitochondrial volume in RGC axons, both in the retina and the myelination transition zone (~50% reduction vs. sham, t-test p<0.001, n=16/grp). Intravitreal administration of AAV.Disc1 fully restored mitochondrial mobility and volume in RGC axons subjected to OHT (ANOVA p<0.01, n=10/grp). Remarkably, enhanced mitochondrial transport restored axonal ATP levels preventing energetic decline (ANOVA p<0.05, n=4/grp) and promoted robust RGC survival (ANOVA p<0.001, n=10/grp). Furthermore, AAV.Disc1 prevented loss of light-evoked pSTR responses (ANOVA p<0.01, n=12/grp) and improved visual acuity relative to sham animals (ANOVA p<0.01, n=8/grp).

Conclusions : Glaucomatous damage disrupts mitochondrial anterograde transport along RGC axons leading to mitochondria depletion and energy decline. Disc1 adaptor supplementation improved mitochondrial anterograde transport, replenished axonal mitochondria, rescued energy homeostasis, and restored light-evoked responses and visual acuity in glaucoma.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.