Nuclear PKR in retinal neurons in the early stage of diabetic retinopathy in streptozotocin‑induced diabetic rats

Abstract

retinal neuron apoptosis is a key component of diabetic retinopathy (dr), one of the most common complications of diabetes. Stress due to persistent hyperglycaemia and corresponding glucotoxicity represents one of the primary pathogenic mechanisms of diabetes and its complications. apoptosis of retinal neurons serves a critical role in the pathogenesis of dr observed in patients with diabetes and streptozotocin (STZ)-induced diabetic rats. retinal neuron apoptosis occurs one month after STZ injection, which is considered the early stage of dr. The molecular mechanism involved in the suppression of retinal neuron apoptosis during the early stage of dr remains unclear. rna-dependent protein kinase (PKr) is a stress-sensitive pro-apoptotic kinase. our previous study indicated that PKR-associated protein X, a stress-sensitive activator of PKr, is upregulated in the early stage of STZ-induced diabetes. in order to assess the role of PKr in dr prior to apoptosis of retinal neurons, immunofluorescence and western blotting were performed to investigate the cellular localization and expression of PKr in the retina in the early stage of STZ-induced diabetes in rats. PKr activity was indirectly assessed by expression levels of phosphorylated eukaryotic translation initiation factor 2α (p-eiF2-α) and the presence of apoptotic cells in the retina was investigated by Tunel assay. The findings revealed that PKR was localized in the nucleus of retinal ganglion and inner nuclear layer cells from normal and diabetic rats. To the best of our knowledge, the present study is the first to demonstrate nuclear localization of PKR in retinal neurons. Immunofluorescence analysis demonstrated that PKR was expressed in the nuclei of retinal neurons at 3 and 6 days and its expression was decreased at 15 days after STZ treatment. in addition, p-eiF2-α expression and cellular localization followed the trend of PKr, suggesting that this pro-apoptotic kinase was active in the nuclei of retinal neurons. These findings are consistent with the hypothesis that nuclear translocation of PKr may be a mechanism to sequester active PKr, thus preventing upregulation of cytosolic signalling pathways that induce apoptosis in retinal neurons. apoptotic cells were not detected in the retina in the early stage of dr. a model was proposed to explain the mechanism by which apoptosis of retinal neurons by PKr is suppressed in the early stage of dr. The possible role of mitochondrial rna (mtrna) and Alu rna in this phenomenon is also discussed since it was demonstrated that the cellular stress due to prolonged hyperglycaemia induces the release of mtrna and transcription of Alu rna. Moreover, it mtrna activates PKr, whereas Alu rna inhibits the activation of this protein kinase.

Mitochondrial dysfunction decreases cisplatin sensitivity in gastric cancer cells through upregulation of integrated stress response and mitokine GDF15

“…Previous evidence demonstrated that mitochondrial stress might activate PERK and GCN2 pathways [91][92][93]. Recently, PKR has been regarded as a possible crosslink between mitochondrial dysfunction and ISR [94][95][96][97][98][99]. Additionally, mitochondrial dysfunction might relate to activated PKR via endoplasmic reticulum stress, mitochondrial ROS, and mitochondrial RNAs [94,98,99].…”

Research Progress on Mitochondrial Dysfunction in Diabetic Retinopathy

“…Santiago et al found that high glucose-induced apoptosis in retinal neurons was related to the release of apoptosis-inducing factor (AIF) by mitochondria, but not dependent on the activation of caspases [ 141 ]. It is worth mentioning that RNA in mitochondria can also be released into the cytosol during mitochondrial damage induced by high glucose and exist as double-stranded RNA [ 142 ], which can interact with RNA-dependent protein kinase (PKR), mediating apoptosis of retinal neurons [ 143 ]. High glucose activates the NF-κB signaling pathway, enhances oxidative stress in Müller cells, and is also involved in inducing apoptosis in the mitochondrial pathway [ 144 ].…”

SARS-CoV-2 infection and Diabetes: Pathophysiological Mechanism of Multi-System Organ Failure

“…Recent studies have reported that vascular changes are preceded by the damage and loss of retinal neurons due to apoptosis or autophagy. According to Silva et al, STZ-induced diabetic rats started to show DR symptoms after one month of STZ injection[140]. STZ-induced diabetic mice showed loss of rod cells, reduced thickness of the outer and inner synaptic layers along with the upregulation of autophagic proteins, including Beclin-1 and Atg5.…”