Hypothalamic ERK mediates the anorectic and thermogenic sympathetic effects of leptin

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, hind- limb, 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. © 2009 by the American Diabetes Association.