Rapamycin and fasting sustain autophagy response activated by ischemia/reperfusion injury and promote retinal ganglion cell survival

Rossella Russo,Luigi Antonio Morrone,Federica Cavaliere,Valentina Cianfanelli,Gianluca Tettamanti,Annagrazia Adornetto,Rossana Girardello,Francesca Nazio,Francesco Cecconi,Giacinto Bagetta,Giuseppe Pasquale Varano,Carlo Nucci,Maria Tiziana Corasaniti

doi:10.1038/s41419-018-1044-5

Abstract

Autophagy, the cellular process responsible for degradation and recycling of cytoplasmic components through the autophagosomal–lysosomal pathway, is fundamental for neuronal homeostasis and its deregulation has been identified as a hallmark of neurodegeneration. Retinal hypoxic–ischemic events occur in several sight-treating disorders, such as central retinal artery occlusion, diabetic retinopathy, and glaucoma, leading to degeneration and loss of retinal ganglion cells. Here we analyzed the autophagic response in the retinas of mice subjected to ischemia induced by transient elevation of intraocular pressure, reporting a biphasic and reperfusion time-dependent modulation of the process. Ischemic insult triggered in the retina an acute induction of autophagy that lasted during the first hours of reperfusion. This early upregulation of the autophagic flux limited RGC death, as demonstrated by the increased neuronal loss observed in mice with genetic impairment of basal autophagy owing to heterozygous ablation of the autophagy-positive modulator Ambra1 (Ambra1+/gt). Upregulation of autophagy was exhausted 24 h after the ischemic event and reduced autophagosomal turnover was associated with build up of the autophagic substrate SQSTM-1/p62, decreased ATG12-ATG5 conjugate, ATG4 and BECN1/Beclin1 expression. Animal fasting or subchronic systemic treatment with rapamycin sustained and prolonged autophagy activation and improved RGC survival, providing proof of principle for autophagy induction as a potential therapeutic strategy in retinal neurodegenerative conditions associated with hypoxic/ischemic stresses.

Highlights

During macroautophagy, cytosolic components are sequestered in a doublemembrane vesicle called autophagosome and delivered to lysosomes[2,3]
In GFP-LC3 mice subjected to retinal ischemia followed by 6 h of reperfusion, increased endogenous fluorescence was mostly evident in the inner retinal layers (Fig. 1D)
By using a mouse model of retinal ischemia, here we showed that ischemic insult triggers an acute autophagy response lasting the initial hours of reperfusion

Summary

Introduction

During macroautophagy (hereafter referred to as autop-Autophagy is a highly conserved catabolic process responsible for degradation of cytoplasmic content[1].hagy), cytosolic components are sequestered in a doublemembrane vesicle called autophagosome and delivered to lysosomes[2,3]. Through the mobilization of intracellular resources, autophagy enables cells to adapt to stressful environments, allowing the survival under states of increased. These authors contributed : Giuseppe Pasquale Varano, Annagrazia Adornetto. Autophagy overactivation, and the consequent self-digestion, has been associated with cellular death[6]. Owing to their post-mitotic nature, high energy demand and distinctive morphology, neurons are strictly dependent on autophagy efficiency[7], and several studies have shown that maintaining the appropriate level of autophagy is fundamental for neuronal health[8,9,10]. Hypoxic/ischemic events are common in several of the above disorders[21,22] and retinal hypoperfusion has been shown to occur in glaucoma patients, this contributing to the initiation and progression of the neuropathy[23,24]

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Conclusion