Melanin-concentrating hormone as a mediator of intestinal inflammation

Melanin concentrating hormone regulates the JNK/ERK signaling pathway to alleviate influenza A virus infection-induced neuroinflammation

Melanin concentrating hormone (MCH) controls many brain functions, such as sleep/wake cycle and memory, and modulates the inflammation response. Previous studies have shown that influenza A virus (IAV) infection-induced neuroinflammation leads to central nervous damage. This study investigated the potential effects of MCH against neuroinflammation induced by IAV infection and its mechanism. MCH (1 and 2 mg/ml) was administrated for 5 consecutive days before IAV infection. Pentobarbital-induced sleep tests, an open-field test, and a Morris water maze were performed to measure sleep quality, spatial learning and memory ability. Neuronal loss and microglial activation were observed with Nissl staining and immunofluorescence assay. The levels of inflammatory cytokines and the expression of the JNK/ERK signaling pathway were examined by ELISA and western blot. IAV infection led to poor sleep quality, impaired the ability of spatial learning and memory, caused neuronal loss and microglial activation in mice's hippocampus and cortex. Meanwhile the level of inflammatory cytokines increased, and the JNK/ERK signaling pathway was activated after IAV infection. MCH administration significantly alleviated IAV-induced neuroinflammation, cognitive impairment, and sleep disorder, decreased the levels of inflammatory cytokines, and inhibited neuronal loss and microglial activation in the hippocampus and cortex by regulating the JNK/ERK signaling pathway. Therefore, MCH alleviated the neuroinflammation, spatial learning and memory impairment, and sleep disorder in IAV-infected mice by regulating the JNK/ERK signaling pathway.

Hypothalamic MCH Neurons: From Feeding to Cognitive Control

Modern neuroscience is progressively elucidating that the classic view positing distinct brain regions responsible for survival, emotion, and cognitive functions is outdated. The hypothalamus demonstrates the interdependence of these roles, as it is traditionally known for fundamental survival functions like energy and electrolyte balance, but is now recognized to also play a crucial role in emotional and cognitive processes. This review focuses on lateral hypothalamic melanin-concentrating hormone (MCH) neurons, producing the neuropeptide MCH-a relatively understudied neuronal population with integrative functions related to homeostatic regulation and motivated behaviors, with widespread inputs and outputs throughout the entire central nervous system. Here, we review early findings and recent literature outlining their role in the regulation of energy balance, sleep, learning, and memory processes.

A Degradation Motif in STAU1 Defines a Novel Family of Proteins Involved in Inflammation

Cancer development is regulated by inflammation. Staufen1 (STAU1) is an RNA-binding protein whose expression level is critical in cancer cells as it is related to cell proliferation or cell death. STAU1 protein levels are downregulated during mitosis due to its degradation by the E3 ubiquitin ligase anaphase-promoting complex/cyclosome (APC/C). In this paper, we map the molecular determinant involved in STAU1 degradation to amino acids 38-50, and by alanine scanning, we shorten the motif to F³⁹PxPxxLxxxxL⁵⁰ (FPL-motif). Mutation of the FPL-motif prevents STAU1 degradation by APC/C. Interestingly, a search in databases reveals that the FPL-motif is shared by 15 additional proteins, most of them being involved in inflammation. We show that one of these proteins, MAP4K1, is indeed degraded via the FPL-motif; however, it is not a target of APC/C. Using proximity labeling with STAU1, we identify TRIM25, an E3 ubiquitin ligase involved in the innate immune response and interferon production, as responsible for STAU1 and MAP4K1 degradation, dependent on the FPL-motif. These results are consistent with previous studies that linked STAU1 to cancer-induced inflammation and identified a novel degradation motif that likely coordinates a novel family of proteins involved in inflammation. Data are available via ProteomeXchange with the identifier PXD036675.

Melanin-concentrating hormone promotes anxiety and intestinal dysfunction via basolateral amygdala in mice

The limbic system plays a pivotal role in stress-induced anxiety and intestinal disorders, but how the functional circuits between nuclei within the limbic system are engaged in the processing is still unclear. In our study, the results of fluorescence gold retrograde tracing and fluorescence immunohistochemistry showed that the melanin-concentrating hormone (MCH) neurons of the lateral hypothalamic area (LHA) projected to the basolateral amygdala (BLA). Both chemogenetic activation of MCH neurons and microinjection of MCH into the BLA induced anxiety disorder in mice, which were reversed by intra-BLA microinjection of MCH receptor 1 (MCHR1) blocker SNAP-94847. In the chronic acute combining stress (CACS) stimulated mice, SNAP94847 administrated in the BLA ameliorated anxiety-like behaviors and improved intestinal dysfunction via reducing intestinal permeability and inflammation. In conclusion, MCHergic circuit from the LHA to the BLA participates in the regulation of anxiety-like behavior in mice, and this neural pathway is related to the intestinal dysfunction in CACS mice by regulating intestinal permeability and inflammation.

Sleep-Wake Control by Melanin-Concentrating Hormone (MCH) Neurons: a Review of Recent Findings

PURPOSE OF THE REVIEW

Melanin-concentrating hormone (MCH)-expressing neurons located in the lateral hypothalamus are considered as an integral component of sleep-wake circuitry. However, the precise role of MCH neurons in sleep-wake regulation has remained unclear, despite several years of research employing a wide range of techniques. We review recent data on this aspect, which are mostly inconsistent, and propose a novel role for MCH neurons in sleep regulation.

RECENT FINDINGS

While almost all studies using "gain-of-function" approaches show an increase in rapid eye movement sleep (or paradoxical sleep; PS), loss-of-function approaches have not shown reductions in PS. Similarly, the reported changes in wakefulness or non-rapid eye movement sleep (slow-wave sleep; SWS) with manipulation of the MCH system using conditional genetic methods are inconsistent. Currently available data do not support a role for MCH neurons in spontaneous sleep-wake but imply a crucial role for them in orchestrating sleep-wake responses to changes in external and internal environments.

Role of melanin-concentrating hormone in drug use disorders

Melanin-concentrating hormone (MCH) is a neuropeptide primarily transcribed in the lateral hypothalamus (LH), with vast projections to many areas throughout the central nervous system that play an important role in motivated behaviors and drug use. Anatomical, pharmacological and genetic studies implicate MCH in mediating the intake and reinforcement of commonly abused substances, acting by influencing several systems including the mesolimbic dopaminergic system, glutamatergic as well as GABAergic signaling and being modulated by inflammatory neuroimmune pathways. Further support for the role of MCH in controlling behavior related to drug use will be discussed as it relates to cerebral ventricular volume transmission and intracellular molecules including cocaine- and amphetamine-regulated transcript peptide, dopamine- and cAMP-regulated phosphoprotein 32 kDa. The primary goal of this review is to introduce and summarize current literature surrounding the role of MCH in mediating the intake and reinforcement of commonly abused drugs, such as alcohol, cocaine, amphetamine, nicotine and opiates.

SNAPshots of the MCHR1: a Comparison Between the PET-Tracers [18F]FE@SNAP and [11C]SNAP-7941

PURPOSE

The melanin-concentrating hormone receptor 1 (MCHR1) has become an important pharmacological target, since it may be involved in various diseases, such as diabetes, insulin resistance, and obesity. Hence, a suitable positron emission tomography radiotracer for the in vivo assessment of the MCHR1 pharmacology is imperative. The current paper contrasts the extensive in vitro, in vivo, and ex vivo assessments of the radiotracers [18F]FE@SNAP and [11C]SNAP-7941 and provides comprehensive information about their biological and physicochemical properties. Furthermore, it examines their suitability for first-in-man imaging studies.

PROCEDURES

Kinetic real-time cell-binding studies with [18F]FE@SNAP and [11C]SNAP-7941 were conducted on adherent Chines hamster ovary (CHO-K1) cells stably expressing the human MCHR1 and MCHR2. Small animal imaging studies on mice and rats were performed under displacement and baseline conditions, as well as after pretreatment with the P-glycoprotein/breast cancer resistant protein inhibitor tariquidar. After the imaging studies, detailed analyses of the ex vivo biodistribution were performed. Ex vivo metabolism was determined in rat blood and brain and analyzed at various time points using a quantitative radio-HPLC assay.

RESULTS

[11C]SNAP-7941 demonstrates high uptake on CHO-K1-hMCHR1 cells, whereas no uptake was detected for the CHO-K1-hMCHR2 cells. In contrast, [18F]FE@SNAP evinced binding to CHO-K1-hMCHR1 and CHO-K1-hMCHR2 cells. Imaging studies with [18F]FE@SNAP and [11C]SNAP-7941 showed an increased brain uptake after tariquidar pretreatment in mice, as well as in rats, and exhibited a significant difference between the time-activity curves of the baseline and blocking groups. Biodistribution of both tracers demonstrated a decreased uptake after displacement. [11C]SNAP-7941 revealed a high metabolic stability in rats, whereas [18F]FE@SNAP was rapidly metabolized.

CONCLUSIONS

Both radiotracers demonstrate appropriate imaging properties for the MCHR1. However, the pronounced metabolic stability as well as superior selectivity and affinity of [11C]SNAP-7941 underlines the decisive superiority over [18F]FE@SNAP.

A Small Aromatic Compound Has Antifungal Properties and Potential Anti-Inflammatory Effects against Intestinal Inflammation

Resistance of the opportunistic pathogen Candida albicans to antifungal drugs has increased significantly in recent years. After screening 55 potential antifungal compounds from a chemical library, 2,3-dihydroxy-4-methoxybenzaldehyde (DHMB) was identified as having potential antifungal activity. The properties of DHMB were then assessed in vitro and in vivo against C. albicans overgrowth and intestinal inflammation. Substitution on the aromatic ring of DHMB led to a strong decrease in its biological activity against C. albicans. The MIC of DHMB was highly effective at eliminating C. albicans when compared to that of caspofungin or fluconazole. Additionally, DHMB was also effective against clinically isolated fluconazole- or caspofungin-resistant C. albicans strains. DHMB was administered to animals at high doses. This compound was not cytotoxic and was well-tolerated. In experimental dextran sodium sulphate (DSS)-induced colitis in mice, DHMB reduced the clinical and histological score of inflammation and promoted the elimination of C. albicans from the gut. This finding was supported by a decrease in aerobic bacteria while anaerobic bacteria populations were re-established in mice treated with DHMB. DHMB is a small organic molecule with antifungal properties and anti-inflammatory activity by exerting protective effects on intestinal epithelial cells.

Dissecting the Genomic Architecture of Resistance to Eimeria maxima Parasitism in the Chicken

Coccidiosis in poultry, caused by protozoan parasites of the genus Eimeria, is an intestinal disease with substantial economic impact. With the use of anticoccidial drugs under public and political pressure, and the comparatively higher cost of live-attenuated vaccines, an attractive complementary strategy for control is to breed chickens with increased resistance to Eimeria parasitism. Prior infection with Eimeria maxima leads to complete immunity against challenge with homologous strains, but only partial resistance to challenge with antigenically diverse heterologous strains. We investigate the genetic architecture of avian resistance to E. maxima primary infection and heterologous strain secondary challenge using White Leghorn populations of derived inbred lines, C.B12 and 15I, known to differ in susceptibility to the parasite. An intercross population was infected with E. maxima Houghton (H) strain, followed 3 weeks later by E. maxima Weybridge (W) strain challenge, while a backcross population received a single E. maxima W infection. The phenotypes measured were parasite replication (counting fecal oocyst output or qPCR for parasite numbers in intestinal tissue), intestinal lesion score (gross pathology, scale 0-4), and for the backcross only, serum interleukin-10 (IL-10) levels. Birds were genotyped using a high density genome-wide DNA array (600K, Affymetrix). Genome-wide association study located associations on chromosomes 1, 2, 3, and 5 following primary infection in the backcross population, and a suggestive association on chromosome 1 following heterologous E. maxima W challenge in the intercross population. This mapped several megabases away from the quantitative trait locus (QTL) linked to the backcross primary W strain infection, suggesting different underlying mechanisms for the primary- and heterologous secondary- responses. Underlying pathways for those genes located in the respective QTL for resistance to primary infection and protection against heterologous challenge were related mainly to immune response, with IL-10 signaling in the backcross primary infection being the most significant. Additionally, the identified markers associated with IL-10 levels exhibited significant additive genetic variance. We suggest this is a phenotype of interest to the outcome of challenge, being scalable in live birds and negating the requirement for single-bird cages, fecal oocyst counts, or slaughter for sampling (qPCR).

Acupuncture Alleviates Levodopa-Induced Dyskinesia via Melanin-Concentrating Hormone in Pitx3-Deficient aphakia and 6-Hydroxydopamine-Lesioned Mice

Although L-3,4-dihydroxyphenylalanine (L-DOPA) is currently the most effective medication for treating Parkinson's disease (PD) motor symptoms, its prolonged administration causes several adverse effects, including dyskinesia. To identify the mechanisms underlying the effects of acupuncture on L-DOPA-induced dyskinesia (LID), antidyskinetic effects of acupuncture were investigated in two mouse models of PD. Acupuncture stimulation at GB34 alleviated abnormal involuntary movements (AIMs) in Pitx3-deficient aphakia mice (ak/ak) following L-DOPA administration and these effects were reproduced in 6-hydroxydopamine (6-OHDA)-lesioned mice with LID. A transcriptome analysis of the hypothalamus revealed pro-melanin-concentrating hormone (Pmch) gene was highly expressed in acupuncture-treated mouse from ak/ak model of LID as well as 6-OHDA model of LID. Acupuncture combined with the administration of MCH receptor antagonist did not have any beneficial effects on dyskinesia in L-DOPA-injected ak/ak mice, but the intranasal administration of MCH attenuated LID to the same degree as acupuncture in both ak/ak and 6-OHDA mice with LID. A gene expression profile with a hierarchical clustering analysis of the dyskinesia-induced ak/ak mouse brain revealed an association between the mechanisms underlying acupuncture and MCH. Additionally, altered striatal responses to L-DOPA injection were observed after prolonged acupuncture and MCH treatments, which suggests that these treatment modalities influenced the compensatory mechanisms of LID. In summary, present study demonstrated that acupuncture decreased LID via hypothalamic MCH using L-DOPA-administered ak/ak and 6-OHDA mouse models and that MCH administration resulted in novel antidyskinetic effects in these models. Thus, acupuncture and MCH might be valuable therapeutic candidates for PD patients suffering from LID.

Supplement comprising of laccase and citric acid as an alternative for antibiotics: In vitro triggers of melanin production

An indiscriminate use of antibiotics in humans and animals has led to the widespread selection of antibiotic-resistance, thus constricting the use of antibiotics. A possible solution to counter this problem could be to develop alternatives that can boost the host immunity, thus reducing the quantity and frequency of antibiotic use. In this work, for the first time, citric acid and laccase were used as extracellular inducers of melanin production in yeast cells and human cell lines. It is proposed that the formulation of laccase and citric acid together could further promote melatonin-stimulated, melanocyte-derived melanin production. Melanization as a probe of immunity described in this study, is an easy and a rapid test compared to other immunity tests and it allows performing statistical analyses. The results showed the synergistic effect of citric acid and laccase on melanin production by yeast cells, with significant statistical differences compared to all other tested conditions (p: 0.0005-0.005). Laccase and citric acid together boosted melanin production after 8 days of incubation. An increase in melanin production by two human colon cells lines (Cacao-2/15 and HT-29) was observed on supplementation with both laccase and citric acid in the cell growth medium. Produced melanin showed antimicrobial properties similar to antibiotics. Therefore, a formulation with citric acid and laccase may prove to be an excellent alternative to reduce the antibiotic use in human and animal subjects.

Novel analgesic effects of melanin-concentrating hormone on persistent neuropathic and inflammatory pain in mice

The melanin-concentrating hormone (MCH) is a peptidergic neuromodulator synthesized by neurons in the lateral hypothalamus and zona incerta. MCHergic neurons project throughout the central nervous system, indicating the involvements of many physiological functions, but the role in pain has yet to be determined. In this study, we found that pMCH^-/- mice showed lower baseline pain thresholds to mechanical and thermal stimuli than did pMCH^+/+ mice, and the time to reach the maximum hyperalgesic response was also significantly earlier in both inflammatory and neuropathic pain. To examine its pharmacological properties, MCH was administered intranasally into mice, and results indicated that MCH treatment significantly increased mechanical and thermal pain thresholds in both pain models. Antagonist challenges with naltrexone (opioid receptor antagonist) and AM251 (cannabinoid 1 receptor antagonist) reversed the analgesic effects of MCH in both pain models, suggesting the involvement of opioid and cannabinoid systems. MCH treatment also increased the expression and activation of CB1R in the medial prefrontal cortex and dorsolateral- and ventrolateral periaqueductal grey. The MCH1R antagonist abolished the effects induced by MCH. This is the first study to suggest novel analgesic actions of MCH, which holds great promise for the application of MCH in the therapy of pain-related diseases.

In vivo evaluation of radiotracers targeting the melanin-concentrating hormone receptor 1: [11C]SNAP-7941 and [18F]FE@SNAP reveal specific uptake in the ventricular system

The MCHR1 is involved in the regulation of energy homeostasis and changes of the expression are linked to a variety of associated diseases, such as diabetes and adiposity. The study aimed at the in vitro and in vivo evaluation of [11C]SNAP-7941 and [18F]FE@SNAP as potential PET-tracers for the MCHR1. Competitive binding studies with non-radioactive derivatives and small-animal PET/CT and MRI brain studies were performed under baseline conditions and tracer displacement with the unlabelled MCHR1 antagonist (±)-SNAP-7941. Binding studies evinced high binding affinity of the non-radioactive derivatives. Small-animal imaging of [11C]SNAP-7941 and [18F]FE@SNAP evinced high tracer uptake in MCHR1-rich regions of the ventricular system. Quantitative analysis depicted a significant tracer reduction after displacement with (±)-SNAP-7941. Due to the high binding affinity of the non-labelled derivatives and the high specific tracer uptake of [11C]SNAP-7941 and [18F]FE@SNAP, there is strong evidence that both radiotracers may serve as highly suitable agents for specific MCHR1 imaging.

Application of Zebrafish Models in Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is a chronic, recurrent, and remitting inflammatory disease with unclear etiology. As a clinically frequent disease, it can affect individuals throughout their lives, with multiple complications. Unfortunately, traditional murine models are not efficient for the further study of IBD. Thus, effective and convenient animal models are needed. Zebrafish have been used as model organisms to investigate IBD because of their suggested highly genetic similarity to humans and their superiority as laboratory models. The zebrafish model has been used to study the composition of intestinal microbiota, novel genes, and therapeutic approaches. The pathogenesis of IBD is still unclear and many risk factors remain unidentified. In this review, we compare traditional murine models and zebrafish models in terms of advantages, pathogenesis, and drug discovery screening for IBD. We also review the progress and deficiencies of the zebrafish model for scientific applications.

[(18)F]FE@SNAP-a specific PET tracer for melanin-concentrating hormone receptor 1 imaging?

BACKGROUND

The melanin-concentrating hormone receptor 1 (MCHR1), which is highly expressed in the lateral hypothalamus, plays a key role in energy homeostasis, obesity and other endocrine diseases. Hence, there is a major interest in in vivo imaging of this receptor. A PET tracer would allow non-invasive in vivo visualization and quantification of the MCHR1. The aim of the study was the ex vivo evaluation of the MCHR1 ligand [(18)F]FE@SNAP as a potential PET tracer for the MCHR1.

METHODS

[(18)F]FE@SNAP was injected directly into the jugular vein of awake naïve rats for ex vivo brain autoradiography, biodistribution and additional blood metabolite analysis. Blocking experiments were conducted using the unlabeled MCHR1 ligand SNAP-7941.

RESULTS

A high uptake of [(18)F]FE@SNAP was observed in the lateral hypothalamus and the ventricular system. Both regions were significantly blocked by SNAP-7941. Biodistribution evinced the highest uptake in the kidneys, adrenals, lung and duodenum. Specific blocking with SNAP-7941 led to a significant tracer reduction in the heart and adrenals. In plasma samples, 47.73 ± 6.1 % of a hydrophilic radioactive metabolite was found 45 min after tracer injection.

CONCLUSIONS

Since [(18)F]FE@SNAP uptake was significantly blocked in the lateral hypothalamus, there is strong evidence that [(18)F]FE@SNAP is a highly suitable agent for specific MCHR1 imaging in the central nervous system. Additionally, this finding is supported by the specific blocking in the ventricular system, where the MCHR1 is expressed in the ependymal cells. These findings suggest that [(18)F]FE@SNAP could serve as a useful imaging and therapy monitoring tool for MCHR1-related pathologies.

Melanin-Concentrating Hormone (MCH): Role in REM Sleep and Depression

The melanin-concentrating hormone (MCH) is a peptidergic neuromodulator synthesized by neurons of the lateral sector of the posterior hypothalamus and zona incerta. MCHergic neurons project throughout the central nervous system, including areas such as the dorsal (DR) and median (MR) raphe nuclei, which are involved in the control of sleep and mood. Major Depression (MD) is a prevalent psychiatric disease diagnosed on the basis of symptomatic criteria such as sadness or melancholia, guilt, irritability, and anhedonia. A short REM sleep latency (i.e., the interval between sleep onset and the first REM sleep period), as well as an increase in the duration of REM sleep and the density of rapid-eye movements during this state, are considered important biological markers of depression. The fact that the greatest firing rate of MCHergic neurons occurs during REM sleep and that optogenetic stimulation of these neurons induces sleep, tends to indicate that MCH plays a critical role in the generation and maintenance of sleep, especially REM sleep. In addition, the acute microinjection of MCH into the DR promotes REM sleep, while immunoneutralization of this peptide within the DR decreases the time spent in this state. Moreover, microinjections of MCH into either the DR or MR promote a depressive-like behavior. In the DR, this effect is prevented by the systemic administration of antidepressant drugs (either fluoxetine or nortriptyline) and blocked by the intra-DR microinjection of a specific MCH receptor antagonist. Using electrophysiological and microdialysis techniques we demonstrated also that MCH decreases the activity of serotonergic DR neurons. Therefore, there are substantive experimental data suggesting that the MCHergic system plays a role in the control of REM sleep and, in addition, in the pathophysiology of depression. Consequently, in the present report, we summarize and evaluate the current data and hypotheses related to the role of MCH in REM sleep and MD.

Inflammation-induced functional connectivity of melanin-concentrating hormone and IL-10

Melanin-concentrating hormone (MCH) was identified in mammals as a hypothalamic neuropeptide regulating appetite and energy balance. However, similarly to most of the brain peptides, MCH is also produced in the gastrointestinal system and can act locally as an immunomodulator. We have previously reported high expression of MCH and its receptor MCHR1 in the affected mucosa of patients with inflammatory bowel disease. Furthermore, MCH deficiency in mice attenuated experimental colitis, pointing to MCH as a mediator of intestinal inflammation. In the present study, in order to gain further insights into the underlying mechanisms of such effects of MCH, we treated mice with established experimental colitis due to IL-10 deficiency with a MCHR1 antagonist (DABA-822). While treatment with the same drug was successful in attenuating TNBS-induced colitis in previous studies, it offered no benefit to the IL-10 knockout mouse model, suggesting that perhaps IL-10 is a downstream target of MCH. Indeed, in experiments focusing on monocytes, we found that treatment with MCH inhibited LPS-mediated IL-10 upregulation. Conversely, in the same cells, exogenous IL-10 prevented LPS-induced MCHR1 expression. Taken together, these findings indicate a functional cross-talk between MCH and IL-10 which prevents resolution of inflammation.

Comparative autoradiographic in vitro investigation of melanin concentrating hormone receptor 1 ligands in the central nervous system

The MCHR1 is an interesting pharmacological and pharmaceutical target, due to its involvement in pathologies as diabetes, gut inflammation and adiposity. in vivo PET-studies of the MCHR1 in energy homeostasis and diabetes could be of great value for deeper understanding of endocrinological hormone status and consequential pharmacological interactions. Furthermore, PET-tracers would facilitate compound dose selection of MCHR1 antagonists for treatment. Therefore, we developed two potential PET-tracers, [(11)C]SNAP-7941 and [(18)F]FE@SNAP, for the in vivo visualization of this receptor. Aim of this study was a preclinical in vitro evaluation of both unlabeled ligands. Therefore, a comparative autoradiographic investigation on CNS (coronal rat brain and 4 different human brain regions) and peripheral tissues (rat tongue as target and rat testes as non-target region) was conducted. Competition experiments, using the two radioligands [(125)I]-MCH and [(125)I]-S36057, were performed with selective and specific MCHR1 ligands as PMC-3886, a MCHR1 agonist, SNAP-7941 and FE@SNAP, two MCHR1 antagonists. Additionally, immunohistochemical staining with a specific MCHR1 antibody was performed. Specific binding was found in all tissues known to express the MCHR1 as human and rat CNS and peripheral rat tongue tissue. No specific binding was found in the non-target region of rat testes. MCHR1 antibody staining complemented the outcome of the autoradiographic experiments. The compounds SNAP-7941 and FE@SNAP were generally comparable with PMC-3886. Hence, the in vitro autoradiographic study of the unlabeled compounds SNAP-7941 and FE@SNAP further qualifies the potential of the PET-tracers [(11)C]SNAP-7941 and [(18)F]FE@SNAP as useful MCHR1 PET-tracers.

Intestinal upregulation of melanin-concentrating hormone in TNBS-induced enterocolitis in adult zebrafish

Background

Melanin-concentrating hormone (MCH), an evolutionarily conserved appetite-regulating neuropeptide, has been recently implicated in the pathogenesis of inflammatory bowel disease (IBD). Expression of MCH is upregulated in inflamed intestinal mucosa in humans with colitis and MCH-deficient mice treated with trinitrobenzene-sulfonic acid (TNBS) develop an attenuated form of colitis compared to wild type animals. Zebrafish have emerged as a new animal model of IBD, although the majority of the reported studies concern zebrafish larvae. Regulation MCH expression in the adult zebrafish intestine remains unknown.

Methods

In the present study we induced enterocolitis in adult zebrafish by intrarectal administration of TNBS. Follow-up included survival analysis, histological assessment of changes in intestinal architecture, and assessment of intestinal infiltration by myeloperoxidase positive cells and cytokine transcript levels.

Results

Treatment with TNBS dose-dependently reduced fish survival. This response required the presence of an intact microbiome, since fish pre-treated with vancomycin developed less severe enterocolitis. At 6 hours post-challenge, we detected a significant influx of myeloperoxidase positive cells in the intestine and upregulation of both proinflammatory and anti-inflammatory cytokines. Most importantly, and in analogy to human IBD and TNBS-induced mouse experimental colitis, we found increased intestinal expression of MCH and its receptor in TNBS-treated zebrafish.

Conclusions

Taken together these findings not only establish a model of chemically-induced experimental enterocolitis in adult zebrafish, but point to effects of MCH in intestinal inflammation that are conserved across species.

Regulated Control of Melanin-Concentrating Hormone Receptor 1 through Posttranslational Modifications

Melanin-concentrating hormone (MCH) is a hypothalamic neuropeptide that plays an important role in feeding behavior. It activates two G-protein-coupled receptors, MCHR1 and MCHR2, of which MCHR1 is the primary regulator of food intake and energy homeostasis in rodents. In mammalian cells transfected with MCHR1, MCH is able to activate multiple signaling pathways including calcium mobilization, extracellular signal-regulated kinase activation, and inhibition of cyclic AMP generation through Gi/o- and Gq-coupled pathways. Further evidence suggests that MCHR1 is regulated through posttranslational modifications, which control its intracellular localization and provide appropriate cellular responses involving G-protein signaling. This review summarizes the current data on the control of MCHR1 function through glycosylation and phosphorylation, as related to cell function. Especially, a series of mutagenesis study highlights the importance of complete glycosylation of MCHR1 for efficient trafficking to the plasma membrane.

Neurotensin receptor 1 overexpression in inflammatory bowel diseases and colitis-associated neoplasia

AIM: To explore the association of neurotensin receptor 1 (NTSR1) with inflammatory bowel diseases (IBD) and colitis-associated neoplasia.

METHODS: NTSR1 was detected by immunohistochemistry in clinical samples of colonic mucosa with IBD colitis, colitis-associated raised low-grade dysplasia (LGD) including dysplasia-associated lesions or masses (DALMs, n = 18) and adenoma-like dysplastic polyps (ALDPs, n = 4), colitis-associated high-grade dysplasia (HGD, n = 11) and colitis-associated colorectal carcinoma (CACRC, n = 13), sporadic colorectal adenomatous polyp (SAP, n = 17), and sporadic colorectal carcinoma (SCRC, n = 12). The immunoreactivity of NTSR1 was semiquantitated (as negative, 1+, 2+, and 3+) and compared among different conditions.

RESULTS: NTSR1 was not detected in normal mucosa but was expressed similarly in both active and inactive colitis. LGD showed a significantly stronger expression as compared with non-dysplastic colitic mucosa, with significantly more cases showing > 2+ intensity (68.75% in LGD vs 32.26% in nondysplastic mucosa, P = 0.001). However, no significant difference existed between DALMs and ALDPs. CACRC and HGD showed a further stronger expression, with significantly more cases showing 3+ intensity than that in LGD (61.54% vs 12.50% for CACRC vs LGD, P = 0.022; 58.33% vs 12.50% for CACRC/HGD vs LGD, P = 0.015). No significant difference existed between colitis-associated and non-colitic sporadic neoplasia.

CONCLUSION: NTSR1 in colonic epithelial cells is overexpressed in IBD, in a stepwise fashion with sequential progress from inflammation to dysplasia and carcinoma.

Preparation and First Preclinical Evaluation of [(18)F]FE@SNAP: A Potential PET Tracer for the Melanin-Concentrating Hormone Receptor-1 (MCHR1)

The melanin-concentrating hormone (MCH) system is a new target for the treatment of human disorders. Since the knowledge of the MCH system’s involvement in a variety of pathologies (obesity, diabetes, and deregulation of metabolic feedback mechanism) is based on in vitro or preclinical studies, a suitable positron emission tomography (PET) tracer needs to be developed. We herein present the preparation and first preclinical evaluation of [¹⁸F]FE@SNAP – a new PET tracer for MCH receptor-1 (MCHR1). The synthesis was performed using a microfluidic device. Preclinical evaluation included binding affinity, plasma stability, plasma free fraction, stability against the cytochrome P-450 (CYP450) system using liver microsomes, stability against carboxyl-esterase, and methods to assess the penetration of the blood-brain barrier (BBB) such as logD analysis and immobilized artificial membrane (IAM) chromatography. Levels at 374 ± 202 MBq [¹⁸F]FE@SNAP were obtained after purification. The obtained K_d value of [¹⁸F]FE@SNAP was 2.9 nM. [¹⁸F]FE@SNAP evinced high stability against carboxylesterase, CYP450 enzymes, and in human plasma. LogD (3.83) and IAM chromatography results (P_m=0.51) were in the same range as for known BBB-penetrating compounds. The synthesis of [¹⁸F]FE@SNAP was reliable and successful. Due to high binding affinity and stability, [¹⁸F]FE@SNAP is a promising tracer for MCHR1.

Anti-melanin-concentrating hormone treatment attenuates chronic experimental colitis and fibrosis

Fibrosis represents a major complication of several chronic diseases, including inflammatory bowel disease (IBD). Treatment of IBD remains a clinical challenge despite several recent therapeutic advances. Melanin-concentrating hormone (MCH) is a hypothalamic neuropeptide shown to regulate appetite and energy balance. However, accumulating evidence suggests that MCH has additional biological effects, including modulation of inflammation. In the present study, we examined the efficacy of an MCH-blocking antibody in treating established, dextran sodium sulfate-induced experimental colitis. Histological and molecular analysis of mouse tissues revealed that mice receiving anti-MCH had accelerated mucosal restitution and lower colonic expression of several proinflammatory cytokines, as well as fibrogenic genes, including COL1A1. In parallel, they spared collagen deposits seen in the untreated mice, suggesting attenuated fibrosis. These findings raised the possibility of perhaps direct effects of MCH on myofibroblasts. Indeed, in biopsies from patients with IBD, we demonstrate expression of the MCH receptor MCHR1 in α-smooth muscle actin(+) subepithelial cells. CCD-18Co cells, a primary human colonic myofibroblast cell line, were also positive for MCHR1. In these cells, MCH acted as a profibrotic modulator by potentiating the effects of IGF-1 and TGF-β on proliferation and collagen production. Thus, by virtue of combined anti-inflammatory and anti-fibrotic effects, blocking MCH might represent a compelling approach for treating IBD.

The role of melanin-concentrating hormone and its receptors in energy homeostasis

Extensive studies in rodents with melanin-concentrating hormone (MCH) have demonstrated that the neuropeptide hormone is a potent orexigen. Acutely, MCH causes an increase in food intake, while chronically it leads to increased weight gain, primarily as an increase in fat mass. Multiple knockout mice models have confirmed the importance of MCH in modulating energy homeostasis. Animals lacking MCH, MCH-containing neurons, or the MCH receptor all are resistant to diet-induced obesity. These genetic and pharmacologic studies have prompted a large effort to identify potent and selective MCH receptor antagonists, initially as tool compounds to probe pharmacology in models of obesity, with an ultimate goal to identify novel anti-obesity drugs. In animal models, MCH antagonists have consistently shown efficacy in reducing food intake acutely and inhibiting body-weight gain when given chronically. Five compounds have proceeded into clinical testing. Although they were reported as well-tolerated, none has advanced to long-term efficacy and safety studies.

Disruption of the melanin-concentrating hormone receptor 1 (MCH1R) affects thyroid function

Melanin-concentrating hormone (MCH) is a peptide produced in the hypothalamus and the zona incerta that acts on one receptor, MCH receptor 1 (MCH1R), in rodents. The MCH system has been implicated in the regulation of several centrally directed physiological responses, including the hypothalamus-pituitary-thyroid axis. Yet a possible direct effect of the MCH system on thyroid function has not been explored in detail. We now show that MCH1R mRNA is expressed in thyroid follicular cells and that mice lacking MCH1R [MCH1R-knockout (KO)] exhibit reduced circulating iodothyronine (T(4), free T(4), T(3), and rT(3)) levels and high TRH and TSH when compared with wild-type (WT) mice. Because the TSH of MCH1R-KO mice displays a normal bioactivity, we hypothesize that their hypothyroidism may be caused by defective thyroid function. Yet expression levels of the genes important for thyroid hormones synthesis or secretion are not different between the MCH1R-KO and WT mice. However, the average thyroid follicle size of the MCH1R-KO mice is larger than that of WT mice and contained more free and total T(4) and T(3) than the WT glands, suggesting that they are sequestered in the glands. Indeed, when challenged with TSH, the thyroids of MCH1R-KO mice secrete lower amounts of T(4). Similarly, secretion of iodothyronines in the plasma upon (125)I administration is significantly reduced in MCH1R-KO mice. Therefore, the absence of MCH1R affects thyroid function by disrupting thyroid hormone secretion. To our knowledge, this study is the first to link the activity of the MCH system to the thyroid function.

Increased susceptibility of melanin-concentrating hormone-deficient mice to infection with Salmonella enterica serovar Typhimurium

Melanin-concentrating hormone (MCH) was initially identified in mammals as a hypothalamic neuropeptide regulating appetite and energy balance. However, the wide distribution of MCH receptors in peripheral tissues suggests additional functions for MCH which remain largely unknown. We have previously reported that mice lacking MCH develop attenuated intestinal inflammation when exposed to Clostridium difficile toxin A. To further characterize the role of MCH in host defense mechanisms against intestinal pathogens, Salmonella enterocolitis (using Salmonella enterica serovar Typhimurium) was induced in MCH-deficient mice and their wild-type littermates. In the absence of MCH, infected mice had increased mortality associated with higher bacterial loads in blood, liver, and spleen. Moreover, the knockout mice developed more-severe intestinal inflammation, based on epithelial damage, immune cell infiltrates, and local and systemic cytokine levels. Paradoxically, these enhanced inflammatory responses in the MCH knockout mice were associated with disproportionally lower levels of macrophages infiltrating the intestine. Hence, we investigated potential direct effects of MCH on monocyte/macrophage functions critical for defense against intestinal pathogens. Using RAW 264.7 mouse monocytic cells, which express endogenous MCH receptor, we found that treatment with MCH enhanced the phagocytic capacity of these cells. Taken together, these findings reveal a previously unappreciated role for MCH in host-bacterial interactions.

Sarcophine-diol inhibits expression of COX-2, inhibits activity of cPLA2, enhances degradation of PLA2 and PLC(γ)1 and inhibits cell membrane permeability in mouse melanoma B16F10 cells

Sarcophine-diol (SD) is a semi-synthetic derivative of sarcophine with a significant chemopreventive effect against non-melanoma skin cancer both in vitro and in vivo. Recently, we have studied the effect of SD on melanoma development using the mouse melanoma B₁₆F₁₀ cell line. In this study, our findings show that SD suppresses cell multiplication and diminishes membrane permeability for ethidium bromide (EB), a model marker used to measure cell permeability for Ca²⁺ ions. SD also decreases protein levels of COX-2, and increases degradation of phospholipases PLA₂ and PLC(γ)1 and diminishes enzymatic activity of the Ca²⁺-dependent cPLA₂. This lower membrane permeability for Ca²⁺-ions, associated with SD, is most likely due to the diminished content of lysophosphosphatidylcholine (lysoPC) within cell membranes caused by the effect of SD on PLA₂. The decrease in diacylglycerol (DAG) and inositol 1,4,5-triphosphate (IP₃) due to inhibition of PLC(γ)1, leads to the downregulation of Ca²⁺-dependent processes within the cell and also inhibits the formation of tumors. These findings support our previous data suggesting that SD may have significant potential in the treatment of melanoma.

[¹⁸F]FE@SNAP-A new PET tracer for the melanin concentrating hormone receptor 1 (MCHR1): microfluidic and vessel-based approaches

Changes in the expression of the melanin concentrating hormone receptor 1 (MCHR1) are involved in a variety of pathologies, especially obesity and anxiety disorders. To monitor these pathologies in-vivo positron emission tomography (PET) is a suitable method. After the successful radiosynthesis of [(11)C]SNAP-7941-the first PET-Tracer for the MCHR1, we aimed to synthesize its [(18)F]fluoroethylated analogue: [(18)F]FE@SNAP. Therefore, microfluidic and vessel-based approaches were tested. [(18)F]fluoroethylation was conducted via various [(18)F]fluoroalkylated synthons and direct [(18)F]fluorination. Only the direct [(18)F]fluorination of a tosylated precursor using a flow-through microreactor was successful, affording [(18)F]FE@SNAP in 44.3 ± 2.6%.

Reduced intestinal tumorigenesis in APCmin mice lacking melanin-concentrating hormone

BACKGROUND

Melanin-concentrating hormone (MCH) is an evolutionary conserved hypothalamic neuropeptide that in mammals primarily regulates appetite and energy balance. We have recently identified a novel role for MCH in intestinal inflammation by demonstrating attenuated experimental colitis in MCH deficient mice or wild type mice treated with an anti-MCH antibody. Therefore, targeting MCH has been proposed for the treatment of inflammatory bowel disease. Given the link between chronic intestinal inflammation and colorectal cancer, in the present study we sought to investigate whether blocking MCH might have effects on intestinal tumorigenesis that are independent of inflammation.

METHODOLOGY

Tumor development was evaluated in MCH-deficient mice crossed to the APCmin mice which develop spontaneously intestinal adenomas. A different cohort of MCH-/- and MCH+/+ mice in the APCmin background was treated with dextran sodium sulphate (DSS) to induce inflammation-dependent colorectal tumors. In Caco2 human colorectal adenocarcinoma cells, the role of MCH on cell survival, proliferation and apoptosis was investigated.

RESULTS

APCmin mice lacking MCH developed fewer, smaller and less dysplastic tumors in the intestine and colon which at the molecular level are characterized by attenuated activation of the wnt/beta-catenin signaling pathway and increased apoptotic indices. Form a mechanistic point of view, MCH increased the survival of colonic adenocarcinoma Caco2 cells via inhibiting apoptosis, consistent with the mouse studies.

CONCLUSION

In addition to modulating inflammation, MCH was found to promote intestinal tumorigenesis at least in part by inhibiting epithelial cell apoptosis. Thereby, blocking MCH as a therapeutic approach is expected to decrease the risk for colorectal cancer.

Radiosynthesis of [11C]SNAP-7941--the first PET-tracer for the melanin concentrating hormone receptor 1 (MCHR1)

The melanin concentrating hormone (MCH) system is a new target to treat human disorders. Our aim was the preparation of the first PET-tracer for the MCHR1. [(11)C]SNAP-7941 is a carbon-11 labeled analog of the published MCHR1 antagonist SNAP-7941. The optimum reaction conditions were 2 min reaction time, ≤25°C reaction temperature, and 2 mg/mL precursor (SNAP-acid) in acetonitrile, using [(11)C]CH(3)OTf as methylation agent. [(11)C]SNAP-7941 was prepared in a reliable and feasible manner with high radiochemical yields (2.9±1.6 GBq; 11.5±6.4% EOB, n=15).

Melanin-concentrating hormone: a new sleep factor?

Neurons containing the neuropeptide melanin-concentrating hormone (MCH) are mainly located in the lateral hypothalamus and the incerto-hypothalamic area, and have widespread projections throughout the brain. While the biological functions of this neuropeptide are exerted in humans through two metabotropic receptors, the MCHR1 and MCHR2, only the MCHR1 is present in rodents. Recently, it has been shown that the MCHergic system is involved in the control of sleep. We can summarize the experimental findings as follows: (1) The areas related to the control of sleep and wakefulness have a high density of MCHergic fibers and receptors. (2) MCHergic neurons are active during sleep, especially during rapid eye movement (REM) sleep. (3) MCH knockout mice have less REM sleep, notably under conditions of negative energy balance. Animals with genetically inactivated MCHR1 also exhibit altered vigilance state architecture and sleep homeostasis. (4) Systemically administered MCHR1 antagonists reduce sleep. (5) Intraventricular microinjection of MCH increases both slow wave sleep (SWS) and REM sleep; however, the increment in REM sleep is more pronounced. (6) Microinjection of MCH into the dorsal raphe nucleus increases REM sleep time. REM seep is inhibited by immunoneutralization of MCH within this nucleus. (7) Microinjection of MCH in the nucleus pontis oralis of the cat enhances REM sleep time and reduces REM sleep latency. All these data strongly suggest that MCH has a potent role in the promotion of sleep. Although both SWS and REM sleep are facilitated by MCH, REM sleep seems to be more sensitive to MCH modulation.

You deserve what you eat: lessons learned from the study of the melanin-concentrating hormone (MCH)-deficient mice

OBJECTIVES

Diet plays a crucial role in the development of obesity and insulin resistance via multiple mechanisms. Saturated fatty acids can directly trigger tissue specific proinflammatory pathways via Toll-like receptor-4 (TLR4)-dependent mechanisms. Moreover, diet can change the gut microbiome and increase gut permeability. However, very few studies have addressed the obesity-independent role of diet. Dissecting the effects of diet from those of obesity per se will enhance our understanding of the underlying pathogenesis, and, at the translational level, advance our treatment approaches for obesity and its co-morbidities.

METHODS

Melanin-concentrating hormone (MCH) is an important regulator of appetite and energy balance. MCH-deficient mice are resistant to diet-induced obesity, primarily due to increased locomotor activity. We took advantage of the unique phenotype of these mice to examine the metabolic and inflammatory consequences of a 15-week consumption of a diet high in saturated fat.

RESULTS

MCH-deficient mice chronically exposed to a high-fat diet gain less weight compared to their wild-type littermates, despite similar food intake, and are protected from hepatosteatosis. They also lack obesity-associated upregulation of serum leptin and insulin levels and have improved total body insulin sensitivity. Nevertheless, we found indistinguishable liver-specific innate immune responses in both genotypes associated with high-fat feeding, which involved activation of TLR4 and its downstream effectors, MyD88, p38 MAP kinase and STAT-3.

CONCLUSIONS

Our findings indicate that high-fat feeding is deleterious to the liver, independently of the obesity status. They also suggest that MCH is not necessary for the TLR4-dependent immune response triggered by the high-fat diet.

Immunoneutralization of melanin-concentrating hormone (MCH) in the dorsal raphe nucleus: effects on sleep and wakefulness

Hypothalamic neurons that utilize melanin-concentrating hormone (MCH) as a neuromodulator exert a positive control over energy homeostasis, inducing feeding and decreasing metabolism. Recent studies have shown also that this system plays a role in the generation and/or maintenance of sleep. MCHergic neurons project to the serotonergic dorsal raphe nucleus (DR), a neuroanatomical structure involved in several functions during wakefulness (W), and in the regulation of rapid-eye movements (REM) sleep. Recently, we determined the effect of MCH microinjected into the DR on sleep variables in the rat. MCH produced a marked increment of REM sleep, whereas slow wave sleep (SWS) showed only a moderate increase. In the present study, we analyze the effect of immunoneutralization of MCH in the DR on sleep and W in the rat. Compared to the control solution, microinjections of anti-MCH antibodies (1/100 solution in 0.2 μl) induced a significant increase in REM sleep latency (31.2±7.1 vs. 84.2±24.8 min, p<0.05) and a decrease of REM sleep time (37.8±5.4 vs. 17.8±2.9 min, p<0.05) that was related to the reduction in the number of REM sleep episodes. In addition, there was an increase of total W time (49.8±4.6 vs. 72.0±5.7 min, p<0.01). Light sleep and SWS remained unchanged. The intra-DR administration of a more diluted solution of anti-MCH antibodies (1/500) or rabbit pre-immune serum did not modify neither W nor REM sleep variables. Our findings strongly suggest that MCH released in the DR facilitates the occurrence of REM sleep.

Melanin-concentrating hormone facilitates migration of preadipocytes

Adipose tissue develops from differentiating preadipocytes that expand and migrate. 3T3-L1 preadipocytes respond to melanin-concentrating hormone (MCH) by increasing leptin production. Here, we investigate whether MCH elicits remodeling of the actin cytoskeleton and whether this translates into altered migratory capacity of these cells. Incubation with MCH resulted in a loss of actin stress fibers accompanied by a change in morphology from a stretched-out fibroblast to a rounded cell. PMC-3881-PI, a MCH receptor 1 antagonist blocked the effect, confirming this receptor is solely responsible for MCH-mediated actin rearrangements. Both a pharmacological activator and inhibitor of phospholipase C were used to demonstrate this molecule's importance to the signaling pathway. Finally, MCH was shown to facilitate preadipocyte migration into a scratch wound, revealing a previously unknown role for MCH in the regulation of cellular migration. We conclude that MCH could influence the expansion of adipose tissue through its ability to enhance preadipocyte migration.

Melanin-concentrating hormone producing neurons: Activities and modulations

Regulation of energy homeostasis in animals involves adaptation of energy intake to its loss, through a perfect regulation of feeding behavior and energy storage/expenditure. Factors from the periphery modulate brain activity in order to adjust food intake as needed. Particularly, "first order" neurons from arcuate nucleus are able to detect modifications in homeostatic parameters and to transmit information to "second order" neurons, partly located in the lateral hypothalamic area. These "second order" neurons have widespread projections throughout the brain and their proper activation leads them to a coordinated response associated to an adapted behavior. Among these neurons, melanin-concentrating hormone (MCH) expressing neurons play an integrative role of the various factors arising from periphery, first order neurons and extra-hypothalamic arousal systems neurons and modulate regulation of feeding, drinking and seeking behaviors. As regulation of MCH release is correlated to regulation of MCH neuronal activity, we focused this review on the electrophysiological properties of MCH neurons from the lateral hypothalamic area. We first reviewed the knowledge on the endogenous electrical properties of MCH neurons identified according to various criteria which are described. Then, we dealt with the modulations of the electrical activity of MCH neurons by different factors such as glucose, glutamate and GABA, peptides and hormones regulating feeding and transmitters of extra-hypothalamic arousal systems. Finally, we described the current knowledge on the modulation of MCH neuronal activity by cytokines and chemokines. Because of such regulation, MCH neurons are some of the best candidate to account for infection-induced anorexia, but also obesity.

MCH receptors/gene structure-in vivo expression

Melanin-concentrating hormone (MCH) is a cyclic peptide which was originally discovered in fish to lighten skin color by affecting melanosomes aggregation. This peptide is highly conserved and also found in rodents whose gene is overexpressed upon fasting. However, the site of MCH action remained obscure until its receptor was discovered in 1999 as a G protein-coupled receptor. After this receptor structure was identified, the functional domains important for MCH-MCHR interaction were revealed. Moreover, the cloning of the MCH receptor led us to identify the in vivo sites of MCH action which suggested potential physiological functions of the MCH system. Furthermore, the MCH receptor identification allow for designing surrogate molecules which can block MCH activity. Studies using these molecules revealed various physiological functions of the MCH system not only in feeding but also in other physiological responses such as stress and emotion. This review will discuss how the MCH receptor was discovered and its impact on many studies investigating the MCH receptor's structure, signaling pathways, and expression pattern.

Electrophysiological effects of MCH on neurons in the hypothalamus

Melanin concentrating hormone (MCH) has been implicated in many brain functions and behaviors essential to the survival of animals. The hypothalamus is one of the primary targets where MCH-containing nerve fibers and MCH receptors are extensively expressed and its actions in the brain are exerted. Since the identification of MCH receptors as orphan G protein coupled receptors, the cellular effects of MCH have been revealed in many non-neuronal expression systems (including Xenopus oocytes and cell lines), however, the mechanism by which MCH modulates the activity in the neuronal circuitry of the brain is still under investigation. This review summarizes our current knowledge of electrophysiological effects of MCH on neurons in the hypothalamus, particularly in the lateral hypothalamus. Generally, MCH exerts inhibitory effects on neurons in this structure and may serve as a homeostatic regulator in the lateral hypothalamic area. Given the contrast between the limited data on cellular functions of MCH in the hypothalamus versus a fast growing body of evidence on the vital role of MCH in animal behavior, further investigations of the former are warranted.

MCH receptor peptide agonists and antagonists

Melanin-concentrating hormone (MCH) is an important neuropeptide hormone involved in multiple physiological processes. Peptide derivatives of MCH have been developed as tools to aid research including potent radioligands, receptor selective agonists, and potent antagonists. These tools have been used to further understand the role of MCH in physiology, primarily in rodents. However, the tools could also help elucidate the role for MCHR1 and MCHR2 in mediating MCH signaling in higher species.

Melanin-concentrating hormone and immune function

To date, melanin-concentrating hormone (MCH) has been generally considered as peptide acting almost exclusively in the central nervous system. In the present paper, we revise the experimental evidence, demonstrating that MCH and its receptors are expressed by cells of the immune system and directly influence the response of these cells in some circumstances. This therefore supports the idea that, as with other peptides, MCH could be considered as a modulator of the immune system. Moreover, we suggest that this could have important implications in several immune-mediated disorders and affirm that there is a clear need for further investigation.

Neuropeptides and inflammatory bowel disease

PURPOSE OF REVIEW

Inflammatory bowel disease (IBD) is a chronic intestinal inflammatory condition, the pathophysiology of which is not well understood. It has, however, become increasingly evident that interactions between the enteric nervous system and the immune system play an important role in the cause of IBD. Both the enteric nervous system and the central nervous system can amplify or modulate the aspects of intestinal inflammation through secretion of neuropeptides or small molecules. The purpose of this study is to present recent data on the role that neuropeptides play in the pathophysiology of IBD.

RECENT FINDINGS

The best studied of the neuropeptides thought to play a role in the pathogenesis of IBD include substance P, corticotropin-releasing hormone, neurotensin, and vasoactive intestinal peptide; small molecules include acetylcholine and serotonin. Recently discovered functions of each of these neuropeptides with a discussion of implications of the data for therapy are reviewed.

SUMMARY

Although the available data suggest an important role for neuropeptides in the pathophysiology of intestinal inflammation, there does yet not appear to be a function that can be taken as established for any of these molecules. The complexity of neuroimmune-endocrine systems, conflicting study results and dual mechanisms of action, warrant further research in this field. Clarification of the molecular mechanisms of action of neuropeptides and on immune and inflammatory reactions will likely yield new treatment options in the future.

Inflammation and proliferation act together to mediate intestinal cell fusion

Cell fusion between circulating bone marrow-derived cells (BMDCs) and non-hematopoietic cells is well documented in various tissues and has recently been suggested to occur in response to injury. Here we illustrate that inflammation within the intestine enhanced the level of BMDC fusion with intestinal progenitors. To identify important microenvironmental factors mediating intestinal epithelial cell fusion, we performed bone marrow transplantation into mouse models of inflammation and stimulated epithelial proliferation. Interestingly, in a non-injury model or in instances where inflammation was suppressed, an appreciable baseline level of fusion persisted. This suggests that additional mediators of cell fusion exist. A rigorous temporal analysis of early post-transplantation cellular dynamics revealed that GFP-expressing donor cells first trafficked to the intestine coincident with a striking increase in epithelial proliferation, advocating for a required fusogenic state of the host partner. Directly supporting this hypothesis, induction of augmented epithelial proliferation resulted in a significant increase in intestinal cell fusion. Here we report that intestinal inflammation and epithelial proliferation act together to promote cell fusion. While the physiologic impact of cell fusion is not yet known, the increased incidence in an inflammatory and proliferative microenvironment suggests a potential role for cell fusion in mediating the progression of intestinal inflammatory diseases and cancer.

The versatility of the vagus

The gut is one of several organs contributing to the peripheral signalling network that controls food intake. Afferent neurons of the vagus nerve provide an important pathway for gut signals that act by triggering ascending pathways from the brain stem to hypothalamus. Recent work indicates the existence of mechanisms operating at the level of vagal afferent neurons to modulate the effect of gastrointestinal satiety signals. Thus, the well known satiety hormone cholecystokinin (CCK) not only stimulates the discharge of these neurons but also controls their expression of both G-protein coupled receptors and peptide neurotransmitters known to influence food intake. When plasma CCK concentrations are low e.g. in fasting, the expression by vagal afferent neurons of cannabinoid (CB)-1 and melanin concentrating hormone (MCH)-1 receptors is increased. Release of CCK by feeding leads to a rapid down-regulation of expression of both receptors and to increased expression of Y2 receptors. In fasting, there is also increased expression in these neurons of the appetite-stimulating neuropeptide transmitter MCH, and depressed expression of the satiety-peptide cocaine and amphetamine regulated transcript (CARTp); endogenous CCK decreases MCH expression and stimulates CART expression. The gastric orexigenic hormone ghrelin blocks these actions of CCK at least in part by excluding phosphoCREB from the nucleus. The data suggest that CCK acts as a gatekeeper to determine the capacity of other neuroendocrine signals to act via vagal afferent neurons to influence food intake.

Melanin-concentrating hormone (MCH) modulates C difficile toxin A-mediated enteritis in mice

OBJECTIVE

Melanin-concentrating hormone (MCH) is a hypothalamic orexigenic neuropeptide that regulates energy balance. However, the distribution of MCH and its receptor MCHR1 in tissues other than brain suggested additional, as yet unappreciated, roles for this neuropeptide. Based on previous paradigms and the presence of MCH in the intestine as well as in immune cells, its potential role in gut innate immune responses was examined.

METHODS

In human intestinal xenografts grown in mice, changes in the expression of MCH and its receptors following treatment with Clostridium difficile toxin A, the causative agent of antibiotic-associated diarrhoea in hospitalised patients, were examined. In colonocytes, the effect of C difficile toxin A treatment on MCHR1 expression, and of MCH on interleukin 8 (IL8) expression was examined. MCH-deficient mice and immunoneutralisation approaches were used to examine the role of MCH in the pathogenesis of C difficile toxin A-mediated acute enteritis.

RESULTS

Upregulation of MCH and MCHR1 expression was found in the human intestinal xenograft model, and of MCHR1 in colonocytes following exposure to toxin A. Treatment of colonocytes with MCH resulted in IL8 transcriptional upregulation, implying a link between MCH and inflammatory pathways. In further support of this view, MCH-deficient mice developed attenuated toxin A-mediated intestinal inflammation and secretion, as did wild-type mice treated with an antibody against MCH or MCHR1.

CONCLUSION

These findings signify MCH as a mediator of C difficile-associated enteritis and possibly of additional gut pathogens. MCH may mediate its proinflammatory effects at least in part by acting on epithelial cells in the intestine.