Age and skeletal sites affect BMP-2 responsiveness of human bone marrow stromal cells

Bone marrow stromal cells (BMSCs) contain osteoprogenitors responsive to stimulation by osteogenic growth factors like bone morphogenetic proteins (BMPs). When used as grafts, BMSCs can be harvested from different skeletal sites such as axial, appendicular, and orofacial bones, but the lower therapeutic efficacy of BMPs on BMSCs-responsiveness in humans compared to animal models may be due partly to effects of skeletal site and age of donor. We previously reported superior differentiation capacity and osteogenic properties of orofacial BMSCs relative to iliac crest BMSCs in same individuals. This study tested the hypothesis that recombinant human BMP-2 (rhBMP-2) stimulates human BMSCs differently based on age and skeletal site of harvest. Adult maxilla, mandible, and iliac crest BMSCs from same individuals and pediatric iliac crest BMSCs were comparatively assessed for BMP-2 responsiveness under serum-containing and serum-free insulin-supplemented culture conditions. Adult orofacial BMSCs were more BMP-2-responsive than iliac crest BMSCs based on higher gene transcripts of alkaline phosphatase, osteopontin, and osteogenic transcription factors MSX-2 and Osterix in serum-free insulin-containing medium. Pediatric iliac crest BMSCs were more responsive to rhBMP-2 than adult iliac crest BMSCs based on higher expression of alkaline phosphatase and osteopontin in serum-containing medium. Unlike orofacial BMSCs, MSX-2 and Osterix transcripts were similarly expressed by adult and pediatric iliac crest BMSCs in response to rhBMP-2. These data demonstrate that age and skeletal site-specific differences exist in BMSC osteogenic responsiveness to BMP-2 stimulation and suggest that MSX-2 and Osterix may be potential regulatory transcription factors in BMP-mediated osteogenesis of adult orofacial cells.