Modulating the physical microenvironment to study regenerative processes in vitro using cells from mouse phalangeal elements.

Epimorphic regeneration in humans of complex multitissue structures is primarily limited to the digit tip. In a comparable mouse model, the response is level-specific in that regeneration occurs after amputation at the distal end of the terminal phalanx, but not more proximally. Recent isolation of stromal cells from CD1 murine phalangeal elements two and three (P2 and P3) allow for comparative studies of cells prevalent at the amputation plane of a more proximal region (considered nonregenerative) and a more distal region (considered regenerative), respectively. This study used adherent, suspension, and collagen gel cultures to investigate cellular processes relevant to the initial response to injury. Overall, P2 cells were both more migratory and able to compact collagen gels to a greater extent compared to P3 cells. This observed increased capacity of P2 cells to generate traction forces was likely related to the higher expression of key cytoskeletal proteins (e.g., microfilament, nonkeratin intermediate filaments, and microtubules) compared to P3 cells. In contrast, P3 cells were found to be more proliferative than P2 cells under all three culture conditions and to have higher expression of keratin proteins. In addition, when cultured in suspension rather than on adherent surfaces, P3 cells were both more proliferative and had greater gene expression for matrix proteins. Together these results add to the known inherent differences in these stromal cells by characterizing responses to the physical microenvironment. Further, while compaction by P2 cells confirm that collagen gels is a useful model to study wound healing, the response of P3 cells indicate that suspension culture, in which cell-cell interactions dominate like in the blastema, may be better suited to study regeneration. Therefore, this study can help develop clinical strategies for promoting regeneration through increased understanding in the properties of cells involved in endogenous repair as well as informed selection of useful in vitro models.