Serelaxin Inhibits Lipopolysaccharide-induced Inflammatory Response in Cardiac Fibroblasts by Activating Peroxisome Proliferator-activated Receptor- and Suppressing the Nuclear Factor-Kappa B Signaling Pathway

Serelaxin (sRLX) has an inhibitory effect on fibrosis. However, whether the antifibrotic effects of sRLX are achieved by inhibiting the inflammatory response has not been clarified. This study aimed to investigate the role of sRLX in lipopolysaccharide (LPS)-induced inflammation in cardiac fibroblasts and elucidate the underlying mechanisms. Cardiac fibroblasts were isolated from adult rat hearts. The effect of sRLX on the inhibition of the inflammatory response after LPS induction was examined. Cell viability was measured by MMT assay. Cell proliferation was determined using the Cell Counting Kit-8. The levels of inflammatory cytokines IL-1 beta, IL-6, TNF-alpha, and IL-10 were measured using an enzyme-linked immunosorbent assay. The mRNA levels of a-smooth muscle actin (alpha-SMA), collagen I/III, MMP-2, MMP-9, IL-1 beta, IL-6, TNF-alpha, IL-10, IkBa, p-IkBa, p65 subunit of nuclear factor-kappa B (NF-kB), and peroxisome proliferator-activated receptor-g (PPAR-gamma) were assessed by real-time quantitative PCR. The protein levels of alpha-SMA, collagen I/III, MMP-2, MMP-9, IkBa, p-IkBa, p65, p-p65, and PPAR-gamma were examined by western blotting. sRLX inhibited LPS-induced IL-1 beta, IL-6, TNF-alpha, alpha-SMA, and collagen I/III, and elevated the expression of IL-10, MMP-2, and MMP-9. Moreover, LPS-induced activation of NF-kB pathway was suppressed by sRLX treatment. Further studies showed that sRLX did not significantly increase the expression of PPAR-gamma mRNA and protein, but activated PPAR-gamma activity, and the PPAR-g inhibitor GW9662 reversed the inhibitory effect of sRLX on IL-1 beta, IL-6, and TNF-alpha production. These results suggest that sRLX alleviates cardiac fibrosis by stimulating PPAR-gamma through a ligand-independent mechanism that subsequently abolish the expression of NF-kB signaling pathway.