The role of cell adhesion and Cbfa1 expression in osteoblasts

Bone formation is dependent on osteoblasts which synthesize matrix proteins and initiate mineralization. Osteoblast differentiation and gene expression are dependent on interactions with the matrix proteins and on Cbfa1, which is the predominant transcriptional activator of osteoblasts. Interactions through cell adhesion may activate focal adhesion kinase (FAK) and downstream signaling cascades that can activate Cbfa1.; The hypothesis of this dissertation is that cell adhesion facilitates the development of a mature osteoblast phenotype, through processes which may involve Cbfa1 expression. Aim one was to determine if there are compromised osteoblasts in osteoporotic bone due to deficiencies in cell adhesion and adhesion-mediated signaling. Aim two was to determine if the osteoporotic osteoblasts are compromised in Cbfa1 expression. Aim three was to determine if Cbfa1 expression is compromised in slower mineralizing UMR osteoblastic cell cultures.; Cell adhesion and adhesion-mediated signaling were compromised in the osteoporotic osteoblasts. Primary human osteoblasts from osteoporotic femoral head bone were slower to attach and spread on serum-coated surfaces, with fewer focal adhesions and less organized cytoskeletons, compared to the non-osteoporotic cells. FAK tyrosine phosphorylation patterns were also altered in the osteoporotic cells.; Cbfa1 expression was initially depressed in the osteoporotic cultures. Steady state Cbfa1 message levels were initially depressed in the osteoporotic cultures. Then, following growth and elaboration of more adherent cell morphology, the Cbfa1 message levels recovered to similar values in both the osteoporotic and non-osteoporotic cultures.; Cbfa1 expression was also compromised in slower mineralizing rat UMR osteoblastic cell cultures. Cbfa1 message levels were similar in variant mineralizing rat UMR106-01 subclones, but the Cbfa1 N-terminal isoform was markedly depressed in the slower mineralizing cultures. Furthermore, the inhibition of Cbfa1 expression reduced mineralization.; These findings support the notion that cell adhesion and adhesion-mediated signaling may facilitate the development of a mature osteoblast phenotype through the activation of Cbfa1 expression. The osteoblast phenotype can be compromised in osteoporosis. This may be related to deficiencies in cell adhesion, signaling and Cbfa1 expression. Furthermore, compromised Cbfa1 expression in osteoblastic cell cultures may reduce their initiation of matrix mineralization in vitro.