Frustrated differentiation of mesenchymal stem cells.

Mesenchymal stem cells (MSCs) are one of the most useful cell resources for clinical application in regenerative medicine. However, standardization and quality assurance of MSCs are still essential problems because the stemness of MSCs depends on such factors as the collection method, individual differences associated with the source, and cell culture history. As such, the establishment of culture techniques which assure the stemness of MSCs is of vital importance. One important factor affecting MSCs during culture is the effect of the mechanobiological memory of cultured MSCs built up by their encounter with particular mechanical properties of the extracellular mechanical milieu. How can we guarantee that MSCs will remain in an undifferentiated state? Procedures capable of eliminating effects related to the history of the mechanical dose for cultured MSCs are required. For this problem, we have tried to establish the design of microelastically patterned cell-culture matrix which can effectively induce mechanical oscillations during the period of nomadic migration of cells among different regions of the matrix. We have previously observed before that the MSCs exposed to such a growth regimen during nomadic culture keep their undifferentiated state-with this maintenance of stemness believed due to lack of a particular regular mechanical dosage that is likely to determine a specific lineage. We have termed this situation as "frustrated differentiation". In this minireview, I introduce the concept of frustrated differentiation of MSCs and show possibility of purposeful regulation of this phenomenon.