Toll-like receptor 4-induced ryanodine receptor 2 oxidation and sarcoplasmic reticulum Ca2+ leakage promote cardiac contractile dysfunction in sepsis

Studies suggest the potential role of a sarcoplasmic reticulum (SR) CA²⁺ leak in cardiac contractile dysfunction in sepsis. However, direct supporting evidence is lacking, and the mechanisms underlying this SR leak are poorly understood. Here, we investigated the changes in cardiac CA²⁺ handling and contraction in LPS-treated rat cardiomyocytes and a mouse model of polymicrobial sepsis produced by cecal ligation and puncture (CLP). LPS decreased the systolic CA²⁺ transient and myocyte contraction as well as SR CA²⁺ content. Meanwhile, LPS increased CA²⁺ spark-mediated SR CA²⁺ leak. Preventing the SR leak with ryanodine receptor (RyR) blocker tetracaine restored SR load and increased myocyte contraction. Similar alterations in CA²⁺ handling were observed in cardiomyocytes from CLP mice. Treatment with JTV-519, an anti-SR leak drug, restored CA²⁺ handling and improved cardiac function. In the LPS-treated cardiomyocytes, mitochondrial Reactive Oxygen Species and oxidative stress in RyR2 were increased, whereas the levels of the RyR2-associated FK506-binding protein 1B (FKBP12.6) were decreased. The Toll-like Receptor 4 (TLR4)-specific inhibitor TAK-242 reduced the oxidative stress in LPS-treated cells, decreased the SR leak, and normalized CA²⁺ handling and myocyte contraction. Consistently, TLR4 deletion significantly improved cardiac function and corrected abnormal CA²⁺ handling in the CLP mice. This study provides evidence for the critical role of the SR CA²⁺ leak in the development of septic cardiomyopathy and highlights the therapeutic potential of JTV-519 by preventing SR leak. Furthermore, it reveals that TLR4 activation-induced mitochondrial Reactive Oxygen Species production and the resulting oxidative stress in RyR2 contribute to the SR CA²⁺ leak.