We recently reported that genetic deletion of
myeloperoxidase (MPO) alleviates
obesity-related
insulin resistance in mice in vivo. How MPO impairs
insulin sensitivity in adipocytes is poorly characterized. As
hypochlorous acid (HOCl) is a principal
oxidant product generated by MPO, we evaluated the effects of HOCl on
insulin signaling in adipocytes differentiated from 3T3-L1 cells. Exposure of 3T3-L1 adipocytes to exogenous HOCl (200 μmol/l) attenuated
insulin-stimulated
2-deoxyglucose uptake, GLUT4 translocation, and
insulin signals, including
tyrosine phosphorylation of
insulin receptor substrate 1 (IRS1) and phosphorylation of Akt. Furthermore, treatment with HOCl induced phosphorylation of IRS1 at
serine 307, inhibitor κB
kinase (IKK), c-Jun NH2-terminal
kinase (JNK), and phosphorylation of PKCθ (PKCθ). In addition, genetic and pharmacological inhibition of IKK and JNK abolished
serine phosphorylation of IRS1 and impairment of
insulin signaling by HOCl. Furthermore, knockdown of PKCθ using
siRNA transfection suppressed phosphorylation of IKK and JNK and consequently attenuated the HOCl-impaired
insulin signaling pathway. Moreover, activation of PKCθ by
peroxynitrite was accompanied by increased phosphorylation of IKK, JNK, and IRS1-serine 307. In contrast, ONOO(-) inhibitors abolished HOCl-induced phosphorylation of PKCθ, IKK, JNK, and IRS1-serine 307, as well as
insulin resistance. Finally, high-fat diet (HFD)-induced
insulin resistance was associated with enhanced phosphorylation of PKCθ, IKK, JNK, and IRS1 at
serine 307 in white adipose tissues from WT mice, all of which were not found in Mpo knockout mice fed HFDs. We conclude that HOCl impairs
insulin signaling pathway by increasing ONOO(-) mediated phosphorylation of PKCθ, resulting in phosphorylation of IKK/JNK and consequent
serine phosphorylation of IRS1 in adipocytes.