Innate Immunity Signaling in Neonatal Rat Cardiac Myocytes

Abstract

Neonates have a heightened inflammatory response to pathogens & are uniquely susceptible to sepsis‐related cardiac dysfunction. MAP‐kinase signaling plays a critical role in innate immunity/inflammation wherein MAPK phosphatase‐1 (MKP‐1) is a key negative regulator, but its roles in cardiac myocyte inflammatory signaling are not defined. Our hypothesis was that MKP‐1 deficiency amplifies inflammatory responses in neonatal rat cardiomyocytes, and is related to MAPK, Gαs & Gαq signaling pathways. H9c2 cells were transfected with siMKP‐1 or scrambled control (H9WT) and treated with 5μg/ml LPS. IL6 & TNFα mRNA and protein expression was detected by qRTPCR & ELISA. cAMP, PC‐PLC & activated PKC were detected by EIA. siMKP‐1 cells had a greater increase in TNFα (p<0.001) & IL6 (p<0.001) mRNA & protein expression at 1h & 4h after LPS vs. H9WT. MKP‐1 deficient cells also had greater increases in cAMP, PC‐PLC & PKC activity (P<0.001) after LPS. Inhibition of P38 completely blocked the increases in TNFα, IL6, cAMP & PC‐PLC, but significantly increased activated PKC (P<0.001) in siMKP‐1 cells. Neonatal rat cardiac myocytes generate inflammatory cytokines in direct response to LPS, which is enhanced by MKP‐1 deficiency, mediated by the MAP kinase P38 & associated with increased cAMP, PC‐PLC & PKC. Defining these cardiac myocyte signaling processes may lead to novel therapeutic targets for sepsis‐related cardiac dysfunction.