Autophagy-mediated neuroprotection induced by octreotide in an ex vivo model of early diabetic retinopathy

Abstract

Neuronal injury plays a major role in diabetic retinopathy (DR). Our hypothesis was that the balance between neuronal death and survival may depend on a similar equilibrium between apoptosis and autophagy and that a neuroprotectant may act by influencing this equilibrium. Ex vivo mouse retinal explants were treated with high glucose (HG) for 10days and the somatostatin analog octreotide (OCT) was used as a neuroprotectant. Chloroquine (CQ) was used as an autophagy inhibitor. Apoptotic and autophagic markers were evaluated using western blot and immunohistochemistry. HG-treated explants displayed a significant increase of apoptosis paralleled by a significant decrease of the autophagic flux, which was likely to be due to increased activity of the autophagy regulator mTOR (mammalian target of rapamycin). Treatment with OCT rescued HG-treated retinal explants from apoptosis and determined an increase of autophagic activity with concomitant mTOR inhibition. Blocking the autophagic flux with CQ completely abolished the anti-apoptotic effect of OCT. Immunohistochemical observations showed that OCT-induced autophagy is localized to populations of bipolar and amacrine cells and to ganglion cells. These observations revealed the antithetic role of apoptosis and autophagy, highlighting their equilibrium from which neuronal survival is likely to depend. These data suggest the crucial role covered by autophagy, which could be considered as a molecular target for DR neuroprotective treatment strategies.

The Beta Adrenergic Receptor Blocker Propranolol Counteracts Retinal Dysfunction in a Mouse Model of Oxygen Induced Retinopathy: Restoring the Balance between Apoptosis and Autophagy

“…Protein expression was analyzed following published protocols ( Cervia et al, 2002 , 2003 , 2007 , 2016 ; Cazzato et al, 2014 ; De Palma et al, 2014 ; Lulli et al, 2015 ; Amato et al, 2017 ). Briefly, pooled sample retinas (2 retinas from 2 mice for each experimental condition) were sonicated in 10 mM Tris-HCl (pH 7.6) containing 5 mM EDTA, 3 mM EGTA, 250 mM sucrose, 10% SDS, and supplemented with a cocktail of protease and phosphatase inhibitors.…”

“…Autophagy is a catabolic pathway that promotes the degradation and recycling of cellular components. It functions in retinal cell death, but also serves as a cell survival mechanism and its modulation may be either beneficial or deleterious depending on the retinal cell type involved and the disease context ( Mitter et al, 2012 ; Russo et al, 2013 ; Chinskey et al, 2014 ; Frost et al, 2014 ; Boya et al, 2016 ; Chai et al, 2016 ; Rosa et al, 2016 ; Amato et al, 2017 ). In this respect, drugs targeting the autophagic pathway may provide a new therapeutic strategy to ameliorate retinal disorders.…”

Endoplasmic reticulum stress and the protein degradation system in ophthalmic diseases

“…Some studies have shown that autophagy deficiency is a pathological factor leading to many ophthalmic diseases such as corneal opacification, elevated IOP, retinal dystrophy, mucopolysaccharide storage disease type VI, and AMD (Claudepierre et al, 2010;Golestaneh et al, 2017;Karnati et al, 2016;Lőrincz et al, 2016). Moreover, it was reported that exposure of ex-vivo mice retinal explants to high glucose resulted in the death of retinal neuronal cells, while treatment the explants with octreotide may protect neuronal cells against high glucose damage by enhancing autophagy (Amato et al, 2018). Although proper autophagy is beneficial to cell survival under stress, overactivated autophagy may lead to cell death, which is called autophagic cell death (ACD) (Liu & Levine, 2015;Vegliante & Ciriolo, 2018).…”

Peer Review #3 of "Endoplasmic reticulum stress and the protein degradation system in ophthalmic diseases (v0.1)"

“…Some studies have shown that autophagy deficiency is a pathological factor leading to many ophthalmic diseases such as corneal opacification, elevated IOP, retinal dystrophy, mucopolysaccharide storage disease type VI, and AMD (Claudepierre et al 2010;Golestaneh et al 2017;Karnati et al 2016;Lőrincz et al 2016). Moreover, it was reported that exposure of exvivo mice retinal explants to high glucose resulted in the death of retinal neuronal cells, while treatment the explants with octreotide may protect neuronal cells against high glucose damage by enhancing autophagy (Amato et al 2018). Although proper autophagy is beneficial to cell survival under stress, overactivated autophagy may lead to cell death, which is called autophagic cell death (ACD) (Liu & Levine 2015;Vegliante & Ciriolo 2018).…”