Astragaloside IV alleviates hypoxia/reoxygenation-induced neonatal rat cardiomyocyte injury via the protein kinase a pathway

Background: Astragaloside IV (As-IV) exerts beneficial effects on hypoxia/reoxygenation (H/R)-induced cardiomyocyte injury, possibly through normalization of sarcoplasmic reticulum Ca²⁺ ATPase (SERCA2a) function. The exact mechanisms remain unknown. This study was designed to investigate the role of protein kinase A (PKA) in the protective effect of As-IV on SERCA2a function. Methods: Cultured cardiomyocytes from neonatal rats were exposed to 6 h of hypoxia followed by 3 h of reoxygenation (H/R) with or without As-IV treatment. Myocyte injury was determined by the creatine kinase (CK)-MB fraction in supernatant. Myocardial SERCA2a activity and PKA kinase activity were assessed. PKA subunit mRNA expression and Ser¹⁶ phosphorylated phospholamban (Ser¹⁶-PLN) protein expression were detected by real-time PCR and Western blot, respectively. Results: The administration of As-IV significantly decreased CK-MB release and restored SERCA2a activity in H/R cardiomyocytes. The mRNAs of PKA subunits, PKA-RIα, PKA-RIIα, PKA-RIIβ, PKA-Cα and PKA-Cβ, were downregulated in H/R cardiomyocytes. However, PKA-Cα mRNA expression was significantly increased after As-IV treatment. Meanwhile, there was a tendency to recovery of the H/R-induced PKA kinase activity decrease after As-IV treatment. The expression of Ser¹⁶-PLN protein, which is specifically phosphorylated by PKA, was upregulated in As-IV-treated H/R cardiomyocytes. Conclusions: These results suggest that the cardioprotection of As-IV may be through the upregulation of PKA and Ser¹⁶-PLN, thereby restoring SERCA2a function in H/R injury.