:It is recognized that a chronic low-grade inflammation and an activation of the immune system are involved in the pathogenesis of obesity-related insulin resistance and type 2 diabetes. Systemic inflammatory markers are risk factors for the development of type 2 diabetes and its macrovascular complications. Adipose tissue, liver, muscle and pancreas are themselves sites of inflammation in presence of obesity. An infiltration of macrophages and other immune cells is observed in these tissues associated with a cell population shift from an anti-inflammatory to a pro-inflammatory profile. These cells are crucial for the production of pro-inflammatory cytokines, which act in an autocrine and paracrine manner to interfere with insulin signaling in peripheral tissues or induce β-cell dysfunction and subsequent insulin deficiency. Particularly, the pro-inflammatory interleukin-1β is implicated in the pathogenesis of type 2 diabetes through the activation of the NLRP3 inflammasome. The objectives of this review are to expose recent data supporting the role of the immune system in the pathogenesis of insulin resistance and type 2 diabetes and to examine various mechanisms underlying this relationship. If type 2 diabetes is an inflammatory disease, anti-inflammarory therapies could have a place in prevention and treatment of type 2 diabetes.

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Aims/hypothesis Obesity is a heterogeneous condition comprising both individuals who remain metabolically healthy (MHO) and those who develop metabolic disorders (metabolically unhealthy, MUO). Adipose tissue is also heterogeneous in that its visceral component is more frequently associated with metabolic dysfunction than its subcutaneous component. The development of metabolic disorders is partly mediated by the NLR family pyrin domain containing-3 (NLRP3) inflammasome, which increases the secretion of inflammatory cytokines via activation of caspase-1. We compared the immunological profile and NLRP3 activity in adipose tissue between MUO and MHO individuals. Methods MHO and MUO phenotypes were defined, respectively, as the absence and the presence of the metabolic syndrome. Cellular composition and intrinsic inflammasome activity were investigated by flow cytometry, quantitative RT-PCR and tissue culture studies in subcutaneous and visceral adipose tissue from 23 MUO, 21 MHO and nine lean individuals.Results We found significant differences between the three study groups, including an increased secretion of IL-1β, increased expression of IL1B and NLRP3, increased number of adipose tissue macrophages and decreased number of regulatory T cells in the visceral adipose tissue of MUO patients compared with MHO and lean participants. In macrophages derived from visceral adipose tissue, both caspase-1 activity and IL-1β levels were higher in MUO patients than in MHO patients. Furthermore, caspase-1 activity was higher in CD11c + CD206 + adipose tissue macrophages than in CD11c − CD206 + cells. Conclusions/interpretation The MUO phenotype seems to be associated with an increased activation of the NLPR3 inflammasome in macrophages infiltrating visceral adipose tissue, and a less favourable inflammatory profile compared with the MHO phenotype.

Activation of transcription factor NF-κB involves the signal-dependent degradation of basally phosphorylated inhibitors such as IκBα. In response to proinflammatory cytokines or mitogens, the transduction machinery has recently been characterized, but the activation mechanism upon oxidative stress remains unknown. In the present work, we provide several lines of evidence that NF-κB activation in a T lymphocytic cell line (EL4) by hydrogen peroxide (H2O2) did not involve phosphorylation of the serine residues 32 and 36 in the amino-terminal part of IκBα. Indeed, mutation of Ser32 and Ser36 blocked IL-1β- or PMA-induced NF-κB activation, but had no effect on its activation by H2O2. Although IκBα was phosphorylated upon exposure to H2O2, tyrosine residue 42 and the C-terminal PEST (proline-glutamic acid-serine-threonine) domain played an important role. Indeed, mutation of tyrosine 42 or serine/threonine residues of the PEST domain abolished NF-κB activation by H2O2, while it had no effect on activation by IL-1β or PMA-ionomycin. This H2O2-inducible phosphorylation was not dependent on IκB kinase activation, but could involve casein kinase II, because an inhibitor of this enzyme (5,6-dichloro-1-β-d-ribofuranosyl-benzimidazole) blocks NF-κB activation. H2O2-induced IκBα phosphorylation was followed by its degradation by calpain proteases or through the proteasome. Taken together, our findings suggest that NF-κB activation by H2O2 involves a new mechanism that is totally distinct from those triggered by proinflammatory cytokines or mitogens.

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