P2Y2 receptor expression is altered in rats after spinal cord injury

The activation of dormant ependymal cells following spinal cord injury

Ependymal cells, a dormant population of ciliated progenitors found within the central canal of the spinal cord, undergo significant alterations after spinal cord injury (SCI). Understanding the molecular events that induce ependymal cell activation after SCI represents the first step toward controlling the response of the endogenous regenerative machinery in damaged tissues. This response involves the activation of specific signaling pathways in the spinal cord that promotes self-renewal, proliferation, and differentiation. We review our current understanding of the signaling pathways and molecular events that mediate the SCI-induced activation of ependymal cells by focusing on the roles of some cell adhesion molecules, cellular membrane receptors, ion channels (and their crosstalk), and transcription factors. An orchestrated response regulating the expression of receptors and ion channels fine-tunes and coordinates the activation of ependymal cells after SCI or cell transplantation. Understanding the major players in the activation of ependymal cells may help us to understand whether these cells represent a critical source of cells contributing to cellular replacement and tissue regeneration after SCI. A more complete understanding of the role and function of individual signaling pathways in endogenous spinal cord progenitors may foster the development of novel targeted therapies to induce the regeneration of the injured spinal cord.

Therapeutic potential for P2Y2 receptor antagonism

G protein-coupled receptors are the target of more than 30% of all FDA-approved drug therapies. Though the purinergic P2 receptors have been an attractive target for therapeutic intervention with successes such as the P2Y₁₂ receptor antagonist, clopidogrel, P2Y₂ receptor (P2Y₂R) antagonism remains relatively unexplored as a therapeutic strategy. Due to a lack of selective antagonists to modify P2Y₂R activity, studies using primarily genetic manipulation have revealed roles for P2Y₂R in a multitude of diseases. These include inflammatory and autoimmune diseases, fibrotic diseases, renal diseases, cancer, and pathogenic infections. With the advent of AR-C118925, a selective and potent P2Y₂R antagonist that became commercially available only a few years ago, new opportunities exist to gain a more robust understanding of P2Y₂R function and assess therapeutic effects of P2Y₂R antagonism. This review discusses the characteristics of P2Y₂R that make it unique among P2 receptors, namely its involvement in five distinct signaling pathways including canonical Gα_q protein signaling. We also discuss the effects of other P2Y₂R antagonists and the pivotal development of AR-C118925. The remainder of this review concerns the mounting evidence implicating P2Y₂Rs in disease pathogenesis, focusing on those studies that have evaluated AR-C118925 in pre-clinical disease models.

Corrigendum: Purinergic signaling systems across comparative models of spinal cord injury

[This corrects the article DOI: 10.4103/1673-5374.338993].

Comprehensive analysis of microglia gene and subpathway signatures for glioma prognosis and drug screening: linking microglia to glioma

Glioma is the most common malignant tumors in the brain. Previous studies have revealed that, as the innate immune cells in nervous system, microglia cells were involved in glioma pathology. And, the resident microglia displayed its specific biological roles which distinguished with peripheral macrophages. In this study, an integrated analysis was performed based on public resource database to explore specific biological of microglia within glioma. Through comprehensive analysis, the biological characterization underlying two conditions, glioma microglia compared to glioma macrophage (MicT/MacT) as well as glioma microglia compared to normal microglia (MicT/MicN), were revealed. Notably, nine core MicT/MicN genes displayed closely associations with glioma recurrence and prognosis, such as P2RY2, which was analyzed in more than 2800 glioma samples from 25 studies. Furthermore, we applied a random walk based strategy to identify microglia specific subpathways and developed SubP28 signature for glioma prognostic analysis. Multiple validation data sets confirmed the predictive performance of SubP28 and involvement in molecular subtypes. The associations between SuP28 score and microglia M1/M2 polarization were also explored for both GBM and LGG types. Finally, a comprehensive drug-subpathway network was established for screening candidate medicable molecules (drugs) and identifying therapeutic subpathway targets. In conclusions, the comprehensive analysis of microglia related gene and functional signatures in glioma pathobiologic events by large-scale data sets displayed a framework to dissect inner connection between microglia and glioma, and identify robust signature for glioma clinical implications.

P2Y2 Receptor Mediated Neuronal Regeneration and Angiogenesis to Affect Functional Recovery in Rats with Spinal Cord Injury

The aim of this study was to investigate the effect of the P2Y2 receptor (P2Y2R) signaling pathway on neuronal regeneration and angiogenesis during spinal cord injury (SCI). The rats were randomly divided into 3 groups, including the sham+dimethyl sulfoxide (DMSO), SCI+DMSO, and SCI+P2Y2R groups. The SCI animal models were constructed. A locomotor rating scale was used for behavioral assessments. The apoptosis of spinal cord tissues was detected by TUNEL staining. The expression levels of P2Y2R, GFAP, nestin, Tuj1, and CD34 were detected by immunofluorescence staining, and the expression levels of TNF-α, IL-1β, and IL-6 were detected by enzyme-linked immunosorbent assay. The locomotor score in the model group was significantly lower than the sham group. The expression of P2Y2R was increased after SCI. The expression levels of TNF-α, IL-1β, and IL-6 were increased remarkably in the SCI model group compared with the sham group. The P2Y2R inhibitor relieved neuronal inflammation after SCI. Compared with the sham group, the apoptotic rate of spinal cord tissue cells in the model group was significantly increased. The P2Y2R inhibitor reduced the apoptosis of the spinal cord tissue. The expressions of CD34, Tuj1, and nestin in the model group were decreased, while the expressions of GFAP and P2Y2R were increased. The P2Y2R inhibitor reversed their expression levels. The P2Y2R inhibitor could alleviate SCI by relieving the neuronal inflammation, inhibiting the spinal cord tissue apoptosis, and promoting neuronal differentiation and vascular proliferation after SCI. P2Y2R may serve as a target for the treatment of SCI.

Role of the Purinergic P2Y2 Receptor in Pulmonary Hypertension

Pulmonary arterial hypertension (PAH), group 1 pulmonary hypertension (PH), is a fatal disease that is characterized by vasoconstriction, increased pressure in the pulmonary arteries, and right heart failure. PAH can be described by abnormal vascular remodeling, hyperproliferation in the vasculature, endothelial cell dysfunction, and vascular tone dysregulation. The disease pathomechanisms, however, are as yet not fully understood at the molecular level. Purinergic receptors P2Y within the G-protein-coupled receptor family play a major role in fluid shear stress transduction, proliferation, migration, and vascular tone regulation in systemic circulation, but less is known about their contribution in PAH. Hence, studies that focus on purinergic signaling are of great importance for the identification of new therapeutic targets in PAH. Interestingly, the role of P2Y2 receptors has not yet been sufficiently studied in PAH, whereas the relevance of other P2Ys as drug targets for PAH was shown using specific agonists or antagonists. In this review, we will shed light on P2Y receptors and focus more on the P2Y2 receptor as a potential novel player in PAH and as a new therapeutic target for disease management.

The protective effect and mechanism of COA-Cl in acute phase after spinal cord injury

Spinal cord injury (SCI) induces severe motor and sensory dysfunction. We previously showed the neuroprotective effects of COA-Cl, a novel synthesized adenosine analog, in a rat stroke model. In this study, we evaluated the neuroprotective effects of COA-Cl in acute phase of SCI. SCI was induced in rats at the T9 vertebra by using a drop device. Rats were divided into acute and subacute groups. A 5-day dose of 6 mg/kg COA-Cl in saline was given to the acute group immediately after SCI and the subacute group 4 days after SCI. Motor function assessed by Basso-Beattie-Bresnahan scoring and inclined plane test improved significantly in the acute group while the subacute group did not. Histological evaluation and TUNEL staining revealed that both the cavity volume and apoptosis were significantly decreased in the acute group compared with the subacute group. In addition, pERK/ERK was increased in the acute group 7 days after SCI. These results suggest that COA-Cl exerts neuroprotective effects via the ERK pathway when administered in the acute phase after SCI, resulting in the recovery of motor function. COA-Cl could be a novel therapeutic agent for the acute phase of SCI.

A Selective P2Y Purinergic Receptor Agonist 2-MesADP Enhances Locomotor Recovery after Acute Spinal Cord Injury

INTRODUCTION

Spinal cord injury (SCI) causes most severe motor and sensory dysfunctions. In Chinese traditional medicine, the agonist of a purinergic receptor is believed to have a positive effect on SCIs, and 2-Methylthio-adenosine-5'-diphosphate (2-MesADP) is a selective agonist of the P2Y purinergic receptor.

METHODS

To investigate its therapeutic function and molecular mechanism in SCI, transcriptome analysis associated with weighted gene co-expression network analysis (WGCNA) was carried out at various time points after T9 crush injury.

RESULTS

2-MesADP demonstrated recovery of limb motor function at the 6 weeks after injury, accompanied by neuronal regeneration and axon remyelination at 2 and 6 weeks. Furthermore, gene profiling revealed alternated gene expression with the treatment of 2-MesADP. These genes were assigned to a total of 38 modules, followed by gene ontology analysis; of these, 18 represented neuronal apoptosis and regeneration, immune response, synaptic transmission, cell cycle, and angiogenesis. In the neuronal apoptosis and regeneration module, Nefh, NeuroD6, and Dcx in the 2-MesADP group were noticed due to their interesting expression pattern. The gene expression patterns of Mag, Mog, and Cnp, which played key roles in myelination, were significantly changed with the treatment of 2-MesADP. Wnt signal pathway was the most important pathway in 2-MesADP treatment for acute SCI.

CONCLUSION

2-MesADP enhanced locomotor recovery in mouse SCI by altering the expression of neuronal apoptosis and remyelination-related genes and Wnt signaling pathways.

Protein Degradome of Spinal Cord Injury: Biomarkers and Potential Therapeutic Targets

Degradomics is a proteomics sub-discipline whose goal is to identify and characterize protease-substrate repertoires. With the aim of deciphering and characterizing key signature breakdown products, degradomics emerged to define encryptic biomarker neoproteins specific to certain disease processes. Remarkable improvements in structural and analytical experimental methodologies as evident in research investigating cellular behavior in neuroscience and cancer have allowed the identification of specific degradomes, increasing our knowledge about proteases and their regulators and substrates along with their implications in health and disease. A physiologic balance between protein synthesis and degradation is sought with the activation of proteolytic enzymes such as calpains, caspases, cathepsins, and matrix metalloproteinases. Proteolysis is essential for development, growth, and regeneration; however, inappropriate and uncontrolled activation of the proteolytic system renders the diseased tissue susceptible to further neurotoxic processes. In this article, we aim to review the protease-substrate repertoires as well as emerging therapeutic interventions in spinal cord injury at the degradomic level. Several protease substrates and their breakdown products, essential for the neuronal structural integrity and functional capacity, have been characterized in neurotrauma including cytoskeletal proteins, neuronal extracellular matrix glycoproteins, cell junction proteins, and ion channels. Therefore, targeting exaggerated protease activity provides a potentially effective therapeutic approach in the management of protease-mediated neurotoxicity in reducing the extent of damage secondary to spinal cord injury.

MicroRNA-135a-5p reduces P2X7 -dependent rise in intracellular calcium and protects against excitotoxicity

Excitotoxic cell death because of the massive release of glutamate and ATP contributes to the secondary extension of cellular and tissue loss following traumatic spinal cord injury (SCI). Evidence from blockage experiments suggests that over-expression and activation of purinergic receptors, especially P2X₇ , produces excitotoxicity in neurodegenerative diseases and trauma of the central nervous system. We hypothesize that the down-regulation of specific miRNAs after the SCI contributes to the over-expression of P2X₇ and that restorative strategies can be used to reduce the excitotoxic response. In the present study, we have employed bioinformatic analyses to identify microRNAs whose down-regulation following SCI can be responsible for P2X₇ over-expression and excitotoxic activity. Additional luciferase assays validated microRNA-135a-5p (miR-135a) as a posttranscriptional modulator of P2X₇ . Moreover, gene expression analysis in spinal cord samples from a rat SCI model confirmed that the decrease in miR-135a expression correlated with P2X₇ over-expression after injury. Transfection of cultures of Neuro-2a neuronal cell line with a miR-135a inhibitory sequences (antagomiR-135a), simulating the reduction of miR-135a observed after SCI, resulted in the increase of P2X₇ expression and the subsequent ATP-dependent rise in intracellular calcium concentration. Conversely, a restorative strategy employing miR-135a mimicked reduced P2X₇ expression, attenuating the increase in intracellular calcium concentration that depends on this receptor and protecting cells from excitotoxic death. Therefore, we conclude that miR-135a is a potential therapeutic target for SCI and that restoration of its expression may reduce the deleterious effects of ATP-dependent excitotoxicity induced after a traumatic spinal cord injury.

Regulation of proteasome activity by P2Y2 receptor underlies the neuroprotective effects of extracellular nucleotides

The Ubiquitin-Proteasome System (UPS) is essential for the regulation of the cellular proteostasis. Indeed, it has been postulated that an UPS dysregulation is the common mechanism that underlies several neurological disorders. Considering that extracellular nucleotides, through their selective P2Y₂ receptor (P2Y₂R), play a neuroprotective role in various neurological disorders that course with an UPS impairment, we wonder if this neuroprotective capacity resulted from their ability to modulate the UPS. Using a cellular model expressing two different UPS reporters, we found that the stimulation of P2Y₂R by its selective agonist Up₄U induced a significant reduction of UPS reporter levels. This reduction was due to an increase in two of the three peptidase proteasome activities, chymotrypsin and postglutamyl, caused by an increased expression of proteasome constitutive catalytic subunits β1 and β5. The intracellular signaling pathway involved required the activation of IP₃/MEK1/2/ERK but was independent of PKC or PKA. Interestingly, the P2Y₂R activation was able to revert both UPS-reporter accumulation and the cell death induced by a prolonged inhibition of UPS. Finally, we also observed that intracerebroventricular administration of Up₄U induced a significant increase both of chymotrypsin and postglutamyl activities as well as an increased expression of proteasome subunits β1 and β5 in the hippocampus of wild-type mice, but not in P2Y₂R KO mice. All these results strongly suggest that the capacity to modulate the UPS activity via P2Y₂R is the molecular mechanism which is how the nucleotides play a neuroprotective role in neurological disorders.

Caveolin-1 Regulates the P2Y2 Receptor Signaling in Human 1321N1 Astrocytoma Cells

Damage to the CNS can cause a differential spatio-temporal release of multiple factors, such as nucleotides, ATP and UTP. The latter interact with neuronal and glial nucleotide receptors. The P2Y2 nucleotide receptor (P2Y2R) has gained prominence as a modulator of gliotic responses after CNS injury. Still, the molecular mechanisms underlying these responses in glia are not fully understood. Membrane-raft microdomains, such as caveolae, and their constituent caveolins, modulate receptor signaling in astrocytes; yet, their role in P2Y2R signaling has not been adequately explored. Hence, this study evaluated the role of caveolin-1 (Cav-1) in modulating P2Y2R subcellular distribution and signaling in human 1321N1 astrocytoma cells. Recombinant hP2Y2R expressed in 1321N1 cells and Cav-1 were found to co-fractionate in light-density membrane-raft fractions, co-localize via confocal microscopy, and co-immunoprecipitate. Raft localization was dependent on ATP stimulation and Cav-1 expression. This hP2Y2R/Cav-1 distribution and interaction was confirmed with various cell model systems differing in the expression of both P2Y2R and Cav-1, and shRNA knockdown of Cav-1 expression. Furthermore, shRNA knockdown of Cav-1 expression decreased nucleotide-induced increases in the intracellular Ca(2+) concentration in 1321N1 and C6 glioma cells without altering TRAP-6 and carbachol Ca(2+) responses. In addition, Cav-1 shRNA knockdown also decreased AKT phosphorylation and altered the kinetics of ERK1/2 activation in 1321N1 cells. Our findings strongly suggest that P2Y2R interaction with Cav-1 in membrane-raft caveolae of 1321N1 cells modulates receptor coupling to its downstream signaling machinery. Thus, P2Y2R/Cav-1 interactions represent a novel target for controlling P2Y2R function after CNS injury.

Purinergic Modulation of Spinal Neuroglial Maladaptive Plasticity Following Peripheral Nerve Injury

Modulation of spinal reactive gliosis following peripheral nerve injury (PNI) is a promising strategy to restore synaptic homeostasis. Oxidized ATP (OxATP), a nonselective antagonist of purinergic P2X receptors, was found to recover a neuropathic behavior following PNI. We investigated the role of intraperitoneal (i.p.) OxATP treatment in restoring the expression of neuronal and glial markers in the mouse spinal cord after sciatic spared nerve injury (SNI). Using in vivo two-photon microscopy, we imaged Ca(2+) transients in neurons and astrocytes of the dorsal horn of spinal cord at rest and upon right hind paw electrical stimulation in sham, SNI, and OxATP-treated mice. Neuropathic behavior was investigated by von Frey and thermal plantar test. Glial [glial fibrillary acidic protein (GFAP), ionized calcium-binding adaptor molecule 1 (Iba1)] and GABAergic [vesicular GABA transporter (vGAT) and glutamic acid decarboxylase 65/76 (GAD65/67)] markers and glial [glutamate transporter (GLT1) and GLAST] and neuronal amino acid [EAAC1, vesicular glutamate transporter 1 (vGLUT1)] transporters have been evaluated. In SNI mice, we found (i) increased glial response, (ii) decreased glial amino acid transporters, and (iii) increased levels of neuronal amino acid transporters, and (iv) in vivo analysis of spinal neurons and astrocytes showed a persistent increase of Ca(2+) levels. OxATP administration reduced glial activation, modulated the expression of glial and neuronal glutamate/GABA transporters, restored neuronal and astrocytic Ca(2+) levels, and prevented neuropathic behavior. In vitro studies validated that OxATP (i) reduced levels of reactive oxygen species (ROS), (ii) reduced astrocytic proliferation, (iii) increase vGLUT expression. All together, these data support the correlation between reactive gliosis and perturbation of the spinal synaptic homeostasis and the role played by the purinergic system in modulating spinal plasticity following PNI.

P2Y receptors in Alzheimer's disease

Alzheimer's disease (AD) is the most common cause of dementia, affecting more than 10% of people over the age of 65. Age is the greatest risk factor for AD, although a combination of genetic, lifestyle and environmental factors also contribute to disease development. Common features of AD are the formation of plaques composed of beta-amyloid peptides (Aβ) and neuronal death in brain regions involved in learning and memory. Although Aβ is neurotoxic, the primary mechanisms by which Aβ affects AD development remain uncertain and controversial. Mouse models overexpressing amyloid precursor protein and Aβ have revealed that Aβ has potent effects on neuroinflammation and cerebral blood flow that contribute to AD progression. Therefore, it is important to consider how endogenous signalling in the brain responds to Aβ and contributes to AD pathology. In recent years, Aβ has been shown to affect ATP release from brain and blood cells and alter the expression of G protein-coupled P2Y receptors that respond to ATP and other nucleotides. Accumulating evidence reveals a prominent role for P2Y receptors in AD pathology, including Aβ production and elimination, neuroinflammation, neuronal function and cerebral blood flow.

The regulation of Sox2 and Sox9 stimulated by ATP in spinal cord astrocytes

After spinal cord injury (SCI), the level of adenosine triphosphate (ATP) and extracellular matrix (ECM) is increased. Formation of the glial scar is a complex process that is primarily attributed to astrocytic proliferation, and the fibrotic scar results from ECM deposition. In our previous researches, ATP and fibronectin was able to separately stimulate the proliferation of astrocytes. Moreover, fibronectin increases the expression of P2Y1 receptor and offers more binding sites for ATP, which aggravates the proliferation. Meanwhile, ATP was also able to stimulate the release of interleukin (IL)-6 and tumor necrosis factor-α (TNF-α), but fibronectin does not. Recently, it has been reported that over-expressing P2Y1 receptor could promote the level of Sox9. However, the regulation of Sox genes by ATP is still little known in spinal cord astrocytes. In the present study, we discovered that ATP was able to increase the expression of Sox2 and Sox9; fibronectin did not have this direct function. Sox9 was only involved in the proliferation increased by ATP, and Sox2 influenced the release of IL-6 stimulated by ATP. Understanding the critical role of Sox2 and Sox9 mediated by ATP may provide a potential target for therapeutic intervention in spinal cord injury.

Uridine 5'-triphosphate promotes in vitro Schwannoma cell migration through matrix metalloproteinase-2 activation

In response to peripheral nerve injury, Schwann cells adopt a migratory phenotype and modify the extracellular matrix to make it permissive for cell migration and axonal re-growth. Uridine 5′-triphosphate (UTP) and other nucleotides are released during nerve injury and activate purinergic receptors expressed on the Schwann cell surface, but little is known about the involvement of purine signalling in wound healing. We studied the effect of UTP on Schwannoma cell migration and wound closure and the intracellular signaling pathways involved. We found that UTP treatment induced Schwannoma cell migration through activation of P2Y₂ receptors and through the increase of extracellular matrix metalloproteinase-2 (MMP-2) activation and expression. Knockdown P2Y₂ receptor or MMP-2 expression greatly reduced wound closure and MMP-2 activation induced by UTP. MMP-2 activation evoked by injury or UTP was also mediated by phosphorylation of all 3 major mitogen-activated protein kinases (MAPKs): JNK, ERK1/2, and p38. Inhibition of these MAPK pathways decreased both MMP-2 activation and cell migration. Interestingly, MAPK phosphorylation evoked by UTP exhibited a biphasic pattern, with an early transient phosphorylation 5 min after treatment, and a late and sustained phosphorylation that appeared at 6 h and lasted up to 24 h. Inhibition of MMP-2 activity selectively blocked the late, but not the transient, phase of MAPK activation. These results suggest that MMP-2 activation and late MAPK phosphorylation are part of a positive feedback mechanism to maintain the migratory phenotype for wound healing. In conclusion, our findings show that treatment with UTP stimulates in vitro Schwannoma cell migration and wound repair through a MMP-2-dependent mechanism via P2Y₂ receptors and MAPK pathway activation.

The activation of P2Y6 receptor in cultured spinal microglia induces the production of CCL2 through the MAP kinases-NF-κB pathway

Rat primary cultures of spinal microglia were stimulated by UTP, a known P2Y2/4 receptor agonist, which resulted in the production and release of the C-C chemokine CCL2 (monocyte chemoattractant protein-1; MCP-1) measured by real-time PCR and ELISA, respectively. In an in vitro preparation of rat spinal microglia, with regard to the P2Y subtypes, the expression of P2Y1, 2, 6, 12, 13 and P2Y14, but not P2Y4, were detected by RT-PCR. The subtype of microglial P2Y receptor which could be involved in the production of CCL2 was also determined. The UTP-induced production of CCL2 was significantly blocked by pretreatment with reactive blue 2 and suramin, nonselective P2Y receptor antagonists, and MRS2578, a selective P2Y6 receptor antagonist. By contrast, knockdown of the P2Y2 receptor by RNA interference had no effect. The stimulatory effect of UTP was inhibited by phospholipase C (PLC) inhibitor U73122 and Src tyrosine kinase inhibitor PP2. A potential role of mitogen activated protein kinases was suggested since UTP-induced CCL2 production was significantly blocked by both U0126 and SB 202190, which are potent inhibitors of extracellular signal-regulated kinase (ERK) and p38, respectively. Moreover, UTP-stimulated phosphorylation of these kinases involved the activation of the P2Y6 receptor. Lastly, activation of nuclear factor-κB (NF-κB) by UTP is likely to be essential in the expression of CCL2. Together, these findings suggest that stimulation of spinal microglia P2Y6 receptors induce the production of CCL2 through either PLC-mediated ERK or p38 phosphorylation and the subsequent activation of NF-κB.

P2Y receptors in the mammalian nervous system: pharmacology, ligands and therapeutic potential

P2Y receptors for extracellular nucleotides are coupled to activation of a variety of G proteins and stimulate diverse intracellular signaling pathways that regulate functions of cell types that comprise the central nervous system (CNS). There are 8 different subtypes of P2Y receptor expressed in cells of the CNS that are activated by a select group of nucleotide agonists. Here, the agonist selectivity of these 8 P2Y receptor subtypes is reviewed with an emphasis on synthetic agonists with high potency and resistance to degradation by extracellular nucleotidases that have potential applications as therapeutic agents. In addition, the recent identification of a wide variety of subtype-selective antagonists is discussed, since these compounds are critical for discerning cellular responses mediated by activation of individual P2Y receptor subtypes. The functional expression of P2Y receptor subtypes in cells that comprise the CNS is also reviewed and the role of each subtype in the regulation of physiological and pathophysiological responses is considered. Other topics include the role of P2Y receptors in the regulation of blood-brain barrier integrity and potential interactions between different P2Y receptor subtypes that likely impact tissue responses to extracellular nucleotides in the CNS. Overall, current research suggests that P2Y receptors in the CNS regulate repair mechanisms that are triggered by tissue damage, inflammation and disease and thus P2Y receptors represent promising targets for the treatment of neurodegenerative diseases.

MCM7 expression is altered in rat after spinal cord injury

Minichromosome maintenance protein 7 (MCM7), a member of the minichromosome maintenance protein family, is essential for eukaryotic DNA replication initiation and the early stage of the elongation process. MCM7 participates in the cell cycle control of genome duplication. While it is ubiquitously expressed in all tissues, the biological function of MCM7 in the central nervous system is still with limited acquaintance. In the present study, we performed a spinal cord injury (SCI) model in adult rats. Western blotting indicated a marked alteration of MCM7 after SCI. Immunohistochemistry analysis revealed a wide distribution of MCM7 in the spinal cord. Double immunofluorescence staining showed that MCM7 immunoreactivity was increased predominantly in neurons, astrocytes, and microglia after SCI. We also examined the expression profiles of active caspase-3, proliferating cell nuclear antigen (PCNA), and Ki67, whose changes were correlated with the expression profiles of MCM7. Moreover, colocalization of MCM7/active caspase-3 was detected in neuronal nuclei (NeuN), and colocalization of MCM7/PCNA was detected in NeuN, glial fibrillary acidic protein, and CD11b, respectively. Our results suggest that MCM7 might be implicated in the apoptosis of neuron and proliferation of astrocytes and microglia after SCI.

P2Y purinergic receptors: new targets for analgesic and antimigraine drugs

Millions of individuals worldwide suffer from acute and, more severely, chronic pain conditions (e.g., neuropathic pain, and migraine). The latter bear tremendous personal, familial, and social costs, since sufferers and their relatives undergo a complete turnaround of their lives with the search of relief from pain becoming their pivotal thought. Sadly, to date no effective pharmacological approaches are available which can alleviate chronic pain significantly or in the long run in all patients. The current central strategy for the development of new and effective painkillers lies in the hypothesis that cellular and/or molecular players in nociception must exists that are not targeted by "classical" analgesics, and therefore researchers have put tremendous efforts into the in-depth analysis of the pathways leading to pain development and maintenance over time. In this complex scenario, two outsiders are now taking the center stage: glial cells in sensory ganglia and in the central nervous system, thanks to their ability to communicate with neurons and to modulate their firing, and the purinergic system. Extracellular purine and pyrimidine nucleotides are involved in the physiology of virtually every body district, and their extracellular concentrations massively increase under pathological situations, suggesting that they might represent potential targets for the modulation of disease-associated symptoms, like pain. Here, we provide an overview of the present knowledge of the role of nucleotides in nociception, with a particular emphasis on G protein-coupled P2Y receptors and their involvement in the communication between first- and second-order neurons in sensory nerve pathways and surrounding glial cells.

Neuroprotective roles of the P2Y(2) receptor

Purinergic signaling plays a unique role in the brain by integrating neuronal and glial cellular circuits. The metabotropic P1 adenosine receptors and P2Y nucleotide receptors and ionotropic P2X receptors control numerous physiological functions of neuronal and glial cells and have been implicated in a wide variety of neuropathologies. Emerging research suggests that purinergic receptor interactions between cells of the central nervous system (CNS) have relevance in the prevention and attenuation of neurodegenerative diseases resulting from chronic inflammation. CNS responses to chronic inflammation are largely dependent on interactions between different cell types (i.e., neurons and glia) and activation of signaling molecules including P2X and P2Y receptors. Whereas numerous P2 receptors contribute to functions of the CNS, the P2Y(2) receptor is believed to play an important role in neuroprotection under inflammatory conditions. While acute inflammation is necessary for tissue repair due to injury, chronic inflammation contributes to neurodegeneration in Alzheimer's disease and occurs when glial cells undergo prolonged activation resulting in extended release of proinflammatory cytokines and nucleotides. This review describes cell-specific and tissue-integrated functions of P2 receptors in the CNS with an emphasis on P2Y(2) receptor signaling pathways in neurons, glia, and endothelium and their role in neuroprotection.

P2 receptors for extracellular nucleotides in the central nervous system: role of P2X7 and P2Y₂ receptor interactions in neuroinflammation

Extracellular nucleotides induce cellular responses in the central nervous system (CNS) through the activation of ionotropic P2X and metabotropic P2Y nucleotide receptors. Activation of these receptors regulates a wide range of physiological and pathological processes. In this review, we present an overview of the current literature regarding P2X and P2Y receptors in the CNS with a focus on the contribution of P2X7 and P2Y(2) receptor-mediated responses to neuroinflammatory and neuroprotective mechanisms.

Expression and activation of ephexin is altered after spinal cord injury

Failure of axon regeneration after traumatic spinal cord injury (SCI) is attributable in part to the presence of inhibitory molecular interactions. Recent evidence demonstrates that activation of Eph signaling pathways leads to modulation of growth cone dynamics and repulsion through the activation of ephexin, a novel guanine nucleotide exchange factor (GEF). However, little is known about the expression and modulation of Eph molecular targets in the injured spinal cord. In this study, we determined the expression profile of ephexin after a moderate spinal cord contusion at thoracic level (T10) in young adult rats. Western-blot studies showed increased protein expression in injured rats at 4 and 7 days postinjury (DPI) when compared with control animals. The protein levels returned to normal at 14 DPI and remained steady until 28 DPI. However, immunoprecipitation studies of the phosphorylated ephexin demonstrated that this protein is activated by day 2 until 14 DPI. Expression of ephexin was noticeable in neurons, axons, microglia/macrophages, and reactive astrocytes, and co-localized with EphA3, A4, and A7. These results demonstrate the presence of ephexin in the adult spinal cord and its activation after SCI. Therefore, we show, for the first time, the spatiotemporal pattern of ephexin expression and activation after contusive SCI. Collectively, our data support our previous findings on the putative nonpermissive roles of Eph receptors after SCI and the possible involvement of ephexin in the intracellular cascade of events.

Blockade of P2 nucleotide receptors after spinal cord injury reduced the gliotic response and spared tissue

Spinal cord injury (SCI) triggers a sequel of events commonly associated with cell death and dysfunction of glias and neurons surrounding the lesion. Although astrogliosis and glial scar formation have been involved in both damage and repair processes after SCI, their role remains controversial. Our goal was to investigate the effects of the P2 receptors antagonists, PPADS and suramin, in the establishment of the reactive gliosis and the formation of the glial scar. Molecular biology, immunohistochemistry, spared tissue, and locomotor behavioral studies were used to evaluate astrogliosis, in adult female Sprague-Dawley rats treated with P2 antagonists after moderate injury with the NYU impactor device. Semi-quantitative RT-PCR confirmed the presence of P2Y(1,) P2Y(2,) P2Y(4,) P2Y(6,) P2Y(12), and P2X(2) receptors in the adult spinal cord. Immunohistochemistry studies confirmed a significant decrease in GFAP-labeled cells at the injury epicenter as well as a decrease in spared tissue after treatment with the antagonists. Functional open field testing revealed no significant locomotor score differences between treated and control animals. Our work is consistent with studies suggesting that astrogliosis is an important event after SCI that limits tissue damage and lesion spreading.

Role of purinergic receptors in CNS function and neuroprotection

The purinergic receptor family contains some of the most abundant receptors in living organisms. A growing body of evidence indicates that extracellular nucleotides play important roles in the regulation of neuronal and glial functions in the nervous system through purinergic receptors. Nucleotides are released from or leaked through nonexcitable cells and neurons during normal physiological and pathophysiological conditions. Ionotropic P2X and metabotropic P2Y purinergic receptors are expressed in the central nervous system (CNS), participate in the synaptic processes, and mediate intercellular communications between neuron and gila and between glia and other glia. Glial cells in the CNS are classified into astrocytes, oligodendrocytes, and microglia. Astrocytes express many types of purinergic receptors, which are integral to their activation. Astrocytes release adenosine triphosphate (ATP) as a "gliotransmitter" that allows communication with neurons, the vascular walls of capillaries, oligodendrocytes, and microglia. Oligodendrocytes are myelin-forming cells that construct insulating layers of myelin sheets around axons, and using purinergic receptor signaling for their development and for myelination. Microglia also express many types of purinergic receptors and are known to function as immunocompetent cells in the CNS. ATP and other nucleotides work as "warning molecules" especially by activating microglia in pathophysiological conditions. Studies on purinergic signaling could facilitate the development of novel therapeutic strategies for disorder of the CNS.