The adipose tissue-derived hormone adiponectin improves insulin sensitivity and its circulating levels are decreased in obesityinduced insulin resistance. Here, we report the generation of a mouse line with a genomic disruption of the adiponectin locus. We aimed to identify whether these mice develop insulin resistance and which are the primary target tissues affected in this model. Using euglycemic/insulin clamp studies, we demonstrate that these mice display severe hepatic but not peripheral insulin resistance. Furthermore, we wanted to test whether the lack of adiponectin magnifies the impairments of glucose homeostasis in the context of a dietary challenge. When exposed to high fat diet, adiponectin null mice rapidly develop glucose intolerance. Specific PPAR␥ agonists such as thiazolidinediones (TZDs) improve insulin sensitivity by mechanisms largely unknown. Circulating adiponectin levels are significantly up-regulated in vivo upon activation of PPAR␥. Both TZDs and adiponectin have been shown to activate AMP-activated protein kinase (AMPK) in the same target tissues. We wanted to address whether the ability of TZDs to improve glucose tolerance is dependent on adiponectin and whether this improvement involved AMPK activation. We demonstrate that the ability of PPAR␥ agonists to improve glucose tolerance in ob/ob mice lacking adiponectin is diminished. Adiponectin is required for the activation of AMPK upon TZD administration in both liver and muscle. In summary, adiponectin is an important contributor to PPAR␥-mediated improvements in glucose tolerance through mechanisms that involve the activation of the AMPK pathway.Adiponectin/ACRP30 (adipocyte complement-related protein of 30 kDa), an adipocyte-specific secretory protein, has been shown to modulate insulin sensitivity; however, the mechanism(s) by which it acts are not fully understood (1). A number of clinical studies revealed a strong link between whole body insulin sensitivity and circulating adiponectin levels (2). Furthermore, circulating adiponectin is negatively correlated with the body mass index (3). Weight reduction leads to a significant increase in adiponectin plasma levels slightly preceding improvements in insulin sensitivity, thus suggesting a causative role of adiponectin in enhancing insulin sensitivity (4). Adiponectin null mouse models were described previously, however, with somewhat varying outcomes regarding their metabolic phenotype. Kubota et al. (5) noted mild insulin resistance under basal conditions in heterozygotes (60% reduction in adiponectin serum levels) and more severe insulin resistance in adiponectin null animals. This report differed from adiponectin null mice described by Maeda et al. (6) that showed nearly normal insulin sensitivity when fed on a standard laboratory diet but developed severe insulin resistance in as few as 2 weeks on a high fat/high sucrose diet. However, a third independent report of adiponectin null mice by Ma et al. (7) described an unexpected increase in fatty acid oxidation in skeletal muscle...

Melanin-concentrating hormone (MCH) is a cyclic 19-aa hypothalamic neuropeptide derived from a larger prohormone precursor of MCH (Pmch), which also encodes neuropeptide EI (NEI) and neuropeptide GE (NGE). Pmch-deficient (PmchM elanin-concentrating hormone (MCH) is expressed in the central nervous system predominantly in neurons in the lateral hypothalamus and zona incerta, which project broadly throughout the brain (1, 2). MCH mRNA levels are increased in response to fasting and are elevated in leptin-deficient ob͞ob mice relative to control mice (3), suggesting that leptin negatively regulates MCH. Rodent pharmacology further supports a role for MCH in the control of energy homeostasis, as centrally administered MCH stimulates food intake in rats (3, 4).In addition to MCH, prohormone precursor of MCH (Pmch) also encodes neuropeptide EI (NEI) and neuropeptide GE (NGE) (5) and may potentially give rise to an alternative splice variant termed MCH-gene-overprinted-polypeptide (MGOP; ref. 6), as well as encode a portion of the recently identified antisense-RNA-overlapping-MCH (AROM; ref. 7). Two recently described mouse genetic models further implicate MCH in the regulation of energy homeostasis. Pmch Ϫ/Ϫ mice are lean, hypophagic, and have an increased metabolic rate (8). In contrast, transgenic mice overexpressing Pmch develop mild obesity, are hyperphagic, and become insulin-resistant (9). As both these models represent genetic manipulations of Pmch, one must consider the possibility that in addition to alterations in MCH, changes in the levels of NEI and NGE, as well as potentially MGOP and AROM, may also contribute to the phenotypes of these models.The MCH 1 receptor (MCH1R) was initially identified as an orphan G protein-coupled receptor that bound MCH with high affinity (10). Subsequently, a second high-affinity MCH receptor (MCH2R) with moderate amino acid identity to MCH1R was identified in humans (11-15). Both receptors are highly selective for MCH and are not activated by NEI, neuropeptide GE, or MCH-gene-overprinted-polypeptide (13, 16, 17); however, in vivo validation for these receptors is still lacking. We generated Mch1r Ϫ/Ϫ mice to evaluate the physiological function of MCH1R, and to determine whether it is involved in mediating the effects of MCH on energy homeostasis. Additionally, we hoped to gain insight into what aspects of the Pmch Ϫ/Ϫ and Pmch overexpressing phenotypes are likely attributed to MCH. Materials and MethodsAnimal Care and Maintenance. All animal protocols used in these studies were approved by the Merck Research Laboratories Institutional Animal Care and Use Committee in Rahway, NJ. We housed mice in microisolator cages (Lab Products, Maywood, NJ) in a barrier facility with an air shower entrance or in a specific pathogen-free facility. Mice were maintained on either regular chow [Teklad (Madison, WI) 7012: 14.8% kcal from fat; Harlan Teklad], a moderate-fat diet (D12266B: 32% kcal from fat; Research Diets, New Brunswick, NJ), or a high-fat diet (Teklad 97070: 60% kcal from fat)...

In this study we have characterized the anti-inflammatory profile of a selective melanocortin type 3 receptor (MC3-R) ligand [D-Trp8]-gamma-MSH, validating in vitro results with analyses in mice deficient for this receptor subtype. In wild-type (WT) macrophages, [D-Trp8]-gamma-MSH activated MC3-R (as tested by accumulation of cyclic AMP) and inhibited (approximately 50%) the release of interleukin (IL)-1 and the chemokine KC (CXCL1), but was ineffective in cells taken from MC3-R null mice. In vivo, administration of 3-30 microg [D-Trp8]-gamma-MSH significantly inhibited leukocyte influx and cytokine production in a model of crystal-induced peritonitis, and these effects were absent in MC3-R null mice or blocked by coadministration of an MC3-R antagonist. Finally, in a model of gouty arthritis, direct injection of urate crystals into the rat joint provoked a marked inflammatory reaction that was significantly inhibited (approximately 70%) by systemic or local administration of [D-Trp8]-gamma-MSH. In conclusion, using an integrated transgenic and pharmacological approach, we provide strong proof of concept for the development of selective MC3-R agonists as novel anti-inflammatory therapeutics.

Background-The melanocortin (MC) system is composed of peptides that are cleaved from the polypeptide precursor proopiomelanocortin. A growing body of literature suggests that the MC system modulates neurobiological responses to drugs of abuse. Because ethanol has direct effects on central proopiomelanocortin activity, it is possible that MC neuropeptides participate in the control of voluntary ethanol consumption. Here we assessed the possibility that MC receptor (MCR) agonists modulate ethanol intake via the MC3 receptor (MC3R) and/or the MC4 receptor (MC4R) and whether the MCR antagonist AgRP-(83-132) controls ethanol consumption.