肥胖症会导致过氧化物酶体增殖物激活受体 γ（PPARγ）活性降低和转化生长因子-β（TGFβ）-SMAD 信号转导升高，从而使脂肪细胞无法维持其细胞特性。
Adipocytes fail to maintain cellular identity during obesity due to reduced PPARγ activity and elevated TGFβ-SMAD signaling.
机构信息
Division of Endocrinology, Diabetes and Obesity, Beth Israel Deaconess Medical Center, Boston, MA, 02215, USA; Broad Institute, Cambridge, MA, 02142, USA; Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN, 46202, USA.
Division of Endocrinology, Diabetes and Obesity, Beth Israel Deaconess Medical Center, Boston, MA, 02215, USA.
出版信息
Mol Metab. 2020 Dec;42:101086. doi: 10.1016/j.molmet.2020.101086. Epub 2020 Sep 28.
OBJECTIVE
Obesity due to overnutrition causes adipose tissue dysfunction, which is a critical pathological step on the road to type 2 diabetes (T2D) and other metabolic disorders. In this study, we conducted an unbiased investigation into the fundamental molecular mechanisms by which adipocytes transition to an unhealthy state during obesity.
METHODS
We used nuclear tagging and translating ribosome affinity purification (NuTRAP) reporter mice crossed with Adipoq-Cre mice to determine adipocyte-specific 1) transcriptional profiles (RNA-seq), 2) promoter and enhancer activity (H3K27ac ChIP-seq), 3) and PPARγ cistrome (ChIP-seq) profiles in mice fed chow or a high-fat diet (HFD) for 10 weeks. We also assessed the impact of the PPARγ agonist rosiglitazone (Rosi) on gene expression and cellular state of adipocytes from the HFD-fed mice. We integrated these data to determine the transcription factors underlying adipocyte responses to HFD and conducted functional studies using shRNA-mediated loss-of-function approaches in 3T3-L1 adipocytes.
RESULTS
Adipocytes from the HFD-fed mice exhibited reduced expression of adipocyte markers and metabolic genes and enhanced expression of myofibroblast marker genes involved in cytoskeletal organization, accompanied by the formation of actin filament structures within the cell. PPARγ binding was globally reduced in adipocytes after HFD feeding, and Rosi restored the molecular and cellular phenotypes of adipocytes associated with HFD feeding. We identified the TGFβ1 effector protein SMAD to be enriched at HFD-induced promoters and enhancers and associated with myofibroblast signature genes. TGFβ1 treatment of mature 3T3-L1 adipocytes induced gene expression and cellular changes similar to those seen after HFD in vivo, and knockdown of Smad3 blunted the effects of TGFβ1.
CONCLUSIONS
Our data demonstrate that adipocytes fail to maintain cellular identity after HFD feeding, acquiring characteristics of a myofibroblast-like cell type through reduced PPARγ activity and elevated TGFβ-SMAD signaling. This cellular identity crisis may be a fundamental mechanism that drives functional decline of adipose tissues during obesity.
目的
营养过剩导致的肥胖会引起脂肪组织功能障碍，这是 2 型糖尿病（T2D）和其他代谢紊乱发生的关键病理步骤。在这项研究中，我们进行了一项无偏见的研究，以探究脂肪细胞在肥胖过程中向不健康状态转变的基本分子机制。
方法
我们使用核标记和翻译核糖体亲和纯化（NuTRAP）报告小鼠与 Adipoq-Cre 小鼠杂交，以确定脂肪细胞特异性的 1）转录谱（RNA-seq），2）启动子和增强子活性（H3K27ac ChIP-seq），3）以及 PPARγ 顺式作用元件（ChIP-seq）图谱在喂食标准饮食或高脂肪饮食（HFD）10 周的小鼠中。我们还评估了 PPARγ 激动剂罗格列酮（Rosi）对 HFD 喂养小鼠脂肪细胞基因表达和细胞状态的影响。我们整合这些数据以确定 HFD 诱导脂肪细胞反应的转录因子，并使用 3T3-L1 脂肪细胞中的 shRNA 介导的功能丧失方法进行功能研究。
结果
HFD 喂养的小鼠脂肪细胞表现出脂肪细胞标记物和代谢基因表达减少，参与细胞骨架组织的肌成纤维细胞标记基因表达增强，细胞内形成肌动蛋白丝结构。HFD 喂养后，PPARγ 结合在脂肪细胞中整体减少，而 Rosi 恢复了与 HFD 喂养相关的脂肪细胞的分子和细胞表型。我们发现 TGFβ1 效应蛋白 SMAD 在 HFD 诱导的启动子和增强子中富集，并与肌成纤维细胞特征基因相关。TGFβ1 处理成熟的 3T3-L1 脂肪细胞可诱导与体内 HFD 相似的基因表达和细胞变化，而 Smad3 的敲低可削弱 TGFβ1 的作用。
结论
我们的数据表明，脂肪细胞在 HFD 喂养后无法维持细胞特性，通过降低 PPARγ 活性和升高 TGFβ-SMAD 信号转导，获得肌成纤维细胞样细胞类型的特征。这种细胞身份危机可能是驱动肥胖过程中脂肪组织功能下降的基本机制。
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