Mechanical Control of Mesenchymal Stem Cell Lineage Allocation

描述（由申请人提供）：骨髓中的间充质干细胞（MSC）为脂肪细胞和成骨细胞提供祖细胞，MSC池的输出反映了这两种谱系之间的相互关系。机械信号促进成骨谱系的能力提出了运动可能能够调节MSC谱系的令人兴奋的可能性。我们的工作表明，机械输入可以抑制脂肪形成，通过控制连环蛋白信号对MSC的相互作用施加显着的控制。促进MSC脂肪形成的信号包括β-连环蛋白信号的减少，随后是PPAR β的增加，脂联素和脂质含量。我们有令人信服的数据表明，机械应变诱导持续的<$-连环蛋白激活MSC通过改变GSK 3 <$磷酸化通过AKT在MSC。重复的负荷增加了ω-连环蛋白信号的持续时间，从而抑制了下游事件，如脂联素和脂滴的升高。我们的研究结果表明，即使是一个强烈的脂肪形成的微环境可以抵消以这种方式通过重复的机械输入。这使我们能够假设“机械刺激通过抑制PPAR的连环蛋白抑制脂肪形成转化？行动”。通过这项资助计划，我们建议测试这一假设，充分表征机械输入阻止脂肪形成和控制MSC谱系选择的机制。我们将研究信号的时间性质：调节脂肪形成需要多少重复，我们将询问机械输入是否诱导替代谱系选择，例如，骨祖细胞或肌细胞的独特的报告小鼠的帮助下，我们从MSC克隆研究。将探测局部细胞之间的相互作用，询问从应变细胞分泌的可溶性因子是否可以作用于未应变的细胞（SA 1）。我们将确定机械应变激活β-连环蛋白（通过AKT和GSK 32）的机制，以及考虑其他可能发挥局部控制作用的机械靶点（Wnt和BMP）。我们将考虑GSK 3的替代靶点，如NFATc 1和mTOR（SA 2）。我们将定义如何机械激活扰动过氧化物酶体增殖物激活受体？直接和间接促进SA 3的脂肪形成。我们的建议对于了解MSC在久坐和老龄化人群中的命运具有重要意义。表征MSC谱系选择的机械调节中涉及的信号级联将是至关重要的，因为这将确定抑制脂肪生成和刺激骨生成的途径中的可修改步骤。

DESCRIPTION (provided by applicant): Mesenchymal stem cells (MSCs) in bone marrow provide progenitors for both adipocyte and osteoblast cells and the output of the MSC pool reflects a reciprocal relationship between these two lineages. The ability of mechanical signals to promote osteogenic lineage has raised the exciting possibility that exercise might be able to regulate MSC lineage. Our work indicates that mechanical input can inhibit adipogenesis, exerting a significant control over MSC reciprocity through control of ¿-catenin signaling. Signals which promote MSC adipogenesis involve diminution in ¿-catenin signaling, followed by a rise in PPAR?, adiponectin and lipid content. We have compelling data showing that mechanical strain induces persistent ¿-catenin activation in MSC through alteration of GSK3¿ phosphorylation via AKT in MSCs. Repetitive loading bouts increase the ¿-catenin signal duration such that downstream events such as the rise in adiponectin and lipid droplets are inhibited. Our results suggest that even a strongly adipogenic microenvironment can be counteracted in this way by repetitive bouts of mechanical input. This allows us to hypothesize that "mechanical stimulation represses adipogenic conversion through ¿-catenin inhibition of PPAR? action". With this grant proposal we propose to test this hypothesis, fully characterizing the mechanisms by which mechanical input prevents adipogenesis and controls MSC lineage selection. We will investigate the temporal nature of the signal: how much and how many repetitions are required to regulate adipogenesis, and we will ask if mechanical input induces an alternate lineage selection, e.g., osteoprogenitor or myocyte with the help of unique reporter mice from which we make MSC clones for study. Interactions between local cells will be probed asking whether soluble factors secreted from strained cells can act on unstrained cells (SA1). We will ascertain the mechanisms by which mechanical strain activates ¿-catenin (via AKT and GSK32), as well consider other mechanical targets (Wnts and BMPs) that could exert local control. We will consider alternative targets of GSK3¿ such as NFATc1 and mTOR (SA2). We will define how mechanical activation perturbs PPAR? promotion of adipogenesis directly and indirectly in SA3. Our proposal has significance for understanding the fate of MSC in a sedentary and aging population. It will be critically important to characterize the cascade of signals involved in mechanical regulation of MSC lineage selection, as this should identify modifiable steps in pathways that suppress adipogenesis and stimulate osteogenesis.