Osteogenesis is a tightly regulated process that involves coordinated extracellular signals from autocrine and paracrine loops. Secretory proteins during osteogenesis can inhibit cell proliferation and activate cell differentiation toward mature osteoblasts, which are characterized by mineralization. In this study, we attempted to identify these secretory proteins during osteogenesis using LC-MS/MS analysis. We compared the secretome between undifferentiated human bone marrow-derived mesenchymal stem cells (hBMSCs) and differentiated osteoblasts. Among 315 proteins that were identified, 177 proteins were present at increased levels in osteoblasts, whereas 88 proteins were present at decreased levels. Among the identified proteins, several were validated by quantitative RT-PCR and immunoblot analysis. Of particular interest, calcium homeostasis-related proteins were upregulated, whereas stem cell proliferation-related proteins and other lineage-related proteins were downregulated during osteogenesis. These findings provide information about the dynamic changes in the expression and secretion of proteins during osteogenesis and suggest the putative role of secretory proteins in osteogenesis.
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