UC San Diego

We previously demonstrated a significant role for NLRP3 inflammasome activation in cardiomyocytes in cardiac inflammation, remodeling and contractile dysfunction in response to stressors such as Angiotensin II infusion and pressure overload. There is limited data regarding responses of cardiomyocytes to interleukin-1 β (IL-1β) and interleukin 18 (IL-18), which are generated as a result of NLRP3 activation during the cardiac inflammatory response. To determine the effects of IL-1β and IL-18 on cardiomyocytes, isolated neonatal rat ventricular myocytes (NRVMs) were treated for various times with 1ng/mL recombinant IL-1β or 10ng/mL recombinant IL-18. Western blotting was used to measure the activation state of protein kinases and downstream signaling pathways. Quantitative Polymerase Chain Reaction (qPCR) was used to assess the expression of pro-inflammatory cytokines and chemokines in cardiomyocytes. Proteins and genes showed enhanced phosphorylation and expression when treated with either cytokine, but the majority of NRVMs responded with greater significance to IL-1β stimulation. After treatment with IL-1β, Western blotting showed a several-fold increase in nuclear translocation of NF-κB p65 subunit and phosphorylation of mitogen-activated protein kinases (MAPKs) and P-STAT3, which regulate inflammatory functions. qPCR data showed significant increases in gene expression of pro-inflammatory chemokines and cytokines CXCL1, TGF-β and IL-1β by exogenous IL-1β. We have previously shown that the cardiomyocyte is a source of proinflammatory cytokines and chemokines, including IL-1β and IL-18. Our results suggest the possibility that IL-1β and IL-18 activate a pro-inflammatory positive feedback loop in cardiomyocytes which enhances and sustains cardiac inflammation, contributing to cardiac remodeling under stress conditions.