Atypical protein kinase C activity in the hypothalamus is required for lipopolysaccharide-mediated sickness responses

By activating the Toll-like receptor 4-nuclear factor-kappaB signal transduction pathway, the bacterial endotoxin lipopolysaccharide (LPS) induces anorexia, weight loss, fever, and other components of the sickness response. By comparison, the hormones leptin and insulin cause anorexia without sickness via a central mechanism involving the phosphatidylinositol-3 kinase signaling pathway. In the current study, we investigated whether a common Toll-like receptor 4 and phosphatidylinositol-3 kinase signaling intermediate, atypical protein kinase Czeta/lambda (aPKC), contributes to changes of energy balance induced by these stimuli. Immunohistochemistry analysis revealed that aPKC is expressed in the arcuate and paraventricular nuclei of the hypothalamus, key sites of leptin, insulin, and LPS action. Although administration of LPS, insulin, and leptin each acutely increased hypothalamic aPKC activity at doses that also reduce food intake, LPS treatment caused over 10-fold greater activation of hypothalamic a PKC signaling than that induced by leptin or insulin. Intracerebroventricular pretreatment with an aPKC inhibitor blocked anorexia induced by LPS but not insulin or leptin. Similarly, LPS-induced hypothalamic inflammation (as judged by induction of proinflammatory cytokine gene expression) and neuronal activation in the paraventricular nucleus (as judged by c-fos induction) were reduced by central aPKC inhibition. Although intracerebroventricular aPKC inhibitor administration also abolished LPS-induced fever, it had no effect on sickness-related hypoactivity or weight loss. We conclude that although hypothalamic aPKC signaling is not required for food intake inhibition by insulin or leptin, it plays a key role in inflammatory anorexia and fever induced by LPS.