Expression of NLRP3 inflammasome and T cell population markers in adipose tissue are associated with insulin resistance and impaired glucose metabolism in humans

Abstract

Recent studies in rodents indicate that the nucleotide-binding domain, leucine-rich-containing family, pyrin domain-containing-3 (NLRP3) inflammasome and a proinflammatory shift in the T cell population in adipose tissue (AT) contribute to AT inflammation and insulin resistance. We investigated: (1) the interplay between the NLRP3 inflammasome and T cell populations in abdominal subcutaneous AT in obese and lean humans in relation to AT inflammatory processes, and (2) involvement of the NLRP3 inflammasome and T cell populations in insulin resistance. Abdominal subcutaneous AT biopsies were collected in 10 obese men with impaired glucose tolerance and 9 lean normal glucose tolerant age-matched controls. AT gene expression of NLRP3 inflammasome-related genes and markers of T cell populations, chemoattraction, macrophage infiltration and other aspects of inflammation were examined. Furthermore, we examined systemic adaptive immune activation and insulin sensitivity (hyperinsulinemic-euglycemic clamp). CASPASE-1 mRNA and the proportion of T_h1 transcripts (TBX21/CD3ɛ) were significantly higher in AT from obese compared with lean subjects. CASPASE-1 expression and a relative increase in T_h1 transcripts in AT were strongly associated with insulin resistance and impairments in glucose homeostasis. Gene expression of NLRP3, CASPASE-1, CD3ɛ (pan T cells), TBX21 (T_h1 cells) and RORC (T_h17 cells) was positively, whereas GATA3 (T_h2 cells) was inversely correlated with AT inflammation. Our data suggest that NLRP3 inflammasome activation and a T_h1 shift in the T cell population in AT of obese subjects is related to insulin resistance and impaired glucose metabolism, which may be explained by AT inflammatory processes.

Introduction

Adipose tissue (AT) inflammation is an important hallmark of AT dysfunction in obesity and contributes to several obesity-related disorders, including insulin resistance and type 2 diabetes (Goossens, 2008). The evidence that AT inflammation is causally related to insulin resistance in obesity is derived from studies in rodents (Goossens, 2008). Although the inciting event causing AT inflammation and subsequent insulin resistance in obese individuals remains to be established, previous studies have indicated that macrophage infiltration and activation in AT is of critical importance in insulin resistance (Weisberg et al., 2003, Odegaard and Chawla, 2008). However, recent studies indicate involvement of other inflammatory cells as well in AT inflammation and insulin resistance.

In rodents, it has been shown that activated T cell populations are present in the expanded AT in obesity, and may contribute to AT inflammation and metabolic disturbances (Wu et al., 2007, Kintscher et al., 2008, Rocha et al., 2008, Duffaut et al., 2009, Feuerer et al., 2009, Nishimura et al., 2009, Winer et al., 2009, Strissel et al., 2010, Yang et al., 2010). The T cell subpopulations seem to exert distinct effects, with T-helper (T_h)1 and cytotoxic T cells having detrimental effects, whereas T_h2 and regulatory T cells (T_reg) may have beneficial effects on AT inflammation and insulin sensitivity (Feuerer et al., 2009, Nishimura et al., 2009, Winer et al., 2009). In addition, evidence has emerged that a protein cluster in AT called the inflammasome, consisting of caspase-1 and proteins of the NACHT-LRR (NLR) family such as NLRP3 and ASC may underlie AT inflammation (Zhou et al., 2010, Koenen et al., 2011, Vandanmagsar et al., 2011) and insulin resistance (Stienstra et al., 2010, Zhou et al., 2010, Vandanmagsar et al., 2011). The NLRP3 inflammasome is implicated in recognizing certain nonmicrobial-originated danger-associated molecular patterns (DAMPs), leading to caspase-1 activation and subsequent production of IL-1β and IL-18 (Kanneganti et al., 2007, Petrilli et al., 2007, Wilmanski et al., 2008), which are major proinflammatory cytokines important in the differentiation of naive CD4+ T cells in T_h17 and T_h1 cells, respectively (Dinarello, 1999, Chung et al., 2009). Interestingly, genetic ablation of NLRP3, CASPASE-1 (Stienstra et al., 2010, Zhou et al., 2010, Vandanmagsar et al., 2011) and T_h1 cell-derived interferon (IFN)-γ (Rocha et al., 2008) improved glucose homeostasis in rodent models. Furthermore, weight-loss in obese subjects with type 2 diabetes reduced NLRP3 and IL-1β gene expression in abdominal subcutaneous AT (Vandanmagsar et al., 2011). Until now, however, the importance of the NLRP3 inflammasome and T cell populations in AT inflammation and, importantly, their relationship with insulin sensitivity has not yet been investigated in lean and obese humans.

The aim of the present study was to investigate: (1) the interplay between the NLRP3 inflammasome and T cell population markers in abdominal subcutaneous AT of obese and lean subjects in relation to AT inflammatory processes, and (2) possible involvement of the NLRP3 inflammasome and T cell populations in insulin resistance in human obesity. All subjects were phenotyped in detail with respect to body composition, glucose tolerance and insulin sensitivity.