RESUMO
A healthy skeleton relies on bone's ability to respond to external mechanical forces. The molecular mechanisms by which bone cells sense and convert mechanical stimuli into biochemical signals, a process known as mechanotransduction, are unclear. Focal adhesions play a critical role in cell survival, migration and sensing physical force. Focal adhesion kinase (FAK) is a non-receptor protein tyrosine kinase that controls focal adhesion dynamics and can mediate reparative bone formation in vivo and osteoblast mechanotransduction in vitro. Based on these data, we hypothesized that FAK plays a role in load-induced bone formation. To test this hypothesis, we performed in vitro fluid flow experiments and in vivo bone loading studies in FAK-/- clonal lines and conditional FAK knockout mice, respectively. FAK-/- osteoblasts showed an ablated prostaglandin E(2) (PGE(2)) response to fluid flow shear. This effect was reversed with the re-expression of wild-type FAK. Re-expression of FAK containing site-specific mutations at Tyr-397 and Tyr-925 phosphorylation sites did not rescue the phenotype, suggesting that these sites are important in osteoblast mechanotransduction. Interestingly, mice in which FAK was conditionally deleted in osteoblasts and osteocytes did not exhibit altered load-induced periosteal bone formation. Together these data suggest that although FAK is important in mechanically-induced signaling in osteoblasts in vitro, it is not required for an adaptive response in vivo, possibly due to a compensatory mechanism that does not exist in the cell culture system.
Assuntos
Proteína-Tirosina Quinases de Adesão Focal/metabolismo , Mecanotransdução Celular , Osteoblastos/metabolismo , Osteogênese , Adaptação Biológica/genética , Animais , Peso Corporal/genética , Osso e Ossos/metabolismo , Linhagem Celular , Dinoprostona/metabolismo , Feminino , Quinase 2 de Adesão Focal/metabolismo , Proteína-Tirosina Quinases de Adesão Focal/genética , Adesões Focais/genética , Deleção de Genes , Expressão Gênica , Masculino , Mecanotransdução Celular/genética , Camundongos , Camundongos Knockout , Osteogênese/genética , Fosforilação , Transporte Proteico , Ulna/anatomia & histologia , Ulna/metabolismoRESUMO
Therapeutic effects from injection of stem cells are often hampered by acute donor cell death as well as migration away from damaged areas. This is likely due to the fact that injected cells do not have the physical and biochemical cues for ordered engrafment. Here we evaluate 3 common biomatrices (Matrigel, Collagen I, Purmatrix) that has the potential of providing suitable scaffolds needed to enhance stem cell survival. The longitudinal fate of transplanted stem cells was monitored by reporter imaging techniques.
