Autophagy: a new way to retinal neuroprotection

Abstract

AbstractPurpose Autophagy is a highly conserved catabolic pathway in which proteins and organelles are engulfed by autophagic vacuoles (AVs) that are then targeted to lysosomes for degradation. Basal autophagy serves homeostatic function and it is induced during periods of cell stress. Defects in the autophagic machinery have been described in several neurodegenerative diseases. In this study we investigated the role of autophagy in the retinal neurodegeneration associated to ischemic conditions.Methods Retinal ischemia was induced in adult rats by acute elevation of intraocular pressure. Expression of autophagy related proteins, beclin‐1 and LC3, was studied by western blotting and immunofluorescence. NMDA antagonists, calpain inhibitors or siRNA were intravitreally administered. Effects of autophagy modulation on retinal ganglion cell (RGC) survival was evaluated in serum‐starved RGC‐5 treated with autophagy inhibitors or transfected with beclin‐1 siRNA.Results Beclin‐1 is part of the complex involved in the induction of autophagy, while LC3 plays an essential role in the expansion of AVs. Retinal ischemia produced a reduction of the autophagosome‐associated form of LC3 (LC3II) and induced a significant decrease of beclin‐1 expression. The latter event was dependent on NMDA receptors and calpain activation as shown by the prevention afforded by MK801, calpain inhibitors or calpain siRNA. Inhibition of autophagy or beclin‐1 silencing in RGC‐5 significantly reduced cell viability under serum starvation conditions.Conclusion Our results, while provide the first in vivo evidence of a calpain‐mediated cleavage of beclin‐I, show that retinal ischemia alters the dynamic of the autophagic process and suggest a neuroprotective role of autophagy in RGCs exposed to detrimental stimuli.