Serelaxin inhibits LPS-induced inflammatory response in cardiac fibroblasts by activating PPAR-γ and suppressing NF-κB signaling pathway

Serelaxin has an inhibitory effect on fibrosis. However, whether the anti-fibrotic effects of serelaxin are achieved by inhibiting the inflammatory response has not been clarified. This study aimed to investigate the role of serelaxin in lipopolysaccharide (LPS)-induced inflammation in cardiac fibroblasts (CFs) and elucidate the underlying mechanisms.CFs were isolated from adult rat hearts. The effect of serelaxin 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-1β, IL-6, TNF-α, and IL-10 were measured using an enzyme-linked immunosorbent assay (ELISA). The mRNA levels of α-SMA, collagen I/III, MMP-2, MMP-9, IL-1β, IL-6,TNF-α, IL-10, IκBα, p-IκBα, p65 subunit of nuclear factor-kappa B (NF-κB) and peroxisome proliferator-activated receptor-γ (PPAR-γ) were assessed by real-time quantitative PCR (RT-qPCR). The protein levels of α-SMA, collagen I/III, MMP-2, MMP-9, IκBα, p-IκBα, p65, p-p65 and PPAR-γ were examined by western blotting.Serelaxin inhibited LPS-induced IL-1β, IL-6, TNF-α, α-SMA, and collagen I/III, and elevated the expression of IL-10, MMP-2 and MMP-9. Moreover, LPS-induced activation of NF-κB pathway was suppressed by serelaxin treatment. Further studies showed that serelaxin did not significantly increase the expression of PPAR-γ mRNA and protein, but activated PPAR-γ activity, and the PPAR-γ inhibitor GW9662 reversed the inhibitory effect of serelaxin on IL-1β, IL-6, and TNF-α production. These results suggest that serelaxin alleviates cardiac fibrosis by stimulating PPAR-γ via a ligand-independent mechanism which subsequently abolish the expression of NF-κB signalling pathway.