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Background:Inflammatory factors derived from adipose tissue have been implicated in mediating insulin resistance in obesity. We sought to identify these using explanted human adipose tissue exposed to innate and adaptive immune stimuli.Methods:Subcutaneous and omental adipose tissue from obese, insulin-resistant donors was cultured in the presence of macrophage and T-cell stimuli, and the conditioned medium tested for its ability to inhibit insulin-stimulated glucose uptake into human Simpson–Golabi–Behmel Syndrome (SGBS) adipocytes. The nature of the inhibitory factor in conditioned medium was characterized physicochemically, inferred by gene microarray analysis and confirmed by antibody neutralization.Results:Conditioned medium from omental adipose tissue exposed to a combination of macrophage- and T-cell stimuli inhibited insulin action and adiponectin secretion in SGBS adipocytes. This effect was associated with a pronounced change in adipocyte morphology, characterized by a decreased number of lipid droplets of increased size. The bioactivity of conditioned medium was abolished by trypsin treatment and had a molecular weight of 46 kDa by gel filtration. SGBS adipocytes exposed to a bioactive medium expressed multiple gene transcripts regulated by interferon-gamma (IFN-γ). Recombinant human IFN-γ recapitulated the effects of the bioactive medium and neutralizing antibody against IFN-γ but not other candidate factors abrogated medium bioactivity.Conclusions:IFN-γ released from inflamed omental adipose tissue may contribute to the metabolic abnormalities seen in human obesity.

Aims:: The association between central obesity and insulin resistance reflects the properties of visceral adipose tissue. Our aim was to gain further insight into this association by analysing the lipid composition of subcutaneous and omental adipose tissue in obese women with and without insulin resistance. Methods:: Subcutaneous and omental adipose tissue and serum were obtained from 29 obese non-diabetic women, 13 of whom were hyperinsulinemic. Histology, lipid and gene profiling were performed. Results:: In omental adipose tissue of obese, insulin-resistant women, adipocyte hypertrophy and macrophage infiltration were accompanied by an increase in GM3ganglioside and its synthesis enzyme ST3GAL5; in addition, phosphatidylethanolamine (PE) lipids were increased and their degradation enzyme, phosphatidylethanolamine methyl transferase (PEMT), decreased. ST3GAL5was expressed predominantly in adipose stromovascular cells and PEMTin adipocytes. Insulin resistance was also associated with an increase in PE lipids in serum. Interpretation:: The relevance of these findings to insulin resistance in humans is supported by published mouse studies, in which adipocyte GM3ganglioside, increased by the inflammatory cytokine tumour necrosis factor-a, impaired insulin action and PEMT was required for adipocyte lipid storage. Thus in visceral adipose tissue of obese humans, an increase in GM3ganglioside secondary to inflammation may contribute to insulin resistance and a decrease in PEMT may be a compensatory response to adipocyte hypertrophy.

Events controlling differentiation to insulin-secreting beta-cells in the pancreas are not well understood, although beta-cells are thought to arise from pluripotent ductal precursor cells. To search for signaling proteins that might be involved in beta-cell maturation, we analyzed protein kinase expression in two developmentally and functionally distinct pancreatic beta-cell lines, RIN-5AH and RIN-A12, by reverse transcriptase polymerase chain reaction. A number of tyrosine and serine/threonine kinases were identified in both lines. One protein kinase, mixed lineage kinase-1 (MLK-1), was expressed at both the RNA and protein levels in RIN-5AH cells, which display an immature beta-cell phenotype, but was not detected in the more mature RIN-A12 cells. Furthermore, levels of MLK-1 mRNA and protein were increased after brief stimulation of RIN-5AH cells with either the differentiation inducer, sodium butyrate, or with serum after serum starvation. These increases in expression were independent of phenotypic markers such as insulin secretion or surface expression of major histocompatibility class I- and A2B5-reactive ganglioside. In addition, increases in MLK-1 expression in the stimulated RIN-5AH cells were accompanied by phosphorylation of MLK-1 on serine but not tyrosine. Antisense oligonucleotides to two distinct regions of MLK-1 caused RIN-5AH cells, but not RIN-A12 cells, to adopt a highly undifferentiated morphology, with a reduction in DNA synthesis and MLK-1 protein levels and elevated glucagon mRNA levels, but with no effect on insulin mRNA. In an immunohistochemical survey of embryonic mouse tissues, we found that temporal expression of MLK-1 was regulated in a tissue-specific manner. In the embryonic pancreas, MLK-1 expression was evident in ductal cells from day 13 to 16 but was not detected in late stage gestation or neonatal pancreas. These data suggest that MLK-1 is regulated in immature pancreatic beta-cells and their ductal precursors at the level of functional maturity and may therefore play a role in beta-cell development.

Disseminated non-tuberculous mycobacterial (NTM) infections typically occur in the context of iatrogenic immunosuppression or inherited genetic mutations. Rarely, cytokine-specific autoantibodies have also been described in patients with disseminated infections. Here, we present two cases of disseminated NTM infection in unrelated healthy adult females associated with autoantibodies to interferon-gamma (IFN-γ).