Upregulation of Id-1 via BMP-2 receptors induces reactive oxygen species in podocytes

Bone morphogenetic proteins (BMPs) are secreted signaling molecules, which play a major role in kidney development and disease. Here, we show the existence of mRNA for BMP-2 and for the BMP receptors BMPR1A, BMPR1B, BMPRII, ACVR1A, ACVR2, and ACVR2B in differentiated mouse podocytes and the protein expression of BMPR1A in human glomerular podocytes. BMP-2 dose dependently increases the free cytosolic Ca2+ concentration in podocytes proving the existence of a functional receptor in these cells. Recent data indicate that in a myoblastic cell line and in a breast cancer cell line, BMP-2 increases the expression of Id-1, a negative regulator of basic helix-loop-helix transcription factors, but the role of BMP-2 stimulated Id-1 expression in the kidney has not been further characterized. Here, we show that BMP-2 increases the expression of Id-1 in differentiated podocytes. To investigate a role of Id-1 for podocyte function, overexpression of Id-1 was induced in differentiated mouse podocytes. Id-1-overexpressing podocytes show an increased NADPH-dependent production of reactive oxygen species (ROS). This effect can be evoked by BMP-2 and can be antagonized by anti-Id-1 antisense oligonucleotides. The data indicate that BMP-2 may, via an increased expression of Id-1 and an increased generation of ROS, contribute to important cellular functions in podocytes. ROS supposedly play a major role in cell adhesion, cell injury, ion transport, fibrogenesis, angiogenesis and are involved in the pathogenesis of membranous nephropathy.