Mineralization in vitro of matrix formed by osteoblasts isolated by collagenase digestion

Sustained In Vitro Expansion of Bone Progenitors Is Cell Density Dependent

“…Consistent with the findings of an earlier study on the proliferation and differentiation of osteoprogenitor cells in the presence or absence of dex [32], CFU-O were not detectable beyond 18-20 population doublings. It is also of interest that in the hematopoietic system dex in combination with erythropoietin and stem cell factor was able to induce erythroid progenitors to undergo a similar number of cell divisions (15)(16)(17)(18)(19)(20)(21)(22), corresponding to a 10 5 -10 6 -fold amplification before a loss in proliferation and differentiation capacity was measured [43]. Dex acts directly on human erythroid progenitors, maintaining their colony-forming capacity and delaying their differentiation, with the glucocorticoid receptor acting as a key regulator for the decision between self-renewal and differentiation [43,44].…”

“…Osteoblast activities including bone matrix synthesis and mineralization are regulated by various local and systemic factors. Osteoblasts express alkaline phosphatase (ALP) and synthesize type I collagen and noncollagenous proteins such as osteopontin, osteonectin, osteocalcin, bone sialoprotein, and bone morphogenetic histological, ultrastructural, and immunohistochemical characteristics of woven bone when grown in the presence of ascorbic acid and organic phosphate [11,[20][21][22]. These nodules are thought to represent the end stage of the proliferation-differentiation sequence of individual osteoprogenitor cells present in the input cell population.…”

An immortalized osteogenic cell line derived from mouse teratocarcinoma is able to mineralize in vivo and in vitro.

“…4) revealed that the matrix contained type I collagen, whereas type III collagen could not be detected. (b) a clustering of the cells (see Material and Methods), which was a prerequisite for mineralization (1,3,8,35), and led by day 10 to the formation of numerous large nodules composed of cells staining intensively for alkaline phosphatase activity (Fig. 5, B and C) and surrounded by a dense fibrous material.…”

“…(a) The former are normal explanted cells capable of progressively synthesizing a bone-like tissue in the presence of organic phosphate and ascorbic acid (1,3,8,9,28,35,46). This process and its hormonal regulation can therefore be studied in vitro.…”

“…These involve, in the case of intramembranous ossification, (a) proliferation of primitive mesoblasts, (b) differentiation of these cells into an osteoprogenitor cell, then into osteoblasts, and (c) maturation of osteoblasts with synthesis of a collagen matrix and mineralization (5,10,39,44). Up until now, models for following bone differentiation in vitro have been of two types: (a) osteoblast-like clones explanted from normal bone, and (b) clones derived from osteogenic osteosarcomas.(a) The former are normal explanted cells capable of progressively synthesizing a bone-like tissue in the presence of organic phosphate and ascorbic acid (1,3,8,9,28,35,46). This process and its hormonal regulation can therefore be studied in vitro.…”