Dopamine D2L receptor-interacting proteins regulate dopaminergic signaling

Impact of gene-by-trauma interaction in MDD-related multimorbidity clusters

BACKGROUND

Major depressive disorder (MDD) is considerably heterogeneous in terms of comorbidities, which may hamper the disentanglement of its biological mechanism. In a previous study, we classified the lifetime trajectories of MDD-related multimorbidities into seven distinct clusters, each characterized by unique genetic and environmental risk-factor profiles. The current objective was to investigate genome-wide gene-by-environment (G × E) interactions with childhood trauma burden, within the context of these clusters.

METHODS

We analyzed 77,519 participants and 6,266,189 single-nucleotide polymorphisms (SNPs) of the UK Biobank database. Childhood trauma burden was assessed using the Childhood Trauma Screener (CTS). For each cluster, Plink 2.0 was used to calculate SNP × CTS interaction effects on the participants' cluster membership probabilities. We especially focused on the effects of 31 candidate genes and associated SNPs selected from previous G × E studies for childhood maltreatment's association with depression.

RESULTS

At SNP-level, only the high-multimorbidity Cluster 6 revealed a genome-wide significant SNP rs145772219. At gene-level, MPST and PRH2 were genome-wide significant for the low-multimorbidity Clusters 1 and 3, respectively. Regarding candidate SNPs for G × E interactions, individual SNP results could be replicated for specific clusters. The candidate genes CREB1, DBH, and MTHFR (Cluster 5) as well as TPH1 (Cluster 6) survived multiple testing correction.

LIMITATIONS

CTS is a short retrospective self-reported measurement. Clusters could be influenced by genetics of individual disorders.

CONCLUSIONS

The first G × E GWAS for MDD-related multimorbidity trajectories successfully replicated findings from previous G × E studies related to depression, and revealed risk clusters for the contribution of childhood trauma.

CHL1 depletion affects dopamine receptor D2-dependent modulation of mouse behavior

Introduction

The dopaminergic system plays a key role in the appropriate functioning of the central nervous system, where it is essential for emotional balance, arousal, reward, and motor control. The cell adhesion molecule close homolog of L1 (CHL1) contributes to dopaminergic system development, and CHL1 and the dopamine receptor D2 (D2R) are associated with mental disorders like schizophrenia, addiction, autism spectrum disorder and depression.

Methods

Here, we investigated how the interplay between CHL1 and D2R affects the behavior of young adult male and female wild-type (CHL+/+) and CHL1-deficient (CHL1-/-) mice, when D2R agonist quinpirole and antagonist sulpiride are applied.

Results

Low doses of quinpirole (0.02 mg/kg body weight) induced hypolocomotion of CHL1+/+ and CHL1-/- males and females, but led to a delayed response in CHL1-/- mice. Sulpiride (1 mg/kg body weight) affected locomotion of CHL1-/- females and social interaction of CHL1+/+ females as well as social interactions of CHL1-/- and CHL1+/+ males. Quinpirole increased novelty-seeking behavior of CHL1-/- males compared to CHL1+/+ males. Vehicle-treated CHL1-/- males and females showed enhanced working memory and reduced stress-related behavior.

Discussion

We propose that CHL1 regulates D2R-dependent functions in vivo. Deficiency of CHL1 leads to abnormal locomotor activity and emotionality, and to sex-dependent behavioral differences.

Gm527 deficiency in dentate gyrus improves memory through upregulating dopamine D1 receptor pathway

AIMS

Dopamine D1 receptor (D1R) hypofunction is associated with negative and cognitive symptoms in schizophrenia; therefore, the mechanism of D1R function modulation needs further investigation. Gm527 is the rodent homologous of the schizophrenia-related gene C14orf28, encoding a predicated D1R-interacting protein. However, the role of Gm527-D1R interaction in schizophrenia needs to be clarified.

METHODS

Gm527-floxed mice were generated and crossed with D1-Cre mice (D1:Gm527-/-) to knockout Gm527 in D1R-positive neurons. Then behavioral tests were performed to explore the schizophrenia-related phenotypes. Immunofluorescence, fluorescence in situ hybridization, electrophysiological recording, quantitative real-time PCR, and western blotting were conducted to investigate the mechanisms.

RESULTS

Working memory, long-term memories, and adult neurogenesis in the DG were enhanced in D1:Gm527-/- mice. LTP was also increased in the DG in D1:Gm527-/- mice, resulting from the Gm527 knockout-induced D1R expression enhancement on the plasma membrane and subsequently cAMP signaling and NMDA receptor pathways activation. The requirement of Gm527 knockout in the DG was confirmed by reversing Gm527 expression or knockdown Gm527 in the DG D1R-positive neurons through AAV-CAG-FLEX-Gm527-GFP or AAV-CMV-FLEX-EGFP-Gm527-RNAi injection.

CONCLUSIONS

The DG Gm527 knockout induces D1R hyperfunction in improving schizophrenia cognitive symptoms.

Chemogenetic stimulation of the Gi pathway in astrocytes suppresses neuroinflammation

Engineered G protein-coupled receptors (GPCRs) are commonly used in chemogenetics as designer receptors exclusively activated by designer drugs (DREADDs). Although several GPCRs have been studied in astrocytes using a chemogenetic approach, the functional role of the astrocytic Gi pathway is not clear, as the literature is conflicting depending on the brain regions or behaviors investigated. In this study, we evaluated the role of the astrocytic Gi pathway in neuroinflammation using a Gi -coupled DREADD (hM4Di). Gi -DREADD was expressed in hippocampal astrocytes of a lipopolysaccharide (LPS)-induced neuroinflammation mouse model using adeno-associated viruses. We found that astrocyte Gi -DREADD stimulation using clozapine N-oxide (CNO) inhibits neuroinflammation, as characterized by decreased levels of proinflammatory cytokines, glial activation, and cognitive impairment in mice. Subsequent experiments using primary astrocyte cultures revealed that Gi -DREADD stimulation significantly downregulated LPS-induced expression of Nos2 mRNA and nitric oxide production. Similarly, in vitro calcium imaging showed that activation of the astrocytic Gi pathway attenuated intracellular calcium transients triggered by LPS treatment, suggesting a positive correlation between enhanced calcium transients and the inflammatory phenotype of astrocytes observed in the inflamed brain. Taken together, our results indicate that the astrocytic Gi pathway plays an inhibitory role in neuroinflammation, providing an opportunity to identify potential cellular and molecular targets to control neuroinflammation.

Multiple alterations in glutamatergic transmission and dopamine D2 receptor splicing in induced pluripotent stem cell-derived neurons from patients with familial schizophrenia

An increasing body of evidence suggests that impaired synapse development and function are associated with schizophrenia; however, the underlying molecular pathophysiological mechanism of the disease remains largely unclear. We conducted a family-based study combined with molecular and cellular analysis using induced pluripotent stem cell (iPSC) technology. We generated iPSCs from patients with familial schizophrenia, differentiated these cells into neurons, and investigated the molecular and cellular phenotypes of the patient's neurons. We identified multiple altered synaptic functions, including increased glutamatergic synaptic transmission, higher synaptic density, and altered splicing of dopamine D2 receptor mRNA in iPSC-derived neurons from patients. We also identified patients' specific genetic mutations using whole-exome sequencing. Our findings support the notion that altered synaptic function may underlie the molecular and cellular pathophysiology of schizophrenia, and that multiple genetic factors cooperatively contribute to the development of schizophrenia.

Membrane Nanoscopic Organization of D2L Dopamine Receptor Probed by Quantum Dot Tracking

The role of lateral mobility and nanodomain organization of G protein-coupled receptors in modulating subcellular signaling has been under increasing scrutiny. Investigation of D2 dopamine receptor diffusion dynamics is of particular interest, as these receptors have been linked to altered neurotransmission in affective disorders and represent the primary target for commonly prescribed antipsychotics. Here, we applied our single quantum dot tracking approach to decipher intrinsic diffusion patterns of the wild-type long isoform of the D2 dopamine receptor and its genetic variants previously identified in several cohorts of schizophrenia patients. We identified a subtle decrease in the diffusion rate of the Val96Ala mutant that parallels its previously reported reduced affinity for potent neuroleptics clozapine and chlorpromazine. Slower Val96Ala variant diffusion was not accompanied by a change in receptor-receptor transient interactions as defined by the diffraction-limited quantum dot colocalization events. In addition, we implemented a Voronoї tessellation-based algorithm to compare nanoclustering of the D2 dopamine receptor to the dominant anionic phospholipid phosphatidylinositol 4,5-bisphosphate in the plasma membrane of live cells.

Cannabinoid 2 receptors regulate dopamine 2 receptor expression by a beta-arrestin 2 and GRK5-dependent mechanism in neuronal cells

We have previously reported that the repeated exposure to cannabinoids upregulates and enhances the activity of serotonin 2A (5-HT_2A) and dopamine 2 (D₂) receptors and facilitates the formation of D₂-5-HT_2A receptor heterodimers in the rat prefrontal cortex and two neuronal cell lines. Because the repeated exposure to cannabinoids has been associated with adverse neuropsychiatric disorders, this study investigated the mechanisms that underly the cannabinoid-mediated regulation of D₂ receptor expression in a neuronal cell model, CLU213 cells. We initially tested the effects of repeated exposure (72 h) to a non-selective cannabinoid agonist (1 nM CP55940), a selective CB₁ receptor agonist (15 nM ACEA), or a selective CB₂ receptor drug (1 nM GP1a) on the expression of postsynaptic D₂ (D₂L) receptors in CLU213 cells. Repeated CP55940, GP1a, or ACEA treatments significantly increased D₂L receptor protein levels (99 % ± 7%, 30 % ± 7%, and 39 % ± 5% increases compared with control levels, respectively). Repeated exposure to both GP1a and ACEA increased D₂L receptor protein levels by 73 % ± 8%. Interestingly, CP55940 and GP1a, but not ACEA, upregulated D₂ mRNA. Using cells that were stably transfected with short-hairpin RNA (shRNA) lentiviral particles targeting CB₂ receptors, G protein-coupled receptor kinase 5 (GRK5), and β-arrestin 2, we found that CB₂ receptors regulated D₂ expression through a mechanism that is dependent on GRK5, β-arrestin 2, and extracellular signal-related kinase (ERK)1/2. We also found that repeated exposure to either ACEA or GP1a selectively stimulated the protein and mRNA expression of GRK proteins. ACEA significantly upregulated GRK2 proteins, whereas GP1a upregulated GRK5 protein expression. Our results identified mechanisms associated with the upregulation of D₂ receptors in neuronal cells after the repeated exposure to cannabinoids. These data can shed light on the mechanisms that can be targeted to prevent potential adverse effects, while simultaneously determining the therapeutic benefits of cannabinoids.

Influence of serum concentration in retinoic acid and phorbol ester induced differentiation of SH-SY5Y human neuroblastoma cell line

Numerous protocols to establish dopaminergic phenotype in SH-SY5Y cells have been reported. In most of these protocols there are variations in concentration of serum used. In this paper, we compared the effects of high (10%), low (3%) and descending (2.5%/1%) serum concentration in differentiation medium containing different proportion of retinoic acid (RA) and 12-O-Tetradecanoylphorbol-13-acetate (TPA) or RA-only on the undifferentiated SH-SY5Y cells with regards to cell morphology, biochemical and gene expression alterations. Cells differentiated in culture medium containing low and descending serum concentrations showed increased number of neurite projections and reduced proliferation rates when compared to undifferentiated cells. The SH-SY5Y cells differentiated in culture medium containing 3% RA and low serum or descending (2.5%/1% RA/TPA) were found to be more susceptible to 6-hydroxydopamine (6-OHDA) induced cytotoxicity. Cells differentiated with RA/TPA or RA differentiated showed increased production of the α-synuclein (SNCA) neuroprotein and dopamine neurotransmitter compared to undifferentiated cells, regardless serum concentrations used. There was no significant difference in the expression of tyrosine hydroxylase (TH) gene between undifferentiated and differentiated SH-SY5Y cells. However, the expression of dopamine receptor D2 (DRD2) gene was markedly increased (p<0.05) in differentiated cells with 3% serum and RA only when compared to undifferentiated cells. In conclusion, to terminally differentiate SH-SY5Y cells to be used as a cell-based model to study Parkinson's disease (PD) to investigate molecular mechanisms and drug discovery, the optimal differentiation medium should contain 3% serum in RA-only.

Critical Impact of Different Conserved Endoplasmic Retention Motifs and Dopamine Receptor Interacting Proteins (DRIPs) on Intracellular Localization and Trafficking of the D2 Dopamine Receptor (D2-R) Isoforms

The type 2 dopamine receptor D₂ (D₂-R), member of the G protein-coupled receptor (GPCR) superfamily, exists in two isoforms, short (D_2S-R) and long (D_2L-R). They differ by an additional 29 amino acids (AA) in the third cytoplasmic loop (ICL3) of the D_2L-R. These isoforms differ in their intracellular localization and trafficking functionality, as D_2L-R possesses a larger intracellular pool, mostly in the endoplasmic reticulum (ER). This review focuses on the evolutionarily conserved motifs in the ICL3 of the D₂-R and proteins interacting with the ICL3 of both isoforms, specifically with the 29 AA insert. These motifs might be involved in D₂-R exit from the ER and have an impact on cell-surface and intracellular localization and, therefore, also play a role in the function of dopamine receptor signaling, ligand binding and possible homo/heterodimerization. Our recent bioinformatic data on potential new interaction partners for the ICL3 of D₂-Rs are also presented. Both are highly relevant, and have clinical impacts on the pathophysiology of several diseases such as Parkinson’s disease, schizophrenia, Tourette’s syndrome, Huntington’s disease, manic depression, and others, as they are connected to a variety of essential motifs and differences in communication with interaction partners.

Dopamine Receptor Subtypes, Physiology and Pharmacology: New Ligands and Concepts in Schizophrenia

Dopamine receptors are widely distributed within the brain where they play critical modulator roles on motor functions, motivation and drive, as well as cognition. The identification of five genes coding for different dopamine receptor subtypes, pharmacologically grouped as D1- (D1 and D5) or D2-like (D2S, D2L, D3, and D4) has allowed the demonstration of differential receptor function in specific neurocircuits. Recent observation on dopamine receptor signaling point at dopamine-glutamate-NMDA neurobiology as the most relevant in schizophrenia and for the development of new therapies. Progress in the chemistry of D1- and D2-like receptor ligands (agonists, antagonists, and partial agonists) has provided more selective compounds possibly able to target the dopamine receptors homo and heterodimers and address different schizophrenia symptoms. Moreover, an extensive evaluation of the functional effect of these agents on dopamine receptor coupling and intracellular signaling highlights important differences that could also result in highly differentiated clinical pharmacology. The review summarizes the recent advances in the field, addressing the relevance of emerging new targets in schizophrenia in particular in relation to the dopamine - glutamate NMDA systems interactions.

Synergistic effects between ADORA2A and DRD2 genes on anxiety disorders in children with ADHD

The prevalence of anxiety disorders in patients with Attention Deficit/Hyperactivity Disorder (ADHD) is around 15-40%, three times higher than in the general population. The dopaminergic system, classically associated with ADHD, interacts directly with the adenosinergic system through adenosine A_2A receptors (A_2A) and dopamine D₂ receptors (D₂) forming A_2A-D₂ heterodimers. Both dopaminergic and adenosinergic systems are implicated in anxiety disorders. Therefore, the aims of this study were: a) to investigate the main effects of ADORA2A and DRD2 gene variants on anxiety disorders in an ADHD sample of children and adolescents; b) to test potential synergism between ADORA2A and DRD2 genes on the same outcome; c) to explore ADORA2A variants functionality using an in silico approach. The sample consists of 478 children and adolescents with ADHD and their parents, totalizing 1.239 individuals. An association between the ADORA2A rs2298383 TT genotype with the presence of anxiety disorders (P = .004) and an interaction between ADORA2A-DRD2 risk haplotypes with the same outcome (P = .005) was detected. The in silico analyses showed that rs2298383 has the highest score for regulatory function among all variants in the ADORA2A gene described up to date. Altogether, the present findings suggested that the ADORA2A gene and the interaction of ADORA2A and DRD2 genes may play a role in anxiety disorders in children and adolescents with ADHD.

Dopamine: Functions, Signaling, and Association with Neurological Diseases

The dopaminergic system plays important roles in neuromodulation, such as motor control, motivation, reward, cognitive function, maternal, and reproductive behaviors. Dopamine is a neurotransmitter, synthesized in both central nervous system and the periphery, that exerts its actions upon binding to G protein-coupled receptors. Dopamine receptors are widely expressed in the body and function in both the peripheral and the central nervous systems. Dopaminergic signaling pathways are crucial to the maintenance of physiological processes and an unbalanced activity may lead to dysfunctions that are related to neurodegenerative diseases. Unveiling the neurobiology and the molecular mechanisms that underlie these illnesses may contribute to the development of new therapies that could promote a better quality of life for patients worldwide. In this review, we summarize the aspects of dopamine as a catecholaminergic neurotransmitter and discuss dopamine signaling pathways elicited through dopamine receptor activation in normal brain function. Furthermore, we describe the potential involvement of these signaling pathways in evoking the onset and progression of some diseases in the nervous system, such as Parkinson's, Schizophrenia, Huntington's, Attention Deficit and Hyperactivity Disorder, and Addiction. A brief description of new dopaminergic drugs recently approved and under development treatments for these ailments is also provided.