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AIM: To investigate the effect of interleukin-8 (IL-8) on neural retinal ganglion cells (RGCs) and whether it can be alleviated by G31P. METHODS: RGC-5 cells were exposed to IL-8 with or without its specific receptor antagonist G31P for 24h, and the cell viability was assessed by Cell Counting Kit 8 (CCK-8). Apoptosis was measured by examining nuclear morphology and quantifying with flow cytometry. Reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR) and Western blot were used to investigate the expression of apoptosis-related genes. RESULTS: CCK-8 assay showed that IL-8 significantly inhibits the viability of RGC-5 cells in a dose-dependent manner. Cell apoptosis assays exhibited higher apoptotic rate in IL-8 treatment group compared to control group. We further found that IL-8 could promote Bax and caspase-3 expressions, but decrease the level of Bcl-2 in the aspect of mRNA and protein. However, pre-treatment with G31P partly attenuated these effects in RGC-5 cells (P

Pituitary adenylate cyclase-activating polypeptide (PACAP) is an endogenous peptide with neuroprotective effects on retinal neurons, but the precise mechanism underlying these effects remains unknown. Considering the abundance of mitochondria in retinal ganglion cells (RGCs), we postulate that the protective effect of PACAP is associated with the regulation of mitochondrial function. RGC-5 cells were subjected to serum deprivation for 48 hours to induce apoptosis in the presence or absence of 100 nM PACAP. As revealed with the Cell Counting Kit-8 assay, PACAP at different concentrations significantly increased the viability of RGC-5 cells. PACAP also inhibited the excessive generation of reactive oxygen species in RGC-5 cells subjected to serum deprivation. We also showed by flow cytometry that PACAP inhibited serum deprivation-induced apoptosis in RGC-5 cells. The proportions of apoptotic cells and cells with mitochondria depolarization were significantly decreased with PACAP treatment. Western blot assays demonstrated that PACAP increased the levels of Bcl-2 and inhibited the compensatory increase of PAC1. Together, these data indicate protective effects of PACAP against serum deprivation-induced apoptosis in RGCs, and that the mechanism of this action is associated with maintaining mitochondrial function.

Receptor‐interacting protein 3 (RIP3) plays an important role in the necroptosis signaling pathway. Our previous studies have shown that the RIP3/mixed lineage kinase domain‐like protein (MLKL)‐mediated necroptosis occurs in retinal ganglion cell line 5 (RGC‐5) following oxygen‐glucose deprivation (OGD). However, upstream regulatory pathways of RIP3 are yet to be uncovered. The purpose of the present study was to investigate the role of p90 ribosomal protein S6 kinase 3 (RSK3) in the phosphorylation of RIP3 in RGC‐5 cell necroptosis following OGD. Our results showed that expression of RSK3, RIP3, and MLKL was upregulated in necroptosis of RGC‐5 after OGD. A computer simulation based on our preliminary results indicated that RSK3 might interact with RIP3, which was subsequently confirmed by co‐immunoprecipitation. Further, we found that the application of a specific RSK inhibitor, LJH685, or rsk3 small interfering RNA (siRNA), downregulated the phosphorylation of RIP3. However, the overexpression of rip3 did not affect the expression of RSK3, thereby indicating that RSK3 could be a possible upstream regulator of RIP3 phosphorylation in OGD‐induced necroptosis of RGC‐5 cells. Moreover, our in vivo results showed that pretreatment with LJH685 before acute high intraocular pressure episodes could reduce the necroptosis of retinal neurons and improve recovery of impaired visual function. Taken together, our findings suggested that RSK3 might work as an upstream regulator of RIP3 phosphorylation during RGC‐5 necroptosis. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the effect of inhibition of calpain on retinal ganglion cell-5 (RGC-5) necroptosis following oxygen glucose deprivation (OGD). RGC-5 cells were cultured in Dulbecco's-modified essential medium and necroptosis was induced by 8-h OGD. PI staining and flow cytometry were performed to detect RGC-5 necrosis. The calpain expression was detected by Western blotting and immunofluorescence staining. The calpain activity was tested by activity detection kit. Flow cytometry was used to detect the effect of calpain on RGC-5 necroptosis following OGD with or without N-acetyl-leucyl-leucyl-norleucinal (ALLN) pre-treatment. Western blot was used to detect the protein level of truncated apoptosis inducing factor (tAIF) in RGC-5 cells following OGD. The results showed that there was an up-regulation of the calpain expression and activity following OGD. Upon adding ALLN, the calpain activity was inhibited and tAIF was reduced following OGD along with the decreased number of RGC-5 necroptosis. In conclusion, calpain was involved in OGD-induced RGC-5 necroptosis with the increased expression of its downstream molecule tAIF. [ABSTRACT FROM AUTHOR]

Background: Necroptosis is a type of regulated form of cell death that has been implicated in the pathogenesis ofvari-ous diseases. Receptor-interacting protein 3 (RIP3), a member of the RIP family of proteins, has been reported asan important necroptotic pathway mediator in regulating a variety of human diseases, such asmyocardial ischemia, inflammatory bowel disease, and ischemie brain injury. Our previous study showed that RIP3 was expressed in rat retinal ganglion cells (RGCs), where it was significantly upregulated during the early stage of acute high intraocular pressure. Furthermore, RIP3 expression was co-localized with propidium iodide (PI)-positive staining (necrotic cells). These results suggested that RIP3 up-regulation might be involved in the necrosis of injured RGCs. In thisstudy, weaimed to reveal the possible involvement of RIP3 in oxygen glucose deprivation (OGD)-induced retinal ganglion cell-5 (RGC-5) necroptosis. Methods: RGC-5 cells were cultured in Dulbecco's-modified essential medium and necroptosis was induced by 8 h OGD. PI staining and flow cytometry were performed to detect RGC-5 necrosis. RIP3 expression was detected by western blot and flow cytometry was used to detect the effect of RIP3 on RGC-5 necroptosis following OGD in rip3 knockdown cells. Malondialdehyde (MDA) lipid peroxidation assay was performed to determine the degree of oxida-tive stress. Results: PI staining showed that necrosis was present in the early stage of OGD-induced RGC-5 cell death. The presence of RGC-5 necroptosis after OGD was detected by flow cytometry using necrostatin-1,a necroptosis inhibitor. Western blot demonstrated that RIP3 up-regulation may be involved in RGC-5 necroptosis. Flow cytometry revealed that the number of OGD-induced necrotic RGC-5 cells was reduced after rip3 knockdown. Furthermore, MDA levels in the normal RGC-5 cells were much higher than in the rip3-knockdown cells after OGD. Conclusions: Our findings suggest that RGC-5 cell necroptosis following OGD is mediated by a RIP3-induced increase in oxidative stress. [ABSTRACT FROM AUTHOR]

Aim: To investigate the effect of interleukin-8 (IL-8) on neural retinal ganglion cells (RGCs) and whether it can be alleviated by G31P., Methods: RGC-5 cells were exposed to IL-8 with or without its specific receptor antagonist G31P for 24h, and the cell viability was assessed by Cell Counting Kit 8 (CCK-8). Apoptosis was measured by examining nuclear morphology and quantifying with flow cytometry. Reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR) and Western blot were used to investigate the expression of apoptosis-related genes., Results: CCK-8 assay showed that IL-8 significantly inhibits the viability of RGC-5 cells in a dose-dependent manner. Cell apoptosis assays exhibited higher apoptotic rate in IL-8 treatment group compared to control group. We further found that IL-8 could promote Bax and caspase-3 expressions, but decrease the level of Bcl-2 in the aspect of mRNA and protein. However, pre-treatment with G31P partly attenuated these effects in RGC-5 cells ( P <0.05)., Conclusion: These results indicate that anti-proliferation effects of IL-8 through induction of cell apoptosis regulated by Bcl-2, Bax and caspase-3 expressions, can be ameliorated by G31P.

Pituitary adenylate cyclase-activating polypeptide (PACAP) is an endogenous peptide with neuroprotective effects on retinal neurons, but the precise mechanism underlying these effects remains unknown. Considering the abundance of mitochondria in retinal ganglion cells (RGCs), we postulate that the protective effect of PACAP is associated with the regulation of mitochondrial function. RGC-5 cells were subjected to serum deprivation for 48 hours to induce apoptosis in the presence or absence of 100 nM PACAP. As revealed with the Cell Counting Kit-8 assay, PACAP at different concentrations significantly increased the viability of RGC-5 cells. PACAP also inhibited the excessive generation of reactive oxygen species in RGC-5 cells subjected to serum deprivation. We also showed by flow cytometry that PACAP inhibited serum deprivation-induced apoptosis in RGC-5 cells. The proportions of apoptotic cells and cells with mitochondria depolarization were significantly decreased with PACAP treatment. Western blot assays demonstrated that PACAP increased the levels of Bcl-2 and inhibited the compensatory increase of PAC1. Together, these data indicate protective effects of PACAP against serum deprivation-induced apoptosis in RGCs, and that the mechanism of this action is associated with maintaining mitochondrial function., Competing Interests: None declared

Receptor-interacting protein 3 (RIP3) is an essential component of the necroptosis signaling pathway. Phosphorylation of its downstream target, mixed lineage kinase domain-like protein (MLKL), has been proposed to induce necroptosis by initiating Ca2+ influx. Our previous studies have shown that RGC-5 retinal ganglion cells undergo RIP3-mediated necroptosis following elevated hydrostatic pressure (EHP). However, the molecular mechanism underlying necroptosis induction downstream of RIP3 is still not well understood. Here, we investigated the effects of MLKL during EHP-induced necroptosis, and primarily explored the relationship between MLKL and Ca2+ influx. Immunofluorescence staining showed that the expression of MLKL was increased 12 h after EHP. Western blot analysis demonstrated that the phosphorylated and unphosphorylated forms of both RIP3 and MLKL were up-regulated 12 h after EHP, while inhibition of RIP3 by GSK'872 decreased the expression of phosphorylated MLKL at the same stage. Propidium iodide staining, lactate dehydrogenase release assays, flow cytometry, and electron microscopy revealed the increased necrosis of RGC-5 cells 12 h after EHP, which coincided with elevated cytosolic Ca2+ concentrations. Depletion of extracellular Ca2+ and siRNA-mediated silencing of MLKL significantly reduced EHP-induced necrosis. Both MLKL-specific siRNA and GSK'872 treatment diminished Ca2+ influx. Thus, our findings suggest that MLKL may be the key mediator of necroptosis downstream of RIP3 phosphorylation and may be involved in increasing intracellular Ca2+ concentrations in EHP-induced RGC-5 necroptosis., (© The Author 2017. Published by Oxford University Press on behalf of the Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Necroptosis is a type of regulated cell death that has been implicated in various diseases. Receptor-interacting protein 3 (RIP3), a member of the RIP family, is an important mediator of the necroptotic pathway. Cleavage of RIP3 at Asp328 by caspase-8 abolishes the kinase activity of RIP3, which is critical for necroptosis. Moreover, RIP3 is significantly upregulated during the early stages of acute high intra-ocular pressure and oxygen glucose deprivation. In this study, the effects of RIP3 during elevated hydrostatic pressure (EHP) were investigated and the possible mechanism through which caspase-8 regulated RIP3 cleavage was explored. Flow cytometry analysis revealed that the number of EHP-induced necrotic retinal ganglion cell 5 (RGC-5) cells was reduced after RIP3-knockdown. Furthermore, malondialdehyde (MDA) levels and glycogen phosphorylase (PYGL) activity in normal RGC-5 cells were much higher than those in RIP3-knockdown cells after EHP. EHP-induced RGC-5 necrosis was significantly reduced after treatment with butylated hydroxyanisole (BHA), a reactive oxygen species (ROS) scavenger. MDA levels and PYGL activity were lower in normal RGC-5 cells than those in cells with caspase-8 inhibition after EHP. Western blot analysis demonstrated that the RIP3 cleavage product was upregulated in cells with caspase-8 inhibition. Additionally, flow cytometry analysis revealed that the number of EHP-induced necrotic RGC-5 cells was increased after caspase-8 inhibition. Our results suggested that RGC-5 necroptosis following EHP was mediated by RIP3 through induction of PYGL activity and subsequent ROS accumulation. Thus, caspase-8 may participate in the regulation of RGC-5 necroptosis via RIP3 cleavage., (© The Author 2016. Published by Oxford University Press on behalf of the Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)