From the Department of Metabolism and Endocrinology, Metabolic Syndrome Research Center, Key Laboratory of Diabetes Immunology, National Clinical Research Center for Metabolic Diseases, The Second Xiangya Hospital of Central South University, Changsha, Hunan, China (Q.Z., J.H., Y.W., H.L., W.M., B.X., Z.Z., F.L.).
Department of Metabolism and Endocrinology, First Affiliated Hospital of University of South China, Hengyang, Hunan (Q.Z.).
Arterioscler Thromb Vasc Biol. 2019 Sep;39(9):1787-1801. doi: 10.1161/ATVBAHA.119.312870. Epub 2019 Jul 18.
Macrophage foam cell formation is an important process in atherosclerotic plaque development. The small GTPase Rheb (Ras homolog enriched in brain 1) regulates endocytic trafficking that is critical for foam cell formation. However, it is unclear whether and how macrophage Rheb regulates atherogenesis, which are the focuses of the current study. Approach and Results: Immunofluorescence study confirmed the colocalization of Rheb in F4/80 and Mac-2 (galectin-3)-labeled lesional macrophages. Western blot and fluorescence-activated cell sorting analysis showed that Rheb expression was significantly increased in atherosclerotic lesions of atherosclerosis-prone (apoE [apolipoprotein E deficient]) mice fed with Western diet. Increased Rheb expression was also observed in oxidized LDL (low-density lipoprotein)-treated macrophages. To investigate the in vivo role of macrophage Rheb, we established mature Rheb (macrophage-specific Rheb knockout) mice by crossing the Rheb floxed mice with F4/80-cre mice. Macrophage-specific knockout of Rheb in mice reduced Western diet-induced atherosclerotic lesion by 32%, accompanied with a decrease in macrophage content in plaque. Mechanistically, loss of Rheb in macrophages repressed oxidized LDL-induced lipid uptake, inflammation, and macrophage proliferation. On the contrary, lentivirus-mediated overexpression of Rheb in macrophages increased oxidized LDL-induced lipid uptake and inflammation, and the stimulatory effect of Rheb was suppressed by the mTOR (mammalian target of rapamycin) inhibitor rapamycin or the PKA (protein kinase A) activator forskolin.
Macrophage Rheb plays important role in Western diet-induced atherosclerosis by promoting macrophage proliferation, inflammation, and lipid uptake. Inhibition of expression and function of Rheb in macrophages is beneficial to prevent diet-induced atherosclerosis.
巨噬细胞泡沫细胞的形成是动脉粥样硬化斑块发展的一个重要过程。小分子 GTP 酶 Rheb（富含脑的 Ras 同源物 1）调节内吞作用，这对泡沫细胞的形成至关重要。然而，尚不清楚巨噬细胞 Rheb 是否以及如何调节动脉粥样硬化形成，这是当前研究的重点。
免疫荧光研究证实了 Rheb 在 F4/80 和 Mac-2（半乳糖凝集素-3）标记的病变巨噬细胞中的共定位。Western blot 和荧光激活细胞分选分析显示，富含西方饮食的动脉粥样硬化易感（载脂蛋白 E 缺乏）小鼠动脉粥样硬化病变中 Rheb 表达显著增加。在氧化型 LDL（低密度脂蛋白）处理的巨噬细胞中也观察到 Rheb 表达增加。为了研究巨噬细胞 Rheb 的体内作用，我们通过将 Rheb 基因敲除小鼠与 F4/80-cre 小鼠杂交，建立了成熟的 Rheb（巨噬细胞特异性 Rheb 敲除）小鼠。在小鼠中，巨噬细胞特异性敲除 Rheb 可使西方饮食诱导的动脉粥样硬化病变减少 32%，同时斑块中的巨噬细胞含量减少。在机制上，巨噬细胞中 Rheb 的缺失抑制了氧化型 LDL 诱导的脂质摄取、炎症和巨噬细胞增殖。相反，通过慢病毒介导的巨噬细胞中 Rheb 的过表达增加了氧化型 LDL 诱导的脂质摄取和炎症，并且 mTOR（雷帕霉素哺乳动物靶标）抑制剂 rapamycin 或 PKA（蛋白激酶 A）激活剂 forskolin 抑制了 Rheb 的刺激作用。
巨噬细胞 Rheb 通过促进巨噬细胞增殖、炎症和脂质摄取，在西方饮食诱导的动脉粥样硬化中发挥重要作用。抑制巨噬细胞中 Rheb 的表达和功能有利于预防饮食诱导的动脉粥样硬化。
