In this study, we used Bmp4 heterozygous knockout mice (Bmp4+/−), podocyte-specific Bmp4 knockout mice, induced Bmp4 tgm, and podocyte-specific Bmp4 tgm to examine the molecular mechanism by which the BMP4/Smad1/p38 signaling pathway mediates glomerular injury in a mouse model of DN. The gene discussed is SMAD1; the disease is liver dysplastic nodule.