To examine the role of adipose-resident macrophages in insulin resistance, we examined the gene expression of CD68, a macrophage marker, along with macrophage chemoattractant protein-1 (MCP-1) in human subcutaneous adipose tissue using real-time RT-PCR. Both CD68 and MCP-1 mRNAs were expressed in human adipose tissue, primarily in the stromal vascular fraction. When measured in the adipose tissue from subjects with normal glucose tolerance, covering a wide range of BMI (21-51 kg/m 2 ) and insulin sensitivity (S I ) (0.6 -8.0 ؋ 10 ؊4 min ؊1 ⅐ U -1 ⅐ ml -1 ), CD68 mRNA abundance, which correlated with the number of CD68-positive cells by immunohistochemistry, tended to increase with BMI but was not statistically significant. However, there was a significant inverse relation between CD68 mRNA and S I (r ‫؍‬ ؊0.55, P ‫؍‬ 0.02). In addition, there was a strong positive relationship among adipose tissue CD68 mRNA, tumor necrosis factor-␣ (TNF-␣) secretion in vitro (r ‫؍‬ 0.79, P < 0.005), and plasma interleukin-6 (r ‫؍‬ 0.67, P < 0.005). To determine whether improving S I in subjects with impaired glucose tolerance (IGT) was associated with decreased CD68 expression, IGT subjects were treated for 10 weeks with pioglitazone or metformin. Pioglitazone increased S I by 60% and in the same subjects reduced both CD68 and MCP-1 mRNAs by >50%.

We describe the cloning from a rat islet somatostatin‐producing cell line of a 1.4 kb cDNA encoding a new homeoprotein, IDX‐1 (islet/duodenum homeobox‐1), with close sequence similarity to the Drosophila melanogaster homeobox protein Antennapedia (Antp) and the Xenopus laevis endoderm‐specific homeoprotein XlHbox8. Analyses of IDX‐1 mRNA and protein in rat tissues show that IDX‐1 is expressed in pancreatic islets and ducts and in the duodenum. In electrophoretic mobility shift assays IDX‐1 binds to three sites in the 5′ flanking region of the rat somatostatin gene. In co‐transfection experiments IDX‐1 transactivates reporter constructs containing somatostatin promoter sequences, and mutation of the IDX‐1 binding sites attenuates transactivation. Reverse transcription‐polymerase chain reaction of islet RNA using degenerate amplimers for mRNAs encoding homeoproteins indicates that IDX‐1 is the most abundant of 12 different Antp‐like homeodomain mRNAs expressed in adult rat islets. The pattern of expression, relative abundance and transcriptional regulatory activity suggests that IDX‐1 may be involved in the regulation of islet hormone genes and in cellular differentiation in the endocrine pancreas and the duodenum.

Obesity is characterized by adipose tissue expansion as well as macrophage infiltration of adipose tissue. This results in an increase in circulating inflammatory cytokines and nonesterified fatty acids, factors that cause skeletal muscle insulin resistance. Whether obesity also results in skeletal muscle inflammation is not known. In this study, we quantified macrophages immunohistochemically in vastus lateralis biopsies from eight obese and eight lean subjects. Our study demonstrates that macrophages infiltrate skeletal muscle in obesity, and we developed an in vitro system to study this mechanistically. Myoblasts were isolated from vastus lateralis biopsies and differentiated in culture. Coculture of differentiated human myotubes with macrophages in the presence of palmitic acid, to mimic an obese environment, revealed that macrophages in the presence of palmitic acid synergistically augment cytokine and chemokine expression in myotubes, decrease IkappaB-alpha protein expression, increase phosphorylated JNK, decrease phosphorylated Akt, and increase markers of muscle atrophy. These results suggest that macrophages alter the inflammatory state of muscle cells in an obese milieu, inhibiting insulin signaling. Thus in obesity both adipose tissue and skeletal muscle inflammation may contribute to insulin resistance.

The adipose tissue from obese/insulin-resistant subjects has fewer capillaries and more large vessels as compared with lean subjects. The ECM of adipose tissue may play an important role in regulating the expandability as well as angiogenesis of adipose tissue.

No abstract