Calpain-mediated cleavage of Beclin-1 and autophagy deregulation following retinal ischemic injury in vivo

Abstract

Autophagy is the major intracellular degradation pathway that regulates long-lived proteins and organelles turnover. This process occurs at basal levels in all cells but it is rapidly upregulated in response to starvation and cellular stress. Although being recently implicated in neurodegeneration, it remains still unclear whether autophagy has a detrimental or protective role. In this study, we investigated the dynamics of the autophagic process in retinal tissue that has undergone transient ischemia, an experimental model that recapitulates features of ocular pathologies, including glaucoma, anterior ischemic optic neuropathy and retinal vessels occlusion. Retinal ischemia, induced in adult rats by increasing the intraocular pressure, was characterized by a reduction in the phosphatidylethanolamine-modified form of LC3 (LC3II) and by a significant decrease in Beclin-1. The latter event was associated with a proteolytic cleavage of Beclin-1, leading to the accumulation of a 50-kDa fragment. This event was prevented by intravitreal treatment with the non-competitive N-methyl-D-aspartate antagonist MK801 and calpain inhibitors or by calpain knockdown. Blockade of autophagy by pharmacological inhibition or Beclin-1 silencing in RGC-5 increased cell death, suggesting a pro-survival role of the autophagic process in this neuronal cell type. Altogether, our results provide original evidence for calpain-mediated cleavage of Beclin-1 and deregulation of basal autophagy in the rat retina that has undergone ocular ischemia/reperfusion injury.

Hypoxia promotes noncanonical autophagy in nucleus pulposus cells independent of MTOR and HIF1A signaling

“…Moreover, western blot analysis showed insensitivity of levels of BECN1 or the ATG12-ATG5 complex to hypoxia. While prolonged starvation has been shown to increase the levels of BECN1 and the ATG12-ATG5 complex, 31,58,59 it is not entirely unusual that Moreover, autophagy in NP cells is largely independent of the MTOR-ULK1 axis. This noncanonical pathway also does not involve changes in the levels of autophagy-related proteins such as BECN1 and the ATG12-ATG5 complex.…”

Simultaneous inhibition of the ubiquitin-proteasome system and autophagy enhances apoptosis induced by ER stress aggravators in human pancreatic cancer cells

“…It has been reported that CAPN is involved in proteasome inhibitorinduced androgen receptor breakdown, 41,42 and the autophagic proteins BECN1 is cleaved by CAPN. 43 The involvement of CAPN and other proteases in autophagic SNARE protein breakdown will be further explored in future studies. Indeed, although the underlying molecular mechanisms for WA's effects on the SNAREs require further investigation, this is the first report describing inhibition of the SNAREs by a natural compound.…”

Beclin1: A role in membrane dynamics and beyond

“…2C). [77][78][79][80][81][82] The Beclin 1 fragments generated by caspases are unable to induce autophagy, demonstrating that a proteolysis-dependent mechanism controls Beclin 1 function. 79,80 Beclin 1 is also kept in check at the post-translational level.…”