Regulatory Kinases in BMP-mediated hMSC Osteogenesis

描述（由申请人提供）：骨形态发生蛋白（BMPs）是通过调节细胞增殖、分化和凋亡来控制大多数组织发育和维持的生长因子。bmp还能刺激产后动物的骨修复和生长。由于bmp在多种动物体内和体外模型中具有成骨能力，因此bmp作为骨治疗剂受到了广泛的关注。然而，人体临床试验显示BMP反应相对较差，患者间差异较大。成人骨髓间充质干细胞（hMSC）培养物对bmp的成骨反应的特点是早期成骨细胞基因碱性磷酸酶和骨桥蛋白的诱导能力较差，尽管bmp在大鼠或小鼠骨髓间充质干细胞培养物中能有效诱导这些基因。我们的一般假设是bmp介导的体外hMSC成骨受血清诱导的ERK活性升高的负调控，而受p38和PI3-K/AKT信号的正调控。在本研究中，我们拟研究激酶通路调控bmp介导的hMSC体外成骨的机制，并阐明bmp激活的Smads是否与激酶通路联合作用，诱导早期成骨基因。Aim1将验证血清激活的ERK磷酸化Smads，从而降低Smads的BMP激活、Smad核定位和Smad转录活性的假设。Aim2将验证bmp诱导的早期成骨基因是p38和PI3-K/ AKT信号的直接靶点，而不是Smad信号的直接靶点。从本研究中获得的知识将为人类间充质干细胞中BMP成骨作用的机制提供新的见解，并为更广泛地研究BMP调节的人类成骨奠定基础。我们的长期目标是利用bmp和人骨髓间充质干细胞开发临床改良的骨疗法。

DESCRIPTION (provided by applicant): Bone morphogenetic proteins (BMPs) are growth factors that control the development and maintenance of most tissues by regulating cell proliferation, differentiation and apoptosis. BMPs also stimulate bone repair and augmentation in post-natal animals. Because of the bone forming capacity of BMPs in several animal in vivo and in vitro models, BMPs have received much attention as bone therapeutic agents. However, human clinical trials show show a relatively poor BMP response and large patient-to-patient variabilities. The osteogenic response to BMPs of adult human bone-marrow derived mesenchymal stem cell (hMSC) cultures is charactarized by poor induction of the early osteoblast genes alkaline phosphatase and osteopontin, although BMPs efficiently induce these genes in rat or mouse MSC cultures. Our general hypothesis is that BMP-mediated osteogenesis of hMSC in vitro is negatively regulated by elevated ERK activity induced by serum, and positively regulated by p38 and PI3-K/AKT signaling. In this application we propose to investigate mechanisms by which kinase pathways regulate BMP-mediated in vitro osteogenesis of hMSC and elucidate whether BMP-activated Smads operate in conjuction with kinase pathways to induce early osteoblast genes. Aim1 will test the hypothesis that serum-activated ERK phosphorylates Smads, thereby reducing BMP activation of Smads, Smad nuclear localization and Smad transcriptional activity. Aim2 will tests the hypothesis that BMP-induced early osteogenic genes are direct targets of p38 and PI3-K/ AKT signaling, rather than direct Smad signaling. The knowledge gained from the present study will provide new insights into mechanisms of BMP osteogenic action in human MSC and form the basis for more extensive examination of BMP-regulated osteogenesis in humans. Our long-term goal is to develop clinically improved bone therapies with BMPs and human MSC.