Relaxin Inhibits the Cardiac Myofibroblast NLRP3 Inflammasome as Part of Its Anti‐Fibrotic Actions via the Angiotensin Type 2 and ATP (P2X7) Receptors

Chronic NLRP3 inflammasome activation can promote fibrosis through its production of interleukin (IL)‐1β and IL‐18. Conversely, recombinant human relaxin (RLX) can inhibit the pro-fibrotic interactions between IL‐1β, IL‐18 and transforming growth factor (TGF)‐β1. Here, the broader extent by which RLX targeted the myofibroblast NLRP3 inflammasome to mediate its anti-fibrotic effects was elucidated. Primary human cardiac fibroblasts (HCFs), stimulated with TGF‐β1 (to promote myofibroblast (HCMF) differentiation), LPS (to prime the NLRP3 inflammasome) and ATP (to activate the NLRP3 inflammasome) (T+L+A) or benzoylbenzoyl‐ATP (to activate the ATP receptor; P2X7R) (T+L+Bz), co‐expressed relaxin family peptide receptor‐1 (RXFP1), the angiotensin II type 2 receptor (AT2R) and P2X7R, and underwent increased protein expression of toll‐like receptor (TLR)‐4, NLRP3, caspase‐1, IL‐1β and IL‐18. Whilst RLX co‐administration to HCMFs signifi-cantly prevented the T+L+A‐ or T+L+Bz‐stimulated increase in these end points, the inhibitory effects of RLX were annulled by the pharmacological antagonism of either RXFP1, AT2R, P2X7R, TLR‐ 4, reactive oxygen species (ROS) or caspase‐1. The RLX‐induced amelioration of left ventricular in-flammation, cardiomyocyte hypertrophy and fibrosis in isoproterenol (ISO)‐injured mice, was also attenuated by P2X7R antagonism. Thus, the ability of RLX to ameliorate the myofibroblast NLRP3 inflammasome as part of its anti‐fibrotic effects, appeared to involve RXFP1, AT2R, P2X7R and the inhibition of TLR‐4, ROS and caspase‐1.