Activation of Toll‐like receptor 7 provides cardioprotection in septic cardiomyopathy‐induced systolic dysfunction

ABSTRACT Background: As a pattern recognition receptor, Toll-like receptor 7 (TLR7) widely presented in the endosomal membrane ofvarious cells. However, the pre- cise role and mechanism of TLR7 in septic cardiomyopathy remain unknown. This study aims to determine the role ofTLR7 in cardiac dysfunction during sep- sis and explore the mechanism of TLR7 in septic cardiomyopathy. Methods: We generated a mouse model of septic cardiomyopathy by challeng- ing with lipopolysaccharide (LPS). TLR7-knockout (TLR7−/−), wild-type (WT) mice, cardiac-specific TLR7-transgenic (cTG-TLR7) overexpression, and litter- mates WT (LWT) mice were subjected to septic model. Additionally, to verify the role andmechanism ofTLR7 in vitro, we transfected neonatal rat ventricular myocytes (NRVMs) with Ad-TLR7 and TLR7 siRNA before LPS administration. The effects ofTLR7 were assessed by Ca2+ imaging, western blotting, immunos- taining, and quantitative real-time polymerase chain reaction (qPCR). Results: We found that TLR7 knockout markedly exacerbated sepsis-induced systolic dysfunction. Moreover, cardiomyocytes isolated from TLR7−/− mice displayed weaker Ca2+ handling than that in WT mice in response to LPS. Conversely, TLR7 overexpression alleviated LPS-induced systolic dysfunction, and loxoribine (TLR7-specific agonist) improved LPS-induced cardiac dys- function. Mechanistically, these optimized effects were associated with enhanced the adenosine (cAMP)-protein kinase A (PKA) pathway, which upregulated phosphorylate-phospholamban (p-PLN) (Ser16) and promoted sarco/endoplasmic reticulum Ca2+ ATPase (Serca) and Ryanodine Receptor 2 (RyR2) expression in the sarcoplasmic reticulum (SR), and ultimately restored Ca2+ handling in response to sepsis. While improved Ca2+ handling was abrogated after H89 (a specific PKA inhibitor) pretreatment in cardiomyocytes isolated from cTG-TLR7 mice. Consistently, TLR7 overexpression improved LPS- induced Ca2+-handling decrement in NRVMs. Nevertheless, TLR7 knockdown showed a deteriorative phenotype. Conclusions: Our data demonstrated that activation of TLR7 protected against sepsis-induced cardiac dysfunction through promoting cAMP-PKA-PLN path- way, and we revealed that TLR7 might be a novel therapeutic target to block the septic cardiomyopathy and support systolic function during sepsis.