FZD5 regulates cellular senescence in human mesenchymal stem/stromal cells

Human mesenchymal stem/stromal cells (hMSCs) have garnered enormous interest as a potential resource for cell-based therapies. However, the molecular mechanisms regulating senescence in hMSCs remain unclear. To elucidate these mechanisms, we performed gene expression profiling to compare clonal immature MSCs exhibiting multipotency with less potent MSCs. We found that the transcription factor Frizzled 5 (FZD5) is expressed specifically in immature hMSCs. The FZD5 cell surface antigen was also highly expressed in the primary MSC fraction (LNGFR+ THY-1+ ) and cultured MSCs. Treatment of cells with the FZD5 ligand WNT5A promoted their proliferation. Upon FZD5 knockdown, hMSCs exhibited markedly attenuated proliferation and differentiation ability. The observed increase in the levels of senescence markers suggested that FZD5 knockdown promotes cellular senescence by regulating the non-canonical Wnt pathway. Conversely, FZD5 overexpression delayed cell cycle arrest during the continued culture of hMSCs. These results indicated that the intrinsic activation of FZD5 plays an essential role in negatively regulating senescence in hMSCs and suggested that controlling FZD5 signaling offers the potential to regulate hMSC quality and improve the efficacy of cell-replacement therapies using hMSCs. © AlphaMed Press 2020 SIGNIFICANCE STATEMENT: Mesenchymal stem/stromal cells (MSCs) hold considerable promise for cell therapy. Generally, MSCs are cultured in vitro to increase cell numbers and ensure functionality. However, long-term culture can lead to cellular senescence, wherein cells no longer replicate. Here, we evaluated the clones derived from single MSCs, revealing that the FZD5 regulatory protein is specifically expressed in highly functional MSCs. FZD5 prevents senescence and preserves multipotency in the most immature, rapidly proliferating subtype of MSCs. Controlling FZD5 gene expression may thus allow the suppression of MSC senescence, while maintaining their stem cell properties throughout long-term culture in vitro.