Hypothalamic ERK Mediates the Anorectic and Thermogenic Sympathetic Effects of Leptin

Hypothalamic ERK Mediates the Anorectic and Thermogenic Sympathetic Effects of Leptin Kamal Rahmouni 1 2 , Curt D. Sigmund 1 2 , William G. Haynes 2 and Allyn L. Mark 1 2 1 Center on Functional Genomics of Hypertension, Department of Internal Medicine, University of Iowa, Iowa City, Iowa 2 Cardiovascular Research Center, Department of Internal Medicine, University of Iowa, Iowa City, Iowa Corresponding author: Kamal Rahmouni, kamal-rahmouni{at}uiowa.edu Abstract OBJECTIVE— Leptin is an adipocyte hormone that plays a major role in energy balance. Leptin receptors in the hypothalamus are known to signal via distinct mechanisms, including signal transducer and activator of transcription-3 (STAT3) and phosphoinositol-3 kinase (PI 3-kinase). Here, we tested the hypothesis that extracellular signal–regulated kinase (ERK) is mediating leptin action in the hypothalamus. RESEARCH DESIGN AND METHODS— Biochemical, pharmacological, and physiological approaches were combined to characterize leptin activation of ERK in the hypothalamus in rats. RESULTS— Leptin activates ERK1/2 in a receptor-mediated manner that involves JAK2. Leptin-induced ERK1/2 activation was restricted to the hypothalamic arcuate nucleus. Pharmacological blockade of hypothalamic ERK1/2 reverses the anorectic and weight-reducing effects of leptin. The pharmacological antagonists of ERK1/2 did not attenuate leptin-induced activation of STAT3 or PI 3-kinase. Blockade of ERK1/2 abolishes leptin-induced increases in sympathetic nerve traffic to thermogenic brown adipose tissue (BAT) but does not alter the stimulatory effects of leptin on sympathetic nerve activity to kidney, hindlimb, or adrenal gland. In contrast, blockade of PI 3-kinase prevents leptin-induced sympathetic activation to kidney but not to BAT, hindlimb, or adrenal gland. CONCLUSIONS— Our findings indicate that hypothalamic ERK plays a key role in the control of food intake, body weight, and thermogenic sympathetic outflow by leptin but does not participate in the cardiovascular and renal sympathetic actions of leptin. Footnotes Published ahead of print at http://diabetes.diabetesjournals.org on 9 December 2008. Readers may use this article as long as the work is properly cited, the use is educational and not for profit, and the work is not altered. See http://creativecommons.org/licenses/by-nc-nd/3.0/ for details. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be