The role of IL-6R/IL-6 axis in metabolic inflammation remains controversial. We determined the changes in adipose tissue expression of IL-6R and IL-6 in obese, overweight, and lean non-diabetic individuals. Subcutaneous adipose tissue biopsies were collected from 33 obese, 22 overweight, and 10 lean individuals and the expression of IL-6R, IL-6, TNF-α, MCP-1, IP-10, CD11b, CD163, and CD68 was detected by immunohistochemistry; results were also confirmed by real-time RT-PCR and confocal microscopy. The data were compared using unpaired t-test and the dependence between two variables was assessed by Pearson’s correlation test. Obese individuals showed higher IL-6R expression (103.8±4.807) in the adipose tissue as compared with lean/overweight (68.06±4.179) subjects (P<0.0001). The elevated IL-6R expression correlated positively with body mass index (BMI) (r=0.80 P<0.0001) and percent body fat (r=0.69 P=0.003). The increased IL-6R expression in obesity was also confirmed by RT-PCR (Obese: 3.921±0.712 fold; Lean/Overweight: 2.191±0.445 fold; P=0.0453) and confocal microscopy. IL-6 expression was also enhanced in obese adipose tissue (127.0±15.91) as compared with lean/overweight (86.69±5.25) individuals (P=0.03) which correlated positively with BMI (r=0.58 P=0.008). IL-6 mRNA expression was concordantly higher in obese (16.60±2.214 fold) versus lean/overweight (9.376±1.656 fold) individuals (P=0.0108). These changes in the IL-6R/IL-6 expression correlated positively with the adipose tissue expression of CD11b (IL-6R r=0.44 P=0.063; IL-6 r=0.77 P<0.0001), CD163 (IL-6R r=0.45 P=0.045; IL-6 r=0.55 P=0.013), TNF-α (IL-6R r=0.73 P=0.0003; IL-6 r=0.60 P=0.008), MCP-1 (IL-6R r=0.61 P=0.005; IL-6 r=0.63 P=0.004) and IP-10 (IL-6R r=0.41 P=0.08; IL-6 r=0.50 P=0.026). It was, therefore, concluded that obesity was a positive modulator of IL-6R and IL-6 expression in the adipose tissue which might be a contributory mechanism to induce metabolic inflammation.

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Human sialidase (neuraminidase) Neu1 catalyzes lysosomal catabolism of sialylated glycoconjugates. Here we show that during the differentiation of monocytes and the monocytic cell line, THP-1, into macrophages, the majority of Neu1 relocalizes from the lysosomes to the cell surface. In contrast to other cellular sialidases Neu2, Neu3, and Neu4, whose expression either remains unchanged or is down-regulated, Neu1 mRNA, protein and activity are specifically increased during the phorbol 12-myristate 13-acetate-induced differentiation, consistent with a significant induction of the transcriptional activity of the Neu1 gene promoter. The lysosomal carboxypeptidase, cathepsin A, which forms a complex with and activates Neu1 in the lysosome, is sorted to the plasma membrane of the differentiating cells similarly to Neu1. Both proteins are first targeted to the lysosome and then are sorted to the LAMP-2-negative, major histocompatibility complex II-positive vesicles, which later merge with the plasma membrane. Similar trafficking was observed for the internalized fluorescent dextran or horseradish peroxidase initially stored in the lysosomal/endosomal compartment. The suppression of Neu1 expression in the THP-1-derived macrophages by small interfering RNA or with anti-Neu1 antibodies significantly reduced the ability of the cells to engulf bacteria or to produce cytokines. Altogether our data suggest that the upregulation of the Neu1 expression is important for the primary function of macrophages and establish the link between Neu1 and the cellular immune response.

BackgroundExpression profile of the toll like receptors (TLRs) on PBMCs is central to the regulation of proinflammatory markers. An imbalance in the TLRs expression may lead to several types of inflammatory disorders. Furthermore, the dynamic regulation of inflammatory activity and associated impaired production of cytokines by peripheral blood mononuclear cells (PBMCs) in obese individulas remain poorly understood. Therefore, we determined the perturbation in TLRs (TLR2 and TLR4), their adaptor proteins (MyD88, IRAK1 and TRAF6) expression in PBMCs/subcutaneous adipose tissue (AT) as well as inflammatory cytokines changes in obese individuals.MethodsmRNA expression levels of TLR2, TLR4, IL-6, TNF-α and adaptor proteins were determined by RT-PCR. TLR2, TLR4 and adaptor proteins expression in AT was determined by immunohistochemistry.ResultsObese and overweight individuals showed significantly increased expression of TLR2, TLR4 and MyD88 in both PBMCs and AT as compared with lean individuals (P < 0.05). Interestingly, we found a remarkably higher expression of TLRs in obese and overweight individuals with type 2 diabetes (P < 0.05). Increased expression of TLR2, TLR4, MyD88 and IRAK1 correlated with body mass index (BMI) (TLR2: r = 0.91; TLR4: r = 0.88, P <0.0001; MyD88: r = 0.95, P < 0.0001; IRAK1 r = 0.78, P < 0.002). TLRs’ expression was also correlated with fasting blood glucose (FBG) (TLR2: r = 0.61, P < 0.002; TLR4: r = 0.52, P < 0.01) and glycated haemoglobin (HbA1c) ( TLR2: r = 0.44, P <0.03; TLR4: r = 0.48, P < 0.03). Transcript levels of IL-6 and TNF-α were highly elevated in obese subjects compared to lean subjects. There was a strong association of TLRs’ expression in PBMCs with TNF-α (TLR2: r = 0.92; TLR4: r = 0.92; P < 0.0001) and IL-6 (TLR2: r = 0.91, P < 0.0001; TLR4: r = 0.81; P < 0.001). Similarly adaptor proteins were significantly correlated with TNF-α (MyD88: r = 0.9, P < 0.0001; IRAK1: r = 0.86; P < 0.0002) and IL-6 (MyD88: r = 0.91, P < 0.0001; IRAK1: 0.77; P < 0.002).ConclusionsTLRs and adapter proteins were overexpressed in PBMCs from obese subjects, which correlated with increased expression of TNF-α and IL-6. This association may explain a potential pathophysiological link between obesity and inflammation leading to insulin resistance.

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