Osteoblasts (HOB) are specialized fibroblast cells that secrete and mineralize the bone matrix. They develop from mesenchymal precursors. The mineralized extracellular matrix is mainly composed of type I collagen and smaller but significant amounts of osteocalcin (OC), matrix gla protein, osteopontin (OPN), bone sialoprotein (BSP), BMPs, TGFβ, and the inorganic mineral hydroxylapatite. Osteoblast differentiation can be characterized in three stages: (a) cell proliferation, (b) matrix maturation, and (c) matrix mineralization.1 In vitro, matrix maturation and mineralization are usually enhanced by growing the cells to complete confluency and by adding specific osteogenic factors.2 During proliferation, several extracellular matrix proteins (procollagen I, TGFβ, and fibronectin) can be detected. The matrix maturation phase is characterized by maximal expression of alkaline phosphatase (AP). Finally, at the beginning of matrix mineralization, genes for proteins such as OC, BSP, and OPN are expressed and once mineralization is completed, calcium deposition can be visualized using adequate staining methods. Analysis of bone cellspecific markers like AP, OC, and collagen type I or detection of fuctional mineralization is frequently used to characterize osteoblasts in vitro.2 The mineralization process of osteoblasts in in vitro culture has also been used as a model for testing the effects of drug treatments and mechanical loading on bone cell differentiation and bone formation.3, 4 PromoCell offers primary human osteoblasts isolated from adult tissue of individual donors (C12720, C12760) along with optimized growth (C27001) and mineralization (C27020) media to ensure consistent cell culture performance.
Figure 1.Overview of osteoblast bone formation and mineralization.
Figure 2. Microscopic appearance of HOB after mineralization in vitro. A) Mineralized osteoblasts in Osteoblast Mineralization Medium show vast extracellular calcium deposits, stained in bright orange-red. Right: The negative control in HOB Growth Medium is slightly reddish.
Figure 3. Macroscopic appearance of HOB after mineralization in vitro. A) The negative control in Osteoblast Growth Medium (upper row) is slightly reddish, whereas the mineralized osteoblasts in Osteoblast Mineralization Medium show vast extracellular calcium deposits, stained in bright orange-red (lower row). B) HUVEC (AP negative, upper row) are colorless or faintly bluish, whereas osteoblasts (AP positive, lower row) are dark blue-violet. The higher the AP activity, the more intense the color.
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