Myofibrillogenesis regulator-1 attenuates hypoxia/reoxygenation-induced injury by repairing microfilaments in neonatal rat cardiomyocytes

• H/R induces cardiomyocyte injury and disruption of filamentous actin and α-actinin.
• MR-1 attenuates H/R-induced injury and disruption of F-actin and α-actinin.
• MR-1 protects cardiomyocytes from H/R injury by promoting F-actin reorganization.
• The mechanism relies on the influence of MLCK/MLC-2 pathway.

Hypoxia/reoxygenation (H/R) injury is characterized by microfilament reorganization in cardiomyocytes. Previous studies have shown that myofibrillogenesis regulator-1 (MR-1) is expressed in the myocardium and promotes actin organization in cardiomyocytes. The purpose of this study was to investigate the role of MR-1 in attenuating hypoxia/reoxygenation injury in cardiomyocytes through promoting restoration of the microfilament. To address this aim, an H/R model of cultured neonatal cardiomyocytes was used to assess filamentous actin (F-actin) and α-actinin organization through immunofluorescence microscopy analysis. RT-PCR was used to detect mRNA levels of MR-1 and myosin regulatory light chain-2 (MLC-2). Western blot analysis was used to detect protein levels of MR-1 and filamentous actin/globular actin (F-/G-actin) as well as MLC-2 and myosin light chain kinase (MLCK) phosphorylation and protein expression. We also explored the effects of overexpressing or knocking down MR-1 on H/R injury and the MLCK/MLC-2/F-actin pathway. We found that H/R induced cardiomyocyte injury and disruption of F-actin and α-actinin with a decrease in the F-/G-actin ratio compared with controls. Compared with the H/R group, MR-1 overexpression attenuated H/R-induced injury and disruption of F-actin and α-actinin in cardiomyocytes with an increase in the F-/G-actin ratio. MR-1 overexpression also up-regulated H/R-induced MLCK and MLC-2 phosphorylation. However, MR-1 knockdown aggravated H/R injury by further disrupting F-actin and α-actinin, as well as decreasing the F-/G-actin ratio. MR-1 knockdown also down-regulated MLCK and MLC-2 phosphorylation induced by H/R injury. These findings suggest that MR-1 attenuates H/R-induced cardiomyocyte injury by promoting microfilament reorganization through the activation of the MLCK/MLC-2 pathway.