Peptides 25 (2004) 667–674 Increased hypothalamic melanin concentrating hormone gene expression during energy restriction involves a melanocortin-independent, estrogen-sensitive mechanism Gregory J. Morton a , Paul Mystkowski a , Alvin M. Matsumoto b , Michael W. Schwartz a,∗ a Department of Medicine, Harborview Medical Center, University of Washington, 325 Ninth Avenue, Box 359757, Seattle, WA 98104, USA b VA Puget Sound Health Care System, Geriatric Research, Education and Clinical Center, Seattle, WA 98108, USA Received 13 January 2004; received in revised form 12 February 2004; accepted 20 February 2004 Available online 15 April 2004 Abstract Increased expression of melanin concentrating hormone (MCH), an orexigenic neuropeptide produced by neurons in the lateral hypotha- lamic area (LHA), is implicated in the effect of energy restriction to increase food intake. Since melanocortins inhibit Mch gene expression, this effect of energy restriction to increase Mch signaling may involve reduced hypothalamic melanocortin signaling. Consistent with this hypothesis, we detected increased hypothalamic Mch mRNA levels in agouti (A y ) mice (by 102%; P< 0.05), a model of genetic obesity resulting from impaired melanocortin signaling, compared to wild-type controls. If reduced melanocortin signaling mediates the effect of energy restriction, hypothalamic Mch gene expression in A y mice should not be increased further by energy restriction, since melanocortin signaling is impaired in these animals regardless of nutritional state. We therefore investigated the effects of energy restriction on hy- pothalamic Mch gene expression in both A y mice and in wild-type mice with diet-induced obesity (DIO). Responses in these mice were compared to those induced by administration of 17-estradiol (E2) at a dose previously shown to reduce food intake and Mch expression in rats. In both A y and DIO mice, energy restriction increased hypothalamic Mch mRNA levels (P< 0.05 for each) via a mechanism that was fully blocked by E2. However, E2 did not lower levels of Mch mRNA below basal values in A y mice, whereas it did so in DIO mice. Thus, the effect of energy restriction to increase hypothalamic Mch gene expression involves an E2-sensitive mechanism that is not altered by impaired melanocortin signaling. By comparison, impaired melanocortin signaling increases hypothalamic Mch gene expression via a mechanism that is insensitive to E2. These findings suggest that while both energy restriction and reduced melanocortin signaling stimulate hypothalamic Mch gene expression, they do so via distinct mechanisms. © 2004 Elsevier Inc. All rights reserved. Keywords: Melanin-concentrating hormone; Agouti; Melanocortins; Estrogen; Hypothalamus 1. Introduction For more than 50 years, the lateral hypothalamic area (LHA) has been considered a key brain area for the regu- lation of food intake and body weight [1]. Recent studies identify LHA neurons that contain the orexigenic peptide melanin concentrating hormone (MCH) as being critical for energy homeostasis, since MCH deficiency causes hy- pophagia and reduced body fat stores, reminiscent of that induced by LHA lesions [21], while central injection of MCH stimulates feeding [19]. Moreover, hypothalamic Mch gene expression is upregulated during acute or chronic energy restriction [19]. These findings collectively suggest that in response to weight loss, adaptive increases of MCH ∗ Corresponding author. Tel.: +1-206-341-5288; fax: +1-206-341-5293. E-mail address: mschwart@u.washington.edu (M.W. Schwartz). signaling contribute importantly to the recovery of depleted fuel stores. Among potential mechanisms responsible for adaptive increases of hypothalamic Mch gene expression during weight loss is reduced inhibitory input to MCH neurons from hypothalamic melanocortin neurons. Located in the arcuate nucleus (ARC), melanocortin neurons produce peptides such as alpha-melanocyte stimulating hormone (-MSH) that are derived from the polypeptide precur- sor, pro-opiomelanocortin (POMC), and act on neuronal melanocortin receptors (e.g., Mc4r) to reduce food intake [8]. These POMC neurons are stimulated by leptin [6,20] and by overfeeding [10], while they are inhibited by energy restriction [13]. Because projections from these POMC neurons densely innervate the LHA [4,7], melanocortin signaling is hypothesized to reduce food intake, at least in part, by inhibiting orexigenic MCH neurons. Indeed, central 0196-9781/$ – see front matter © 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.peptides.2004.02.007