Prolyl carboxypeptidase in Agouti-related Peptide neurons modulates food intake and body weight

Dynamic regulation of CeA gene expression during acute and protracted abstinence from chronic binge drinking of male and female C57BL/6J mice

Binge alcohol consumption is a major risk factor for developing Alcohol Use Disorder (AUD) and is associated with alcohol-related problems like accidental injury, acute alcohol poisoning, and black-outs. While there are numerous brain regions that have been shown to play a role in this AUD in humans and animal models, the central nucleus of the amygdala (CeA) has emerged as a critically important locus mediating binge alcohol consumption. In this study, we sought to understand how relative gene expression of key signaling molecules in the CeA changes during different periods of abstinence following bouts of binge drinking. To test this, we performed drinking in the dark (DID) on two separate cohorts of C57BL/6J mice and collected CeA brain tissue at one day (acute) and 7 days (protracted) abstinence after DID. We used qRTPCR to evaluate relative gene expression changes of 25 distinct genes of interest related to G protein-coupled receptors (GPCRs), neuropeptides, ion channel subunits, and enzymes that have been previously implicated in AUD. Our findings show that during acute abstinence CeA punches collected from female mice had upregulated relative mRNA expression of the gamma-aminobutyric acid receptor subunit alpha 2 (Gabra2), and the peptidase, angiotensinase c (Prcp). CeA punches from male mice at the same time point in abstinence had upregulated relative mRNA encoding for neuropeptide-related molecules, neuropeptide Y (Npy) and somatostatin (Sst), as well as the neuropeptide Y receptor Y2 (Npyr2) but downregulated, Glutamate ionotropic receptor NMDA type subunit 1 (Grin1). After protracted abstinence CeA punches collected from female mice had increased mRNA expression of corticotropin releasing hormone (Crh) and Npy. While CeA punches collected from male mice at the same timepoint had upregulated relative mRNA expression of Npy2r and downregulated mRNA expression of Gabra2, Grin1 and opioid receptor kappa 1 (Oprk1). Our findings support that there are differences in how the CeA of male and female respond to binge-alcohol exposure, highlighting the need to understand the implications of such differences in the context of AUD and binge drinking behavior.

The Mechanism of the Gut-Brain Axis in Regulating Food Intake

With the increasing prevalence of energy metabolism disorders such as diabetes, cardiovascular disease, obesity, and anorexia, the regulation of feeding has become the focus of global attention. The gastrointestinal tract is not only the site of food digestion and absorption but also contains a variety of appetite-regulating signals such as gut-brain peptides, short-chain fatty acids (SCFAs), bile acids (BAs), bacterial proteins, and cellular components produced by gut microbes. While the central nervous system (CNS), as the core of appetite regulation, can receive and integrate these appetite signals and send instructions to downstream effector organs to promote or inhibit the body's feeding behaviour. This review will focus on the gut-brain axis mechanism of feeding behaviour, discussing how the peripheral appetite signal is sensed by the CNS via the gut-brain axis and the role of the central "first order neural nuclei" in the process of appetite regulation. Here, elucidation of the gut-brain axis mechanism of feeding regulation may provide new strategies for future production practises and the treatment of diseases such as anorexia and obesity.

Prolyl Carboxypeptidase Activity Is Present in Human Adipose Tissue and Is Elevated in Serum of Obese Men with Type 2 Diabetes

Prolyl carboxypeptidase (PRCP) is involved in metabolic disorders by hydrolyzing anorexigenic peptides. A link between serum PRCP activity and obesity has been reported, but its origin/source is still unclear. Previously proven correlations between human serum PRCP activity and the amount of adipose tissue may suggest that adipose tissue is an important source of circulating PRCP. We investigated PRCP activity in visceral, subcutaneous adipose tissue (VAT and SCAT), skeletal muscle tissue and serum of lean and obese men with or without type 2 diabetes (T2D). Correlations between PRCP activity, metabolic and biochemical parameters and immune cell populations were assessed. PRCP activity was the highest in VAT, compared to SCAT, and was very low in skeletal muscle tissue in the overall group. Serum PRCP activity was significantly higher in T2-diabetic obese men, compared to lean and obese non-diabetic men, and was positively correlated with glycemic control. A positive correlation was observed between serum PRCP activity and VAT immune cell populations, which might indicate that circulating PRCP activity is deriving rather from the immune fraction than from adipocytes. In conclusion, PRCP activity was observed in human adipose tissue for the first time and serum PRCP activity is correlated with T2D in obese men.

MC4R Signaling in Dorsal Raphe Nucleus Controls Feeding, Anxiety, and Depression

Major depressive disorder is associated with weight loss and decreased appetite; however, the signaling that connects these conditions is unclear. Here, we show that MC₄R signaling in the dorsal raphe nucleus (DRN) affects feeding, anxiety, and depression. DRN infusion of α-MSH decreases DRN neuronal activation and feeding. DRN MC₄R is expressed in GABAergic PRCP-producing neurons. DRN selective knockdown of PRCP (Prcp^DRNKD), an enzyme inactivating α-MSH, decreases feeding and DRN neuronal activation. Interestingly, Prcp^DRNKD mice present lower DRN serotonin levels and depressive-like behavior. Similarly, PRCP-ablated MC₄R mice (Prcp^MC4RKO) show metabolic and behavioral phenotypes comparable to those of Prcp^DRNKD mice. Selective PRCP re-expression in DRN MC₄R neurons of Prcp^MC4RKO mice partially reverses feeding, while fully restoring mood behaviors. Chemogenetic inhibition of DRN MC₄R neurons induces anxiety, depression, and reduced feeding, whereas chemogenetic activation reverses these effects. Our results indicate that MC₄R signaling in DRN plays a role in feeding, anxiety, and depression.

Research Progress on Dipeptidyl Peptidase Family: Structure, Function and Xenobiotic Metabolism

Prolyl-specific peptidases or proteases, including Dipeptidyl Peptidase 2, 4, 6, 8, 9, 10, Fibroblast Activation Protein, prolyl endopeptidase and prolyl carboxypeptidase, belong to the dipeptidyl peptidase family. In human physiology and anatomy, they have homology amino acid sequences, similarities in structure, but play distinct functions and roles. Some of them also play important roles in the metabolism of drugs containing endogenous peptides, xenobiotics containing peptides, and exogenous peptides. The major functions of these peptidases in both the metabolism of human health and bioactive peptides are of significant importance in the development of effective inhibitors to control the metabolism of endogenous bioactive peptides. The structural characteristics, distribution of tissue, endogenous substrates, and biological functions were summarized in this review. Furthermore, the xenobiotics metabolism of the dipeptidyl peptidase family is illustrated. All the evidence and information summarized in this review would be very useful for researchers to extend the understanding of the proteins of these families and offer advice and assistance in physiology and pathology studies.

Sex difference feeding behaviour of NOD SCID mice in a pharmacological model of type 1 diabetes

This study aimed to assess the sex differences in the feeding behaviour of non-obese diabetic severe combined immunodeficient (NOD SCID) mice in a pharmacological model of type 1 diabetes mellitus (T1Dm). In our study, we chose NOD SCID mice of both sexes and assessed their feeding behaviour, body weight, body fat and water content under identical experimental conditions and diets. After 1 month of diabetes mellitus in mice in the experimental group, males and females did not show any increase in body weight, and they weighed significantly less than the control group. However, compared with the control group, in females with a background of T1Dm, there was a significant decrease in body fat. The amount of water consumed in the experimental groups was higher than that in the control groups. The amount of food consumed by males increased when they increased their water consumption, whereas food consumption in females decreased significantly with an increase in water consumption. Thus, we discovered sex differences in the feeding behaviour, body weight and body fat and water content in the pharmacological model of T1Dm after 1 month in NOD SCID mice.

Prolyl Carboxypeptidase Mediates the C-Terminal Cleavage of (Pyr)-Apelin-13 in Human Umbilical Vein and Aortic Endothelial Cells

The aim of this study was to investigate the C-terminal cleavage of (pyr)-apelin-13 in human endothelial cells with respect to the role and subcellular location of prolyl carboxypeptidase (PRCP). Human umbilical vein and aortic endothelial cells, pre-treated with prolyl carboxypeptidase-inhibitor compound 8o and/or angiotensin converting enzyme 2 (ACE2)-inhibitor DX600, were incubated with (pyr)-apelin-13 for different time periods. Cleavage products of (pyr)-apelin-13 in the supernatant were identified by mass spectrometry. The subcellular location of PRCP was examined via immunocytochemistry. In addition, PRCP activity was measured in supernatants and cell lysates of LPS-, TNFα-, and IL-1β-stimulated cells. PRCP cleaved (pyr)-apelin-13 in human umbilical vein and aortic endothelial cells, while ACE2 only contributed to this cleavage in aortic endothelial cells. PRCP was found in endothelial cell lysosomes. Pro-inflammatory stimulation induced the secretion of PRCP in the extracellular environment of endothelial cells, while its intracellular level remained intact. In conclusion, PRCP, observed in endothelial lysosomes, is responsible for the C-terminal cleavage of (pyr)-apelin-13 in human umbilical vein endothelial cells, while in aortic endothelial cells ACE2 also contributes to this cleavage. These results pave the way to further elucidate the relevance of the C-terminal Phe of (pyr)-apelin-13.

Early-life perfluorooctanoic acid exposure induces obesity in male offspring and the intervention role of chlorogenic acid

Perfluorooctanoic acid (PFOA) is an emerging organic pollutant (EOP) hazardous to human health. Effects of maternal PFOA exposure on offspring as well as the underlying mechanisms remain unclear. In this study, ICR mouse models of gestational low PFOA exposure (0.05 mg/kg/day) were established to investigate the roles on metabolic disorders of offspring. Body weight, body composition, hepatic lipid levels, transcriptome and metabolome were analyzed. Expression of genes related to lipid metabolism, inflammasome formation and gut barrier integrity were measured. Furthermore, oral administration of chlorogenic acid (CGA) (100 mg/kg/day) was performed to observe the rescue effect on lipid disorders caused by PFOA exposure. Our findings demonstrated that gestational exposure to PFOA resulted in obesity, hepatic inflammation, disorders of lipid metabolism, and disruption of gut barrier integrity in male offspring. Notably, these adverse effects were attenuated by CGA supplementation. These data suggested that PFOA exposure during early life stage induced potential risks for later onset of obesity and metabolic disorder which could be ameliorated by CGA treatment.

Prenatal low-dose DEHP exposure induces metabolic adaptation and obesity: Role of hepatic thiamine metabolism

Di-(2-ethylhexyl)-phthalate (DEHP) is a ubiquitous environmental pollutant and is widely used in industrial plastics. However, the long-term health implications of prenatal exposure to DEHP remains unclear. We set out to determine whether prenatal DEHP exposure can induce metabolic syndrome in offspring and investigate the underlying mechanisms. A mouse model of prenatal DEHP exposure (0.2, 2, and 20 mg/kg/day) was established to evaluate the long-term metabolic disturbance in offspring. The mice were profiled for the hepatic metabolome, transcriptome and gut microbiota to determine the underlying mechanisms. Thiamine supplementation (50 mg/kg/day) was administered to offspring to investigate the role of thiamine in ameliorating metabolic syndrome. Prenatal exposure to low-dose DEHP (0.2 mg/kg/day) resulted in metabolic syndrome, including abnormal adipogenesis, energy expenditure and glucose metabolism, along with dysbiosis of the gut microbiome, in male offspring. Notably, hepatic thiamine metabolism was disrupted in these offspring due to the dysregulation of thiamine transport enzymes, which caused abnormal glucose metabolism. Prenatal low-dose DEHP exposure caused life-long metabolic consequences in a sex-dependent manner, and these consequences were be attenuated by thiamine supplementation in offspring. Our findings suggest low-dose DEHP exposure during early life stages is a potential risk factor for later obesity and metabolic syndrome.

Cataloguing and Selection of mRNAs Localized to Dendrites in Neurons and Regulated by RNA-Binding Proteins in RNA Granules

Spatiotemporal translational regulation plays a key role in determining cell fate and function. Specifically, in neurons, local translation in dendrites is essential for synaptic plasticity and long-term memory formation. To achieve local translation, RNA-binding proteins in RNA granules regulate target mRNA stability, localization, and translation. To date, mRNAs localized to dendrites have been identified by comprehensive analyses. In addition, mRNAs associated with and regulated by RNA-binding proteins have been identified using various methods in many studies. However, the results obtained from these numerous studies have not been compiled together. In this review, we have catalogued mRNAs that are localized to dendrites and are associated with and regulated by the RNA-binding proteins fragile X mental retardation protein (FMRP), RNA granule protein 105 (RNG105, also known as Caprin1), Ras-GAP SH3 domain binding protein (G3BP), cytoplasmic polyadenylation element binding protein 1 (CPEB1), and staufen double-stranded RNA binding proteins 1 and 2 (Stau1 and Stau2) in RNA granules. This review provides comprehensive information on dendritic mRNAs, the neuronal functions of mRNA-encoded proteins, the association of dendritic mRNAs with RNA-binding proteins in RNA granules, and the effects of RNA-binding proteins on mRNA regulation. These findings provide insights into the mechanistic basis of protein-synthesis-dependent synaptic plasticity and memory formation and contribute to future efforts to understand the physiological implications of local regulation of dendritic mRNAs in neurons.

Phosphorylation of Forkhead Protein FoxO1 at S253 Regulates Glucose Homeostasis in Mice

The transcription factor forkhead box O1 (FoxO1) is a key mediator in the insulin signaling pathway and controls multiple physiological functions, including hepatic glucose production (HGP) and pancreatic β-cell function. We previously demonstrated that S256 in human FOXO1 (FOXO1-S256), equivalent to S253 in mouse FoxO1 (FoxO1-S253), is a key phosphorylation site mediating the effect of insulin as a target of protein kinase B on suppression of FOXO1 activity and expression of target genes responsible for gluconeogenesis. Here, we investigated the role of FoxO1-S253 phosphorylation in control of glucose homeostasis in vivo by generating global FoxO1-S253A/A knockin mice, in which FoxO1-S253 alleles were replaced with alanine (A substitution) blocking FoxO1-S253 phosphorylation. FoxO1-S253A/A mice displayed mild increases in feeding blood glucose and insulin levels but decreases in fasting blood glucose and glucagon concentrations, as well as a reduction in the ratio of pancreatic α-cells/β-cells per islet. FoxO1-S253A/A mice exhibited a slight increase in energy expenditure but barely altered food intake and glucose uptake among tissues. Further analyses revealed that FoxO1-S253A/A enhances FoxO1 nuclear localization and promotes the effect of glucagon on HGP. We conclude that dephosphorylation of S253 in FoxO1 may reflect a molecular basis of pancreatic plasticity during the development of insulin resistance.

Neurobiological characteristics underlying metabolic differences between males and females

The hypothalamus is the main integrating center for metabolic control. Our understanding of how hypothalamic circuits function to control appetite and energy expenditure has increased dramatically in recent years, due to the rapid rise in the incidence of obesity and the search for effective treatments. Increasing evidence indicates that these treatments will most likely differ between males and females. Indeed, sex differences in metabolism have been demonstrated at various levels, including in two of the most studied neuronal populations involved in metabolic control: the anorexigenic proopiomelanocortin neurons and the orexigenic neuropeptide Y/Agouti-related protein neurons. Here we review what is known to date regarding the sex differences in these two neuronal populations, as well as other neuronal populations involved in metabolic control and glial cells.