Nobuhiro Wada

Neuronal circuits involving neuropeptide Y in hypothalamic arcuate nucleus-mediated feeding regulation

Neuropeptide Y (NPY) is a 36-amino-acid neuropeptide that was first discovered in porcine brain extracts and later in the porcine intestine. It is widely distributed in both the central and peripheral nervous systems and exerts a powerful orexigenic effect. NPY-producing neuronal cell bodies are abundantly localized in the medial arcuate nucleus of the hypothalamus, this being a brain center that integrates signals for energy homeostasis. Accumulated evidence shows that hypothalamic neuropeptides such as ghrelin, orexin, melanin-concentrating hormone (MCH), galanin-like peptide (GALP) and proopiomelanocortin (POMC) are involved in the regulation of feeding behavior and energy homeostasis via neuronal circuits in the hypothalamus. NPY also forms part of the feeding-regulating neuronal circuitry in conjunction with other feeding-regulating peptide-containing neurons within the hypothalamus. We summarize here current knowledge of the neuronal interactions between NPY and the different types of feeding-regulating peptide-containing neurons in the hypothalamus based on evidence at the immunohistochemicl level and with calcium imaging techniques.

Leptin and its receptors

Leptin is mainly produced in the white adipose tissue before being secreted into the blood and transported across the blood-brain barrier. Leptin binds to a specific receptor (LepR) that has numerous subtypes (LepRa, LepRb, LepRc, LepRd, LepRe, and LepRf). LepRb, in particular, is expressed in several brain nuclei, including the arcuate nucleus, the paraventricular nucleus, and the dorsomedial, lateral and ventromedial regions of the hypothalamus. LepRb is also co-expressed with several neuropeptides, including proopiomelanocortin, neuropeptide Y, galanin, galanin-like peptide, gonadotropin-releasing hormone, tyrosine hydroxylase and neuropeptide W. Functionally, LepRb induces activation of the JAK2/ERK, /STAT3, /STAT5 and IRS/PI3 kinase signaling cascades, which are important for the regulation of energy homeostasis and appetite in mammals. In this review, we discuss the structure, genetics and distribution of the leptin receptors, and their role in cell signaling mechanisms.

Pleiotropic and retinoprotective functions of PACAP.

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a 27- or 38-amino acid neuropeptide, which belongs to the vasoactive intestinal polypeptide/glucagon/secretin family. PACAP and its three receptor subtypes are expressed in neural tissues of the eye, including the retina, cornea and lacrimal gland, and PACAP is known to exert pleiotropic effects throughout the central nervous system. This review provides an overview of current knowledge regarding the cell protective effects, mechanisms of action and therapeutic potential of PACAP in response to several types of eye injury.

Activation of SF1 Neurons in the Ventromedial Hypothalamus by DREADD Technology Increases Insulin Sensitivity in Peripheral Tissues

The ventromedial hypothalamus (VMH) regulates glucose and energy metabolism in mammals. Optogenetic stimulation of VMH neurons that express steroidogenic factor 1 (SF1) induces hyperglycemia. However, leptin acting via the VMH stimulates whole-body glucose utilization and insulin sensitivity in some peripheral tissues, and this effect of leptin appears to be mediated by SF1 neurons. We examined the effects of activation of SF1 neurons with DREADD (designer receptors exclusively activated by designer drugs) technology. Activation of SF1 neurons by an intraperitoneal injection of clozapine-N-oxide (CNO), a specific hM3Dq ligand, reduced food intake and increased energy expenditure in mice expressing hM3Dq in SF1 neurons. It also increased whole-body glucose utilization and glucose uptake in red-type skeletal muscle, heart, and interscapular brown adipose tissue, as well as glucose production and glycogen phosphorylase a activity in the liver, thereby maintaining blood glucose levels. During hyperinsulinemic-euglycemic clamp, such activation of SF1 neurons increased insulin-induced glucose uptake in the same peripheral tissues and tended to enhance insulin-induced suppression of glucose production by suppressing gluconeogenic gene expression and glycogen phosphorylase a activity in the liver. DREADD technology is thus an important tool for studies of the role of the brain in the regulation of insulin sensitivity in peripheral tissues.

Anti-obesity effect of intranasal administration of galanin-like peptide (GALP) in obese mice

Galanin-like peptide (GALP) has an anti-obesity effect in rats and mice. It has been reported that the uptake of GALP by the brain is higher after intranasal administration than with intravenous injection. This study therefore aimed to clarify the effect of intranasal administration of GALP on the feeding behavior of lean and obese mice. Autoradiography revealed the presence of 125I-GALP in the olfactory bulb and the brain microcirculation. The body weights of ob/ob mice gradually increased during vehicle treatment, but remained unchanged in response to repeated intranasal administration of GALP, with both ob/ob and diet-induced obese mice displaying significantly decreased food intake, water intake and locomotor activity when treated with GALP. These results suggest that intranasal administration is an effective route whereby GALP can exert its effect as an anti-obesity drug.

The relationship between aquaglyceroporin expression and development of fatty liver in diet-induced obesity and ob/ob mice

Aquaporin (AQP) 7 and AQP9 are subcategorised as aquaglyceroporins which transport glycerin in addition to water. These AQPs may play a role in the homeostasis of energy metabolism. We examined the effect of AQP7, AQP9, and lipid metabolism-related gene expression in obese mice. In diet-induced obese (DIO) mice, excess lipid accumulated in the liver, which was hyperleptinemic and hyperinsulinemic. Hepatic AQP9 gene expression was significantly increased in both DIO and ob/ob mice compared to controls. The mRNA expression levels of fatty acid and triglyceride synthesis-related genes and fatty acid β oxidation-related genes in the liver were also higher in both mouse models, suggesting that triglyceride synthesis in this organ is promoted as a result of glycerol release from adipocytes. Adipose AQP7 and AQP9 gene expressions were increased in DIO mice, but there was no difference in ob/ob mice compared to wild-type mice. In summary, adipose AQP7 and AQP9 gene expressions are increased by diet-induced obesity, indicating that this is one of the mechanisms by which lipid accumulates in response to a high fat diet, not the genetic mutation of ob/ob mice. Hepatic AQP9 gene expression was increased in both obesity model mice. AQP7 and AQP9 therefore have the potential of defining molecules for the characterisation of obesity or fatty liver and may be a target molecules for the treatment of those disease.

Autonomic nervous system-mediated effects of galanin-like peptide on lipid metabolism in liver and adipose tissue.

Galanin-like peptide (GALP) is a neuropeptide involved in the regulation of feeding behavior and energy metabolism in mammals. While a weight loss effect of GALP has been reported, its effects on lipid metabolism have not been investigated. The aim of this study was to determine if GALP regulates lipid metabolism in liver and adipose tissue via an action on the sympathetic nervous system. The respiratory exchange ratio of mice administered GALP intracerebroventricularly was lower than that of saline-treated animals, and fatty acid oxidation-related gene mRNA levels were increased in the liver. Even though the respiratory exchange ratio was reduced by GALP, this change was not significant when mice were treated with the sympatholytic drug, guanethidine. Lipolysis-related gene mRNA levels were increased in the adipose tissue of GALP-treated mice compared with saline-treated animals. These results show that GALP stimulates fatty acid β-oxidation in liver and lipolysis in adipose tissue, and suggest that the anti-obesity effect of GALP may be due to anorexigenic actions and improvement of lipid metabolism in peripheral tissues via the sympathetic nervous system.

Neuropeptide W-Induced Hypophagia is Mediated Through Corticotropin-Releasing Hormone-Containing Neurons

Neuropeptide W (NPW), which was originally isolated from the porcine hypothalamus, has been identified as the endogenous ligand for both the NPBWR1 (GPR7) and NPBWR2 (GPR8) receptors. These receptors, which belong to the orphan G protein-coupled receptor (GPCR) family, share a high sequence homology with the opioid and somatostatin receptor families. NPW and NPBWR1 are widely distributed in the rat central nervous system (CNS). While the intracerebroventricular (i.c.v.) injection of NPW elevates plasma corticosterone levels, the intravenous administration of NPW in conjunction with a corticotropin-releasing hormone (CRH) antagonist blocks NPW-induced corticosterone secretion. It has been reported that NPW is involved in regulating the hypothalamus-pituitary-adrenal cortex (HPA) axis and that i.c.v. administration of NPW decreases feeding behavior. The aim of the present study was to ascertain if NPW’s role in feeding regulation is mediated (or not) through corticotropin-releasing hormone (CRH)-containing neurons. We found that NPW-containing axon terminals make synapses with CRH-immunoreactive cell bodies and dendritic processes in the hypothalamic paraventricular nucleus (PVN). The central infusion of NPW significantly induced c-Fos expression in CRH-immunoreactive neurons in the mouse PVN, but not in vasopressin- or oxytocin-immunoreactive neurons. To determine if NPW regulates feeding behavior through CRH neurons, the feeding behavior of mice was studied following the i.c.v. administration NPW in the presence or absence of pretreatment with a CRH antagonist. While NPW administration decreased feeding activity, the CRH antagonist inhibited this effect. These results strongly suggest that NPW regulates feeding behavior through CRH neurons in the mouse brain.

Effect of sodium-glucose cotransporter 2 (SGLT2) inhibition on weight loss is partly mediated by liver-brain-adipose neurocircuitry

Sodium-glucose cotransporter 2 (SGLT2) inhibitors have both anti-diabetic and anti-obesity effects. However, the precise mechanism of the anti-obesity effect remains unclear. We previously demonstrated that the glycogen depletion signal triggers lipolysis in adipose tissue via liver-brain-adipose neurocircuitry. In this study, therefore, we investigated whether the anti-obesity mechanism of SGLT2 inhibitor is mediated by this mechanism. Diet-induced obese mice were subjected to hepatic vagotomy (HVx) or sham operation and loaded with high fat diet containing 0.015% tofogliflozin (TOFO), a highly selective SGLT2 inhibitor, for 3 weeks. TOFO-treated mice showed a decrease in fat mass and the effect of TOFO was attenuated in HVx group. Although both HVx and sham mice showed a similar level of reduction in hepatic glycogen by TOFO treatment, HVx mice exhibited an attenuated response in protein phosphorylation by protein kinase A (PKA) in white adipose tissue compared with the sham group. As PKA pathway is known to act as an effector of the liver-brain-adipose axis and activate triglyceride lipases in adipocytes, these results indicated that SGLT2 inhibition triggered glycogen depletion signal and actuated liver-brain-adipose axis, resulting in PKA activation in adipocytes. Taken together, it was concluded that the effect of SGLT2 inhibition on weight loss is in part mediated via the liver-brain-adipose neurocircuitry.

Behavioral and omics analyses study on potential involvement of dipeptide balenine through supplementation in diet of senescence-accelerated mouse prone 8.

This study investigates effects of dipeptide balenine, as a major component of whale meat extract (hereafter, WME), supplementation on senescence-accelerated mouse prone 8 (SAMP8), an Alzheimers disease (AD) model at level of learning and memory formation and brain expression profiles genome-wide in brain. Mice fed experimental balenine (+ WME) supplemented diet for 26 weeks were subjected to four behavioral tests – open field, Y-maze, novel object recognition, and water-filled multiple T-maze – to examine effects on learning and memory. Brain transcriptome of SAMP8 mice-fed the WME diet over control low-safflower oil (LSO) diet-fed mice was delineated on a 4 × 44 K mouse whole genome DNA microarray chip. Results revealed the WME diet not only induced improvements in the learning and memory formation but also positively modulated changes in the brain of the SAMP8 mouse; the gene inventories are publically available for analysis by the scientific community. Interestingly, the SAMP8 mouse model presented many genetic characteristics of AD, and numerous novel molecules (Slc2a5, Treh, Fbp1, Aldob, Ppp1r1a, DNase1, Agxt2l1, Cyp2e1, Acsm1, Acsm2, and Pah) were revealed over the SAMR1 (senescence-accelerated mouse resistant 1) mouse, to be oppositely regulated/recovered under the balenine (+ WME) supplemented diet regime by DNA microarray and bioinformatics analyses. Our present study demonstrates an experimental strategy to understand the effects of dipeptide balenine, prominetly contained in meat diet, on SAMP8, providing new insight into whole brain transcriptome changes genome-wide. The gene expression data has been deposited into the Gene Expression Omnibus (GEO): GSE76459. The data will be a valuable resource in examining the effects of natural products, and which could also serve as a human model for further functional analysis and investigation.