Establishing reliable criteria for isolating myogenic cell fractions with stem cell properties and enhanced regenerative capacity.

Despite a focused effort within the myogenic cell transplantation community, little progress has been made toward the reliable identification and isolation of progenitors that are capable of tolerating the initial posttransplantation environment and effectively regenerating clinically relevant quantities of muscle. The future success of myogenic-based treatment modalities requires an enhanced understanding of the highly heterogeneous nature of the myogenic progenitor cell pool, which has been previously documented by numerous researchers. Further, for translation of experimental animal results to clinical application, reliable in vitro selection criteria must be established and must be translatable across species. While research into the utility of surface markers is ongoing, as an alternative we have investigated in vitro cell behavioral characteristics under imposed conditions which challenge the propensity of myogenic progenitors to choose between various cell fates (i.e., proliferation, quiescence, or differentiation). Previous observations in the mouse suggest an enhanced in vivo regenerative capacity of myogenic populations with respect to their in vitro ability to maintain a proliferative and undifferentiated state [J. Cell Sci. 115 (2002) 4361]. From these observations it is thus proposed that such behavior may represent an a priori indicator of regenerative capacity following transplantation. To challenge this proposition, a rat cell isolation and transplantation model was evaluated in an identical manner. In agreement with the results obtained from the mouse, a significant correlation between regenerative capacity and induction of differentiation was observed. These results contribute to the growing body of scientific evidence documenting the underlying behavioral differences that exist between various myogenic progenitors while also, importantly, providing evidence that such differences may significantly impact the functional capabilities of these cells posttransplantation. This information further implies that from a therapeutic standpoint isolation strategies aimed toward obtaining efficient myogenic progenitors should, in the absence of a reliable surface marker(s), focus on identifying populations displaying desirable in vitro behavior (i.e., high proliferative capacity and low induced differentiation). Incorporating such criteria into cell isolation and/or purification schemes may yield significant returns in the clinical myogenic transplantation setting.