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The ATP-P2X7 signaling axis is dispensable for obesity-associated inflammasome activation in adipose tissue

ABSTRACT: Inflammasome activation in adipose tissue has been implicated in obesity-associated insulin resistance and type 2 diabetes. However, when and how inflammasome is activated in adipose tissue remains speculative. Here we test the hypothesis that extracellular ATP, a potent stimulus of inflammasome in macrophages via purinergic receptor P2X, ligand-gated ion channel, 7 (P2X7), may play a role in inflammasome activation in adipose tissue in obesity. Our data show that inflammasome is activated in adipose tissue upon 8-week feeding of 60% HFD, coinciding with the onset of hyperglycemia and hyperinsulinemia as well as the induction of P2X7 in adipose tissue. Unexpectedly, P2X7-deficient animals on HFD exhibit no changes in metabolic phenotypes, nor in inflammatory responses or inflammasome activation when compared to the wildtype controls. Similar observations have been obtained in hematopoietic cell-specific P2X7-deficient animals generated by bone marrow transplantation. Thus, we conclude that inflammasome activation in adipose tissue in obesity coincides with the onset of hyperglycemia and hyperinsulinemia, but unexpectedly, is not mediated by the ATP-P2X7 signaling axis. The nature of the inflammasome-activating danger signal(s) in adipose tissue in obesity remains to be characterized.

ORGANISM(S): Mus musculus

PROVIDER: GSE36033 | GEO | 2012/02/24

SECONDARY ACCESSION(S): PRJNA151751

REPOSITORIES: GEO

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Project description:Abstract Background In obesity, adipose tissue undergoes a remodeling process characterized by increased adipocyte size (hypertrophia) and number (hyperplasia). The individual ability to tip the balance toward the hyperplastic growth, with recruitment of new fat cells through adipogenesis, seems to be critical for a healthy adipose tissue expansion, as opposed to the development of inflammation and detrimental metabolic consequences. However, the molecular mechanisms underlying this fine-tuned regulation are far from being understood. Methods We analyzed by mass spectrometry-based proteomics visceral white adipose tissue (vWAT) samples collected from C57BL6 mice fed with a HFD for 8 weeks. A subset of these mice, called low responders (LowR HFD), showed a low susceptibility to the onset of adipose tissue inflammation, as opposed to their HFD counterpart. We identified the discriminants between LowR HFD and HFD vWAT samples and explored their function in Adipose Derived human Mesenchymal Stem Cells (AD-hMSCs) differentiated to adipocytes. Results We quantified 6051 proteins. Among the candidates that most differentiate LowR HFD from HFD vWAT, we found proteins involved in adipocyte function, including adiponectin and hormone sensitive lipase, suggesting that adipocyte differentiation is enhanced in LowR HFD, as compared to HFD. The chromatin modifier SET and MYND Domain Containing 3 (SMYD3), whose function in adipose tissue was totally unknown, was another top-scored hit. SMYD3 expression was significantly higher in LowR HFD vWAT, as confirmed by western blot analysis. In vitro, we found that SMYD3 mRNA and protein levels decrease rapidly along the differentiation process of AD-hMSCs. Moreover, SMYD3 knock-down at the beginning of adipocyte differentiation resulted in reduced cell proliferation and, at longer term, reduced lipid accumulation in adipocytes. Conclusions Our study describes for the first time the role of SMYD3 as a regulator of adipocyte proliferation during the early steps of adipogenesis.

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The ATP-P2X7 signaling axis is dispensable for obesity-associated inflammasome activation in adipose tissue

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