The role of the BMP4/Smad1 signaling pathway in mesangial cell proliferation: A possible mechanism of diabetic nephropathy.

ABSTRACT

AIMS: This study explored the role of the BMP4/Smad1 signaling pathway in mesangial matrix expansion during the process of diabetic nephropathy. MAIN METHODS: Diabetic rats were induced by high-fat feeding followed by an intraperitoneal injection of streptozotocin. Glomerular lesions were examined. Immunohistochemical analysis was performed in order to identify BMP4/Smad1 signaling proteins (BMP4, ALK3, and Smad1) and mesangial ECM proteins (Col1 and Col4) in kidney tissue. Cell proliferation and the expression of BMP4, Smad1 and Col4 were determined in cultured mesangial cells exposed to high glucose. The specific regulatory role of BMP4 was evaluated by detecting BMP4/Smad1 signaling pathway proteins and mesangial ECM proteins after blocking BMP4 both at the gene and protein levels. KEY FINDINGS: Rats with DN exhibited mesangial expansion and a thickened glomerular basement membrane. Immunohistochemical analysis of glomeruli showed increased expression of BMP4, Smad1, ALK3, Col1, and Col4 but less expression of MMP9 than observed in controls. High glucose induced slight proliferation of cultured rat mesangial cells after 48 h of incubation but there was no significant different from the control (p > 0.05). High glucose activated the BMP4/Smad1 signaling pathway and stimulated Col4 expression in mesangial cells. Both silencing of the bmp4 gene (with siRNA) and blocking BMP4 protein signaling (with the BMP4 protein antagonist Noggin) reduced the expression of ALK3, Smad1, Col4, and Col1 in high glucose-stimulated mesangial cells. SIGNIFICANCE: The BMP4/Smad1 signaling pathway is crucial to the progression of mesangial expansion, and suppressing this signaling pathway may present a novel therapeutic strategy for DN.