Palmitate-Induced Interleukin 6 Production Is Mediated by Protein Kinase C and Nuclear-Factor κB Activation and Leads to Glucose Transporter 4 Down-Regulation in Skeletal Muscle Cells

Abstract

The mechanisms by which elevated levels of free fatty acids cause insulin resistance are not well understood. In addition, accumulating evidence suggests a link between inflammation and type 2 diabetes. Here, we report that exposure of C2C12 skeletal muscle cells to 0.5 mm palmitate results in increased mRNA levels (3.5-fold induction; P < 0.05) and secretion (control 375 +/- 57 vs. palmitate 1129 +/- 177 pg/ml; P < 0.001) of the proinflammatory cytokine IL-6. Palmitate increased nuclear factor-kappaB activation and coincubation of the cells with palmitate and the nuclear factor-kappaB inhibitor pyrrolidine dithiocarbamate prevented both IL-6 expression and secretion. Furthermore, incubation of palmitate-treated cells with calphostin C, a strong and specific inhibitor of protein kinase C, and phorbol myristate acetate, that down-regulates protein kinase C in long-term incubations, abolished induction of IL-6 production. Finally, exposure of skeletal muscle cells to palmitate caused a fall in the mRNA levels of glucose transporter 4 and insulin-stimulated glucose uptake, whereas in the presence of anti-IL-6 antibody, which neutralizes the biological activity of mouse IL-6 in cell culture, these reductions were prevented. These findings suggest that IL-6 may mediate several of the prodiabetic effects of palmitate.

Palmitate-Mediated Downregulation of Peroxisome Proliferator–Activated Receptor-γ Coactivator 1α in Skeletal Muscle Cells Involves MEK1/2 and Nuclear Factor-κB Activation

“…These data seem to rule out the involvement of PKC activation in palmitate-mediated PGC-1␣ downregulation in skeletal muscle cells. Finally, since we have recently reported that skeletal muscle cells exposed to palmitate secrete IL-6 into culture media (19), and that this IL may affect cell metabolism, we determined whether IL-6 was involved in palmitate-mediated PGC-1␣ downregulation using an anti-IL-6 antibody. While treatment with palmitate led to a reduction in PGC-1␣ mRNA levels, coincubation with anti-IL-6 antibody did not prevent this change (Fig.…”

“…Measurements of mRNA. Levels of PGC-1␣ and -␤ mRNA were assessed by RT-PCR, as previously described (19). Total RNA was isolated by using the Ultraspec reagent (Biotecx, Houston).…”

Toll-like receptor 2 deficiency improves insulin sensitivity and hepatic insulin signalling in the mouse

“…Particularly, palmitic and stearic acids are known to be major fatty acids acylated in the lipoprotein or lipopeptide to activate TLR2 [31,32]. NEFA possess the capacity to induce stress/inflammatory signals not only in immune cells but also other cell types and tissues [13,14,33]. This phenomenon is of particular importance in conditions of nutrient excess such as obesity and diabetes or after ingestion of a fatty meal.…”

“…NEFAs and triacylglycerols are elevated in obese and diabetic individuals and animals. Previous studies demonstrated that exposure to elevated NEFA causes activation of inflammatory signals and production of cytokines in multiple cell types, and these findings have been correlated with impairments of insulin actions [13,14]. Thus, circulating lipid and associated inflammation appear to be a link between nutrient excess and insulin resistance.…”

Dietary determinants of subclinical inflammation, dyslipidemia and components of the metabolic syndrome in overweight children: a review

“…69 High levels of free fatty acids impair glucose and lipid metabolism 69 and induce the expression of proinflammatory cytokines in adipocytes, but this may not be a generalized effect of all fatty acids. Palmitate, but not laurate or docosahexanoic acid (DHA), induces IL-6 in adipocytes, 70 skeletal muscle cells 71 and endothelial cells. 72 Palmitate, but not other plasma-free fatty acids, correlates in vivo with IL-6 concentrations, independent of body fat mass.…”