Astrocytic P2Y(1) receptor is involved in the regulation of cytokine/chemokine transcription and cerebral damage in a rat model of cerebral ischemia

P2Y1 receptor in Alzheimer's disease

Alzheimer's disease is the most frequent form of dementia characterized by the deposition of amyloid-beta plaques and neurofibrillary tangles consisting of hyperphosphorylated tau. Targeting amyloid-beta plaques has been a primary direction for developing Alzheimer's disease treatments in the last decades. However, existing drugs targeting amyloid-beta plaques have not fully yielded the expected results in the clinic, necessitating the exploration of alternative therapeutic strategies. Increasing evidence unravels that astrocyte morphology and function alter in the brain of Alzheimer's disease patients, with dysregulated astrocytic purinergic receptors, particularly the P2Y1 receptor, all of which constitute the pathophysiology of Alzheimer's disease. These receptors are not only crucial for maintaining normal astrocyte function but are also highly implicated in neuroinflammation in Alzheimer's disease. This review delves into recent insights into the association between P2Y1 receptor and Alzheimer's disease to underscore the potential neuroprotective role of P2Y1 receptor in Alzheimer's disease by mitigating neuroinflammation, thus offering promising avenues for developing drugs for Alzheimer's disease and potentially contributing to the development of more effective treatments.

In vitro modelling of the neurovascular unit for ischemic stroke research: Emphasis on human cell applications and 3D model design

Ischemic stroke has garnered global medical attention as one of the most serious cerebrovascular diseases. The mechanisms involved in both the development and recovery phases of ischemic stroke are complex, involving intricate interactions among different types of cells, each with its own unique functions. To better understand the possible pathogenesis, neurovascular unit (NVU), a concept comprising neurons, endothelial cells, mural cells, glial cells, and extracellular matrix components, has been used in analysing various brain diseases, particularly in ischemic stroke, aiming to depict the interactions between cerebral vasculature and neural cells. While in vivo models often face limitations in terms of reproducibility and the ability to precisely mimic human pathophysiology, it is now important to establish in vitro NVU models for ischemic stroke research. In order to accurately portray the pathological processes occurring within the brain, a diverse array of NVU 2D and 3D in vitro models, each possessing unique characteristics and advantages, have been meticulously developed. This review presents a comprehensive overview of recent advancements in in vitro models specifically tailored for investigating ischemic stroke. Through a systematic categorization of these developments, we elucidate the intricate links between NVU components and the pathogenesis of ischemic stroke. Furthermore, we explore the distinct advantages offered by innovative NVU models, notably 3D models, which closely emulate in vivo conditions. Additionally, an examination of current therapeutic modalities for ischemic stroke developed utilizing in vitro NVU models is provided. Serving as a valuable reference, this review aids in the design and implementation of effective in vitro models for ischemic stroke research.

Disease-relevant upregulation of P2Y1 receptor in astrocytes enhances neuronal excitability via IGFBP2

Reactive astrocytes play a pivotal role in the pathogenesis of neurological diseases; however, their functional phenotype and the downstream molecules by which they modify disease pathogenesis remain unclear. Here, we genetically increase P2Y1 receptor (P2Y1R) expression, which is upregulated in reactive astrocytes in several neurological diseases, in astrocytes of male mice to explore its function and the downstream molecule. This astrocyte-specific P2Y1R overexpression causes neuronal hyperexcitability by increasing both astrocytic and neuronal Ca2+ signals. We identify insulin-like growth factor-binding protein 2 (IGFBP2) as a downstream molecule of P2Y1R in astrocytes; IGFBP2 acts as an excitatory signal to cause neuronal excitation. In neurological disease models of epilepsy and stroke, reactive astrocytes upregulate P2Y1R and increase IGFBP2. The present findings identify a mechanism underlying astrocyte-driven neuronal hyperexcitability, which is likely to be shared by several neurological disorders, providing insights that might be relevant for intervention in diverse neurological disorders.

TRPC Channels Activated by G Protein-Coupled Receptors Drive Ca2+ Dysregulation Leading to Secondary Brain Injury in the Mouse Model

Canonical transient receptor potential (TRPC) non-selective cation channels, particularly those assembled with TRPC3, TRPC6, and TRPC7 subunits, are coupled to Gαq-type G protein-coupled receptors for the major classes of excitatory neurotransmitters. Sustained activation of this TRPC channel-based pathophysiological signaling hub in neurons and glia likely contributes to prodigious excitotoxicity-driven secondary brain injury expansion. This was investigated in mouse models with selective Trpc gene knockout (KO). In adult cerebellar brain slices, application of glutamate and the class I metabotropic glutamate receptor agonist (S)-3,5-dihydroxyphenylglycine to Purkinje neurons expressing the GCaMP5g Ca2+ reporter demonstrated that the majority of the Ca2+ loading in the molecular layer dendritic arbors was attributable to the TRPC3 effector channels (Trpc3KO compared with wildtype (WT)). This Ca2+ dysregulation was associated with glutamate excitotoxicity causing progressive disruption of the Purkinje cell dendrites (significantly abated in a GAD67-GFP-Trpc3KO reporter brain slice model). Contribution of the Gαq-coupled TRPC channels to secondary brain injury was evaluated in a dual photothrombotic focal ischemic injury model targeting cerebellar and cerebral cortex regions, comparing day 4 post-injury in WT mice, Trpc3KO, and Trpc1/3/6/7 quadruple knockout (TrpcQKO), with immediate 2-h (primary) brain injury. Neuroprotection to secondary brain injury was afforded in both brain regions by Trpc3KO and TrpcQKO models, with the TrpcQKO showing greatest neuroprotection. These findings demonstrate the contribution of the Gαq-coupled TRPC effector mechanism to excitotoxicity-based secondary brain injury expansion, which is a primary driver for mortality and morbidity in stroke, traumatic brain injury, and epilepsy.

Mechanisms of immune response and cell death in ischemic stroke and their regulation by natural compounds

Ischemic stroke (IS), which is the third foremost cause of disability and death worldwide, has inflammation and cell death as its main pathological features. IS can lead to neuronal cell death and release factors such as damage-related molecular patterns, stimulating the immune system to release inflammatory mediators, thereby resulting in inflammation and exacerbating brain damage. Currently, there are a limited number of treatment methods for IS, which is a fact necessitating the discovery of new treatment targets. For this review, current research on inflammation and cell death in ischemic stroke was summarized. The complex roles and pathways of the principal immune cells (microglia, astrocyte, neutrophils, T lymphocytes, and monocytes/macrophage) in the immune system after IS in inflammation are discussed. The mechanisms of immune cell interactions and the cytokines involved in these interactions are summarized. Moreover, the cell death mechanisms (pyroptosis, apoptosis, necroptosis, PANoptosis, and ferroptosis) and pathways after IS are explored. Finally, a summary is provided of the mechanism of action of natural pharmacological active ingredients in the treatment of IS. Despite significant recent progress in research on IS, there remain many challenges that need to be overcome.

Graphene Oxide Nanosheets Hamper Glutamate Mediated Excitotoxicity and Protect Neuronal Survival In An In vitro Stroke Model

Small graphene oxide (s-GO) nanosheets reversibly downregulate central nervous system (CNS) excitatory synapses, with potential developments as future therapeutic tools to treat neuro-disorders characterized by altered glutamatergic transmission. Excitotoxicity, namely cell death triggered by exceeding ambient glutamate fueling over-activation of excitatory synapses, is a pathogenic mechanism shared by several neural diseases, from ischemic stroke to neurodegenerative disorders. In this work, CNS cultures were exposed to oxygen-glucose deprivation (OGD) to mimic ischemic stroke in vitro, and it is show that the delivery of s-GO following OGD, during the endogenous build-up of secondary damage and excitotoxicity, improved neuronal survival. In a different paradigm, excitotoxicity cell damage was reproduced through exogenous glutamate application, and s-GO co-treatment protected neuronal integrity, potentially by directly downregulating the synaptic over-activation brought about by exogenous glutamate. This proof-of-concept study suggests that s-GO may find novel applications in therapeutic developments for treating excitotoxicity-driven neural cell death.

Alterations of Purinergic Receptors Levels and Their Involvement in the Glial Cell Morphology in a Pre-Clinical Model of Autism Spectrum Disorders

Recent data suggest that defects in purinergic signalling are a common denominator of autism spectrum disorders (ASDs), though nothing is known about whether the disorder-related imbalance occurs at the receptor level. In this study, we investigated whether prenatal exposure to valproic acid (VPA) induces changes in purinergic receptor expression in adolescence and whether it corresponds to glial cell activation. Pregnant dams were subjected to an intraperitoneal injection of VPA at embryonic day 12.5. In the hippocampi of adolescent male VPA offspring, we observed an increase in the level of P2X1, with concomitant decreases in P2X7 and P2Y1 receptors. In contrast, in the cortex, the level of P2X1 was significantly reduced. Also, significant increases in cortical P2Y1 and P2Y12 receptors were detected. Additionally, we observed profound alterations in microglial cell numbers and morphology in the cortex of VPA animals, leading to the elevation of pro-inflammatory cytokine expression. The changes in glial cells were partially reduced via a single administration of a non-selective P2 receptor antagonist. These studies show the involvement of purinergic signalling imbalance in the modulation of brain inflammatory response induced via prenatal VPA exposure and may indicate that purinergic receptors are a novel target for pharmacological intervention in ASDs.

Pilocarpine-induced acute seizure causes rapid area-specific astrogliosis and alters purinergic signaling in rat hippocampus

The progressive nature of acquired epilepsy warrants a thorough examination of acute changes that occur immediately after an epileptogenic insult to better understand the cellular and molecular mechanisms that trigger epileptogenesis. Astrocytes are important regulators of neuronal functions and emerging evidence suggests an involvement of astrocytic purinergic signaling in the etiology of acquired epilepsies. However, how astrocytic purinergic signaling responds immediately after an acute seizure or an epileptogenic insult to impact epileptogenesis is not well studied. In the present study, we report area-specific rapid onset of astrocytic changes in morphology, as well as in expression and functional activity of the purinergic signaling in the hippocampus that occur immediately after pilocarpine-induced stage 5 seizure. After 3 hours of stage 5 acute seizure, hippocampal astrocytes show increased intrinsic calcium activity in stratum radiatum as well as reactive astrogliosis in the stratum lacunosum moleculare and hilus regions of the hippocampus. Hilar astrocytes also upregulated the expression of P2Y1 and P2Y2 metabotropic purinergic receptors. Subsequently, P2Y1 exhibited a functional upregulation by showing a significantly higher intracellular calcium rise in ex-vivo hippocampal slices on P2Y1 activation. Our results suggest that hippocampal astrocytes undergo rapid area-specific morphological and functional changes immediately after the commencement of the seizure activity and purinergic receptors upregulation is one of the earliest changes in response to seizure activity. These changes can be considered acute astrocytic responses to seizure activity which can potentially drive the epileptogenesis and can be explored further to identify astrocyte-specific targets for seizure therapy.

Involvement of purinergic P2Y1R in antidepressant-like effects of electroacupuncture treatment on social isolation stress mice

Depression is a common neuropsychiatric disorder with high incidence and disability. Electroacupuncture (EA) is effective in the treatment of depression. However, the underlying mechanisms are not fully understood. Social isolation stress during post-weaning period can impair purinergic signaling in the brain of rodents and has emerged as a major risk factor for depression. The purpose of this study was to investigate the involvement of P2Y1 receptor (P2Y1R) in the antidepressant-like effects of EA. In this study, C57BL/6 mice were randomly assigned to group-housed (GH) or social isolated (SI) groups at post-natal day 21. After 6 weeks of social isolation, EA was performed on acupoints "Bai-hui" (GV20) and "Yin-tang" (GV29), or non-acupoints for 4 weeks. The SI mice received either intracerebroventricular injection of a selective P2Y1R agonist, MRS2365 (1 nmol); or a selective P2Y1R antagonist, MRS2179 (2 μmol), before and after EA. We found that SI mice exhibited depression-like behaviors accompanied with anxiety-like behaviors. The expressions of P2Y1R were well co-localized with GFAP-positive astrocytes and increased in the prefrontal cortex and hippocampus of SI mice. After treated with MRS2179, the depression-like behaviors of SI mice were attenuated, but not with MRS2365. Meanwhile, we found that EA could attenuate social isolation caused depression- and anxiety-like behaviors, and inhibited the up-regulation of P2Y1R in the prefrontal cortex and hippocampus of SI mice. Notably, the positive effects of EA on depression-like behaviors of SI mice could be reversed by MRS2365, while MRS2365 had no effect on the anxiolytic-like effects of EA. Therefore, we provide new evidence that EA could ameliorate depression- and anxiety-like behaviors in social isolation stress mice, and P2Y1R was involved in the antidepressant-like effects of EA.

Role of P2Y receptors in astrocyte physiology and pathophysiology

Astrocytes are active constituents of the brain that manage ion homeostasis and metabolic support of neurons and directly tune synaptic transmission and plasticity. Astrocytes express all known P2Y receptors. These regulate a multitude of physiological functions such as cell proliferation, Ca²⁺ signalling, gliotransmitter release and neurovascular coupling. In addition, P2Y receptors are fundamental in the transition of astrocytes into reactive astrocytes, as occurring in many brain disorders such as neurodegenerative diseases, neuroinflammation and epilepsy. This review summarizes the current literature addressing the function of P2Y receptors in astrocytes in the healthy brain as well as in brain diseases.

Neutrophil Heterogeneity and its Roles in the Inflammatory Network after Ischemic Stroke

As the first peripheral immune cells to enter the brain after ischemic stroke, neutrophils are important participants in stroke-related neuroinflammation. Neutrophils are quickly mobilized from the periphery in response to a stroke episode and cross the blood-brain barrier to reach the ischemic brain parenchyma. This process involves the mobilization and activation of neutrophils from peripheral immune organs (including the bone marrow and spleen), their chemotaxis in the peripheral blood, and their infiltration into the brain parenchyma (including disruption of the blood-brain barrier, inflammatory effects on brain tissue, and interactions with other immune cell types). In the past, it was believed that neutrophils aggravated brain injuries through the massive release of proteases, reactive oxygen species, pro-inflammatory factors, and extracellular structures known as neutrophil extracellular traps (NETs). With the failure of early clinical trials targeting neutrophils and uncovering their underlying heterogeneity, our view of their role in ischemic stroke has become more complex and multifaceted. As neutrophils can be divided into N1 and N2 phenotypes in tumors, neutrophils have also been found to have similar phenotypes after ischemic stroke, and play different roles in the development and prognosis of ischemic stroke. N1 neutrophils are dominant during the acute phase of stroke (within three days) and are responsible for the damage to neural structures via the aforementioned mechanisms. However, the proportion of N2 neutrophils gradually increases in later phases, and this has a beneficial effect through the release of anti-inflammatory factors and other neuroprotective mediators. Moreover, the N1 and N2 phenotypes are highly plastic and can be transformed into each other under certain conditions. The pronounced differences in their function and their high degree of plasticity make these neutrophil subpopulations promising targets for the treatment of ischemic stroke.

Glial Cells Response in Stroke

As the second-leading cause of death, stroke faces several challenges in terms of treatment because of the limited therapeutic interventions available. Previous studies primarily focused on metabolic and blood flow properties as a target for treating stroke, including recombinant tissue plasminogen activator and mechanical thrombectomy, which are the only USFDA approved therapies. These interventions have the limitation of a narrow therapeutic time window, the possibility of hemorrhagic complications, and the expertise required for performing these interventions. Thus, it is important to identify the contributing factors that exacerbate the ischemic outcome and to develop therapies targeting them for regulating cellular homeostasis, mainly neuronal survival and regeneration. Glial cells, primarily microglia, astrocytes, and oligodendrocytes, have been shown to have a crucial role in the prognosis of ischemic brain injury, contributing to inflammatory responses. They play a dual role in both the onset as well as resolution of the inflammatory responses. Understanding the different mechanisms driving these effects can aid in the development of therapeutic targets and further mitigate the damage caused. In this review, we summarize the functions of various glial cells and their contribution to stroke pathology. The review highlights the therapeutic options currently being explored and developed that primarily target glial cells and can be used as neuroprotective agents for the treatment of ischemic stroke.

Sex-related differences in the response of anti-platelet drug therapies targeting purinergic signaling pathways in sepsis

Sepsis, a complex clinical syndrome resulting from a serious infection, is a major healthcare problem associated with high mortality. Sex-related differences in the immune response to sepsis have been proposed but the mechanism is still unknown. Purinergic signaling is a sex-specific regulatory mechanism in immune cell physiology. Our studies have shown that blocking the ADP-receptor P2Y12 but not P2Y1 receptor was protective in male mice during sepsis, but not female. We now hypothesize that there are sex-related differences in modulating P2Y12 or P2Y1 signaling pathways during sepsis. Male and female wild-type (WT), P2Y12 knock-out (KO), and P2Y1 KO mice underwent sham surgery or cecal ligation and puncture (CLP) to induce sepsis. The P2Y12 antagonist ticagrelor or the P2Y1 antagonist MRS2279 were administered intra-peritoneally after surgery to septic male and female mice. Blood, lungs and kidneys were collected 24 hours post-surgery. Sepsis-induced changes in platelet activation, secretion and platelet interaction with immune cells were measured by flow cytometry. Neutrophil infiltration in the lung and kidney was determined by a myeloperoxidase (MPO) colorimetric assay kit. Sepsis-induced platelet activation, secretion and aggregate formation were reduced in male CLP P2Y12 KO and in female CLP P2Y1 KO mice compared with their CLP WT counterpart. Sepsis-induced MPO activity was reduced in male CLP P2Y12 KO and CLP P2Y1 KO female mice. CLP males treated with ticagrelor or MRS2279 showed a decrease in sepsis-induced MPO levels in lung and kidneys, aggregate formation, and platelet activation as compared to untreated male CLP mice. There were no differences in platelet activation, aggregate formation, and neutrophil infiltration in lung and kidney between female CLP mice and female CLP mice treated with ticagrelor or MRS2279. In human T lymphocytes, blocking P2Y1 or P2Y12 alters cell growth and secretion in vitro in a sex-dependent manner, supporting the data obtained in mice. In conclusion, targeting purinergic signaling represents a promising therapy for sepsis but drug targeting purinergic signaling is sex-specific and needs to be investigated to determine sex-related targeted therapies in sepsis.

P2Y1 Receptor as a Catalyst of Brain Neurodegeneration

Different brain disorders display distinctive etiologies and pathogenic mechanisms. However, they also share pathogenic events. One event systematically occurring in different brain disorders, both acute and chronic, is the increase of the extracellular ATP levels. Accordingly, several P2 (ATP/ADP) and P1 (adenosine) receptors, as well as the ectoenzymes involved in the extracellular catabolism of ATP, have been associated to different brain pathologies, either with a neuroprotective or neurodegenerative action. The P2Y1 receptor (P2Y1R) is one of the purinergic receptors associated to different brain diseases. It has a widespread regional, cellular, and subcellular distribution in the brain, it is capable of modulating synaptic function and neuronal activity, and it is particularly important in the control of astrocytic activity and in astrocyte–neuron communication. In diverse brain pathologies, there is growing evidence of a noxious gain-of-function of P2Y1R favoring neurodegeneration by promoting astrocyte hyperactivity, entraining Ca2+-waves, and inducing the release of glutamate by directly or indirectly recruiting microglia and/or by increasing the susceptibility of neurons to damage. Here, we review the current evidence on the involvement of P2Y1R in different acute and chronic neurodegenerative brain disorders and the underlying mechanisms.

Therapeutic Potential of Astrocyte Purinergic Signalling in Epilepsy and Multiple Sclerosis

Epilepsy and multiple sclerosis (MS), two of the most common neurological diseases, are characterized by the establishment of inflammatory environment in the central nervous system that drives disease progression and impacts on neurodegeneration. Current therapeutic approaches in the treatments of epilepsy and MS are targeting neuronal activity and immune cell response, respectively. However, the lack of fully efficient responses to the available treatments obviously shows the need to search for novel therapeutic candidates that will not exclusively target neurons or immune cells. Accumulating knowledge on epilepsy and MS in humans and analysis of relevant animal models, reveals that astrocytes are promising therapeutic candidates to target as they participate in the modulation of the neuroinflammatory response in both diseases from the initial stages and may play an important role in their development. Indeed, astrocytes respond to reactive immune cells and contribute to the neuronal hyperactivity in the inflamed brain. Mechanistically, these astrocytic cell to cell interactions are fundamentally mediated by the purinergic signalling and involve metabotropic P2Y1 receptors in case of astrocyte interactions with neurons, while ionotropic P2X7 receptors are mainly involved in astrocyte interactions with autoreactive immune cells. Herein, we review the potential of targeting astrocytic purinergic signalling mediated by P2Y1 and P2X7 receptors to develop novel approaches for treatments of epilepsy and MS at very early stages.

Activation and Role of Astrocytes in Ischemic Stroke

Ischemic stroke refers to the disorder of blood supply of local brain tissue caused by various reasons. It has high morbidity and mortality worldwide. Astrocytes are the most abundant glial cells in the central nervous system (CNS). They are responsible for the homeostasis, nutrition, and protection of the CNS and play an essential role in many nervous system diseases’ physiological and pathological processes. After stroke injury, astrocytes are activated and play a protective role through the heterogeneous and gradual changes of their gene expression, morphology, proliferation, and function, that is, reactive astrocytes. However, the position of reactive astrocytes has always been a controversial topic. Many studies have shown that reactive astrocytes are a double-edged sword with both beneficial and harmful effects. It is worth noting that their different spatial and temporal expression determines astrocytes’ various functions. Here, we comprehensively review the different roles and mechanisms of astrocytes after ischemic stroke. In addition, the intracellular mechanism of astrocyte activation has also been involved. More importantly, due to the complex cascade reaction and action mechanism after ischemic stroke, the role of astrocytes is still difficult to define. Still, there is no doubt that astrocytes are one of the critical factors mediating the deterioration or improvement of ischemic stroke.

CCL2 (C-C Motif Chemokine Ligand 2) Biomarker Responses in Central Versus Peripheral Compartments After Focal Cerebral Ischemia

Background and Purpose

Inflammatory mediators in blood have been proposed as potential biomarkers in stroke. However, a direct relationship between these circulating factors and brain-specific ischemic injury remains to be fully defined.

Methods

An unbiased screen in a nonhuman primate model of stroke was used to find out the most responsive circulating biomarker flowing ischemic stroke. Then this phenomenon was checked in human beings and mice. Finally, we observed the temporospatial responsive characteristics of this biomarker after ischemic brain injury in mice to evaluate the direct relationship between this circulating factor and central nervous system–specific ischemic injury.

Results

In a nonhuman primate model, an unbiased screen revealed CCL2 (C-C motif chemokine ligand 2) as a major response factor in plasma after stroke. In mouse models of focal cerebral ischemia, plasma levels of CCL2 showed a transient response, that is, rapidly elevated by 2 to 3 hours postischemia but then renormalized back to baseline levels by 24 hours. However, a different CCL2 temporal profile was observed in whole brain homogenate, cerebrospinal fluid, and isolated brain microvessels, with a progressive increase over 24 hours, demonstrating a mismatch between brain versus plasma responses. In contrast to the lack of correlation with central nervous system responses, 2 peripheral compartments showed transient profiles that matched circulating plasma signatures. CCL2 protein in lymph nodes and adipose tissue was significantly increased at 2 hours and renormalized by 24 hours.

Conclusions

These findings may provide a cautionary tale for biomarker pursuits in plasma. Besides a direct central nervous system response, peripheral organs may also contribute to blood signatures in complex and indirect ways.

Microglial- and Astrocyte-Specific Expression of Purinergic Signaling Components and Inflammatory Mediators in the Rat Hippocampus During Trimethyltin-Induced Neurodegeneration

The present study examined the involvement of purinergic signaling components in the rat model of hippocampal degeneration induced by trimethyltin (TMT) intoxication (8 mg/kg, single intraperitoneal injection), which results in behavioral and neurological dysfunction similar to neurodegenerative disorders. We investigated spatial and temporal patterns of ecto-nucleoside triphosphate diphosphohydrolase 1 (NTPDase1/CD39) and ecto-5′ nucleotidase (eN/CD73) activity, their cell-specific localization, and analyzed gene expression pattern and/or cellular localization of purinoreceptors and proinflammatory mediators associated with reactive glial cells. Our study demonstrated that all Iba1+ cells at the injured area, irrespective of their morphology, upregulated NTPDase1/CD39, while induction of eN/CD73 has been observed at amoeboid Iba1+ cells localized within the hippocampal neuronal layers with pronounced cell death. Marked induction of P2Y₁₂R, P2Y₆R, and P2X₄-messenger RNA at the early stage of TMT-induced neurodegeneration might reflect the functional properties, migration, and chemotaxis of microglia, while induction of P2X₇R at amoeboid cells probably modulates their phagocytic role. Reactive astrocytes expressed adenosine A₁, A_2A, and P2Y₁ receptors, revealed induction of complement component C3, inducible nitric oxide synthase, nuclear factor-kB, and proinflammatory cytokines at the late stage of TMT-induced neurodegeneration. An increased set of purinergic system components on activated microglia (NTPDase1/CD39, eN/CD73, and P2X₇) and astrocytes (A₁R, A_2AR, and P2Y₁), and loss of homeostatic glial and neuronal purinergic pathways (P2Y₁₂ and A₁R) may shift purinergic signaling balance toward excitotoxicity and inflammation, thus favoring progression of pathological events. These findings may contribute to a better understanding of the involvement of purinergic signaling components in the progression of neurodegenerative disorders that could be target molecules for the development of novel therapies.

Targeting Neuroinflammation via Purinergic P2 Receptors for Disease Modification in Drug-Refractory Epilepsy

Treatment of epilepsy remains a clinical challenge, with >30% of patients not responding to current antiseizure drugs (ASDs). Moreover, currently available ASDs are merely symptomatic without altering significantly the progression of the disease. Inflammation is increasingly recognized as playing an important role during the generation of hyperexcitable networks in the brain. Accordingly, the suppression of chronic inflammation has been suggested as a promising therapeutic strategy to prevent epileptogenesis and to treat drug-refractory epilepsy. As a consequence, a strong focus of ongoing research is identification of the mechanisms that contribute to sustained inflammation in the brain during epilepsy and whether these can be targeted. ATP is released in response to several pathological stimuli, including increased neuronal activity within the central nervous system, where it functions as a neuro- and gliotransmitter. Once released, ATP activates purinergic P2 receptors, which are divided into metabotropic P2Y and ionotropic P2X receptors, driving inflammatory processes. Evidence from experimental models and patients demonstrates widespread expression changes of both P2Y and P2X receptors during epilepsy, and critically, drugs targeting both receptor subtypes, in particular the P2Y₁ and P2X₇ subtypes, have been shown to possess both anticonvulsive and antiepileptic potential. This review provides a detailed summary of the current evidence suggesting ATP-gated receptors as novel drug targets for epilepsy and discusses how P2 receptor–driven inflammation may contribute to the generation of seizures and the development of epilepsy.

Extracellular Adenosine Diphosphate Stimulates CXCL10-Mediated Mast Cell Infiltration Through P2Y1 Receptor to Aggravate Airway Inflammation in Asthmatic Mice

Asthma is an inflammatory disease associated with variable airflow obstruction and airway inflammation. This study aimed to explore the role and mechanism of extracellular adenosine diphosphate (ADP) in the occurrence of airway inflammation in asthma. The expression of ADP in broncho-alveolar lavage fluid (BALF) of asthmatic patients was determined by enzyme linked immunosorbent assay (ELISA) and the expression of P2Y1 receptor in lung tissues was determined by reverse transcription-quantitative polymerase chain reaction. Asthmatic mouse model was induced using ovalbumin and the mice were treated with ADP to assess its effects on the airway inflammation and infiltration of mast cells (MCs). Additionally, alveolar epithelial cells were stimulated with ADP, and the levels of interleukin-13 (IL-13) and C-X-C motif chemokine ligand 10 (CXCL10) were measured by ELISA. We finally analyzed involvement of NF-κB signaling pathway in the release of CXCL10 in ADP-stimulated alveolar epithelial cells. The extracellular ADP was enriched in BALF of asthmatic patients, and P2Y1 receptor is highly expressed in lung tissues of asthmatic patients. In the OVA-induced asthma model, extracellular ADP aggravated airway inflammation and induced MC infiltration. Furthermore, ADP stimulated alveolar epithelial cells to secrete chemokine CXCL10 by activating P2Y1 receptor, whereby promoting asthma airway inflammation. Additionally, ADP activated the NF-κB signaling pathway to promote CXCL10 release. As a “danger signal” extracellular ADP could trigger and maintain airway inflammation in asthma by activating P2Y1 receptor. This study highlights the extracellular ADP as a promising anti-inflammatory target for the treatment of asthma.

Purinergic Receptors of the Central Nervous System: Biology, PET Ligands, and Their Applications

Purinergic receptors play important roles in central nervous system (CNS). These receptors are involved in cellular neuroinflammatory responses that regulate functions of neurons, microglial and astrocytes. Based on their endogenous ligands, purinergic receptors are classified into P1 or adenosine, P2X and P2Y receptors. During brain injury or under pathological conditions, rapid diffusion of extracellular adenosine triphosphate (ATP) or uridine triphosphate (UTP) from the damaged cells, promote microglial activation that result in the changes in expression of several of these receptors in the brain. Imaging of the purinergic receptors with selective Positron Emission Tomography (PET) radioligands has advanced our understanding of the functional roles of some of these receptors in healthy and diseased brains. In this review, we have accumulated a list of currently available PET radioligands of the purinergic receptors that are used to elucidate the receptor functions and participations in CNS disorders. We have also reviewed receptors lacking radiotracer, laying the foundation for future discoveries of novel PET radioligands to reveal these receptors roles in CNS disorders.

Glial Cells as Therapeutic Approaches in Brain Ischemia-Reperfusion Injury

Ischemic stroke is the second cause of mortality and the first cause of long-term disability constituting a serious socioeconomic burden worldwide. Approved treatments include thrombectomy and rtPA intravenous administration, which, despite their efficacy in some cases, are not suitable for a great proportion of patients. Glial cell-related therapies are progressively overcoming inefficient neuron-centered approaches in the preclinical phase. Exploiting the ability of microglia to naturally switch between detrimental and protective phenotypes represents a promising therapeutic treatment, in a similar way to what happens with astrocytes. However, the duality present in many of the roles of these cells upon ischemia poses a notorious difficulty in disentangling the precise pathways to target. Still, promoting M2/A2 microglia/astrocyte protective phenotypes and inhibiting M1/A1 neurotoxic profiles is globally rendering promising results in different in vivo models of stroke. On the other hand, described oligodendrogenesis after brain ischemia seems to be strictly beneficial, although these cells are the less studied players in the stroke paradigm and negative effects could be described for oligodendrocytes in the next years. Here, we review recent advances in understanding the precise role of mentioned glial cell types in the main pathological events of ischemic stroke, including inflammation, blood brain barrier integrity, excitotoxicity, reactive oxygen species management, metabolic support, and neurogenesis, among others, with a special attention to tested therapeutic approaches.

Glial Purinergic Signaling in Neurodegeneration

Purinergic signaling regulates neuronal and glial cell functions in the healthy CNS. In neurodegenerative diseases, purinergic signaling becomes dysregulated and can affect disease-associated phenotypes of glial cells. In this review, we discuss how cell-specific expression patterns of purinergic signaling components change in neurodegeneration and how dysregulated glial purinergic signaling and crosstalk may contribute to disease pathophysiology, thus bearing promising potential for the development of new therapeutical options for neurodegenerative diseases.

Cross-Talk Between Key Players in Patients with COVID-19 and Ischemic Stroke: A Review on Neurobiological Insight of the Pandemic

The global pandemic of novel coronavirus disease 2019 (COVID-19) has taken the entire human race by surprise and led to an unprecedented number of mortalities worldwide so far. Current clinical studies have interpreted that angiotensin-converting enzyme 2 (ACE2) is the host receptor for severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2). In addition, ACE2 is the major component of the renin-angiotensin system. ACE2 deteriorates angiotensin II, a peptide that is responsible for the promotion of stroke. The downregulation of ACE2 further activates an immunological cascade. Thus, researchers need to explore and examine the possible links between COVID-19 and ischemic stroke (IS). Human ACE2 expression level and pattern in various tissues might be decisive for the vulnerability, symptoms, and treatment outcomes of the SARS-CoV-2 infection. The swift increase in the knowledge of SARS-CoV-2 has given creditable evidence that SARS-CoV-2 infected patients also encounter neurological deficits. As the SARS-CoV-2 binds to ACE2, it will hamper the activity of ACE2 in providing neuroprotection, especially in the case of stroke patients. Due to the downregulation of ACE2, the inflammatory response is activated in the ischemic penumbra. The COVID-19 pandemic has affected people with various pre-existing diseases, including IS, in such a way that these patients need special care and attention for their survival. Several clinical trials are currently ongoing worldwide as well as many other projects are in different stages of conceptualization and planning to facilitate the effective management of stroke patients with COVID-19 infection.

Nucleotide P2Y1 receptor agonists are in vitro and in vivo prodrugs of A1/A3 adenosine receptor agonists: implications for roles of P2Y1 and A1/A3 receptors in physiology and pathology

Rapid phosphoester hydrolysis of endogenous purine and pyrimidine nucleotides has challenged the characterization of the role of P2 receptors in physiology and pathology. Nucleotide phosphoester stabilization has been pursued on a number of medicinal chemistry fronts. We investigated the in vitro and in vivo stability and pharmacokinetics of prototypical nucleotide P2Y₁ receptor (P2Y₁R) agonists and antagonists. These included the riboside nucleotide agonist 2-methylthio-ADP and antagonist MRS2179, as well as agonist MRS2365 and antagonist MRS2500 containing constrained (N)-methanocarba rings, which were previously reported to form nucleotides that are more slowly hydrolyzed at the α-phosphoester compared with the ribosides. In vitro incubations in mouse and human plasma and blood demonstrated the rapid hydrolysis of these compounds to nucleoside metabolites. This metabolism was inhibited by EDTA to chelate divalent cations required by ectonucleotidases for nucleotide hydrolysis. This rapid hydrolysis was confirmed in vivo in mouse pharmacokinetic studies that demonstrate that MRS2365 is a prodrug of the nucleoside metabolite AST-004 (MRS4322). Furthermore, we demonstrate that the nucleoside metabolites of MRS2365 and 2-methylthio-ADP are adenosine receptor (AR) agonists, notably at A₃ and A₁ARs. In vivo efficacy of MRS2365 in murine models of traumatic brain injury and stroke can be attributed to AR activation by its nucleoside metabolite AST-004, rather than P2Y₁R activation. This research suggests the importance of reevaluation of previous in vitro and in vivo research of P2YRs and P2XRs as there is a potential that the pharmacology attributed to nucleotide agonists is due to AR activation by active nucleoside metabolites.

Purinergic signaling in infectious diseases of the central nervous system

The incidence of infectious diseases affecting the central nervous system (CNS) has been increasing over the last several years. Among the reasons for the expansion of these diseases and the appearance of new neuropathogens are globalization, global warming, and the increased proximity between humans and wild animals due to human activities such as deforestation. Neurotropism affecting normal brain function is shared by organisms such as viruses, bacteria, fungi, and parasites. Neuroinfections caused by these agents activate immune responses, inducing neuroinflammation, excitotoxicity, and neurodegeneration. Purinergic signaling is an evolutionarily conserved signaling pathway associated with these neuropathologies. During neuroinfections, host cells release ATP as an extracellular danger signal with pro-inflammatory activities. ATP is metabolized to its derivatives by ectonucleotidases such as CD39 and CD73; ATP and its metabolites modulate neuronal and immune mechanisms through P1 and P2 purinergic receptors that are involved in pathophysiological mechanisms of neuroinfections. In this review we discuss the beneficial or deleterious effects of various components of the purinergic signaling pathway in infectious diseases that affect the CNS, including human immunodeficiency virus (HIV-1) infection, herpes simplex virus type 1 (HSV-1) infection, bacterial meningitis, sepsis, cryptococcosis, toxoplasmosis, and malaria. We also provide a description of this signaling pathway in emerging viral infections with neurological implications such as Zika and SARS-CoV-2.

Central nervous system-infiltrated immune cells induce calcium increase in astrocytes via astroglial purinergic signaling

Interaction between autoreactive immune cells and astroglia is an important part of the pathologic processes that fuel neurodegeneration in multiple sclerosis. In this inflammatory disease, immune cells enter into the central nervous system (CNS) and they spread through CNS parenchyma, but the impact of these autoreactive immune cells on the activity pattern of astrocytes has not been defined. By exploiting naïve astrocytes in culture and CNS-infiltrated immune cells (CNS IICs) isolated from rat with experimental autoimmune encephalomyelitis (EAE), here we demonstrate previously unrecognized properties of immune cell-astrocyte interaction. We show that CNS IICs but not the peripheral immune cell application, evokes a rapid and vigorous intracellular Ca²⁺ increase in astrocytes by promoting glial release of ATP. ATP propagated Ca²⁺ elevation through glial purinergic P2X7 receptor activation by the hemichannel-dependent nucleotide release mechanism. Astrocyte Ca²⁺ increase is specifically triggered by the autoreactive CD4⁺ T-cell application and these two cell types exhibit close spatial interaction in EAE. Therefore, Ca²⁺ signals may mediate a rapid astroglial response to the autoreactive immune cells in their local environment. This property of immune cell-astrocyte interaction may be important to consider in studies interrogating CNS autoimmune disease.

Glial Cells: Role of the Immune Response in Ischemic Stroke

Ischemic stroke, which accounts for 75-80% of all strokes, is the predominant cause of morbidity and mortality worldwide. The post-stroke immune response has recently emerged as a new breakthrough target in the treatment strategy for ischemic stroke. Glial cells, including microglia, astrocytes, and oligodendrocytes, are the primary components of the peri-infarct environment in the central nervous system (CNS) and have been implicated in post-stroke immune regulation. However, increasing evidence suggests that glial cells exert beneficial and detrimental effects during ischemic stroke. Microglia, which survey CNS homeostasis and regulate innate immune responses, are rapidly activated after ischemic stroke. Activated microglia release inflammatory cytokines that induce neuronal tissue injury. By contrast, anti-inflammatory cytokines and neurotrophic factors secreted by alternatively activated microglia are beneficial for recovery after ischemic stroke. Astrocyte activation and reactive gliosis in ischemic stroke contribute to limiting brain injury and re-establishing CNS homeostasis. However, glial scarring hinders neuronal reconnection and extension. Neuroinflammation affects the demyelination and remyelination of oligodendrocytes. Myelin-associated antigens released from oligodendrocytes activate peripheral T cells, thereby resulting in the autoimmune response. Oligodendrocyte precursor cells, which can differentiate into oligodendrocytes, follow an ischemic stroke and may result in functional recovery. Herein, we discuss the mechanisms of post-stroke immune regulation mediated by glial cells and the interaction between glial cells and neurons. In addition, we describe the potential roles of various glial cells at different stages of ischemic stroke and discuss future intervention targets.

Inhibiting the LPS-induced enhancement of mEPSC frequency in superficial dorsal horn neurons may serve as an electrophysiological model for alleviating pain

Pain is a major primary health care problem. Emerging studies show that inhibition of spinal microglial activation reduces pain. However, the precise mechanisms by which microglial activation contributes to nociceptive synaptic transmission remain unclear. In this study, we measured spontaneous synaptic activity of miniature excitatory postsynaptic currents (mEPSCs) in rat spinal cord superficial dorsal horn (SDH, laminae I and II) neurons. Lipopolysaccharide (LPS) and adenosine triphosphate (ATP) increased the frequency, but not amplitude, of mEPSCs in SDH neurons. Microglial inhibitors minocycline and paeonol, as well as an astrocyte inhibitor, a P2Y1 receptor (P2Y1R) antagonist, and a metabotropic glutamate receptor 5 (mGluR5) antagonist, all prevented LPS-induced enhancement of mEPSC frequency. In mouse behavioral testing, minocycline and paeonol effectively reduced acetic acid-induced writhing and LPS-induced hyperalgesia. These results indicate that LPS-activated microglia release ATP, which stimulates astrocyte P2Y1Rs to release glutamate, triggering presynaptic mGluR5 receptors and increasing presynaptic glutamate release, leading to an increase in mEPSC frequency and enhancement of nociceptive transmission in SDH neurons. We propose that these effects can serve as a new electrophysiological model for evaluating pain. Moreover, we predict that pharmacologic agents capable of inhibiting the LPS-induced enhancement of mEPSC frequency in SDH neurons will have analgesic effects.

Neuroprotective effects of microglial P2Y1 receptors against ischemic neuronal injury

Extracellular ATP, which is released from damaged cells after ischemia, activates P2 receptors. P2Y₁ receptors (P2Y₁R) have received considerable attention, especially in astrocytes, because their activation plays a central role in the regulation of neuron-to-glia communication. However, the functions or even existence of P2Y₁R in microglia remain unknown, despite the fact that many microglial P2 receptors are involved in several brain diseases. Herein, we demonstrate the presence and functional capability of microglial P2Y₁R to provide neuroprotective effects following ischemic stress. Cerebral ischemia resulted in increased microglial P2Y₁R expression. The number of injured hippocampal neurons was significantly higher in P2Y₁ R knockout (KO) mice than wildtype mice after forebrain ischemia. Propidium iodide (PI) uptake, a marker for dying cells, was significantly higher in P2Y₁R KO hippocampal slices compared with wildtype hippocampal slices at 48 h after 40-min oxygen-glucose deprivation (OGD). Furthermore, increased PI uptake following OGD was rescued by ectopic overexpression of P2Y₁R in microglia. In summary, these data suggest that microglial P2Y₁R mediate neuroprotective effects against ischemic stress and OGD insult.

Context-Specific Switch from Anti- to Pro-epileptogenic Function of the P2Y1 Receptor in Experimental Epilepsy

Extracellular ATP activates inflammatory responses to tissue injury. It is also implicated in establishing lasting network hyperexcitability in the brain by acting upon independent receptor systems. Whereas the fast-acting P2X channels have well-established roles driving neuroinflammation and increasing hyperexcitability, the slower-acting metabotropic P2Y receptors have received much less attention. Recent studies of P2Y₁ receptor function in seizures and epilepsy have produced contradictory results, suggesting that the role of this receptor during seizure pathology may be highly sensitive to context. Here, by using male mice, we demonstrate that the metabotropic P2Y₁ receptor mediates either proconvulsive or anticonvulsive responses, dependent on the time point of activation in relation to the induction of status epilepticus. P2Y₁ deficiency or a P2Y₁ antagonist (MRS2500) administered before a chemoconvulsant, exacerbates epileptiform activity, whereas a P2Y₁ agonist (MRS2365) administered at this time point is anticonvulsant. When these drugs are administered after the onset of status epilepticus, however, their effect on seizure severity is reversed, with the antagonist now anticonvulsant and the agonist proconvulsant. This result was consistent across two different mouse models of status epilepticus (intra-amygdala kainic acid and intraperitoneal pilocarpine). Pharmacologic P2Y₁ blockade during status epilepticus reduces also associated brain damage, delays the development of epilepsy and, when applied during epilepsy, suppresses spontaneous seizures, in mice. Our data show a context-specific role for P2Y₁ during seizure pathology and demonstrate that blocking P2Y₁ after status epilepticus and during epilepsy has potent anticonvulsive effects, suggesting that P2Y₁ may be a novel candidate for the treatment of drug-refractory status epilepticus and epilepsy.SIGNIFICANCE STATEMENT This is the first study to fully characterize the contribution of a metabotropic purinergic P2Y receptor during acute seizures and epilepsy. The findings suggest that targeting P2Y₁ may offer a potential novel treatment strategy for drug-refractory status epilepticus and epilepsy. Our data demonstrate a context-specific role of P2Y₁ activation during seizures, switching from a proconvulsive to an anticonvulsive role depending on physiopathological context. Thus, our study provides a possible explanation for seemingly conflicting results obtained between studies of different brain diseases where P2Y₁ targeting has been proposed as a potential treatment strategy and highlights that the timing of pharmacological interventions is of critical importance to the understanding of how receptors contribute to the generation of seizures and the development of epilepsy.

HIV-1 Tat enhances purinergic P2Y4 receptor signaling to mediate inflammatory cytokine production and neuronal damage via PI3K/Akt and ERK MAPK pathways

BACKGROUND

HIV-associated neurocognitive disorders (HANDs) afflict more than half of HIV-1-positive individuals. The transactivator of transcription (Tat) produced by HIV virus elicits inflammatory process and is a major neurotoxic mediator that induce neuron damage during HAND pathogenesis. Activated astrocytes are important cells involved in neuroinflammation and neuronal damage. Purinergic receptors expressed in astrocytes participate in a positive feedback loop in virus-induced neurotoxicity. Here, we investigated that whether P2Y4R, a P2Y receptor subtype, that expressed in astrocyte participates in Tat-induced neuronal death in vitro and in vivo.

METHODS

Soluble Tat protein was performed to determine the expression of P2Y4R and proinflammatory cytokines in astrocytes using siRNA technique via real-time PCR, Western blot, and immunofluorescence assays. Cytometric bead array was used to measure proinflammatory cytokine release. The TUNEL staining and MTT cell viability assay were analyzed for HT22 cell apoptosis and viability, and the ApopTag® peroxidase in situ apoptosis detection kit and cresyl violet staining for apoptosis and death of hippocampal neuron in vivo.

RESULTS

We found that Tat challenge increased the expression of P2Y4R in astrocytes. P2Y4R signaling in astrocytes was involved in Tat-induced inflammatory cytokine production via PI3K/Akt- and ERK1/2-dependent pathways. Knockdown of P2Y4R expression significantly reduced inflammatory cytokine production and relieved Tat-mediated neuronal apoptosis in vitro. Furthermore, in vivo challenged with Tat, P2Y4R knockdown mice showed decreased inflammation and neuronal damage, especially in hippocampal CA1 region.

CONCLUSIONS

Our data provide novel insights into astrocyte-mediated neuron damage during HIV-1 infection and suggest a potential therapeutic target for HANDs.

Identification of P2Y receptors involved in oleamide-suppressing inflammatory responses in murine microglia and human dendritic cells

Microglia, a type of immune cell in the central nervous system, are involved in inflammation leading to neurodegenerative diseases. We previously identified oleamide from fermented dairy products as a neuroprotective compound suppressing microglial inflammation. Oleamide is an endocannabinoid and displays anti-inflammatory activity via the cannabinoid-2 (CB2) receptor; however, the mechanism underlying this anti-inflammatory activity has not been fully elucidated. Here, we found that the suppressive effect of oleamide on microglial tumor necrosis factor-α (TNF-α) production was canceled by inhibitors of G-protein-coupled receptor (GPCR) downstream signaling but not by a CB2 antagonist, suggesting that GPCRs other than CB2 are involved in the anti-inflammatory effects of oleamide. An extensive screen for GPCRs using a transforming growth factor-α shedding assay system identified P2Y1, P2Y4, P2Y6, P2Y10, and P2Y11 as candidates for the oleamide target. P2Y1 and P2Y10 agonists suppressed microglial TNF-α production, while a pan P2 receptor antagonist canceled the suppressive effect. Furthermore, we observed a relationship between the P2Y1 agonistic activities and the suppressive activities of oleamide and its analogs. Taken together, our results suggest that, in addition to CB2, P2Y type receptors are the potential targets of oleamide, and P2Y1 plays a role in the suppression of microglial inflammatory responses by oleamide. (200/200 words)

Aberrant Calcium Signals in Reactive Astrocytes: A Key Process in Neurological Disorders

Astrocytes are abundant cells in the brain that regulate multiple aspects of neural tissue homeostasis by providing structural and metabolic support to neurons, maintaining synaptic environments and regulating blood flow. Recent evidence indicates that astrocytes also actively participate in brain functions and play a key role in brain disease by responding to neuronal activities and brain insults. Astrocytes become reactive in response to injury and inflammation, which is typically described as hypertrophy with increased expression of glial fibrillary acidic protein (GFAP). Reactive astrocytes are frequently found in many neurological disorders and are a hallmark of brain disease. Furthermore, reactive astrocytes may drive the initiation and progression of disease processes. Recent improvements in the methods to visualize the activity of reactive astrocytes in situ and in vivo have helped elucidate their functions. Ca²⁺ signals in reactive astrocytes are closely related to multiple aspects of disease and can be a good indicator of disease severity/state. In this review, we summarize recent findings concerning reactive astrocyte Ca²⁺ signals. We discuss the molecular mechanisms underlying aberrant Ca²⁺ signals in reactive astrocytes and the functional significance of aberrant Ca²⁺ signals in neurological disorders.

P2 receptor interaction and signalling cascades in neuroprotection

Nucleotides can contribute to the survival of different glial and neuronal models at the nervous system via activation of purinergic P2X and P2Y receptors. Their activation counteracts different proapoptotic events, such as excitotoxicity, mitochondrial impairment, oxidative stress and DNA damage, which concur to elicit cell loss in different processes of neurodegeneration and brain injury. Thus, it is frequent to find that different neuroprotective mediators converge in the activation of the same intracellular survival pathways to protect cells from death. The present review focuses on the role of P2Y₁ and P2Y₁₃ metabotropic receptors, and P2X7 ionotropic receptors to regulate the balance between survival and apoptosis. In particular, we analyze the intracellular pathways involved in the signaling of these nucleotide receptors to elicit survival, including calcium/PLC, PI3K/Akt/GSK3, MAPK cascades, and the expression of antioxidant and antiapoptotic genes. This review emphasizes the novel contribution of nucleotide receptors to maintain cell homeostasis through the regulation of MAP kinases and phosphatases. Unraveling the different roles found for nucleotide receptors in different models and cellular contexts may be crucial to delineate future therapeutic applications based on targeting nucleotide receptors for neuroprotection.

Purinergic signaling in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that is characterized by three major histopathological markers: amyloid-β (Aβ) plaques, neurofibrillary tangles and gliosis in the central nervous system (CNS). It is now accepted that neuroinflammatory events in the CNS play a crucial role in the development of AD. This review focuses on neuroinflammatory signaling mediated by purinergic receptors (P1 adenosine receptors, P2X ATP-gated ion channels and G protein-coupled P2Y nucleotide receptors) and how therapeutic modulation of purinergic signaling influences disease progression in AD patients and animal models of AD.

Spontaneous astrocytic Ca2+ activity abounds in electrically suppressed ischemic penumbra of aged mice

Experimental focal cortical ischemic lesions consist of an ischemic core and a potentially salvageable peri-ischemic region, the ischemic penumbra. The activity of neurons and astrocytes is assumed to be suppressed in the penumbra because the electrical function is interrupted, but this is incompletely elucidated. Most experimental stroke studies used young adult animals, whereas stroke is prevalent in the elderly population. Using two-photon imaging in vivo, we here demonstrate extensive but electrically silent, spontaneous Ca²⁺ activity in neurons and astrocytes in the ischemic penumbra of 18- to 24-month-old mice 2-4 hr after middle cerebral artery occlusion. In comparison, stroke reduced spontaneous Ca²⁺ activity in neurons and astrocytes in adult mice (3-4 months of age). In aged mice, stroke increased astrocytic spontaneous Ca²⁺ activity considerably while neuronal spontaneous Ca²⁺ activity was unchanged. Blockade of action potentials and of purinergic receptors strongly reduced spontaneous Ca²⁺ activity in both neurons and astrocytes in the penumbra of old stroke mice. This indicates that stroke had a direct influence on mechanisms in presynaptic terminals and on purinergic signaling. Thus, highly dynamic variations in spontaneous Ca²⁺ activity characterize the electrically compromised penumbra, with remarkable differences between adult and old mice. The data are consistent with the notion that aged neurons and astrocytes take on a different phenotype than young mice. The increased activity of the aged astrocyte phenotype may be harmful to neurons. We suggest that the abundant spontaneous Ca²⁺ activity in astrocytes in the ischemic penumbra of old mice may be a novel target for neuroprotection strategies. A video abstract of this article can be found at https://youtu.be/AKlwKFsz1qE.

CCL2 and CXCL10 are associated with poor outcome after intracerebral hemorrhage

OBJECTIVE

Intracerebral hemorrhage carries a high mortality and survivors are frequently left with significant disability. Immunological mechanisms may play an important role in hemorrhage-induced brain injury, however, research linking these mechanisms with clinical outcome remains limited. We aim to identify serum inflammatory mediators that are associated with outcome after intracerebral hemorrhage in order to translate data from experimental models to a patient cohort and identify potential targets worthy of reverse translation.

METHODS

A prospective cohort study at two comprehensive stroke centers enrolled patients with spontaneous intracerebral hemorrhage. Peripheral blood was collected at 6, 24, and 72 h from onset. Functional outcome was assessed at 90 days using the modified Rankin Scale (mRS). Serum inflammatory mediators were measured using multiplex ELISA. Multivariable modeling identified serum biomarkers independently associated with functional outcome at 90 days.

RESULTS

115 patients completed the study. At 6 h after onset, patients with elevated CCL2 had worse mRS score at day 90 (OR 4.07, 95% CI 1.27-13.10, P = 0.02) after adjusting for age, gender, ICH volume, IVH, infratentorial location and NIHSS score. At 24 and 72 h after onset, elevation in CXCL10 was independently associated with worse 90 days mRS score (24 h: OR 8.08, 95% CI 2.69-24.30, P < 0.001; 72 h: OR 3.89, 95% CI 1.12-13.49, P = 0.03).

INTERPRETATION

Acute and subacute elevations in specific immune factors are associated with poor outcome, highlighting potential pathways that may contribute to ongoing brain injury in patients with intracerebral hemorrhage.

Cooperation between NMDA-Type Glutamate and P2 Receptors for Neuroprotection during Stroke: Combining Astrocyte and Neuronal Protection

Excitotoxicity is the principle mechanism of acute injury during stroke. It is defined as the unregulated accumulation of excitatory neurotransmitters such as glutamate within the extracellular space, leading to over-activation of receptors, ionic disruption, cell swelling, cytotoxic Ca2+ elevation and a feed-forward loop where membrane depolarisation evokes further neurotransmitter release. Glutamate-mediated excitotoxicity is well documented in neurons and oligodendrocytes but drugs targeting glutamate excitotoxicity have failed clinically which may be due to their inability to protect astrocytes. Astrocytes make up ~50% of the brain volume and express high levels of P2 adenosine triphosphate (ATP)-receptors which have excitotoxic potential, suggesting that glutamate and ATP may mediate parallel excitotoxic cascades in neurons and astrocytes, respectively. Mono-cultures of astrocytes expressed an array of P2X and P2Y receptors can produce large rises in [Ca2+]i; mono-cultured neurons showed lower levels of functional P2 receptors. Using high-density 1:1 neuron:astrocyte co-cultures, ischemia (modelled as oxygen-glucose deprivation: OGD) evoked a rise in extracellular ATP, while P2 blockers were highly protective of both cell types. GluR blockers were only protective of neurons. Neither astrocyte nor neuronal mono-cultures showed significant ATP release during OGD, showing that cell type interactions are required for ischemic release. P2 blockers were also protective in normal-density co-cultures, while low doses of combined P2/GluR blockers where highly protective. These results highlight the potential of combined P2/GluR block for protection of neurons and glia.

Glutamate-induced and NMDA receptor-mediated neurodegeneration entails P2Y1 receptor activation

Despite the characteristic etiologies and phenotypes, different brain disorders rely on common pathogenic events. Glutamate-induced neurotoxicity is a pathogenic event shared by different brain disorders. Another event occurring in different brain pathological conditions is the increase of the extracellular ATP levels, which is now recognized as a danger and harmful signal in the brain, as heralded by the ability of P2 receptors (P2Rs) to affect a wide range of brain disorders. Yet, how ATP and P2R contribute to neurodegeneration remains poorly defined. For that purpose, we now examined the contribution of extracellular ATP and P2Rs to glutamate-induced neurodegeneration. We found both in vitro and in vivo that ATP/ADP through the activation of P2Y1R contributes to glutamate-induced neuronal death in the rat hippocampus. We found in cultured rat hippocampal neurons that the exposure to glutamate (100 µM) for 30 min triggers a sustained increase of extracellular ATP levels, which contributes to NMDA receptor (NMDAR)-mediated hippocampal neuronal death through the activation of P2Y1R. We also determined that P2Y1R is involved in excitotoxicity in vivo as the blockade of P2Y1R significantly attenuated rat hippocampal neuronal death upon the systemic administration of kainic acid or upon the intrahippocampal injection of quinolinic acid. This contribution of P2Y1R fades with increasing intensity of excitotoxic conditions, which indicates that P2Y1R is not contributing directly to neurodegeneration, rather behaving as a catalyst decreasing the threshold from which glutamate becomes neurotoxic. Moreover, we unraveled that such excitotoxicity process began with an early synaptotoxicity that was also prevented/attenuated by the antagonism of P2Y1R, both in vitro and in vivo. This should rely on the observed glutamate-induced calpain-mediated axonal cytoskeleton damage, most likely favored by a P2Y1R-driven increase of NMDAR-mediated Ca²⁺ entry selectively in axons. This may constitute a degenerative mechanism shared by different brain diseases, particularly relevant at initial pathogenic stages.

Role of Purinergic Receptor P2Y1 in Spatiotemporal Ca2+ Dynamics in Astrocytes

Fine processes of astrocytes enwrap synapses and are well positioned to sense neuronal information via synaptic transmission. In rodents, astrocyte processes sense synaptic transmission via Gq-protein coupled receptors (GqPCR), including the P2Y1 receptor (P2Y1R), to generate Ca²⁺ signals. Astrocytes display numerous spontaneous microdomain Ca²⁺ signals; however, it is not clear whether such signals are due to local synaptic transmission and/or in what timeframe astrocytes sense local synaptic transmission. To ask whether GqPCRs mediate microdomain Ca²⁺ signals, we engineered mice (both sexes) to specifically overexpress P2Y1Rs in astrocytes, and we visualized Ca²⁺ signals via a genetically encoded Ca²⁺ indicator, GCaMP6f, in astrocytes from adult mice. Astrocytes overexpressing P2Y1Rs showed significantly larger Ca²⁺ signals in response to exogenously applied ligand and to repetitive electrical stimulation of axons compared with controls. However, we found no evidence of increased microdomain Ca²⁺ signals. Instead, Ca²⁺ waves appeared and propagated to occupy areas that were up to 80-fold larger than microdomain Ca²⁺ signals. These Ca²⁺ waves accounted for only 2% of total Ca²⁺ events, but they were 1.9-fold larger and 2.9-fold longer in duration than microdomain Ca²⁺ signals at processes. Ca²⁺ waves did not require action potentials for their generation and occurred in a probenecid-sensitive manner, indicating that the endogenous ligand for P2Y1R is elevated independently of synaptic transmission. Our data suggest that spontaneous microdomain Ca²⁺ signals occur independently of P2Y1R activation and that astrocytes may not encode neuronal information in response to synaptic transmission at a point source of neurotransmitter release.SIGNIFICANCE STATEMENT Astrocytes are thought to enwrap synapses with their processes to receive neuronal information via Gq-protein coupled receptors (GqPCRs). Astrocyte processes display numerous microdomain Ca²⁺ signals that occur spontaneously. To determine whether GqPCRs play a role in microdomain Ca²⁺ signals and the timeframe in which astrocytes sense neuronal information, we engineered mice whose astrocytes specifically overexpress the P2Y1 receptor, a major GqPCR in astrocytes. We found that overexpression of P2Y1 receptors in astrocytes did not increase microdomain Ca²⁺ signals in astrocyte processes but caused Ca²⁺ wavelike signals. Our data indicate that spontaneous microdomain Ca²⁺ signals do not require activation of P2Y1 receptors.

Electroacupuncture ameliorating post-stroke cognitive impairments via inhibition of peri-infarct astroglial and microglial/macrophage P2 purinoceptors-mediated neuroinflammation and hyperplasia

Background

During ischemic stroke (IS), adenosine 5′-triphosphate (ATP) is released from damaged nerve cells of the infract core region to the extracellular space, invoking peri-infarct glial cellular P2 purinoceptors singling, and causing pro-inflammatory cytokine secretion, which is likely to initiate or aggravate motor and cognitive impairment. It has been proved that electroacupuncture (EA) is an effective and safe strategy used in anti-inflammation. However, EA for the role of purine receptors in the central nervous system has not yet been reported.

Methods

Ischemia-reperfusion injured rat model was induced by middle cerebral artery occlusion and reperfusion (MCAO/R). EA treatment at the DU 20 and DU 24 acupoints treatment were conducted to rats from the 12 h after MCAO/R injury for consecutive 7 days. The neurological outcomes, infarction volumes and the level of astroglial and microglial/macrophage hyperplasia, inflammatory cytokine and P2X7R and P2Y1R expression in the peri-infarct hippocampal CA1and sensorimotor cortex were investigated after IS to evaluate the MCAO/R model and therapeutic mechanism of EA treatment.

Results

EA effectively reduced the level of pro-inflammatory cytokine interleukin-1β (IL-1β) as evidenced by reduction in astroglial and microglial/macrophage hyperplasia and the levels of P2X7R and ED1, P2X7R and GFAP, P2Y1R and ED1, P2Y1R and GFAP co-expression in peri-infarct hippocampal CA1 and sensorimotor cortex compared with that of MCAO/R model and Non-EA treatment, accompanied by the improved neurological deficit and the motor and memory impairment outcomes. Therefore, our data support the hypothesis that EA could exert its anti-inflammatory effect via inhibiting the astroglial and microglial/macrophage P2 purinoceptors (P2X7R and P2Y1R)-mediated neuroinflammation after MCAO/R injury.

Conclusion

Astroglial and microglial/macrophage P2 purinoceptors-mediated neuroinflammation and hyperplasia in peri-infarct hippocampal CA1 and sensorimotor cortex were attenuated by EA treatment after ischemic stroke accompanied by the improved motor and memory behavior performance.

Electronic supplementary material

The online version of this article (10.1186/s12906-017-1974-y) contains supplementary material, which is available to authorized users.

Blockade of ATP P2X7 receptor enhances ischiatic nerve regeneration in mice following a crush injury

Preventing damage caused by nerve degeneration is a great challenge. There is a growing body of evidence implicating extracellular nucleotides and their P2 receptors in many pathophysiological mechanisms. In this work we aimed to investigate the effects of the administration of Brilliant Blue G (BBG) and Pyridoxalphosphate-6-azophenyl-2', 4'- disulphonic acid (PPADS), P2X7 and P2 non-selective receptor antagonists, respectively, on sciatic nerve regeneration. Four groups of mice that underwent nerve crush lesion were used: two control groups treated with vehicle (saline), a group treated with BBG and a group treated with PPADS during 28days. Gastrocnemius muscle weight was evaluated. For functional evaluation we used the Sciatic Functional Index (SFI) and the horizontal ladder walking test. Nerves, dorsal root ganglia and spinal cords were processed for light and electron microscopy. Antinoceptive effects of BBG and PPADS were evaluated through von Frey E, and the levels of IL-1β and TNF-α were analyzed by ELISA. BBG promoted an increase in the number of myelinated fibers and on axon, fiber and myelin areas. BBG and PPADS led to an increase of TNF-α and IL-1β in the nerve on day 1 and PPADS caused a decrease of IL-1β on day 7. Mechanical allodynia was reversed on day 7 in the groups treated with BBG and PPADS. We concluded that BBG promoted a better morphological regeneration after ischiatic crush injury, but this was not followed by anticipation of functional improvement. In addition, both PPADS and BBG presented anti-inflammatory as well as antinociceptive effects.

Neuroprotection by progesterone after transient cerebral ischemia in stroke-prone spontaneously hypertensive rats

We investigated the neuroprotective effects of progesterone (P4) treatment in stroke-prone spontaneously hypertensive rats (SHRSPs) given 60-min transient middle cerebral artery occlusion (tMCAO). The treatment groups were: (1) Wistar-Kyoto (normotensive sham), (2) SHRSP (hypertensive sham), (3) tMCAO SHRSPs (SHRSP+tMCAO), and (4) SHRSP+tMCAO+P4. P4 (8mg/kg) was administered 1h after occlusion and then daily for 14days. We measured cerebral infarction volume, blood pressure and body weight. Behavioral outcomes were analyzed at post-stroke days 3, 9, and 14. To assess morphological protection we measured activation of microglia and astrocytes, oxidative stress, apoptosis, expression of vascular endothelial growth factor (VEGF), an angiogenic marker, and IL-1β, a marker of inflammation, on day 14 post-stroke. There was no effect of P4 on body weight or systolic blood pressure compared to the SHRSP+tMCAO group. However, grip strength and sensory neglect measures in the P4 group were improved compared to SHRSP+tMCAO. In addition, significantly larger infarct volumes were seen in the SHRSP+tMCAO group compared to SHRSP+tMCAO+P4. Increased markers of the injury cascade such as macrophages, activated astrocytes, superoxide anion and apoptotic cells observed in the SHRSP+tMCAO group were significantly decreased by P4. We conclude that, despite hypertensive comorbidity, P4 improves functional outcomes and attenuates stroke infarct in hypertensive rats by reducing superoxide anion expression and by decreasing inflammation and neuronal apoptosis.

Hippo/MST1 signaling mediates microglial activation following acute cerebral ischemia-reperfusion injury

Cerebral ischemia-reperfusion injury is a major public health concern that causes high rates of disability and mortality in adults. Microglial activation plays a crucial role in ischemic stroke-induced alteration of the immune microenvironment. However, the mechanism underlying the triggering of microglial activation by ischemic stroke remains to be elucidated. Previously, we demonstrated that the protein kinase Hippo/MST1 plays an important role in oxidative stress-induced cell death in mammalian primary neurons and that the protein kinase c-Abl phosphorylates MST1 at Y433, which increases MST1 kinase activity. Microglial activation has been implicated as a secondary detrimental cellular response that contributes to neuronal cell death in ischemic stroke. Here, we are the first, to our knowledge, to demonstrate that MST1 mediates stroke-induced microglial activation by directly phosphorylating IκBα at residues S32 and S36. We further demonstrate that Src kinase functions upstream of MST1-IκB signaling during microglial activation. Specific deletion of MST1 in microglia mitigates stroke-induced brain injury. Therefore, we propose that Src-MST1-IκB signaling plays a critical role in stroke-induced microglial activation. Together with our previous work demonstrating that MST1 is important for oxidative stress-induced neuronal cell death, our results indicate that MST1 could represent a potent therapeutic target for ischemic stroke.

P2Y Receptors in Synaptic Transmission and Plasticity: Therapeutic Potential in Cognitive Dysfunction

ATP released from neurons and astrocytes during neuronal activity or under pathophysiological circumstances is able to influence information flow in neuronal circuits by activation of ionotropic P2X and metabotropic P2Y receptors and subsequent modulation of cellular excitability, synaptic strength, and plasticity. In the present paper we review cellular and network effects of P2Y receptors in the brain. We show that P2Y receptors inhibit the release of neurotransmitters, modulate voltage- and ligand-gated ion channels, and differentially influence the induction of synaptic plasticity in the prefrontal cortex, hippocampus, and cerebellum. The findings discussed here may explain how P2Y₁ receptor activation during brain injury, hypoxia, inflammation, schizophrenia, or Alzheimer's disease leads to an impairment of cognitive processes. Hence, it is suggested that the blockade of P2Y₁ receptors may have therapeutic potential against cognitive disturbances in these states.

Progesterone improves long-term functional and histological outcomes after permanent stroke in older rats

Previous studies have shown progesterone to be beneficial in animal models of central nervous system injury, but less is known about its longer-term sustained effects on recovery of function following stroke. We evaluated progesterone's effects on a panel of behavioral tests up to 8 weeks after permanent middle cerebral artery occlusion (pMCAO). Male Sprague-Dawley rats 12m.o. were subjected to pMCAO and, beginning 3h post-pMCAO, given intraperitoneal injections of progesterone (8mg/kg) or vehicle, followed by subcutaneous injections at 8h and then every 24h for 7 days, with tapering of the last 2 treatments. The rats were then tested on functional recovery at 3, 6 and 8 weeks post-stroke. We observed that progesterone-treated animals showed attenuation of infarct volume and improved functional outcomes at 8 weeks after stroke on grip strength, sensory neglect, motor coordination and spatial navigation tests. Progesterone treatments significantly improved motor deficits in the affected limb on a number of gait parameters. Glial fibrillary acidic protein expression was increased in the vehicle group and considerably lowered in the progesterone group at 8 weeks post-stroke. With repeated post-stroke testing, sensory neglect and some aspects of spatial learning performance showed spontaneous recovery, but on gait and grip-strength measres progesterone given only in the acute stage of stroke (first 7 days) showed sustained beneficial effects on all other measures of functional recovery up to 8 weeks post-stroke.

Purinergic signalling in brain ischemia

Ischemia is a multifactorial pathology characterized by different events evolving in the time. After ischemia a primary damage due to the early massive increase of extracellular glutamate is followed by activation of resident immune cells, i.e microglia, and production or activation of inflammation mediators. Protracted neuroinflammation is now recognized as the predominant mechanism of secondary brain injury progression. Extracellular concentrations of ATP and adenosine in the brain increase dramatically during ischemia in concentrations able to stimulate their respective specific P2 and P1 receptors. Both ATP P2 and adenosine P1 receptor subtypes exert important roles in ischemia. Although adenosine exerts a clear neuroprotective effect through A1 receptors during ischemia, the use of selective A1 agonists is hampered by undesirable peripheral effects. Evidence up to now in literature indicate that A2A receptor antagonists provide protection centrally by reducing excitotoxicity, while agonists at A2A (and possibly also A2B) and A3 receptors provide protection by controlling massive infiltration and neuroinflammation in the hours and days after brain ischemia. Among P2X receptors most evidence indicate that P2X7 receptor contribute to the damage induced by the ischemic insult due to intracellular Ca(2+) loading in central cells and facilitation of glutamate release. Antagonism of P2X7 receptors might represent a new treatment to attenuate brain damage and to promote proliferation and maturation of brain immature resident cells that can promote tissue repair following cerebral ischemia. Among P2Y receptors, antagonists of P2Y12 receptors are of value because of their antiplatelet activity and possibly because of additional anti-inflammatory effects. Moreover strategies that modify adenosine or ATP concentrations at injury sites might be of value to limit damage after ischemia. This article is part of the Special Issue entitled 'Purines in Neurodegeneration and Neuroregeneration'.