GPR39 (zinc receptor) knockout mice exhibit depression-like behavior and CREB/BDNF down-regulation in the hippocampus

Investigating the role of GPR39 in treatment of stress-induced depression and anxiety

RATIONALE

Chronic stress is one of the leading causes of depression. Yet, knowledge of the pathomechanism of this process still eludes us. Chronic unpredictable mild stress (CUMS) model of depression enables researchers to look for a root cause of the disease in mice by mimicking a stressful human environment.

OBJECTIVE

Since zinc has already been shown to impact the treatment of depression, in our study we aimed to shed light on the role of the zinc receptor GPR39 in stress-induced depression. We also aimed to highlight the role of GPR39 activation in monoamine-based antidepressant treatment.

METHODS

Using large battery of behavioural tests, we provided a detailed description of CUMS-induced phenotype in both - CD-1 and GPR39 knock-out mice.

RESULTS

Our experiments showed that combined treatment with TC-G 1008 (GPR39 agonist) and antidepressants produces stronger antidepressant-like effect of classic antidepressants. We also demonstrated the inter-strain differences in stress response and the greater stress susceptibility of GPR39 knock-out mice. The lack of GPR39 expression also either diminished or completely abolished the response to treatment with different antidepressants combined with TC-G 1008.

CONCLUSIONS

The results show that GPR39 KO mice are more susceptible to chronic stress and that they are non-responsive to SSRI treatment. Utilizing various behavioural tests gave us much broader understanding not only of the role of GPR39 in depression treatment, but also of the importance of detailed behavioural description in a proper interpretation of the results. Further research with known selective agonists and antagonists of GPR39 will be necessary to understand the full potential of this receptor as a pharmacological target.

The pathophysiological functions and therapeutic potential of GPR39: Focus on agonists and antagonists

G protein-coupled receptor 39 (GPR39), a member of the growth hormone-releasing peptide family, exhibits widespread expression across various tissues and demonstrates high constitutive activity, primarily activated by zinc ions. It plays critical roles in cell proliferation, differentiation, survival, apoptosis, and ion transport through the recruitment of Gq/11, Gs, G12/13, and β-arrestin proteins. GPR39 is involved in anti-inflammatory and antioxidant responses, highlighting its diverse pathophysiological functions. Recent discoveries of endogenous ligands have enhanced our understanding of GPR39's physiological roles. Aberrant expression and reactivation of GPR39 have been implicated in a range of diseases, particularly central nervous system disorders, endocrine disruptions, cardiovascular diseases, cancers, and liver conditions. These findings position GPR39 as a promising therapeutic target, with the efficacy of synthetic ligands validated in various in vivo models. Nonetheless, their clinical applicability remains uncertain, necessitating further exploration of novel agonists-especially biased agonists-and antagonists. This review examines the unique residues contributing to the high constitutive activity of GPR39, its endogenous and synthetic ligands, and its pathophysiological implications, aiming to elucidate its pharmacological potential for clinical application in disease treatment.

Loss of the zinc receptor ZnR/GPR39 in mice enhances anxiety-related behavior and motor deficits, and modulates KCC2 expression in the amygdala

BACKGROUND

Mood disorders, particularly depression and anxiety, are associated with zinc dyshomeostasis and aberrant GABAergic signaling. Activation of ZnR/GPR39 by synaptic zinc in the hippocampus triggers phosphorylation of extracellular regulated kinase (ERK1/2), which regulates the K+/Cl- cotransporter (KCC2) and thereby GABAergic inhibitory neurotransmission and seizure activity. Therefore, we studied whether impaired ZnR/GPR39 signaling is linked to anxiety-related behavior in male or female mice.

RESULTS

Using the acoustic startle response, elevated plus maze, and open field test, we found increased anxiety-related behavior in ZnR/GPR39 knockout (KO) mice. Despite a well-established sex difference, where females are typically more prone to anxiety, both male and female ZnR/GPR39 KO mice exhibited increased anxiety-related behavior compared to wildtype (WT) mice. Additionally, ZnR/GPR39 KO mice displayed impaired motor coordination in the pole and rotarod tests but did not show reduced muscle strength, as indicated by a grip test. Finally, we found intrinsic alterations in the expression level of KCC2, a major Cl- transporter regulating GABAergic signaling, in the amygdala of naïve ZnR/GPR39 KO mice compared to controls.

CONCLUSIONS

Our findings indicate that loss of ZnR/GPR39 enhances anxiety-related behavior in both male and female mice. Moreover, ZnR/GPR39 KO mice exhibit impaired motor coordination, which may be associated with increased anxiety. Finally, we demonstrate that loss of ZnR/GPR39 modulates the expression of KCC2 in the amygdala. Thus, we propose that ZnR/GPR39 can serve as a target for regulating GABAergic signaling in anxiety treatment.

Bone-marrow macrophage-derived GPNMB protein binds to orphan receptor GPR39 and plays a critical role in cardiac repair

Glycoprotein nonmetastatic melanoma protein B (GPNMB) is a type I transmembrane protein initially identified in nonmetastatic melanomas and has been associated with human heart failure; however, its role in cardiac injury and function remains unclear. Here we show that GPNMB expression is elevated in failing human and mouse hearts after myocardial infarction (MI). Lineage tracing and bone-marrow transplantation reveal that bone-marrow-derived macrophages are the main source of GPNMB in injured hearts. Using genetic loss-of-function models, we demonstrate that GPNMB deficiency leads to increased mortality, cardiac rupture and rapid post-MI left ventricular dysfunction. Conversely, increasing circulating GPNMB levels through viral delivery improves heart function after MI. Single-cell transcriptomics show that GPNMB enhances myocyte contraction and reduces fibroblast activation. Additionally, we identified GPR39 as a receptor for circulating GPNMB, with its absence negating the beneficial effects. These findings highlight a pivotal role of macrophage-derived GPNMBs in post-MI cardiac repair through GPR39 signaling.

Antioxidants and the risk of sleep disorders: results from NHANES and two-sample Mendelian randomization study

Background

Sleep disorders have emerged as a major public health concern. Observational research indicates that antioxidants might mitigate the risk of sleep disturbances, yet the causal relationship remains uncertain.

Materials and methods

This study utilized data from the National Health and Nutrition Examination Survey (NHANES) spanning 2011 to 2018, focusing on adults who reported sleep disorders. The analysis included 25,178 American adults. We examined the association between the Composite Dietary Antioxidant Index (CDAI) and the prevalence of sleep disorders. Additionally, a two-sample Mendelian randomization analysis was conducted to explore the potential causal link between CDAI and the risk of sleep disorders.

Results

Analysis of data from the 2011-2018 NHANES survey revealed a significant negative association between CDAI and sleep disorders (OR = 0.854, 95% CI 0.821-0.888, P < 0.001). A multivariable logistic regression model showed that each unit increase in CDAI corresponded to a 14.6% reduction in sleep disorder risk, exhibiting a nonlinear trend where the risk decreased until reaching the inflection point of -0.134. Additionally, MR analysis demonstrated that genetically determined selenium reduces the risk of OSA (OR = 0.992, 95% CI 0.860-0.989, P = 0.023). Furthermore, vitamin E (γ-tocopherol) and vitamin C were protective against sleep-wake disorders (OR = 0.016, 95% CI 0.001-0.674, P = 0.03) and (OR = 0.049, 95% CI 0.007-0.346, P = 0.002), respectively.

Conclusion

Dietary antioxidants may help prevent sleep disorders. However, further studies are required to clarify the pathways through which antioxidants exert this protective effect.

The Changes of Blood and CSF Ion Levels in Depressed Patients: a Systematic Review and Meta-analysis

Micronutrient deficiencies and excesses are closely related to developing and treating depression. Traditional and effective antidepressants include tricyclic antidepressants (TCAs), selective serotonin reuptake inhibitors (SSRIs), and lithium. There is no consensus on the fluctuation of zinc (Zn2+), magnesium (Mg2+), calcium (Ca2+), copper (Cu2+), iron (Fe2+), and manganese (Mn2+) ion levels in depressed individuals before and after therapy. In order to determine whether there were changes in blood and cerebrospinal fluid (CSF) levels of these ions in depressed patients compared with healthy controls and depressed patients treated with TCAs, SSRIs, or lithium, we applied a systematic review and meta-analysis. Using the Stata 17.0 software, we performed a systematic review and meta-analysis of the changes in ion levels in human samples from healthy controls, depressive patients, and patients treated with TCAs, SSRIs, and lithium, respectively. By searching the PubMed, EMBASE, Google Scholar, Web of Science, China National Knowledge Infrastructure (CNKI), and WAN FANG databases, 75 published analyzable papers were chosen. In the blood, the levels of Zn2+ and Mg2+ in depressed patients had decreased while the Ca2+ and Cu2+ levels had increased compared to healthy controls, Fe2+ and Mn2+ levels have not significantly changed. After treatment with SSRIs, the levels of Zn2+ and Ca2+ in depressed patients increased while Cu2+ levels decreased. Mg2+ and Ca2+ levels were increased in depressed patients after Lithium treatment. The findings of the meta-analysis revealed that micronutrient levels were closely associated with the onset of depression and prompted more research into the underlying mechanisms as well as the pathophysiological and therapeutic implications.

A systematic review of the association between zinc and anxiety

CONTEXT

The incidence of anxiety, which stems from both intrinsic and extrinsic factors, has been increasing worldwide. Various methods by which it can be treated or prevented have been reported thus far. One of the most popular and effective treatments is supplementation therapy. Zinc, which is an essential nutrient found in various plants, animal foods, and supplements, has been shown to be a potential nutrient in anxiety reduction by acting on γ-aminobutyric acid (GABA), glutamatergic, serotonergic, neurogenesis, and immune systems. It can also influence important receptors, such as GPR39. Thus, zinc has received considerable attention with respect to its potential role as a therapeutic or detrimental factor for anxiety; yet, the available evidence needs to be analyzed systematically to reach a convergent conclusion.

OBJECTIVE

The objective was to systematically review any potential connection between adult human anxiety and zinc intake.

DATA SOURCES AND EXTRACTION

Nine original human studies, of which 2 assessed the relationship between zinc consumption and anxiety (based on a questionnaire) and 7 assessed the relationship between serum zinc levels and anxiety, were included based on specific selection criteria. Studies that had been written in English and published in peer-reviewed publications with no restrictions on the date of publication were searched in the Google Scholar and PubMed databases. This project was also reported according to the PRISMA guidelines.

DATA ANALYSIS

As per the studies analyzed in this review, there was a noticeable relationship between serum zinc levels and anxiety, which means that patients with anxiety have lower levels of zinc in their serum, as compared with healthy individuals. Furthermore, zinc consumption was inversely associated with anxiety.

CONCLUSION

The results provide plausible evidence for the positive role of zinc in the treatment of patients afflicted with anxiety, albeit with some limitations.

Chronic memantine disrupts spatial memory and up-regulates Htr1a gene expression in the hippocampus of GPR39 (zinc-sensing receptor) KO male mice

GPR39 is a receptor involved in zincergic neurotransmission, and its role in regulating psychological functions is an active area of research. The purported roles of GPR39 at the cellular level include regulation of inflammatory and oxidative stress response, and modulation of GABAergic and endocannabinoid neurotransmission. GPR39 knock-out (KO) mice exhibit episodic-like and spatial memory (ELM and SM, respectively) deficits throughout their lifetime, and are similar in that respect to senescent wild-type (WT) conspecifics. Since a role for zinc has been postulated in neurodegenerative disorders, in this study we investigated the possibility of a pharmacological rescue of both types of declarative memory with memantine - a noncompetitive NMDAR antagonist used for slowing down dementia; or, a putative GPR39 agonist - TC-G 1008. First, we tested adult WT and GPR39KO male mice under acute 5 mg/kg memantine or vehicle treatment in an object recognition task designed to simultaneously probe the "what?", "where?" and "when?" components of ELM. Next, we investigated the impact of chronic memantine or TC-G 1008 on ELM and SM (Morris water maze, MWM) in both WT and GPR39KO mice. Following chronic experiments, we assessed with qRT-PCR hippocampal gene expression of targets previously associated with GPR39. We report: no effects of acute memantine on ELM; a tendency to improve the "where?" component of ELM in both WT and GPR39 KO mice following 12 days of memantine; and, a disruption of SM in GPR39KO mice after 24 days of memantine treatment. The latter result was associated with upregulation of Htr1a hippocampal expression.

Pro-neurogenic effects of Lilii Bulbus on hippocampal neurogenesis and memory

Lilii Bulbus, the bulb of tiger lily, has anti-oxidant and anti-tumorigenic properties. However, the effects of Lilii Bulbus on learning, memory, and hippocampal neurogenesis remain unknown. This study investigated whether water extract of Lilii Bulbus (WELB) affects memory ability and hippocampal neurogenesis. Behavioral analyses (Morris water maze and passive avoidance test), immunohistochemistry, cell proliferation assay, and immunoblot analysis were performed. WELB (50 and 100 mg/kg; for 14 days) enhanced memory retention and spatial memory in normal mice as well as in scopolamine-treated mice with memory deficits. Furthermore, the administration of WELB significantly increased the number of proliferating cells and surviving newborn cells in the dentate gyrus of the hippocampus in normal mice. We found that WELB has a pro-neurogenic effect by increasing the activation of brain-derived neurotrophic factor (BDNF)/cAMP response element-binding protein (CREB) and mitogen-activated protein kinase kinase/extracellular signal-regulated kinase (MEK/ERK) in the hippocampus. Moreover, we confirmed that WELB (100 and 200 μg/ml) significantly increased NE-4 C and primary embryonic NSCs proliferation. Inhibition/knockdown of MEK/ERK blocked WELB-induced MEK/ERK phosphorylation and NSCs proliferation. Hence, MEK/ERK activation was required in WELB-induced NSCs proliferation. Our study demonstrates the first evidence for WELB promoting hippocampal neurogenesis and memory; pro-neurogenic activity may enhance brain plasticity, with implications for treating neurodegenerative diseases.

Signaling pathway mechanisms of neurological diseases induced by G protein-coupled receptor 39

BACKGROUND

G protein-coupled receptor 39 (GPR39) is a transmembrane zinc receptor with two splice variants, which belongs to the G-protein-coupled receptor growth hormone-releasing peptide family. Its expression is induced by zinc, which activates GPR39, and its activation mediates cell proliferation, ion homeostasis, and anti-inflammatory, antioxidant, and other pathophysiological effects via different signaling pathways.

AIMS

The article reviews the latest literature in this field. In particular, the role of GPR39 in nervous system is discussed.

MATERIALS AND METHODS

GPR39 can be a promising target in neurological diseases for targeted therapy, which will help doctors overcome the associated problems.

DISCUSSION

GPR39 is expressed in vivo at several sites. Increasing evidence suggests that GPR39 plays an important role as a neuroprotective agent in vivo and regulates various neurological functions, including neurodegeneration, neuroelectrophysiology, and neurovascular homeostasis.

CONCLUSION

This review aims to provide an overview of the functions, signal transduction pathways, and pathophysiological role of GPR39 in neurological diseases and summarize the GPR39 agonists that have been identified in the recent years.

Ketamine and Zinc: Treatment of Anorexia Nervosa Via Dual NMDA Receptor Modulation

Anorexia nervosa is a disorder associated with serious adverse health outcomes, for which there is currently considerable treatment ineffectiveness. Characterised by restrictive eating behaviours, distorted body image perceptions and excessive physical activity, there is growing recognition anorexia nervosa is associated with underlying dysfunction in excitatory and inhibitory neurometabolite metabolism and signalling. This narrative review critically explores the role of N-methyl-D-aspartate receptor-mediated excitatory and inhibitory neurometabolite dysfunction in anorexia nervosa and its associated biomarkers. The existing magnetic resonance spectroscopy literature in anorexia nervosa is reviewed and we outline the brain region-specific neurometabolite changes that have been reported and their connection to anorexia nervosa psychopathology. Considering the proposed role of dysfunctional neurotransmission in anorexia nervosa, the potential utility of zinc supplementation and sub-anaesthetic doses of ketamine in normalising this is discussed with reference to previous research in anorexia nervosa and other neuropsychiatric conditions. The rationale for future research to investigate the combined use of low-dose ketamine and zinc supplementation to potentially extend the therapeutic benefits in anorexia nervosa is subsequently explored and promising biological markers for assessing and potentially predicting treatment response are outlined.

The Zinc-sensing Receptor (GPR39) Modulates Declarative Memory and Age-related Hippocampal Gene Expression in Male Mice

As a neuromodulator, zinc regulates synaptic plasticity, learning and memory. Synaptic zinc is also a crucial factor in the development of toxic forms of amyloid beta protein and, subsequently, of Alzheimer's dementia (AD). Therefore, efforts to pinpoint mechanisms underlying zinc-dependent cognitive functions might aid AD research, by providing potential novel targets for drugs. One of the most understudied proteins in this regard is a zinc-sensing metabotropic receptor: GPR39. In this study we investigated the impact of GPR39 knock-out (KO) on age-related memory decline in mice of both sexes, by comparing them to age-matched wild-type (WT) littermates. We also tested the effects of a GPR39 agonist (TC-G 1008) on declarative memory of old animals, and its disruption in adult mice. We observed episodic-like memory (ELM) and spatial memory (SM) deficits in male GPR39 KO mice, as well as intact procedural memory in GPR39 KO mice regardless of age and sex. ELM was also absent in old WT male mice, and all female mice regardless of their genotype. Acute application of TC-G 1008 (10 mg/kg) reversed a deficit in two of three ELM components in old WT male mice, and had no promnesic effect on consolidation interference of ELM in adult WT mice. We discuss the possible neurobiological mechanisms and the translational value of these results for potential add-on pharmacotherapy of AD aimed at the zinc-sensing receptor.

GPR39 Deficiency Impairs Memory and Alters Oxylipins and Inflammatory Cytokines Without Affecting Cerebral Blood Flow in a High-Fat Diet Mouse Model of Cognitive Impairment

Vascular cognitive impairment (VCI) is the second most common cause of dementia. There is no treatment for VCI, in part due to a lack of understanding of the underlying mechanisms. The G-protein coupled receptor 39 (GPR39) is regulated by arachidonic acid (AA)-derived oxylipins that have been implicated in VCI. Furthermore, GPR39 is increased in microglia of post mortem human brains with VCI. Carriers of homozygous GPR39 SNPs have a higher burden of white matter hyperintensity, an MRI marker of VCI. We tested the hypothesis that GPR39 plays a protective role against high-fat diet (HFD)-induced cognitive impairment, in part mediated via oxylipins actions on cerebral blood flow (CBF) and neuroinflammation. Homozygous (KO) and heterozygous (Het) GPR39 knockout mice and wild-type (WT) littermates with and without HFD for 8 months were tested for cognitive performance using the novel object recognition (NOR) and the Morris water maze (MWM) tests, followed by CBF measurements using MRI. Brain tissue and plasma oxylipins were quantified with high-performance liquid chromatography coupled to mass spectrometry. Cytokines and chemokines were measured using a multiplex assay. KO mice, regardless of diet, swam further away from platform location in the MWM compared to WT and Het mice. In the NOR test, there were no effects of genotype or diet. Brain and plasma AA-derived oxylipins formed by 11- and 15-lipoxygenase (LOX), cyclooxygenase (COX) and non-enzymatically were increased by HFD and GPR39 deletion. Interleukin-10 (IL-10) was lower in KO mice on HFD than standard diet (STD), whereas IL-4, interferon γ-induced protein-10 (IP-10) and monocyte chemotactic protein-3 (MCP-3) were altered by diet in both WT and KO, but were not affected by genotype. Resting CBF was reduced in WT and KO mice on HFD, with no change in vasoreactivity. The deletion of GPR39 did not change CBF compared to WT mice on either STD or HFD. We conclude that GPR39 plays a role in spatial memory retention and protects against HFD-induced cognitive impairment in part by modulating inflammation and AA-derived oxylipins. The results indicate that GPR39 and oxylipin pathways play a role and may serve as therapeutic targets in VCI.

Control of Coronary Vascular Resistance by Eicosanoids via a Novel GPCR

Arachidonic acid metabolites epoxyeicosatrienoates (EETs) and hydroxyeicosatetraenoates (HETEs) are important regulators of myocardial blood flow and coronary vascular resistance (CVR), but their mechanisms of action are not fully understood. We applied a chemoproteomics strategy using a clickable photoaffinity probe to identify G protein coupled receptor 39 (GPR39) as a microvascular smooth muscle cell (mVSMC) receptor selective for two endogenous eicosanoids, 15-HETE and 14,15-EET, which act on the receptor to oppose each other's activity. The former increases mVSMC intracellular calcium via GPR39 and augments coronary microvascular resistance, and the latter inhibits these actions. Furthermore, we find that the efficacy of both ligands is potentiated by zinc acting as an allosteric modulator. Measurements of coronary perfusion pressure (CPP) in GPR39-null hearts using the Langendorff preparation indicate the receptor senses these eicosanoids to regulate microvascular tone. These results implicate GPR39 as an eicosanoid receptor and key regulator of myocardial tissue perfusion. Our findings will have a major impact on understanding the roles of eicosanoids in cardiovascular physiology and disease and provide an opportunity for the development of novel GPR39-targeting therapies for cardiovascular disease.

Brain-derived neurotrophic factor in Alzheimer's disease and its pharmaceutical potential

Synaptic abnormalities are a cardinal feature of Alzheimer's disease (AD) that are known to arise as the disease progresses. A growing body of evidence suggests that pathological alterations to neuronal circuits and synapses may provide a mechanistic link between amyloid β (Aβ) and tau pathology and thus may serve as an obligatory relay of the cognitive impairment in AD. Brain-derived neurotrophic factors (BDNFs) play an important role in maintaining synaptic plasticity in learning and memory. Considering AD as a synaptic disorder, BDNF has attracted increasing attention as a potential diagnostic biomarker and a therapeutical molecule for AD. Although depletion of BDNF has been linked with Aβ accumulation, tau phosphorylation, neuroinflammation and neuronal apoptosis, the exact mechanisms underlying the effect of impaired BDNF signaling on AD are still unknown. Here, we present an overview of how BDNF genomic structure is connected to factors that regulate BDNF signaling. We then discuss the role of BDNF in AD and the potential of BDNF-targeting therapeutics for AD.

The role of carbonic anhydrase III and autophagy in type 2 diabetes with cardio-cerebrovascular disease

Type 2 diabetes mellitus (T2DM) is one of the most common chronic diseases among the elderly people. The T2DM increases the risk of cardio-cerebrovascular disease (CCD), and the main pathological change of the CCD is atherosclerosis (AS). Meanwhile, the carbonic anhydrases (CAs) are involved in the formation and progression of plaques in AS. However, the exact physiological mechanism of carbonic anhydrase III (CAIII) has not been clear yet, and there are also no correlation study between CAIII protein and T2DM with CCD. The 8-week old diabetic mice (db/db^-/- mice) and wild-type mice (wt mice) were feed by a normal diet till 32 weeks, and detected the carotid artery vascular opening angle using the method of biomechanics; The changes of cerebral cortex and myocardium were watched by the ultrastructure, and the autophagy were observed by electron microscope; The tissue structure, inflammation and cell injury were observed by Hematoxylin and eosin (HE) staining; The apoptosis of cells were observed by TUNEL staining; The protein levels of CAIII, IL-17, p53 were detected by immunohistochemical and Western Blot, and the Beclin-1, LC3, NF-κB were detected by Western Blot. All statistical analysis is performed using PRISM software. Compared with wt mice, db/db^-/- mice' carotid artery open angle increased significantly. Electron microscope results indicated that autophagy in db/db^-/- mice cerebral cortex and heart tissue decreased and intracellular organelle ultrastructure were damaged. HE staining indicated that, db/db^-/- mice' cerebral cortex and heart tissue stained lighter, inflammatory cells infiltration, cell edema were obvious, myocardial fibers were disorder, and myocardial cells showed different degrees of degeneration. Compared with wt mice, TUNEL staining showed that there was obviously increase in db/db^-/- mice cortex and heart tissue cell apoptosis. The results of immunohistochemistry and Western Blot indicated that CAIII, Beclin-1 and LC3II/I expression levels conspicuously decreased in cortex and heart tissue of db/db^-/- mice, and the expression level of IL-17, NF-κB and p53 obviously increased. The carotid artery' vascular stiffness was increased and which was probably related with formation of AS in diabetic mice. And the autophagy participated in the occurrence and development of diabetic CCD. CAIII protein might somehow be involved in the regulation of autophagy probably through affecting cell apoptosis and inflammation, but the underlying mechanism remains to be further studied.

miR-182 mediated the inhibitory effects of NF-κB on the GPR39/CREB/BDNF pathway in the hippocampus of mice with depressive-like behaviors

BACKGROUND

Chronic stress is one of the most important causes of depression, accompanied by neuroinflammation and hippocampal injuries. Long-term elevation of glucocorticoid leads to activation of NF-κB and inhibition of GPR39/CREB/BDNF pathway, which is pivotal for neuroprotection and neurogenesis. The present study thus was designed to determine the relationship between NF-κB and GPR39/CREB/BDNF pathway.

METHODS

Depressive-like behaviors were induced by chronic unpredictable mild stress (CUMS) and chronic restraint stress (CRS) in mice. Corticosterone, inflammatory cytokines, and GPR39/CREB/BDNF pathway were determined by ELISA and Western Blot assays. The activation of NF-κB and inhibition of GPR39 were connected by bioinformatic analysis and experimentally validated in hippocampus cells by knock-in and knock-down techniques.

RESULTS

CUMS and CRS led to an elevation of serum corticosterone and depressive-like behaviors in mice, with activation of NF-κB subunit p65 in the hippocampus and elevations of TNFα and IL-6. The expression of GPR39/CREB/BDNF pathway in the hippocampus was inhibited. Bioinformatic analysis revealed that four miRNAs, miR-96, miR-143, miR-150, and miR-182, were potentially transcribed by NF-κB and bound with GPR39 mRNA. NF-κB overexpression increased miR-182 expression and decreased GPR39 expression in hippocampus cells. Its inhibitor led to reverse effects. miR-182 mimics or inhibitors also regulated GPR39 expression in hippocampus cells and more importantly, blocked the regulation of NF-κB on GPR39.

CONCLUSIONS

The results suggested that activation of NF-κB inhibited GPR39/CREB/BDNF pathway through increasing miR-182 in chronic stress-induced depressive-like behaviors. The negative-regulation features of miRNAs might be important for neuroinflammation-induced inhibition of neurofunction in depression.

GPR39 localization in the aging human brain and correlation of expression and polymorphism with vascular cognitive impairment

INTRODUCTION

The pathogenesis of vascular cognitive impairment (VCI) is not fully understood. GPR39, an orphan G-protein coupled receptor, is implicated in neurological disorders but its role in VCI is unknown.

METHODS

We performed GPR39 immunohistochemical analysis in post mortem brain samples from mild cognitive impairment (MCI) and control subjects. DNA was analyzed for GPR39 single nucleotide polymorphisms (SNPs), and correlated with white matter hyperintensity (WMH) burden on pre mortem magnetic resonance imaging.

RESULTS

GPR39 is expressed in aged human dorsolateral prefrontal cortex, localized to microglia and peri-capillary cells resembling pericytes. GPR39-capillary colocalization, and density of GPR39-expressing microglia was increased in aged brains compared to young. SNP distribution was equivalent between groups; however, homozygous SNP carriers were present only in the MCI group, and had higher WMH volume than wild-type or heterozygous SNP carriers.

DISCUSSION

GPR39 may play a role in aging-related VCI, and may serve as a therapeutic target and biomarker for the risk of developing VCI.

Neuronal correlates underlying the role of the zinc sensing receptor (GPR39) in passive-coping behaviour

The Zn²⁺ receptor GPR39 is proposed to be involved in the pathophysiology of depression. GPR39 knockout (KO) animals show depressive- and anxiety-like behaviour, and resistance to conventional monoamine-based antidepressants. However, it is unclear as to which brain regions are involved in the pro-depressive phenotype of GPR39KO mice and the resistance to monoamine-targeting antidepressant treatment. Our current study confirmed previous results, showing that mice lacking GPR39 display enhanced passive coping-like behaviour compared with their wild-type controls. Furthermore, this study shows for the first time that GPR39KO displayed aberrant challenge-induced neuronal activity in key brain regions associated with passive coping behaviour. Imipramine induced only a marginal reduction in the enhanced passive coping behaviour in GPR39KO mice, which was associated with attenuation of the hyperactive prefrontal cortex. Similarly, the aberrant activity within the amygdalar subregions was normalized following imipramine treatment in the GPR39KO mice, indicating that imipramine mediates these effects independently of GPR39 in the prefrontal cortex and amygdala. However, imipramine failed to modulate the aberrant brain activity in other brain regions, such as the anterior CA3 and the dentate gyrus, in GPR39KO mice. Normalization of aberrant activity in these areas has been shown previously to accompany successful behavioural effects of antidepressants. Taken together, our data suggest that monoamine-based antidepressants such as imipramine exert their action via GPR39-dependent and -independent pathways. Failure to modulate passive-coping related aberrant activity in important brain areas of the depression circuitry is proposed to mediate/contribute to the greatly reduced antidepressant action of monoamine-based antidepressants in GPR39KO mice.

Role of GPR39 in Neurovascular Homeostasis and Disease

GPR39, a member of the ghrelin family of G protein-coupled receptors, is zinc-responsive and contributes to the regulation of diverse neurovascular and neurologic functions. Accumulating evidence suggests a role as a homeostatic regulator of neuronal excitability, vascular tone, and the immune response. We review GPR39 structure, function, and signaling, including constitutive activity and biased signaling, and summarize its expression pattern in the central nervous system. We further discuss its recognized role in neurovascular, neurological, and neuropsychiatric disorders.

Downregulation of miR-383 reduces depression-like behavior through targeting Wnt family member 2 (Wnt2) in rats

This study aimed to evaluate the role of miR-383 in the regulation of Wnt-2 signaling in the rat model of chronic stress. The male SD rats with depressive-like behaviors were stimulated with chronic unpredictable mild stress (CUMS) including ice-water swimming for 5 min, food deprivation for 24 h, water deprivation for 24 h, stimulating tail for 1 min, turning night into day, shaking for 15 min (once/s), and wrap restraint (5 min/time) every day for 21 days. The expression levels of miRNAs were detected by qRT-PCR, and the expression levels of Wnt2, depression-impacted proteins (GFAP, BDNF, CREB), brain neurotransmitters (5-HT, NE, DA) and apoptosis-related proteins (Bax and Bcl-2) were evaluated by qRT-PCR and western blot. Bioinformatic analysis and luciferase reporter assay were performed to determine the relationship between miR-383 and Wnt2. Ethological analysis was evaluated by sugar preference test, refuge island test and open field tests. Rescue experiments including knockdown of miR-383, overexpression and silencing of Wnt2 were performed to determine the role of miR-383. High expression levels of miR-383 were observed in the hippocampus of rats submitted to CUMS model. Downregulation of miR-383 significantly inhibited the apoptosis and inflammatory response of hippocampal neurons, and increased the expression levels of GFAP, BDNF and CREB which were impacted in depression, as well as neurotransmitters, then attenuated neural injury in rats induced by CUMS. Furthermore, Wnt family member 2 (Wnt2) was identified as a target of miR-383, and silencing of Wnt2 obviously attenuated the protective effect of miR-383 inhibitor on the apoptosis and inflammatory response in hippocampal neurons, as well as neural injury in CUMS-induced rats. Downregulation of miR-383 ameliorated the behavioral and neurochemical changes induced by chronic stress in rats by directly targeting Wnt2, indicating that the miR-383/Wnt2 axis might be a potential therapeutic target for MDD.

The Zinc-Sensing Receptor GPR39 in Physiology and as a Pharmacological Target

The G-protein coupled receptor GPR39 is abundantly expressed in various tissues and can be activated by changes in extracellular Zn²⁺ in physiological concentrations. Previously, genetically modified rodent models have been able to shed some light on the physiological functions of GPR39, and more recently the utilization of novel synthetic agonists has led to the unraveling of several new functions in the variety of tissues GPR39 is expressed. Indeed, GPR39 seems to be involved in many important metabolic and endocrine functions, but also to play a part in inflammation, cardiovascular diseases, saliva secretion, bone formation, male fertility, addictive and depression disorders and cancer. These new discoveries offer opportunities for the development of novel therapeutic approaches against many diseases where efficient therapeutics are still lacking. This review focuses on Zn²⁺ as an endogenous ligand as well as on the novel synthetic agonists of GPR39, placing special emphasis on the recently discovered physiological functions and discusses their pharmacological potential.

Effects of Quercetin and Resveratrol on Zinc Chloride- and Sodium Metavanadate-Induced Passive Avoidance Memory Retention Deficits in Male Mice

Quercetin and resveratrol are found in a variety of fruits and vegetables and have several biological and pharmacological properties. In this study, the effects of quercetin [50 mg/kg, intraperitoneal (i.p.)] and resveratrol (50 mg/kg, i.p.) on zinc chloride (ZnCl₂; 75 mg/kg/d, 2 weeks oral gavage) and sodium metavanadate (SMV; 22.5 mg/kg/d, 2 weeks oral gavage) induced passive avoidance memory retention were investigated in step-through passive avoidance tasks. ZnCl₂ was dissolved in saline and SMV was dissolved in drinking water. Mice received ZnCl₂ or SMV orally for two weeks and were administered quercetin or resveratrol by i.p. injection on day 14, days 12 and 14, or days 10, 12, and 14. At the end of treatment, animals were trained for one day in a step-through passive avoidance task, then alterations in avoidance memory retention were evaluated after 24, 48, 96, and 168 h. Oral consumption of ZnCl₂ and SMV decreased latency time compared with control groups. Both quercetin and resveratrol (50 mg/kg, i.p.) prevented ZnCl₂- and SMV-induced avoidance memory retention impairments and did not significantly alter muscle strength, as demonstrated in rotarod tasks. No significant differences were observed between mice who received single, double, or triple doses of quercetin or resveratrol. The results suggest that quercetin and resveratrol may have preventive effects on ZnCl₂- and SMV-induced memory impairment in male mice.

The Way to a Human's Brain Goes Through Their Stomach: Dietary Factors in Major Depressive Disorder

Globally, more than 250 million people are affected by depression (major depressive disorder; MDD), a serious and debilitating mental disorder. Currently available treatment options can have substantial side effects and take weeks to be fully effective. Therefore, it is important to find safe alternatives, which act more rapidly and in a larger number of patients. While much research on MDD focuses on chronic stress as a main risk factor, we here make a point of exploring dietary factors as a somewhat overlooked, yet highly promising approach towards novel antidepressant pathways. Deficiencies in various groups of nutrients often occur in patients with mental disorders. These include vitamins, especially members of the B-complex (B6, B9, B12). Moreover, an imbalance of fatty acids, such as omega-3 and omega-6, or an insufficient supply with minerals, including magnesium and zinc, are related to MDD. While some of them are relevant for the synthesis of monoamines, others play a crucial role in inflammation, neuroprotection and the synthesis of growth factors. Evidence suggests that when deficiencies return to normal, changes in mood and behavior can be, at least in some cases, achieved. Furthermore, supplementation with dietary factors (so called "nutraceuticals") may improve MDD symptoms even in the absence of a deficiency. Non-vital dietary factors may affect MDD symptoms as well. For instance, the most commonly consumed psychostimulant caffeine may improve behavioral and molecular markers of MDD. The molecular structure of most dietary factors is well known. Hence, dietary factors may provide important molecular tools to study and potentially help treat MDD symptoms. Within this review, we will discuss the role of dietary factors in MDD risk and symptomology, and critically discuss how they might serve as auxiliary treatments or preventative options for MDD.

Proteasome Inhibitor MG132 is Toxic and Inhibits the Proliferation of Rat Neural Stem Cells but Increases BDNF Expression to Protect Neurons

Regulation of protein expression is essential for maintaining normal cell function. Proteasomes play important roles in protein degradation and dysregulation of proteasomes is implicated in neurodegenerative disorders. In this study, using a proteasome inhibitor MG132, we showed that proteasome inhibition reduces neural stem cell (NSC) proliferation and is toxic to NSCs. Interestingly, MG132 treatment increased the percentage of neurons in both proliferation and differentiation culture conditions of NSCs. Proteasome inhibition reduced B-cell lymphoma 2 (Bcl-2)/Bcl-2 associated X protein ratio. In addition, MG132 treatment induced cAMP response element-binding protein phosphorylation and increased the expression of brain-derived neurotrophic factor transcripts and proteins. These data suggest that proteasome function is important for NSC survival and differentiation. Moreover, although MG132 is toxic to NSCs, it may increase neurogenesis. Therefore, by modifying MG132 chemical structure and developing none toxic proteasome inhibitors, neurogenic chemicals can be developed to control NSC cell fate.

GPR39 protects against corticosterone-induced neuronal injury in hippocampal cells through the CREB-BDNF signaling pathway

BACKGROUND

The release of zinc from glutamatergic terminals in the hippocampal CA3 region can activate postsynaptic GPR39 receptors and regulate cognition and depression. However, the role and mechanism of GPR39 in the stress-induced depression is still poorly understood.

METHODS

In this study, hippocampal cells (HT-22) were treated with corticosterone (CORT). Then the effects of stress on the activity, mitochondrial function and apoptosis of HT-22 cells were observed. The effects of GPR39 on CORT-induced stress injury were analyzed by both siRNA and agonist (TC-G-1008).

RESULTS

Compared with the 500 nM CORT group, the cell viability, apoptosis, mitochondrial membrane potential, and expression levels of BCL-2, CREB and BDNF mRNA were significantly decreased in the GPR39 siRNA+500 nM CORT group, while the expression levels of caspase3, caspase9, AIF and BAX mRNA were significantly increased in the GPR39 siRNA+500 nM CORT group. Compared with the 1 μM CORTgroup, the cell viability, apoptosis, mitochondrial membrane potential, and expression levels of BCL-2, CREB and BDNF were significantly increased in the GPR39 agonist+1 μΜ CORT group, while the expression levels of caspase3, caspase9, AIF and BAX mRNA were significantly decreased in the GPR39 siRNA+500 nM CORT group. Compared with the control group, the mRNA and protein levels of GPR39, CREB and BDNF were significantly increased, and the mRNA and protein levels of CREB and BDNF were significantly decreased after 50 μM zinc sulfate treatment for 6 h.

CONCLUSIONS

GPR39 may play a neuroprotective role in CORT-induced cell injury via the improvement of CREB-BDNF expression, by inhibiting pro-apoptotic proteins and by upregulating anti-apoptotic proteins.

MicroRNA-202-3p Targets Brain-Derived Neurotrophic Factor and Is Involved in Depression-Like Behaviors

BACKGROUND

Brain-derived neurotrophic factor (BDNF) and microRNA (miRNA) play crucial roles in the etiology of depression. However, the molecular mechanisms underlying this disease are not fully understood. The primary objective of this study was to investigate the relationship between miR-202-3p and BDNF in a chronic unpredictable mild stress (CUMS) model.

METHODS

Depression model was established with chronic mild unpredictable mild stimulation (CUMS) combined with solitary feeding. The expression levels of miR-202-3p and BDNF in rat hippocampus were measured by qRT-PCR. The novelty inhibition feeding test (NSFT), sucrose preference test (SPT), and forced swimming test (FST) were used to evaluate the functions of miR-202-3p and BDNF. Target gene prediction and screening and luciferase reporter assay were used to verify the target of miR-202-3p. The expression levels of BNDF, CREB1 and p-CREB1 were detected by Western blot.

RESULTS

Upregulation of miR-202-3p was associated with decreased expression of BDNF in the hippocampus of the CUMS model. Antidepressant was observed when LV-BDNF or LV-si-miR-202-3p was injected into the hippocampus. In addition, in the rat hippocampus and cultured nerve cells, the expression levels of BDNF and cyclic AMP response element binding protein 1 (CREB1), which is a target gene of BDNF, were reduced after LV-miR-202-3p injection. Overexpression of miR-202-3p aggravated depressive behavior and decreased the expression levels of BDNF. Luciferase reporter assay also confirmed that BDNF was a target of miR-202-3p.

CONCLUSION

Silencing miR-202-3p can reduce the damage to hippocampal nerve in CUMS rats; the mechanism may be related to the upregulation of BNDF expression. miR-202-3p may be an effective target for the treatment of depression.

Rare-variant pathogenicity triage and inclusion of synonymous variants improves analysis of disease associations of orphan G protein-coupled receptors

The pace of deorphanization of G protein-coupled receptors (GPCRs) has slowed, and new approaches are required. Small molecule targeting of orphan GPCRs can potentially be of clinical benefit even if the endogenous receptor ligand has not been identified. Many GPCRs lack common variants that lead to reproducible genome-wide disease associations, and rare-variant approaches have emerged as a viable alternative to identify disease associations for such genes. Therefore, our goal was to prioritize orphan GPCRs by determining their associations with human diseases in a large clinical population. We used sequence kernel association tests to assess the disease associations of 85 orphan or understudied GPCRs in an unselected cohort of 51,289 individuals. Using rare loss-of-function variants, missense variants predicted to be pathogenic or likely pathogenic, and a subset of rare synonymous variants that cause large changes in local codon bias as independent data sets, we found strong, phenome-wide disease associations shared by two or more variant categories for 39% of the GPCRs. To validate the bioinformatics and sequence kernel association test analyses, we functionally characterized rare missense and synonymous variants of GPR39, a family A GPCR, revealing altered expression or Zn²⁺-mediated signaling for members of both variant classes. These results support the utility of rare variant analyses for identifying disease associations for GPCRs that lack impactful common variants. We highlight the importance of rare synonymous variants in human physiology and argue for their routine inclusion in any comprehensive analysis of genomic variants as potential causes of disease.

Modulation of Gpr39, a G-protein coupled receptor associated with alcohol use in non-human primates, curbs ethanol intake in mice

Alcohol use disorder (AUD) is a chronic condition with devastating health and socioeconomic effects. Still, pharmacotherapies to treat AUD are scarce. In a prior study aimed at identifying novel AUD therapeutic targets, we investigated the DNA methylome of the nucleus accumbens core (NAcc) of rhesus macaques after chronic alcohol use. The G-protein coupled receptor 39 (GPR39) gene was hypermethylated and its expression downregulated in heavy alcohol drinking macaques. GPR39 encodes a Zn2+-binding metabotropic receptor known to modulate excitatory and inhibitory neurotransmission, the balance of which is altered in AUD. These prior findings suggest that a GPR39 agonist would reduce alcohol intake. Using a drinking-in-the-dark two bottle choice (DID-2BC) model, we showed that an acute 7.5 mg/kg dose of the GPR39 agonist, TC-G 1008, reduced ethanol intake in mice without affecting total fluid intake, locomotor activity or saccharin preference. Furthermore, repeated doses of the agonist prevented ethanol escalation in an intermittent access 2BC paradigm (IA-2BC). This effect was reversible, as ethanol escalation followed agonist "wash out". As observed during the DID-2BC study, a subsequent acute agonist challenge during the IA-2BC procedure reduced ethanol intake by ~47%. Finally, Gpr39 activation was associated with changes in Gpr39 and Bdnf expression, and in glutamate release in the NAcc. Together, our findings suggest that GPR39 is a promising target for the development of prevention and treatment therapies for AUD.

MiR-221 is involved in depression by regulating Wnt2/CREB/BDNF axis in hippocampal neurons

OBJECTIVE

The aim of this study was to investigate the mechanism of miR-221 in depression.

METHODS

The molecules expressions were measured by qRT-PCR and western blot. The sucrose preference test (SPT), forced swimming test (FST) and tail suspension test (TST) were used to detect depressive-like symptoms. MTT assay and flow cytometric was used to measure the proliferation and apoptosis of hippocampal neuronal.

RESULTS

MiR-221 expression in the cerebrospinal fluid and serum of major depressive disorder patients and the hippocampus of chronic unpredictable mild stress (CUMS) mice were increased, while the expression of Wnt2, p-CREB and BDNF were decreased. Additionally, silence of miR-221 increased sucrose preference of CUMS mice and shortened the immobility time of CUMS mice in SPT and FST. MiR-221 could targeted regulate Wnt2, and knockdown of Wnt2 reversed the effect of miR-221 inhibitor on the proliferation and apoptosis of hippocampal neurons and countered the promoting effect of miR-221 inhibitor on the expression of Wnt2, p-CREB and BDNF.

CONCLUSION

MiR-221 could promote the development of depression by regulating Wnt2/CREB/BDNF axis.

Orexin/hypocretin receptor modulation of anxiolytic and antidepressive responses during social stress and decision-making: Potential for therapy

Hypothalmic orexin/hypocretin (Orx) neurons in the lateral and dorsomedial perifornical region (LH-DMH/PeF) innervate broadly throughout the brain, and receive similar inputs. This wide distribution, as well as two Orx peptides (Orx_A and Orx_B) and two Orx receptors (Orx₁ and Orx₂) allow for functionally related but distinctive behavioral outcomes, that include arousal, sleep-wake regulation, food seeking, metabolism, feeding, reward, addiction, and learning. These are all motivational functions, and tie the orexin systems to anxiety and depression as well. We present evidence, that for affective behavior, Orx₁ and Orx₂ receptors appear to have opposing functions. The majority of research on anxiety- and depression-related outcomes has focused on Orx₁ receptors, which appear to have primarily anxiogenic and pro-depressive actions. Although there is significant research suggesting contrary findings, the primary potential for pharmacotherapies linked to the Orx₁ receptor is via antagonists to block anxious and depressive behavior. Dual orexin receptor antagonists have been approved for treatment of sleep disorders, and are likely candidates for adaptation for affect disorder treatments. However, we present evidence here that demonstrates the Orx₂ receptors are anxiolytic and antidepressive. Using a new experimental pre-clinical model of anxious and depressive behavior stimulated by social stress and decision-making that produces two stable behavioral phenotypes, Escape/Resilient and Stay/Susceptible, we tested the effects of intracerebroventricular injections of Orx₂ agonist and antagonist drugs. Over ten behavioral measures, we have demonstrated that Orx₂ agonists promote resilience, as well as anxiolytic and antidepressive behavior. In contrast, Orx₂ antagonists or knockdown kindle anxious and pro-depressive behavior plus increase susceptibility. The results suggest that the Orx₂ receptor may be a useful target for pharmacotherapies to treat anxiety and depression.

EGb761 improves the cognitive function of elderly db/db-/- diabetic mice by regulating the beclin-1 and NF-κB signaling pathways

To assess whether EGb761 could protect elderly diabetic mice with cognitive disorders and explore the role of beclin-1-mediated autophagy in these protective effects. Two-month-old male db/db^-/- mice and wild-type C57/BL6 mice were randomly divided into six groups: db/db^-/- control, db/db^-/- 50 mg, db/db^-/- 100 mg, wild-type (WT) control, WT 50 mg, and WT 100 mg. EGb761 (50 mg/kg or 100 mg/kg of bodyweight) was given by gavage once a day for 1 month from the age of 6 months. Y-maze and social choice tests were performed at 8th months. The blood pressure was measured. The imaging changes in the brain were measured using magnetic resonance imaging (MRI). The expression and distribution of beclin-1, LC3, and NF-κB were detected using immunohistochemistry staining and western blotting. Ultrastructure alterations in the hippocampus were observed using transmission electron microscopy. Compared with WT mice, the learning ability, memory and overall cognitive function of db/db^-/- mice decreased (P < 0.05), and EGb761 could significantly improve the learning and memory function of db/db^-/- mice (P < 0.05). EGb761 significantly improved systolic blood pressure in db/db^-/- mice (P < 0.01). In addition, fMRI-bold showed a decline in the hippocampus of mice in the db/db^-/- group compared with WT. EGb761 could improve these above changes. Immunohistochemistry staining and western blotting confirmed that EGb761 significantly increased beclin-1 and reduced LC3-II/I levels in the brains of db/db^-/- mice (P < 0.05). NF-κB levels were obviously higher in the db/db^-/- group than that in the WT group, and EGb761 significantly reduced NF-κB levels in db/db^-/- mice (P < 0.05). There was a trend of increased autophagosomes in db/db^-/- mice, but EGb761 did not change obviously the number of autophagosomes. Compared with normal aged WT mice, aging db/db^-/- mice had more common complications of cerebral small vessel disease and cognitive dysfunction. EGb761 could significantly improve the cognitive function of aging db/db^-/- mice via a mechanism that may involve the regulation of beclin-1, LC3, and NF-κB.

G protein-coupled receptor 39 plays an anti-inflammatory role by enhancing IL-10 production from macrophages under inflammatory conditions

The possible role of G protein-coupled receptor 39 (GPR39) in inflammation was examined in macrophages. Gpr39 expression increased in thioglycollate-induced peritoneal macrophages. TC-G 1008, a G protein-coupled receptor 39 agonist, enhanced interleukin (IL)-10 production from thioglycollate-induced peritoneal macrophages stimulated with lipopolysaccharide (LPS) in vitro. In addition, the oral administration of TC-G 1008 enhanced serum IL-10 concentrations in an LPS-induced murine model of sepsis. The ablation of G protein-coupled receptor 39 significantly reduced IL-10 production by TC-G 1008 in thioglycollate-induced peritoneal macrophages stimulated with LPS and in the LPS-induced murine model of sepsis. Moreover, the oral administration of TC-G 1008 significantly improved the survival rate in the LPS-induced murine model of sepsis. Taken together, our data suggest that G protein-coupled receptor 39 exhibits an anti-inflammatory activity by enhancing IL-10 production from macrophages.

Zinc regulates vascular endothelial cell activity through zinc-sensing receptor ZnR/GPR39

Zn2+ is an essential element for cell survival/growth, and its deficiency is linked to many disorders. Extracellular Zn2+ concentration changes participate in modulating fundamental cellular processes such as proliferation, secretion, ion transport, and cell signal transduction in a mechanism that is not well understood. Here, we hypothesize that the Zn2+-sensing receptor ZnR/G protein-coupled receptor 39 (GPR39), found in tissues where dynamic Zn2+ homeostasis takes place, enables extracellular Zn2+ to trigger intracellular signaling pathways regulating key cell functions in vascular cells. Thus, we investigated how extracellular Zn2+ regulates cell viability, proliferation, motility, angiogenesis, vascular tone, and inflammation through ZnR/GPR39 in endothelial cells. Knockdown of GPR39 through siRNA largely abolished Zn2+-triggered cellular activity changes, Ca2+ responses, as well as the downstream activation of Gαq-PLC pathways. Extracellular Zn2+ promoted vascular cell survival/growth through activation of cAMP and Akt as well as overexpressing of platelet-derived growth factor-α receptor and vascular endothelial growth factor A. It also enhanced cell adhesion and mobility, endothelial tubule formation, and cytoskeletal reorganization. Such effects from extracellular Zn2+ were not observed in GPR39-/- endothelial cells. Zn2+ also regulated inflammation-related key molecules such as heme oxygenase-1, selectin L, IL-10, and platelet endothelial cell adhesion molecule 1, as well as vascular tone-related prostaglandin I2 synthase and nitric oxide synthase-3. In sum, extracellular Zn2+ regulates endothelial cell activity in a ZnR/GPR39-dependent manner and through the downstream Gαq-PLC pathways. Thus, ZnR/GPR39 may be a therapeutic target for regulating endothelial activity.

Orphan G protein-coupled receptors: The role in CNS disorders

There are various types of receptors in the central nervous system (CNS). G protein-coupled receptors (GPCRs) have the highest expression with a wide range of physiological functions. A newer sub group of these receptors namely orphan GPCRs have been discovered. GPR3, GPR6, GPR17, GPR26, GPR37, GPR39, GPR40, GPR50, GPR52, GPR54, GPR55, GPR85, GPR88, GPR103, and GPR139 are the selected orphan GPCRs for this article. Their roles in the central nervous system have not been understood well so far. However, recent studies show that they may have very important functions in the CNS. Hence, in the present study, we reviewed most recent findings regarding the physiological roles of the selected orphan GPCRs in the CNS. After a brief presentation of each receptor, considering the results from genetic and pharmacological manipulation of the receptors, their roles in the pathophysiology of different diseases and disorders including anxiety, depression, schizophrenia, epilepsy, Alzheimer's disease, Parkinson's disease, and substance abuse will be discussed. At present, our knowledge regarding the role of GPCRs in the brain is very limited. However, previous limited studies show that orphan GPCRs have an important place in psychopharmacology and these receptors are potential new targets for the treatment of major CNS diseases.

Dietary Zinc Acts as a Sleep Modulator

While zinc is known to be important for many biological processes in animals at a molecular and physiological level, new evidence indicates that it may also be involved in the regulation of sleep. Recent research has concluded that zinc serum concentration varies with the amount of sleep, while orally administered zinc increases the amount and the quality of sleep in mice and humans. In this review, we provide an exhaustive study of the literature connecting zinc and sleep, and try to evaluate which molecular mechanism is likely to be involved in this phenomenon. A better understanding should provide critical information not only about the way zinc is related to sleep but also about how sleep itself works and what its real function is.

The Emerging Role for Zinc in Depression and Psychosis

Zinc participation is essential for all physiological systems, including neural functioning, where it participates in a myriad of cellular processes. Converging clinical, molecular, and genetic discoveries illuminate key roles for zinc homeostasis in association with clinical depression and psychosis which are not yet well appreciated at the clinical interface. Intracellular deficiency may arise from low circulating zinc levels due to dietary insufficiency, or impaired absorption from aging or medical conditions, including alcoholism. A host of medications commonly administered to psychiatric patients, including anticonvulsants, oral medications for diabetes, hormones, antacids, anti-inflammatories and others also impact zinc absorption. Furthermore, inefficient genetic variants in zinc transporter molecules that transport the ion across cellular membranes impede its action even when circulating zinc concentrations is in the normal range. Well powered clinical studies have shown beneficial effects of supplemental zinc in depression and it important to pursue research using zinc as a potential therapeutic option for psychosis as well. Meta-analyses support the adjunctive use of zinc in major depression and a single study now supports zinc for psychotic symptoms. This manuscript reviews the biochemistry and bench top evidence on putative molecular mechanisms of zinc as a psychiatric treatment.

Neuro-psychopharmacological perspective of Orphan receptors of Rhodopsin (class A) family of G protein-coupled receptors

BACKGROUND

In the central nervous system (CNS), G protein-coupled receptors (GPCRs) are the most fruitful targets for neuropsychopharmacological drug development. Rhodopsin (class A) is the most studied class of GPCR and includes orphan receptors for which the endogenous ligand is not known or is unclear. Characterization of orphan GPCRs has proven to be challenging, and the production pace of GPCR-based drugs has been incredibly slow.

OBJECTIVE

Determination of the functions of these receptors may provide unexpected insight into physiological and neuropathological processes. Advances in various methods and techniques to investigate orphan receptors including in situ hybridization and knockdown/knockout (KD/KO) showed extensive expression of these receptors in the mammalian brain and unmasked their physiological and neuropathological roles. Due to these rapid progress and development, orphan GPCRs are rising as a new and promising class of drug targets for neurodegenerative diseases and psychiatric disorders.

CONCLUSION

This review presents a neuropsychopharmacological perspective of 26 orphan receptors of rhodopsin (class A) family, namely GPR3, GPR6, GPR12, GPR17, GPR26, GPR35, GPR39, GPR48, GPR49, GPR50, GPR52, GPR55, GPR61, GPR62, GPR63, GPR68, GPR75, GPR78, GPR83, GPR84, GPR85, GPR88, GPR153, GPR162, GPR171, and TAAR6. We discussed the expression of these receptors in mammalian brain and their physiological roles. Furthermore, we have briefly highlighted their roles in neurodegenerative diseases and psychiatric disorders including Alzheimer's disease, Parkinson's disease, neuroinflammation, inflammatory pain, bipolar and schizophrenic disorders, epilepsy, anxiety, and depression.

Zinc in the Monoaminergic Theory of Depression: Its Relationship to Neural Plasticity

Preclinical and clinical studies have demonstrated that zinc possesses antidepressant properties and that it may augment the therapy with conventional, that is, monoamine-based, antidepressants. In this review we aim to discuss the role of zinc in the pathophysiology and treatment of depression with regard to the monoamine hypothesis of the disease. Particular attention will be paid to the recently described zinc-sensing GPR39 receptor as well as aspects of zinc deficiency. Furthermore, an attempt will be made to give a possible explanation of the mechanisms by which zinc interacts with the monoamine system in the context of depression and neural plasticity.

Model-Based Discovery of Synthetic Agonists for the Zn2+-Sensing G-Protein-Coupled Receptor 39 (GPR39) Reveals Novel Biological Functions

The G-protein-coupled receptor 39 (GPR39) is a G-protein-coupled receptor activated by Zn²⁺. We used a homology model-based approach to identify small-molecule pharmacological tool compounds for the receptor. The method focused on a putative binding site in GPR39 for synthetic ligands and knowledge of ligand binding to other receptors with similar binding pockets to select iterative series of minilibraries. These libraries were cherry-picked from all commercially available synthetic compounds. A total of only 520 compounds were tested in vitro, making this method broadly applicable for tool compound development. The compounds of the initial library were inactive when tested alone, but lead compounds were identified using Zn²⁺ as an allosteric enhancer. Highly selective, highly potent Zn²⁺-independent GPR39 agonists were found in subsequent minilibraries. These agonists identified GPR39 as a novel regulator of gastric somatostatin secretion.

Evidence for the involvement of heme oxygenase-1 in the antidepressant-like effect of zinc

BACKGROUND

Considering that heme oxygenase-1 (HO-1) and the brain-derived neurotrophic factor (BDNF)-mediated pathway are involved in the pathophysiology of depression and that zinc has been shown to exert beneficial effects in the management of depression, this study investigated the influence of these targets on the antidepressant-like effect of zinc.

METHODS

Mice were treated with sub-effective or effective doses of zinc chloride (ZnCl₂, 10 mg/kg, po), and 45 min later, they received intracerebroventricular (icv) injections of sub-effective doses of either zinc protoporphyrin IX (ZnPP, 10 μg/mouse, HO-1 inhibitor), cobalt protoporphyrin IX (CoPP, 0.01 μg/mouse, HO-1 inducer) or K-252a (1 μg/mouse, TrkB receptor antagonist). Immobility time and locomotor activity were evaluated through the tail suspension test (TST) and open-field test (OFT), respectively. HO-1 immunocontents were evaluated in the prefrontal cortex and hippocampus 60 min after ZnCl₂ (10 mg/kg, po) treatment.

RESULTS

The antidepressant-like effect of ZnCl₂ was prevented by the treatment with ZnPP and K-252a. Furthermore, sub-effective doses of CoPP and ZnCl₂ produced a synergistic antidepressant-like effect in the TST. None of the treatments altered locomotor activity. ZnCl₂ administration increased HO-1 immunocontents only in the prefrontal cortex.

CONCLUSIONS

The results indicate that the antidepressant-like effect of ZnCl₂ in the TST may depend on the induction of HO-1, and activation of TrkB receptor.

[Role of cAMP/CREB/BDNF signaling pathway in anti-depressive effect of vortioxetine in mice]

OBJECTIVE

To investigate the effects of vortioxetine on cAMP/CREB/BDNF signal pathway.

METHODS

Forty Kunming mice were randomized into control group and chronic unpredictable mild stress (CUMS) group. After establishment of depressive models verified by sucrose preference test, the mice in CUMS group were divided into model group, fluoxetine group and vortioxetine group. The antidepressive effect of vortioxetine was analyzed by tail suspension test, forced swim test and open field test. The levels of cAMP were detected using a commercial ELISA kit, and the expressions of pCREB and brain-derived neurotrophic factor (BDNF) were evaluated with Western blotting.

RESULTS

Vortioxetine significantly shortened the immobility time of the depressive mice in tail suspension test and forced swim test without affecting the locomotor activity of the mice in open fields, suggesting the antidepressive effect of against depression in mice. Vortioxetine significantly increased the levels of cAMP and promoted the expression of pCREB and BDNF in the hippocampus of the mice (P<0.01).

CONCLUSION

Vortioxetine improves the behaviors of mice with depression possibly by affecting the cAMP/CREB/BDNF signal pathway.

Beclin-1- mediated autophagy may be involved in the elderly cognitive and affective disorders in streptozotocin-induced diabetic mice

Background

Diabetes is the most common metabolic disease with many chronic complications, and cognitive disorders are one of the common complications in patients with diabetes. Previous studies have showed that autophagy played important roles in the progression of metabolic syndrome, diabetes and other diseases. So we investigated whether aged diabetic mice are prone to be associated with the cognitive and affective disorders and whether Beclin-1-mediated autophagy might be involved in thepahological process.

Methods

High-fat diet/streptozotocin (STZ) injection-induced diabetic C57 mice were adopted in this study. Cognitive disorders were detected by Morris water maze and fear conditional test. Affective disorders were detected by tail suspension test and forced swimming test. Magnetic resonance imaging was applied to observe changes of morphology and metabolism in the brain. The 18 F-fluorodeoxyglucose positron emission tomography (FDG-PET) was used to assess metabolism changes in the brain of aged diabetic mice. Autophagy were evaluated by Beclin- 1, LC3II/I and P62, which were detected by western blot analysis and observed by electron microscopy.

Results

1. Compared with control group, diabetes mice showed significantly decreasing abilities in spatial memory and conditioned fear memory (all P < 0.05), and increasing tendency of depression (P < 0.05). 2. MRI showed that the majority of elderly diabetic mice were associated with multiple cerebral small vessel disease. Some even showed hippocampal atrophy, ventricular dilatation and leukoaraiosis. 3. FDG-PET-CT discovered that the glucose metabolism in the amygdala and hippocampus was significantly decreased compared with normal aged mice (P < 0.05). 4. Electron microscopy found that, although autophagy bodies was not widespread, and there was no significant difference between the two groups, yet compared with normal aged mice, apparent cell edema, myelinated tow reduction and intracellular lipofuscin augmentation existed in elderly diabetic mice brain. 5. The level of p62 was increased in the STZ-induced diabetic mice hippocampus and striatum, and beclin1 protein expression were significantly decreased in diabetic mice hippocampus compared with normal aged mice (P < 0.05). There was a upward trend of the ratio of LC3II/I in hippocampus, cortex and striatum, but no statistically difference between the two groups.

Conclusion

Compared with normal aged mice, diabetic aged mice were apt to cerebral small vessel disease and associated with cognitive and affective disorders, which may be related to the significantly reduced glucose metabolism in hippocampus and amygdala. Beclin1 mediated autophagy in hippocampus probably played an important role in cognitive and affective disorders of STZ-induced aged diabetic mice.

The Role of Elements in Anxiety

Elements (bioelements) are necessary factors required for the physiological function of organisms. They are critically involved in fundamental processes of life. Extra- and intracellular message and metabolic pathway factors as well as structural components include one or many elements in their functional structure. Recent years have seen an intensification in terms of knowledge gained about the roles of elements in anxiety disorders. In this chapter we present a review of the most important current data concerning the involvement of zinc, magnesium, copper, lithium, iron, and manganese, and their deficiency, in the pathophysiology and treatment of anxiety.

Selective Inducible Nitric Oxide Synthase Inhibitor Reversed Zinc Chloride-Induced Spatial Memory Impairment via Increasing Cholinergic Marker Expression

Zinc, an essential micronutrient and biochemical element of the human body, plays structural, catalytic, and regulatory roles in numerous physiological functions. In the current study, the effects of a pretraining oral administration of zinc chloride (10, 25, and 50 mg/kg) for 14 consecutive days and post-training bilateral intra-hippocampal infusion of 1400W as a selective inducible nitric oxide synthase (iNOS) inhibitor (10, 50, and 100 μM/side), alone and in combination, on the spatial memory retention in Morris water maze (MWM) were investigated. Animals were trained for 4 days and tested 48 h after completion of training. Also, the molecular effects of these compounds on the expression of choline acetyltransferase (ChAT), as a cholinergic marker in the CA1 region of the hippocampus and medial septal area (MSA), were evaluated. Behavioral and molecular findings of this study showed that a 2-week oral administration of zinc chloride (50 mg/kg) impaired spatial memory retention in MWM and decreased ChAT expression. Immunohistochemical analysis of post-training bilateral intra-hippocampal infusion of 1400W revealed a significant increase in ChAT immunoreactivity. Furthermore, post-training bilateral intra-hippocampal infusion of 1400W into the CA1 region of the hippocampus reversed zinc chloride-induced spatial memory impairment in MWM and significantly increased ChAT expression in comparison with zinc chloride-treated animals. Taken together, these results emphasize the role of selective iNOS inhibitors in reversing zinc chloride-induced spatial memory deficits via modulation of cholinergic marker expression.

Ultra-sensitive detection of brain-derived neurotrophic factor (BDNF) in the brain of freely moving mice using an interdigitated microelectrode (IME) biosensor

Brain-derived neurotrophic factor (BDNF) plays a critical role in cognitive processes including learning and memory. However, it has been difficult to detect BDNF in the brains of behaving animals because of its extremely low concentration, i.e., at the sub-nanogram/mL level. Here, we developed an interdigitated microelectrode (IME) biosensor coated with an anti-BDNF an anti-BDNF antibody in a polydimethylsiloxane (PDMS)-based microfluidic channel chip. This sensor could detect BDNF from microliter volumes of liquid samples even at femtogram/mL concentrations with high selectivity over other growth factors. Using this biosensor, we examined whether BDNF is detectable from periodical collection of cerebrospinal fluid microdialysate, sampled every 10 min from the hippocampus of mice during the context-dependent fear-conditioning test. We found that the IME biosensor could detect a significant increase in BDNF levels after the memory task. This increase in BDNF levels was prevented by gene silencing of BDNF, indicating that the IME biosensor reliably detected BDNF in vivo. We propose that the IME biosensor provides a general-purpose probe for ultrasensitive detection of biomolecules with low abundance in the brains of behaving animals.

Growth factors as clinical biomarkers of prognosis and diagnosis in psychiatric disorders

The psychiatric disorders are one of the most disabling illnesses in the world and represent a major problem for public health. These disorders are characterized by neuroanatomical or biochemical changes and it has been suggested that such changes may be due to inadequate neurodevelopment. Diverse alterations in the gene expression and/or serum level of specific growth factors have been implicated in the etiology, symptoms and progression of some psychiatric disorders. Herein, we summarize the latest information regarding the role of brain-derived neurotrophic factor (BDNF), epidermal growth factor (EGF), fibroblast growth factor (FGF), Insulin-like growth factor (IGF-1), neuroregulin-1 (NGR-1), erythropoietin (EPO), vascular growth factor (VEGF), transforming growth factor beta (TGF-β), nerve growth factor (NGF) and others cytokines in the pathogenesis of schizophrenia, depression, bipolar and anxiety disorders. Focusing on the role of these growth factors and their relationship with the main impairments (cognitive, emotional and social) of these pathologies. Some of these signaling molecules may be suitable biological markers for diagnosis and prognosis in cognitive, mood and social disabilities across different mental disorders.