School of Pharmaceutical Sciences, Tsinghua University, Beijing, China.
Department of Bioengineering and Therapeutic Sciences, Schools of Pharmacy and Medicine, University of California, San Francisco, California.
PLoS Biol. 2019 Jan 17;17(1):e2006571. doi: 10.1371/journal.pbio.2006571. eCollection 2019 Jan.
Beiging of white adipose tissue (WAT) is a particularly appealing target for therapeutics in the treatment of metabolic diseases through norepinephrine (NE)-mediated signaling pathways. Although previous studies report NE clearance mechanisms via SLC6A2 on sympathetic neurons or proinflammatory macrophages in adipose tissues (ATs), the low catecholamine clearance capacity of SLC6A2 may limit the cleaning efficiency. Here, we report that mouse organic cation transporter 3 (Oct3; Slc22a3) is highly expressed in WAT and displays the greatest uptake rate of NE as a selective non-neural route of NE clearance in white adipocytes, which differs from other known routes such as adjacent neurons or macrophages. We further show that adipocytes express high levels of NE degradation enzymes Maoa, Maob, and Comt, providing the molecular basis on NE clearance by adipocytes together with its reuptake transporter Oct3. Under NE administration, ablation of Oct3 induces higher body temperature, thermogenesis, and lipolysis compared with littermate controls. After prolonged cold challenge, inguinal WAT (ingWAT) in adipose-specific Oct3-deficient mice shows much stronger browning characteristics and significantly elevated expression of thermogenic and mitochondrial biogenesis genes than in littermate controls, and this response involves enhanced β-adrenergic receptor (β-AR)/protein kinase A (PKA)/cyclic adenosine monophosphate (cAMP)-responsive element binding protein (Creb) pathway activation. Glycolytic genes are reprogrammed to significantly higher levels to compensate for the loss of ATP production in adipose-specific Oct3 knockout (KO) mice, indicating the fundamental role of glucose metabolism during beiging. Inhibition of β-AR largely abolishes the higher lipolytic and thermogenic activities in Oct3-deficient ingWAT, indicating the NE overload in the vicinity of adipocytes in Oct3 KO adipocytes. Of note, reduced functional alleles in human OCT3 are also identified to be associated with increased basal metabolic rate (BMR). Collectively, our results demonstrate that Oct3 governs β-AR activity as a NE recycling transporter in white adipocytes, offering potential therapeutic applications for metabolic disorders.
米色化白色脂肪组织(WAT)是通过去甲肾上腺素(NE)介导的信号通路治疗代谢疾病的一个特别有吸引力的治疗靶点。尽管先前的研究报告了通过交感神经元上的 SLC6A2 或脂肪组织(AT)中的促炎巨噬细胞清除 NE 的机制,但 SLC6A2 的低儿茶酚胺清除能力可能限制了清除效率。在这里,我们报告说,小鼠有机阳离子转运体 3(Oct3;Slc22a3)在 WAT 中高度表达,并表现出对 NE 的最大摄取率,作为白色脂肪细胞中 NE 清除的非神经选择性途径,这与其他已知途径(如相邻神经元或巨噬细胞)不同。我们进一步表明,脂肪细胞表达高水平的 NE 降解酶 Maoa、Maob 和 Comt,为脂肪细胞通过其再摄取转运体 Oct3 清除 NE 提供了分子基础。在 NE 给药下,与对照相比,Oct3 缺失诱导更高的体温、产热和脂肪分解。经过长时间的冷挑战后,脂肪特异性 Oct3 缺失小鼠腹股沟白色脂肪组织(ingWAT)显示出更强的褐色特征,并且其产热和线粒体生物发生基因的表达显著升高,而这一反应涉及增强β-肾上腺素能受体(β-AR)/蛋白激酶 A(PKA)/环腺苷酸(cAMP)反应元件结合蛋白(Creb)途径的激活。糖酵解基因被重新编程到更高的水平,以补偿脂肪特异性 Oct3 敲除(KO)小鼠中 ATP 产生的损失,这表明在米色化过程中葡萄糖代谢的基本作用。β-AR 的抑制在很大程度上消除了 Oct3 缺失 ingWAT 中更高的脂肪分解和产热活性,表明 Oct3 KO 脂肪细胞中脂肪细胞附近的 NE 过载。值得注意的是,人类 OCT3 的功能性降低等位基因也被鉴定与基础代谢率(BMR)的增加有关。总的来说,我们的结果表明,Oct3 作为白色脂肪细胞中的 NE 再循环转运体调节β-AR 活性,为代谢疾病提供了潜在的治疗应用。