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Adipose tissue macrophages are associated with insulin resistance and are linked to changes in the extracellular matrix. To better characterize adipose macrophages, the extracellular matrix, and adipocyte-macrophage interactions, gene expression from adipose tissue and the stromal vascular fraction was assessed for markers of inflammation and fibrosis, and macrophages from obese and lean subjects were counted and characterized immunohistochemically. Coculture experiments examined the effects of adipocyte-macrophage interaction. Collagen VI gene expression was associated with insulin sensitivity and CD68 (r = -0.56 and 0.60, P < 0.0001) and with other markers of inflammation and fibrosis. Compared with adipose tissue from lean subjects, adipose tissue from obese subjects contained increased areas of fibrosis, which correlated inversely with insulin sensitivity (r = -0.58, P < 0.02) and positively with macrophage number (r = 0.70, P < 0.01). Although macrophages in crownlike structures (CLS) were more abundant in obese adipose tissue, the majority of macrophages were associated with fibrosis and were not organized in CLS. Macrophages in CLS were predominantly M1, but most other macrophages, particularly those in fibrotic areas, were M2 and also expressed CD150, a marker of M2c macrophages. Coculture of THP-1 macrophages with adipocytes promoted the M2 phenotype, with a lower level of IL-1 expression and a higher ratio of IL-10 to IL-12. Transforming growth factor-[beta] (TGF-[beta]) was more abundant in M2 macrophages and was further increased by coculture with adipocytes. Downstream effectors of TGF-[beta], such as plasminogen activator inhibitor-l, collagen VI, and phosphorylated Smad, were increased in macrophages and adipocytes. Thus adipose tissue of insulin-resistant humans demonstrated increased fibrosis, M2 macrophage abundance, and TGF-[beta] activity. alternatively activated macrophages; inflammation; crownlike structures doi: 10.1152/ajpendo.00329.2010.

Adiponectin, made exclusively by adipocytes, is a 30-kDa secretory protein assembled posttranslationally into low-molecular weight, middle-molecular weight, and high-molecular weight homo-oligomers. PPAR[gamma] ligand thiozolidinediones, which are widely used in the treatment of type II diabetes, increase adiponectin levels. PPAR[gamma] also has several putative ligands that include fatty acid derivatives. Overnight treatment of rat adipocytes with pioglitazone, docosahexaenoic acid (DHA), or eicosapentaenoic acid (EPA) triggered a twofold increase in the synthesis and secretion of HMW adiponectin, and this increase was blocked by the addition of PPAR[gamma] inhibitor GW-9662. Inhibition of glycosylation using 2,2'-dipyridyl decreased the synthesis of high-molecular weight adiponectin by pioglitazone, EPA, and DHA, but there was increased secretion of trimeric adiponectin resulting from increased translation. Although pioglitazone, DHA, and EPA increased adiponectin synthesis by more than 60%, there was no increase in total protein synthesis and no corresponding change in adiponectin mRNA expression, indicating the upregulation of translation. We examined the possibility of transacting factors in the cytoplasmic extracts from adipocytes treated with pioglitazone or DHA. In vitro translation of adiponectin mRNA was inhibited by S-100 fraction of control adipocytes and increased by S-100 extracts from adipocytes treated with pioglitazone or DHA. Consistent with this observation, both pioglitazone and DHA treatments increased the association of adiponectin mRNA with the heavier polysome fractions. Together, these data suggest that pioglitazone and the fish oils DHA or EPA are PPAR[gamma] agonists in adipocytes with regard to adiponectin expression, and the predominant mode of adiponectin stimulation is via an increase in translation. peroxisome proliferator-activated receptor-[gamma]; translational regulation; adipocyte biology; ribonucleic acid-binding proteins; fish oils; thiazolidinediones

Context and Objective: Stearoyl-coenzyme A desaturase (SCD1) is the rate-limiting enzyme that converts palmitoyl- and stearoyl-coenzyme A to palmitoleoyl- and oleoyl-cownzyme A, respectively. SCD-deficient mice are protected from obesity, and the ob/ob mouse has high levels of SCD. This study was designed to better characterize SCD1 gene and protein expression in humans with varying insulin sensitivity., Design, Participants, and Setting: In a university hospital clinical research center setting, SCD1 gene expression was measured in sc adipose and vastus lateralis muscle of 86 nondiabetic subjects; 10 wk of pioglitazone (45 mg daily) and metformin (1000 mg twice daily) treatment were assessed in 36 impaired glucose-tolerant subjects. Adipocytes were treated with pioglitazone, and SCD1 expression was attenuated with small interfering RNA (siRNA) to examine other adipocyte genes., Results: There was no significant relationship between adipose or muscle SCD1 mRNA and either body mass index or insulin sensitivity. After pioglitazone (but not metformin) treatment, there was a 2-fold increase in SCD1 mRNA and protein in adipose tissue. Pioglitazone also increased SCD1 in vitro. There were significant positive correlations between SCD1 and peroxisomal proliferator-activated receptor gamma (PPARgamma) as well as other PPARgamma-responsive genes, including lipin-beta, AGPAT2, RBP4, adiponectin receptors, CD68, and MCP1. When SCD1 expression was inhibited with a siRNA, lipin-beta, AGPAT2, and the adiponectin R2 receptor expression were decreased, and adipocyte MCP-1 was increased., Conclusions: SCD1 is closely linked to PPARgamma expression in humans, and is increased by PPARgamma agonists. The change in expression of some downstream PPARgamma targets after SCD1 knockdown suggests that PPARgamma up-regulation of SCD1 leads to increased lipogenesis and potentiation of adiponectin signaling.