Studies Of The Role Of Hippo-TAZ Pathway In Inhibited Osteogenic Differentiation Of BMSCs Under Simulated Microgravity

Exposure to microgravity during space flight affects almost all human physiological systems, and bone loss seriously puzzles astronauts. It has been widely accepted that reduced bone formation and increased bone resorption attribute bone loss under microgravity. Bone marrow-derived mesenchymal stem cells(BMSCs) are important progenitor and supporting cells that have the intrinsic ability to self-renew and differentiate into multiple types of cells, which act as a major source for osteoblasts. There is extensive evidence that microgravity inhibits osteogenesis of BMSCs, while promoting their adipogenesis. The blocking of BMSCs osteogenesis may contribute to bone loss induced by microgravity. Although efforts have been spent to illuminate the mechanisms and several signal pathways have been identified to play an important role in the decreased osteogenesis of BMSCs under simulated microgravity(SMG), the underlying mechanisms are not well understood. An increased understanding of the interaction of microgravity with BMSCs differentiation may provide novel insights into the mechanisms of bone loss during space flight.The transcriptional coactivator with PDZ-binding motif(TAZ) is a core factor of Hippo pathway, which accelerates BMSCs osteogenic differentiation through interacting with Runt-related transcription factor 2(Runx2). Moreover, it has been demonstrated that TAZ plays as a mechanical sensor. Several mechanical stimulis and cytoskeleton tension obviously regulate the activation of TAZ. Here, we isolated SD rat bone marrow mesenchymal stem cells(BMSCs) though whole bone marrow adherent. We utilized a clinostat to model SMG and detected the impact of SMG on osteogenic differentiation of BMSCs. The response of TAZ activation and F-actin under SMG was also evaluated. Through Jasplakinolide(Jasp) and Cytochalasin B(Cyt B), which can directly depolymerize and polymerize F-actin, we explored the effect of F-actin reorganization on osteogenesis of BMSCs and the role of TAZ in this process. Finally, we investigated the possibility and efficiency of lysophosphatidic acid(LPA) and Jasp to rescue osteogenic potential of BMSCs under SMG.The result of flow cytometry demonstrated the cells we isolated had key features of BMSCs. SMG obviously inhibited the osteogenic differentiation of BMSCs and depolymerized F-actin. The results of BMSCs exposured to Cyt B or Jasp demonstrated that the depolymerized F-actin dramatically impeded the nuclear translocation of TAZ and osteogenesis of BMSCs, independently of LATS(the upstream kinase of TAZ). Jasp and LPA both efficiently recovered the osteogenic differentiation of BMSCs under SMG mainly via F-actin-TAZ pathway. Thus, our research confirmed the negative influence of SMG on osteogenic differentiation of BMSCs. We proposed that depolymerized actin cytoskeleton inhibits osteogenic differentiation of BMSCs through impeding nuclear aggregation of TAZ, and stabilizing actin cytoskeleton can be an efficient intervention to reverse the reduced osteogenic differentiation of BMSCs in SMG via TAZ signaling.Our findings clarify the role of Hippo-TAZ pathway in the decreased osteogenic differentiation of BMSCs caused by SMG, and provide a novel connection between F-actin cytoskeleton and osteogenesis of BMSCs. We propose possible intervention targets for bone loss caused by microgravity, which will do help for the prevention and treatment of diseases related to microgravity.