脂源性载脂蛋白E在残粒脂蛋白致脂肪间充质干细胞成脂分化中的作用机制

Obesity, which is an important risk factor for diabetes mellitus, coronary heart disease and hypertension, is involved in white adipocyte hypertrophy, hyperplasia and lipogenesis. It is significant to study the mechanism of adipocyte hyperplasia for preventing and treating obesity. Obesity and hypertriglyceridemia commonly coexist. Both of them are closely related to apolipoprotein E(ApoE) polymorphism. The applicant isolated remnant-like lipoproteins(RLPs) from patients with postprandial hypertriglyceridemia and found that RLPs with the co-incubation of insulin induced the adipogenic differentiation in adipose-derived mesenchymal stem cells（AMSCs）, accompanying with the upregulation of peroxisome proliferator-activated receptors γ and adiponectin, however, ApoE gene did not show a significant upregulation in RLPs-induced AMSCs group when compared with that in cocktail inducer-treated AMSCs group. Moreover, destroying the structure of lipid rafts obviously inhibited the adipogenic differentiation induced by RLPs that are rich in ApoE. Lipid raft is a key site for ApoE to play its role in adipocytes. It has been known that both lipid rafts and ApoE are associated with the adipogenic differentiation and lipoprotein endocytosis in mesenchymal stem cells. So the applicant reasonably conjectures that RLPs-bound ApoE could exert a very important role in the adipogenic differentiation in AMSCs by making up for a deficiency in endogenous ApoE through lipid rafts-mediated lipoprotein endocytosis. The applicant wants to verify that RLPs-bound ApoE could contribute to transport adipogeneic signal from RLPs into AMSCs through lipid rafts, and ApoE polymorphism could lead to a difference in the ability of RLPs-induced adipogenic differentiation in AMSCs. The present study is helpful to explore and enrich the mechanism of obesity, and the result of this study is expected to begin a new train of thought for preventing and treating obesity.

研究白色脂肪细胞增生的机制对于防治肥胖有重要意义。肥胖常与高甘油三酯血症并存，二者与载脂蛋白E（ApoE）基因多态性密切相关。申请人发现：从餐后高甘油三酯血症患者血浆中分离的残粒脂蛋白（RLPs）能在胰岛素辅助下诱导脂肪间充质干细胞（AMSCs）分化为脂肪细胞，但成脂分化标志ApoE的mRNA表达没有明显上调，破坏脂质筏结构显著抑制AMSCs成脂分化。已知RLPs富含ApoE，脂质筏和ApoE都与间充质干细胞的成脂分化、脂蛋白内吞有关，故推测RLPs中的ApoE通过脂质筏介导的脂蛋白内吞来弥补AMSCs内源性ApoE表达的不足，在AMSCs成脂分化过程中发挥重要作用。申请人试图证实ApoE通过脂质筏将RLPs促成脂分化的信号传递到细胞内，诱导AMSCs分化为成熟的脂肪细胞； ApoE基因多态性导致了RLPs诱导AMSCs成脂分化能力的差异。本项目有望为防治肥胖开拓新的思路。

肥胖常与高甘油三酯血症并存。申请人推测脂蛋白上的载脂蛋白E（ApoE）可能在餐后血浆中分离的富含甘油三酯脂蛋白（TRL）与胰岛素诱导的脂肪前体细胞成脂分化过程中发挥重要作用。研究发现：在一定浓度胰岛素辅助下，餐后TRL具有诱导多种脂肪前体细胞发生成脂分化的作用，提示这种不依赖于化学药物的成脂分化细胞模型非常接近体内真实情况，并且这一过程依赖于TRL上的ApoE；分化中的脂肪细胞能够内吞餐后TRL颗粒，同样依赖于TRL上的ApoE，支持ApoE依赖性的TRL内吞与成脂分化密切相关；没有观察到含有不同基因型的ApoE3/3、ApoE2/3、ApoE3/4的餐后TRL在诱导成脂分化方面的差异，这一现象可能源自载脂蛋白单一等位基因的差异不足以导致脂蛋白功能的变化；发现含有人重组ApoE3/3、ApoE2/2、ApoE4/4的餐后TRL被分化中的脂肪细胞内吞的程度存在差异，以含有人重组ApoE2/2的餐后TRL的内吞最为明显，这与临床上ApoE2/2纯合子升高的肥胖发生率相一致；分化中的脂肪细胞对餐后TRL的内吞依赖于低密度脂蛋白受体家族；低密度脂蛋白受体相关蛋白1（LRP1）的蛋白表达在脂肪前体细胞的基础水平高，餐后TRL和胰岛素能进一步上调其表达，提示LRP1是介导成脂分化的关键受体；磷酸化Akt的蛋白表达水平随成脂分化而上调，PI3K抑制剂能够抑制TRL诱导的成脂分化，说明餐后TRL与胰岛素可能通过ApoE/LRP1/PI3K/Akt的途径诱导成脂分化；脂筏蛋白caveolin-1的表达随成脂分化而上调，破坏脂质筏结构不仅抑制脂肪前体细胞的成脂分化，而且下调caveolin-1的表达，提示餐后TRL与胰岛素诱导的成脂分化依赖于脂质筏结构的完整性。研究结果有望为防治肥胖确立新的治疗靶点。