Endogenous Wnt signaling promotes proliferation and suppresses osteogenic differentiation in human adipose derived stromal cells

Multipotential adult mesenchymal stem cells (MSC) are able to differentiate along several known lineages, and lineage commitment is tightly regulated through specific cellular mediators and interactions. Human adipose tissues contain cell populations that have similar characteristics to bone marrow stromal cells. Wnt proteins have been reported to be involved in proliferation and differentiation of stem cells. RNA interference (RNAi) has recently emerged as a specific and efficient method to silence gene expression in mammalian cells. To analyze the role of beta-catenin signaling in human adipose stromal cells (hADSC), the effects of beta-catenin short hairpin RNAs (shRNA) expression and Wnt3a conditioned media on the growth and differentiation properties of hADSC were examined. Expression of an RNAi molecule to beta-catenin from a lentivirus vector decreased beta-catenin expression in hADSC, as indicated by Western blot and immunohistochemistry. Cells transduced with si beta-catenin lentivirus had decreased CFU and lower numbers of cells per colony than transduced control cells, but this outcome did not result from altered attachment efficiency of hADSC. The inhibition of beta-catenin signal by RNAi expression increased osteogenic differentiation. The treatment of Wnt3a conditioned media increased cellular beta-catenin levels and the rate of cellular proliferation, but inhibited osteogenic differentiation. Transduction of beta-catenin RNAi lentivirus blocked the effect of Wnt3a on proliferation of hADSC. Taken together, these findings indicate that endogenous Wnt3a plays an important role in the regulation of proliferation and differentiation of hADSC.