TISSUE-SPECIFIC STEM CELLS 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 criti-cal 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 expres-sion was upregulated by limiting cell-matrix adhesion using micropatterned substrates, knocking down beta5 integrin or placing cells in suspension culture. Interest-ingly, we noted that suspending human MSCs (hMSCs) did not induce substantial apoptosis (anoikis) as is typi-cally observed in adherent cells. Although miR-125b appeared to have some effects on hMSC differentiation, we demonstrated a striking role for miR-125b in protect-ing 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 transfec-tion 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 upregu-lated during reprogramming of MEFs to induced pluripo-tent 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 heal-ing. STEM CELLS 2012;30:956–964 Disclosure of potential conflicts of interest is found at the end of this article