Erythropoietin inhibits apoptosis of retinal ganglion cells induced by high glucose through JNK signaling pathway

The aim of this study was to investigate the effect of erythropoietin (EPO) on the apoptosis of retinal ganglion cells (RGCs) induced by high glucose and its mechanism. Rat primary RGCs were extracted to establish high glucose-induced apoptosis models using a 30 mM high-glucose medium. Then flow cytometry, cell counting kit-8 (CCK-8) assay and Western blotting assay were performed to detect the effects of high-, medium- and low-dose EPO on the apoptosis of RGCs induced by high glucose. Next, the molecular mechanism by which EPO suppressed the high glucose-induced apoptosis of RGCs was explored via gene array assay and bioinformatics analysis. The results and mechanism of bioinformatics analysis were verified by Western blotting assay. Finally, the small interfering ribonucleic acid (siRNA) experiment was applied to knock down tyrosine-protein phosphatase non-receptor type 1 (PTPN1) and PTPN11 to verify their roles in the inhibition of EPO on the apoptosis of RGCs triggered by high glucose. Flow cytometry-Annexin V/propidium iodide (PI) staining and CCK-8 assay confirmed that the high-, medium- and low-dose EPO inhibited the apoptosis of RGCs induced by high glucose in a dose-dependent manner (P<0.05). Subsequently, Western blotting assay results manifested that the high-, medium- and low-dose EPO reduced the expression levels of apoptosis-related proteins active-cysteinyl aspartate specific proteinase 3 (Caspase 3) and active- Caspase 9 in a dose-dependent manner (P<0.05). Moreover, according to gene array assay and bioinformatics analysis results, the c-Jun N-terminal kinase (JNK) signaling pathway, PTPN1 and PTPN11 might exert crucial effects in the inhibition of EPO on the apoptosis of RGCs induced by high glucose. Western blotting assay results also demonstrated that, compared with the high-glucose treatment, the high-dose EPO treatment decreased the protein expression level of phosphorylated (p)-JNK1/JNK but increased the protein expression levels of PTPN1 and PTPN11 (P<0.05). Moreover, flow cytometry-Annexin V/PI staining and CCK-8 assay results revealed that in EPO-treated cells, knocking down PTPN1 and PTPN11 significantly reversed the protective effect of EPO against high glucose-induced retinal ganglion cell apoptosis (P<0.05). Lastly, Western blotting assay illustrated that knocking down PTPN1 and PTPN11 significantly abolished the inhibition of high-dose EPO on the JNK signaling pathway. EPO may suppress the JNK signaling pathway by raising the expression levels of PTPN1 and PTPN11, so as to inhibit the apoptosis of RGCs triggered by high glucose.