Lipid induced overexpression of NF-κB in skeletal muscle cells is linked to insulin resistance

Lipid induced NF-kappa B activation is known to be associated with insulin resistance and type2 diabetes. Here we show that incubation of L6 skeletal muscle cells with palmitate significantly increased NF-kappa B p65 and NF-kappa B p50 expression along with their phosphorylation. NF-kappa B p65 siRNA inhibited palmitate induced overexpression of NF-kappa B p65 indicating palmitate effect on transcriptional activation. RT-PCR and real time PCR experiments also showed a significant increase in NF-kappa B p65 gene expression due to palmitate. Overexpression of NF-kappa B p65 by palmitate was linked to impairment of insulin activity. Palmitate effect on NF-kappa B gene and protein expression was found to be mediated by phospho-PKC epsilon as calphostin C (an inhibitor of PKC) and epsilon V1 (PKC epsilon translocation inhibitor) significantly reduced NF-kappa B expression. To understand the underlying mechanism. we purified NF-kappa B and pPKC epsilon from palmitate incubated skeletal muscle cells and their interaction in cell free system demonstrated the transfer of phosphate from PKC epsilon to NF-kappa B. This prompted us to transduct pPKC epsilon to the skeletal muscle cells. These cells showed increased amount of pNF-kappa B and NF-kappa B. Excess of NF-kappa B p65 pool thus created in the cells made them insulin resistant. Addition of NF-kappa B p65 siRNA and SN50 inhibited palmitate induced NF-kappa B p65 expression indicating NF-kappa B regulation of its gene expression. Increase of NF-kappa B did not affect the activation of IKK/I kappa B indicating NF-kappa B p65 expression to be a distinct effect of palmitate. Since NF-kappa B p65 is linked to several diseases, including type2 diabetes, this report may be important in understanding the pathogenicity of these diseases. (C) 2008 Elsevier B.V. All rights reserved.