High glucose impairs insulin signaling via activation of PKR pathway in L6 muscle cells

Double stranded RNA (dsRNA) activated protein kinase R (PKR), a ubiquitously expressed serine/threonine kinase is a key inducer of inflammation, insulin resistance and glucose homeostasis in obesity. Recent studies have demonstrated that PKR can respond to metabolic stress in mice as well as in humans. However the underlying molecular mechanism is not fully understood. The aim of the present study was to examine the effect of high glucose on cultured rat L6 muscle cells and to investigate whether inhibition of PKR could prevent any deleterious effects of high glucose in these cells. PKR expression was determined by immunofluorescence and immunoblotting. The expression of different insulin signaling gene markers were measured by RT-PCR. Oxidative stress and apoptosis were determined by flow cytometry. High glucose treated L6 muscle cells developed a significant increase in PKR expression. Impaired insulin signaling as well as reduced insulin stimulated glucose uptake was observed in high glucose treated L6 muscle cells. A significant increase in reactive oxygen species generation and apoptosis formation was also observed in high glucose treated cultured L6 muscle cells. All these effects of high glucose were attenuated by a selective PKR inhibitor imoxin. Our study demonstrates PKR may have an additive role against the deleterious effects of high glucose in diabetes. Prevention of PKR activation, by safer and specific inhibitors is a therapeutic option in metabolic disorders that needs to be explored further.