Biomarkers of Alzheimer's disease and neurodegeneration in dried blood spots-A new collection method for remote settings

BACKGROUND

We aimed to evaluate the precision of Alzheimer's disease (AD) and neurodegeneration biomarker measurements from venous dried plasma spots (DPSv enous) for the diagnosis and monitoring of neurodegenerative diseases in remote settings.

METHODS

In a discovery (n = 154) and a validation cohort (n = 115), glial fibrillary acidic protein (GFAP); neurofilament light (NfL); amyloid beta (Aβ) 40, Aβ42; and phosphorylated tau (p-tau181 and p-tau217) were measured in paired DPSvenous and ethylenediaminetetraacetic acid plasma samples with single-molecule array. In the validation cohort, a subset of participants (n = 99) had cerebrospinal fluid (CSF) biomarkers.

RESULTS

All DPSvenous and plasma analytes correlated significantly, except for Aβ42. In the validation cohort, DPSvenous GFAP, NfL, p-tau181, and p-tau217 differed between CSF Aβ-positive and -negative individuals and were associated with worsening cognition.

DISCUSSION

Our data suggest that measuring blood biomarkers related to AD pathology and neurodegeneration from DPSvenous extends the utility of blood-based biomarkers to remote settings with simplified sampling conditions, storage, and logistics.

HIGHLIGHTS

A wide array of biomarkers related to Alzheimer's disease (AD) and neurodegeneration were detectable in dried plasma spots (DPSvenous). DPSvenous biomarkers correlated with standard procedures and cognitive status. DPSvenous biomarkers had a good diagnostic accuracy discriminating amyloid status. Our findings show the potential interchangeability of DPSvenous and plasma sampling. DPSvenous may facilitate remote and temperature-independent sampling for AD biomarker measurement. Innovative tools for blood biomarker sampling may help recognizing the earliest changes of AD.

Feasibility and usability of remote monitoring in Alzheimer's disease

Introduction

Remote monitoring technologies (RMTs) can measure cognitive and functional decline objectively at-home, and offer opportunities to measure passively and continuously, possibly improving sensitivity and reducing participant burden in clinical trials. However, there is skepticism that age and cognitive or functional impairment may render participants unable or unwilling to comply with complex RMT protocols. We therefore assessed the feasibility and usability of a complex RMT protocol in all syndromic stages of Alzheimer's disease and in healthy control participants.

Methods

For 8 weeks, participants (N = 229) used two activity trackers, two interactive apps with either daily or weekly cognitive tasks, and optionally a wearable camera. A subset of participants participated in a 4-week sub-study (N = 45) using fixed at-home sensors, a wearable EEG sleep headband and a driving performance device. Feasibility was assessed by evaluating compliance and drop-out rates. Usability was assessed by problem rates (e.g., understanding instructions, discomfort, forgetting to use the RMT or technical problems) as discussed during bi-weekly semi-structured interviews.

Results

Most problems were found for the active apps and EEG sleep headband. Problem rates increased and compliance rates decreased with disease severity, but the study remained feasible.

Conclusions

This study shows that a highly complex RMT protocol is feasible, even in a mild-to-moderate AD population, encouraging other researchers to use RMTs in their study designs. We recommend evaluating the design of individual devices carefully before finalizing study protocols, considering RMTs which allow for real-time compliance monitoring, and engaging the partners of study participants in the research.

Focusing on Earlier Management of Alzheimer Disease: Expert Opinion Based on a Modified Nominal Group Technique

BACKGROUND

Despite the number of people living with Alzheimer disease (AD), awareness of the early stages of this condition, including mild cognitive impairment due to AD-which poses management challenges-continues to be low. To identify areas for improvement in early AD management, dementia specialists convened in a virtual roundtable meeting.

METHODOLOGY

A modified version of the nominal group technique was followed to prioritize specific topics and allow experts to provide their opinions. The overarching topics prioritized and discussed were (1) education and support for primary care physicians on cognitive assessment, detection of mild cognitive impairment, and patient monitoring; (2) nonpharmacological interventions; (3) and the introduction of disease-modifying therapies.

CONCLUSIONS

Consensus was achieved regarding the need for educating primary care physicians on identifying people with cognitive impairment and for better diagnostic tools for its detection and early management. Management of mild cognitive impairment due to AD should encompass an adequate follow-up schedule aiming to maintain function for as long as possible, and primary care physicians and patients should be aware of the benefits of nonpharmacological interventions.

Development of a Novel σ1 Receptor Biosensor Based on Its Heterodimerization with Binding Immunoglobulin Protein in Living Cells

The σ₁ receptor (S1R) is a ligand-regulated non-opioid intracellular receptor involved in several pathological conditions. The development of S1R-based drugs as therapeutic agents is a challenge due to the lack of simple functional assays to identify and classify S1R ligands. We have developed a novel nanoluciferase binary technology (NanoBiT) assay based on the ability of S1R to heteromerize with the binding immunoglobulin protein (BiP) in living cells. The S1R-BiP heterodimerization biosensor allows for rapid and accurate identification of S1R ligands by monitoring the dynamics of association-dissociation of S1R and BiP. Acute treatment of cells with the S1R agonist PRE-084 produced rapid and transient dissociation of the S1R-BiP heterodimer, which was blocked by haloperidol. The effect of PRE-084 was enhanced by calcium depletion, leading to a higher reduction in heterodimerization even in the presence of haloperidol. Prolonged incubation of cells with S1R antagonists (haloperidol, NE-100, BD-1047, and PD-144418) increased the formation of S1R-BiP heteromers, while agonists (PRE-084, 4-IBP, and pentazocine) did not alter heterodimerization under the same experimental conditions. The newly developed S1R-BiP biosensor is a simple and effective tool for exploring S1R pharmacology in an easy cellular setting. This biosensor is suitable for high-throughput applications and a valuable resource in the researcher's toolkit.

A randomized, open-label clinical trial in mild cognitive impairment with EGb 761 examining blood markers of inflammation and oxidative stress

Although beta-amyloid (Aβ) and phosphorylated tau remain the preferred targets for disease-modifying treatments (DMT) against Alzheimer's disease (AD), part of the pathophysiological mechanisms of cognitive impairment are related to neuroinflammation and oxidative stress. In mild cognitive impairment (MCI), a prodromal stage of AD and other neurodegenerative conditions, the joint appearance of inflammation, oxidative stress, and metabolic alterations are the common pathways of neurotoxicity and neurodegeneration. The standardized extract of Ginkgo biloba EGb 761 interferes with the pathogenic mechanisms involved in both the development of cognitive impairment due to AD and that of vascular origin. The primary objective of this study is to compare changes in the levels of blood markers of inflammation and oxidative stress after treatment with EGb 761 in a cohort of 100 patients with MCI. In addition, we aim to assess changes in these blood markers during an additional 12-month extension phase in which patients in the control group will also receive EGb 761 and patients in the active group will extend their treatment duration. Secondary objectives include comparing changes in neuropsychiatric and cognitive test scores between the baseline (v0) and 12-month visits (v2). This study is a Phase IV, single-center, randomized, open-label, parallel-group clinical trial consisting of the 12-month follow-up of a cohort of participants with MCI [Global Deterioration Scale (GDS) = 3] and an extension with an additional 12-month follow-up. During the first 12 months, participants will be randomized into two arms: in one arm, patients will receive 1 daily tablet of EGb 761 240 mg orally (study group, n = 50), while in the other arm, patients will not receive EGb 761 and will undergo the same assessments as the treated group (control group, n = 50). After the first 12 months of the study, patients in the EGb 761-treated group will continue treatment, and patients in the control group will be offered one EGb 761 240 mg tablet per day orally. All participants will be monitored for an additional 12 months. A battery of blood markers of inflammation and oxidative stress will be quantified at v0, v1, v2, v3, and v4. The Olink Proteomics panel of inflammation markers ( https://www.olink.com/products/inflammation/ ) will be used to evaluate 92 proteins associated with inflammatory diseases and related biological processes. The second panel measures 92 proteins involved in neurological processes. At v0, v2, and v4, neuropsychological and neurological evaluations will be conducted in addition to vital signs and anthropometric studies using a body composition monitor with bioimpedance technology (Tanita). Sixty percent of the 100 MCI patients recruited were women. The mean age was 73.1 years, and the mean time between symptom onset and MCI diagnosis was 2.9 years. The mean Mini-Mental State Examination (MMSE) score was 26.7. Depressive and anxiety disorders, as well as vascular risk factors, were the most frequent comorbidities among the cohort. The study is still ongoing, and results for the first year of treatment (v0, v1, v2) are expected by 2023. Individuals with MCI have an elevated risk of developing dementia. EGb 761 is used worldwide for the symptomatic treatment of cognitive disorders due to its neuroprotective effects. In experimental models and clinical observational studies, EGb 761 has shown strong antioxidant and anti-inflammatory activity. As a result, this study has been proposed to evaluate the antioxidant and anti-inflammatory effects on plasma markers and their potential clinical correlation with the progression of cognitive decline in patients with MCI.Trial registration: Registro Español de estudios clínicos (REec) number 2020-003776-41, ClinicalTrials.gov Identifier: NCT05594355.

Symptomatic and Disease-Modifying Therapy Pipeline for Alzheimer’s Disease: Towards a Personalized Polypharmacology Patient-Centered Approach

Since 1906, when Dr. Alois Alzheimer first described in a patient “a peculiar severe disease process of the cerebral cortex”, people suffering from this pathology have been waiting for a breakthrough therapy. Alzheimer’s disease (AD) is an irreversible, progressive neurodegenerative brain disorder and the most common form of dementia in the elderly with a long presymptomatic phase. Worldwide, approximately 50 million people are living with dementia, with AD comprising 60–70% of cases. Pathologically, AD is characterized by the deposition of amyloid β-peptide (Aβ) in the neuropil (neuritic plaques) and blood vessels (amyloid angiopathy), and by the accumulation of hyperphosphorylated tau in neurons (neurofibrillary tangles) in the brain, with associated loss of synapses and neurons, together with glial activation, and neuroinflammation, resulting in cognitive deficits and eventually dementia. The current competitive landscape in AD consists of symptomatic treatments, of which there are currently six approved medications: three AChEIs (donepezil, rivastigmine, and galantamine), one NMDA-R antagonist (memantine), one combination therapy (memantine/donepezil), and GV-971 (sodium oligomannate, a mixture of oligosaccharides derived from algae) only approved in China. Improvements to the approved therapies, such as easier routes of administration and reduced dosing frequencies, along with the developments of new strategies and combined treatments are expected to occur within the next decade and will positively impact the way the disease is managed. Recently, Aducanumab, the first disease-modifying therapy (DMT) has been approved for AD, and several DMTs are in advanced stages of clinical development or regulatory review. Small molecules, mAbs, or multimodal strategies showing promise in animal studies have not confirmed that promise in the clinic (where small to moderate changes in clinical efficacy have been observed), and therefore, there is a significant unmet need for a better understanding of the AD pathogenesis and the exploration of alternative etiologies and therapeutic effective disease-modifying therapies strategies for AD. Therefore, a critical review of the disease-modifying therapy pipeline for Alzheimer’s disease is needed.

Automatized FACEmemory® scoring is related to Alzheimer's disease phenotype and biomarkers in early-onset mild cognitive impairment: the BIOFACE cohort

Background

FACEmemory® is the first computerized, self-administered verbal episodic memory test with voice recognition. It can be conducted under minimal supervision and contains an automatic scoring system to avoid administrator errors. Moreover, it is suitable for discriminating between cognitively healthy and amnestic mild cognitive impairment (MCI) individuals, and it is associated with Alzheimer’s disease (AD) cerebrospinal fluid (CSF) biomarkers. This study aimed to determine whether FACEmemory scoring is related to performance on classical memory tests and to AD biomarkers of brain magnetic resonance imaging (MRI) and CSF in patients with early-onset MCI (EOMCI).

Methods

Ninety-four patients with EOMCI from the BIOFACE study completed FACEmemory, classical memory tests (the Spanish version of the Word Free and Cued Selective Reminding Test -FCSRT-, the Word List from the Wechsler Memory Scale, third edition, and the Spanish version of the Rey–Osterrieth Complex Figure Test), and a brain MRI. Eighty-two individuals also underwent a lumbar puncture.

Results

FACEmemory scoring was moderately correlated with FCSRT scoring. With regard to neuroimaging MRI results, worse execution on FACEmemory was associated with lower cortical volume in the right prefrontal and inferior parietal areas, along with the left temporal and associative occipital areas. Moreover, the total FACEmemory score correlated with CSF AD biomarkers (Aβ1-42/Aβ1-40 ratio, p181-tau, and Aβ1-42/p181-tau ratio). When performance on FACEmemory was compared among the ATN classification groups, significant differences between the AD group and normal and SNAP groups were found.

Conclusions

FACEmemory is a promising tool for detecting memory deficits sensitive to early-onset AD, but it also allows the detection of memory-impaired cases due to other etiologies. Our findings suggest that FACEmemory scoring can detect the AD endophenotype and that it is also associated with AD-related changes in MRI and CSF in patients with EOMCI. The computerized FACEmemory tool might be an opportunity to facilitate early detection of MCI in younger people than 65, who have a growing interest in new technologies.

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.

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.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40035-021-00232-7.

Inhibition of Tryptophan Hydroxylases and Monoamine Oxidase-A by the Proton Pump Inhibitor, Omeprazole-In Vitro and In Vivo Investigations

Serotonin (5-HT) is a hormone and neurotransmitter that modulates neural activity as well as a wide range of other physiological processes including cardiovascular function, bowel motility, and platelet aggregation. 5-HT synthesis is catalyzed by tryptophan hydroxylase (TPH) which exists as two distinct isoforms; TPH1 and TPH2, which are responsible for peripheral and central 5-HT, respectively. Due to the implication of 5-HT in a number of pathologies, including depression, anxiety, autism, sexual dysfunction, irritable bowel syndrome, inflammatory bowel disease, and carcinoid syndrome, there has been a growing interest in finding modulators of these enzymes in recent years. We thus performed high-throughput screening (HTS) using a fluorescence-based thermal shift assay (DSF) to search the Prestwick Chemical Library containing 1,280 compounds, mostly FDA-approved drugs, for TPH1 binders. We here report the identification of omeprazole, a proton pump inhibitor, as an inhibitor of TPH1 and TPH2 with low micromolar potency and high selectivity over the other aromatic amino acid hydroxylases. The S-enantiomer of omeprazole, esomeprazole, has recently also been described as an inhibitor of monoamine oxidase-A (MAO-A), the main enzyme responsible for 5-HT degradation, albeit with lower potency compared to the effect on TPH1 and TPH2. In order to investigate the net effect of simultaneous inhibition of TPH and MAO-A in vivo, we administered high-dose (100 mg/kg) omeprazole to CD-1 mice for 4 days, after which the animals were subjected to the tail suspension test. Finally, central (whole brain) and peripheral (serum) 5-HT content was measured using liquid chromatography-mass spectrometry (LC-MS). Omeprazole treatment significantly increased 5-HT concentrations, both in brain and in serum, and reduced the time spent immobile in the tail suspension test relative to vehicle control. Thus, the MAO-A inhibition afforded by high-dose omeprazole appears to overcome the opposing effect on 5-HT produced by inhibition of TPH1 and TPH2. Further modification of proton pump inhibitor scaffolds may yield more selective modulators of 5-HT metabolism.

Metabotropic glutamate type 5 receptor requires contactin-associated protein 1 to control memory formation

The hippocampus is a key brain region for memory formation. Metabotropic glutamate type 5 receptors (mGlu5R) are strongly expressed in CA1 pyramidal neurons and fine-tune synaptic plasticity. Accordingly, mGlu5R pharmacological manipulation may represent an attractive therapeutic strategy to manage hippocampal-related neurological disorders. Here, by means of a membrane yeast two-hybrid screening, we identified contactin-associated protein 1 (Caspr1), a type I transmembrane protein member of the neurexin family, as a new mGlu5R partner. We report that mGlu5R and Caspr1 co-distribute and co-assemble both in heterologous expression systems and in rat brain. Furthermore, downregulation of Caspr1 in rat hippocampal primary cultures decreased mGlu5R-mediated signaling. Finally, silencing Caspr1 expression in the hippocampus impaired the impact of mGlu5R on spatial memory. Our results indicate that Caspr1 plays a pivotal role controlling mGlu5R function in hippocampus-dependent memory formation. Hence, this new protein-protein interaction may represent novel target for neurological disorders affecting hippocampal glutamatergic neurotransmission.

Chronic adenosine A2A receptor blockade induces locomotor sensitization and potentiates striatal LTD IN GPR37-deficient mice

Adenosine A_2A receptors (A_2A R) play a key role in modulating dopamine-dependent locomotor activity, as heralded by the sensitization of locomotor activity upon chronic A_2A R blockade, which is associated with elevated dopamine levels and altered corticostriatal synaptic plasticity. Since the orphan receptor GPR37 has been shown to modulate A_2A R function in vivo, we aimed to test whether the A_2A R-mediated sensitization of locomotor activity is GPR37-dependent and involves adaptations of synaptic plasticity. To this end, we administered a selective A_2A R antagonist, SCH58261 (1 mg/kg, i.p.), daily for 14 days, and the locomotor sensitization, striatum-dependent cued learning, and corticostriatal synaptic plasticity (i.e., long-term depression) were compared in wild-type and GPR37^-/- mice. Notably, GPR37 deletion promoted A_2A R-associated locomotor sensitization but not striatum-dependent cued learning revealed upon chronic SCH58261 treatment of mice. Furthermore, chronic A_2A R blockade potentiated striatal long-term depression in corticostriatal synapses of GPR37^-/- but not of wild-type mice, thus correlating well with neurochemical alterations of the adenosinergic system. Overall, these results revealed the importance of GPR37 regulating A_2A R-dependent locomotor sensitization and synaptic plasticity in the basal ganglia circuitry. OPEN SCIENCE BADGES: This article has received a badge for *Open Materials* because it provided all relevant information to reproduce the study in the manuscript. The complete Open Science Disclosure form for this article can be found at the end of the article. More information about the Open Practices badges can be found at https://cos.io/our-services/open-science-badges/. Open Science: This manuscript was awarded with the Open Materials Badge. For more information see: https://cos.io/our-services/open-science-badges/.

Triglyceride Form of Docosahexaenoic Acid Mediates Neuroprotection in Experimental Parkinsonism

Parkinson’s disease (PD) is a neurodegenerative disorder of unknown etiology. The main treatment of PD consists of medication with dopamine-based drugs, which palliate the symptoms but may produce adverse effects after chronic administration. Accordingly, there is a need to develop novel neuroprotective therapies. Several studies suggest that omega-3 polyunsaturated fatty acids (n-3 PUFA) might provide protection against brain damage. Here, we studied several experimental models of PD, using striatal neuronal cultures, striatal slices, and mice, to assess the neuroprotective effects of docosahexaenoic acid (DHA), the main n-3 PUFA in the brain, administered in its triglyceride form (TG-DHA). Hence, we determined the beneficial effects of TG-DHA on neural viability following 6-hydroxydopamine (6-OHDA)-induced neurotoxicity, a well-established PD model. We also implemented a novel mouse behavioral test, the beam walking test, to finely assess mouse motor skills following dopaminergic denervation. This test showed potential as a useful behavioral tool to assess novel PD treatments. Our results indicated that TG-DHA-mediated neuroprotection was independent of the net incorporation of PUFA into the striatum, thus suggesting a tight control of brain lipid homeostasis both in normal and pathological conditions.

MicroRNA alterations in iPSC-derived dopaminergic neurons from Parkinson disease patients

MicroRNA (miRNA) misregulation in peripheral blood has been linked to Parkinson disease (PD) but its role in the disease progression remains elusive. We performed an explorative genome-wide study of miRNA expression levels in dopaminergic neurons (DAn) from PD patients generated by somatic cell reprogramming and induced pluripotent stem cells differentiation. We quantified expression levels of 377 miRNAs in DAn from 3 sporadic PD patients (sPD), 3 leucine-rich repeat kinase 2-associated PD patients (L2PD) (total 6 PD), and 4 healthy controls. We identified differential expression of 10 miRNA of which 5 were upregulated in PD (miR-9-5p, miR-135a-5p, miR-135b-5p, miR-449a, and miR-449b-5p) and 5 downregulated (miR-141-3p, miR-199a-5p, miR-299-5p, miR-518e-3p, and miR-519a-3p). Changes were similar in sPD and L2PD. Integrative analysis revealed significant correlations between miRNA/mRNA expression. Moreover, upregulation of miR-9-5p and miR-135b-5p was associated with downregulation of transcription factors related to the DNA hypermethylation of enhancer elements in PD DAn (FOXA1 and NR3C1). In summary, miRNA changes are associated with monogenic L2PD and sPD and co-occur with epigenetic changes in DAn from PD patients.

The Parkinson's disease-associated GPR37 receptor interacts with striatal adenosine A2A receptor controlling its cell surface expression and function in vivo

G protein-coupled receptor 37 (GPR37) is an orphan receptor associated to Parkinson’s disease (PD) neuropathology. Here, we identified GPR37 as an inhibitor of adenosine A_2A receptor (A_2AR) cell surface expression and function in vivo. In addition, we showed that GPR37 and A_2AR do oligomerize in the striatum. Thus, a close proximity of GPR37 and A_2AR at the postsynaptic level of striatal synapses was observed by double-labelling post-embedding immunogold detection. Indeed, the direct receptor-receptor interaction was further substantiated by proximity ligation in situ assay. Interestingly, GPR37 deletion promoted striatal A_2AR cell surface expression that correlated well with an increased A_2AR agonist-mediated cAMP accumulation, both in primary striatal neurons and nerve terminals. Furthermore, GPR37−/− mice showed enhanced A_2AR agonist-induced catalepsy and an increased response to A_2AR antagonist-mediated locomotor activity. Overall, these results revealed a key role for GPR37 controlling A_2AR biology in the striatum, which may be relevant for PD management.

Brain Membrane Fractionation: An Ex Vivo Approach to Assess Subsynaptic Protein Localization

Assessing the synaptic protein composition and function constitutes an important challenge in neuroscience. However, it is not easy to evaluate neurotransmission that occurs within synapses because it is highly regulated by dynamic protein-protein interactions and phosphorylation events. Accordingly, when any method is used to study synaptic transmission, a major goal is to preserve these transient physiological modifications. Here, we present a brain membrane fractionation protocol that represents a robust procedure to isolate proteins belonging to different synaptic compartments. In other words, the protocol describes a biochemical methodology to carry out protein enrichment from presynaptic, postsynaptic, and extrasynaptic compartments. First, synaptosomes, or synaptic terminals, are obtained from neurons that contain all synaptic compartments by means of a discontinuous sucrose gradient. Of note, the quality of this initial synaptic membrane preparation is critical. Subsequently, the isolation of the different subsynaptic compartments is achieved with light solubilization using mild detergents at differential pH conditions. This allows for separation by gradient and isopycnic centrifugations. Finally, protein enrichment at the different subsynaptic compartments (i.e., pre-, post- and extrasynaptic membrane fractions) is validated by means of immunoblot analysis using well-characterized synaptic protein markers (i.e., SNAP-25, PSD-95, and synaptophysin, respectively), thus enabling a direct assessment of the synaptic distribution of any particular neuronal protein.

Angiotensin II type 1/adenosine A 2A receptor oligomers: a novel target for tardive dyskinesia

Tardive dyskinesia (TD) is a serious motor side effect that may appear after long-term treatment with neuroleptics and mostly mediated by dopamine D₂ receptors (D₂Rs). Striatal D₂R functioning may be finely regulated by either adenosine A_2A receptor (A_2AR) or angiotensin receptor type 1 (AT₁R) through putative receptor heteromers. Here, we examined whether A_2AR and AT₁R may oligomerize in the striatum to synergistically modulate dopaminergic transmission. First, by using bioluminescence resonance energy transfer, we demonstrated a physical AT₁R-A_2AR interaction in cultured cells. Interestingly, by protein-protein docking and molecular dynamics simulations, we described that a stable heterotetrameric interaction may exist between AT₁R and A_2AR bound to antagonists (i.e. losartan and istradefylline, respectively). Accordingly, we subsequently ascertained the existence of AT₁R/A_2AR heteromers in the striatum by proximity ligation in situ assay. Finally, we took advantage of a TD animal model, namely the reserpine-induced vacuous chewing movement (VCM), to evaluate a novel multimodal pharmacological TD treatment approach based on targeting the AT₁R/A_2AR complex. Thus, reserpinized mice were co-treated with sub-effective losartan and istradefylline doses, which prompted a synergistic reduction in VCM. Overall, our results demonstrated the existence of striatal AT₁R/A_2AR oligomers with potential usefulness for the therapeutic management of TD.

Systematic protein-protein interaction mapping for clinically relevant human GPCRs

G‐protein‐coupled receptors (GPCRs) are the largest family of integral membrane receptors with key roles in regulating signaling pathways targeted by therapeutics, but are difficult to study using existing proteomics technologies due to their complex biochemical features. To obtain a global view of GPCR‐mediated signaling and to identify novel components of their pathways, we used a modified membrane yeast two‐hybrid (MYTH) approach and identified interacting partners for 48 selected full‐length human ligand‐unoccupied GPCRs in their native membrane environment. The resulting GPCR interactome connects 686 proteins by 987 unique interactions, including 299 membrane proteins involved in a diverse range of cellular functions. To demonstrate the biological relevance of the GPCR interactome, we validated novel interactions of the GPR37, serotonin 5‐HT4d, and adenosine ADORA2A receptors. Our data represent the first large‐scale interactome mapping for human GPCRs and provide a valuable resource for the analysis of signaling pathways involving this druggable family of integral membrane proteins.

Parkinson's disease-associated GPR37 receptor regulates cocaine-mediated synaptic depression in corticostriatal synapses

GPR37 is an orphan G protein-coupled receptor highly expressed in the brain. The precise function of GPR37 is still unknown, but a number of evidences indicate it modulates the dopaminergic system. Here, we aimed to determine the role of GPR37 on the control of cocaine-mediated electrophysiological effects (synaptic transmission and short-term plasticity) in corticostriatal synapses. Accordingly, we evaluated basal synaptic transmission and paired-pulse stimulation (PPS) in wild-type and GPR37KO mice slices. Regardless of the genotype, a low concentration of cocaine (2μM) did not modify basal synaptic transmission. Conversely, a higher dose of cocaine (30μM) decreased synaptic transmission in both genotypes, although with different intensities: approximately 30% in slices from wild-type mice and 45% in slices from GPR37-KO mice. On the other hand, no differences in PPS ratio were observed between wild-type and GPR37-KO cocaine-treated mice. Overall, our data suggest that GPR37 is involved in cocaine-induced modification of basal synaptic transmission without modifying cocaine effects in short-term plasticity.

The role of parkinson's disease-associated receptor GPR37 in the hippocampus: functional interplay with the adenosinergic system

GPR37 is an orphan G protein-coupled receptor mostly enriched in brain areas such as the cerebellum, striatum, and hippocampus. Identified as a substrate of parkin, GPR37 has been suggested to play a role in Parkinson's disease. Distributed throughout the brain, the function of GPR37, however, remains unknown. We now provide the first mapping of GPR37 within the hippocampus, where GPR37 is widely expressed and localized at the level of the extrasynaptic plasma membrane of dendritic spines, dendritic shafts, and axon terminals. GPR37 per se does not appear to play a role in learning and memory, since knocking out GPR37 (GPR37-KO) did not alter the performance in different hippocampal-related memory tasks. This is in agreement with slice electrophysiology experiments showing no differences both in short-term plasticity paired-pulse facilitation and long-term potentiation between WT and GPR37-KO mice. However, we report a potential functional interaction between GPR37 and adenosine A2A receptors (A2 A R) in the hippocampus, with A2 A R modulating the GPR37-associated phenotype. Thus, the absence of GPR37 appeared to sensitize mice to hippocampal A2 A R-mediated signaling, as observed by the effect of the A2 A R antagonist SCH58261 increasing synaptic depotentiation, reducing novel object recognition memory and reverting the anxiolytic effect of GPR37 deletion. Collectively, these findings afford insight into the localization and role of the orphan GPR37 within the hippocampus with potential involvement in A2 A R function (i.e., A2 A R sensitization). GPR37 is an orphan G protein-coupled receptor widely expressed in the hippocampus and localized at the level of the extrasynaptic plasma membrane of dendritic spines, dendritic shafts and axon terminals. This orphan receptor per se does not appear to directly control the learning and memory processes; however knocking-out GPR37 triggers anxiolytic-like effects and sensitizes mice to hippocampal A2A R-mediated signalling.

Adenosine A2A receptor-mediated control of pilocarpine-induced tremulous jaw movements is Parkinson's disease-associated GPR37 receptor-dependent

GPR37, also known as parkin associated endothelin-like receptor (Pael-R), is an orphan GPCR that aggregates intracellularly in a juvenile form of Parkinson's disease. However, little is known about the function of this orphan receptor. Here, using a model for parkisonian tremor, the pilocarpine-induced tremulous jaw movements (TJMs), we show that the deletion of GPR37 attenuated the TJMs in response to this cholinomimetic. Interestingly, the control that adenosine A2A receptor exerted over TJMs was lost in the absence of GPR37, thus pointing to a pivotal role of this orphan receptor in the adenosinergic control of parkinsonian tremor.

Dopamine D(2) receptor-mediated modulation of adenosine A(2A) receptor agonist binding within the A(2A)R/D(2)R oligomer framework

The molecular interaction between adenosine A2A and dopamine D2 receptors (A2ARs and D2Rs, respectively) within an oligomeric complex has been postulated to play a pivotal role in the adenosine-dopamine interplay in the central nervous system, in both normal and pathological conditions (e.g. Parkinson's disease). While the effects of A2AR challenge on D2R functioning have been largely studied, the reverse condition is still unexplored, a fact that might have impact in therapeutics. Here, we aimed to examine in a real-time mode the D2R-mediated allosteric modulation of A2AR binding when an A2AR/D2R oligomer is established. Thus, we synthesized fluorescent A2AR agonists and evaluated, by means of a flow cytometry homogeneous no-wash assay and a real-time fluorescence resonance energy transfer (FRET)-based approach, the effects on A2AR binding of distinct antiparkinsonian drugs in current clinical use (i.e. pramipexole, rotigotine and apomorphine). Our results provided evidence for the existence of a differential D2R-mediated negative allosteric modulation on A2AR agonist binding that was oligomer-formation dependent, and with apomorphine being the best antiparkinsonian drug attenuating A2AR agonist binding. Overall, the here-developed methods were found valid to explore the ability of drugs acting on D2Rs to modulate A2AR binding, thus serving to facilitate the preliminary selection of D2R-like candidate drugs in the management of Parkinson's disease.

The Parkinson's disease-associated GPR37 receptor-mediated cytotoxicity is controlled by its intracellular cysteine-rich domain

GPR37, also known as parkin-associated endothelin-like receptor (Pael-R), is an orphan G protein-coupled receptor (GPCR) that aggregates intracellularly in a juvenile form of Parkinson's disease. However, little is known about the structure or function of this receptor. Here, in order to better understand the functioning of this receptor, we focused on the GPR37 C-terminal tail, in particular on a cystein-enriched region. Thus, we aimed to reveal the role of these residues on receptor plasma membrane expression and function, and also whether the presence of this cysteine-rich domain is linked to the previously described receptor-mediated cytotoxicity. Interestingly, while the deletion of six cysteine residues within this region did not affect receptor internalization it promoted GPR37 plasma membrane expression and signaling. Furthermore, the removal of the C-terminal cysteine-rich domain protected against GPR37-mediated apoptosis and cell death. Overall, we identified a GPR37 domain, namely the C-terminal tail cysteine-rich domain, which played a critical role in receptor cell surface expression, function and GPR37-mediated cytotoxicity. These results might contribute to better comprehend the pathophysiology (i.e. in Parkinson's disease) of this rather unknown member of the GPCR family.