Melanocortin 4 receptor activates ERK-cFos pathway to increase brain-derived neurotrophic factor expression in rat astrocytes and hypothalamus

MC4R Variants Modulate α-MSH and Setmelanotide Induced Cellular Signaling at Multiple Levels

CONTEXT

The melanocortin-4 receptor (MC4R) plays an important role in body weight regulation. Pathogenic MC4R variants are the most common cause of monogenic obesity.

OBJECTIVE

We have identified 17 MC4R variants in adult and pediatric patients with obesity. Here we aimed to functionally characterize these variants by analyzing 4 different aspects of MC4R signaling. In addition, we aimed to analyze the effect of setmelanotide, a potent MC4R agonist, on these MC4R variants.

MATERIALS AND METHODS

Cell surface expression and α-melanocyte stimulating hormone (α-MSH)- or setmelanotide-induced cAMP response, β-arrestin-2 recruitment, and ERK activation were measured in cells expressing either wild type or variant MC4R.

RESULTS

We found a large heterogeneity in the function of these variants. We identified variants with a loss of response for all studied MC4R signaling, variants with no cAMP accumulation or ERK activation but normal β-arrestin-2 recruitment, and variants with normal cAMP accumulation and ERK activation but decreased β-arrestin-2 recruitment, indicating disrupted desensitization and signaling mechanisms. Setmelanotide displayed a greater potency and similar efficacy as α-MSH and induced significantly increased maximal cAMP responses of several variants compared to α-MSH. Despite the heterogeneity in functional response, there was no apparent difference in the obesity phenotype in our patients.

CONCLUSION

We show that these obesity-associated MC4R variants affect MC4R signaling differently yet lead to a comparable clinical phenotype. Our results demonstrate the clinical importance of assessing the effect of MC4R variants on a range of molecular signaling mechanisms to determine their association with obesity, which may aid in improving personalized treatment.

Arc and BDNF mediated effects of hippocampal astrocytic glutamate uptake blockade on spatial memory stages

Glutamate is involved in fundamental functions, including neuronal plasticity and memory. Astrocytes are integral elements involved in synaptic function, and the GLT-1 transporter possesses a critical role in glutamate uptake. Here, we study the role of GLT-1, specifically located in astrocytes, in the consolidation, expression, reconsolidation and persistence of spatial object recognition memory in rats. Administration of dihydrokainic acid (DHK), a selective GLT-1 inhibitor, into the dorsal hippocampus around a weak training which only induces short-term memory, promotes long-term memory formation. This promotion is prevented by hippocampal administration of protein-synthesis translation inhibitor, blockade of Activity-regulated cytoskeleton-associated protein (Arc) translation or Brain-Derived Neurotrophic Factor (BDNF) action, which are plasticity related proteins necessary for memory consolidation. However, DHK around a strong training, which induces long-term memory, does not affect memory consolidation. Administration of DHK before the test session impairs the expression of long-term memory, and this effect is dependent of Arc translation. Furthermore, DHK impairs reconsolidation if applied before a reactivation session, and this effect is independent of Arc translation. These findings reveal specific consequences on spatial memory stages developed under hippocampal GLT-1 blockade, shedding light on the intricate molecular mechanisms, governed in part for the action of glia.

Polysorbate 80 coated chitosan nanoparticles for delivery of α-melanocyte stimulating hormone analog (NDP-MSH) to the brain reverse cognitive impairment related to neuroinflammation produced by a high-fat diet (HFD)

This study aimed to develop polysorbate 80-coated chitosan nanoparticles (PS80/CS NPs) as a delivery system for improved brain targeting of α-Melanocyte Stimulating Hormone analog (NDP-MSH). Chitosan nanoparticles loaded with NDP-MSH were surface-modified with polysorbate 80 ([NDP-MSH]-PS80/CS NP), which formed a flattened layer on their surface. Nanoparticle preparation involved ionic gelation, followed by characterization using scanning electron microscopy (SEM) for morphology, dynamic light scattering (DLS) for colloidal properties, and ATR-FTIR spectroscopy for structure. Intraperitoneal injection of FITC-PS80/CS NPs and [NDP-MSH]-PS80/CS NP in rats demonstrated their ability to cross the blood-brain barrier, reach the brain, and accumulate in CA1 neurons of the dorsal hippocampus within 2 h. Two experimental models of neuroinflammation were employed with Male Wistar rats: a short-term model involving high-fat diet (HFD) consumption for 5 days followed by an immune stimulus with LPS, and a long-term model involving HFD consumption for 8 weeks. In both models, [NDP-MSH]-PS80/CS NPs could reverse the decreased expression of contextual fear memory induced by the diets. These findings suggest that [NDP-MSH]-PS80/CS NPs offer a promising strategy to overcome the limitations of NDP-MSH regarding pharmacokinetics and enzymatic stability. By facilitating NDP-MSH delivery to the hippocampus, these nanoparticles can potentially mitigate the cognitive impairments associated with HFD consumption and neuroinflammation.

Activation of the melanocortin-1 receptor attenuates neuronal apoptosis after traumatic brain injury by upregulating Merlin expression

Traumatic brain injury (TBI) is a common disease worldwide with high mortality and disability rates. Besides the primary mechanical injury, the secondary injury associated with TBI can also induce numerous pathological changes, such as brain edema, nerve apoptosis, and neuroinflammation, which further aggravates neurological dysfunction and even causes the death due to the primary injury. Among them, neuronal apoptosis is a key link in the injury. Melanocortin-1 receptor (MC1R) is a G protein coupled receptor, belonging to the melanocortin receptor family. Studies have shown that activation of MC1R inhibits oxidative stress and apoptosis, and confers neuroprotective effects against various neurological diseases. Merlin is a protein product of the NF2 gene, which is widely expressed in the central nervous system (CNS) of mice, rats, and humans. Studies have indicated that Merlin is associated with MC1R. In this study, we explored the anti-apoptotic effects and potential mechanisms of MC1R. A rat model of TBI was established through controlled cortical impact. The MC1R-specific agonist Nle4-D-Phe7-α-Melanocyte (NDP-MSH) and the inhibitor MSG-606 were employed to explore the effects of MC1R and Merlin following TBI and investigated the associated mechanisms. The results showed that the expression levels of MC1R and Merlin were upregulated after TBI, and activation of MC1R promoted Merlin expression. Further, we found that MC1R activation significantly improved neurological dysfunction and reduced brain edema and neuronal apoptosis induced by TBI in rats. Mechanistically, its neuroprotective function and anti-apoptotic were partly associated with MC1R activation. In conclusion, we demonstrated that MC1R activation after TBI may inhibit apoptosis and confer neuroprotection by upregulating the expression of Merlin.

The rs17782313 polymorphism near MC4R gene confers a high risk of obesity and hyperglycemia, while PGC1α rs8192678 polymorphism is weakly correlated with glucometabolic disorder: a systematic review and meta-analysis

Background

The relationships of the rs17782313 polymorphism near melanocortin 4 receptor gene (MC4R) and the rs8192678 polymorphism in peroxisome proliferator-activated receptor gamma coactivator 1 alpha gene (PGC1α) with metabolic abnormalities have been explored in many populations around the world, but the findings were not all consistent and sometimes even a bit contradictory.

Methods

Electronic databases including Medline, Scopus, Embase, Web of Science, CNKI and Google Scholar were checked for studies that met the inclusion criteria. Data were carefully extracted from eligible studies. Standardized mean differences (SMDs) were calculated by using a random-effects model to examine the differences in the indexes of obesity, glucometabolic disorder and dyslipidemia between the genotypes of the rs17782313 and rs8192678 polymorphisms. Cochran's Q-statistic test and Begg's test were employed to identify heterogeneity among studies and publication bias, respectively.

Results

Fifty studies (58,716 subjects) and 51 studies (18,660 subjects) were respectively included in the pooled meta-analyses for the rs17782313 and rs8192678 polymorphisms. The C-allele carriers of the rs17782313 polymorphism had a higher average level of body mass index (SMD = 0.21 kg/m2, 95% confidence interval [95% CI] = 0.12 to 0.29 kg/m2, p < 0.001), waist circumference (SMD = 0.14 cm, 95% CI = 0.06 to 0.23 cm, p < 0.001) and blood glucose (SMD = 0.09 mg/dL, 95% CI = 0.02 to 0.16 mg/dL, p = 0.01) than the TT homozygotes. Regarding the rs8192678 polymorphism, no significant associations with the indexes of obesity, glucometabolic disorder and dyslipidemia were detected. However, significant correlations between the rs8192678 polymorphism and multiple glucometabolic indexes were observed in subgroup analyses stratified by sex, age, ethnicity and health status.

Conclusion

The meta-analysis demonstrates that the C allele of the MC4R rs17782313 polymorphism confers a higher risk of obesity and hyperglycemia, and the PGC1α rs8192678 polymorphism is weakly correlated with glucometabolic disorder. These findings may partly explain the relationships between these variants and diabetes as well as cardiovascular disease.

Systematic review registration

https://www.crd.york.ac.uk/prospero/, identifier CRD42022373543.

The Melanocortin System: A Promising Target for the Development of New Antidepressant Drugs

Major depression is one of the most prevalent mental disorders, causing significant human suffering and socioeconomic loss. Since conventional antidepressants are not sufficiently effective, there is an urgent need to develop new antidepressant medications. Despite marked advances in the neurobiology of depression, the etiology and pathophysiology of this disease remain poorly understood. Classical and newer hypotheses of depression suggest that an imbalance of brain monoamines, dysregulation of the hypothalamic-pituitary-adrenal axis (HPAA) and immune system, or impaired hippocampal neurogenesis and neurotrophic factors pathways are cause of depression. It is assumed that conventional antidepressants improve these closely related disturbances. The purpose of this review was to discuss the possibility of affecting these disturbances by targeting the melanocortin system, which includes adrenocorticotropic hormone-activated receptors and their peptide ligands (melanocortins). The melanocortin system is involved in the regulation of various processes in the brain and periphery. Melanocortins, including peripherally administered non-corticotropic agonists, regulate HPAA activity, exhibit anti-inflammatory effects, stimulate the levels of neurotrophic factors, and enhance hippocampal neurogenesis and neurotransmission. Therefore, endogenous melanocortins and their analogs are able to complexly affect the functioning of those body’s systems that are closely related to depression and the effects of antidepressants, thereby demonstrating a promising antidepressant potential.

Identification of MRAP protein family as broad-spectrum GPCR modulators

BACKGROUND

The melanocortin receptor accessory proteins (MRAP1 and MRAP2) are well-known endocrine regulators for the trafficking and signalling of all five melanocortin receptors (MC1R-MC5R). The observation of MRAP2 on regulating several non-melanocortin G protein-coupled receptors (GPCRs) has been sporadically reported, whereas other endogenous GPCR partners of the MRAP protein family are largely unknown.

METHODS

Here, we performed single-cell transcriptome analysis and drew a fine GPCR blueprint and MRAPs-associated network of two major endocrine organs, the hypothalamus and adrenal gland at single-cell resolution. We also integrated multiple bulk RNA-seq profiles and single-cell datasets of human and mouse tissues, and narrowed down a list of 48 GPCRs with strong endogenous co-expression correlation with MRAPs.

RESULTS

36 and 46 metabolic-related GPCRs were consequently identified as novel interacting partners of MRAP1 or MRAP2, respectively. MRAPs exhibited protein-protein interactions and varying pharmacological properties on the surface translocation, constitutive activities and ligand-stimulated downstream signalling of these GPCRs. Knockdown of MRAP2 expression by hypothalamic administration of adeno-associated virus (AAV) packed shRNA stimulated body weight gain in mouse model. Co-injection of corticotropinreleasing factor (CRF), the agonist of corticotropin releasing hormone receptor 1 (CRHR1), suppressed feeding behaviour in a MRAP2-dependent manner.

CONCLUSIONS

Collectively, our study has comprehensively elucidated the complex GPCR networks in two major endocrine organs and redefined the MRAP protein family as broad-spectrum GPCR modulators. MRAP proteins not only serve as a vital endocrine pivot on the regulation of global GPCR activities in vivo that could explain the composite physiological phenotypes of the MRAP2 null murine model but also provide us with new insights of the phenotyping investigation of GPCR-MRAP functional complexes.

Effects of maternal high-fat diet on the hypothalamic components related to food intake and energy expenditure in mice offspring

Maternal exposure to a high-fat diet (HFD) during pregnancy and lactation has been related to changes in the hypothalamic circuits involved in the regulation of food intake. Furthermore, maternal HFD during the critical period of development can alter the offspring's metabolic programming with long-term repercussions. This study systematically reviewed the effects of HFD consumption during pre-pregnancy, pregnancy and/or lactation. The main outcomes evaluated were food intake; body weight; cellular or molecular aspects of peptides and hypothalamic receptors involved in the regulation of energy balance in mice. Two independent authors performed a search in the electronic databases Medline/PubMed, LILACS, Web of Science, EMBASE, SCOPUS and Sigle via Open Gray. Included were experimental studies of mice exposed to HFD during pregnancy and/or lactation that evaluated body composition, food intake, energy expenditure and hypothalamic components related to energy balance. Internal validity was assessed using the SYRCLE risk of bias. The Kappa index was measured to analyze the agreement between reviewers. The PRISMA statement was used to report this systematic review. Most studies demonstrated that there was a higher body weight, body fat deposits and food intake, as well as alterations in the expression of hypothalamic neuropeptides in offspring that consumed HFD. Therefore, the maternal diet can affect the phenotype and metabolism of the offspring, in addition to harming the hypothalamic circuits and favoring the orexigenic pathways.

Interactions between Polygenic Risk Scores, Dietary Pattern, and Menarche Age with the Obesity Risk in a Large Hospital-Based Cohort

Obese Asians are more susceptible to metabolic diseases than obese Caucasians of the same body mass index (BMI). We hypothesized that the genetic variants associated with obesity risk interact with the lifestyles of middle-aged and elderly adults, possibly allowing the development of personalized interventions based on genotype. We aimed to examine this hypothesis in a large city hospital-based cohort in Korea. The participants with cancers, thyroid diseases, chronic kidney disease, or brain-related diseases were excluded. The participants were divided into case and control according to their BMI: ≥25 kg/m2 (case; n = 17,545) and <25 kg/m2 (control; n = 36,283). The genetic variants that affected obesity risk were selected using a genome-wide association study, and the genetic variants that interacted with each other were identified by generalized multifactor dimensionality reduction analysis. The selected genetic variants were confirmed in the Ansan/Ansung cohort, and polygenetic risk scores (PRS)-nutrient interactions for obesity risk were determined. A high BMI was associated with a high-fat mass (odds ratio (OR) = 20.71) and a high skeletal muscle-mass index (OR = 3.38). A high BMI was positively related to metabolic syndrome and its components, including lipid profiles, whereas the initial menstruation age was inversely associated with a high BMI (OR = 0.78). The best model with 5-SNPs included SEC16B_rs543874, DNAJC27_rs713586, BDNF_rs6265, MC4R_rs6567160, and GIPR_rs1444988703. The high PRS with the 5-SNP model was positively associated with an obesity risk of 1.629 (1.475-1.798) after adjusting for the covariates. The 5-SNP model interacted with the initial menstruation age, fried foods, and plant-based diet for BMI risk. The participants with a high PRS also had a higher obesity risk when combined with early menarche, low plant-based diet, and a high fried-food intake than in participants with late menarche, high plant-based diet, and low fried-food intake. In conclusion, people with a high PRS and earlier menarche age are recommended to consume fewer fried foods and a more plant-based diet to decrease obesity risk. This result can be applied to personalized nutrition for preventing obesity.

Downregulation of connexin43 potentiates noradrenaline-induced expression of brain-derived neurotrophic factor in primary cultured cortical astrocytes

Decreased expression of brain-derived neurotrophic factor (BDNF) is involved in the pathology of depressive disorders. Astrocytes produce BDNF following antidepressant treatment or stimulation of adrenergic receptors. Connexin43 (Cx43) is mainly expressed in central nervous system astrocytes and its expression is downregulated in patients with major depression. How changes in Cx43 expression affect astrocyte function, including BDNF production, is poorly understood. The current study examined the effect of Cx43 knockdown on BDNF expression in cultured cortical astrocytes after stimulation of adrenergic receptors. The expression of Cx43 in rat primary cultured cortical astrocytes was downregulated with RNA interference. Levels of messenger RNAs (mRNAs) or proteins were measured by real-time PCR and western blotting, respectively. Knockdown of Cx43 potentiated noradrenaline (NA)-induced expression of BDNF mRNA in cultured astrocytes. NA treatment induced proBDNF protein expression in astrocytes transfected with small interfering RNA (siRNA) targeting Cx43, but not with control siRNA. This potentiation was mediated by the Src tyrosine kinase-extracellular signal-regulated kinase (ERK) pathway through stimulation of adrenergic α1 and β receptors. Furthermore, the Gq/11 protein-Src-ERK pathway and the G-protein coupled receptor kinase 2-Src-ERK pathway were involved in α1 and β adrenergic receptor-mediated potentiation of BDNF mRNA expression, respectively. The current studies demonstrate a novel mechanism of BDNF expression in cortical astrocytes mediated by Cx43, in which downregulation of Cx43 increases, through adrenergic receptors, the expression of BDNF. The current findings indicate a potentially novel mechanism of action of antidepressants, via regulation of astrocytic Cx43 expression and subsequent BDNF expression.

Lipocalin-2 counteracts metabolic dysregulation in obesity and diabetes

Regulation of food intake is a recently identified endocrine function of bone that is mediated by Lipocalin-2 (LCN2). Osteoblast-secreted LCN2 suppresses appetite and decreases fat mass while improving glucose metabolism. We now show that serum LCN2 levels correlate with insulin levels and β-cell function, indices of healthy glucose metabolism, in obese mice and obese, prediabetic women. However, LCN2 serum levels also correlate with body mass index and insulin resistance in the same individuals and are increased in obese mice. To dissect this apparent discrepancy, we modulated LCN2 levels in mice. Silencing Lcn2 expression worsens metabolic dysfunction in genetic and diet-induced obese mice. Conversely, increasing circulating LCN2 levels improves metabolic parameters and promotes β-cell function in mouse models of β-cell failure acting as a growth factor necessary for β-cell adaptation to higher metabolic load. These results indicate that LCN2 up-regulation is a protective mechanism to counteract obesity-induced glucose intolerance by decreasing food intake and promoting adaptive β-cell proliferation.

Activation of the Melanocortin-1 Receptor by NDP-MSH Attenuates Oxidative Stress and Neuronal Apoptosis through PI3K/Akt/Nrf2 Pathway after Intracerebral Hemorrhage in Mice

Oxidative stress and neuronal apoptosis play crucial roles in secondary brain injury (SBI) after intracerebral hemorrhage (ICH). Recently, Nle4-D-Phe7-α-melanocyte-stimulating hormone (NDP-MSH), a synthetic agonist of the melanocortin-1 receptor (Mc1r), has been proved to inhibit neuroinflammatory in several diseases. This study is aimed at exploring if NDP-MSH could reduce oxidative stress and neuronal apoptosis following ICH, as well as the potential mechanism. A mouse ICH model was induced by autologous blood injection. NDP-MSH was intraperitoneally injected at 1 h after ICH. Mc1r siRNA and PI3K inhibitor LY294002 were administrated to inhibit the expression of Mc1r and phosphorylation of PI3K, respectively. Neurological test, brain water content, enzyme-linked immunosorbent assay (ELISA), terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL), immunofluorescence, and Western blot analysis were utilized in this study. The results exhibited that Mc1r was mainly expressed in neurons, and its level in the ipsilateral hemisphere was significantly elevated after ICH. NDP-MSH treatment significantly attenuated the neurological deficits and brain water content 24 hours after ICH, which was accompanied by the inhibition of oxidative stress and neuronal apoptosis. The administration of NDP-MSH after ICH significantly promoted the expression of Mc1r, p-PI3K, p-Akt, and p-Nrf2, followed by an increase of Bcl-2 and reduction of cleaved caspase-3. Conversely, downregulating the expression of Mc1r and phosphorylation of PI3K aggravated the neurological deficits and brain edema at 24 hours after ICH, meanwhile, the effect of NDP-MSH on the expression of Mc1r, p-PI3K, p-Akt, p-Nrf2, Bcl-2, and cleaved caspase 3 was also abolished. In conclusion, our data suggest that the activation of Mc1r by NDP-MSH ameliorates oxidative stress and neuronal apoptosis through the PI3K/Akt/Nrf2 signaling pathway after ICH in mice.

Mitogen- and stress-activated protein kinase-1 activation is involved in melanocortin-induced BDNF expression in Neuro2a neuronal cells

Melanocortins are neuropeptides exerting versatile functions in the nervous system. Melanocortin 4 receptor (MC4R) is primarily expressed in the brain and is thought to be a major mediator for melanocortin. Brain-derived neurotrophic factor (BDNF) may be a crucial downstream molecule of MC4R activation, to yield neurite outgrowth, neuroregenerative, anorexigenic and other actions. In this study, we stimulated Neuro2a murine neuronal cells with an α-melanocyte stimulating hormone (α-MSH) analog, [Nle(4), D-Phe(7)]melanocyte-stimulating hormone (NDP-MSH). In Neuro2a cells, NDP-MSH promoted neurite outgrowth. Upon NDP-MSH administration, BDNF expression was greatly enhanced. Furthermore, this effect was effectively reversed by the MC4R antagonist, JKC-363. We found that NDP-MSH treatment activated the ERK cascade and its downstream kinase MSK1 (mitogen- and stress-activated protein kinase-1). Antagonism of the MSK1 cascade by a specific inhibitor or overexpression of a defective MSK1 mutant interrupted the phosphorylation of the transcription factor cAMP-response element binding protein (CREB), blocking BDNF upregulation. In addition, MSK1 activation triggered an epigenetic alteration in histone H3 (Ser10), facilitating the expression of the BDNF gene. Taken together, our results showed that MSK1 kinase positively activates MC4R-induced BDNF expression via modulating the phosphorylation of CREB and histone H3 in Neuro2a neuronal cells.

Astrocytes from cortex and striatum show differential responses to mitochondrial toxin and BDNF: implications for protection of striatal neurons expressing mutant huntingtin

Background

Evidence shows significant heterogeneity in astrocyte gene expression and function. We previously demonstrated that brain-derived neurotrophic factor (BDNF) exerts protective effects on whole brain primary cultured rat astrocytes treated with 3-nitropropionic acid (3NP), a mitochondrial toxin widely used as an in vitro model of Huntington’s disease (HD). Therefore, we now investigated 3NP and BDNF effects on astrocytes from two areas involved in HD: the striatum and the entire cortex, and their involvement in neuron survival.

Methods

We prepared primary cultured rat cortical or striatal astrocytes and treated them with BDNF and/or 3NP for 24 h. In these cells, we assessed expression of astrocyte markers, BDNF receptor, and glutamate transporters, and cytokine release. We prepared astrocyte-conditioned medium (ACM) from cortical and striatal astrocytes and tested its effect on a cellular model of HD.

Results

BDNF protected astrocytes from 3NP-induced death, increased expression of its own receptor, and activation of ERK in both cortical and striatal astrocytes. However, BDNF modulated glutamate transporter expression differently by increasing GLT1 and GLAST expression in cortical astrocytes but only GLT1 expression in striatal astrocytes. Striatal astrocytes released higher amounts of tumor necrosis factor-α than cortical astrocytes in response to 3NP but BDNF decreased this effect in both populations. 3NP decreased transforming growth factor-β release only in cortical astrocytes, whereas BDNF treatment increased its release only in striatal astrocytes. Finally, we evaluated ACM effect on a cellular model of HD: the rat striatal neuron cell line ST14A expressing mutant human huntingtin (Q120) or in ST14A cells expressing normal human huntingtin (Q15). Neither striatal nor cortical ACM modified the viability of Q15 cells. Only ACM from striatal astrocytes treated with BDNF and ACM from 3NP + BDNF-treated striatal astrocytes protected Q120 cells, whereas ACM from cortical astrocytes did not.

Conclusions

Data suggest that cortical and striatal astrocytes respond differently to mitochondrial toxin 3NP and BDNF. Moreover, striatal astrocytes secrete soluble neuroprotective factors in response to BDNF that selectively protect neurons expressing mutant huntingtin implicating that BDNF modulation of striatal astrocyte function has therapeutic potential against neurodegeneration.

Graphical abstract

NDP-MSH binding melanocortin-1 receptor ameliorates neuroinflammation and BBB disruption through CREB/Nr4a1/NF-κB pathway after intracerebral hemorrhage in mice

Background

Neuroinflammation and blood-brain barrier (BBB) disruption are two vital mechanisms of secondary brain injury following intracerebral hemorrhage (ICH). Recently, melanocortin-1 receptor (Mc1r) activation by Nle4-D-Phe7-α-MSH (NDP-MSH) was shown to play a neuroprotective role in an experimental autoimmune encephalomyelitis (EAE) mouse model. This study aimed to investigate whether NDP-MSH could alleviate neuroinflammation and BBB disruption after experimental ICH, as well as the potential mechanisms of its neuroprotective roles.

Methods

Two hundred and eighteen male C57BL/6 mice were subjected to autologous blood-injection ICH model. NDP-MSH, an agonist of Mc1r, was administered intraperitoneally injected at 1 h after ICH insult. To further explore the related protective mechanisms, Mc1r small interfering RNA (Mc1r siRNA) and nuclear receptor subfamily 4 group A member 1 (Nr4a1) siRNA were administered via intracerebroventricular (i.c.v) injection before ICH induction. Neurological test, BBB permeability, brain water content, immunofluorescence staining, and Western blot analysis were implemented.

Results

The Expression of Mc1r was significantly increased after ICH. Mc1r was mainly expressed in microglia, astrocytes, and endothelial cells following ICH. Treatment with NDP-MSH remarkably improved neurological function and reduced BBB disruption, brain water content, and the number of microglia in the peri-hematoma tissue after ICH. Meanwhile, the administration of NDP-MSH significantly reduced the expression of p-NF-κB p65, IL-1β, TNF-α, and MMP-9 and increased the expression of p-CREB, Nr4a1, ZO-1, occludin, and Lama5. Inversely, the knockdown of Mc1r or Nr4a1 abolished the neuroprotective effects of NDP-MSH.

Conclusions

Taken together, NDP-MSH binding Mc1r attenuated neuroinflammation and BBB disruption and improved neurological deficits, at least in part through CREB/Nr4a1/NF-κB pathway after ICH.

Hypothalamic nesfatin-1 mediates feeding behavior via MC3/4R-ERK signaling pathway after weight loss in obese Sprague-Dawley rats

Nesfatin-1 is an anorexic peptide derived from nucleobindin 2 (NUCB2). An increase in hypothalamic nesfatin-1 inhibits feeding behavior and promotes weight loss. However, the effects of weight loss on hypothalamic nesfatin-1 levels are unclear. In this study, obese rats lost weight in three ways: Calorie Restriction diet (CRD), Sleeve gastrectomy (SG) and Roux-en-Y gastric bypass (RYGB). We found an increase in nesfatin-1 serum and cerebrospinal fluid levels after weight loss in obese Sprague-Dawley (SD) rats. Moreover, weight loss also increased hypothalamic melanocortin 3/4 receptor (MC3/4R) and extracellular regulated kinase phosphorylation (p-ERK) signaling. Third ventricle administration of antisense morpholino oligonucleotide (MON) against the gene encoding NUCB2 inhibited hypothalamic nesfatin-1 and p-ERK signaling, increased food intake and reduced body weight loss in SG and RYGB obese rats. Third ventricle administration of SHU9119 (MC3/4R blocker) blocked hypothalamic MC3/4R, inhibited p-ERK signaling, increased food intake and reduced body weight loss in SG and RYGB obese rats. These findings indicate that weight loss leads to an increase in hypothalamic nesfatin-1. The increase in hypothalamic nesfatin-1 participates in regulating feeding behavior through the MC3/4R-ERK signaling especially after SG and RYGB.

NDP-MSH reduces oxidative damage induced by palmitic acid in primary astrocytes

Recent findings relate obesity to inflammation in key hypothalamic areas for body weight control. Hypothalamic inflammation has also been related to oxidative stress. Palmitic acid (PA) is the most abundant free fatty acid found in food, and in vitro studies indicate that it triggers a pro-inflammatory response in the brain. Melanocortins are neuropeptides with proven anti-inflammatory and neuroprotective action mediated by melanocortin receptor 4 (MC4R), but little is known about the effect of melanocortins on oxidative stress. The aim of this study was to investigate whether melanocortins could alleviate oxidative stress induced by a high fat diet (HFD) model. We found that NDP-MSH treatment decreased PA-induced reactive oxygen species production in astrocytes, an effect blocked by the MC4R inhibitor JKC363. NDP-MSH abolished nuclear translocation of Nrf2 induced by PA and blocked the inhibitory effect of PA on superoxide dismutase (SOD) activity and glutathione levels while it also per se increased activity of SOD and γ-glutamate cysteine ligase (γ-GCL) antioxidant enzymes. However, HFD reduced hypothalamic MC4R and brain derived neurotrophic factor mRNA levels, thereby preventing the neuroprotective mechanism induced by melanocortins.

Melanocortin 4 receptor activation protects striatal neurons and glial cells from 3-nitropropionic acid toxicity

α-Melanocyte stimulating hormone (α-MSH) is a melanocortin which exerts potent anti-inflammatory and anti-apoptotic effects. Melanocortin 4 receptors (MC4R) are abundantly expressed in the brain and we previously demonstrated that [Nle(4), D-Phe(7)]melanocyte-stimulating hormone (NDP-MSH), an α-MSH analogue, increased expression of brain derived-neurotrophic factor (BDNF), and peroxisome proliferator-activated receptor-γ (PPAR-γ). We hypothesized that melanocortins could affect striatal cell survival through BDNF and PPAR-γ. First, we determined the expression of these factors in the striatum. Acute intraperitoneal administration (0.5 mg/kg) of α-MSH increased the levels of BDNF mRNA in rat striatum but not in rat cerebral cortex. Also, protein expression of PPAR-γ and MC4R was increased by acute treatment with α-MSH in striatum but not in cortex. No changes were observed by 48 h treatment. Next, we evaluated melanocortins effect on neuron and glial survival. 3-nitropropionic acid (3-NP), which is known to induce striatal degeneration, was used to induce cell death in the rat striatal cell line ST14A expressing mutant human huntingtin (Q120) or in ST14A cells expressing normal human huntingtin (Q15), in primary cultured astrocytes, and in BV2 cells. NDP-MSH protected Q15 cells, astrocytes and BV2 cells from death by 3-NP whereas it did not fully protect Q120 cells. Protection of Q15 cells and astrocytes was blocked by a MC4R specific inhibitor (JKC-363) and a PPAR-γ antagonist (GW9662). The BDNF receptor antagonist (ANA-12) abolished NDP-MSH protective effect in astrocytes but not in Q15 cells. We demonstrate for the first time that melanocortins, acting through PPAR-γ and BDNF, protect neurons and glial cells from 3-NP toxicity.

Quetiapine prevents Aβ25-35-induced cell death in cultured neuron by enhancing brain-derived neurotrophic factor release from astrocyte

β-Amyloid (Aβ)-induced neuronal toxicity is an early event in the pathogenesis of Alzheimer's disease. Quetiapine (QTP) is an atypical antipsychotic drug that has neuroprotectant properties, but little is known about its direct protective effects on neurons against the Aβ-induced cell toxicity. In the present study, we investigated the neuroprotective effects of QTP on Aβ25-35-induced cell death and the possible underlying mechanisms in primary cultures of neurons. Exposure of cortical neurons to 10 μM or more Aβ25-35 caused significant viability loss in a MTT assay, and the toxic effects were not significantly prevented by the simultaneous coadministration of QTP. However, pretreated astrocyte conditioned medium (ACM) with QTP (ACMQTP) for 24 h markedly protected the neurons against the amyloid-induced cell loss. Furthermore, we revealed that QTP increased both the release of brain-derived neurotrophic factor from cultured astrocytes and the phosphorylation of extracellular signal-regulated kinase after 24 h of treatment, which might be responsible for its protective effects on neurons. Consistent with the aforementioned findings, the protective effects of ACM on neurons could potentially be abolished by the extracellular signal-regulated kinase inhibitor and tropomyosin receptor kinase B receptor blocker. In conclusion, our data demonstrated that QTP exerted its neuroprotective effects against amyloid toxicity by enhancing the brain-derived neurotrophic factor release from astrocytes.

Activation of melanocortin receptor 4 with RO27-3225 attenuates neuroinflammation through AMPK/JNK/p38 MAPK pathway after intracerebral hemorrhage in mice

Background

Neuroinflammation plays an important role in the pathogenesis of intracerebral hemorrhage (ICH)-induced secondary brain injury. Activation of melanocortin receptor 4 (MC4R) has been shown to elicit anti-inflammatory effects in many diseases. The objective of this study was to explore the role of MC4R activation on neuroinflammation in a mouse ICH model and to investigate the contribution of adenosine monophosphate-activated protein kinase (AMPK)/c-Jun N-terminal kinase (JNK)/p38 mitogen-activated protein kinase (p38 MAPK) pathway in MC4R-mediated protection.

Methods

Adult male CD1 mice (n = 189) were subjected to intrastriatal injection of bacterial collagenase or sham surgery. The selective MC4R agonist RO27-3225 was administered by intraperitoneal injection at 1 h after collagenase injection. The specific MC4R antagonist HS024 and selective AMPK inhibitor dorsomorphin were administered prior to RO27-3225 treatment to elucidate potential mechanism. Short- and long-term neurobehavioral assessments, brain water content, immunofluorescence staining, and western blot were performed.

Results

The expression of MC4R and p-AMPK increased after ICH with a peak at 24 h. MC4R was expressed by microglia, neurons, and astrocytes. Activation of MC4R with RO27-3225 improved the neurobehavioral functions, decreased brain edema, and suppressed microglia/macrophage activation and neutrophil infiltration after ICH. RO27-3225 administration increased the expression of MC4R and p-AMPK while decreasing p-JNK, p-p38 MAPK, TNF-α, and IL-1β expression, which was reversed with inhibition of MC4R and AMPK.

Conclusions

Our study demonstrated that activation of MC4R with RO27-3225 attenuated neuroinflammation through AMPK-dependent inhibition of JNK and p38 MAPK signaling pathway, thereby reducing brain edema and improving neurobehavioral functions after experimental ICH in mice. Therefore, the activation of MC4R with RO27-3225 may be a potential therapeutic approach for ICH management.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1140-6) contains supplementary material, which is available to authorized users.

Melanocortins, Melanocortin Receptors and Multiple Sclerosis

The melanocortins and their receptors have been extensively investigated for their roles in the hypothalamo-pituitary-adrenal axis, but to a lesser extent in immune cells and in the nervous system outside the hypothalamic axis. This review discusses corticosteroid dependent and independent effects of melanocortins on the peripheral immune system, central nervous system (CNS) effects mediated through neuronal regulation of immune system function, and direct effects on endogenous cells in the CNS. We have focused on the expression and function of melanocortin receptors in oligodendroglia (OL), the myelin producing cells of the CNS, with the goal of identifying new therapeutic approaches to decrease CNS damage in multiple sclerosis as well as to promote repair. It is clear that melanocortin signaling through their receptors in the CNS has potential for neuroprotection and repair in diseases like MS. Effects of melanocortins on the immune system by direct effects on the circulating cells (lymphocytes and monocytes) and by signaling through CNS cells in regions lacking a mature blood brain barrier are clear. However, additional studies are needed to develop highly effective MCR targeted therapies that directly affect endogenous cells of the CNS, particularly OL, their progenitors and neurons.

Chronic intrahypothalamic rather than subcutaneous liraglutide treatment reduces body weight gain and stimulates the melanocortin receptor system

Background:

The GLP-1 receptor agonist liraglutide is marketed for obesity treatment where it induces body weight reduction possibly via the hypothalamus, which regulates energy homeostasis. In animal studies, acute liraglutide treatment triggers satiety, weight loss and activates thermogenesis in adipose tissue. However, the precise mechanisms how liraglutide affects in particular chronic weight loss are still under investigation.

Objectives:

We aimed to evaluate whether chronic hypothalamic or chronic subcutaneous administration of liraglutide induces sustained weight loss through altered adipose tissue function and to what extent hypothalamic neuronal appetite regulators are involved in the liraglutide-induced weight loss in healthy lean rats on a normal diet.

Materials/Methods:

We continuously administered liraglutide either intrahypothalamically (10 μg per day) or subcutaneously (200 μg kg⁻¹ per day) for 28 days to lean Sprague Dawley rats (n=8 each). We assessed changes in body weight, adipose tissue mass, adipocyte size and adipose tissue volume in the abdominal region by using micro-CT. We analyzed genetic expression patterns of browning, thermogenic and adipocyte differentiation regulators in adipose tissues as well as particular neuronal appetite regulators in the hypothalamus.

Results:

Intrahypothalamic liraglutide administration induced an 8% body weight reduction at day 9 compared with the control group (P<0.01) and a 7% body weight loss at day 9 compared with subcutaneous liraglutide treatment (P<0.01), supported by a significant reduction in adipose tissue mass and volume with intrahypothalamic liraglutide administration (P<0.05). Our data show that chronic intrahypothalamic liraglutide treatment triggered an 18-fold induction of the hypothalamic mc4r gene (P<0.01) accompanied by a significant increase in circulating thyroxine (T4) levels (P<0.05).

Conclusions:

Chronic intrahypothalamic liraglutide administration resulted in a profound reduction in body weight and fat mass loss most likely mediated by the hypothalamic melanocortin system rather than by adipose tissue browning or improved thermogenesis.

Dual activation of Toll-like receptors 7 and 9 impairs the efficacy of antitumor vaccines in murine models of metastatic breast cancer

PURPOSE

Since combination of Toll-like receptor (TLR) ligands could boost antitumor immunity, we evaluated the efficacy of dendritic cell (DC) vaccines upon dual activation of TLR9 and TLR7 in breast cancer models.

METHODS

DCs were generated from mouse bone marrow or peripheral blood from healthy human donors and stimulated with CpG1826 (mouse TLR9 agonist), CpG2006 or IMT504 (human TLR9 agonists) and R848 (TLR7 agonist). Efficacy of antitumor vaccines was evaluated in BALB/c mice bearing metastatic mammary adenocarcinomas.

RESULTS

CpG-DCs improved the survival of tumor-bearing mice, reduced the development of lung metastases and generated immunological memory. However, dual activation of TLRs impaired the efficacy of DC vaccines. In vitro, we found that R848 inhibited CpG-mediated maturation of murine DCs. A positive feedback loop in TLR9 mRNA expression was observed upon CpG stimulation that was inhibited in the presence of R848. Impaired activation of NF-κB was detected when TLR9 and TLR7 were simultaneously activated. Blockade of nitric oxide synthase (NOS) and indoleamine-pyrrole-2,3-dioxygenase (IDO) improved the activation of CpG-DCs. When we evaluated the effect of combined activation of TLR9 and TLR7 in human DCs, we found that R848 induced robust DC activation that was inhibited by TLR9 agonists.

CONCLUSIONS

These observations provide insight in the biology of TLR9 and TLR7 crosstalk and suggest caution in the selection of agonists for multiple TLR stimulation. Blockade of NOS and IDO could improve the maturation of antitumor DC vaccines. R848 could prove a useful adjuvant for DC vaccines in human patients.

Direct modulation of GFAP-expressing glia in the arcuate nucleus bi-directionally regulates feeding

Multiple hypothalamic neuronal populations that regulate energy balance have been identified. Although hypothalamic glia exist in abundance and form intimate structural connections with neurons, their roles in energy homeostasis are less known. Here we show that selective Ca²⁺ activation of glia in the mouse arcuate nucleus (ARC) reversibly induces increased food intake while disruption of Ca²⁺ signaling pathway in ARC glia reduces food intake. The specific activation of ARC glia enhances the activity of agouti-related protein/neuropeptide Y (AgRP/NPY)-expressing neurons but induces no net response in pro-opiomelanocortin (POMC)-expressing neurons. ARC glial activation non-specifically depolarizes both AgRP/NPY and POMC neurons but a strong inhibitory input to POMC neurons balances the excitation. When AgRP/NPY neurons are inactivated, ARC glial activation fails to evoke any significant changes in food intake. Collectively, these results reveal an important role of ARC glia in the regulation of energy homeostasis through its interaction with distinct neuronal subtype-specific pathways.

Exchange factors directly activated by cAMP mediate melanocortin 4 receptor-induced gene expression

G_s protein-coupled receptors regulate many vital body functions by activation of cAMP response elements (CRE) via cAMP-dependent kinase A (PKA)-mediated phosphorylation of the CRE binding protein (CREB). Melanocortin 4 receptors (MC4R) are prototypical G_s-coupled receptors that orchestrate the hypothalamic control of food-intake and metabolism. Remarkably, the significance of PKA for MC4R-induced CRE-dependent transcription in hypothalamic cells has not been rigorously interrogated yet. In two hypothalamic cell lines, we observed that blocking PKA activity had only weak or no effects on reporter gene expression. In contrast, inhibitors of exchange factors directly activated by cAMP-1/2 (EPAC-1/2) mitigated MC4R-induced CRE reporter activation and mRNA induction of the CREB-dependent genes c-fos and thyrotropin-releasing hormone. Furthermore, we provide first evidence that extracellular-regulated kinases-1/2 (ERK-1/2) activated by EPACs and not PKA are the elusive CREB kinases responsible for MC4R-induced CREB/CRE activation in hypothalamic cells. Overall, these data emphasize the pivotal role of EPACs rather than PKA in hypothalamic gene expression elicited by a prototypical G_s-coupled receptor.

Biased signaling initiated by agouti-related peptide through human melanocortin-3 and -4 receptors

The neural melanocortin receptors (MCRs), melanocortin-3 and -4 receptors (MC3R and MC4R), have been increasingly recognized as important regulators of energy homeostasis. The orexigenic agouti-related peptide (AgRP), initially identified as an endogenous antagonist for both neural MCRs, has been suggested to be a biased agonist of MC4R independent of its antagonizing effects. In the present study, we sought to determine the potential of AgRP to regulate the activation of intracellular kinases, including extracellular signal-regulated kinase 1 and 2 (ERK1/2), AKT and AMP-activated protein kinase (AMPK), through neural MCRs. We showed that AgRP acted as a biased agonist in human MC3R (hMC3R), decreasing cAMP activity of constitutively active mutant (F347A) hMC3R but stimulating ERK1/2 activation in both wide type and F347A hMC3Rs. AgRP-stimulated ERK1/2 phosphorylation through MC3R was abolished by protein kinase A (PKA) inhibitor H-89 but not Rp-cAMPS, whereas AgRP-initiated ERK1/2 activation through MC4R was inhibited by phosphatidylinositol 3-kinase (PI3K) inhibitors wortmannin and LY294002. Both NDP-MSH and AgRP treatment induced significant AKT phosphorylation in GT1-7 cells but not in MC3R- or MC4R-transfected HEK293T cells. The phosphorylated AMPK levels in both GT1-7 cells and HERK293T cells transfected with neural MCRs were significantly decreased upon stimulation with NDP-MSH but not with AgRP. In summary, we provided novel data for AgRP-initiated multiple intracellular signaling pathways, demonstrating biased agonism of AgRP in both neural MCRs, leading to a better understanding of neural MCR pharmacology.

Amitriptyline induces brain-derived neurotrophic factor (BDNF) mRNA expression through ERK-dependent modulation of multiple BDNF mRNA variants in primary cultured rat cortical astrocytes and microglia

A significant role of brain-derived neurotrophic factor (BDNF) has been previously implicated in the therapeutic effect of antidepressants. To ascertain the contribution of specific cell types in the brain that produce BDNF following antidepressant treatment, the effects of the tricyclic antidepressant amitriptyline on rat primary neuronal, astrocytic and microglial cortical cultures were examined. Amitriptyline increased the expression of BDNF mRNA in astrocytic and microglial cultures but not neuronal cultures. Antidepressants with distinct mechanisms of action, such as clomipramine, duloxetine and fluvoxamine, also increased BDNF mRNA expression in astrocytic and microglial cultures. There are multiple BDNF mRNA variants (exon I, IIA, IV and VI) expressed in astrocytes and microglia and the variant induced by antidepressants has yet to be elaborated. Treatment with antidepressants increased the expression of exon I, IV and VI in astrocyte and microglia. Clomipramine alone significantly upregulated expression of exon IIA. The amitriptyline-induced expression of both total and individual BDNF mRNA variants (exon I, IV and VI) were blocked by MEK inhibitor U0126, indicating MEK/ERK signaling is required in the expression of BDNF. These findings indicate that non-neural cells are a significant target of antidepressants and further support the contention that glial production of BDNF is crucial role in the therapeutic effect of antidepressants. The current data suggest that targeting of glial function could lead to the development of antidepressants with a truly novel mechanism of action.