Guoxin Zhang, Yuyin Wu, Huiqin Lin
Myocardial ischemia/reperfusion (I/R) injury is a major cause of morbidity and mortality. Although both nuclear factor erythroid 2-related factor 2 (Nrf2) and O-GlcNAcylation play critical protective roles in myocardial I/R injury, it remains unclear the role of Nrf2 O-GlcNAcylation in cardiac injury following I/R. An in vivo I/R model in mice and an in vitro oxygen-glucose deprivation/reperfusion (OGD/R) model in AC16 cardiomyocytes were employed. Histology, serum markers, and oxidative stress assays were used to assess injury. Site-directed mutagenesis, co-immunoprecipitation, western blot, and qPCR were utilized to identify O-GlcNAcylation sites and investigate the functional consequences of Nrf2 mutations (S215A and S33A) on its localization, transcriptional activity, and cell injury. Nrf2 underwent time-dependent O-GlcNAcylation following myocardial I/R injury in vivo and in vitro. During the early phase (6 h) of OGD/R, O-GlcNAcylation at Ser215 promoted Nrf2 nuclear translocation, activated the expression of antioxidant genes (HO-1, NQO1, and SOD2), and conferred cyto-protection in AC16 cardiomyocytes. In contrast, during the later phase (24 h), O-GlcNAcylation at Ser33 inhibited Nrf2 nuclear accumulation, suppressed its transcriptional activity, and exacerbated oxidative injury. The S215A mutation abolished the early protective effects, whereas the S33A mutation significantly attenuated the late-phase damage. This study identified a novel O-GlcNAcylation switch at Nrf2 Ser215 and Ser33 that governs the shift from protection to injury in the myocardium following I/R, highlighting the therapeutic potential of site-specific O-GlcNAcylation for cardioprotection.