Role Of Endoplasmic Reticulum Stress In Retinal Ischemia And Reperfusion Injury

Retinal ischemia and reperfusion (I/R) injury contributes to the pathogenesis of many ocular diseases including acute closed-angle glaucoma and diabetic retinopathy, which are leading causes of visual impairment and blindness around the world. Retinal I/R has been reported to induce neuronal degeneration, vascular degeneration and glial cell activation, however, the underlying meachanisms are not fully understood. In this thesis, a mouse model of retinal I/R injury, and a retinal cell cultue model of ischemia were used to investigate the possible mechanisms of the I/R injury.Accumulating evidences demonstrate that endoplasmic reticulum (ER) stress-mediated cell death plays a vital role in the development of retinal damage. For the first time, we demonstrated that.intravitreal injection of tunicamycin, an ER stress inducer, caused a significant vascular degeneration. ER stress marks, such as CHOP, were significantly elevated in the retinas, especially the retinal vasculatures, after I/R injury and tunicamycin injection. Resveratrol is a natural polyphenolic phytoalexin with multiple bioactivities including anti-inflammatory, anti-oxidative stress and anit-tumogeneisis effects. Both ER stresss activation and vascular degeneration induced by retinal I/R injury and tunicamycin injection were suppressed by resveratrol treatment (25mg kg-1day-1). However, resveratrol treatment showed no effects on the I/R-induced neurodegeneration. This result suggests that ER stress is involved in the vascular degeneration in retina, and resveratrol exhibits vasoprotective effects via suppression ER stress activation, especially in the retinal vasculture.Poly(ADP-ribose) polymerase (PARP) has been previously reported to be over-activated after retinal I/R injury. The first generation PARP inhibitors have neuroprotective effects. Administration of second generation PARP inhibitor, GPI15427(40mg kg-1day-1), before or after I/R injury suppressed retinal I/R induced neurodegeneration. GPI15427inhibited neuronal cell death via suppression of I/R injury-induced CHOP and Bip over-expression, especially on the neuronal part of the retina. Nonetheless, injury-induced CHOP expression in the retinal vasculatures and vascular degeneration were not effected by GPI15427.We also demonstrated that ER stress-related proteins were elevated in the rMC1cells treated with serum and glucose deprivation. Besides the activation of ER stress, mTOR signaling pathway was dramatically stimulated after the injury, however, rapamycin, a specific mTOR inhibitor, did not inhibit the retinal I/R induced neuronal or vascular degeneration. Moreover,4E-BP1, a substrate of mTOR, was significantly induced at both mRNA and protein levels after the injury, but its role in the pathogenesis of retinal I/R injury is still unknown. Retinal I/R injury also triggered up-regulation ofp53and p53acetylation, and down-regulation of SIRT1.In summary, ER stress contributes to not only neuronal degeneration, but also vascular degeneration after retinal I/R injury. Resveratrol and GPI15427showed vascular and neuronal protection after I/R injury separately, possibly through suppression of ER stress in vascular and neuronal cells, respectively. Besides, many other molecules such as4E-BP1, p53and SIRT1may also participate in the development of I/R-induced pathological lesions. Our present study provides new mechanisms of the development of neuronal and vascular degeneration after retinal I/R injury, and suggests possible therapeutical targets to prevent these degenerations.