Insulin signaling can be modulated by several isoforms of PKC in peripheral tissues. Here, we assessed whether one specific isoform, PKC-θ, was expressed in critical CNS regions that regulate energy balance and whether it mediated the deleterious effects of diets high in fat, specifically palmitic acid, on hypothalamic insulin activity in rats and mice. Using a combination of in situ hybridization and immunohistochemistry, we found that PKC-θ was expressed in discrete neuronal populations of the arcuate nucleus, specifically the neuropeptide Y/agouti-related protein neurons and the dorsal medial nucleus in the hypothalamus. CNS exposure to palmitic acid via direct infusion or by oral gavage increased the localization of PKC-θ to cell membranes in the hypothalamus, which was associated with impaired hypothalamic insulin and leptin signaling. This finding was specific for palmitic acid, as the monounsaturated fatty acid, oleic acid, neither increased membrane localization of PKC-θ nor induced insulin resistance. Finally, arcuate-specific knockdown of PKC-θ attenuated diet-induced obesity and improved insulin signaling. These results suggest that many of the deleterious effects of high-fat diets, specifically those enriched with palmitic acid, are CNS mediated via PKC-θ activation, resulting in reduced insulin activity.
Stephen C. Benoit ... William L. Holland, Deborah J. Clegg
i.c.v. palmitic acid (but not oleic acid) attenuates insulin-induced suppression of hepatic glucose production.
Rats (6–8/group) received a 3-day i.c.v. infusion of palmitic acid, oleic acid, or control (cont) (PBS), before a carotid-artery insulin infusion under euglycemic clamp conditions. Comparable glucose use rates (~100 mg/dl) were achieved in all groups, beginning 90 minutes after the start of the experiment. All groups had plasma insulin values of approximately 900 pmol/l (data not shown). Carotid insulin infusions reduced hepatic glucose production in control and oleic acid–infused rats but not in rats infused with palmitic acid (data are mean ± SEM; ***
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