Arrestin scaffolds NHERF1 to the P2Y12 receptor to regulate receptor internalization

We have recently shown in a patient with mild bleeding that the PDZ-binding motif of the platelet G protein-coupled P2Y(12) receptor (P2Y(12)R) is required for effective receptor traffic in human platelets. In this study we show for the first time that the PDZ motif-binding protein NHERF1 exerts a major role in potentiating G protein-coupled receptor (GPCR) internalization. NHERF1 interacts with the C-tail of the P2Y(12)R and unlike many other GPCRs, NHERF1 interaction is required for effective P2Y(12)R internalization. In vitro and prior to agonist stimulation P2Y(12)R/NHERF1 interaction requires the intact PDZ binding motif of this receptor. Interestingly on receptor stimulation NHERF1 no longer interacts directly with the receptor but instead binds to the receptor via the endocytic scaffolding protein arrestin. These findings suggest a novel model by which arrestin can serve as an adaptor to promote NHERF1 interaction with a GPCR to facilitate effective NHERF1-dependent receptor internalization.     

P2Y12 receptor gene polymorphisms are associated with epilepsy

The basic research indicated that microglial P2Y12 receptors (P2Y12Rs) are involved in the pathophysiology of epilepsy through regulated microglial-neuronal interactions, aberrant neurogenesis, or immature neuronal projections. However, whether the clinic case of epilepsy would be associated with P2Y12 receptor gene polymorphisms is presented with few data. In our study, a total of 176 patients with epilepsy and 50 healthy controls were enrolled. Two single-nucleotide polymorphisms, namely rs1491974 and rs6798347, were selected for analysis. The results revealed that carriers of the G allele of rs1491974 G>A or rs6798347 G>A may be associated with an increased risk of epilepsy (OR = 0.576, 95% CI = 0.368–0.901, p = 0.015; OR = 0.603, 95% CI = 0.367–0.988, p = 0.043). Interestingly, we found that the rs1491974 G>A genotype and allele frequencies have only a significant difference in female instead of male case (p = 0.004 for genotype; p = 0.001 for allele). The subgroup analysis demonstrated that individuals with the rs1491974 G>A genotype might have more frequent seizure (OR = 0.476, 95% CI = 0.255–0.890; p = 0.019). These data implied that both rs1491974 and rs6798347 polymorphisms of P2Y12R would be able to play import roles in epilepsy susceptibility, whereas the rs1491974 polymorphism may be specifically related to seizure frequency.     

Regulation of P2Y1 Receptor Traffic by Sorting Nexin 1 is Retromer Independent

The activity and traffic of G‐protein coupled receptors (GPCRs) is tightly controlled. Recent work from our laboratory has shown that P2Y₁ and P2Y₁₂ responsiveness is rapidly and reversibly modulated in human platelets and that the underlying mechanism requires receptor trafficking as an essential part of this process. However, little is known about the molecular mechanisms underlying P2Y receptor traffic. Sorting nexin 1 (SNX1) has been shown to regulate the endosomal sorting of cell surface receptors either to lysosomes where they are downregulated or back to the cell surface. These functions may in part be due to interactions of SNX1 with the mammalian retromer complex. In this study, we investigated the role of SNX1 in P2Y receptor trafficking. We show that P2Y₁ receptors recycle via a slow recycling pathway that is regulated by SNX1, whereas P2Y₁₂ receptors return to the cell surface via a rapid route that is SNX1 independent. SNX1 inhibition caused a dramatic increase in the rate of P2Y₁ receptor recycling, whereas inhibition of Vps26 and Vps35 known to be present in retromer had no effect, indicating that SNX1 regulation of P2Y₁ receptor recycling is retromer independent. In addition, inhibition of SNX4, 6 and 17 proteins did not affect P2Y₁ receptor recycling. SNX1 has also been implicated in GPCR degradation; however, we provide evidence that P2Y receptor degradation is SNX1 independent. These data describe a novel function of SNX1 in the regulation of P2Y₁ receptor recycling and suggest that SNX1 plays multiple roles in endocytic trafficking of GPCRs.     

阿片肽与P2Y12受体信号通路的研究进展

糖尿病可增加心血管疾病危险性,因此糖尿病和心血管疾病的密切关系也日益被人们所重视。糖尿病引发的血小板功能亢进以及抗血小板药物抵抗的机制尚不明确。阿片肽类物质能够抑制血小板细胞活性以及凝集作用。本文对2型糖尿病血小板P2Y12信号通路高反应性、阿片肽及阿片受体对抗P2Y12信号通路高反应性的可能机制进行了归纳总结。     

阿片肽与P2Y12 受体信号通路的研究进展

糖尿病可增加心血管疾病危险性,因此糖尿病和心血管疾病的密切关系也日益被人们所重视。糖尿病引发的血小板功能亢进以及抗血小板药物抵抗的机制尚不明确。阿片肽类物质能够抑制血小板细胞活性以及凝集作用,本文对2型糖尿病血小板P2Y12信号通路高反应性、阿片肽及阿片受体对抗P2Y12信号通路高反应性的可能机制进行了归纳总结。     

P2Y12 antagonist attenuates eosinophilic inflammation and airway hyperresponsiveness in a mouse model of asthma

Leukotriene E4 (LTE4) that plays a key role in airway inflammation is expressed on platelets and eosinophils. We investigated whether blocking of the P2Y12 receptor can suppress eosinophilic inflammation in a mouse model of asthma because platelets and eosinophils share this receptor to be activated. BALB/c mice were sensitized by intraperitoneal injection of ovalbumin (OVA), followed by OVA nebulization. On each challenge day, clopidogrel, a P2Y12 antagonist was administered 30 min. before each challenge. Forty‐eight hours after the last OVA challenge, mice were assessed for airway hyperresponsiveness (AHR), cell composition and cytokine levels, including chemokine ligand 5 (CCL5), in bronchoalveolar lavage (BAL) fluid. EOL cells were treated with LTE4, with or without clopidogrel treatment, and intracellular and extracellular eosinophil cationic protein (ECP) expressions were measured to find the inhibiting function of P2Y12 antagonist on eosinophilic activation. The levels of P2Y12 expression were increased markedly in the lung homogenates of OVA‐sensitized and ‐challenged mice after platelet depletion. Administration of clopidogrel decreased AHR and the number of airway inflammatory cells, including eosinophils, in BAL fluid following OVA challenge. These results were associated with decreased levels of Th2 cytokines and CCL5. Histological examination showed that inflammatory cells as well as mucus‐containing goblet cells were reduced in clopidogrel‐administered mice compared to vehicle‐treated mice. Clopidogrel inhibited extracellular ECP secretion after LTE4 stimulation in EOL‐1 cells. Clopidogrel could prevent development of AHR and airway inflammation in a mouse model of asthma. P2Y12 can be a novel therapeutic target to the suppression of eosinophils in asthma.     

The role of P2Y14 and other P2Y receptors in degranulation of human LAD2 mast cells

Mast cell degranulation affects many conditions, e.g., asthma and urticaria. We explored the potential role of the P2Y₁₄ receptor (P2Y₁₄R) and other P2Y subtypes in degranulation of human LAD2 mast cells. All eight P2YRs were expressed at variable levels in LAD2 cells (quantitative real-time RT-PCR). Gene expression levels of ADP receptors, P2Y₁R, P2Y₁₂R, and P2Y₁₃R, were similar, and P2Y₁₁R and P2Y₄R were highly expressed at 5.8- and 3.8-fold of P2Y₁R, respectively. Least expressed P2Y₂R was 40-fold lower than P2Y₁R, and P2Y₆R and P2Y₁₄R were ≤50 % of P2Y₁R. None of the native P2YR agonists alone induced β-hexosaminidase (β-Hex) release, but some nucleotides significantly enhanced β-Hex release induced by C3a or antigen, with a rank efficacy order of ATP > UDPG ≥ ADP >> UDP, UTP. Although P2Y₁₁R and P2Y₄R are highly expressed, they did not seem to play a major role in degranulation as neither P2Y₄R agonist UTP nor P2Y₁₁R agonists ATPγS and NF546 had a substantial effect. P2Y₁R-selective agonist MRS2365 enhanced degranulation, but ~1,000-fold weaker compared to its P2Y₁R potency, and the effect of P2Y₆R agonist 3-phenacyl-UDP was negligible. The enhancement by ADP and ATP appears mediated via multiple receptors. Both UDPG and a synthetic agonist of the P2Y₁₄R, MRS2690, enhanced C3a-induced β-Hex release, which was inhibited by a P2Y₁₄R antagonist, specific P2Y₁₄R siRNA and pertussis toxin, suggesting a role of P2Y₁₄R activation in promoting human mast cell degranulation.     

P2Y12 deficiency in mouse impairs noradrenergic system in brain,and alters anxiety‐like neurobehavior and memory

Purinergic receptor P2Y₁₂ (P2Y₁₂), a G protein‐coupled purinergic receptor, is widely distributed in nervous system and involved in the progression of neurological diseases such as multiple sclerosis and neuropathic pain. The central noradrenergic system actively participates in a number of neurophysiological processes. Nevertheless, whether there is any direct relevance between P2Y₁₂ and noradrenergic signal transduction remains unknown. In the present study, we tested the hypothesis that lack of P2Y₁₂ impaired noradrenergic signal transduction in mouse brain. Our results showed that P2Y₁₂ knockout (KO) mice exhibited increased anxiety‐like behavior in the open‐field test (OFT) and elevated plus maze test and displayed deficits in memory in the radial‐arm maze test (RAMT) and Morris water maze test (MWMT). They also exhibited reduced locomotion in the OFT and MWMT. Moreover, loss of P2Y₁₂ decreased the level of noradrenaline and the expression of noradrenergic α receptors, subtypes α2 (ARα2b) in mouse cerebellum and hippocampus. Meanwhile, it hampered the protein kinase A (PKA)/cAMP response element‐binding protein (CREB)/brain‐derived neurotrophic factor (BDNF) signaling pathway in these brain regions. Taken together, our results showed for the first time that P2Y₁₂ KO altered the anxiety, memory and locomotion of mice, which was closely associated with abnormal state of noradrenergic system in the brain. The findings implicate that P2Y₁₂ plays an indispensable role in noradrenergic signal transduction; its deficit is insufficient to limit anxiety responses or supports cognitive performance and activity.     

P2Y1R and P2Y2R: potential molecular triggers in muscle regeneration

Muscle regeneration is indispensable for skeletal muscle health and daily life when injury, muscular disease, and aging occur. Among the muscle regeneration, muscle stem cells’ (MuSCs) activation, proliferation, and differentiation play a key role in muscle regeneration. Purines bind to its specific receptors during muscle development, which transmit environmental stimuli and play a crucial role of modulator of muscle regeneration. Evidences proved P2R expression during development and regeneration of skeletal muscle, both in human and mouse. In contrast to P2XR, which have been extensively investigated in skeletal muscles, the knowledge of P2YR in this tissue is less comprehensive. This review summarized muscle regeneration via P2Y1R and P2Y2R and speculated that P2Y1R and P2Y2R might be potential molecular triggers for MuSCs’ activation and proliferation via the p-ERK1/2 and PLC pathways, explored their cascade effects on skeletal muscle, and proposed P2Y1/2 receptors as potential pharmacological targets in muscle regeneration, to advance the purinergic signaling within muscle and provide promising strategies for alleviating muscular disease.     

Developmental expression of metabotropic P2Y(1) and P2Y(2) receptors in freshly isolated astrocytes from rat hippocampus

There are at least three subtypes of cloned metabotropic P2 receptors linked to intracellular Ca(2+) rises in rat brain cells, namely, P2Y(1), P2Y(2) and P2Y(4). In this study we explore the subtypes of the metabotropic P2 receptors seen in freshly isolated astrocytes (FIAs) from P8-P25 rats. We found by single cell RT-PCR that in process-bearing FIAs from hippocampi of P8-P12 rats, 31% of the glial fibrillary acidic protein (GFAP) mRNA (+) cells expressed P2Y(1) mRNA while only 5% of the cells tested expressed P2Y(2) mRNA. The expression of P2Y(1) receptor mRNA was not changed in FIAs from the hippocampi of P18-P25 rats, but 38% of the GFAP mRNA (+) cells in the P18-P25 age group then showed P2Y(2) mRNA. We also studied whether the mRNA was expressing functional receptor protein by measuring Ca(2+) responses to specific agonists for P2Y(1) and P2Y(2). We found that similar proportions of GFAP mRNA (+) FIAs responded to ATP or UTP as showed mRNAs for P2Y (1) and P2Y(2,) respectively. Total tissue RNA from P9 and P24 rat hippocampus showed a 2.8-fold increase in P2Y(2) mRNA levels from P9 to P24 with a decrease in P2Y(1) mRNA. Thus, this study shows a marked up-regulation of mRNA for P2Y(2) from 9 to 24 days in rat hippocampus, and some of this increase is likely due to the protoplasmic astrocytes which is being translated into functional receptor protein in these cells.     

Molecular Insights into Rab7‐Mediated Endosomal Recruitment of Core Retromer: Deciphering the Role of Vps26 and Vps35

Retromer, a peripheral membrane protein complex, plays an instrumental role in host of cellular processes by its ability to recycle receptors from endosomes to the trans‐Golgi network. It consists of two distinct sub‐complexes, a membrane recognizing, sorting nexins (SNX) complex and a cargo recognition, vacuolar protein sorting (Vps) complex. Small GTPase, Rab7 is known to recruit retromer on endosomal membrane via interactions with the Vps sub‐complex. The molecular mechanism underlying the recruitment process including the role of individual Vps proteins is yet to be deciphered. In this study, we developed a FRET‐based assay in HeLa cells that demonstrated the interaction of Rab7 with Vps35 and Vps26 in vivo. Furthermore, we showed that Rab7 recruits retromer to late endosomes via direct interactions with N‐terminal conserved regions in Vps35. However, the single point mutation, which disrupts the interaction between Vps35 and Vps26, perturbed the Rab7‐mediated recruitment of retromer in HeLa cells. Using biophysical measurements, we demonstrate that the association of Vps26 with Vps35 resulted in high affinity binding between the Vps sub‐complex and the activated Rab7 suggesting for a possible allosteric role of Vps26. Thus, this study provides molecular insights into the essential role of Vps26 and Vps35 in Rab7‐mediated recruitment of the core retromer complex.      

G-protein coupled purinergic P2Y12 receptor interacts and internalizes TauRD-mediated by membrane-associated actin cytoskeleton remodeling in microglia

In Alzheimer’s disease, the microtubule-associated protein, Tau misfolds to form aggregates and filaments in the intra- and extracellular region of neuronal cells. Microglial cells are the resident brain macrophage cells involved in constant surveillance and activated by the extracellular deposits. Purinergic receptors are involved in the chemotactic migration of microglial cells towards the site of inflammation. From our recent study, we have observed that the microglial P2Y12 receptor is involved in phagocytosis of full-length Tau species such as monomers, oligomers and aggregates by actin-driven chemotaxis. This study shows the interaction of repeat-domain of Tau (Tau^RD) with the microglial P2Y12 receptor and the corresponding residues for interaction have been analysed by various in-silico approaches. In the cellular studies, Tau^RD was found to interact with microglial P2Y12R and induces its cellular expression confirmed by co-immunoprecipitation and western blot analysis. Furthermore, the P2Y12R-mediated Tau^RD internalization has demonstrated activation of microglia with an increase in the Iba1 level, and Tau^RD becomes accumulated at the peri-nuclear region for the degradation. Similarly, immunofluorescence microscopic studies emphasized that Tau^RD is phagocytosed by microglial P2Y12R via the membrane-associated actin remodeling as filopodia extension. Upon internalization, we have demonstrated the P2Y12R signaling-mediated degradation of accumulated Tau^RD by lysosomal pathway. Altogether, microglial P2Y12R interacts with Tau^RD and mediates directed migration and activation for its internalization and degradation.     

Autoregulation in PC12 cells via P2Y receptors: Evidence for non-exocytotic nucleotide release from neuroendocrine cells

Nucleotides are released not only from neurons, but also from various other types of cells including fibroblasts, epithelial, endothelial and glial cells. While ATP release from non-neural cells is frequently Ca²⁺ independent and mostly non-vesicular, neuronal ATP release is generally believed to occur via exocytosis. To evaluate whether nucleotide release from neuroendocrine cells might involve a non-vesicular component, the autocrine/paracrine activation of P2Y₁₂ receptors was used as a biosensor for nucleotide release from PC12 cells. Expression of a plasmid coding for the botulinum toxin C1 light chain led to a decrease in syntaxin 1 detected in immunoblots of PC12 membranes. In parallel, spontaneous as well as depolarization-evoked release of previously incorporated [³H]noradrenaline from transfected cells was significantly reduced in comparison with the release from untransfected cells, thus indicating that exocytosis was impaired. In PC12 cells expressing the botulinum toxin C1 light chain, ADP reduced cyclic AMP synthesis to the same extent as in non-transfected cells. Likewise, the enhancement of cyclic AMP synthesis either due to the blockade of P2Y₁₂ receptors or due to the degradation of extracellular neucleotides by apyrase was not different between non-transfected and botulinum toxin C1 light chain expressing cells. However, the inhibition of cyclic AMP synthesis caused by depolarization-evoked release of endogenous nucleotides was either abolished or greatly reduced in cells expressing the botulinum toxin C1 light chain. Together, these results show that spontaneous nucleotide release from neuroendocrine cells may occur independently of vesicle exocytosis, whereas depolarization-evoked nucleotide release relies predominantly on exocytotic mechanisms.     

Construction of hypothetical three-dimensional structure of P2Y1 receptor based on Fourier transform analysis

G protein-coupled receptors constitute a large family of homologous transmembrane proteins that represents one of the most important classes of confirmed drug targets. For novel drug discovery, the 3D structure of target protein is indispensable. To construct hypothetical 3D structures of G protein-coupled receptors, several prediction methods have been proposed. But none of the them has confirmed a correct ligand binding site. In this study we constructed the 3D structure of bovine rhodopsin using the prediction method proposed by Donnelly et al., with some modification. We found that our 3D model showed a good agreement with the reported retinal binding site. Using the similar method, we constructed the 3D structure of the P2Y₁ receptor; one of the G protein-coupled receptors, and showed a binding site of an endogenous ligand, ADP, on the basis of the 3D model and in vitro experimental data. These results should be valuable for design of a specific antagonist for P2Y₁ receptor.     

Neuroprotective roles of the P2Y2 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.     

周围神经损伤中P2Y12受体-p38MAPK通路的研究进展

周围神经损伤是临床中常见的神经损伤之一,神经胶质细胞和信号通路转导在周围神经损伤和再生修复中发挥重要作用。小胶质细胞的活化与周围神经损伤导致的神经损伤及疼痛密切相关,小胶质细胞是周围神经损伤与修复的关键场所。脊髓背角的小胶质细胞可被嘌呤信号通路的P2Y_(12)受体活化,进而导致p38MAPK磷酸化,造成相关神经损伤及感觉功能障碍。以脊髓背角的小胶质细胞为靶点,从P2Y_(12)受体-p38MAPK通路的角度可揭示周围神经损伤的部分可能机制。探究从嘌呤信号通路与小胶质细胞活化的新角度,将神经损伤后的P2Y_(12)受体与p38MAPK的磷酸化表达联系为P2Y_(12)受体-p38MAPK通路,可为临床治疗周围神经损伤提供新的思路。本文就周围神经损伤中P2Y_(12)受体-p38MAPK通路的研究进展作一综述。     

Alanine‐(87)‐threonine polymorphism impairs signaling and internalization of the human P2Y11 receptor,when co‐expressed with the P2Y1 receptor

The P2Y₁₁ nucleotide receptor detects high extracellular ATP concentrations. Mutations of the human P2RY₁₁ gene can play a role in brain autoimmune responses, and the P2Y₁₁ receptor alanine‐87‐threonine (A87T) polymorphism has been suggested to affect immune‐system functions. We investigated receptor functionality of the P2Y₁₁A87T mutant using HEK293 and 1321N1 astrocytoma cells. In HEK293 cells, the P2Y₁₁ receptor agonist 3′‐O‐(4‐benzoylbenzoyl)adenosine 5′‐triphosphate (BzATP) was completely inactive in evoking intracellular calcium release while the potency of ATP was reduced. ATP was also less potent in triggering cAMP generation. However, 1321N1 astrocytoma cells, which lack any endogenous P2Y₁ receptors, did not display a reduction. Only when 1321N1 cells were co‐transfected with P2Y₁₁A87T and P2Y₁ receptors, the calcium responses to the P2Y₁₁ receptor‐specific agonist BzATP were reduced. It is already known that P2Y₁ and P2Y₁₁ receptors interact. We thus conclude that the physiological impact of A87T mutation of the P2Y₁₁ receptor derives from detrimental effects on P2Y₁–P2Y₁₁ receptor interaction. We additionally investigated alanine‐87‐serine and alanine‐87‐tyrosine P2Y₁₁ receptor mutants. Both mutations rescue the response to BzATP in HEK293 cells, thus ruling out polarity of amino acid‐87 to be the molecular basis for altered receptor characteristics. We further found that the P2Y₁₁A87T receptor shows complete loss of nucleotide‐induced internalization in HEK293 cells. Thus, we demonstrate impaired signaling of the P2Y₁₁ A87T‐mutated receptors when co‐operating with P2Y₁ receptors.