microRNA在干细胞向脂肪细胞定向分化过程中的调控机制

Adipose tissue plays an important role in energy storage, recent studies indicates that it is also an active endocrine organ. More and less adipose tissue can both lead to the metabolic syndrome. The developmental pathway of adipocyte development can be divided into four stages: lineage commitment, preadipocyte proliferation, growth arrest and terminal differentiation. While the molecular mechanism in the latter phases of the adipocyte development program, i.e., mitotic clonal expansion and terminal differentiation, has been well characterized, little is known about the factors/genes that trigger the commitment process. Recently， much work has been focused on uncovering the molecular events during adipogenic commitment of MSCs. We have established two adipocyte lineage commitment cell models, one is the established cell line A33 from C3H10T1/2 stem cells by treating with 5-azaC at low/cloning density. The other is C3H10T1/2 cells treated with BMP2/4 which induces nearly complete commitment and subsequently differentiate into the adipocyte. In this study, we will apply microRNA chips to compare the two established adipocyte lineage commitment cell models to uncover the mechanism involved in the commitment process, especially microRNA changes during commitment. Adipose tissue-specific BMP4 expression or conditional BMP4 knock out mice are also used to verify the mechanism involved in the adipogenetic commitment process in study. Our study will provide insights in the molecular mechanism under which stem cells are committed to adipocyte lineage, and is very important for uncovering the target genes of obesity and obesity related diseases.

脂肪组织不但是人体重要能量贮存器官，还是重要的内分泌器官；过多或过少的脂肪组织都会引起代谢综合征。肥胖不仅源于过多的甘油三酯累积引起的脂肪细胞体积增大，更源于干细胞分化为脂肪细胞引起的数目增多。本课题拟研究miRNA是如何调控干细胞向脂肪细胞的定向分化。我们已建立2种稳定的将干细胞定向为前脂肪细胞的模型：分别是BMP4处理的C3H10T1/2细胞以及A33细胞株，将应用这两种细胞模型研究干细胞定向为脂肪细胞过程中miRNA表达变化；筛选出脂肪细胞命运决定过程中起关键作用的miRNA, 结合生物信息学和蛋白表达谱分析找到关键miRNA的靶基因；在细胞水平验证这些关键因子在多潜能干细胞命运决定过程中的调控机理；在脂肪组织特异高表达BMP4小鼠和特异敲除BMP4的小鼠体内探索miRNA在干细胞命运决定过程中的作用机理。该研究对深刻理解肥胖的发生机制以及寻找肥胖及相关疾病的干预靶点有重要意义。

肥胖是糖尿病、脂肪肝等多种疾病的高危因素，肥胖不仅源于过多的甘油三酯累积引起的脂肪细胞体积增大，更源于干细胞分化为脂肪细胞引起的数目增多。本课题研究miRNA是如何调控干细胞向脂肪细胞的定向分化以及脂质生成。我们已经建立BMP4诱导多潜能干细胞向前脂肪细胞定向的模型，利用该细胞模型我们筛选出脂肪细胞命运决定过程中起关键作用的miR-140。 miR-140直接响应BMP信号通路的调节，并且可以正向调控脂肪细胞的生成。进一步研究发现miR-140通过抑制靶基因OSTM1(OSTM1是一个脂肪生成的负调控因子)来实现了干细胞向前脂肪细胞的定向，在BMP4过表达的小鼠体内我们也验证了同样的结果。我们的研究对于深刻理解肥胖的发生以及开发防止肥胖的新药有一定的理论价值。.研究发现肥胖是诱导非酒精性脂肪肝发生的重要因素，主要原因是能量以甘油三酯的形式在肝细胞中累积，它进一步可发展成脂肪性肝炎，肝纤维化甚至肝癌。研究发现绝经前女性由于受到雌激素的保护作用，非酒精性脂肪肝的发病率明显低于同龄的男性和绝经期后的女性。我们研究发现雌激素可以通过雌激素受体ERα直接调控miR-125b的表达，并且miR-125b可以抑制肝细胞中脂肪酸合成关键酶FAS的表达及其他甘油三酯合成和脂肪酸转运相关基因的表达，进而抑制肝脏中脂滴的累积，抑制脂肪肝的形成。在卵巢切除小鼠或者雌激素受体ERα敲低的肝脏中过表达了miR-125b，明显抑制脂肪肝的形成。相反，在雌性小鼠的肝脏中敲低miR-125b，在HFD的情况下可明显促进了脂肪肝的形成。在雄性小鼠肝脏中过表达miR-125b同样可以抑制高脂饮食诱导的脂肪肝。我们的研究对于将miRNA开发为治疗脂肪肝的新药提供了理论基础。

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