Spontaneous osteogenesis of MSCs cultured on 3D microcarriers through alteration of cytoskeletal tension

3-dimensional microcarrier (3D-MC) cell culture systems are often used for expansion of stem cells including mesenchymal stem cells (MSCs) for high cell volumes required in clinical applications. However, compared to 2-dimensional (2D) cell culture, effects of 3D-MC systems on MSC differentiation have not been well studied. In this study, the behavior of various sources of MSCs from two species was observed and compared on 3D collagen I-coated-MCs (COL-MC) versus 2D culture. Proliferation of all MSCs cultured on 3D COL-MC was much decreased compared to 2D culture. Unexpectedly, COL-MC-cultured MSCs underwent spontaneous osteogenesis without exogenous addition of biochemical factors, as evidenced by increased osteogenic genes expression, ALP activity, calcium deposition, and collagen I secretion. Furthermore, MSCs cultured on 3D-MC alone without collagen I coating is sufficient to induce osteogenesis. The spontaneous lineage commitment induced by 3D-MC culture was mediated by increased cytoskeletal tension and actomyosin contraction of MSCs, which could be prevented by latrunculin B and blebbistatin, inhibitors of cytoskeletal tension and actomyosin contraction respectively. Our findings show that the combination of bioengineered MC and MSCs alone can induce specific lineage commitment very efficiently. These data have strong implications in simplifying tissue engineering strategies for therapeutic applications.