Objective

Expansion of visceral adipose tissue (VAT) and metabolic inflammation are consequences of obesity and associated with type 2 diabetes (T2DM). Metabolically activated adipose tissue macrophages (ATMs) undergo qualitative and quantitative changes that influence their inflammatory responses. How these cells contribute to insulin resistance (IR) in humans is not well understood. Cholesterol 25-Hydroxylase (CH25H) converts cholesterol into 25-Hydroxycholesterol (25-HC), an oxysterol that modulates immune responses. Using human and murine models, we investigated the role of CH25H in metabolic inflammation.

Methods

We performed transcriptomic (RNASeq) analysis on the human whole AT biopsies and sorted ATMs from obese non-diabetic (NDM) and obese diabetic (DM) subjects to inquire if CH25H was increased in DM. We challenged mice lacking Ch25h with a high-fat diet (HFD) to characterize their metabolic and immunologic profiling. Ch25h KO mice and human adipose tissue biopsies from NDM and DM subjects were analyzed. LC-MS was conducted to measure 25-HC level in AT. In vitro analysis permitted us to investigate the effect of 25-HC on cytokine expression.

Results

In our RNASeq analysis of human visceral and subcutaneous biopsies, gene pathways related to inflammation were increased in obese DM vs. non-DM subjects that included CH25H. CH25H was enriched in the stromal vascular fraction of human adipose tissue and highly expressed in CD206⁺ human ATMs by flow cytometry analysis. We measured the levels of the oxysterols, 25-HC and 7α25diHC, in human visceral adipose tissue samples and showed a correlation between BMI and 25-HC. Using mouse models of diet-induced obesity (DIO), we found that HFD-induced Ch25h expression in eWAT and increased levels of 25-HC in AT. On HFD, Ch25h KO mice became obese but exhibited reduced plasma insulin levels, improved insulin action, and decreased ectopic lipid deposit. Improved insulin sensitivity in Ch25h KO mice was due to attenuation of CD11c⁺ adipose tissue macrophage infiltration in eWAT. Finally, by testing AT explants, bone marrow-derived macrophages (BMDMs) and SVF cells from Ch25h deficient mice, we observed that 25-HC is required for the expression of pro-inflammatory genes. 25-HC was also able to induce inflammatory genes in preadipocytes.

Conclusions

Our data suggest a critical role for CH25H/25-HC in the progression of meta-inflammation and insulin resistance in obese humans and mouse models of obesity. In response to obesogenic stimuli, CH25H/25-HC could exert a pro-inflammatory role.

中文翻译：

---

胆固醇 25-羟化酶 (CH25H) 作为肥胖和糖尿病中脂肪组织炎症的促进剂。

客观的

内脏脂肪组织 (VAT) 的扩张和代谢性炎症是肥胖的后果，与 2 型糖尿病 (T2DM) 相关。代谢激活的脂肪组织巨噬细胞 (ATM) 会发生影响其炎症反应的定性和定量变化。这些细胞如何导致人类胰岛素抵抗 (IR) 尚不清楚。胆固醇 25-羟化酶 (CH25H) 将胆固醇转化为 25-羟基胆固醇 (25-HC)，这是一种调节免疫反应的氧化甾醇。我们使用人类和小鼠模型研究了 CH25H 在代谢性炎症中的作用。

方法

我们对人类整体 AT 活检进行了转录组学 (RNASeq) 分析，并对来自肥胖非糖尿病 (NDM) 和肥胖糖尿病 (DM) 受试者的 ATM 进行了分类，以询问 CH25H 在 DM 中是否增加。我们用高脂肪饮食 (HFD) 挑战缺乏 Ch25h 的小鼠，以表征它们的代谢和免疫分析。分析了来自 NDM 和 DM 受试者的Ch25h KO 小鼠和人类脂肪组织活检。进行 LC-MS 以测量 AT 中的 25-HC 水平。体外分析使我们能够研究 25-HC 对细胞因子表达的影响。

结果

在我们对人类内脏和皮下活组织检查的 RNASeq 分析中，与包含CH25H的非 DM 受试者相比，肥胖 DM 受试者与炎症相关的基因通路增加。通过流式细胞术分析，CH25H 富含人体脂肪组织的基质血管部分，并在 CD206 ^{+人体 ATM 中高表达。}我们测量了人体内脏脂肪组织样本中氧固醇、25-HC 和 7α25diHC 的水平，并显示了 BMI 和 25-HC 之间的相关性。使用饮食诱导肥胖 (DIO) 的小鼠模型，我们发现 HFD 诱导eWAT 中的Ch25h表达和 AT 中 25-HC 水平的增加。在 HFD 上，Ch25hKO 小鼠变得肥胖，但表现出血浆胰岛素水平降低、胰岛素作用改善和异位脂质沉积减少。Ch25h KO 小鼠胰岛素敏感性的改善是由于 eWAT 中 CD11c ⁺脂肪组织巨噬细胞浸润的减弱。最后，通过测试来自Ch25h缺陷小鼠的 AT 外植体、骨髓来源的巨噬细胞 (BMDM) 和 SVF 细胞，我们观察到促炎基因的表达需要 25-HC。25-HC 还能够在前脂肪细胞中诱导炎症基因。

结论

我们的数据表明 CH25H/25-HC 在肥胖人类和肥胖小鼠模型的后炎症和胰岛素抵抗的进展中起着关键作用。作为对致肥胖刺激的反应，CH25H/25-HC 可以发挥促炎作用。