Up‐regulation of BMP‐2 antagonizes TGF‐β1/ROCK‐enhanced cardiac fibrotic signalling through activation of Smurf1/Smad6 complex

Abstract Rho‐associated kinase ( ROCK ) plays a critical role in pressure overload‐induced left ventricular remodelling. However, the underlying mechanism remains unclear. Here, we reported that TGF ‐β1‐induced ROCK elevation suppressed BMP ‐2 level and strengthened fibrotic response. Exogenous BMP ‐2 supply effectively attenuated TGF ‐β1 signalling pathway through S mad6‐ S murf‐1 complex activation. In vitro cultured cardiomyocytes, mechanical stretch up‐regulated cardiac TGF ‐β1, TGF ‐β1‐dependent ROCK and down‐regulated BMP‐2, but BMP ‐2 level could be reversed through blocking TGF ‐β1 receptor by SB ‐431542 or inhibition of ROCK by Y‐27632. TGF ‐β1 could also activate ROCK and suppress endogenous BMP ‐2 level in a dose‐dependent manner. Knock‐down BMP ‐2 enhanced TGF ‐β1‐mediated PKC ‐δ and S mad3 signalling cascades. In contrast, treatment with Y‐27632 or SB ‐431542, respectively suppressed ROCK‐dependent PKC‐δ and Smad3 activation, but BMP ‐2 was only up‐regulated by Y‐27632. In addition, BMP ‐2 silencing abolished the effect of Y‐27632, but not SB ‐431542 on suppression of TGF ‐β1 pathway. Further experiments showed that S mad6 S murf1 interaction were required for BMP ‐2‐evoked antagonizing effects. S mad6 overexpression attenuated TGF ‐β1‐induced activation of PKC ‐δ and S mad3, promoted TGF ‐β RI degradation in BMP ‐2 knock‐down cardiomyocytes, and could be abolished after knocking‐down Smurf‐1, in which S mad6/ S murf1 complex formation was critically involved. In vivo data showed that pressure overload‐induced collagen deposition was attenuated, cardiac function was improved and TGF ‐β1‐dependent activation of PKC ‐δ and S mad3 was reduced after 2 weeks treatment with rh BMP ‐2(0.5 mg/kg) or Y‐27632 (10 mg/kg) in mice that underwent surgical transverse aortic constriction. In conclusion, we propose that BMP ‐2, as a novel fibrosis antagonizing cytokine, may have potential beneficial effect in attenuating pressure overload‐induced cardiac fibrosis.