Exercise training attenuates cardiac dysfunction induced by excessive sympathetic activation through an AMPK-KLF4-FMO2 axis

Cardiovascular diseases (CVDs) are a leading cause of mortality worldwide and are associated with an overactivated sympathetic system. Although exercise training has shown promise in mitigating sympathetic stress-induced cardiac remodeling, the precise mechanisms remain elusive. Here, we demonstrate that exercise significantly upregulates cardiac flavin-containing monooxygenase 2 (FMO2) expression. Notably, we find that exercise training effectively counteracts sympathetic overactivation-induced cardiac dysfunction and fibrosis by enhancing FMO2 expression via adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) activation. Functional investigations employing FMO2 knockdown with adeno-associated virus 9 (AAV9) underscore the necessity for FMO2 expression to protect the heart during exercise in vivo. Furthermore, we identify the krüppel-like factor 4 (KLF4) as a transcriptional mediator of FMO2 that is crucial for the mechanism through which AMPK activation protects against sympathetic overactivation-induced cardiac dysfunction and fibrosis. Taken together, our study reveals a cardioprotective mechanism for exercise training through an AMPK-KLF4-FMO2 signaling pathway that underscores how exercise alleviates cardiac dysfunction induced by excessive sympathetic activation.