Sharma Monika, Schlegel Martin, Brown Emily J, Sansbury Brian E, Weinstock Ada, Afonso Milessa S, Corr Emma M, van Solingen Coen, Shanley Lianne C, Peled Daniel, Ramasamy Ravichandran, Schmidt Ann Marie, Spite Matthew, Fisher Edward A, Moore Kathryn J
Department of Medicine, New York University School of Medicine, New York, NY 10016, USA.
Center for Experimental Therapeutics and Reperfusion Injury, Department of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115, USA.
Immunometabolism. 2019;1(2). doi: 10.20900/immunometab20190010. Epub 2019 Aug 7.
Macrophages accumulate prominently in the visceral adipose tissue (VAT) of obese humans and high fat diet (HFD) fed mice, and this is linked to insulin resistance and type II diabetes. While the mechanisms regulating macrophage recruitment in obesity have been delineated, the signals directing macrophage persistence in VAT are poorly understood. We previously showed that the neuroimmune guidance cue netrin-1 is expressed in the VAT of obese mice and humans, where it promotes macrophage accumulation. To better understand the source of netrin-1 and its effects on adipose tissue macrophage (ATM) fate and function in obesity, we generated mice with myeloid-specific deletion of netrin-1 ( ; Ntn1). Interestingly, Ntn1 mice showed a modest decrease in HFD-induced adiposity and adipocyte size, in the absence of changes in food intake or leptin, that was accompanied by an increase in markers of adipocyte beiging (, UCP-1). Using single cell RNA-seq, combined with conventional histological and flow cytometry techniques, we show that myeloid-specific deletion of netrin-1 caused a 50% attrition of ATMs in HFD-fed mice, particularly of the resident macrophage subset, and altered the phenotype of residual ATMs to enhance lipid handling. Pseudotime analysis of single cell transcriptomes showed that in the absence of netrin-1, macrophages in the obese VAT underwent a phenotypic switch with the majority of ATMs activating a program of genes specialized in lipid handling, including fatty acid uptake and intracellular transport, lipid droplet formation and lipolysis, and regulation of lipid localization. Furthermore, Ntn1 macrophages had reduced expression of genes involved in arachidonic acid metabolism, and targeted LCMS/MS metabololipidomics analysis revealed decreases in proinflammatory eicosanoids (5-HETE, 6- LTB, TXB, PGD) in the obese VAT. Collectively, our data show that targeted deletion of netrin-1 in macrophages reprograms the ATM phenotype in obesity, leading to reduced adipose inflammation, and improved lipid handling and metabolic function.
巨噬细胞在肥胖人类和高脂饮食（HFD）喂养小鼠的内脏脂肪组织（VAT）中显著积聚，这与胰岛素抵抗和II型糖尿病有关。虽然肥胖中调节巨噬细胞募集的机制已被阐明，但指导巨噬细胞在VAT中持续存在的信号却知之甚少。我们之前表明，神经免疫导向因子netrin-1在肥胖小鼠和人类的VAT中表达，它促进巨噬细胞积聚。为了更好地了解netrin-1的来源及其对肥胖中脂肪组织巨噬细胞（ATM）命运和功能的影响，我们构建了髓系特异性缺失netrin-1的小鼠（ ；Ntn1）。有趣的是，Ntn1小鼠在高脂饮食诱导的肥胖和脂肪细胞大小方面有适度降低，在食物摄入量或瘦素无变化的情况下，同时伴有脂肪细胞米色化标志物（ ，UCP-1）增加。使用单细胞RNA测序，结合传统组织学和流式细胞术技术，我们表明髓系特异性缺失netrin-1导致高脂饮食喂养小鼠中ATM减少50%，特别是驻留巨噬细胞亚群，并改变了残余ATM的表型以增强脂质处理。对单细胞转录组的伪时间分析表明，在没有netrin-1的情况下，肥胖VAT中的巨噬细胞发生了表型转换，大多数ATM激活了专门用于脂质处理的基因程序，包括脂肪酸摄取和细胞内运输、脂滴形成和脂解以及脂质定位调节。此外，Ntn1巨噬细胞中参与花生四烯酸代谢的基因表达降低，靶向LCMS/MS代谢脂质组学分析显示肥胖VAT中促炎类二十烷酸（5-HETE、6-LTB、TXB、PGD）减少。总体而言，我们的数据表明，巨噬细胞中netrin-1的靶向缺失在肥胖中重塑了ATM表型，导致脂肪炎症减轻，脂质处理和代谢功能改善。
