Metabolic roles of the M3 muscarinic acetylcholine receptor studied with M3 receptor mutant mice: a review

Acute sub-diaphragmatic anterior vagus nerve stimulation increases peripheral glucose uptake in anaesthetized rats

The sub-diaphragmatic vagus innervates various organs involved in the control of glucose homeostasis including the liver, pancreas and the intestines. In the current study, we investigated the effect of acute electrical stimulation of the anterior trunk of the sub-diaphragmatic vagus on glucose fluxes in anaesthetized adult male rats. After overnight fast, rats underwent either vagus nerve stimulation (VNS+, n = 11; rectangular pulses at 5 Hz, 1.5 mA, 1 msec pulse width) or sham stimulation (VNS-; n = 11) for 120 min under isoflurane anesthesia. Before stimulation, the rats received an i.v. bolus of 1 mL/kg of a sterilized aqueous solution containing 125 mg/mL of D-[6,6-²H₂] glucose. Endogenous glucose production (EGP) and glucose clearance rate (GCR) were calculated by kinetic analysis from the wash-out of injected D-[6,6-²H₂]glucose from the circulation. VNS+ resulted in lower glucose levels compared to the VNS- group (p < 0.05), with similar insulin levels. EGP was similar in both groups, but the GCR was higher in the VNS+ group compared to the VNS- group (p < 0.001). Circulating levels of the sympathetic transmitter norepinephrine were reduced by VNS+ relative to VNS- treatment (p < 0.01). It is concluded that acute anterior sub-diaphragmatic VNS causes stimulation of peripheral glucose uptake, while plasma insulin levels remained similar, and this is associated with lower activity of the sympathetic nervous system.

An emerging role of arecoline on growth performance, intestinal digestion and absorption capacities and intestinal structural integrity of adult grass carp (Ctenopharyngodon idella)

Arecoline is an alkaloid with important pharmacological effects in the plant areca nut, which has been demonstrated to be an agonist of muscarinic receptors (M receptor). This study explored the influences of dietary arecoline on growth performance, intestinal digestion and absorption abilities, antioxidant capacity, and the apical junction complex (AJC) of adult grass carp (Ctenopharyngodon idella). Adult grass carp (608 to 1512 g) were fed at 6 graded levels of dietary arecoline (0, 0.5, 1.0, 1.5, 2.0, and 2.5 mg/kg diet) for 9 weeks. The results suggested that appropriate dietary supplementation of arecoline (1.0 mg/kg) increased growth parameters and intestinal growth in adult grass carp (P < 0.05), enhanced digestion and absorption capacities (P < 0.05), up-regulated muscarinic receptor 3 (M3) mRNA level (P < 0.05), increased the content of neuropeptide fish substance P (P < 0.05), improved antioxidant capacity by activating the Keap1a/Nrf2 signaling pathway (P < 0.05), reduced intestinal mucosal permeability (P < 0.05), and increased mRNA levels of tight junction (TJ) and adherent junction AJ-related proteins in fish by inhibiting the RhoA/ROCK signaling pathway (RhoA/ROCK/MLCK/NMII) (P < 0.05). In addition, the appropriate arecoline supplementation for adult grass carp was determined to be 1.20, 1.21, 1.07, and 1.19 mg/kg based on percentage weight gain, lipase activity, serum diamine oxidase, and protein carbonyl, respectively. Overall, to the best of our knowledge, we investigated for the first time the effects and possible mechanisms of dietary arecoline on intestinal digestive and absorptive capacities and structural integrity in fish and evaluated the appropriate level of supplementation.

Subtype-dependent regulation of Gβγ signalling

G protein-coupled receptors (GPCRs) transmit information to the cell interior by transducing external signals to heterotrimeric G protein subunits, Gα and Gβγ subunits, localized on the inner leaflet of the plasma membrane. Though the initial focus was mainly on Gα-mediated events, Gβγ subunits were later identified as major contributors to GPCR-G protein signalling. A broad functional array of Gβγ signalling has recently been attributed to Gβ and Gγ subtype diversity, comprising 5 Gβ and 12 Gγ subtypes, respectively. In addition to displaying selectivity towards each other to form the Gβγ dimer, numerous studies have identified preferences of distinct Gβγ combinations for specific GPCRs, Gα subtypes and effector molecules. Importantly, Gβ and Gγ subtype-dependent regulation of downstream effectors, representing a diverse range of signalling pathways and physiological functions have been found. Here, we review the literature on the repercussions of Gβ and Gγ subtype diversity on direct and indirect regulation of GPCR/G protein signalling events and their physiological outcomes. Our discussion additionally provides perspective in understanding the intricacies underlying molecular regulation of subtype-specific roles of Gβγ signalling and associated diseases.

Dangerous Liaisons: Tau Interaction with Muscarinic Receptors

The molecular processes underlying neurodegenerative diseases (such as Alzheimer's Disease - AD) remain poorly understood. There is also an imperative need for disease-modifying therapies in AD since the present treatments, acetylcholinesterase inhibitors and NMDA antagonists, do not halt its progression. AD and other dementias present unique pathological features such as that of microtubule associated protein tau metabolic regulation. Tau has numerous binding partners, including signaling molecules, cytoskeletal elements and lipids, which suggests that it is a multifunctional protein. AD has also been associated with severe loss of cholinergic markers in the brain and such loss may be due to the toxic interaction of tau with cholinergic muscarinic receptors. By using specific antagonists of muscarinic receptors it was found in vitro that extracellular tau binds to M1 and M3 receptors and which the increase of intracellular calcium found in neuronal cells upon tau-binding. However, so far, the significance of tau signaling through muscarinic receptor in vivo in tauopathic models remains uncertain. The data reviewed in the present paper highlight the significant effect of M1 receptor/tau interaction in exacerbating tauopathy related pathological features and suggest that selective M1 agonists may serve as a prototype for future therapeutic development toward modification of currently intractable neurodegenerative diseases, such as tauopathies.

In vivo cardiopulmonary impact of skeletal M3Dq DREADD expression: a pilot study

The muscarinic M₃ receptor (M₃R) is implicated in cardiopulmonary control and many other peripheral physiologic functions. Previous observations report mortality in mice expressing a Gq-linked designer G-protein coupled receptor (Dq) selectively in striated muscle, while M₃Dq DREADD (Designer Receptor Exclusively Activated by Designer Drug), selectively expressed in skeletal muscle (SKM) impacts glucose metabolism. We investigated whether activation of SKM M₃Dq impacts cardiopulmonary function. Heart rate (HR), body temperature (Tb) and locomotor activity (ACT) were measured in 4 conscious, chronically instrumented M₃Dq DREADD mice and 4 wildtype controls. Circadian values of HR, BT and ACT were not different between genotypes (p > 0.05). Activation of the M₃Dq DREADD by clozapine N-oxide (CNO; 0.1 mg/kg) resulted in: a significant drop in heart rate, 2 h after injection, compared with a time-matched baseline control period from the same animals (460 ± 28 vs. 532 ± 6, p < 0.05), significantly lower ACT compared to the baseline control (p < 0.05) and reduced pulmonary minute ventilation compared to pre-CNO control (p < 0.05). M₃Dq DREADD activation did not cause bronchoconstriction (separate protocol), however, there was a concomitant reduction in HR, Tb and ventilation, accompanied by cardiac arrhythmias. We speculate that reductions in Tb, HR and ventilation reflect a mechanistic link between SKM Gq signaling and the metabolic responses associated with the initiation of torpor. Supported by the Canadian Institutes of Health Research (CIHR MOP-81211).

Blockade of the M1 muscarinic acetylcholine receptors impairs eyeblink serial feature-positive discrimination learning in mice

The serial feature-positive discrimination task requires the subjects to respond differentially to the identical stimulus depending on the temporal context given by a preceding cue stimulus. In the present study, we examined the involvement of the M1 muscarinic acetylcholine receptors using a selective M1 antagonist VU0255035 in the serial feature-positive discrimination task of eyeblink conditioning in mice. In this task, mice received a 2-s light stimulus as the conditional cue 5 or 6 s before the presentation of a 350-ms tone conditioned stimulus (CS) paired with a 100-ms peri-orbital electrical shock (cued trials), while they did not receive the cue before the presentation of the CS alone (non-cued trials). Each day mice randomly received 30 cued and 30 non-cued trials. We found that VU0255035 impaired acquisition of the conditional discrimination as well as the overall acquisition of the conditioned response (CR) and diminished the difference in onset latency of the CR between the cued and non-cued trials. VU0255035 administration to the control mice after sufficient learning did not impair the pre-acquired conditional discrimination or the CR expression itself. These effects of VU0255035 were almost similar to those with the scopolamine in our previous study, suggesting that among the several types of muscarinic acetylcholine receptors, the M1 receptors may play an important role in the acquisition of the conditional discrimination memory but not in mediating the discrimination itself after the memory had formed in the eyeblink serial feature-positive discrimination learning.

Central muscarinic receptor subtypes (M1 and M3) involved in carbacol-induced hypophagia in neonatal broiler chicken

Aim: Food intake regulated by a complex of physiologic mechanisms in the nervous system. Muscarinergic system has an important role in the central regulation of appetite in mammals, but there is no information for Muscarinic receptors in avian. The purpose of this study was to examine the effects of intracerebroventricular injection of carbachol (cholinergic agonist), Telenzepine (M₁ receptor antagonist), AF-DX116 (M₂ receptor antagonist), 4-DAMP (M₃ receptor antagonist), and PD102807 (M₄ receptor antagonist) on feeding behavior in 3-h food-deprived (FD₃) neonatal broiler chicken.Materials and Methods: In experiment 1, chicken intracerebroventricular injected with carbachol (125, 250, and 500 nmol). In experiment 2, birds intracerebroventricular injected with telenzepine (125, 250, and 500 nmol). In experiments 3-5, birds intracerebroventricular injected with AF-DX 116 (125, 250, and 500 nmol), 4-DAMP (125, 250, and 500 nmol), and PD102807 (125, 250, and 500 nmol), respectively. In experiment 6, broilers intracerebroventricular injected with carbacol (500 nmol), co-injection of telenzepine (125 nmol)+carbacol (500 nmol), and 4-DAMP (125 nmol)+carbacol (500 nmol). In experiment 7, injection procedure was carbacol (500 nmol), co-injection of AF-DX116 (125 nmol)+carbacol (500 nmol), and PD102807 (125 nmol)+carbacol (500 nmol). Then, food intake measured until 120 min after injection.Results: According to the data, carbachol (250 and 500 nmol) significantly decreased food intake in comparison with control group (P < 0.05). Intracerebroventricular injection of telenzepine (250 and 500 nmol) and 4-DAMP (250 and 500 nmol) significantly increased food intake (P < 0.05). In addition, carbacol-induced hypophagia was significantly attenuated by co-injection of telenzepine + carbacol (P < 0.05). Also, co-injection of 4-DAMP + carbacol decreased the effect of carbacol on food intake (P < 0.05). However, AF-DX116 and PD102807 had no effect on hypophagia induced by carbacol (P > 0.05).Conclusion: These results suggest, hypophagic effect of muscarinergic system is mediated via M₁ and M₃ receptors in neonatal chicken.

Muscarinic receptors in energy homeostasis: Physiology and pharmacology

Despite increased awareness and intensified biomedical research efforts, the prevalence of obesity continues to rise worldwide. This is alarming, because obesity accelerates the progression of several chronic disorders, including type 2 diabetes, cancer and cardiovascular disease. Individuals who experience significant weight loss must combat powerful counter-regulatory energy homeostatic processes, and, typically, most individuals regain the lost weight. Therefore, decoding the neural mechanisms underlying the regulation of energy homeostasis is necessary for developing breakthroughs in obesity management. It has been known for decades that cholinergic neurotransmission both directly and indirectly modulates energy homeostasis and metabolic health. Despite this insight, the molecular details underlying the modulation remain ill-defined, and the potential for targeting cholinergic muscarinic receptors for treating metabolic disease is largely uncharted. In this MiniReview, we scrutinize the literature that has formed our knowledge of muscarinic acetylcholine receptors (mAChRs) in energy homeostasis. The role of mAChRs in canonical appetite-regulating circuits will be discussed as will the more indirect regulation of energy homoeostasis via neurocircuits linked to motivated behaviours and emotional states. Finally, we discuss the therapeutic prospects of targeting mAChRs for the treatment of obesity and type 2 diabetes.

Therapeutic Potential of Multifunctional Tacrine Analogues

Abstract: Tacrine is a potent inhibitor of cholinesterases (acetylcholinesterase and butyrylcholinesterase) that shows limiting clinical application by liver toxicity. In spite of this, analogues of tacrine are considered as a model inhibitor of cholinesterases in the therapy of Alzheimer’s disease. The interest in these compounds is mainly related to a high variety of their structure and biological properties. In the present review, we have described the role of cholinergic transmission and treatment strategies in Alzheimer’s disease as well as the synthesis and biological activity of several recently developed classes of multifunctional tacrine analogues and hybrids, which consist of a new paradigm to treat Alzheimer’s disease. We have also reported potential of these analogues in the treatment of Alzheimer’s diseases in various experimental systems.

Brain signalling systems: A target for treating type I diabetes mellitus

From early to later stages of Type I Diabetes Mellitus (TIDM), signalling molecules including brain indolamines and protein kinases are altered significantly, and that has been implicated in the Metabolic Disorders (MD) as well as impairment of retinal, renal, neuronal and cardiovascular systems. Considerable attention has been focused to the effects of diabetes on these signalling systems. However, the exact pathophysiological mechanisms of these signals are not completely understood in TIDM, but it is likely that hyperglycemia, acidosis, and insulin resistance play significant roles. Insulin maintains normal glycemic levels and it acts by binding to its receptor, so that it activates the receptor's tyrosine kinase activity, resulting in phosphorylation of several substrates. Those substrates provide binding/interaction sites for signalling molecules, including serine/threonine kinases and indolamines. For more than two decades, our research has been focused on the mechanisms of protein kinases, CaM Kinase and Serotonin transporter mediated alterations of indolamines in TIDM. In this review, we have also discussed how discrete areas of brain respond to insulin or some of the pharmacological agents that triggers or restores these signalling molecules, and it may be useful for the treatment of specific region wise changes/disorders of diabetic brain.

Prospective associations of maternal choline status with offspring body composition in the first 5 years of life in two large mother-offspring cohorts: the Southampton Women's Survey cohort and the Growing Up in Singapore Towards healthy Outcomes cohort

BACKGROUND

Choline status has been positively associated with weight and fat mass in animal and human studies. As evidence examining maternal circulating choline concentrations and offspring body composition in human infants/children is lacking, we investigated this in two cohorts.

METHODS

Maternal choline concentrations were measured in the UK Southampton Women's Survey (SWS; serum, n = 985, 11 weeks' gestation) and Singapore Growing Up Towards healthy Outcomes (GUSTO); n = 955, 26-28 weeks' gestation) mother-offspring cohorts. Offspring anthropometry was measured at birth and up to age 5 years. Body fat mass was determined using dual-energy x-ray absorptiometry at birth and age 4 years for SWS; and using air-displacement plethysmography at birth and age 5 years for GUSTO. Linear-regression analyses were performed, adjusting for confounders.

RESULTS

In SWS, higher maternal choline concentrations were associated with higher neonatal total body fat mass {β = 0.60 standard deviation [SD]/5 µmol/L maternal choline [95% confidence interval (CI) 0.04-1.16]} and higher subscapular skinfold thickness [β = 0.55 mm/5 µmol/L (95% CI, 0.12-1.00)] at birth. In GUSTO, higher maternal choline concentrations were associated with higher neonatal body mass index-for-age z-score [β = 0.31 SD/5 µmol/L (0.10-0.51)] and higher triceps [β = 0.38 mm/5 µmol/L (95% CI, 0.11-0.65)] and subscapular skinfold thicknesses [β = 0.26 mm/5 µmol/L (95% CI, 0.01-0.50)] at birth. No consistent trends were observed between maternal choline and offspring gain in body mass index, skinfold thicknesses, abdominal circumference, weight, length/height and adiposity measures in later infancy and early childhood.

CONCLUSION

Our study provides evidence that maternal circulating choline concentrations during pregnancy are positively associated with offspring BMI, skinfold thicknesses and adiposity at birth, but not with growth and adiposity through infancy and early childhood to the age of 5 years.

Cholinergic Agonists and Antagonists Have an Effect on the Metabolism of the Beetle Tenebrio Molitor

Synthetic insecticides are still widely used in plant protection. The main target for their action is the nervous system, in which the cholinergic system plays a vital role. Currently available insecticides have low selectivity and act on the cholinergic systems of invertebrates and vertebrates. Acetylcholine, a cholinergic system neurotransmitter, acts on cells by two types of receptors: nicotinic and muscarinic. In mammals, the role of muscarinic acetylcholine receptors (mAChRs) is quite well-known but in insects, is still not enough. Based on data indicating that the muscarinic cholinergic system strongly affects mammalian metabolism, we investigated if it similarly occurs in insects. We investigated the influence of agonists (acetylcholine, carbachol, and pilocarpine) and antagonists (tropane alkaloids: atropine and scopolamine) of mAChRs on the level of selected metabolites in Tenebrio molitor beetle trophic tissues. We analyzed the glycogen content in the fat body and midgut, the total free sugar concentration in the hemolymph and the lipid amount in the fat body. Moreover, we analyzed the levels of insulin-like peptides in the hemolymph. The tested compounds significantly influenced the mentioned parameters. They increased the glycogen content in the fat body and midgut but decreased the concentration of free sugars in the hemolymph. The observed effects were tissue-specific, and were also time- and dose-dependent. We used nonligated and neck-ligated larvae (to eliminate the influence of head factors on tissue metabolism) to determine whether the observed changes are the result of direct or indirect impacts on tissues. The obtained data suggest that the cholinergic system affects the fat body and midgut indirectly and directly and a pleiotropic role for mAChRs exists in the regulation of energy metabolism in insects. Moreover, tested compounds significantly affected the level of insulin-like peptides in hemolymph. Our studies for the first time showed that mAChRs are involved in regulation of insect metabolism of trophic tissues, and act on them directly and indirectly. Improved knowledge about insect cholinergic system may help in searching more selective and environment-friendly solutions in pest management.

Antipsychotic Drugs: From Receptor-binding Profiles to Metabolic Side Effects

BACKGROUND

Antipsychotic-induced metabolic side effects are major concerns in psychopharmacology and clinical psychiatry. Their pathogenetic mechanisms are still not elucidated.

METHODS

Herein, we review the impact of neurotransmitters on metabolic regulation, providing insights into antipsychotic-induced metabolic side effects.

RESULTS

Antipsychotic drugs seem to interfere with feeding behaviors and energy balance, processes that control metabolic regulation. Reward and energy balance centers in central nervous system constitute the central level of metabolic regulation. The peripheral level consists of skeletal muscles, the liver, the pancreas, the adipose tissue and neuroendocrine connections. Neurotransmitter receptors have crucial roles in metabolic regulation and they are also targets of antipsychotic drugs. Interaction of antipsychotics with neurotransmitters could have both protective and harmful effects on metabolism.

CONCLUSION

Emerging evidence suggests that antipsychotics have different liabilities to induce obesity, diabetes and dyslipidemia. However this diversity cannot be explained merely by drugs'pharmacodynamic profiles, highlighting the need for further research.

Teaching an Old Drug New Tricks: Agonism, Antagonism, and Biased Signaling of Pilocarpine through M3 Muscarinic Acetylcholine Receptor

Pilocarpine is a prototypical drug used to treat glaucoma and dry mouth and is classified as either a full or partial muscarinic agonist. Here, we report several unexpected results pertaining to its interaction with muscarinic M3 receptor (M3R). We found that pilocarpine was 1000 times less potent in stimulating mouse-eye pupil constriction than muscarinic agonists oxotremorin-M (Oxo-M) or carbachol (CCh), although all three ligands have similar K_d values for M3R. In contrast to CCh or Oxo-M, pilocarpine does not induce Ca²⁺ mobilization via endogenous M3R in human embryonic kidney cell line 293T (HEK293T) or mouse insulinoma (MIN6) cells. Pilocarpine also fails to stimulate insulin secretion and, instead, antagonizes the insulinotropic effect of Oxo-M and CCh-induced Ca²⁺ upregulation; however, in HEK293T or Chinese hamster ovary-K1 cells overexpressing M3R, pilocarpine induces Ca²⁺ transients like those recorded with another cognate G protein-coupled muscarinic receptor, M1R. Stimulation of cells overexpressing M1R or M3R with CCh resulted in a similar reduction in phosphatidylinositol 4,5-bisphosphate (PIP2). In contrast to CCh, pilocarpine stimulated PIP2 hydrolysis only in cells overexpressing M1R but not M3R. Moreover, pilocarpine blocked CCh-stimulated PIP2 hydrolysis in M3R-overexpressing cells, thus, it acted as an antagonist. Pilocarpine activates extracellular regulated kinase 1/2 in MIN6 cells. The stimulatory effect on extracellular regulated kinase (ERK1/2) was blocked by the Src family kinase inhibitor PP2, indicating that the action of pilocarpine on endogenous M3R is biased toward β-arrestin. Taken together, our findings show that pilocarpine can act as either an agonist or antagonist of M3R, depending on the cell type, expression level, and signaling pathway downstream of this receptor.

The Different Faces of the Pancreatic Islet

Type 1 diabetes (T1D) patients who receive pancreatic islet transplant experience significant improvement in their quality-of-life. This comes primarily through improved control of blood sugar levels, restored awareness of hypoglycemia, and prevention of serious and potentially life-threatening diabetes-associated complications, such as kidney failure, heart and vascular disease, stroke, nerve damage, and blindness. Therefore, beta cell replacement through transplantation of isolated islets is an important option in the treatment of T1D. However, lasting success of this promising therapy depends on durable survival and efficacy of the transplanted islets, which are directly influenced by the islet isolation procedures. Thus, isolating pancreatic islets with consistent and reliable quality is critical in the clinical application of islet transplantation.Quality of isolated islets is important in pre-clinical studies as well, as efforts to advance and improve clinical outcomes of islet transplant therapy have relied heavily on animal models ranging from rodents, to pigs, to nonhuman primates. As a result, pancreatic islets have been isolated from these and other species and used in a variety of in vitro or in vivo applications for this and other research purposes. Protocols for islet isolation have been somewhat similar across species, especially, in mammals. However, given the increasing evidence about the distinct structural and functional features of human and mouse islets, using similar methods of islet isolation may contribute to inconsistencies in the islet quality, immunogenicity, and experimental outcomes. This may also contribute to the discrepancies commonly observed between pre-clinical findings and clinical outcomes. Therefore, it is prudent to consider the particular features of pancreatic islets from different species when optimizing islet isolation protocols.In this chapter, we explore the structural and functional features of pancreatic islets from mice, pigs, nonhuman primates, and humans because of their prevalent use in nonclinical, preclinical, and clinical applications.

Metabolomics-identified metabolites associated with body mass index and prospective weight gain among Mexican American women

Objective

Obesity is a metabolic disease. However, the underlying molecular mechanisms linking metabolic profiles and weight gain are largely unknown.

Methods

Here, we used semi‐targeted metabolomics to assay 156 metabolites selected from 25 key metabolic pathways in plasma samples from 300 non‐smoking healthy women identified from Mano‐A‐Mano, the Mexican American Cohort study. The study subjects were randomly divided into two cohorts: training (N = 200) and testing (N = 100) cohorts. Linear regression and Cox proportional hazard regression were used to assess the effect of body mass index (BMI) at baseline on metabolite levels and the effects of metabolites on significant weight gain during a 5‐year follow‐up.

Results

At baseline, we observed 7 metabolites significantly associated with BMI in both training and testing cohorts. They were Methyl succinate, Asparagine, Urate, Kynurenic acid, Glycine, Glutamic acid, and Serine. In further analysis, we identified 6 metabolites whose levels at baseline predicted significant weight gain during 5‐year follow‐up in both cohorts. They were Acetylcholine, Leucine, Hippuric acid, Acetylglycine, Urate, and Xanthine.

Conclusions

The findings establish the baseline metabolic profiles for BMI, and suggest new metabolic targets for researchers attempting to understand the molecular mechanisms of weight gain and obesity.

Regulation of arcuate genes by developmental exposures to endocrine-disrupting compounds in female rats

Developmental exposure to endocrine-disrupting compounds (EDCs) alters reproduction and energy homeostasis, both of which are regulated by the arcuate nucleus (ARC). Little is known about the effects of EDC on ARC gene expression. In Experiment #1, pregnant dams were treated with either two doses of bisphenol A (BPA) or oil from embryonic day (E)18-21. Neonates were injected from postnatal day (PND)0-7. Vaginal opening, body weights, and ARC gene expression were measured. Chrm3 (muscarinic receptor 3) and Adipor1 (adiponectin receptor 1) were decreased by BPA. Bdnf (brain-derived neurotropic factor), Igf1 (insulin-like growth factor 1), Htr2c (5-hydroxytryptamine receptor), and Cck2r (cholescystokinin 2 receptor) were impacted. In Experiment #2, females were exposed to BPA, diethylstilbestrol (DES), di(2-ethylhexyl)phthalate, or methoxychlor (MXC) during E11-PND7. MXC and DES advanced the age of vaginal opening and ARC gene expression was impacted. These data indicate that EDCs alter ARC genes involved in reproduction and energy homeostasis in females.

Mapping physiological G protein-coupled receptor signaling pathways reveals a role for receptor phosphorylation in airway contraction

G protein-coupled receptors (GPCRs) are known to initiate a plethora of signaling pathways in vitro. However, it is unclear which of these pathways are engaged to mediate physiological responses. Here, we examine the distinct roles of Gq/11-dependent signaling and receptor phosphorylation-dependent signaling in bronchial airway contraction and lung function regulated through the M3-muscarinic acetylcholine receptor (M3-mAChR). By using a genetically engineered mouse expressing a G protein-biased M3-mAChR mutant, we reveal the first evidence, to our knowledge, of a role for M3-mAChR phosphorylation in bronchial smooth muscle contraction in health and in a disease state with relevance to human asthma. Furthermore, this mouse model can be used to distinguish the physiological responses that are regulated by M3-mAChR phosphorylation (which include control of lung function) from those responses that are downstream of G protein signaling. In this way, we present an approach by which to predict the physiological/therapeutic outcome of M3-mAChR-biased ligands with important implications for drug discovery.

Brain signaling systems in the Type 2 diabetes and metabolic syndrome: promising target to treat and prevent these diseases

The changes in the brain signaling systems play an important role in etiology and pathogenesis of Type 2 diabetes mellitus (T2DM) and metabolic syndrome (MS), being a possible cause of these diseases. Therefore, their restoration at the early stages of T2DM and MS can be regarded as a promising way to treat and prevent these diseases and their complications. The data on the functional state of the brain signaling systems regulated by insulin, IGF-1, leptin, dopamine, serotonin, melanocortins and glucagon-like peptide-1, in T2DM and MS, are analyzed. The pharmacological approaches to restoration of these systems and improvement of insulin sensitivity, energy expenditure, lipid metabolism, and to prevent diabetic complications are discussed.

M1 muscarinic acetylcholine receptor in Alzheimer's disease

The degeneration of cholinergic neurons and cholinergic hypofunction are pathologies associated with Alzheimer's disease (AD). Muscarinic acetylcholine receptors (mAChRs) mediate acetylcholine-induced neurotransmission and five mAChR subtypes (M1-M5) have been identified. Among them, M1 mAChR is widely expressed in the central nervous system and has been implicated in many physiological and pathological brain functions. In addition, M1 mAChR is postulated to be an important therapeutic target for AD and several other neurodegenerative diseases. In this article, we review recent progress in understanding the functional involvement of M1 mAChR in AD pathology and in developing M1 mAChR agonists for AD treatment.

A systems-pharmacology analysis of herbal medicines used in health improvement treatment: predicting potential new drugs and targets

For thousands of years, tonic herbs have been successfully used all around the world to improve health, energy, and vitality. However, their underlying mechanisms of action in molecular/systems levels are still a mystery. In this work, two sets of tonic herbs, so called Qi-enriching herbs (QEH) and Blood-tonifying herbs (BTH) in TCM, were selected to elucidate why they can restore proper balance and harmony inside body, organ and energy system. Firstly, a pattern recognition model based on artificial neural network and discriminant analysis for assessing the molecular difference between QEH and BTH was developed. It is indicated that QEH compounds have high lipophilicity while BTH compounds possess high chemical reactivity. Secondly, a systematic investigation integrating ADME (absorption, distribution, metabolism, and excretion) prediction, target fishing and network analysis was performed and validated on these herbs to obtain the compound-target associations for reconstructing the biologically-meaningful networks. The results suggest QEH enhance physical strength, immune system and normal well-being, acting as adjuvant therapy for chronic disorders while BTH stimulate hematopoiesis function in body. As an emerging approach, the systems pharmacology model might facilitate to understand the mechanisms of action of the tonic herbs, which brings about new development for complementary and alternative medicine.

Overview of muscarinic receptor subtypes

The physiological role of muscarinic receptors is highly complex and, although not completely understood, has become clearer over the last decade. Recent pharmacological evidence with novel compounds, together with data from transgenic mice, suggests that all five subtypes have defined functions in the nervous system as well as mediating the non neuronal, hormonal actions of acetylcholine. Numerous novel agonists, allosteric regulators, and antagonists have now been identified with authentic subtype specificity in vitro and in vivo. These compounds provide additional pharmacological opportunities for selective subtype modulation as well as a new generation of muscarinic receptor-based therapeutics.

Muscarinic mechanisms in psychotic disorders

Schizophrenia is a devastating disease with several broad symptom clusters and the current monoamine-based treatments do not adequately treat the disease, especially negative and cognitive symptoms. A proposed alternative approach for treating schizophrenia is through the use of compounds that activate certain muscarinic receptor subtypes, the so-called muscarinic cholinergic hypothesis theory. This theory has been revitalized with a number of recent and provocative findings including postmortem reports in schizophrenia patients showing decreased numbers of muscarinic M(1) and M(4) receptors in brain regions associated with schizophrenia as well as decreased muscarinic receptors in an in vivo imaging study. Studies with M(4) knockout mice have shown that there is a reciprocal relationship between M(4) and dopamine receptor function, and a number of muscarinic agonists have shown antidopaminergic activity in a variety of preclinical assays predictive of antipsychotic efficacy in the clinic. Furthermore, the M(1)/M(4) preferring partial agonist xanomeline has been shown to have antipsychotic-like and pro-cognitive activity in preclinical models and in clinical trials to decrease psychotic-like behaviors in Alzheimer's patients and positive, negative, and cognitive symptoms in patients with schizophrenia. Therefore, we propose that an agonist with M(1) and M(4) interactions would effectively treat core symptom clusters associated with schizophrenia. Currently, research is focused on developing subtype-selective muscarinic agonists and positive allosteric modulators that have reduced propensity for parasympathetic side-effects, but retain the therapeutic benefit observed with their less selective predecessors.

Non-neuronal regulation and repertoire of cholinergic receptors in organs

Many studies on the cholinergic pathway have indicated that cholinergic receptors, which are widely expressed in various cells, play an important role in all body organs. In this review, we present the concept that cholinergic responses are regulated through a neuronal or non-neuronal mechanism. The neuronal mechanism is a system in which acetylcholine binds to cholinergic receptors on target cells through the nerves. In the non-neuronal mechanism, acetylcholine, produced by neighboring cells in an autocrine/paracrine manner, binds to cholinergic receptors on target cells. Both mechanisms subsequently lead to physiological and pathophysiological responses. We also investigated the subunits/subtypes of cholinergic receptors on target cells, physiological and pathophysiological responses of the organs via cholinergic receptors, and extracellular factors that alter the subtypes/subunits of cholinergic receptors. Collectively, this concept will elucidate how cholinergic responses occur and will help us conduct further experiments to develop new therapeutic agents.

Genome-wide linkage and peak-wide association study of obesity-related quantitative traits in Caribbean Hispanics

Although obesity is more prevalent in Hispanics than non-Hispanic whites in the United States, little is known about the genetic etiology of the related traits in this population. To identify genetic loci influencing obesity in non-Mexican Hispanics, we performed a genome-wide linkage scan in 1,390 subjects from 100 Caribbean Hispanic families on six obesity-related quantitative traits: body mass index (BMI), body weight, waist circumference, waist-to-hip ratio, abdominal and average triceps skinfold thickness after adjusting for significant demographic and lifestyle factors. We then carried out an association analysis of the linkage peaks and the FTO gene in an independent community-based Hispanic subcohort (N = 652, 64% Caribbean Hispanics) from the Northern Manhattan Study. Evidence of linkage was strongest on 1q43 with multipoint LOD score of 2.45 (p = 0.0004) for body weight. Suggestive linkage evidence of LOD > 2.0 was also identified on 1q43 for BMI (LOD = 2.03), 14q32 for abdominal skinfold thickness (LOD = 2.17), 16p12 for BMI (LOD = 2.27) and weight (LOD = 2.26), and 16q23-24 for average triceps skinfold thickness (LOD = 2.32). In the association analysis of 6,440 single nucleotide polymorphisms (SNPs) under 1-LOD unit down regions of our linkage peaks on chromosome 1q43 and 16p12 as well as in the FTO gene, we found that two SNPs (rs6665519 and rs669231) on 1q43 and one FTO SNP (rs12447427) were significantly associated with BMI or body weight after adjustment for multiple testing. Our results suggest that in addition to FTO, multiple genetic loci, particularly those on 1q43 region, may contribute to the variations in obesity-related quantitative traits in Caribbean Hispanics.

Vagal control of pancreatic ß-cell proliferation

The physiological mechanisms that preserve pancreatic β-cell mass (BCM) are not fully understood. Although the regulation of islet function by the autonomic nervous system (ANS) is well established, its potential roles in BCM homeostasis and compensatory growth have not been adequately explored. The parasympathetic vagal branch of the ANS serves to facilitate gastrointestinal function, metabolism, and pancreatic islet regulation of glucose homeostasis, including insulin secretion. Given the functional importance of the vagus nerve and its branches to the liver, gut, and pancreas in control of digestion, motility, feeding behavior, and glucose metabolism, it may also play a role in BCM regulation. We have begun to examine the potential roles of the parasympathetic nervous system in short-term BCM maintenance by performing a selective bilateral celiac branch-vagus nerve transection (CVX) in normal Sprague-Dawley rats. CVX resulted in no detectable effects on basic metabolic parameters or food intake through 1 wk postsurgery. Although there were no differences in BCM or apoptosis in this 1-wk time frame, β-cell proliferation was reduced 50% in the CVX rats, correlating with a marked reduction in activated protein kinase B/Akt. Unexpectedly, acinar proliferation was increased 50% in these rats. These data suggest that the ANS, via the vagus nerve, contributes to the regulation of BCM maintenance at the level of cell proliferation and may also mediate the drive for enhanced growth under physiological conditions when insulin requirements have increased. Furthermore, the disparate effects of CVX on β-cell and acinar cells suggest that the endocrine and exocrine pancreas respond to different neural signals in regard to mass homeostasis.

Allosteric ligands of the glucagon-like peptide 1 receptor (GLP-1R) differentially modulate endogenous and exogenous peptide responses in a pathway-selective manner: implications for drug screening

The glucagon-like peptide-1 (GLP-1) receptor is a key regulator of insulin secretion and a major therapeutic target for treatment of diabetes. However, GLP-1 receptor function is complex, with multiple endogenous peptides that can interact with the receptor, including full-length (1-37) and truncated (7-37) forms of GLP-1 that can each exist in an amidated form and the related peptide oxyntomodulin. We have investigated two GLP-1 receptor allosteric modulators, Novo Nordisk compound 2 (6,7-dichloro2-methylsulfonyl-3-tert-butylaminoquinoxaline) and quercetin, and their ability to modify binding and signaling (cAMP formation, intracellular Ca(2+) mobilization, and extracellular signal-regulated kinase 1/2 phosphorylation) of each of the naturally occurring endogenous peptide agonists, as well as the clinically used peptide mimetic exendin-4. We identified and quantified stimulus bias across multiple endogenous peptides, with response profiles for truncated GLP-1 peptides distinct from those of either the full-length GLP-1 peptides or oxyntomodulin, the first demonstration of such behavior at the GLP-1 receptor. Compound 2 selectively augmented cAMP signaling but did so in a peptide-agonist dependent manner having greatest effect on oxyntomodulin, weaker effect on truncated GLP-1 peptides, and negligible effect on other peptide responses; these effects were principally driven by parallel changes in peptide agonist affinity. In contrast, quercetin selectively modulated calcium signaling but with effects only on truncated GLP-1 peptides or exendin and not oxyntomodulin or full-length peptides. These data have significant implications for how GLP-1 receptor targeted drugs are screened and developed, whereas the allosterically driven, agonist-selective, stimulus bias highlights the potential for distinct clinical efficacy depending on the properties of individual drugs.

Regulation of Golgi structure and secretion by receptor-induced G protein βγ complex translocation

We show that receptor induced G protein betagamma subunit translocation from the plasma membrane to the Golgi allows a receptor to initiate fragmentation and regulate secretion. A lung epithelial cell line, A549, was shown to contain an endogenous translocating G protein gamma subunit and exhibit receptor-induced Golgi fragmentation. Receptor-induced Golgi fragmentation was inhibited by a shRNA specific to the endogenous translocating gamma subunit. A kinase defective protein kinase D and a phospholipase C beta inhibitor blocked receptor-induced Golgi fragmentation, suggesting a role for this process in secretion. Consistent with betagamma translocation dependence, fragmentation induced by receptor activation was inhibited by a dominant negative nontranslocating gamma3. Insulin secretion was shown to be induced by muscarinic receptor activation in a pancreatic beta cell line, NIT-1. Induction of insulin secretion was also inhibited by the dominant negative gamma3 subunit consistent with the Golgi fragmentation induced by betagamma complex translocation playing a role in secretion.

beta-cell function in obese-hyperglycemic mice [ob/ob Mice]

This review summarizes key aspects of what has been learned about the physiology of pancreatic islets and leptin deficiency from studies in obese ob/ob mice. ob/ob Mice lack functional leptin. They are grossly overweight and hyperphagic particularly at young ages and develop severe insulin resistance with hyperglycemia and hyperinsulinemia. ob/ob Mice have large pancreatic islets. The beta-cells respond adequately to most stimuli, and ob/ob mice have been used as a rich source of pancreatic islets with high insulin release capacity. ob/ob Mice can perhaps be described as a model for the prediabetic state. The large capacity for islet growth and insulin release makes ob/ob mice a good model for studies on how beta-cells can cope with prolonged functional stress.

The Gbeta5-RGS7 complex selectively inhibits muscarinic M3 receptor signaling via the interaction between the third intracellular loop of the receptor and the DEP domain of RGS7

Regulators of G protein signaling (RGS) make up a diverse family primarily known as GTPase-activating proteins (GAPs) for heterotrimeric G proteins. In addition to the RGS domain, which is responsible for GAP activity, most RGS proteins contain other distinct structural motifs. For example, members of the R7 family of RGS proteins contain a DEP, GGL, and novel DHEX domain and are obligatory dimers with G protein beta subunit Gbeta5. Here we show that the Gbeta5-RGS7 complex can inhibit Ca2+ mobilization elicited by muscarinic acetylcholine receptor type 3 (M3R), but not by other Gq-coupled receptors such as M1, M5, histamine H1, and GNRH receptors. The isolated DEP domain of RGS7 is sufficient for the inhibition of M3R signaling, whereas the deletion of the DEP domain renders the Gbeta5-RGS7 complex ineffective. Deletion of a portion of the third intracellular loop allowed the receptor (M3R-short) to signal but rendered it insensitive to the effect of the Gbeta5-RGS7 complex. Accordingly, the recombinant DEP domain bound in vitro to the GST-fused i3 loop of the M3R. These results identify a novel molecular mechanism that can impart receptor subtype selectivity on signal transduction via Gq-coupled muscarinic receptors.

The pancreatic beta-cell in the islet and organ community

The endocrine pancreas consists of highly vascularized and innervated endocrine mini-organs--the islets of Langerhans. These contain multiple types of hormone-producing cells, including the insulin-secreting beta-cell. The major task of the fully differentiated beta-cell is the tight regulation of blood glucose levels by secreting insulin into the blood stream. This requires molecular features to measure glucose and produce, process, and release insulin by exocytosis. Now multiple interactions with endocrine and nonendocrine islet cells as well as with other organs have been shown to affect the developing as well as the mature beta-cell. Therefore, failure of any of these interactions can inhibit beta-cell differentiation and glucohomeostasis. Here we review recent reports on intrapancreatic cell-cell interactions as well as signals derived from extrapancreatic organs that affect the pancreatic beta-cell.

Duck pancreatic acinar cell as a unique model for independent cholinergic stimulation-secretion coupling

This paper investigated the role of acetylcholine (ACh) in physiological regulation of amylase secretion in avian exocrine pancreas. In the isolated duck pancreatic acini, ACh dose dependently stimulated amylase secretion, with a maximal effective concentration at 10 muM. The cAMP-mobilizing compounds forskolin, vasoactive intestinal peptide (VIP)/pituitary adenylate cyclase activating peptide (PACAP) receptor (VPAC) agonists PACAP-38 and PACAP-27 had no effect on the dose-response curve. ACh dose dependently induced increases in cytosolic Ca(2+) concentration ([Ca(2+)]( c )), with increasing concentrations transforming oscillations into plateau increases. Forskolin (10 muM), PACAP-38 (1 nM), PACAP-27 (1 nM), or VIP (10 nM) alone did not stimulate [Ca(2+)]( c ) increase; neither did they modulate ACh-induced oscillations, nor made ACh low concentration effective. These data indicate that ACh-stimulated zymogen secretion in duck pancreatic acinar cells is not subject to modulation from the cAMP signaling pathway; whereas it has been widely reported in the rodents that ACh-stimulated exocrine pancreatic secretion is significantly enhanced by cAMP-mobilizing agents. This makes the duck exocrine pancreas unique in that cholinergic stimulus-secretion coupling is not subject to cAMP regulation.

Islet G protein-coupled receptors as potential targets for treatment of type 2 diabetes

Islet dysfunction - characterized by a combination of defective insulin secretion, inappropriately high glucagon secretion and reduced beta-cell mass - has a central role in the pathophysiology of type 2 diabetes. Several G protein-coupled receptors (GPCRs) expressed in islet beta-cells are known to be involved in the regulation of islet function, and therefore are potential therapeutic targets. This is evident from the recent success of glucagon-like peptide 1 (GLP1) mimetics and dipeptidyl peptidase 4 (DPP4) inhibitors, which promote activation of the GLP1 receptor to stimulate insulin secretion and inhibit glucagon secretion, and also have the potential to increase beta-cell mass. Other islet beta-cell GPCRs that are involved in the regulation of islet function include the glucose-dependent insulinotropic peptide (GIP) receptor, lipid GPCRs, pleiotropic peptide GPCRs and islet biogenic amine GPCRs. This Review summarizes islet GPCR expression, signalling and function, and highlights their potential as targets for the treatment of type 2 diabetes.