Effects of the dynamic modulation of macroautophagy on retinal ganglion cell survival in a mouse model of retinal ischemia/reperfusion

Abstract

Purpose : Dysregulation of autophagy, the catabolic pathway that promotes the degradation and recycling of cellular components through the autophagosome-lysosome system, has been reported in retinas exposed to glaucoma-related stressing conditions. However, the functional role of the process (detrimental vs protective) for retinal ganglion cell (RGC) degeneration is still debated. The purpose of this study was to investigate (1) the modulation of the autophagic pathway and (2) the outcome on RGC survival of treatment able to modulate autophagy in the retina of mice subjected to high intraocular pressure (IOP)-induced ischemia.

Methods : Retinal ischemia was induced in adult wild type C57BL/6J or GFP-LC3 transgenic mice by acute elevation of IOP. Expression of autophagy related proteins (Atg) was studied by western blotting and immunofluorescence. RGCs were retrogradely labeled by fluorogold and survival was assessed in autophagy-deficient mice (AMBRA1^+/-) and upon rapamycin treatment or caloric restriction.

Results : A significant reduction of the autophagosome-associated form of Atg6 (LC3II) was observed at the end of ischemia and this was followed by a significant accumulation of the protein in the ganglion cell layer after 6 hours of reperfusion, where the accumulated LC3 colocalized with lysosomal-associated membrane protein 2 (LAMP2). A biphasic modulation of the autophagic substrate p62 with a significant build up during the late phase of reperfusion, was also reported. Induction of retinal ischemia in autophagy-deficient Ambra^+/- mice was associated with increased RGC death, while autophagy induction by rapamycin or caloric restriction improved RGC survival.

Conclusions : Our results suggest that autophagic pathway is dynamically modulated following retinal ischemia/reperfusion injury and support a neuroprotective role of autophagy for RGCs in vivo.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.