Cannabidiol negatively modulates adenosine A2A receptor functioning in living cells.

OBJECTIVES: Cannabidiol (CBD) is a phytocannabinoid with great potential in clinical applications. The mechanism(s) of action of CBD require further investigation. Previous studies suggested that adenosine A2A receptors (A2ARs) could play a role in CBD-induced effects. Here, we evaluated the ability of CBD to modify the function of A2AR. METHODS: We used HEK-293T cells transfected with the cDNA encoding the human A2AR and Gαs protein, both modified to perform bioluminescence-based assays. We first assessed the effect of CBD on A2AR ligand binding using an A2AR NanoLuciferase sensor. Next, we evaluated whether CBD modified A2AR coupling to mini-Gαs proteins using the NanoBiT™ assay. Finally, we further assessed CBD effects on A2AR intrinsic activity by recording agonist-induced cAMP accumulation. RESULTS: CBD did not bind orthosterically to A2AR but reduced the coupling of A2AR to Gαs protein and the subsequent generation of cAMP. CONCLUSION: CBD negatively modulates A2AR functioning.

GPR37 is processed in the N-terminal ectodomain by ADAM10 and furin.

GPR37 is an orphan G protein-coupled receptor (GPCR) implicated in several neurological diseases and important physiological pathways in the brain. We previously reported that its long N-terminal ectodomain undergoes constitutive metalloprotease-mediated cleavage and shedding, which have been rarely described for class A GPCRs. Here, we demonstrate that the protease that cleaves GPR37 at Glu167↓Gln168 is a disintegrin and metalloprotease 10 (ADAM10). This was achieved by employing selective inhibition, RNAi-mediated downregulation, and genetic depletion of ADAM10 in cultured cells as well as in vitro cleavage of the purified receptor with recombinant ADAM10. In addition, the cleavage was restored in ADAM10 knockout cells by overexpression of the wild type but not the inactive mutant ADAM10. Finally, postnatal conditional depletion of ADAM10 in mouse neuronal cells was found to reduce cleavage of the endogenous receptor in the brain cortex and hippocampus, confirming the physiological relevance of ADAM10 as a GPR37 sheddase. Additionally, we discovered that the receptor is subject to another cleavage step in cultured cells. Using site-directed mutagenesis, the site (Arg54↓Asp55) was localized to a highly conserved region at the distal end of the ectodomain that contains a recognition site for the proprotein convertase furin. The cleavage by furin was confirmed by using furin-deficient human colon carcinoma LoVo cells and proprotein convertase inhibitors. GPR37 is thus the first multispanning membrane protein that has been validated as an ADAM10 substrate and the first GPCR that is processed by both furin and ADAM10. The unconventional N-terminal processing may represent an important regulatory element for GPR37.

Design, Synthesis and Characterization of a New Series of Fluorescent Metabotropic Glutamate Receptor Type 5 Negative Allosteric Modulators.

In recent years, new drug discovery approaches based on novel pharmacological concepts have emerged. Allosteric modulators, for example, target receptors at sites other than the orthosteric binding sites and can modulate agonist-mediated activation. Interestingly, allosteric regulation may allow a fine-tuned regulation of unbalanced neurotransmitter' systems, thus providing safe and effective treatments for a number of central nervous system diseases. The metabotropic glutamate type 5 receptor (mGlu5R) has been shown to possess a druggable allosteric binding domain. Accordingly, novel allosteric ligands are being explored in order to finely regulate glutamate neurotransmission, especially in the brain. However, before testing the activity of these new ligands in the clinic or even in animal disease models, it is common to characterize their ability to bind mGlu5Rs in vitro. Here, we have developed a new series of fluorescent ligands that, when used in a new NanoBRET-based binding assay, will facilitate screening for novel mGlu5R allosteric modulators.

GPR37 processing in neurodegeneration: a potential marker for Parkinson's Disease progression rate.

The orphan G protein-coupled receptor 37 (GPR37), widely associated with Parkinson's disease (PD), undergoes proteolytic processing under physiological conditions. The N-terminus domain is proteolyzed by a disintegrin and metalloproteinase 10 (ADAM-10), which generates various membrane receptor forms and ectodomain shedding (ecto-GPR37) in the extracellular environment. We investigated the processing and density of GPR37 in several neurodegenerative conditions, including Lewy body disease (LBD), multiple system atrophy (MSA), corticobasal degeneration (CBD), progressive supranuclear palsy (PSP), and Alzheimer's disease (AD). The presence of ecto-GPR37 peptides in the cerebrospinal fluid (CSF) of PD, MSA, CBD and PSP patients was assessed through an in-house nanoluciferase-based immunoassay. This study identified increased receptor processing in early-stage LBD within the PFC and striatum, key brain areas in neurodegeneration. In MSA only the 52 kDa form of GPR37 appeared in the striatum. This form was also significantly elevated in the striatum of AD necropsies. On the contrary, GPR37 processing remained unchanged in the brains of CBD and PSP patients. Furthermore, while CSF ecto-GPR37 increased in PD patients, its levels remained unchanged in MSA, CBD, and PSP subjects. Importantly, patients with PD with rapid progression of the disease did not have elevated ecto-GPR37 in the CSF, while those with slow progression showed a significant increase, suggesting a possible prognostic use of ecto-GPR37 in PD. This research underscores the distinctive processing and density patterns of GPR37 in neurodegenerative diseases, providing crucial insights into its potential role as an indicator of PD progression rates.

B2R-D2R interaction in prolactinomas and non-functional adenomas: impact on dopamine resistance.

Prolactinomas, the most common pituitary-secreting adenomas, can be effectively treated with dopamine D2 receptor (D2R) agonists. However, a subset of them (∼20%) are resistant to dopamine (DA)-based therapies and require extirpation. The molecular mechanisms underlying their escape from dopaminergic regulation are not fully elucidated and may include alterations in D2R signaling. D2R can heteromerize with other G protein-coupled receptors, resulting in modulation of dopaminergic signaling. Since the bradykinin receptor type 2 (B2R) is overexpressed in prolactinomas, we interrogated whether this dopaminergic dysregulation observed in some prolactinomas may depend on a physical and functional interaction between D2R and B2R. The formation of B2R-D2R complexes in cultured cells transiently expressing both receptors was validated using NanoBiT technology. Interestingly, while D2R stimulation did not alter B2R-induced intracellular calcium mobilization, B2R stimulation abolished D2R signaling through modulation of cAMP. The existence of B2R-D2R complexes in pituitary adenomas (PitNet) biopsies was evaluated using an ALPHALisa approach. Importantly, B2R-D2R complexes were detected in human prolactinomas and nonfunctioning pituitary adenomas (NFPA), but not in mixed (prolactin + growth hormone) secreting adenomas. These results suggest that overexpression of B2R in resistant prolactinomas may promote the formation of B2R-D2R complexes, with B2R precluding D2R signaling, thus generating resistance to D2R agonists.

Unique effect of clozapine on adenosine A2A-dopamine D2 receptor heteromerization.

The striatal dopamine D2 receptor (D2R) is generally accepted to be involved in positive symptoms of schizophrenia and is a main target for clinically used antipsychotics. D2R are highly expressed in the striatum, where they form heteromers with the adenosine A2A receptor (A2AR). Changes in the density of A2AR-D2R heteromers have been reported in postmortem tissue from patients with schizophrenia, but the degree to which A2R are involved in schizophrenia and the effect of antipsychotic drugs is unknown. Here, we examine the effect of exposure to three prototypical antipsychotic drugs on A2AR-D2R heteromerization in mammalian cells using a NanoBiT assay. After 16 h of exposure, a significant increase in the density of A2AR-D2R heteromers was found with haloperidol and aripiprazole, but not with clozapine. On the other hand, clozapine, but not haloperidol or aripiprazole, was associated with a significant decrease in A2AR-D2R heteromerization after 2 h of treatment. Computational binding models of these compounds revealed distinctive molecular signatures that explain their different influence on heteromerization. The bulky tricyclic moiety of clozapine displaces TM 5 of D2R, inducing a clash with A2AR, while the extended binding mode of haloperidol and aripiprazole stabilizes a specific conformation of the second extracellular loop of D2R that enhances the interaction with A2AR. It is proposed that an increase in A2AR-D2R heteromerization is involved in the extrapyramidal side effects (EPS) of antipsychotics and that the specific clozapine-mediated destabilization of A2AR-D2R heteromerization can explain its low EPS liability.

The ADORA1 mutation linked to early-onset Parkinson's disease alters adenosine A1-A2A receptor heteromer formation and function.

Adenosine modulates neurotransmission through inhibitory adenosine A1 receptors (A1Rs) and stimulatory A2A receptors (A2ARs). These G protein-coupled receptors are involved in motor function and related to neurodegenerative diseases such as Parkinson's disease (PD). An autosomal-recessive mutation (G2797.44S) within the transmembrane helix (TM) 7 of A1R (A1RG279S) has been associated with the development of early onset PD (EOPD). Here, we aimed at investigating the impact of this mutation on the structure and function of the A1R and the A1R-A2AR heteromer. Our results revealed that the G2797.44S mutation does not alter A1R expression, ligand binding, constitutive activity or coupling to transducer proteins (Gαi, Gαq, Gα12/13, Gαs, ß-arrestin2 and GRK2) in transfected HEK-293 T cells. However, A1RG279S weakened the ability of A1R to heteromerize with A2AR, as shown in a NanoBiT assay, which led to the disappearance of the heteromerization-dependent negative allosteric modulation that A1R imposes on the constitutive activity and agonist-induced activation of the A2AR. Molecular dynamic simulations allowed to propose an indirect mechanism by which the G2797.44S mutation in TM 7 of A1R weakens the TM 5/6 interface of the A1R-A2AR heteromer. Therefore, it is demonstrated that a PD linked ADORA1 mutation is associated with dysfunction of adenosine receptor heteromerization. We postulate that a hyperglutamatergic state secondary to increased constitutive activity and sensitivity to adenosine of A2AR not forming heteromers with A1R could represent a main pathogenetic mechanism of the EOPD associated with the G2797.44S ADORA1 mutation.

Ecto-GPR37: a potential biomarker for Parkinson's disease.

OBJECTIVE: α-Synuclein has been studied as a potential biomarker for Parkinson's disease (PD) with no concluding results. Accordingly, there is an urgent need to find out reliable specific biomarkers for PD. GPR37 is an orphan G protein-coupled receptor that toxically accumulates in autosomal recessive juvenile parkinsonism. Here, we investigated whether GPR37 is upregulated in sporadic PD, and thus a suitable potential biomarker for PD. METHODS: GPR37 protein density and mRNA expression in postmortem substantia nigra (SN) from PD patients were analysed by immunoblot and RT-qPCR, respectively. The presence of peptides from the N-terminus-cleaved domain of GPR37 (i.e. ecto-GPR37) in human cerebrospinal fluid (CSF) was determined by liquid chromatography-mass spectrometric analysis. An engineered in-house nanoluciferase-based immunoassay was used to quantify ecto-GPR37 in CSF samples from neurological control (NC) subjects, PD patients and Alzheimer's disease (AD) patients. RESULTS: GPR37 protein density and mRNA expression were significantly augmented in sporadic PD. Increased amounts of ecto-GPR37 peptides in the CSF samples from PD patients were identified by mass spectrometry and quantified by the in-house ELISA method. However, the CSF total α-synuclein level in PD patients did not differ from that in NC subjects. Similarly, the cortical GPR37 mRNA expression and CSF ecto-GPR37 levels in AD patients were also unaltered. CONCLUSION: GPR37 expression is increased in SN of sporadic PD patients. The ecto-GPR37 peptides are significantly increased in the CSF of PD patients, but not in AD patients. These results open perspectives and encourage further clinical studies to confirm the validity and utility of ecto-GPR37 as a potential PD biomarker.

Disease-modifying effects of natural Δ9-tetrahydrocannabinol in endometriosis-associated pain.

Endometriosis is a chronic painful disease highly prevalent in women that is defined by growth of endometrial tissue outside the uterine cavity and lacks adequate treatment. Medical use of cannabis derivatives is a current hot topic and it is unknown whether phytocannabinoids may modify endometriosis symptoms and development. Here we evaluate the effects of repeated exposure to Δ9-tetrahydrocannabinol (THC) in a mouse model of surgically-induced endometriosis. In this model, female mice develop mechanical hypersensitivity in the caudal abdomen, mild anxiety-like behavior and substantial memory deficits associated with the presence of extrauterine endometrial cysts. Interestingly, daily treatments with THC (2 mg/kg) alleviate mechanical hypersensitivity and pain unpleasantness, modify uterine innervation and restore cognitive function without altering the anxiogenic phenotype. Strikingly, THC also inhibits the development of endometrial cysts. These data highlight the interest of scheduled clinical trials designed to investigate possible benefits of THC for women with endometriosis.