[Show abstract][Hide abstract] ABSTRACT: Agouti-related peptide (AgRP) neurons of the hypothalamus play a key role in regulating food intake and body weight, by releasing three different orexigenic molecules: AgRP; GABA; and neuropeptide Y. AgRP neurons express various G protein-coupled receptors (GPCRs) with different coupling properties, including G s -linked GPCRs. At present, the potential role of G s -coupled GPCRs in regulating the activity of AgRP neurons remains unknown. Here we show that the activation of G s -coupled receptors expressed by AgRP neurons leads to a robust and sustained increase in food intake. We also provide detailed mechanistic data linking the stimulation of this class of receptors to the observed feeding phenotype. Moreover, we show that this pathway is clearly distinct from other GPCR signalling cascades that are operative in AgRP neurons. Our data suggest that drugs able to inhibit this signalling pathway may become useful for the treatment of obesity.
Preview · Article · Jan 2016 · Nature Communications
[Show abstract][Hide abstract] ABSTRACT: G protein-coupled receptors (GPCRs) regulate virtually all physiological functions including the release of insulin from pancreatic β-cells. β-Cell M3 muscarinic receptors (M3Rs) are known to play an essential role in facilitating insulin release and maintaining proper whole-body glucose homeostasis. As is the case with other GPCRs, M3R activity is regulated by phosphorylation by various kinases, including GPCR kinases and casein kinase 2 (CK2). At present, it remains unknown which of these various kinases are physiologically relevant for the regulation of β-cell activity. In the present study, we demonstrate that inhibition of CK2 in pancreatic β-cells, knockdown of CK2α expression, or genetic deletion of CK2α in β-cells of mutant mice selectively augmented M3R-stimulated insulin release in vitro and in vivo. In vitro studies showed that this effect was associated with an M3R-mediated increase in intracellular calcium levels. Treatment of mouse pancreatic islets with CX4945, a highly selective CK2 inhibitor, greatly reduced agonist-induced phosphorylation of β-cell M3Rs, indicative of CK2-mediated M3R phosphorylation. We also showed that inhibition of CK2 greatly enhanced M3R-stimulated insulin secretion in human islets. Finally, CX4945 treatment protected mice against diet-induced hyperglycemia and glucose intolerance in an M3R-dependent fashion. Our data demonstrate, for the first time to our knowledge, the physiological relevance of CK2 phosphorylation of a GPCR and suggest the novel concept that kinases acting on β-cell GPCRs may represent novel therapeutic targets.
No preview · Article · Nov 2015 · Proceedings of the National Academy of Sciences
[Show abstract][Hide abstract] ABSTRACT: A balanced interaction between dopaminergic and cholinergic signaling in the striatum is critical to goal-directed behavior. But how this interaction modulates corticostriatal synaptic plasticity underlying learned actions remains unclear-particularly in direct-pathway spiny projection neurons (dSPNs). Our studies show that in dSPNs, endogenous cholinergic signaling through M4 muscarinic receptors (M4Rs) promoted long-term depression of corticostriatal glutamatergic synapses, by suppressing regulator of G protein signaling type 4 (RGS4) activity, and blocked D1 dopamine receptor dependent long-term potentiation (LTP). Furthermore, in a mouse model of L-3,4-dihydroxyphenylalanine (L-DOPA)-induced dyskinesia (LID) in Parkinson's disease (PD), boosting M4R signaling with positive allosteric modulator (PAM) blocked aberrant LTP in dSPNs, enabled LTP reversal, and attenuated dyskinetic behaviors. An M4R PAM also was effective in a primate LID model. Taken together, these studies identify an important signaling pathway controlling striatal synaptic plasticity and point to a novel pharmacological strategy for alleviating LID in PD patients.
[Show abstract][Hide abstract] ABSTRACT: During the past few years, CNO-sensitive designer G protein-coupled receptors (GPCRs) known as
DREADDs (designer receptors exclusively activated by designer drugs) have emerged as powerful new
tools for the study of GPCR physiology. In this chapter, we present protocols employing adeno-associated
viruses (AAVs) to express a Gq-coupled DREADD (Dq) in two metabolically important cell types, AgRP
neurons of the hypothalamus and hepatocytes of the liver. We also provide examples dealing with the metabolic
analysis of the Dq mutant mice after administration of CNO in vivo. The approaches described in this
chapter can be applied to other members of the DREADD family and, of course, different cell types. It is
likely that the use of DREADD technology will identify physiologically important signaling pathways that
can be targeted for therapeutic purpose.
[Show abstract][Hide abstract] ABSTRACT: Cholinergic transmission in the striatum functions as a key modulator of dopamine (DA) transmission and synaptic plasticity, both of which are required for reward and motor learning. Acetylcholine (ACh) can elicit striatal DA release through activation of nicotinic ACh receptors (nAChRs) on DA axonal projections. However, it remains controversial how muscarinic ACh receptors (mAChRs) modulate striatal DA release, with studies reporting both potentiation and depression of striatal DA transmission by mAChR agonists. This study investigates the mAChR-mediated regulation of release from three types of midbrain neurons that project to striatum: DA, DA/glutamate, and glutamate neurons. We found that M5 mAChRs potentiate DA and glutamate release only from DA and DA/glutamate projections from the midbrain. We also show that M2/M4 mAChRs depress the nAChR-dependent mechanism of DA release in the striatum. These results suggest that M5 receptors on DA neuron terminals enhance DA release, whereas M2/M4 autoreceptors on cholinergic terminals inhibit ACh release and subsequent nAChR-dependent DA release. Our findings clarify the mechanisms of mAChR-dependent modulation of DA and glutamate transmission in the striatum.
Full-text · Article · Jun 2015 · Proceedings of the National Academy of Sciences
[Show abstract][Hide abstract] ABSTRACT: Muscarinic receptor-based designer G protein-coupled receptors (GPCRs) have emerged as novel pharmacological tools to address key questions regarding GPCR function and biology. These mutant muscarinic receptors are unable to bind acetylcholine (ACh), the endogenous muscarinic receptor ligand, but can be efficiently activated by clozapine-N-oxide (CNO), an otherwise pharmacologically inert compound. These CNO-sensitive designer GPCRs (alternative name: designer receptors exclusively activated by designer drug/DREADDs) have proven highly useful to explore the in vivo roles of distinct G protein signaling pathways in specific cell types or tissues. Like native GPCRs, CNO-activated DREADDs do not only couple to heterotrimeric G proteins but can also recruit proteins of the arrestin family (arrestin-2 and -3). Many studies have shown that arrestins can act as scaffolding proteins to promote signaling through G protein-independent pathways. To develop a novel tool useful for studying the physiological relevance of these arrestin-dependent signaling pathways, we recently described the development of an M3 muscarinic receptor-based DREADD that is no longer able to couple to G proteins but can recruit arrestins and initiate arrestin-mediated signaling in a CNO-dependent fashion. In this chapter, we provide protocols useful for the pharmacological and functional characterization of this newly developed DREADD. These protocols can be applied more generally to all other members of the DREADD receptor family.
[Show abstract][Hide abstract] ABSTRACT: Introduction Anticholinergics, blocking the muscarinic M3 receptor, are effective bronchodilators for patients with COPD. Recent evidence from M3 receptor deficient mice (M3R(-/-)) indicates that M3 receptors also regulate neutrophilic inflammation in response to cigarette smoke (CS). M3 receptors are present on almost all cell types and in this study we investigated the relative contribution of M3 receptors on structural cells versus inflammatory cells to CS-induced inflammation using bone-marrow chimeric mice. Methods Bone-marrow chimeras (C56Bl/6 mice) were generated and engraftment was confirmed after 10 weeks. Thereafter, irradiated and non-irradiated control animals were exposed to CS or fresh air for four consecutive days. Results CS induced a significant increase in neutrophil numbers in non-irradiated and irradiated control animals (4-35 fold). Interestingly, wild-type animals receiving M3R(-/-) bone marrow showed a similar increase in neutrophil number (15-fold). In contrast, no increase in the number of neutrophils was observed in M3R(-/-) animals receiving wild-type bone marrow. The increase in KC levels was similar in all smoke-exposed groups (2.5-5.0 fold). Micro-array analysis revealed that fibrinogen α and CD177, both involved in neutrophil migration, were downregulated in CS-exposed M3R(-/-) animals receiving wild-type bone marrow compared to CS-exposed wild-type animals, which was confirmed by RT-qPCR (1.6-2.5 fold). Conclusions These findings indicate that the M3 receptor on structural cells plays a pro-inflammatory role in CS-induced neutrophilic inflammation, whereas the M3 receptor on inflammatory cells does not. This effect is probably not mediated via KC release, but may involve altered adhesion and transmigration of neutrophils via fibrinogen α and CD177.
No preview · Article · Nov 2014 · AJP Lung Cellular and Molecular Physiology
[Show abstract][Hide abstract] ABSTRACT: Positive allosteric modulators (PAMs) of the M4 muscarinic acetylcholine receptor (mAChR) represent a novel approach for the treatment of psychotic symptoms associated with schizophrenia and other neuropsychiatric disorders. We recently reported that the selective M4 PAM VU0152100 produced an antipsychotic drug-like profile in rodents after amphetamine challenge. Previous studies suggest that enhanced cholinergic activity may also improve cognitive function and reverse deficits observed with reduced signaling through the N-methyl-d-aspartate subtype of the glutamate receptor (NMDAR) in the central nervous system. Prior to this study, the M1 mAChR subtype was viewed as the primary candidate for these actions relative to the other mAChR subtypes. Here we describe the discovery of a novel M4 PAM, VU0467154, with enhanced in vitro potency and improved pharmacokinetic properties relative to other M4 PAMs, enabling a more extensive characterization of M4 actions in rodent models. We used VU0467154 to test the hypothesis that selective potentiation of M4 receptor signaling could ameliorate the behavioral, cognitive, and neurochemical impairments induced by the noncompetitive NMDAR antagonist MK-801. VU0467154 produced a robust dose-dependent reversal of MK-801-induced hyperlocomotion and deficits in preclinical models of associative learning and memory functions, including the touchscreen pairwise visual discrimination task in wild-type mice, but failed to reverse these stimulant-induced deficits in M4 KO mice. VU0467154 also enhanced the acquisition of both contextual and cue-mediated fear conditioning when administered alone in wild-type mice. These novel findings suggest that M4 PAMs may provide a strategy for addressing the more complex affective and cognitive disruptions associated with schizophrenia and other neuropsychiatric disorders.
Full-text · Article · Aug 2014 · ACS Chemical Neuroscience
[Show abstract][Hide abstract] ABSTRACT: The muscarinic acetylcholine receptors are a subfamily of G protein-coupled receptors that regulate numerous fundamental functions of the central and peripheral nervous system. The past few years have witnessed unprecedented new insights into muscarinic receptor physiology, pharmacology and structure. These advances include the first structural views of muscarinic receptors in both inactive and active conformations, as well as a better understanding of the molecular underpinnings of muscarinic receptor regulation by allosteric modulators. These recent findings should facilitate the development of new muscarinic receptor subtype-selective ligands that could prove to be useful for the treatment of many severe pathophysiological conditions.
Full-text · Article · Jun 2014 · Nature Reviews Drug Discovery
[Show abstract][Hide abstract] ABSTRACT: Stimulation of muscarinic acetylcholine receptors (mAChRs) inhibits nociceptive transmission at the spinal level. However, it is unclear how each mAChR subtype regulates excitatory synaptic input from primary afferents. Here we examined excitatory postsynaptic currents (EPSCs) of dorsal horn neurons evoked by dorsal root stimulation in spinal cord slices from wild-type and mAChR subtype knockout (KO) mice. In wild-type mice, mAChR activation with oxotremorine-M decreased the amplitude of monosynaptic EPSCs in ~67% neurons but increased it in ~10% neurons. The inhibitory effect of oxotremorine-M was attenuated by the M2/M4 antagonist himbacine in the majority of neurons, and the remaining inhibition was abolished by group II/III metabotropic glutamate receptor (mGluR) antagonists in wild-type mice. In M2/M4 double-KO mice, oxotremorine-M inhibited monosynaptic EPSCs in significantly fewer neurons (~26%) and increased EPSCs in significantly more neurons (33%) compared with wild-type mice. Blocking group II/III mGluRs eliminated the inhibitory effect of oxotremorine-M in M2/M4 double-KO mice. In M2 single-KO and M4 single-KO mice, himbacine still significantly reduced the inhibitory effect of oxotremorine-M. However, the inhibitory and potentiating effects of oxotremorine-M on EPSCs in M3 single-KO and M1/M3 double-KO mice were similar to those in wild-type mice. In M5 single-KO mice, oxotremorine-M failed to potentiate evoked EPSCs, and its inhibitory effect was abolished by himbacine. These findings indicate that activation of presynaptic M2 and M4 subtypes reduces glutamate release from primary afferents. Activation of M5 subtype either directly increases primary afferent input or inhibits it through indirectly stimulating group II/III mGluRs.
No preview · Article · Apr 2014 · Journal of Biological Chemistry
[Show abstract][Hide abstract] ABSTRACT: Muscarinic acetylcholine receptor antagonists are widely used as bronchodilating drugs in pulmonary medicine. The therapeutic efficacy of these agents depends on the blockade of M3 muscarinic receptors expressed on airway smooth muscle cells. All muscarinic antagonists currently used as bronchodilating agents show high affinity for all five muscarinic receptor subtypes, thus increasing the likelihood of unwanted side effects. Recent X-ray crystallographic studies have provided detailed structural information about the nature of the orthosteric muscarinic binding site (the conventional acetylcholine binding site) and an 'outer' receptor cavity that can bind allosteric (non-orthosteric) drugs. These new findings should guide the development of selective M3 receptor blockers that have little or no effect on other muscarinic receptor subtypes.
No preview · Article · Mar 2014 · Current Opinion in Pharmacology
[Show abstract][Hide abstract] ABSTRACT: Reactive oxygen species (ROS) contribute to the pathogenesis of many acute and chronic pulmonary disorders, including bronchopulmonary dysplasia (BPD), a respiratory condition that affects preterm infants. However, the mechanisms of susceptibility to oxidant stress in neonatal lungs are not completely understood. We evaluated the role of genetic background in response to oxidant stress in the neonatal lung by exposing mice from 36 inbred strains to hyperoxia (95% O2) for 72 h after birth. Hyperoxia-induced lung injury was evaluated by using bronchoalveolar lavage fluid (BALF) analysis and pathology. Statistically significant interstrain variation was found for BALF inflammatory cells and protein (heritability estimates range: 33.6-55.7%). Genome-wide association mapping using injury phenotypes identified quantitative trait loci (QTLs) on chromosomes 1, 2, 4, 6, and 7. Comparative mapping of the chromosome 6 QTLs identified Chrm2 (cholinergic receptor, muscarinic 2, cardiac) as a candidate susceptibility gene, and mouse strains with a nonsynonymous coding single-nucleotide polymorphism (SNP) in Chrm2 that causes an amino acid substitution (P265L) had significantly reduced hyperoxia-induced inflammation compared to strains without the SNP. Further, hyperoxia-induced lung injury was significantly reduced in neonatal mice with targeted deletion of Chrm2, relative to wild-type controls. This study has important implications for understanding the mechanisms of oxidative lung injury in neonates.-Nichols, J. L., Gladwell, W., Verhein, K. C., Cho, H.-Y., Wess, J., Suzuki, O., Wiltshire, T., Kleeberger, S. R. Genome-wide association mapping of acute lung injury in neonatal inbred mice.
Full-text · Article · Feb 2014 · The FASEB Journal
[Show abstract][Hide abstract] ABSTRACT: X-linked nephrogenic diabetes insipidus (X-NDI) is a disease caused by inactivating mutations of the vasopressin (AVP) type 2 receptor (V2R) gene. Loss of V2R function prevents plasma membrane expression of the AQP2 water channel in the kidney collecting duct cells and impairs the kidney concentration ability. In an attempt to develop strategies to bypass V2R signaling in X-NDI, we evaluated the effects of secretin and fluvastatin, either alone or in combination, on kidney function in a mouse model of X-NDI. The secretin receptor was found to be functionally expressed in the kidney collecting duct cells. Based on this, X-NDI mice were infused with secretin for 14 days but urinary parameters were not altered by the infusion. Interestingly, secretin significantly increased AQP2 levels in the collecting duct but the protein primarily accumulated in the cytosol. Since we previously reported that fluvastatin treatment increased AQP2 plasma membrane expression in wild-type mice, secretin-infused X-NDI mice received a single injection of fluvastatin. Interestingly, urine production by X-NDI mice treated with secretin plus fluvastatin was reduced by nearly 90% and the urine osmolality was doubled. Immunostaining showed that secretin increased intracellular stores of AQP2 and the addition of fluvastatin promoted AQP2 trafficking to the plasma membrane. Taken together, these findings open new perspectives for the pharmacological treatment of X-NDI.Kidney International advance online publication, 12 February 2014; doi:10.1038/ki.2014.10.
Full-text · Article · Feb 2014 · Kidney International
[Show abstract][Hide abstract] ABSTRACT: Accumulating evidence suggests that selective M4 muscarinic acetylcholine receptor (mAChR) activators may offer a novel strategy for the treatment of psychosis. However, previous efforts to develop selective M4 activators were unsuccessful due to the lack of M4 mAChR subtype specificity and off-target muscarinic adverse effects. We recently developed VU0152100, a highly selective M4 positive allosteric modulator (PAM) that exerts central effects after systemic administration. We now report that VU0152100 dose-dependently reverses amphetamine-induced hyperlocomotion in rats and wildtype mice, but not in M4 KO mice. VU0152100 also blocks amphetamine-induced disruption of the acquisition of contextual fear conditioning and prepulse inhibition of the acoustic startle reflex. These effects were observed at doses that do not produce catalepsy or peripheral adverse effects associated with non-selective mAChR agonists. To further understand the effects of selective potentiation of M4 on region-specific brain activation, VU0152100 alone and in combination with amphetamine were evaluated using pharmacologic MRI. Key neural substrates of M4-mediated modulation of the amphetamine response included the nucleus accumbens, caudate-putamen, hippocampus, and medial thalamus. Functional connectivity analysis of phMRI data, specifically assessing correlations in activation between regions, revealed several brain networks involved in the M4 modulation of amphetamine-induced brain activation, including the nucleus accumbens and retrosplenial cortex with motor cortex, hippocampus, and medial thalamus. Using in vivo microdialysis, we found that VU0152100 reversed amphetamine-induced increases in extracellular dopamine levels in nucleus accumbens and caudate-putamen. The present data are consistent with an antipsychotic drug-like profile of activity for VU0152100. Taken together, these data support the development of selective M4 PAMs as a new approach to the treatment of psychosis and cognitive impairments associated with psychiatric disorders such as schizophrenia.Neuropsychopharmacology accepted article preview online, 20 January 2014. doi:10.1038/npp.2014.2.
Full-text · Article · Jan 2014 · Neuropsychopharmacology: official publication of the American College of Neuropsychopharmacology
[Show abstract][Hide abstract] ABSTRACT: Purpose:
We tested the hypothesis that the M3 muscarinic acetylcholine receptor subtype mediates cholinergic responses in murine ophthalmic arteries after endothelial removal.
Muscarinic receptor gene expression was determined in ophthalmic arteries with intact and with removed endothelium using real-time PCR. To examine the role of the M3 receptor in mediating vascular responses, ophthalmic arteries from M3 receptor-deficient mice (M3R(-/-)) and respective wild-type controls were studied in vitro. Functional studies were performed in nonpreconstricted arteries with either intact or removed endothelium using video microscopy.
In endothelium-intact ophthalmic arteries, mRNA for all five muscarinic receptor subtypes was detected, but M3 receptor mRNA was most abundant. In endothelium-removed ophthalmic arteries, M1, M2, and M3 receptors displayed similar mRNA expression levels, which were higher than those for M4 and M5 receptors. In functional studies, acetylcholine evoked vasoconstriction in endothelium-removed arteries from wild-type mice that was virtually abolished after incubation with the muscarinic receptor blocker atropine, indicative of the involvement of muscarinic receptors. In concentration-response experiments, acetylcholine and carbachol concentration-dependently constricted endothelium-removed ophthalmic arteries from wild-type mice, but produced only negligible responses in arteries from M3R(-/-) mice. In contrast, acetylcholine concentration-dependently dilated ophthalmic arteries with intact endothelium from wild-type mice, but not from M3R(-/-) mice. Responses to the nitric oxide donor nitroprusside and to KCl did not differ between ophthalmic arteries from wild-type and M3R(-/-) mice, neither in endothelium-intact nor in endothelium-removed arteries.
These findings provide evidence that in murine ophthalmic arteries the muscarinic M3 receptor subtype mediates cholinergic endothelium-dependent vasodilation and endothelium-independent vasoconstriction.
No preview · Article · Jan 2014 · Investigative ophthalmology & visual science
[Show abstract][Hide abstract] ABSTRACT: Despite recent advances in crystallography and the availability of G-protein-coupled receptor (GPCR) structures, little is known about the mechanism of their activation process, as only the β2 adrenergic receptor (β2AR) and rhodopsin have been crystallized in fully active conformations. Here we report the structure of an agonist-bound, active state of the human M2 muscarinic acetylcholine receptor stabilized by a G-protein mimetic camelid antibody fragment isolated by conformational selection using yeast surface display. In addition to the expected changes in the intracellular surface, the structure reveals larger conformational changes in the extracellular region and orthosteric binding site than observed in the active states of the β2AR and rhodopsin. We also report the structure of the M2 receptor simultaneously bound to the orthosteric agonist iperoxo and the positive allosteric modulator LY2119620. This structure reveals that LY2119620 recognizes a largely pre-formed binding site in the extracellular vestibule of the iperoxo-bound receptor, inducing a slight contraction of this outer binding pocket. These structures offer important insights into the activation mechanism and allosteric modulation of muscarinic receptors.
[Show abstract][Hide abstract] ABSTRACT: Rationale Asthma is a chronic obstructive airway disease, characterized by inflammation and remodeling. Acetylcholine contributes to symptoms by inducing bronchoconstriction via the muscarinic M3 receptor. Recent evidence suggests that bronchoconstriction can regulate airway remodeling and therefore implies a role for the muscarinic M3 receptor. Objectives To study the contribution of the muscarinic M3 receptor to allergen-induced remodeling using muscarinic M3 receptor subtype deficient (M3R(-/-)) mice. Wild-type, M1R(-/-) and M2R(-/-) mice were used as controls. Methods C57Bl/6 mice were sensitized and challenged with ovalbumin (twice weekly, for 4 weeks). Control animals were challenged with saline. Results Allergen exposure induced goblet cell metaplasia, airway smooth muscle thickening (1.7-fold), pulmonary vascular smooth muscle remodeling (1.5-fold) and deposition of collagen I (1.7-fold) and fibronectin (1.6-fold) in the airway wall of wild-type mice. These effects were absent or markedly lower in M3R(-/-) mice (30-100%), whereas M1R(-/-) and M2R(-/-) mice responded similar to wild-type mice. In addition, airway smooth muscle and pulmonary vascular smooth muscle mass were 35-40% lower in saline challenged M3R(-/-) mice compared to wild-type mice. Interestingly, allergen-induced airway inflammation, assessed as infiltrated eosinophils and Th2-cytokine expression, was similar or even enhanced in M3R(-/-) mice. Conclusions Our data indicate that acetylcholine contributes to allergen-induced remodeling and smooth muscle mass via the muscarinic M3 receptor, and not via M1 or M2 receptors. No stimulatory role for muscarinic M3 receptors in allergic inflammation was observed, suggesting that the role of acetylcholine in remodeling is independent of the allergic inflammatory response and may involve bronchoconstriction.
Full-text · Article · Oct 2013 · American Journal of Respiratory Cell and Molecular Biology
[Show abstract][Hide abstract] ABSTRACT: Recent studies with M3 muscarinic acetylcholine receptor (M3R) mutant mice suggest that drugs selectively targeting this receptor subtype may prove useful for the treatment of various pathophysiological conditions. Moreover, the use of M3R-based designer G protein-coupled receptors (GPCRs) has provided novel insights into how Gq-coupled GPCRs can modulate whole-body glucose homeostasis by acting on specific peripheral cell types. More recently, we succeeded in using X-ray crystallography to determine the structure of the M3R bound to the bronchodilating drug tiotropium, a muscarinic antagonist (inverse agonist). This new structural information should facilitate the development of orthosteric or allosteric M3R-selective drugs that are predicted to have considerable therapeutic potential.
No preview · Article · Sep 2013 · Journal of Molecular Neuroscience