Arcuate nucleus of the hypothalamus contributes to the hypophagic effect and plasma metabolic changes induced by vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide

Drastic decline in vasoactive intestinal peptide expression in the suprachiasmatic nucleus in obese mice on a long-term high-fat diet

The suprachiasmatic nucleus (SCN) is the main region for the regulation of circadian rhythms. Although the SCN contains a heterogeneous neurochemical phenotype with a wide variety of neuropeptides, a key role has been suggested for the vasoactive intestinal neuropeptide (VIP) as a modulator circadian, reproductive, and seasonal rhythms. VIP is a 28-amino acid polypeptide hormone that belongs to the secretin-glucagon peptide superfamily and shares 68 % homology with the pituitary adenylate cyclase-activating polypeptide (PACAP). VIP acts as an endogenous appetite inhibitor in the central nervous system, where it participates in the control of appetite and energy homeostasis. In recent years, significant efforts have been made to better understand the role of VIP in the regulation of appetite/satiety and energy balance. This study aimed to elucidate the long-term effect of an obesogenic diet on the distribution and expression pattern of VIP in the SCN and nucleus accumbens (NAc) of C57BL/6 mice. A total of 15 female C57BL/6J mice were used in this study. Female mice were fed ad libitum with water and, either a standard diet (SD) or a high-fat diet (HFD) to induce obesity. There were 7 female mice on the SD and 8 on the HFD. The duration of the experiment was 365 days. The morphological study was performed using immunohistochemistry and double immunofluorescence techniques to study the neurochemical profile of VIP neurons of the SCN of C57BL/6 mice. Our data show that HFD-fed mice gained weight and showed reduced VIP expression in neurons of the SCN and also in fibres located in the NAc. Moreover, we observed a loss of neuropeptide Y (NPY) expression in fibres surrounding the SCN. Our findings on VIP may contribute to the understanding of the pathophysiological mechanisms underlying obesity in regions associated with uncontrolled intake of high-fat foods and the reward system, thus facilitating the identification of novel therapeutic targets.

PACAP and VIP Neuropeptides' and Receptors' Effects on Appetite, Satiety and Metabolism

The overwhelming increase in the prevalence of obesity and related disorders in recent years is one of the greatest threats to the global healthcare system since it generates immense healthcare costs. As the prevalence of obesity approaches epidemic proportions, the importance of elucidating the mechanisms regulating appetite, satiety, body metabolism, energy balance and adiposity has garnered significant attention. Currently, gastrointestinal (GI) bariatric surgery remains the only approach capable of achieving successful weight loss. Appetite, satiety, feeding behavior, energy intake and expenditure are regulated by central and peripheral neurohormonal mechanisms that have not been fully elucidated yet. Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) and Vasoactive Intestinal Polypeptide (VIP) are members of a family of regulatory peptides that are widely distributed in parallel with their specific receptors, VPAC1R, VPAC2R and PAC1R, in the central nervous system (CNS) and in the periphery, such as in the gastrointestinal tract and its associated organs and immune cells. PACAP and VIP have been reported to play an important role in the regulation of body phenotype, metabolism and homeostatic functions. The purpose of this review is to present recent data on the effects of PACAP, VIP, VPAC1R, VPAC2R and PAC1R on the modulation of appetite, satiety, metabolism, calorie intake and fat accumulation, to evaluate their potential use as therapeutic targets for the treatment of obesity and metabolic syndrome.

Deficiency of Adipose Aryl Hydrocarbon Receptor Protects against Diet-Induced Metabolic Dysfunction through Sexually Dimorphic Mechanisms

The molecular mechanisms underlying diet-induced obesity are complex and remain unclear. The activation of the aryl hydrocarbon receptor (AhR), a xenobiotic sensor, by obesogens may contribute to diet-induced obesity through influences on lipid metabolism and insulin resistance acting at various sites, including adipose tissue. Thus, our hypothesis was that conditional AhR depletion, specifically from mature adipose tissue (CadKO), would improve high-fat diet (HFD)-induced metabolic dysfunction. CadKO protects mice from HFD-induced weight gain. CadKO females eat fewer calories, leading to increased energy expenditure (EE) and improved glucose tolerance on HFD. Our exploration of adipose tissue biology suggests that the depletion of AhR from adipocytes provides female mice with an increased capacity for adipogenesis and lipolysis, allowing for the maintenance of a healthy adipocyte phenotype. The HFD-induced leptin rise was reduced in CadKO females, but the hypothalamic leptin receptor (LepR) was increased in the energy regulatory regions of the hypothalamus, suggesting an increased sensitivity to leptin. The estrogen receptor α (ERα) was higher in CadKO female adipose tissue and the hypothalamus. CadKO males displayed a delayed progression of obesity and insulin resistance. In males, CadKO ameliorated proinflammatory adipocytokine secretion (such as TNFα, IL1β, IL6) and displayed reduced inflammatory macrophage infiltration into adipose depots. Overall, CadKO improves weight control and systemic glucose homeostasis under HFD challenge but to a more profound extent in females. CadKO facilitates a lean phenotype in females and mediates healthy adipose-hypothalamic crosstalk. In males, adipose-specific AhR depletion delays the development of obesity and insulin resistance through the maintenance of healthy crosstalk between adipocytes and immune cells.

Female reproductive functions of the neuropeptide PACAP

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neuropeptide originally isolated as a hypothalamic peptide. It has a widespread distribution in the body and has a diverse spectrum of actions. Among other processes, PACAP has been shown to be involved in reproduction. In this review we summarize findings related to the entire spectrum of female reproduction. PACAP is a regulatory factor in gonadal hormone production, influences follicular development and plays a role in fertilization and embryonic/placental development. Furthermore, PACAP is involved in hormonal changes during and after birth and affects maternal behavior. Although most data come from cell cultures and animal experiments, increasing number of evidence suggests that similar effects of PACAP can be found in humans. Among other instances, PACAP levels show changes in the serum during pregnancy and birth. PACAP is also present in the human follicular and amniotic fluids and in the milk. Levels of PACAP in follicular fluid correlate with the number of retrieved oocytes in hyperstimulated women. Human milk contains very high levels of PACAP compared to plasma levels, with colostrum showing the highest concentration, remaining steady thereafter for the first 7 months of lactation. All these data imply that PACAP has important functions in reproduction both under physiological and pathological conditions.