Stypulkowski Ewa, Feng Qiang, Joseph Ivor, Farrell Victoria, Flores Juan, Yu Shiyan, Sakamori Ryotaro, Sun Jiaxin, Bandyopadhyay Sheila, Das Soumyashree, Dobrowolski Radek, Bonder Edward M, Chen Miao-Hsueh, Gao Nan
Department of Biological Sciences, Rutgers University, Newark, New Jersey, USA.
Department of Pediatrics, Baylor College of Medicine, Children's Nutrition Research Center, Houston, Texas, USA.
J Biol Chem. 2021 Jan-Jun;296:100488. doi: 10.1016/j.jbc.2021.100488. Epub 2021 Mar 1.
Differentiation of mesenchymal stem cells into adipocyte requires coordination of external stimuli and depends upon the functionality of the primary cilium. The Rab8 small GTPases are regulators of intracellular transport of membrane-bound structural and signaling cargo. However, the physiological contribution of the intrinsic trafficking network controlled by Rab8 to mesenchymal tissue differentiation has not been fully defined in vivo and in primary tissue cultures. Here, we show that mouse embryonic fibroblasts (MEFs) lacking Rab8 have severely impaired adipocyte differentiation in vivo and ex vivo. Immunofluorescent localization and biochemical analyses of Rab8a-deficient, Rab8b-deficient, and Rab8a and Rab8b double-deficient MEFs revealed that Rab8 controls the Lrp6 vesicular compartment, clearance of basal signalosome, traffic of frizzled two receptor, and thereby a proper attenuation of Wnt signaling in differentiating MEFs. Upon induction of adipogenesis program, Rab8a- and Rab8b-deficient MEFs exhibited severely defective lipid-droplet formation and abnormal cilia morphology, despite overall intact cilia growth and ciliary cargo transport. Our results suggest that intracellular Rab8 traffic regulates induction of adipogenesis via proper positioning of Wnt receptors for signaling control in mesenchymal cells.
间充质干细胞向脂肪细胞的分化需要外部刺激的协调，并且依赖于初级纤毛的功能。Rab8小GTP酶是膜结合结构和信号货物细胞内运输的调节因子。然而，由Rab8控制的内在运输网络对间充质组织分化的生理贡献在体内和原代组织培养中尚未完全明确。在这里，我们表明缺乏Rab8的小鼠胚胎成纤维细胞（MEF）在体内和体外的脂肪细胞分化严重受损。对Rab8a缺陷、Rab8b缺陷以及Rab8a和Rab8b双缺陷MEF的免疫荧光定位和生化分析表明，Rab8控制Lrp6囊泡区室、基础信号小体的清除、卷曲蛋白2受体的运输，从而在分化的MEF中适当减弱Wnt信号。在诱导脂肪生成程序后，尽管总体上纤毛生长和纤毛货物运输完整，但Rab8a和Rab8b缺陷的MEF表现出严重缺陷的脂滴形成和异常的纤毛形态。我们的结果表明，细胞内Rab8运输通过在间充质细胞中正确定位Wnt受体以进行信号控制来调节脂肪生成的诱导。
