The Ubiquitin Ligase Siah2 Regulates Obesity-induced Adipose Tissue Inflammation
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ABSTRACT: Chronic, low-grade adipose tissue inflammation associated with adipocyte hypertrophy is an important link in the relationship between obesity and insulin resistance. Although ubiquitin ligases are essential regulators of inflammatory processes, the role of these enzymes in metabolically driven adipose tissue inflammation is relatively unexplored. In this study, we found that the ubiquitin ligase Siah2 is a central factor in obesity-related adipose tissue inflammation. When challenged with chronic excess energy intake, Siah2-null mice become obese with enlarged adipocytes, but do not develop obesity-induced insulin resistance. Proinflammatory gene expression is substantially reduced in the Siah2-null epididymal adipose tissue of the obese Siah2KO mice.
Project description:The crosstalk between the bone and adipose tissue orchestrates the metabolic homeostasis, but the underlying mechanisms are largely unknown. Herein, we find that GCA+(grancalcin) immune cells accumulate in the bone marrow and release a sufficient amount of GCA into circulation during obesity. Genetic deletion of Gca in myeloid cells attenuates metabolic dysfunction in obese male mice, whereas injection of recombinant GCA into male mice cause adipose tissue inflammation and insulin resistance. Mechanistically, we found that GCA binds to the Prohibitin-2 (PHB2) receptor on adipocytes and activates the innate and adaptive immune response of adipocytes via the PAK1-NF-κB signaling pathway, thus provoking the infiltration of inflammatory immune cells. Moreover, GCA-neutralizing antibodies improve adipose tissue inflammation and insulin sensitivity in obese male mice. Together, these observations uncover a novel mechanism whereby bone marrow factor GCA initiates adipose tissue inflammation and insulin resistance, implicating GCA could be a potential target to treat metainflammation.
Project description:Obesity is a risk factor for numerous metabolic disorders; however, not all obese individuals are prone to insulin resistance. The central aim of this study was to identify molecular pathways directly related to insulin resistance independent of BMI in obesity. We sought to determine the gene expression signature of adipose tissue in a body mass index (BMI)-matched obese cohort of patients that are either insulin sensitive or insulin resistant. We determined the global gene expression signatures of omental and subcutaneous adipose tissue samples obtained from insulin-sensitive obese and insulin-resistant obese patients undergoing gastric bypass surgery.
Project description:Obesity is a risk factor for numerous metabolic disorders; however, not all obese individuals are prone to insulin resistance. The central aim of this study was to identify molecular pathways directly related to insulin resistance independent of BMI in obesity. We sought to determine the gene expression signature of adipose tissue in a body mass index (BMI)-matched obese cohort of patients that are either insulin sensitive or insulin resistant. We determined the global gene expression signatures of omental and subcutaneous adipose tissue samples obtained from insulin-sensitive obese and insulin-resistant obese patients undergoing gastric bypass surgery. The SQ sample for Insulin Resistant Patient 6 has been removed from the study.
Project description:Cytokines of the IL-1 family are important modulators of obesity-induced inflammation and the development of systemic insulin resistance. Here, we report that IL-37, a newly-described antiinflammatory member of the IL-1 family, affects obesity-induced inflammation and insulin resistance. IL-37 transgenic mice (IL-37tg) did not develop an obese phenotype in response to a high-fat diet (HFD). Unlike WT mice, IL-37tg mice exhibited reduced numbers of adipose tissue macrophages and preserved glucose tolerance and insulin sensitivity after 16 weeks of HFD. A short-term HFD intervention revealed that the IL-37-mediated improvement in glucose tolerance is independent of bodyweight. IL-37tg mice manifested a beneficial metabolic profile with higher circulating levels of the anti-inflammatory adipokine adiponectin. In vitro treatment of differentiating adipocytes with recombinant IL-37 reduced adipogenesis. The beneficial effects of recombinant IL-37 involved activation of AMPK signaling. In humans, steady-state IL-37 adipose tissue mRNA levels were positively correlated with insulin sensitivity, lower adipose tissue levels of leptin and a lower inflammatory status of the adipose tissue. These findings reveal IL-37 as an important anti-inflammatory modulator during obesity-induced inflammation and insulin resistance in both mice and humans and suggest that IL-37 is a potential target for the treatment of obesity-induced insulin resistance and type 2 diabetes. Gene arrays were performed on epidydimal white adipose tissue samples from wild type and human IL37-overexpressing transgenic mice fed a high fat diet for 16 weeks.
Project description:To assess changes in expression level of various chemokines and their receptors on diet-induced obesity, we analysed gene expression in adipose tissue of C56BL/6J mice fed a high-fat (HF) diet or normal chow diet for 8 weeks. HF diet-induced obese (DIO) mice showed adipose tissue inflammation and insulin resistance. Comprehensive gene expression analysis showed that MCP-1–CCR2 and CCL5–CCR5 signalling in epididymal white adipose tissue (eWAT) were enhanced during the development of obesity. Surprisingly, the gene expression of Cx3cl1 was decreased in the eWAT of DIO mice compared with lean mice. While Cx3cr1 expression showed no significant difference between DIO and lean mice. Decreased CX3CL1-CX3CR1 signalling in adipose tissue may also be involved in the development of obesity-induced adipose tissue inflammation and insulin resistance.
Project description:Adipose tissue is an active producer of lactate. In obesity, the increased size of adipocytes is accompanied by an increase in lactate production in adipose tissue, caused by hypoxia in obese adipocytes. How lactate affects metabolism in adipocyte and insulin sensitivity remains unclear. Here we develop a mouse model of MCT1,coding by Slc16a1, specific deletion in adipose tissues, using the AP2 promoter to drive Cre expression. This MCT1 AKO mice develop more severe insulin resistance in obesity with 16 weeks high fat diet treatment, while few changes happen to lipid metabolism in adipose tissues. We used RNA-seq to analyze the gene expression patterns of eWAT of obese MCT1 AKO mice compared to WT, and found significant changes in innate immune signaling and adipocyte apoptosis that reflect systemic inflammation and insulin resistance.
Project description:Low-grade, sustained inflammation in white adipose tissue (WAT) characterizes obesity and frequently coincides with insulin resistance and type 2 diabetes (T2D). However, pharmacological targeting of WAT inflammation lacks durable therapeutic effects. Through a computational screen, we identified the FDA-approved rheumatoid arthritis drug auranofin is a putative small molecule for obesity treatment. We discovered that allometrically scaled safe auranofin doses homed to WAT and improved insulin sensitivity in obese wild-type mice. To assess the transcriptional changes underlying the beneficial effects of auranofin, we performed RNA-seq analysis on adipose and liver tissue after 4 weeks of treatment with vehicle or auranofin.
Project description:Metabolic disorders including obesity and insulin resistance have their basis in dysregulated lipid metabolism and low-grade inflammation. In a microarray search of unique lipase-related genes whose expressions are associated with obesity, we found that two secreted phospholipase A2s (sPLA2s), PLA2G5 and PLA2G2E, were robustly induced in adipocytes of obese mice. Analyses of Pla2g5-/- and Pla2g2e-/- mice revealed distinct and previously unrecognized roles of these sPLA2s in diet-induced obesity. PLA2G5 hydrolyzed phosphatidylcholine in fat-overladen low-density lipoprotein to release unsaturated fatty acids, which prevented palmitate-induced M1 macrophage polarization. As such, PLA2G5 tipped the immune balance toward an M2 state, thereby counteracting adipose tissue inflammation, insulin resistance, hyperlipidemia and obesiy. PLA2G2E altered minor lipoprotein phospholipids, phosphatidylserine and phosphatidylethanolamine, and moderately facilitated lipid accumulation in adipose tissue and liver. Collectively, the identification of metabolic sPLA2s adds this gene family to a growing list of lipolytic enzymes that act as metabolic coordinators. white adipose tissues of C57BL/6 mice; two-condition experimentM-bM-^@M-^Shigh fat diet or low fat diet feeding for 18 weeks; 2 replicates, respectively