title: BMP-2 promotes phosphate uptake, phenotypic modulation, and calcification of human vascular smooth muscle cells.
abstract: Vascular calcification is associated with increased risk of cardiovascular events that are the most common cause of death in patients with end-stage renal disease. Clinical and experimental studies indicate that hyperphosphatemia is a risk factor for vascular calcification and cardiovascular mortality in these patients. Our previous studies demonstrated that phosphate transport through the type III sodium-dependent phosphate cotransporter, Pit-1, was necessary for phosphate-induced calcification and osteochondrogenic phenotypic change in cultured human smooth muscle cells (SMC). BMP-2 is a potent osteogenic protein required for osteoblast differentiation and bone formation that has been implicated in vascular calcification. In the present study, we have examined the effects of BMP-2 on human SMC calcification in vitro. We found that treatment of SMC with BMP-2 enhanced elevated phosphate-induced calcification, but did not induce calcification under normal phosphate conditions. mRNAs for BMP receptors, including ALK2, ALK3, ALK6, BMPR-II, ActR-IIA and ActR-IIB were all detected in human SMCs. Mechanistically, BMP-2 dose-dependently stimulated phosphate uptake in SMC (200 ng/ml BMP-2 vs. vehicle: 13.94 vs. 7.09 nmol/30 min/mg protein, respectively). Real-time PCR and Western blot revealed the upregulation of Pit-1 mRNA and protein levels, respectively, by BMP-2. More importantly, inhibition of phosphate uptake by a competitive inhibitor of sodium-dependent phosphate cotransport, phosphonoformic acid, abrogated BMP-2-induced calcification. These results indicate that phosphate transport via Pit-1 is crucial in BMP-2-regulated SMC calcification. In addition, BMP-2-induced Runx2 and inhibited SM22 expression, indicating that it promotes osteogenic phenotype transition in these cells. Thus, BMP-2 may promote vascular calcification via increased phosphate uptake and induction of osteogenic phenotype modulation in SMC.
authors.affiliation: Department of Bioengineering, University of Washington, Seattle, WA 98195-5061, United States.
authors.forename: Xianwu
authors.initials: X
authors.lastname: Li
authors.forename: Hsueh-Ying
authors.initials: HY
authors.lastname: Yang
authors.forename: Cecilia M
authors.initials: CM
authors.lastname: Giachelli
mesh_terms: D001846:Bone Development; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002454:Cell Differentiation; D005786:Gene Expression Regulation; D006801:Humans; D008954:Models, Biological; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D032389:Myocytes, Smooth Muscle / Q000166:cytology; D010006:Osteoblasts / Q000378:metabolism; D010012:Osteogenesis; D010641:Phenotype; D010710:Phosphates / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D050817:Transcription Factor Pit-1 / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000378:metabolism*
chemical_list: C525718:BMP2 protein, human; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins; D010710:Phosphates; D012333:RNA, Messenger; D050817:Transcription Factor Pit-1; D016212:Transforming Growth Factor beta; D002118:Calcium