Preeclampsia (PE) is a pregnancy-specific multisystem disorder and is associated with maladaptation of the maternal cardiovascular system and abnormal placentation. One of the important characteristics in the pathophysiology of PE is a dysfunction of the placenta. Placental insufficiency is associated with poor trophoblast uterine invasion and impaired transformation of the uterine spiral arterioles to high capacity and low impedance vessels and/or abnormalities in the development of chorionic villi. Significant progress in identifying potential molecular targets in the pathophysiology of PE is underway. The human placenta is immunologically functional with the trophoblast able to generate specific and diverse innate immune-like responses through their expression of multimeric self-assembling protein complexes, termed inflammasomes. However, the type of response is highly dependent upon the stimuli, the receptor(s) expressed and activated, the downstream signaling pathways involved, and the timing of gestation. Recent findings highlight that inflammasomes can act as a molecular link for several components at the syncytiotrophoblast surface and also in maternal blood thereby directly influencing each other. Thus, the inflammasome molecular platform can promote adverse inflammatory effects when chronically activated. This review highlights current knowledge in placental inflammasome expression and activity in PE-affected pregnancies, and consequently, vascular dysfunction in PE that must be addressed as an interdependent interactive process.

The recombinant form of the peptide hormone relaxin, serelaxin (RLX), mediates its anti‐fibrotic actions by impeding the profibrotic activity of cytokines including TGF‐β1 and IL‐1β. As IL‐1β can be produced by the nucleotide‐binding oligomerization domain, leucine‐rich repeat and pyrin domains‐containing protein 3 (NLRP3) inflammasome, this study determined whether RLX targeted the inflammasome to inhibit the profibrotic TGF‐β1/IL‐1β axis in primary human cardiac myofibroblasts (HCMFs) in vitro and in mice with isoproterenol (ISO)‐induced cardiomyopathy in vivo. HCMFs stimulated with TGF‐β1 (5 ng/ml), LPS (100 ng/ml), and ATP (5 mM) (T+L+A) for 8 h, to induce the NLRP3 inflammasome, demonstrated significantly increased protein expression of markers of NLRP3 priming (NLRP3, apoptosis‐associated speck‐like protein containing a C‐terminal caspase‐recruitment domain, procaspase‐1) and activity (IL‐1β, IL‐18). After 72 h, there was significantly increased neuronal NOS (nNOS), TLR‐4, procaspase‐1, myofibroblast differentiation, and collagen‐I deposition. These measures, along with interstitial TGF‐β1 expression and collagen deposition, were also increased in the left ventricle (LV) of ISO‐injured mice 14 d postinjury. RLX [16.8 nM (100 ng/ml) in vitro; 0.5 mg/kg per day in vivo ] inhibited T+L+A‐ and ISO‐induced TLR‐4 expression, NLRP3 priming, IL‐1β, IL‐18, myofibroblast differentiation, and interstitial collagen deposition at the time points studied, via the promotion of nNOS; with the NLRP3‐ and IL‐1β‐inhibitory effects of RLX in HCMFs being abrogated by pharmacological blockade of nNOS or TLR‐4. Comparatively, the small molecule NLRP3 inhibitor, N ‐{[(1,2,3,5,6,7‐hexahydro‐s‐indacen‐4‐yl)amino]carbonyl}‐4‐(1‐hydroxy‐1‐methylethyl)‐2‐furansulfonamide (1 μM in vitro, 10 mg/kg/d in vivo ), inhibited components of the NLRP3 inflammasome in vitro and in vivo and ISO‐induced interstitial LV fibrosis in vivo but did not affect nNOS, TLR‐4, myofibroblast differentiation, or myofibroblast‐induced collagen deposition. Hence, RLX can inhibit the TGF‐β1/IL‐1β axis via a nNOS‐TLR‐4‐NLRP3 inflammasome‐dependent mechanism on cardiac myofibroblasts.—Cáceres, F. T., Gaspari, T. A., Samuel, C. S., Pinar, A. A. Serelaxin inhibits the profibrotic TGF‐β1/IL‐1β axis by targeting TLR‐4 and the NLRP3 inflammasome in cardiac myofibroblasts. FASEB J. 33, 14717‐14733 (2019). www.fasebj.org

Introduction: The NLRP3 inflammasome produces interleukin (IL)-1β and IL-18, which when chronically activated by transforming growth factor (TGF)-β1, contribute to fibrosis. The recombinant form of the anti-fibrotic hormone, relaxin (RLX), suppresses the pro-fibrotic influence of TGF-β1 and toll-like receptor (TLR)-4 on NLRP3 inflammasome priming and activity in human cardiac myofibroblasts and mice with cardiomyopathy. However, whether RLX also modulates components of the myofibroblast NLRP3 inflammasome remains unknown. Methods and Results: Stimulation of a human dermal fibroblast (HDF) cell line with TGF-β1 [5 ng/ml; to promote myofibroblast (HDMF) differentiation], LPS (100 ng/ml; to prime the NLRP3 inflammasome) and ATP (5 mM; to activate the NLPR3 inflammasome) (T+L+A) significantly increased NLRP3 inflammasome priming and activity after 8 and 72 h; and α-SMA expression (myofibroblast differentiation) and collagen-I deposition after 72 h. siRNA-induced knock-down of NLRP3 inflammasome priming components (NLRP3, ASC, caspase-1) in T+L+A-stimulated HDMFs for 24 h, completely knocked-down each component after 72 h. RLX (100 ng/ml) administration to T+L+A-stimulated HDMFs after control, NLRP3 or ASC siRNA transfection, equivalently suppressed IL-1β, pro-IL-18, α-SMA, and collagen-I protein levels (by 40%–50%; all p<0.05 vs. T+L+A) after 72 h, as determined by Western blotting. These RLX-induced effects were abrogated by siRNA knock-down of caspase-1. Conclusion: The anti-fibrotic actions of RLX appear to require modulation of caspase-1 within the myofibroblast NLRP3 inflammasome.