Adipose tissue macrophage (ATM)-driven inflammation plays a key role in insulin resistance; however, factors activating ATMs are poorly understood. Using a proteomics approach, we show that markers of classical activation are absent on ATMs from obese humans, but readily detectable on airway macrophages of patients with cystic fibrosis, a disease of chronic bacterial infection. Moreover, treating macrophages with glucose, insulin, and palmitate – conditions characteristic of the metabolic syndrome – produces a ‘metabolically-activated’ phenotype distinct from classical activation. Markers of metabolic activation are expressed by pro-inflammatory ATMs in obese humans/mice and are positively correlated with adiposity. Metabolic activation is driven by independent pro- and anti-inflammatory pathways, which regulate balance between cytokine production and lipid metabolism. We identify PPARγ and p62/SQSTM1 as two key proteins that promote lipid metabolism and limit inflammation in metabolically-activated macrophages. Collectively, our data provide important mechanistic insights into pathways that drive the metabolic disease-specific phenotype of macrophages.

QI, LU, HAIQING SHEN, ILONA LARSON, ERNST J. SCHAEFER, ANDREW S. GREENBERG, DAVID A. TREGOUET, DOLORES CORELLA, AND JOSE M. ORDOVAS. Gender-specific association of a perilipin gene haplotype with obesity risk in a white population. Obes Res. 2004;12:1758 -1765. Objective: Perilipin is a class of protein-coating lipid droplets in adipocytes and steroidogenic cells. Our purpose was to examine the association between common single-nucleotide polymorphisms (SNPs) at the perilipin (PLIN) locus and obesity, as well as related phenotypes, in unrelated American adults. Research Methods and Procedures: Four PLIN SNPs (PLIN 6209TϾC, 11482GϾA, 13041AϾG, and 14995AϾT) were typed in 734 white subjects (373 men and 361 women) attending a residential lifestyle intervention program. The baseline anthropometric and biochemical measures were used. Obesity was defined as BMI Ն 30 kg/m 2 . Results: Multivariate analysis demonstrated that, in women, two of the SNPs (13041AϾG, and 14995AϾT) were significantly associated with percentage body fat (p ϭ 0.016 for 13041AϾG and p ϭ 0.010 for 14995AϾT) and waist circumference (p ϭ 0.020 for 13041AϾG and p ϭ 0.045 for 14995AϾT). Moreover, haplotype analysis using these two SNPs indicated that haplotypes A/T and G/T were both associated with significantly increased obesity risk (odds ratio ϭ 1.76, 95% confidence interval 1.07 to 2.90 for haplotype A/T, and odds ratio ϭ 1.73, 95% confidence interval 1.06 to 2.82 for haplotype G/T) when compared with haplotype A/A. No significant associations between PLIN variations and obesity were found in men. Discussion: Our data support the hypothesis that the PLIN locus may be a significant genetic determinant for obesity risk in whites and that women are more sensitive to the genetic effects of perilipin than men.

Macrophage metalloelastase, a matrix metallopeptidase (MMP12) predominantly expressed by mature tissue macrophages, is implicated in pathological processes. However, physiological functions for MMP12 have not been described. Because mRNA levels for the enzyme increase markedly in adipose tissue of obese mice, we investigated the role of MMP12 in adipose tissue expansion and insulin resistance. In humans, MMP12 expression correlated positively and significantly with insulin resistance, TNF-α expression, and the number of CD14(+)CD206(+) macrophages in adipose tissue. MMP12 was the most abundant matrix metallopeptidase detected by proteomic analysis of conditioned medium of M2 macrophages and dendritic cells. In contrast, it was detected only at low levels in bone marrow derived macrophages and M1 macrophages. When mice received a high-fat diet, adipose tissue mass increased and CD11b(+)F4/80(+)CD11c(-) macrophages accumulated to a greater extent in MMP12-deficient (Mmp12(-/-)) mice than in wild-type mice (Mmp12(+/+)). Despite being markedly more obese, fat-fed Mmp12(-/-) mice were more insulin sensitive than fat-fed Mmp12(+/+) mice. Expression of inducible nitric oxide synthase (Nos2) by Mmp12(-/-) macrophages was significantly impaired both in vivo and in vitro, suggesting that MMP12 might mediate nitric oxide production during inflammation. We propose that MMP12 acts as a double-edged sword by promoting insulin resistance while combatting adipose tissue expansion.

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Context The mechanisms mediating the short- and long-term improvements in glucose homeostasis following bariatric/metabolic surgery remain incompletely understood. Objective To investigate whether a reduction in adipose tissue inflammation plays a role in the metabolic improvements seen after bariatric/metabolic surgery, both in the short-term and longer-term. Design Fasting blood and subcutaneous abdominal adipose tissue were obtained before (n=14), at one month (n=9), and 6–12 months (n=14) after bariatric/metabolic surgery from individuals with obesity who were not on insulin or anti-diabetes medication. Adipose tissue inflammation was assessed by a combination of whole-tissue gene expression and flow cytometry-based quantification of tissue leukocytes. Results One month after surgery, body weight was reduced by 13.5±4.4 kg (p<0.001), with improvements in glucose tolerance reflected by a decrease in area-under-the-curve (AUC) glucose in 3-h oral glucose tolerance tests (−105±98 mmol/L*min; p=0.009) and enhanced pancreatic β-cell function (insulinogenic index: +0.8±0.9 pmol/mmol; p=0.032), but no change in estimated insulin sensitivity (Matsuda insulin sensitivity index [ISI]; p=0.720). Furthermore, although biomarkers of systemic inflammation and pro-inflammatory gene expression in adipose tissue remained unchanged, the number of neutrophils increased in adipose tissue 15–20 fold (p<0.001), with less substantial increases in other leukocyte populations. By the 6–12 month follow-up visit, body weight was reduced by 34.8±10.8 kg (p<0.001) relative to baseline, and glucose tolerance was further improved (AUC glucose −276±229; p<0.001) along with estimated insulin sensitivity (Matsuda ISI: +4.6±3.2; p<0.001). In addition, improvements in systemic inflammation were reflected by reductions in circulating C-reactive protein (CRP; −2.0±5.3 mg/dL; p=0.002), and increased serum adiponectin (+1,358±1,406 pg/mL; p=0.003). However, leukocyte infiltration of adipose tissue remained elevated relative to baseline, with pro-inflammatory cytokine mRNA expression unchanged, while adiponectin mRNA expression trended downward (p=0.069). Conclusion Both the short- and longer-term metabolic improvements following bariatric/metabolic surgery occur without significant reductions in measures of adipose tissue inflammation, as assessed by measuring the expression of genes encoding key mediators of inflammation and by flow cytometric immunophenotyping and quantification of adipose tissue leukocytes.

Adipose tissue inflammation is a major mechanistic link between obesity and chronic disease. To isolate and characterize specific leukocyte populations, e.g. by flow cytometry, tissue needs to be processed to digest the extracellular matrix. We have systematically compared the impact of different commonly used collagenase preparations, digestion times, and normalization strategies on the reproducibility of flow cytometric phenotyping of adipose tissue leukocyte populations. Subcutaneous adipose tissue was obtained from 11 anonymous donors undergoing elective procedures at a plastic surgery clinic in Seattle, WA. We found that collagenase alone consistently produced better cell yields (p=0.007) than when combined with additional proteases such as the commercially available liberases. Moreover, liberase significantly degraded the cell surface expression of CD4 (p<0.001) on T cells and to a lesser extent CD16 (p=0.058) on neutrophils. Extension of the digestion interval from 30 to 120 min did not significantly impact cell viability (p=0.319) or yield (p=0.247). Normalization by either ‘live-gate’, or percentage of CD45pos leukocytes exhibited the lowest coefficient of variation for tissue digests between 60 and 75 min, compared to normalization per gram of tissue, which consistently exhibited the greatest variability. Our data suggest that digestion of adipose tissue using pure collagenase for 60 to 75 min provides the best cell yield and viability, with minimal degradation of cell surface markers used to identify immune cell subpopulations, and best reproducibility independent of the normalization strategy.

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Background: Lipoprotein lipase (LPL) is the rate-limiting enzyme in the hydrolysis of core triglycerides in chylomicrons and VLDL. Methods: We investigated the association between the HindIII polymorphism of the LPL gene and fasting glucose, lipid, and lipoprotein concentrations in 683 Caucasians. We first stabilized the study subjects, using an 8-day diet and exercise intervention program before obtaining blood samples. The use of this standardization period reduced the variance of all glucose and lipid concentrations. Results: In our study, the HindIII allele frequencies for females and males were 0.29 and 0.34 for H− and 0.71 and 0.66 for H+, respectively. We found in females, but not in males, a significant association between the HindIII genotype and total cholesterol (P = 0.007) and LDL-cholesterol (P = 0.018), with females homozygous for the rare H− allele having the lowest, heterozygotes (H−/+) having intermediate, and women homozygous for the common H+ allele having the highest of each of these lipid traits. With regard to triglycerides, HDL-cholesterol, and glucose, no significant effect of the HindIII genotype was noted in either gender. Conclusions: These results suggest that in a gender-specific manner, the rare LPLHindIII H− allele has a cholesterol-lowering and, therefore, potentially cardioprotective effect compared with the common H+ allele.