Signal transducer and activator of transcription (STAT) 4 is one of the seven members of the STAT family. STAT4 has a prominent role in mediating interleukin-12–induced T-helper cell type 1 lineage differentiation. T cells are key players in the maintenance of adipose tissue (AT) inflammation. The role of STAT4 in obesity and AT inflammation is unknown. We sought to determine the role of STAT4 in AT inflammation in obesity-induced insulin resistance. We studied STAT4-null mice on the C57Bl6/J background. We have found that STAT4−/−C57Bl6/J mice develop high-fat diet–induced obesity (DIO) similar to wild-type controls, but that they have significantly improved insulin sensitivity and better glucose tolerance. Using flow cytometry and real-time PCR, we show that STAT4−/− mice with DIO produce significantly reduced numbers of inflammatory cytokines and chemokines in adipocytes, have reduced numbers of CD8+ cells, and display increased alternative (M2) macrophage polarization. CD8+ cells, but not CD4+ cells, from STAT4−/− mice displayed reduced in vitro migration. Also, we found that adipocyte inflammation is reduced and insulin signaling is improved in STAT4−/− mice with DIO. We have identified STAT4 as a key contributor to insulin resistance and AT inflammation in DIO. Targeting STAT4 activation could be a novel approach to reducing AT inflammation and insulin resistance in obesity.

ALOX 12 may have a critical role in regulation of inflammation in VAT in obesity and T2D. Selective ALOX 12 inhibitors may constitute a new approach to limit AT inflammation in human obesity.

Adipose tissue (AT) inflammation is an emerging factor contributing to cardiovascular disease. STAT4 is a transcription factor expressed in adipocytes and in immune cells and contributes to AT inflammation and insulin resistance in obesity. The objective of this study was to determine the effect of STAT4 deficiency on visceral and peri-aortic AT inflammation in a model of atherosclerosis without obesity. Stat4-/-Apoe-/- mice and Apoe-/- controls were kept either on chow or western diet for 12 weeks. Visceral and peri-aortic AT were collected and analyzed for immune composition by flow cytometry and for cytokine/chemokine expression by real-time PCR. Stat4-/-Apoe-/- and Apoe-/- mice had similar body weight, plasma glucose and lipids. Western diet significantly increased macrophage, CD4+, CD8+ and NK cells in peri-aortic and visceral fat in Apoe-/- mice. In contrast, in Stat4-/-Apoe-/- mice, western diet failed to increase the percentage of immune cells infiltrating the AT. Also, IL12p40, TNFα, CCL5, CXCL10 and CX3CL1 were significantly reduced in the peri-aortic fat in Stat4-/-Apoe-/- mice. Importantly, Stat4-/-Apoe-/- mice on western diet had significantly reduced plaque burden vs. Apoe-/- controls. In conclusion, STAT4 deletion reduces inflammation in peri-vascular and visceral AT and this may contribute via direct or indirect effects to reduced atheroma formation.

Twist1 is a transcription factor abundantly expressed by adipocytes, immune and vascular cells in adipose tissue (AT) in humans and rodents. Low twist1 expression in human AT is correlated with insulin resistance and obesity. However the role of twist-1 in different cell types component of AT is not clear. The objective of this study was to determine the role of adipocyte (Adp) twist-1 in obesity and insulin resistance. Adp-specific twist1 knock out mice ( AdiponectinCreTwistflox ) (n=6) on the C57Bl6/J background were maintained on 60%kcal fat diet for 12 weeks. Compared to littermate controls (n=6), the female mutant mice, but not the males, showed a 3- and 1.5- fold increase in visceral and subcutaneous adiposity, respectively. Similarly, only the mutant females had significantly impaired glucose tolerance (P<0.05) compared to the littermate controls. Peri-gonadal AT in mutant females showed increased CD11b+F4/80+ and CD3+CD8+ numbers compared to controls, however no differences were found between the male mice. The female mutant mice had more hypertrophied Adp and displayed a 2-4-fold increase in gene expression of IFN γ, TNF α, CD3e and Jak2 compared to controls. Also, expression of the lipogenic enzymes Acaca and Acls4 were significantly reduced by 2.2-fold in the mutant females. Interestingly expression of Nampt (visfatin) gene was significantly increased in mutant females compared to both controls and mutant males. Importantly, twist1 expression in visceral Adp of obese human females (n=15) and males (n=8) at the time of bariatric surgery was significantly higher in females (p<0.01). Also, in a longitudinal cohort at ~1.2 years following surgical weight loss, twist1 expression was significantly increased in visceral AT of males (n=3) (p<0.05) but not in females (n=6) despite a similar reduction in body weight. Collectively the rodent data suggest that twist1 deficiency in Adp increases AT inflammation and exacerbates adiposity and glucose intolerance only in females and identifies visfatin as a metabolically relevant gene potentially regulated by twist1 in females. Also, obese human females may be protected by constitutively higher expression of twist1 in visceral Adp and surgical weight loss leads to increased twist1 expression in males.

Visceral adipose tissue (AT) inflammation is linked to the complications of obesity, including insulin resistance (IR) and type 2 diabetes. Recent data from our lab showed that germline deficiency in STAT4 reduces inflammation and improves IR in obese mice. The objective of this study was to determine the contribution of selective STAT4 deficiency in subsets of hematopoietic cells to IR and AT inflammation. To determine the contribution of hematopoietic lineage, we sublethally irradiated Stat4−/−C57Bl6 mice and reconstituted them with bone marrow cells (BMC) from Stat4+/+C57Bl6 congenic donors. We also established the contribution of selective STAT4 deficiency in CD4+ or CD8+ T cells using adoptive transfer in Rag1−/− mice. All mice received a HFD for 15 weeks (n = 7–12 mice/group). BMC that expressed STAT4 induced increases in glucose intolerance and IR compared to STAT4-deficient cells. Also, AT inflammation was increased and the numbers of CD8+ cells infiltrating AT were higher in mice with STAT4 expressing BMC. Studies in Rag1−/− mice further confirmed the prominent role of CD8+ cells expressing STAT4 in insulin resistance and AT and islet inflammation. Collectively our results show specific and dominant contribution of STAT4 in the hematopoietic compartment to metabolic health and inflammation in diet-induced obesity.