Bone morphogenetic protein-7 (osteogenic protein-1) inhibits smooth muscle cell proliferation and stimulates the expression of markers that are characteristic of SMC phenotype in vitro

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Abstract
Vascular proliferative disorders are characterized by migration and proliferation of vascular smooth muscle cells (SMCs), loss of expression of SMC phenotype, and enhanced extracellular matrix synthesis (e.g., type I collagen). We report here that bone morphogenetic protein-7 (BMP-7), a member of the transforming growth factor-β (TGF-β) superfamily, is capable of inhibiting both serum-stimulated and growth factor-induced (platelet-derived growth factor [PDGF-BB] and TGF-β1) cell growth as measured by 3H-thymidine uptake into DNA synthesis and cell number in primary human aortic smooth muscle (HASM) cell cultures. Concomitantly, addition of BMP-7 stimulates the expression of SMC-specific markers, namely α-actin and heavy chain myosin as examined by RT-PCR and Northern blot analyses. The collagen type III/I ratio that becomes lower with the transdifferentiation of SMCs into myofibroblasts is also maintained in BMP-7–treated cultures as compared to untreated controls. Studies on the mechanism of action indicate that BMP-7 treatment inhibits cyclin-dependent kinase 2 (cdk-2) that was stimulated during PDGF-BB–induced proliferation of SMCs and upregulates the expression of the inhibitory Smad, Smad6, which was shown to inhibit TGF-β superfamily signaling. These results collectively suggest that BMP-7 maintains the expression of vascular SMC phenotype and may prevent vascular proliferative disorders, thus potentially acting as a palliative after damage to the vascular integrity. J. Cell. Physiol. 184:37–45, 2000.