Abstract

OBJECTIVE—Protein kinase C (PKC) θ activation is associated with insulin resistance and obesity, but the underlying mechanisms have not been fully elucidated. Impairment of insulin-mediated vasoreactivity in muscle contributes to insulin resistance, but it is unknown whether PKCθ is involved. In this study, we investigated whether PKCθ activation impairs insulin-mediated vasoreactivity and insulin signaling in muscle resistance arteries.

RESEARCH DESIGN AND METHODS—Vasoreactivity of isolated resistance arteries of mouse gracilis muscles to insulin (0.02–20 nmol/l) was studied in a pressure myograph with or without PKCθ activation by palmitic acid (PA) (100 μmol/l).

RESULTS—In the absence of PKCθ activation, insulin did not alter arterial diameter, which was caused by a balance of nitric oxide–dependent vasodilator and endothelin-dependent vasoconstrictor effects. Using three-dimensional microscopy and Western blotting of muscle resistance arteries, we found that PKCθ is abundantly expressed in endothelium of muscle resistance arteries of both mice and humans and is activated by pathophysiological levels of PA, as indicated by phosphorylation at Thr⁵³⁸ in mouse resistance arteries. In the presence of PA, insulin induced vasoconstriction (21 ± 6% at 2 nmol/l insulin), which was abolished by pharmacological or genetic inactivation of PKCθ. Analysis of intracellular signaling in muscle resistance arteries showed that PKCθ activation reduced insulin-mediated Akt phosphorylation (Ser⁴⁷³) and increased extracellular signal–related kinase (ERK) 1/2 phosphorylation. Inhibition of PKCθ restored insulin-mediated vasoreactivity and insulin-mediated activation of Akt and ERK1/2 in the presence of PA.

CONCLUSIONS—PKCθ activation induces insulin-mediated vasoconstriction by inhibition of Akt and stimulation of ERK1/2 in muscle resistance arteries. This provides a new mechanism linking PKCθ activation to insulin resistance.