Protection of H2S against Hypoxia/Reoxygenation Injury in Rat Hippocampal Neurons through Inhibiting Phosphorylation of ROCK2 at Thr436 and Ser575

Abstract

Background: H2S (hydrogen sulfide) protects cerebral vasodilatation and endothelial cells against oxygen-glucose deprivation/reoxygenation injury via the inhibition of the RhoA-ROCK pathway and ROCK2 expression. However, the inhibitory mechanism of H2S on ROCK2 expression is still unclear. The study aimed to investigate the target and mechanism of H2S in inhibition of ROCK2. Methods: His-ROCK2wild protein was constructed, expressed, and was used for phosphorylation assay in vitro. Liquid chromatography–tandem mass spectrometry (LC–MS/MS) was used to determine the potential phosphorylation sites of ROCK2. Recombinant ROCK2wild-pEGFP-N1, ROCK2T436A-pEGFP-N1, and ROCK2S575F-pEGFP-N1 plasmids were constructed and transfected into rat hippocampal neurons (RHNs). ROCK2 expression, cell viability, the release of lactate dehydrogenase (LDH), nerve-specific enolase (NSE), and Ca2+ were detected to evaluate the neuroprotective mechanism of H2S. Results: Phosphorylation at Thr436 and Ser575 of ROCK2 was observed by mass spectrometry when Polo-like kinase 1 (PLK1) and protein kinase A (PKA) were added in vitro, and NaHS significantly inhibited phosphorylation at Thr436 and Ser575. Additionally, NaHS significantly inhibited the expression of ROCK2 and recombinant proteins GFP-ROCK2, GFP-ROCK2T436A, and GFP-ROCK2S575F in transfected RHNs. Compared with empty plasmid, GFP-ROCK2T436A, and GFP-ROCK2S575F groups, NaHS significantly inhibited the release of LDH, NSE, and Ca2+ and promoted ROCK2 activity in the GFP-ROCK2wild group. Thr436 and Ser575 may be dominant sites that mediate NaHS inhibition of ROCK2 protein activity in RHNs. Compared with the empty plasmid, GFP-ROCK2T436A, and the GFP-ROCK2S575F group, NaHS had more significant inhibitory effects on hypoxia/reoxygenation (H/R) injury-induced cell viability reduction and increased LDH and NSE release in the GFP-ROCK2wild group. Conclusion: Exogenous H2S protected the RHNs against H/R injury via Thr436 and Ser575 of ROCK2. These findings suggested that Thr436 and Ser575 may be the dominant sites that mediated the effect of NaHS on protecting RHNs against H/R injury.