Comparison of glucose tolerance between wild-type mice and mice with double knockout of neuromedin U and neuromedin S

Vascular endothelial cell-specific overexpression of CNP did not improve liver fibrosis in HFFCD-induced NASH, but did improve renal lesions

Mice with endothelial-cell-specific overexpression of C-type natriuretic peptide (E-CNP Tg mice) were shown to be protected against hepatic fibrosis and inflammation induced by high fat diet (HFD) feeding, with improved insulin sensitivity and attenuated weight gain. A recently developed high-fat, high-fructose, high-cholesterol diet (HFFCD) is considered to be a superior model to HFD, owing to the resemblance to human non-alcoholic steatohepatitis (NASH). In this study, we therefore aimed to reveal whether these previous findings with E-CNP Tg mice on HFD can be observed in a newly developed NASH model.　Patients with NASH have been suggested to be at higher risk of developing chronic kidney disease, so we also assessed the kidney histology of these mice. After 8 months of HFFCD feeding, the livers of E-CNP Tg mice and controls showed progressive fibrosis, which resembled the features of human NASH. However, no significant differences were observed in NAFLD activity scores between E-CNP Tg mice and controls, although there was a tendency for improvement in E-CNP Tg mice. The reduced levels of GCB, a receptor for CNP, may have weakened the action of CNP in the current model. In the kidneys, HFFCD showed glomerular hypertrophy and tubular atrophy in the cortical region, which were suppressed in E-CNP Tg mice. The present study did not prove the therapeutic effect of CNP on NASH in the HFFCD model, but provided evidence of its potential beneficial effects on NASH-associated renal damage.

The neuromedin U system: Pharmacological implications for the treatment of obesity and binge eating behavior

Neuromedin U (NMU) is a bioactive peptide produced in the gut and in the brain, with a role in multiple physiological processes. NMU acts by binding and activating two G protein coupled receptors (GPCR), the NMU receptor 1 (NMU-R1), which is predominantly expressed in the periphery, and the NMU receptor 2 (NMU-R2), mainly expressed in the central nervous system (CNS). In the brain, NMU and NMU-R2 are consistently present in the hypothalamus, commonly recognized as the main "feeding center". Considering its distribution pattern, NMU revealed to be an important neuropeptide involved in the regulation of food intake, with a powerful anorexigenic ability. This has been observed through direct administration of NMU and by studies using genetically modified animals, which revealed an obesity phenotype when the NMU gene is deleted. Thus, the development of NMU analogs or NMU-R2 agonists might represent a promising pharmacological strategy to treat obese individuals. Furthermore, NMU has been demonstrated to influence the non-homeostatic aspect of food intake, playing a potential role in binge eating behavior. This review aims to discuss and summarize the current literature linking the NMU system with obesity and binge eating behavior, focusing on the influence of NMU on food intake and the neuronal mechanisms underlying its anti-obesity properties. Pharmacological strategies to improve the pharmacokinetic profile of NMU will also be reported.

Neuromedin U, a Key Molecule in Metabolic Disorders

Obesity is now a public health concern. The leading cause of obesity is an energy imbalance between ingested and expended calories. The mechanisms of feeding behavior and energy metabolism are regulated by a complex of various kinds of molecules, including anorexigenic and orexigenic neuropeptides. One of these neuropeptides, neuromedin U (NMU), was isolated in the 1980s, and its specific receptors, NMUR1 and NMUR2, were defined in 2000. A series of subsequent studies has revealed many of the physiological roles of the NMU system, including in feeding behavior, energy expenditure, stress responses, circadian rhythmicity, and inflammation. Particularly over the past decades, many reports have indicated that the NMU system plays an essential and direct role in regulating body weight, feeding behavior, energy metabolism, and insulin secretion, which are tightly linked to obesity pathophysiology. Furthermore, another ligand of NMU receptors, NMS (neuromedin S), was identified in 2005. NMS has physiological functions similar to those of NMU. This review summarizes recent observations of the NMU system in relation to the pathophysiology of obesity in both the central nervous systems and the peripheral tissues.