OSTEOBLASTOGENESIS IN MODELED MICROGRAVITY

描述（由申请人提供）：骨质流失是太空飞行以及老化和废弃的主要后果。这些情况的特点是间充质干细胞成骨细胞生成减少，脂肪生成增加。Cbfa1是成骨细胞分化和骨形成的重要转录因子。此外，ppar - γ被证明对脂肪细胞分化至关重要。鉴于成骨和脂肪形成之间的密切关系，我们假设模拟微重力会破坏整合素介导的信号传导，导致人间充质干细胞（hMSC）中Cbfa1和PPAR的表达和/或激活发生改变，从而抑制成骨细胞分化并增加脂肪形成。

DESCRIPTION (provided by applicant): Bone loss is a major consequence of spaceflight as well as aging and disuse. These conditions are marked by a decrease in the osteoblastogenesis of mesenchymal stem cells and an increase in adipogenesis. Cbfa1 is an essential transcription factor in osteoblast differentiation and bone formation. In addition, PPAR-gamma was shown to be crucial for adipocyte differentiation. Given this strong relationship between osteogenesis and adipogenesis, we hypothesize that modeled microgravity disrupts integrin-mediated signaling leading to alterations in the expression and/or activation of both Cbfa1 and PPAR( in human mesenchymal stem cells (hMSC), which results in suppressed osteoblast differentiation and increase adipogenesis. To test this hypothesis, hMSC will be grown in a Rotary Cell Culture System with a high aspect ratio vessel. The aims of this study are: (1) Characterize the effects of modeled microgravity on human mesenchymal stem cell differentiation. Modulation of osteoblastogenesis and adipogenesis will be examined by alkaline phosphatase, von Kossa, oil red O and trichrome staining. RNA analyses will be performed to demonstrate the modulation of osteoblastic and adipogenic gene expression. (2) Characterize the molecular mechanisms responsible for the effects of modeled microgravity on human mesenchymal stem cells. Western blot and gel shift analysis and transactivation studies will be utilized to elucidate the mechanism. (3) Identifying agents capable of reversing the modeled microgravity inhibition of osteoblastogenesis. Using the same techniques employed in Aims 1 and 2, we will identify agent/s capable of blocking microgravity-induced bone loss. Findings from these studies will provide insight into mechanisms involved in the effect of weightlessness on mesenchymal cell function, thus addressing the requirements of this PA (PA-00-088). A viable basis will thereby be provided for the development of drugs that can alter Cbfa1 and/or PPARgamma and mediate increased bone formation in astronauts, elderly and patients with disuse osteoporosis.