| BMP7, also known as osteogenic protein-1, belongs to the TGF-β superfamily of secreted growth factors that orchestrate tissue morphogenesis, homeostasis, and repair across skeletal, renal, and neural systems. Synthesized as inactive pro-BMP7, it undergoes furin-mediated cleavage to yield the mature disulfide-linked homodimer with a characteristic TGF-β fold featuring wrist and knuckle epitopes for receptor engagement. BMP7 binds preformed heterotetrameric complexes of type I (ALK2/3/6) and type II (BMPRII/ActRIIA/B) serine/threonine kinase receptors; type II phosphorylates type I GS domain, activating its kinase to propagate canonical Smad1/5/8 phosphorylation, complex formation with Smad4, and nuclear translocation to drive target genes like ID1, Runx2, and Msx2 for osteoblast/chondrocyte differentiation. Non-canonical arms engage TAK1-TAB1/2/3 for p38/ERK/JNK MAPKs promoting proliferation/migration, or PI3K-Akt-mTOR inhibiting apoptosis and inflammation. Antagonists like noggin, chordin, gremlin, and follistatin sequester BMP7 extracellularly, while intracellularly Smurf1/2 ubiquitinates receptors/Smads for degradation, and Smad6/7 competitively inhibit R-Smad phosphorylation. Physiologically, BMP7 patterns kidney metanephric mesenchyme via ureteric bud branching and nephron progenitor proliferation, maintains renal epithelial integrity against fibrosis, supports brown adipogenesis, and regulates monocyte polarization toward anti-inflammatory M2 macrophages. TGF-β/Smad3 upregulates Smurf2 to suppress BMP7/Smad1/5/8 while BMP7 reciprocally attenuates TGF-β/Smad3 via miR-29/miR-200 induction countering miR-21/192-driven fibrosis. BMP7 loss exacerbates epithelial-mesenchymal transition, leading to tubulointerstitial scarring; recombinant BMP7 restores Smad balance, reverses EMT, and protects against diabetic nephropathy progression. |
