Effect of human hematopoietic stem cells on differentiation of mesenchymal stem cells to osteoblast cells

The correlation between hematopoietic stem cells (HSCs) and the cells comprising the niche especially osteoblast cells is critical for maintaining stem cell activities. Yet little evidence supports the concept that HSCs regulate development of the niche. If true، it may explain why many hematopoietic defects are accompanied by changes in the osseous architecture and provide new therapeutic targets for regulating bone formation. In this exprimental study، we cocultured bone marrow mesenchymal stem cells (MSCs) with umbilical cord blood HSCs in stem span media for 3 days. Then MSCs were differentiated to osteoblast cells by using osteogenesis kit. Evaluation of osteogenic differentiation of MSCs in different days came out to be: expression of osteopontin and osteocalsin (RT-PCR on days 4 and 6)، expression of CD90 (flow cytometry on day 6)، expression of alkaline phosphatase enzyme (alkaline phosphatase staining) and mineralization of MSCs (alizarin red staining on day 10). Our results showed early expression of osteopontin and osteocalsin in HSCs coculture with MSCs. These findings support the role of HSCs in induction of osteoblastic differentiation of MSCs. Decrease in the expression of CD90، higher activation in cell alkaline phosphatase enzyme، and mineralization confirmed the results. In the field of human stem cells، our ex vivo findings demonstrated that HSCs can enhance differentiation of MSCs toward osteoblast cells thereby participating in formation of their niche.