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Summary Obesity-induced inflammation mediated by immune cells in adipose tissue appears to participate in the pathogenesis of insulin resistance. We show that natural killer (NK) cells in adipose tissue play an important role. High fat diet (HFD) increases NK cell numbers and the production of pro-inflammatory cytokines, notably TNFα, in epididymal, but not subcutaneous, fat depots. When NK cells were depleted either with neutralizing antibodies or genetic ablation in E4bp4+/− mice, obesity-induced insulin resistance improved in parallel with decreases in both adipose tissue macrophage (ATM) numbers and ATMs and adipose tissue inflammation. Conversely, expansion of NK cells following IL-15 administration or reconstitution of NK cells into E4bp4−/−mice increased both ATM numbers and adipose tissue inflammation and exacerbated HFD-induced insulin resistance. These results indicate that adipose NK cells control ATMs as an upstream regulator potentially by producing pro-inflammatory mediators including TNFα and thereby contribute to the development of obesity-induced insulin resistance.

According to the Developmental Origin of Health and Disease (DOHaD) concept, alterations of nutrient supply in the fetus or neonate result in long-term programming of individual body weight (BW) setpoint. In particular, maternal obesity, excessive nutrition, and accelerated growth in neonates have been shown to sensitize offspring to obesity. The white adipose tissue may represent a prime target of metabolic programming induced by maternal obesity. In order to unravel the underlying mechanisms, we have developed a rat model of maternal obesity using a high-fat (HF) diet (containing 60% lipids) before and during gestation and lactation. At birth, newborns from obese dams (called HF) were normotrophs. However, HF neonates exhibited a rapid weight gain during lactation, a key period of adipose tissue development in rodents. In males, increased BW at weaning (+30%) persists until 3 months of age. Nine-month-old HF male offspring was normoglycemic but showed mild glucose intolerance, hyperinsulinemia, and hypercorticosteronemia. Despite no difference in BW and energy intake, HF adult male offspring was predisposed to fat accumulation showing increased visceral (gonadal and perirenal) depots weights and hyperleptinemia. However, only perirenal adipose tissue depot exhibited marked adipocyte hypertrophy and hyperplasia with elevated lipogenic (i.e. sterol-regulated element binding protein 1 (Srebp1), fatty acid synthase (Fas), and leptin) and diminished adipogenic (i.e. peroxisome proliferator-activated receptor gamma (Pparγ), 11β-hydroxysteroid dehydrogenase type 1 (11β-Hds1)) mRNA levels. By contrast, very few metabolic variations were observed in HF female offspring. Thus, maternal obesity and accelerated growth during lactation program offspring for higher adiposity via transcriptional alterations of visceral adipose tissue in a depot-and sex-specific manner.

Sterol regulatory element-binding protein (SREBP)-1 transcription factors play a central role in energy homeostasis by promoting glycolysis, lipogenesis, and adipogenesis. The sterol regulatory element-binding protein gene (SREBF)-1 is a good candidate gene for obesity and obesity-related metabolic traits such as type 2 diabetes and dyslipidemia. The SREBF-1 molecular screening of 40 unrelated obese patients by PCR/ single-strand conformation polymorphism revealed 19 single nucleotide polymorphisms (SNPs). Six SNPs were genotyped for an association study in large French obese and nonobese cohorts. Case-control studies using two independent nonobese cohorts indicated that SNP17 (54G/C, exon 18c) is associated with morbid obesity (odds ratio 1.5, P ‫؍‬ 0.006 and P ‫؍‬ 0.02, respectively). SNP3 (؊150G/A, exon 1a), SNP5 (؊36delG, exon 1a), and SNP17 are found in high linkage disequilibrium (D > 0.8). The haplotype including wild-type alleles of these SNPs (C/G/G/T/C/G, HAP2) is identified as a risk factor for morbid obesity (P ‫؍‬ 0.003). In the obese group, SNP3, SNP5, and SNP17 are associated with male-specific hypertriglyceridemia (P ‫؍‬ 0.07, P ‫؍‬ 0.01, and P ‫؍‬ 0.05, respectively). SNP17 is also associated with type 2 diabetes (P ‫؍‬ 0.03) and increased prevalence of nephropathy (P ‫؍‬ 0.028) in a diabetic cohort. Our results indicate a role of the SREBF-1 gene in genetic predisposition of metabolic diseases such as obesity, type 2 diabetes, and dyslipidemia.

Insulin resistance, a hallmark of type 2 diabetes and obesity, is associated with increased activity of MAP and stress-activated protein (SAP) kinases, which results in decreased insulin signaling. Our goal was to investigate the role of MAP kinase phosphatase-4 (MKP-4) in modulating this process. We found that MKP-4 expression is upregulated during adipocyte and myocyte differentiation in vitro and up-regulated during fasting in white adipose tissue in vivo. Overexpression of MKP-4 in 3T3-L1 cells inhibited ERK and JNK phosphorylation and, to a lesser extent, p38MAPK phosphorylation. As a result, the phosphorylation of IRS-1 serine 307 induced by anisomycin was abolished, leading to a sensitization of insulin signaling with recovery of insulin-stimulated IRS-1 tyrosine phosphorylation, IRS-1 docking with phosphatidylinositol 3-kinase, and Akt phosphorylation. MKP-4 also reversed the effect of TNF-␣ to inhibit insulin signaling; alter IL-6, Glut1 and Glut4 expression; and inhibit insulinstimulated glucose uptake in 3T3-L1 adipocytes. Overexpression of MKP-4 in the liver of ob/ob mice decreased ERK and JNK phosphorylation, leading to a reduction in fed and fasted glycemia, improved glucose intolerance, decreased expression of gluconeogenic and lipogenic genes, and reduced hepatic steatosis. Thus, MKP-4 has a protective effect against the development of insulin resistance through its ability to dephosphorylate and inactivate crucial mediators of stress-induced insulin resistance, such as ERK and JNK, and increasing MKP-4 activity might provide a therapy for insulin-resistant disorders.cytokines ͉ diabetes ͉ kinases ͉ obesity

Epidemiological studies demonstrated initially that maternal undernutrition results in low birth weight with increased risk for long-lasting energy balance disorders. Maternal obesity and diabetes associated with high birth weight, excessive nutrition in neonates, and rapid catchup growth also increase the risk of adult-onset obesity. As stated by the Developmental Origin of Health and Disease concept, nutrient supply perturbations in the fetus or neonate result in long-term programming of individual body weight set point. Adipose tissue is a key fuel storage unit involved mainly in the maintenance of energy homeostasis. Studies in numerous animal models have demonstrated that the adipose tissue is the focus of developmental programming events in a sex- and depot-specific manner. In rodents, adipose tissue development is particularly active during the perinatal period, especially during the last week of gestation and during early postnatal life. In contrast to rodents, this process essentially takes place before birth in bigger mammals. Despite these different developmental time windows, altricial and precocial species share several mechanisms of adipose tissue programming. Offspring from malnourished dams present adipose tissue with a series of alterations: impaired glucose uptake, insulin and leptin resistance, low-grade inflammation, modified sympathetic activity with reduced noradrenergic innervations, and thermogenesis. These modifications reprogram adipose tissue metabolism by changing fat distribution and composition and by enhancing adipogenesis, predisposing the offspring to fat accumulation. Subtle adipose tissue circadian rhythm changes are also observed. Inappropriate hormone levels, modified tissue sensitivity (especially glucocorticoid system), and epigenetic mechanisms are key factors for adipose tissue programming during the perinatal period.

A20 or tumor necrosis factor (TNF)-induced protein 3 (TNFAIP3) is a negative regulator of nuclear factor-B (NF-B).We have investigated whether polymorphisms in this gene are associated with increased atherosclerosis in diabetic patients. Five tag single nucleotide polymorphisms (SNPs) were typed in 479 type 2 diabetic patients from Boston, including 239 coronary artery disease (CAD)-positive case subjects and 240 CAD-negative control subjects. Two tag SNPs (rs5029930 and rs610604) were independently associated with CAD; adjusted odds ratios (ORs) for minor allele carriers were 2.3 (95% CI 1.4 -3.8, P ‫؍‬ 0.001) and 2.0 (1.3-2.9, P ‫؍‬ 0.0008), respectively. The association with rs610604 was dependent on glycemic control, with ORs of 3.9 among subjects with A1C <7.0% and 1.2 for those with A1C >7.0% (P for interaction ‫؍‬ 0.015). A similar interaction pattern was found among 231 CADpositive and 332 CAD-negative type 2 diabetic patients from Italy (OR 2.2, P ‫؍‬ 0.05 vs. OR 0.9, P ‫؍‬ 0.63 in the low vs. high A1C strata, P for interaction ‫؍‬ 0.05). Quantitative RT-PCR in blood mononuclear cells from 83 nondiabetic subjects showed that rs610604 and rs5029930 minor allele homozygotes have 30 -45% lower levels of A20 mRNA than major allele homozygotes, and heterozygotes have intermediate levels (P ‫؍‬ 0.04 and 0.028, respectively). These findings point to variability in the A20/TNFAIP3 gene as a modulator of CAD risk in type 2 diabetes. This effect is mediated by allelic differences in A20 expression. Diabetes 56: 499 -505, 2007

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