Concomitant alpha7 and beta2 nicotinic AChR subunit deficiency leads to impaired energy homeostasis and increased physical activity in mice

New Multitarget Molecules Derived from Caffeine as Potentiators of the Cholinergic System

Cholinergic deficit is a characteristic factor of several pathologies, such as myasthenia gravis, some types of congenital myasthenic syndromes, and Alzheimer's Disease. Two molecular targets for its treatment are acetylcholinesterase (AChE) and nicotinic acetylcholine receptor (nAChR). In previous studies, we found that caffeine behaves as a partial nAChR agonist and confirmed that it inhibits AChE. Here, we present new bifunctional caffeine derivatives consisting of a theophylline ring connected to amino groups by different linkers. All of them were more potent AChE inhibitors than caffeine. Furthermore, although some of them also activated muscle nAChR as partial agonists, not all of them stabilized nAChR in its desensitized conformation. To understand the molecular mechanism underlying these results, we performed docking studies on AChE and nAChR. The nAChR agonist behavior of the compounds depends on their accessory group, whereas their ability to stabilize the receptor in a desensitized state depends on the interactions of the linker at the binding site. Our results show that the new compounds can inhibit AChE and activate nAChR with greater potency than caffeine and provide further information on the modulation mechanisms of pharmacological targets for the design of novel therapeutic interventions in cholinergic deficit.

Deletion of Ascl1 in pancreatic β-cells improves insulin secretion, promotes parasympathetic innervation, and attenuates dedifferentiation during metabolic stress

OBJECTIVE

ASCL1, a pioneer transcription factor, is essential for neural cell differentiation and function. Previous studies have shown that Ascl1 expression is increased in pancreatic β-cells lacking functional KATP channels or after feeding of a high fat diet (HFD) suggesting that it may contribute to the metabolic stress response of β-cells.

METHODS

We generated β-cell-specific Ascl1 knockout mice (Ascl1βKO) and assessed their glucose homeostasis, islet morphology and gene expression after feeding either a normal diet or HFD for 12 weeks, or in combination with a genetic disruption of Abcc8, an essential KATP channel component.

RESULTS

Ascl1 expression is increased in response to both a HFD and membrane depolarization and requires CREB-dependent Ca2+ signaling. No differences in glucose homeostasis or islet morphology were observed in Ascl1βKO mice fed a normal diet or in the absence of KATP channels. However, male Ascl1βKO mice fed a HFD exhibited decreased blood glucose levels, improved glucose tolerance, and increased β-cell proliferation. Bulk RNA-seq analysis of islets from Ascl1βKO mice from three studied conditions showed alterations in genes associated with the secretory function. HFD-fed Ascl1βKO mice showed the most extensive changes with increased expression of genes necessary for glucose sensing, insulin secretion and β-cell proliferation, and a decrease in genes associated with β-cell dysfunction, inflammation and dedifferentiation. HFD-fed Ascl1βKO mice also displayed increased expression of parasympathetic neural markers and cholinergic receptors that was accompanied by increased insulin secretion in response to acetylcholine and an increase in islet innervation.

CONCLUSIONS

Ascl1 expression is induced by stimuli that cause Ca2+-signaling to the nucleus and contributes in a multifactorial manner to the loss of β-cell function by promoting the expression of genes associated with cellular dedifferentiation, attenuating β-cells proliferation, suppressing acetylcholine sensitivity, and repressing parasympathetic innervation of islets. Thus, the removal of Ascl1 from β-cells improves their function in response to metabolic stress.

A mysterious triangle of blood, bones, and nerves

The relationship between bone tissue and bone marrow, which is responsible for hematopoiesis, is inseparable. Osteoblasts and osteocytes, which produce and consist of bone tissue, regulate the function of hematopoietic stem cells (HSC), the ancestors of all hematopoietic cells in the bone marrow. The peripheral nervous system finely regulates bone remodeling in bone tissue and modulates HSC function within the bone marrow, either directly or indirectly via modification of the HSC niche function. Peripheral nerve signals also play an important role in the development and progression of malignant tumors (including hematopoietic tumors) and normal tissues, and peripheral nerve control is emerging as a potential new therapeutic target. In this review, we summarize recent findings on the linkage among blood system, bone tissue, and peripheral nerves.

Xenobiotics Delivered by Electronic Nicotine Delivery Systems: Potential Cellular and Molecular Mechanisms on the Pathogenesis of Chronic Kidney Disease

Chronic kidney disease (CKD) is characterized as sustained damage to the renal parenchyma, leading to impaired renal functions and gradually progressing to end-stage renal disease (ESRD). Diabetes mellitus (DM) and arterial hypertension (AH) are underlying diseases of CKD. Genetic background, lifestyle, and xenobiotic exposures can favor CKD onset and trigger its underlying diseases. Cigarette smoking (CS) is a known modified risk factor for CKD. Compounds from tobacco combustion act through multi-mediated mechanisms that impair renal function. Electronic nicotine delivery systems (ENDS) consumption, such as e-cigarettes and heated tobacco devices, is growing worldwide. ENDS release mainly nicotine, humectants, and flavorings, which generate several byproducts when heated, including volatile organic compounds and ultrafine particles. The toxicity assessment of these products is emerging in human and experimental studies, but data are yet incipient to achieve truthful conclusions about their safety. To build up the knowledge about the effect of currently employed ENDS on the pathogenesis of CKD, cellular and molecular mechanisms of ENDS xenobiotic on DM, AH, and kidney functions were reviewed. Unraveling the toxic mechanisms of action and endpoints of ENDS exposures will contribute to the risk assessment and implementation of proper health and regulatory interventions.

Divergent Roles of α5 and β4 Nicotinic Receptor Subunits in Food Reward and Nicotine-induced Weight Loss in Male Mice

A major obstacle to successful smoking cessation is the prospect of weight gain. Despite a clear relationship between cigarette smoking and body weight, surprisingly little is known about the physiological and molecular mechanism by which nicotine affects energy homeostasis and food-motivated behaviors. Here we use loss-of-function mouse models to demonstrate that 2 nicotinic acetylcholine receptor (nAChR) subunits encoded by the CHRNA5-CHRNA3-CHRNB4 gene cluster, α5 and β4, exhibit divergent roles in food reward. We also reveal that β4-containing nAChRs are essential for the weight-lowering effects of nicotine in diet-induced obese mice. Finally, our data support the notion of crosstalk between incretin biology and nAChR signaling, as we demonstrate that the glycemic benefits of glucagon-like peptide-1 receptor activation partially relies on β4-containing nAChRs. Together, these data encourage further research into the role of cholinergic neurotransmission in regulating food reward and the translational pursuit of site-directed targeting of β4-containing nAChRs for treatment of metabolic disease.

TLR2 and TLR4 Modulate Mouse Ileal Motility by the Interaction with Muscarinic and Nicotinic Receptors

Irritable bowel syndrome (IBS) is a chronic functional bowel disorder characterized by intestinal dysmotility. Changes in intestinal microbiota (dysbiosis) can lead to alterations in neuro-muscular functions in the gut. Toll-like receptors (TLRs) 2 and 4 recognize intestinal bacteria and are involved in the motor response induced by gastrointestinal (GI) neurotransmitters. Acetylcholine (ACh) is a well-known neurotransmitter involved in the regulation of GI motility. This study aimed to evaluate the role of TLR2 and TLR4 in the intestinal motor-response induced by ACh in the mouse ileum, as well as the expression and function of the muscarinic and nicotinic ACh receptors. Muscle contractility studies showed that the contractions induced by ACh were significantly lower in TLR2^−/− and TLR4^−/− with respect to WT mice. In WT mice, the contractions induced by ACh were reduced in the presence of AF-DX AF-DX 116 (a muscarinic ACh receptor (mAChR) M2 antagonist), 4-DAMP (a mAChR M3 antagonist), mecamylamine (a nicotinic AChR receptor (nAChR) α3β4 antagonist) and α-bungarotoxin (a nAChR α7 antagonist). In TLR2^−/− mice, the contractions induced by ACh were increased by AF-DX 116 and mecamylamine. In TLR4^−/− mice, the contractions induced by ACh were reduced by α-bungarotoxin and 4-DAMP. The mRNA and protein expressions of M3 and α3 receptors were diminished in the ileum from TLR2^−/− and TLR4^−/− with respect to WT mice. However, the levels of mRNA and protein of β4 were diminished only in TLR4^−/− but not in TLR2^−/− mice. In conclusion, our results show that TLR2 and TLR4 modulates the motor responses to ACh in the mouse ileum. TLR2 acts on muscarinic M2 and M3 and nicotinic α3β4 ACh receptors, while TLR4 acts on muscarinic M3 and nicotinic α3β4 and α7 ACh receptors.

Potential Therapeutic Targeting Neurotransmitter Receptors in Diabetes

Neurotransmitters are signaling molecules secreted by neurons to coordinate communication and proper function among different sections in the central neural system (CNS) by binding with different receptors. Some neurotransmitters as well as their receptors are found in pancreatic islets and are involved in the regulation of glucose homeostasis. Neurotransmitters can act with their receptors in pancreatic islets to stimulate or inhibit the secretion of insulin (β cell), glucagon (α cell) or somatostatin (δ cell). Neurotransmitter receptors are either G-protein coupled receptors or ligand-gated channels, their effects on blood glucose are mainly decided by the number and location of them in islets. Dysfunction of neurotransmitters receptors in islets is involved in the development of β cell dysfunction and type 2 diabetes (T2D).Therapies targeting different transmitter systems have great potential in the prevention and treatment of T2D and other metabolic diseases.

Steroids, steroid associated substances and gestational diabetes mellitus

As gestational diabetes mellitus (GDM) is both a frequent and serious complication, steroid levels in pregnancy are extremely elevated and their role in pregnancy is crucial, this review focuses on the role of steroids and related substances in the GDM pathophysiology. Low SHBG levels are associated with insulin resistance and hyperinsulinemia, while also predicting a predisposition to GDM. Other relevant agents are placental hormones such as kisspeptin and CRH, playing also an important role beyond pregnancy, but which are synthesized here in smaller amounts in the hypothalamus. These hormones affect both the course of pregnancy as well as the synthesis of pregnancy steroids and may also be involved in the GDM pathophysiology. Steroids, whose biosynthesis is mainly provided by the fetal adrenal glands, placenta, maternal adrenal glands, and both maternal and fetal livers, are also synthesized in limited amounts directly in the pancreas and may influence the development of GDM. These substances involve the sulfated Δ5 steroids primarily acting via modulating different ion channels and influencing the development of GDM in different directions, mostly diabetogenic progesterone and predominantly anti-diabetic estradiol acting both in genomic and non-genomic way, androgens associated with IR and hyperinsulinemia, neuroactive steroids affecting the pituitary functioning, and cortisol whose production is stimulated by CRH but which suppresses its pro-inflammatory effects. Due to the complex actions of steroids, studies assessing their predominant effect and studies assessing their predictive values for estimating predisposition to GDM are needed.

Therapeutic potential of α7 nicotinic acetylcholine receptor agonists to combat obesity, diabetes, and inflammation

The cholinergic anti-inflammatory reflex (CAIR) represents an important homeostatic regulatory mechanism for sensing and controlling the body's response to inflammatory stimuli. Vagovagal reflexes are an integral component of CAIR whose anti-inflammatory effects are mediated by acetylcholine (ACh) acting at α7 nicotinic acetylcholine receptors (α7nAChR) located on cells of the immune system. Recently, it is appreciated that CAIR and α7nAChR also participate in the control of metabolic homeostasis. This has led to the understanding that defective vagovagal reflex circuitry underlying CAIR might explain the coexistence of obesity, diabetes, and inflammation in the metabolic syndrome. Thus, there is renewed interest in the α7nAChR that mediates CAIR, particularly from the standpoint of therapeutics. Of special note is the recent finding that α7nAChR agonist GTS-21 acts at L-cells of the distal intestine to stimulate the release of two glucoregulatory and anorexigenic hormones: glucagon-like peptide-1 (GLP-1) and peptide YY (PYY). Furthermore, α7nAChR agonist PNU 282987 exerts trophic factor-like actions to support pancreatic β-cell survival under conditions of stress resembling diabetes. This review provides an overview of α7nAChR function as it pertains to CAIR, vagovagal reflexes, and metabolic homeostasis. We also consider the possible usefulness of α7nAChR agonists for treatment of obesity, diabetes, and inflammation.

The Constitutive Lack of α7 Nicotinic Receptor Leads to Metabolic Disorders in Mouse

Objective: Type 2 diabetes (T2D) occurs by deterioration in pancreatic β-cell function and/or progressive loss of pancreatic β-cell mass under the context of insulin resistance. α7 nicotinic acetylcholine receptor (nAChR) may contribute to insulin sensitivity but its role in the pathogenesis of T2D remains undefined. We investigated whether the systemic lack of α7 nAChR was sufficient to impair glucose homeostasis. Methods: We used an α7 nAChR knock-out (α7^−/−) mouse model fed a standard chow diet. The effects of the lack of α7 nAChR on islet mass, insulin secretion, glucose and insulin tolerance, body composition, and food behaviour were assessed in vivo and ex vivo experiments. Results: Young α7^−/− mice display a chronic mild high glycemia combined with an impaired glucose tolerance and a marked deficit in β-cell mass. In addition to these metabolic disorders, old mice developed adipose tissue inflammation, elevated plasma free fatty acid concentrations and presented glycolytic muscle insulin resistance in old mice. Finally, α7^−/− mice, fed a chow diet, exhibited a late-onset excessive gain in body weight through increased fat mass associated with higher food intake. Conclusion: Our work highlights the important role of α7 nAChR in glucose homeostasis. The constitutive lack of α7 nAChR suggests a novel pathway influencing the pathogenesis of T2D.

Nicotinic acetylcholine receptor signaling regulates inositol-requiring enzyme 1α activation to protect β-cells against terminal unfolded protein response under irremediable endoplasmic reticulum stress

AIMS/INTRODUCTION

Under irremediable endoplasmic reticulum (ER) stress, hyperactivated inositol-requiring enzyme 1α (IRE1α) triggers the terminal unfolded protein response (T-UPR), causing crucial cell dysfunction and apoptosis. We hypothesized that nicotinic acetylcholine receptor (nAChR) signaling regulates IRE1α activation to protect β-cells from the T-UPR under ER stress.

MATERIALS AND METHODS

The effects of nicotine on IRE1α activation and key T-UPR markers, thioredoxin-interacting protein and insulin/proinsulin, were analyzed by real-time polymerase chain reaction and western blotting in rat INS-1 and human EndoC-βH1 β-cell lines. Doxycycline-inducible IRE1α overexpression or ER stress agents were used to induce IRE1α activation. An α7 subunit-specific nAChR agonist (PNU-282987) and small interfering ribonucleic acid for α7 subunit-specific nAChR were used to modulate nAChR signaling.

RESULTS

Nicotine inhibits the increase in thioredoxin-interacting protein and the decrease in insulin 1/proinsulin expression levels induced by either forced IRE1α hyperactivation or ER stress agents. Nicotine attenuated X-box-binding protein-1 messenger ribonucleic acid site-specific splicing and IRE1α autophosphorylation induced by ER stress. Furthermore, PNU-282987 attenuated T-UPR induction by either forced IRE1α activation or ER stress agents. The effects of nicotine on attenuating thioredoxin-interacting protein and preserving insulin 1 expression levels were attenuated by pharmacological and genetic inhibition of α7 nAChR. Finally, nicotine suppressed apoptosis induced by either forced IRE1α activation or ER stress agents.

CONCLUSIONS

Our findings suggest that nAChR signaling regulates IRE1α activation to protect β-cells from the T-UPR and apoptosis under ER stress partly through α7 nAChR. Targeting nAChR signaling to inhibit the T-UPR cascade may therefore hold therapeutic promise by thwarting β-cell death in diabetes.

KLB, encoding β-Klotho, is mutated in patients with congenital hypogonadotropic hypogonadism

Congenital hypogonadotropic hypogonadism (CHH) is a rare genetic form of isolated gonadotropin‐releasing hormone (GnRH) deficiency caused by mutations in > 30 genes. Fibroblast growth factor receptor 1 (FGFR1) is the most frequently mutated gene in CHH and is implicated in GnRH neuron development and maintenance. We note that a CHH FGFR1 mutation (p.L342S) decreases signaling of the metabolic regulator FGF21 by impairing the association of FGFR1 with β‐Klotho (KLB), the obligate co‐receptor for FGF21. We thus hypothesized that the metabolic FGF21/KLB/FGFR1 pathway is involved in CHH. Genetic screening of 334 CHH patients identified seven heterozygous loss‐of‐function KLB mutations in 13 patients (4%). Most patients with KLB mutations (9/13) exhibited metabolic defects. In mice, lack of Klb led to delayed puberty, altered estrous cyclicity, and subfertility due to a hypothalamic defect associated with inability of GnRH neurons to release GnRH in response to FGF21. Peripheral FGF21 administration could indeed reach GnRH neurons through circumventricular organs in the hypothalamus. We conclude that FGF21/KLB/FGFR1 signaling plays an essential role in GnRH biology, potentially linking metabolism with reproduction.

Stoichiometry of the Heteromeric Nicotinic Receptors of the Renshaw Cell

Neuronal nicotinic acetylcholine receptors (nAChRs) are pentamers built from a variety of subunits. Some are homomeric assemblies of α subunits, others heteromeric assemblies of α and β subunits which can adopt two stoichiometries (2α:3β or 3α:2β). There is evidence for the presence of heteromeric nAChRs with the two stoichiometries in the CNS, but it has not yet been possible to identify them at a given synapse. The 2α:3β receptors are highly sensitive to agonists, whereas the 3α:2β stoichiometric variants, initially described as low sensitivity receptors, are indeed activated by low and high concentrations of ACh. We have taken advantage of the discovery that two compounds (NS9283 and Zn) potentiate selectively the 3α:2β nAChRs to establish (in mice of either sex) the presence of these variants at the motoneuron-Renshaw cell (MN-RC) synapse. NS9283 prolonged the decay of the two-component EPSC mediated by heteromeric nAChRs. NS9283 and Zn also prolonged spontaneous EPSCs involving heteromeric nAChRs, and one could rule out prolongations resulting from AChE inhibition by NS9283. These results establish the presence of 3α:2β nAChRs at the MN-RC synapse. At the functional level, we had previously explained the duality of the EPSC by assuming that high ACh concentrations in the synaptic cleft account for the fast component and that spillover of ACh accounts for the slow component. The dual ACh sensitivity of 3α:2β nAChRs now allows to attribute to these receptors both components of the EPSC.SIGNIFICANCE STATEMENT Heteromeric nicotinic receptors assemble α and β subunits in pentameric structures, which can adopt two stoichiometries: 3α:2β or 2α:3β. Both stoichiometric variants are present in the CNS, but they have never been located and characterized functionally at the level of an identified synapse. Our data indicate that 3α:2β receptors are present at the spinal cord synapses between motoneurons and Renshaw cells, where their dual mode of activation (by high concentrations of ACh for synaptic receptors, by low concentrations of ACh for extrasynaptic receptors) likely accounts for the biphasic character of the synaptic current. More generally, 3α:2β nicotinic receptors appear unique by their capacity to operate both in the cleft of classical synapses and at extrasynaptic locations.

Anti-inflammatory and autonomic effects of electroacupuncture in a rat model of diet-induced obesity

OBJECTIVE

To study the effect of electroacupuncture (EA) on the cholinergic anti-inflammatory pathway (CAP) by measurement of vagal activity in rats with high-fat diet (HFD)-induced obesity.

METHODS

Diet-induced obesity (DIO) was induced in 30 rats by feeding them a HFD for 12 weeks. A further 10 rats fed normal food comprised the lean diet (LD) control group. DIO rats were further subdivided into three groups that received a HFD only (HFD group, n=10), a HFD plus electroacupuncture (HFD+EA group, n=10) or a HFD plus minimal acupuncture (HFD+MA group, n=10). EA and MA treatments were continued for 8 weeks. Heart rate variability (HRV) was used to measure the function of the autonomic nervous system before and after treatment. ELISA was used to determine acetylcholine (ACh) and tumour necrosis factor (TNF)-α levels in the serum. Real-time PCR was used to assess the mRNA expression of α7-subtype nicotinic acetylcholine cholinergic receptors (α7nAChRs) and TNF-α in the mesenteric white adipose tissues (MWAT).

RESULTS

EA but not MA significantly reduced rats' bodyweight. No difference was found in the low frequency (LF), high frequency (HF) and the balance between LF and HF (LF/HF) components of HRV before treatment. After the EA intervention, HF was elevated and LF/HF was reduced in the HFD+EA group comparedwith the HFD group. TNF-α in the serum and MWAT were increased in the HFD group, but were reduced in the HFD+EA group. Furthermore, EA promoted expression of α7nAChRs and ACh in the MWAT. There was no difference between the HFD and HFD+MA groups for any indices.

CONCLUSIONS

EA enhanced vagal activity, promoted ACh release and activated α7nAChRs in the MWAT, leading to inhibition of proinflammatory cytokine production.

Designing selective modulators for the nicotinic receptor subtypes: challenges and opportunities

Nicotinic receptors are membrane proteins involved in several physiological processes. They are considered suitable drug targets for various CNS disorders or conditions, as shown by the large number of compounds which have entered clinical trials. In recent years, nonconventional agonists have been discovered: positive allosteric modulators, allosteric agonists, site-specific agonists and silent desensitizers are compounds able to modulate the receptor interacting at sites different from the orthodox one, or to desensitize the receptor without prior opening. While these new findings can further complicate the pharmacology of these proteins and the design and optimization of ligands, they undoubtedly offer new opportunities to find drugs for the many therapeutic indications involving nicotinic receptors.

Cholinergic activation suppresses palmitate-induced macrophage activation and improves acylation stimulating protein resistance in co-cultured adipocytes

Acylation-stimulating protein (ASP), produced through activation of the alternative complement immune system, modulates lipid metabolism. Using a trans-well co-culture cell model, the mitigating role of α7-nicotinic acetylcholine receptor (α7nAChR)-mediated cholinergic pathway on ASP resistance was evaluated. ASP signaling in adipocytes via its receptor C5L2 and signaling intermediates Gαq, Gβ, phosphorylated protein kinase C-α, and protein kinase C-ζ were markedly suppressed in the presence of TNFα or medium from palmitate-treated RAW264.7 macrophages, indicating ASP resistance. There was no direct effect of α7nAChR activation in 3T3-L1 cell culture. However, α7nAChR activation almost completely reversed the ASP resistance in adipocytes co-cultured with palmitate-treated RAW264.7 macrophages. Further, α7nAChR activation could suppress the production of pro-inflammatory molecules TNFα and interleukin-6 produced from palmitate-treated co-cultured macrophages. These results suggest that macrophages play a significant role in the pathogenesis of ASP resistance and α7nAChR activation secondarily improves adipose ASP resistance through suppression of inflammation in macrophages. Impact statement 1. Adipocyte-macrophage interaction in acylation-stimulating protein (ASP) resistance 2. Lipotoxicity induced inflammatory response in ASP resistance 3. A vicious circle between lipotoxicity and inflammatory response in ASP resistance 4. Cholinergic modulation of inflammatory response in adipocyte and macrophage.

Activation of Nicotinic Acetylcholine Receptors Decreases Apoptosis in Human and Female Murine Pancreatic Islets

Type 1 diabetes (T1DM) results from destruction of most insulin-secreting pancreatic β-cells. The persistence of β-cells decades after the onset of the disease indicates that the resistance of individual cells to the autoimmune insult is heterogeneous and might depend on the metabolic status of a cell at a given moment. The aim of this study is to investigate whether activation of nicotinic acetylcholine receptors (nACh-Rs) could increase β-cell resistance against the adverse environment prevailing at the onset of T1DM. Here, we show that nACh-R activation by nicotine and choline, 2 agonists of the receptor, decreases murine and human β-cell apoptosis induced by proinflammatory cytokines known to be present in the islet environment at the onset of T1DM. The protective mechanism activated by nicotine and choline involves attenuation of mitochondrial outer membrane permeabilization via modulation of endoplasmic reticulum stress, of the activity of B-cell lymphoma 2 family proteins and cytoplasmic calcium levels. Local inflammation and endoplasmic reticulum stress being key determinants of β-cell death in T1DM, we conclude that pharmacological activation of nACh-R could represent a valuable therapeutic option in the modulation of β-cell death in T1DM.

Alterations in alpha5* nicotinic acetylcholine receptors result in midbrain- and hippocampus-dependent behavioural and neural impairments

RATIONALE

Evidence links alterations in α5-containing nicotinic receptors (α5*-nAChRs) to nicotine addiction. Notably, the rs16969968 polymorphism in the α5 gene (α5SNP) increases the risk for heavy smoking and impairs nicotine-rewarding properties in mice. Additional work is needed to understand how native and polymorphic α5*-nAChRs contribute to processes associated with the risk for nicotine addiction.

OBJECTIVES

We aimed at understanding the contribution of α5*-nAChRs to endophenotypes like increased responses to novelty and anxiety, known to promote vulnerability to addiction, and to the response of the dopamine and serotonin systems to nicotine.

METHODS

Behavioural phenotypes were investigated in mice lacking the α5 gene (α5(-/-)). Nicotine injections were performed to test the consequences of nicotine exposure on the phenotypes identified. Dopamine and serotonin signalling were assessed using in vivo microdialysis and electrophysiology. We used lentiviral vectors to compare the consequences of re-expressing either the α5 wild-type allele or the α5SNP in specific brain areas of α5(-/-) mice.

RESULTS

α5(-/-) mice did not exhibit high responses to novelty but showed decreased novelty-induced rearing behaviour together with high anxiety. Exposure to high doses of nicotine rescued these phenotypes. We identified altered spontaneous and nicotine-elicited serotonin and dopamine activity in α5(-/-) mice. Re-expression of α5 in the ventral tegmental area and hippocampus rescued rearing and anxiety levels in α5(-/-) mice, respectively. When expressing the α5SNP instead, this resulted in a knockout-like phenotype for both behaviours.

CONCLUSIONS

We propose that altered α5*-nAChR cholinergic signalling contributes to emotional/behavioural impairments that may be alleviated by nicotine consumption.

Evidence for the role of β2* nAChR desensitization in regulating body weight in obese mice

Nicotine's effect on food intake and body weight has been well documented; however, the relevant receptors underlying these effects have not been firmly established. The purpose of the present study was to: (1) identify the nicotinic acetylcholine receptor (nAChR) subtype involved in food intake and body weight; (2) establish whether food intake and body weight reduction produced by nicotinic drugs are due to activation or desensitization of nAChRs; and, (3) assess the role of the melanocortin system in nicotinic drug effects on food intake and body weight. To identify the nAChR, we tested the effect of sazetidine-A (SAZ-A), a relatively selective ligand of β2-containing nAChRs, on food intake and body weight in obese mice. SAZ-A (3 mg/kg; SC) administered twice-daily significantly decreased food intake and body weight. To assess whether these effects involved desensitization, SAZ-A was administered to non-obese mice via osmotic pump, which, due to its slow sustained drug delivery method, causes prolonged desensitization. SAZ-A via osmotic pump delivery significantly decreased the gain in body weight and reduced food intake. In contrast, body weight was unaffected by SAZ-A in β2(-/-) mice or in mice lacking the melanocortin 4 receptor (MC4R). These results indicate that β2 containing nAChRs are essential to SAZ-A's inhibitory effect on body weight and food intake and engage the melanocortin system.

Ion Channels in Obesity: Pathophysiology and Potential Therapeutic Targets

Obesity is a multifactorial disease related to metabolic disorders and associated with genetic determinants. Currently, ion channels activity has been linked to many of these disorders, in addition to the central regulation of food intake, energetic balance, hormone release and response, as well as the adipocyte cell proliferation. Therefore, the objective of this work is to review the current knowledge about the influence of ion channels in obesity development. This review used different sources of literature (Google Scholar, PubMed, Scopus, and Web of Science) to assess the role of ion channels in the pathophysiology of obesity. Ion channels present diverse key functions, such as the maintenance of physiological homeostasis and cell proliferation. Cell biology and pharmacological experimental evidences demonstrate that proliferating cells exhibit ion channel expression, conductance, and electrical properties different from the resting cells. Thereby, a large variety of ion channels has been identified in the pathogenesis of obesity such as potassium, sodium, calcium and chloride channels, nicotinic acetylcholine receptor and transient receptor potential channels. The fundamental involvement of these channels on the generation of obesity leads to the progress in the knowledge about the mechanisms responsible for the obesity pathophysiology, consequently emerging as new targets for pharmacological modulation.

Activation of α7 Nicotinic Acetylcholine Receptor Decreases On-site Mortality in Crush Syndrome through Insulin Signaling-Na/K-ATPase Pathway

On-site mortality in crush syndrome remains high due to lack of effective drugs based on definite diagnosis. Anisodamine (Ani) is widely used in China for treatment of shock, and activation of α7 nicotinic acetylcholine receptor (α7nAChR) mediates such antishock effect. The present work was designed to test whether activation of α7nAChR with Ani decreased mortality in crush syndrome shortly after decompression. Sprague-Dawley rats and C57BL/6 mice with crush syndrome were injected with Ani (20 mg/kg and 28 mg/kg respectively, i.p.) 30 min before decompression. Survival time, serum potassium, insulin, and glucose levels were observed shortly after decompression. Involvement of α7nAChR was verified with methyllycaconitine (selective α7nAChR antagonist) and PNU282987 (selective α7nAChR agonist), or in α7nAChR knockout mice. Effect of Ani was also appraised in C2C12 myotubes. Ani reduced mortality and serum potassium and enhanced insulin sensitivity shortly after decompression in animals with crush syndrome, and PNU282987 exerted similar effects. Such effects were counteracted by methyllycaconitine or in α7nAChR knockout mice. Mortality and serum potassium in rats with hyperkalemia were also reduced by Ani. Phosphorylation of Na/K-ATPase was enhanced by Ani in C2C12 myotubes. Inhibition of tyrosine kinase on insulin receptor, phosphoinositide 3-kinase, mammalian target of rapamycin, signal transducer and activator of transcription 3, and Na/K-ATPase counteracted the effect of Ani on extracellular potassium. These findings demonstrated that activation of α7nAChR could decrease on-site mortality in crush syndrome, at least in part based on the decline of serum potassium through insulin signaling-Na/K-ATPase pathway.

Nicotinic acetylcholine receptors modulate osteoclastogenesis

Background

Our aim was to investigate the role of nicotinic acetylcholine receptors (nAChRs) in in-vitro osteoclastogenesis and in in-vivo bone homeostasis.

Methods

The presence of nAChR subunits as well as the in-vitro effects of nAChR agonists were investigated by ex vivo osteoclastogenesis assays, real-time polymerase chain reaction, Western blot and flow cytometry in murine bone marrow-derived macrophages differentiated in the presence of recombinant receptor activator of nuclear factor kappa B ligand (RANKL) and macrophage colony-stimulating factor (M-CSF). The bone phenotype of mice lacking various nAChR subunits was investigated by peripheral quantitative computed tomography and histomorphometric analysis. Oscillations in the intracellular calcium concentration were detected by measuring the Fura-2 fluorescence intensity.

Results

We could demonstrate the presence of several nAChR subunits in bone marrow-derived macrophages stimulated with RANKL and M-CSF, and showed that they are capable of producing acetylcholine. nAChR ligands reduced the number of osteoclasts as well as the number of tartrate-resistant acidic phosphatase-positive mononuclear cells in a dose-dependent manner. In vitro RANKL-mediated osteoclastogenesis was reduced in mice lacking α7 homomeric nAChR or β2-containing heteromeric nAChRs, while bone histomorphometry revealed increased bone volume as well as impaired osteoclastogenesis in male mice lacking the α7 nAChR. nAChR ligands inhibited RANKL-induced calcium oscillation, a well-established phenomenon of osteoclastogenesis. This inhibitory effect on Ca²⁺ oscillation subsequently led to the inhibition of RANKL-induced NFATc1 and c-fos expression after long-term treatment with nicotine.

Conclusions

We have shown that the activity of nAChRs conveys a marked effect on osteoclastogenesis in mice. Agonists of these receptors inhibited calcium oscillations in osteoclasts and blocked the RANKL-induced activation of c-fos and NFATc1. RANKL-mediated in-vitro osteoclastogenesis was reduced in α7 knockout mice, which was paralleled by increased tibial bone volume in male mice in vivo.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-016-0961-x) contains supplementary material, which is available to authorized users.

High-fat diet during pregnancy and lactation impairs the cholinergic anti-inflammatory pathway in the liver and white adipose tissue of mouse offspring

Cholinergic anti-inflammatory pathway (CAP) prevents inflammatory cytokines production. The main was to evaluate the effect of maternal obesity on cholinergic pathway in the offspring. Female mice were subjected to either standard chow (SC) or high-fat diet (HFD) during pregnancy and the lactation period. After weaning, only male offspring from HFD dams (HFD-O) and from SC dams (SC-O) were fed the SC diet. Key proteins of the CAP were downregulated and serum TNF-α was elevated in the HFD-O mice. STAT3 and NF-κB activation in HFD-O mice ICV injected with nicotine (agonist) were lower than SC-O mice. Basal cholinesterase activity was upregulated in HFD-O mice in both investigated tissues. Lipopolysaccharide increased TNF-α and IL-1β expression in the liver and WAT of SC-O mice, but this effect was greater in HFD-O mice. In conclusion these changes exacerbated cytokine production in response to LPS and contributed to the reduced sensitivity of the CAP.

Nighttime Administration of Nicotine Improves Hepatic Glucose Metabolism via the Hypothalamic Orexin System in Mice

Nicotine is known to affect the metabolism of glucose; however, the underlying mechanism remains unclear. Therefore, we here investigated whether nicotine promoted the central regulation of glucose metabolism, which is closely linked to the circadian system. The oral intake of nicotine in drinking water, which mainly occurred during the nighttime active period, enhanced daily hypothalamic prepro-orexin gene expression and reduced hyperglycemia in type 2 diabetic db/db mice without affecting body weight, body fat content, and serum levels of insulin. Nicotine administered at the active period appears to be responsible for the effect on blood glucose, because nighttime but not daytime injections of nicotine lowered blood glucose levels in db/db mice. The chronic oral treatment with nicotine suppressed the mRNA levels of glucose-6-phosphatase, the rate-limiting enzyme of gluconeogenesis, in the liver of db/db and wild-type control mice. In the pyruvate tolerance test to evaluate hepatic gluconeogenic activity, the oral nicotine treatment moderately suppressed glucose elevations in normal mice and mice lacking dopamine receptors, whereas this effect was abolished in orexin-deficient mice and hepatic parasympathectomized mice. Under high-fat diet conditions, the oral intake of nicotine lowered blood glucose levels at the daytime resting period in wild-type, but not orexin-deficient, mice. These results indicated that the chronic daily administration of nicotine suppressed hepatic gluconeogenesis via the hypothalamic orexin-parasympathetic nervous system. Thus, the results of the present study may provide an insight into novel chronotherapy for type 2 diabetes that targets the central cholinergic and orexinergic systems.

Cross-talk between α7 nAChR-mediated cholinergic pathway and acylation stimulating protein signaling in 3T3-L1 adipocytes: role of NFκB and STAT3

Inflammation is a key feature in adipose tissue, especially in association with obesity comorbidies. The novel adipokine acylation stimulating protein (ASP) is one factor implicated in the inflammatory response. The disruption of the α7 nicotine acetylcholine receptor (α7nAChR), an important component of the endogenous non-neural cholinergic defense system, may exacerbate sustained inflammatory phenotype. We examined cholinergic regulation of ASP-initiated inflammatory response in 3T3-L1 adipocytes. Our results show that preincubation of 3T3-L1 cells with α7nAChR agonist GTS-21 significantly reduces ASP-mediated chemokine MCP-1 secretion, which is regulated though nuclear factor κB (NFκB) and signal transducer and activator of transcription 3 (STAT3). Treatment of 3T3-L1 cells with GTS-21 significantly reduced NFκB activation by DNA binding and STAT3 activation by disturbing post-translational modification.

Small changes in bone structure of female α7 nicotinic acetylcholine receptor knockout mice

Background

Recently, analysis of bone from knockout mice identified muscarinic acetylcholine receptor subtype M3 (mAChR M3) and nicotinic acetylcholine receptor (nAChR) subunit α2 as positive regulator of bone mass accrual whereas of male mice deficient for α7-nAChR (α7KO) did not reveal impact in regulation of bone remodeling. Since female sex hormones are involved in fair coordination of osteoblast bone formation and osteoclast bone degradation we assigned the current study to analyze bone strength, composition and microarchitecture of female α7KO compared to their corresponding wild-type mice (α7WT).

Methods

Vertebrae and long bones of female 16-week-old α7KO (n = 10) and α7WT (n = 8) were extracted and analyzed by means of histological, radiological, biomechanical, cell- and molecular methods as well as time of flight secondary ion mass spectrometry (ToF-SIMS) and transmission electron microscopy (TEM).

Results

Bone of female α7KO revealed a significant increase in bending stiffness (p < 0.05) and cortical thickness (p < 0.05) compared to α7WT, whereas gene expression of osteoclast marker cathepsin K was declined. ToF-SIMS analysis detected a decrease in trabecular calcium content and an increase in C₄H₆N⁺ (p < 0.05) and C₄H₈N⁺ (p < 0.001) collagen fragments whereas a loss of osteoid was found by means of TEM.

Conclusions

Our results on female α7KO bone identified differences in bone strength and composition. In addition, we could demonstrate that α7-nAChRs are involved in regulation of bone remodelling. In contrast to mAChR M3 and nAChR subunit α2 the α7-nAChR favours reduction of bone strength thereby showing similar effects as α7β2-nAChR in male mice. nAChR are able to form heteropentameric receptors containing α- and β-subunits as well as the subunits α7 can be arranged as homopentameric cation channel. The different effects of homopentameric and heteropentameric α7-nAChR on bone need to be analysed in future studies as well as gender effects of cholinergic receptors on bone homeostasis.