Single-cell RNA sequencing of visceral adipose tissue leukocytes reveals that caloric restriction following obesity promotes the accumulation of a distinct macrophage population with features of phagocytic cells. Single-cell RNA sequencing of visceral adipose tissue leukocytes reveals that caloric restriction following obesity promotes the accumulation of a distinct macrophage population with features of phagocytic cells

Obesity can lead to type 2 diabetes and is an epidemic. A major contributor to its adverse effects is inflammation of the visceral adipose tisse (VAT). Life-long caloric restriction (CR), in contrast, results in extended lifespan, enhanced glucose tolerance/ insulin sensitivity, and other favorable phenotypes. The effects of CR following obesity are incompletely established, but studies show multiple benefits. Many leukocyte types, macrophages predominantly, reside in VAT in homeostatic and pathological states. CR following obesity transiently increases VAT macrophage content prior to resolution of inflammation and obesity, suggesting that macrophage content and phenotype play critical roles. Here, we examined the heterogeneity of VAT leukocytes and the effects of obesity and CR. In general, our single-cell RNA-sequencing data demonstrate that macrophages are the most abundant and diverse subpopulation of leukocytes in VAT. Obesity induced significant transcriptional changes in all 15 leukocyte subpopulations, with many genes showing coordinated changes in expression across leukocyte subpopulations. Additionally, obese VAT displayed expansion of one major macrophage subpopulation, which, in silico was enriched in lipid binding and metabolic processes. This subpopulation returned from dominance in obesity to lean proportions after only 2 weeks of CR, although the pattern of gene expression overall remained similar. Surprisingly, CR VAT is dominated by a different macrophage subpopulation, which is absent in lean conditions. This subpopulation is enriched in genes related to phagocytosis and we postulate that its function includes clearance of dead cells as well as excess lipids, contributing to limiting VAT inflammation and restoration of the homeostatic state. Overall design: Single-cell RNA sequencing of CD45+ VAT cells.

肥胖可诱发2型糖尿病，且已成为一种全球性流行病。其不良影响的主要诱因是内脏脂肪组织（visceral adipose tissue, VAT）的炎症反应。与之相反，终生热量限制（caloric restriction, CR）可延长生物体寿命、提升葡萄糖耐量与胰岛素敏感性，并带来其他有益表型。目前关于肥胖后实施热量限制的效应尚未完全明确，但已有研究证实其具备多项益处。在稳态与病理状态下，多种白细胞（以巨噬细胞为主）均定居于内脏脂肪组织中。肥胖后实施热量限制可在炎症与肥胖得到缓解前，一过性增加内脏脂肪组织内的巨噬细胞含量，这提示巨噬细胞的数量与表型发挥着关键作用。本研究针对内脏脂肪组织白细胞的异质性，以及肥胖与热量限制的调控效应展开了探究。总体而言，本研究的单细胞RNA测序（single-cell RNA-sequencing）数据显示，巨噬细胞是内脏脂肪组织白细胞中丰度最高且异质性最强的亚群。肥胖可导致全部15种白细胞亚群发生显著的转录组改变，且多个基因在各类白细胞亚群中呈现协同表达变化。此外，肥胖状态下的内脏脂肪组织可见一类主要巨噬细胞亚群的扩增，经计算机分析（in silico）发现该亚群富含脂质结合与代谢相关基因。仅通过2周的热量限制，该巨噬细胞亚群即可从肥胖时的优势状态回落至瘦态时的占比，尽管整体基因表达模式未发生明显改变。令人意外的是，实施热量限制后的内脏脂肪组织以另一类巨噬细胞亚群为主导，而该亚群在瘦态个体中并不存在。该亚群富含与吞噬作用相关的基因，我们推测其功能包括清除死亡细胞与过量脂质，从而有助于抑制内脏脂肪组织炎症并恢复稳态。实验总体设计：对CD45阳性内脏脂肪组织细胞开展单细胞RNA测序。