miR-125b Is an adhesion-regulated microRNA that protects mesenchymal stem cells from anoikis

Mesenchymal stem cells (MSCs) have the capacity for multilineage differentiation and are being explored as a source for stem cell-based therapies. Previous studies have shown that adhesion to extracellular matrix plays a critical role in guiding MSC differentiation to distinct lineages. Here, we conducted a focused screen of microRNAs to reveal one microRNA, miR-125b, whose expression changes as a function of cell adhesion. miR-125b expression was upregulated by limiting cell-matrix adhesion using micropatterned substrates, knocking down beta5 integrin or placing cells in suspension culture. Interestingly, we noted that suspending human MSCs (hMSCs) did not induce substantial apoptosis (anoikis) as is typically observed in adherent cells. Although miR-125b appeared to have some effects on hMSC differentiation, we demonstrated a striking role for miR-125b in protecting hMSCs from anoikis. Knockdown of miR-125b increased anoikis while expressing a mimic protected cells. Mechanistic studies demonstrated that miR-125b protected against anoikis by increasing ERK phosphorylation and by suppressing p53. Lastly, we found that miR-125b expression is quite limited in endothelial cells and mouse embryonic fibroblasts (MEFs). The rapid anoikis normally observed in endothelial cells was antagonized by transfection of a miR-125b mimic, suggesting that miR-125b can confer resistance to anoikis in multiple cell types. We also found that endogenous miR-125b was significantly upregulated during reprogramming of MEFs to induced pluripotent cells, suggesting that miR-125b expression may be associated with stem cell populations. Collectively, these observations demonstrate a novel link between cell-matrix adhesion, miR-125b expression, and a stem cell-specific survival program triggered in adhesion-limited contexts such as might occur in early development and wound healing.