Clearing the way for efficient stem cell differentiation

Chetty et al. reveal that treating human pluripotent stem cells (hPSCs) with the Src inhibitor PP1 enhances their differentiation.

Efforts to adapt hPSCs for therapeutic purposes have been hampered by the difficulty of obtaining differentiated cell types from stem cell lines. This limits the type and number of studies that can be performed.

Chetty et al. noticed that hPSCs spend little time in the G1 phase of the cell cycle, when cells are most receptive to the signals that drive differentiation; earlier work had shown that exposing stem cells to dimethysulfoxide (DMSO) improves differentiation efficiency by increasing the time cells spend in G1. Because the tyrosine kinase Src regulates cell cycle in many cell types, and Src activity is often up-regulated in rapidly dividing cells including hPSCs, the researchers investigated whether inhibiting Src would also improve the efficiency of stem cell differentiation. Blocking Src activity using the potent inhibitor PP1, or via siRNA-mediated knockdown, dramatically increased the differentiation of a variety of embryonic and induced hPSC lines, and synergized with DMSO to further improve differentiation efficiency.

Enhanced differentiation after Src inhibition was attributable to changes in gene expression brought about by hypophosphorylation of the tumor suppressor retinoblastoma protein. This produced lasting changes in cell behavior that persisted long enough to improve yields even after application of protracted culture protocols aimed at directing stem cells’ differentiation toward specific phenotypes. It will be interesting to see whether Src inhibition enhances the functional utility of differentiated hPSCs transplanted in vivo, says first author Sundari Chetty.