The P2Y(2) nucleotide receptor mediates tissue factor expression in human coronary artery endothelial cells

How selective antagonists and genetic modification have helped characterise the expression and functions of vascular P2Y receptors

Vascular P2Y receptors mediate many effects, but the role of individual subtypes is often unclear. Here we discuss how subtype-selective antagonists and receptor knockout/knockdown have helped identify these roles in numerous species and vessels. P2Y1 receptor-mediated vasoconstriction and endothelium-dependent vasodilation have been characterised using the selective antagonists, MRS2179 and MRS2216, whilst AR-C118925XX, a P2Y2 receptor antagonist, reduced endothelium-dependent relaxation, and signalling evoked by UTP or fluid shear stress. P2Y2 receptor knockdown reduced endothelial signalling and endothelial P2Y2 receptor knockout produced hypertensive mice and abolished vasodilation elicited by an increase in flow. UTP-evoked vasoconstriction was also blocked by AR-C118925XX, but the effects of P2Y2 receptor knockout were complex. No P2Y4 receptor antagonists are available and P2Y4 knockout did not affect the vascular actions of UTP and UDP. The P2Y6 receptor antagonist, MRS2578, identified endothelial P2Y6 receptors mediating vasodilation, but receptor knockout had complex effects. MRS2578 also inhibited, and P2Y6 knockout abolished, contractions evoked by UDP. P2Y6 receptors contribute to the myogenic tone induced by a stepped increase in vascular perfusion pressure and possibly to the development of atherosclerosis. The P2Y11 receptor antagonists, NF157 and NF340, inhibited ATP-evoked signalling in human endothelial cells. Vasoconstriction mediated by P2Y12/P2Y13 and P2Y14 receptors was characterised using the antagonists, cangrelor, ticagrelor, AR-C67085 and MRS2211 or PPTN respectively. This has yet to be backed up by receptor knockout experiments. Thus, subtype-selective antagonists and receptor knockout/knockdown have helped identify which P2Y subtypes are functionally expressed in vascular smooth muscle and endothelial cells and the effects that they mediate.

Cytokine storm in human monkeypox: A possible involvement of purinergic signaling

Some evidence has indicated that monkeypox can induce a cytokine storm. Purinergic signaling is a cell pathway related to the cytokine storm. However, the precise mechanisms that lead to cytokine storms in monkeypox infections and the possible involvement of purinergic signaling in the immune response to this virus remain unknown. In this review article, we aimed to highlight a body of scientific evidence that consolidates the role of the cytokine storm in monkeypox infection and proposes a new hypothesis regarding the roles of purinergic signaling in this immune-mediated mechanism. We further suggested some purinergic signaling modulators to mitigate the deleterious and aggravating effects of immune dysregulation in human monkeypox virus infection by inhibiting P2X3, P2X7, P2Y2, and P2Y12, reducing inflammation, and activating A1 and A2A receptors to promote an anti-inflammatory response.

The P2Y2 receptor mediates terminal adipocyte differentiation and insulin resistance: Evidence for a dual G-protein coupling mode

Several P2Y nucleotide receptors have been shown to be involved in the early stage of adipocyte differentiation in vitro and insulin resistance in obese mice; however, the exact receptor subtype(s) and its underlying molecular mechanism in relevant human cells are unclear. Here, using human primary visceral preadipocytes as a model, we found that during preadipocyte-to-mature adipocyte differentiation, the P2Y2 nucleotide receptor (P2Y2R) was the most upregulated subtype among the eight known P2Y receptors and the only one further dramatically upregulated after inflammatory TNFα treatment. Functional studies indicated that the P2Y2R induced intracellular Ca2+, ERK1/2, and JNK signaling but not the p38 pathway. In addition, stimulation of the P2Y2R suppressed basal and insulin-induced phosphorylation of AKT, accompanied by decreased GLUT4 membrane translocation and glucose uptake in mature adipocytes, suggesting a role of P2Y2R in insulin resistance. Mechanistically, we found that activation of P2Y2R did not increase lipolysis but suppressed PIP3 generation. Interestingly, activation of P2Y2R triggered Gi-protein coupling, and pertussis toxin pretreatment largely inhibited P2Y2R-mediated ERK1/2 signaling and cAMP suppression. Further, treatment of the cells with AR-C 118925XX, a selective P2Y2R antagonist, significantly inhibited adipogenesis, and P2Y2R knockout decreased mouse body weight gain with smaller eWAT mass infiltrated with fewer macrophages as compared to WT mice in response to a Western diet. Thus, we revealed that terminal adipocyte differentiation and inflammation selectively upregulate P2Y2R expression and that P2Y2R mediates insulin resistance by suppressing the AKT signaling pathway, highlighting P2Y2R as a potential new drug target to combat obesity and type-2 diabetes.

P2Y2-P2X7 receptors cross-talk in primed mesenteric endothelial cells upregulates NF-κB signaling favoring mononuclear cell adhesion in schistosomiasis

Schistosomiasis is an intravascular infectious disease that impacts over 200 million people globally. In its chronic stage, it leads to mesenteric inflammation with significant involvement of monocytes/macrophages. Endothelial cells lining the vessel lumens play a crucial role, and mount of evidence links this disease to a downregulation of endoprotective cell signaling favoring a primed and proinflammatory endothelial cell phenotype and therefore the loss of immunovascular homeostasis. One hallmark of infectious and inflammatory conditions is the release of nucleotides into the extracellular milieu, which, in turn, act as innate messengers, activating purinergic receptors and triggering cell-to-cell communication. ATP influences the progression of various diseases through P2X and P2Y purinergic receptor subtypes. Among these receptors, P2Y2 (P2Y2R) and P2X7 (P2X7R) receptors stand out, known for their roles in inflammation. However, their specific role in schistosomiasis has remained largely unexplored. Therefore, we hypothesized that endothelial P2Y2R and P2X7R could contribute to monocyte adhesion to mesenteric endothelial cells in schistosomiasis. Using a preclinical murine model of schistosomiasis associated with endothelial dysfunction and age-matched control mice, we showed that endothelial P2Y2R and P2X7R activation increased monocyte adhesion to cultured primary endothelial cells in both groups. However, a distinct upregulation of endothelial P2Y2R-driven canonical Ca2+ signaling was observed in the infected group, amplifying adhesion. In the control group, the coactivation of endothelial P2Y2R and P2X7R did not alter the maximal monocyte adhesion induced by each receptor individually. However, in the infected group, this coactivation induced a distinct upregulation of P2Y2R-P2X7R-driven canonical signaling, IL-1β release, and VCAM-1 expression, with underlying mechanisms involving inflammasome and NF-κB signaling. Therefore, current data suggest that schistosomiasis alters endothelial cell P2Y2R/P2X7R signaling during inflammation. These discoveries advance our understanding of schistosomiasis. This intricate interplay, driven by PAMP-triggered endothelial P2Y2R/P2X7R cross-talk, emerges as a potential key player in the mesenteric inflammation during schistosomiasis.

A purinergic mechanism underlying metformin regulation of hyperglycemia

Metformin, created in 1922, has been the first-line therapy for treating type 2 diabetes mellitus for almost 70 years; however, its mechanism of action remains controversial, partly because most prior studies used supratherapeutic concentrations exceeding 1 mM despite therapeutical blood concentrations of metformin being less than 40 μM. Here we report metformin, at 10-30 μM, blocks high glucose-stimulated ATP secretion from hepatocytes mediating its antihyperglycemic action. Following glucose administration, mice demonstrate increased circulating ATP, which is prevented by metformin. Extracellular ATP through P2Y₂ receptors (P2Y₂R) suppresses PIP₃ production, compromising insulin-induced AKT activation while promoting hepatic glucose production. Furthermore, metformin-dependent improvements in glucose tolerance are abolished in P2Y₂R-null mice. Thus, removing the target of extracellular ATP, P2Y₂R, mimics the effects of metformin, revealing a new purinergic antidiabetic mechanism for metformin. Besides unraveling long-standing questions in purinergic control of glucose homeostasis, our findings provide new insights into the pleiotropic actions of metformin.

Macrophages M2 polarization is involved in lapatinib-mediated chemopreventive effects in the lung cancer

M2 polarized tumor-associated macrophages (TAMs) have a multifunctional role in cancer initiation, progression, metastasis, and contribute to chemotherapeutic resistance. Therefore, identifying M2 polarized TAMs is a potential target for cancer therapeutic intervention. The underlying mechanism that target the TAMs M2 polarized macrophages remains primarily uncharacterized; however, only a few compounds have been identified that inhibit TAMs M2 polarized macrophages. In this research, we investigated that lapatinib could effectively suppress the expression of IL^_13-induced M2 polarized macrophages surface markers i.e., CD163 and CD206, and downregulation of M2 genes such as Fizz1, Mrc1, Arg1, IL-10, Ym1, nd CCL2 in vitro. Moreover, lapatinib abrogated the M2 polarized macrophage-mediated cancer cells invasion and migration. Mechanistically, in our study, lapatinib inhibited IL-13 triggered STAT6 phosphorylation. Furthermore, in LLCs tumor model, lapatinib significantly reduced tumorigenesis, followed by the downregulation of percentages of M2 marker CD206⁺ and CD68⁺ in the tumor. This downregulation correlates with chemopreventive effect of lapatinib. All taken together, these results demonstrated that lapatinib effectively prevents the macrophage M2 polarization and indicates a potential mechanism for preventing the tumor growth via M2 polarized polarization intervention.

Interleukin-1β Induces Tissue Factor Expression in A549 Cells via EGFR-Dependent and -Independent Mechanisms

Tissue factor (TF) plays an important role in the progression and angiogenesis of tumor cells. The present study investigated the mechanism of interleukin-1β (IL-1β)-induced TF expression in A549 lung cancer cells. Based on mRNA and protein analyses, including appropriate inhibitor experiments, IL-1β was shown to induce TF expression in a time-dependent manner, mediated by IL-1 receptor-dependent phosphorylation of the mitogen-activated protein kinases (MAPK) p38, p42/44 and c-jun N-terminal kinase (JNK), as well as the Src kinase and the epidermal growth factor receptor (EGFR). Thereby, inhibition of EGFR transactivation by the Src inhibitor PP1 or direct EGFR inhibition by the EGFR tyrosine kinase inhibitor (TKI) erlotinib led to a reduction of IL-1β-induced TF expression and to a suppression of p42/44 MAPK and EGFR activation, while IL-1β-induced p38 MAPK and JNK activation remained unchanged. A knockdown of EGFR by siRNA was associated with decreased IL-1β-mediated p42/44 MAPK activation, which was no longer inhibitable by erlotinib. Concentration-dependent inhibition of IL-1β-induced TF expression was also observed in the presence of gefitinib and afatinib, two other EGFR TKIs. In summary, our results suggest that IL-1β leads to increased TF formation in lung cancer cells via both Src/EGFR/p42/44 MAPK-dependent and EGFR-independent signaling pathways, with the latter mediated via p38 MAPK and JNK.

Purinergic Signaling in Controlling Macrophage and T Cell Functions During Atherosclerosis Development

Atherosclerosis is a hardening and narrowing of arteries causing a reduction of blood flow. It is a leading cause of death in industrialized countries as it causes heart attacks, strokes, and peripheral vascular disease. Pathogenesis of the atherosclerotic lesion (atheroma) relies on the accumulation of cholesterol-containing low-density lipoproteins (LDL) and on changes of artery endothelium that becomes adhesive for monocytes and lymphocytes. Immunomediated inflammatory response stimulated by lipoprotein oxidation, cytokine secretion and release of pro-inflammatory mediators, worsens the pathological context by amplifying tissue damage to the arterial lining and increasing flow-limiting stenosis. Formation of thrombi upon rupture of the endothelium and the fibrous cup may also occur, triggering thrombosis often threatening the patient’s life. Purinergic signaling, i.e., cell responses induced by stimulation of P2 and P1 membrane receptors for the extracellular nucleotides (ATP, ADP, UTP, and UDP) and nucleosides (adenosine), has been implicated in modulating the immunological response in atherosclerotic cardiovascular disease. In this review we will describe advancements in the understanding of purinergic modulation of the two main immune cells involved in atherogenesis, i.e., monocytes/macrophages and T lymphocytes, highlighting modulation of pro- and anti-atherosclerotic mediated responses of purinergic signaling in these cells and providing new insights to point out their potential clinical significance.

P2 purinergic receptor signaling and interleukin-1 synergistically induce interleukin-6 production in a human oral squamous carcinoma cell line

OBJECTIVES

The aim of this study was to investigate the inflammatory roles of P2 purinergic receptor (P2R) signaling in oral squamous cell carcinoma (OSCC).

METHODS

Human OSCC cell lines HSC-2, Ca9-22, and HO-1-u-1 were stimulated with P2R agonists. The concentration of interleukin (IL)-6 in culture supernatants was measured using an enzyme-linked immune sorbent assay. Expression levels of messenger RNAs (mRNAs) were analyzed using reverse transcription polymerase chain reaction. Phosphorylation of intracellular signaling molecules was analyzed using western blotting.

RESULTS

HSC-2 cells expressed the mRNAs for P2X4-6 and all P2YRs. ATP or ADP induced significantly greater production of IL-6 by HSC-2 cells. Ca9-22 cells expressed mRNAs for P2X4-6 and all P2YRs except P2Y4. ATP or ADP induced the production of IL-6 by Ca9-22 cells, but the IL-6 concentration was much lower than that in HSC-2 cells. Although HO-1-u-1 cells expressed the mRNAs for P2X4-6 and all P2YRs, ATP or ADP did not induce IL-6 production. The production of IL-6 by HSC-2 cells stimulated with adenine nucleotides was significantly inhibited by P2R antagonists and a p38 mitogen-activated protein kinase inhibitor, but not by extracellular signal-related kinase or c-Jun N-terminal kinase inhibitors. The proinflammatory cytokine IL-1 significantly augmented P2R-induced IL-6 production by HSC-2 cells via the nuclear factor-κB signaling pathway.

CONCLUSIONS

The present study suggests that P2Rs signaling and IL-1 synergistically induce chronic inflammation in OSCC. Because chronic inflammation is a well-known driving force of tumor progression, these results support therapeutic strategies that target P2Rs signaling in OSCC.

Functional evidence for biased inhibition of G protein signaling by YM-254890 in human coronary artery endothelial cells

Small molecular chemicals targeting individual subtype of G proteins including Gs, Gi/o and Gq has been lacking, except for pertussis toxin being an established selective peptide inhibitor of the Gi/o protein. Recently, a cyclic depsipeptide compound YM-254890 isolated from culture broth of Chromobacterium sp. was reported as a selective inhibitor for the Gq protein by blocking GDP exchange of GTP on the α subunit of Gq complex. However, functional selectivity of YM-254890 towards various G proteins was not fully characterized, primarily due to its restricted availability before 2017. Here, using human coronary artery endothelial cells as a model, we performed a systemic pharmacological evaluation on the functional selectivity of YM-254890 on multiple G protein-mediated receptor signaling. First, we confirmed that YM-254890, at 30 nM, abolished UTP-activated P2Y₂ receptor-mediated Ca²⁺ signaling and ERK1/2 phosphorylation, indicating its potent inhibition on the Gq protein. However, we unexpectedly found that YM-254890 also significantly suppressed cAMP elevation and ERK1/2 phosphorylation induced by multiple Gs-coupled receptors including β₂-adrenegic, adenosine A₂ and PGI₂ receptors. Surprisingly, although YM-254890 had no impact on CXCR4/Gi/o protein-mediated suppression of cAMP production, it abolished ERK1/2 activation. Further, no cellular toxicity was observed for YM-254890, and it neither affected A23187- or thapsigargin-induced Ca²⁺ signaling, nor forskolin-induced cAMP elevation and growth factor-induced MAPK signaling. We conclude that YM-254890 is not a selective inhibitor for Gq protein; instead, it acts as a broad-spectrum inhibitor for Gq and Gs proteins and exhibits a biased inhibition on Gi/o signaling, without affecting non-GPCR-mediated cellular signaling.

P2Y Purinergic Receptors, Endothelial Dysfunction, and Cardiovascular Diseases

Purinergic G-protein-coupled receptors are ancient and the most abundant group of G-protein-coupled receptors (GPCRs). The wide distribution of purinergic receptors in the cardiovascular system, together with the expression of multiple receptor subtypes in endothelial cells (ECs) and other vascular cells demonstrates the physiological importance of the purinergic signaling system in the regulation of the cardiovascular system. This review discusses the contribution of purinergic P2Y receptors to endothelial dysfunction (ED) in numerous cardiovascular diseases (CVDs). Endothelial dysfunction can be defined as a shift from a “calm” or non-activated state, characterized by low permeability, anti-thrombotic, and anti-inflammatory properties, to a “activated” state, characterized by vasoconstriction and increased permeability, pro-thrombotic, and pro-inflammatory properties. This state of ED is observed in many diseases, including atherosclerosis, diabetes, hypertension, metabolic syndrome, sepsis, and pulmonary hypertension. Herein, we review the recent advances in P2Y receptor physiology and emphasize some of their unique signaling features in pulmonary endothelial cells.

Signaling Through Purinergic Receptor P2Y2 Enhances Macrophage IL-1β Production

The release of nucleotides during necrosis or apoptosis has been described to have both proinflammatory and anti-inflammatory effect on the surrounding cells. Here we describe how low concentrations of UTP and ATP applied during macrophage priming enhance IL-1β production when subsequently the NLRP3 inflammasome is activated in murine resident peritoneal macrophages. Deficiency or pharmacological inhibition of the purinergic receptor P2Y₂ reverted the increase of IL-1β release induced by nucleotides. IL-1β increase was found dependent on the expression of Il1b gene and probably involving JNK activity. On the contrary, nucleotides decreased the production of a different proinflammatory cytokines such as TNF-α. These results suggest that nucleotides could shape the response of macrophages to obtain a unique proinflammatory signature that might be relevant in unrevealing specific inflammatory conditions.

Understanding Inflammatory Responses in the Manifestation of Prothrombotic Phenotypes

Inflammasome complex is a multimeric protein comprising of upstream sensor protein of nucleotide-binding oligomerization domain (NOD)-like receptor family. It has an adaptor protein apoptosis-associated speck-like protein and downstream effector cysteine protease procaspase-1. Activation of inflammasome complex is body’s innate response to pathogen attack but its abnormal activation results in many inflammatory and cardiovascular disorders including thrombosis. It has displayed a prominent role in the clot formation advocating an interplay between inflammation and coagulation cascades. Therefore, elucidation of inflammasome and its molecular mechanisms in the manifestation of prothrombotic phenotypes becomes pertinent. Thrombosis is the formation and propagation of blood clot in the arterial or venous system due to several interactions of vascular and immune factors. It is a prevalent pathology underlying disorders like venous thromboembolism, stroke and acute coronary syndrome; thus, making thrombosis, a major contributor to the global disease burden. Recently studies have established a strong connection of inflammatory processes with this blood coagulation disorder. The hemostatic balance in thrombosis gets altered by the inflammatory mechanisms resulting in endothelial and platelet activation that subsequently increases secretion of several prothrombotic and antifibrinolytic factors. The upregulation of these factors is the critical event in the pathogenesis of thrombosis. Among various inflammasome, nucleotide-binding domain, leucine-rich-containing family, pyrin domain containing 3 (NLRP3) is one of the best-studied sterile inflammasome strengthening a link between inflammation and coagulation in thrombosis. NLRP3 activation results in the catalytic conversion of procaspase-1 to active caspase-1, which facilitate the maturation of interleukin-1β (IL-1β) and interleukin-18. These cytokines are responsible for immune cells activation critical for immune responses. These responses further results in endothelial and platelet activation and aggregation. However, the exact molecular mechanism related to the pathogenesis of thrombosis is still elusive. There have been several reports that demonstrate Tissue factor (TF)-mediated signaling in the production of pro-inflammatory cytokines enhancing inflammation by activating protease-activated receptors on various cells, which lead to additional cytokine expression. Therefore, it would be illuminating to interpret the inflammasomes regulation in coagulation and inflammation. This review, thus, tries to comprehensively compile emerging regulatory roles of the inflammasomes in thrombosis and discusses their molecular pathways in the manifestation of thrombotic phenotypes.

Stimulation of murine P2Y11-like purinoreceptor protects against hypoxia/reoxygenation injury and decreases heart graft rejection lesions

OBJECTIVE

Myocardial ischemia reperfusion is a major cause of cell injury during cardiac transplantation and is responsible for increased graft rejection. Several in vitro studies demonstrated the protective effect of P2Y11-like purinoreceptor stimulation in the context of myocardial ischemia/reperfusion. In this study, we hypothesized a possible cardioprotective role of P2Y11R stimulation against ischemia/reperfusion lesions and validated its clinical effect in vivo in a heart transplantation model.

METHODS

We subjected H9c2 rat cardiomyocyte-derived cell line to 5 hours of hypoxia and 1 hour of reoxygenation. P2Y11R selective agonist NF546 and antagonist NF340 were added at the onset of reoxygenation. Cell injuries were assessed by microculture tetrazolium reduction and intracellular adenosine triphosphate level. Clinical effect of P2Y11R stimulation was further investigated in vivo. Hearts from BALB/c mice were transplanted intra-abdominally into allogenic C57BL/6 mice (n = 104). Recipient mice were injected with P2Y11R agonist. Mice in the sham group were injected with saline solution. In the control group, hearts from C57BL/6 were transplanted into syngeneic C57BL/6 mice. Rejection lesions were investigated using histology and immunohistochemistry at days 3, 5, and 7 after transplantation. We measured caspase activities to quantify apoptosis. Production of proinflammatory and anti-inflammatory cytokines was investigated.

RESULTS

P2Y11R stimulation at the onset of reoxygenation significantly reduced in vitro hypoxia/reoxygenation injuries. This protection was suppressed with P2Y11R antagonist. In vivo, cardiac allograft survival was significantly prolonged after P2Y11R stimulation. Rejection lesions, classified according to the International Society of Heart Lung Transplantation guidelines and quantified using the mean number of inflammatory cells per field, were significantly reduced in the treated group. At day 5 after transplantation, P2Y11R agonist pretreated allografts also demonstrated less apoptotic lesions.

CONCLUSIONS

Our data suggest a novel cardioprotective role of P2Y11R at the onset of reoxygenation/reperfusion against reperfusion injuries. Pharmacologic conditioning using P2Y11 agonist may be beneficial after cardiac transplantation in improving myocardial ischemia/reperfusion outcomes and decreasing graft rejection lesions.

P2Y11 Receptors: Properties, Distribution and Functions

The P2Y₁₁ receptor is a G protein-coupled receptor that is stimulated by endogenous purine nucleotides, particularly ATP. Amongst P2Y receptors it has several unique properties; (1) it is the only human P2Y receptor gene that contains an intron in the coding sequence; (2) the gene does not appear to be present in the rodent genome; (3) it couples to stimulation of both phospholipase C and adenylyl cyclase. Its absence in mice and rats, along with a limited range of selective pharmacological tools, has hampered the development of our knowledge and understanding of its properties and functions. Nonetheless, through a combination of careful use of the available tools, suppression of receptor expression using siRNA and genetic screening for SNPs, possible functions of native P2Y₁₁ receptors have been identified in a variety of human cells and tissues. Many are in blood cells involved in inflammatory responses, consistent with extracellular ATP being a damage-associated signalling molecule in the immune system. Thus proposed potential therapeutic applications relate, in the main, to modulation of acute and chronic inflammatory responses.

Inhibition of interleukin-1β-induced endothelial tissue factor expression by the synthetic cannabinoid WIN 55,212-2

The role of cannabinoids in thrombosis remains controversial. In view of the primary importance of tissue factor (TF) in blood coagulation and its involvement in the pathology of several cardiovascular, inflammatory and neoplastic diseases, a regulation of this initial procoagulant signal seems to be of particular interest. Using human umbilical vein endothelial cells (HUVEC) the present study investigated the impact of the synthetic cannabinoid WIN 55,212-2 on interleukin (IL)-1β-induced TF expression and activity. WIN 55,212-2 caused a time- and concentration-dependent suppression of IL-1β-induced TF protein accompanied by decreases in TF mRNA and activity. Inhibition of TF protein expression by WIN 55,212-2 was mimicked by its cannabinoid receptor-inactive enantiomer WIN 55,212-3 but not by structurally unrelated phyto-, endo- and synthetic cannabinoids. In addition, the inhibitory effect of WIN 55,212-2 was not reversed by antagonists to cannabinoid receptors (CB₁, CB₂) or transient receptor potential vanilloid 1. Mechanistic approaches revealed WIN 55,212-2 to suppress IL-1β-induced TF expression via inhibition of ceramide formation and via decreased phosphorylation of p38 mitogen-activated protein kinase (MAPK) and c-Jun N-terminal kinases. Further inhibitor experiments demonstrated neutral sphingomyelinase (nSMase) to confer ceramide generation upon IL-1β treatment with the parallel IL-1β-mediated activation of MAPKs occurring via an nSMase-independent pathway. Finally, a receptor-independent inhibition of IL-1β-induced TF protein by WIN 55,212-2 was confirmed in human blood monocytes. Collectively, this data provide a hitherto unknown receptor-independent anticoagulatory action of the cannabinoid WIN 55,212-2.

Gefitinib inhibits M2-like polarization of tumor-associated macrophages in Lewis lung cancer by targeting the STAT6 signaling pathway

M2-like polarized tumor-associated macrophages (TAMs) play a pivotal role in promoting cancer cell growth, invasion, metastasis and angiogenesis. The identification of M2-like TAMs during tumor progression is an attractive approach for cancer therapy. In this study, we investigated the relevance of macrophage polarization and the antitumor effect of gefitinib in Lewis Lung cancer (LLC) in vitro and in vivo. Gefitinib at a concentration below 2.5 μmol/L did not cause significant growth inhibition on LLC and RAW 264.7 cell lines and bone marrow-derived macrophage (BMDMs). However, a small concentration of gefitinib (0.62 μmol/L) significantly inhibited IL-13-induced M2-like polarization of macrophages, evidenced by the decreased expression of the M2 surface markers CD206 and CD163, down-regulation of specific M2-marker genes (Mrc1, Ym1, Fizz1, Arg1, IL-10 and CCL2) as well as inhibition of M2-like macrophage-mediated invasion and migration of LLC cells. In RAW 264.7 cells, gefitinib inhibits IL-13-induced phosphorylation of STAT6, which was a crucial signaling pathway in macrophage M2-like polarization. In LLC mice metastasis model, oral administration of gefitinib (75 mg·kg^-1·d^-1, for 21 d) significantly reduced the number of lung metastasis nodules, down-regulated the expression of M2 marker genes and the percentages CD206⁺ and CD68⁺ macrophages in tumor tissues. These results demonstrated that gefitinib effectively inhibits M2-like polarization both in vitro and in vivo, revealing a novel potential mechanism for the chemopreventative effect of gefitinib.

Purinergic P2Y6 receptors: A new therapeutic target of age-dependent hypertension

Aging has a remarkable effect on cardiovascular homeostasis and it is known as the major non-modifiable risk factor in the development of hypertension. Medications targeting sympathetic nerve system and/or renin-angiotensin-aldosterone system are widely accepted as a powerful therapeutic strategy to improve hypertension, although the control rates remain unsatisfactory especially in the elder patients with hypertension. Purinergic receptors, activated by adenine, uridine nucleotides and nucleotide sugars, play pivotal roles in many biological processes, including platelet aggregation, neurotransmission and hormone release, and regulation of cardiovascular contractility. Since clopidogrel, a selective inhibitor of G protein-coupled purinergic P2Y₁₂ receptor (P2Y₁₂R), achieved clinical success as an anti-platelet drug, P2YRs has been attracted more attention as new therapeutic targets of cardiovascular diseases. We have revealed that UDP-responsive P2Y₆R promoted angiotensin type 1 receptor (AT1R)-stimulated vascular remodeling in mice, in an age-dependent manner. Moreover, the age-related formation of heterodimer between AT1R and P2Y₆R was disrupted by MRS2578, a P2Y₆R-selective inhibitor. These findings suggest that P2Y₆R is a therapeutic target to prevent age-related hypertension.

Metformin prevents cancer metastasis by inhibiting M2-like polarization of tumor associated macrophages

Accumulated evidence suggests that M2-like polarized tumor associated macrophages (TAMs) plays an important role in cancer progression and metastasis, establishing TAMs, especially M2-like TAMs as an appealing target for therapy intervention. Here we found that metformin significantly suppressed IL-13 induced M2-like polarization of macrophages, as illustrated by reduced expression of CD206, down-regulation of M2 marker mRNAs, and inhibition of M2-like macrophages promoted migration of cancer cells and endothelial cells. Metformin triggered AMPKα1 activation in macrophage and silencing of AMPKα1 partially abrogated the inhibitory effect of metformin in IL-13 induced M2-like polarization. Administration of AICAR, another activator of AMPK, also blocked the M2-like polarization of macrophages. Metformin greatly reduced the number of metastases of Lewis lung cancer without affecting tumor growth. In tumor tissues, the percentage of M2-like macrophage was decreased and the area of pericyte-coated vessels was increased. Further, the anti-metastatic effect of metformin was abolished when the animals were treated with macrophages eliminating agent clodronate liposome. These findings suggest that metformin is able to block the M2-like polarization of macrophages partially through AMPKα1, which plays an important role in metformin inhibited metastasis of Lewis lung cancer.

Current knowledge on the role of P2Y receptors in cardioprotection against ischemia-reperfusion

During ischemia, numerous effective endogenous extracellular mediators have been identified, particularly, nucleosides such as adenosine as well as purinergic and pyrimidinergic nucleotides. They may play important regulatory roles within the cardiovascular system and notably as cardio-protectants. Indeed, the distribution of the P2Y receptors in mammalian heart includes several cellular constituents relevant for the pathophysiology of myocardial ischemia. Beside the well-known cardioprotective effect of adenosine, the additional protective role of P2Y receptors has emerged. However, interpretation of experimental results may be sometimes perplexing. This is due to the variability of: the experimental models, the endpoints criteria, the chemical structure of agonist and antagonist ligands and their concentrations, the sequences of drug administration with respect to the model used (before and/or during and/or after ischemia). The net effect may be in the opposite direction after a transient or a prolonged stimulation. Nevertheless, the overall reading of published data highlights the beneficial role of the P2Y_2/4 receptor stimulation, the useful and synergistic role of P2Y_6/11 receptor activation and even of the P2Y₁₁ receptor alone in cardioprotection. More, the P2Y₁₁ receptor could be involved in counter-regulation of profibrotic processes. Paradoxically, transient P2X₇ receptor stimulation could contribute to the net cardioprotective effect of ATP. Recently, experimental data have shown that blocking the P2Y₁₂ receptor after ischemia confers cardioprotection independently of platelet antiaggregatory effect. This suggests for P2Y receptors an important role in primary prevention and as a therapeutic target in myocardial protection during ischemia and reperfusion.

A critical look at the function of the P2Y11 receptor

The P2Y11 receptor is a member of the purinergic receptor family. It has been overlooked, somewhat due to the lack of a P2ry11 gene orthologue in the murine genome, which prevents the generation of knockout mice, which have been so helpful for defining the roles of other P2Y receptors. Furthermore, some of the studies reported to date have methodological shortcomings, making it difficult to determine the function of P2Y11 with certainty. In this review, we discuss the lack of a murine "P2Y11-like receptor" and highlight the limitations of the currently available methods used to investigate the P2Y11 receptor. These methods include protein recognition with antibodies that show very little specificity, gene expression studies that completely overlook the existence of a fusion transcript between the adjacent PPAN gene and P2RY11, and agonists/antagonists reported to be specific for the P2Y11 receptor but which have not been tested for activity on numerous other adenosine 5'-triphosphate (ATP)-binding receptors. We suggest a set of criteria for evaluating whether a dataset describes effects mediated by the P2Y11 receptor. Following these criteria, we conclude that the current evidence suggests a role for P2Y11 in immune activation with cell type-specific effects.

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.

Yes-associated protein (YAP) signaling regulates lipopolysaccharide-induced tissue factor expression in human endothelial cells

BACKGROUND

Sepsis-induced acute lung injury (ALI) is characterized by fibrin deposition, which indicates the local activation of coagulation. Tissue factor (TF), expressed in the pulmonary microvasculature, acts as a critical initiator of blood coagulation and ALI in sepsis. The molecular mechanism of lipopolysaccharide (LPS)-induced TF expression in endothelial cells (ECs), however, has not been determined. In this study, we implicate the Rho-associated protein kinase (ROCK)/Yes associated protein (YAP)/early growth response (Egr-1) signaling pathway in LPS-induced TF expression in vitro and in sepsis-induced ALI in vivo.

METHODS

Human umbilical vein ECs incubated with LPS were pretreated with or without the ROCK inhibitor Y-27632, a YAP small, interfering RNA (siRNA) and an Egr-1 siRNA. ROCK, YAP and Egr-1 signaling-induced protein expression was investigated by Western blot. The LPS-induced activation of YAP was analyzed by an immunofluorescent assay. Furthermore, we intratracheally injected YAP siRNA to assess septic ALI in mice by hematoxylin and eosin staining.

RESULTS

LPS rapidly induced ROCK activation and increased TF expression in ECs. LPS caused YAP shuttling into the nuclei of ECs and combined with Egr-1 via the activation of ROCK. Furthermore, the LPS-mediated TF expression increase was prevented by ROCK inactivation, YAP knockdown and Egr-1 depletion, suggesting that LPS-induced TF expression is closely associated with the ROCK/YAP/Egr-1 signaling pathway in ECs. Finally, an intratracheal injection of YAP siRNA relieved lung injury in septic mice.

CONCLUSION

This study not only suggests that ROCK/YAP/Egr-1 signaling regulates TF expression after stimulation with LPS in ECs, but it also indicates that LPS-induced activation of YAP signaling plays an important role in septic ALI in mice. Our findings provide a new insight into the pathogenic mechanism of TF expression, which is closely linked to septic ALI, and YAP signaling is considered to be a novel target for therapeutic intervention under septic conditions.

Purinergic P2Y2 Receptor Control of Tissue Factor Transcription in Human Coronary Artery Endothelial Cells: NEW AP-1 TRANSCRIPTION FACTOR SITE AND NEGATIVE REGULATOR

We recently reported that the P2Y2 receptor (P2Y2R) is the predominant nucleotide receptor expressed in human coronary artery endothelial cells (HCAEC) and that P2Y2R activation by ATP or UTP induces dramatic up-regulation of tissue factor (TF), a key initiator of the coagulation cascade. However, the molecular mechanism of this P2Y2R-TF axis remains unclear. Here, we report the role of a newly identified AP-1 consensus sequence in the TF gene promoter and its original binding components in P2Y2R regulation of TF transcription. Using bioinformatics tools, we found that a novel AP-1 site at -1363 bp of the human TF promoter region is highly conserved across multiple species. Activation of P2Y2R increased TF promoter activity and mRNA expression in HCAEC. Truncation, deletion, and mutation of this distal AP-1 site all significantly suppressed TF promoter activity in response to P2Y2R activation. EMSA and ChIP assays further confirmed that upon P2Y2R activation, c-Jun, ATF-2, and Fra-1, but not the typical c-Fos, bound to the new AP-1 site. In addition, loss-of-function studies using siRNAs confirmed a positive transactivation role of c-Jun and ATF-2 but unexpectedly revealed a strong negative role of Fra-1 in P2Y2R-induced TF up-regulation. Furthermore, we found that P2Y2R activation promoted ERK1/2 phosphorylation through Src, leading to Fra-1 activation, whereas Rho/JNK mediated P2Y2R-induced activation of c-Jun and ATF-2. These findings reveal the molecular basis for P2Y G protein-coupled receptor control of endothelial TF expression and indicate that targeting the P2Y2R-Fra-1-TF pathway may be an attractive new strategy for controlling vascular inflammation and thrombogenicity associated with endothelial dysfunction.

Nucleotides regulate secretion of the inflammatory chemokine CCL2 from human macrophages and monocytes

CCL2 is an important inflammatory chemokine involved in monocyte recruitment to inflamed tissues. The extracellular nucleotide signalling molecules UTP and ATP acting via the P2Y2 receptor are known to induce CCL2 secretion in macrophages. We confirmed this in the human THP-1 monocytic cell line showing that UTP is as efficient as LPS at inducing CCL2 at early time points (2–6 hours). Expression and calcium mobilisation experiments confirmed the presence of functional P2Y2 receptors on THP-1 cells. UTP stimulation of human peripheral CD14+ monocytes showed low responses to LPS (4-hour stimulation) but a significant increase above background following 6 hours of treatment. The response to UTP in human monocytes was variable and required stimulation >6 hours. With such variability in response we looked for single nucleotide polymorphisms in P2RY2 that could affect the functional response. Sequencing of P2RY2 from THP-1 cells revealed the presence of a single nucleotide polymorphism altering amino acid 312 from arginine to serine (rs3741156). This polymorphism is relatively common at a frequency of 0.276 (n = 404 subjects). Finally, we investigated CCL2 secretion in response to LPS or UTP in human macrophages expressing 312Arg-P2Y2 or 312Ser-P2Y2 where only the latter exhibited significant UTP-induced CCL2 secretion (n = 5 donors per group).

P2Y2 nucleotide receptor activation enhances the aggregation and self-organization of dispersed salivary epithelial cells

Hyposalivation resulting from salivary gland dysfunction leads to poor oral health and greatly reduces the quality of life of patients. Current treatments for hyposalivation are limited. However, regenerative medicine to replace dysfunctional salivary glands represents a revolutionary approach. The ability of dispersed salivary epithelial cells or salivary gland-derived progenitor cells to self-organize into acinar-like spheres or branching structures that mimic the native tissue holds promise for cell-based reconstitution of a functional salivary gland. However, the mechanisms involved in salivary epithelial cell aggregation and tissue reconstitution are not fully understood. This study investigated the role of the P2Y2 nucleotide receptor (P2Y2R), a G protein-coupled receptor that is upregulated following salivary gland damage and disease, in salivary gland reconstitution. In vitro results with the rat parotid acinar Par-C10 cell line indicate that P2Y2R activation with the selective agonist UTP enhances the self-organization of dispersed salivary epithelial cells into acinar-like spheres. Other results indicate that the P2Y2R-mediated response is dependent on epidermal growth factor receptor activation via the metalloproteases ADAM10/ADAM17 or the α5β1 integrin/Cdc42 signaling pathway, which leads to activation of the MAPKs JNK and ERK1/2. Ex vivo data using primary submandibular gland cells from wild-type and P2Y2R(-/-) mice confirmed that UTP-induced migratory responses required for acinar cell self-organization are mediated by the P2Y2R. Overall, this study suggests that the P2Y2R is a promising target for salivary gland reconstitution and identifies the involvement of two novel components of the P2Y2R signaling cascade in salivary epithelial cells, the α5β1 integrin and the Rho GTPase Cdc42.

Atorvastatin inhibits CXCR7 induction to reduce macrophage migration

We have recently reported that CXCR7, the alternate high affinity SDF-1 receptor, is induced during monocyte-to-macrophage differentiation, leading to increased macrophage phagocytosis linked to atherosclerosis. Statins, the most widely used medications for atherosclerosis, were shown to have pleiotropic beneficial effects independent of their cholesterol-lowering activity. This study aimed to determine whether induction of CXCR7 during macrophage differentiation is inhibited by statins and its significance on macrophage physiology. Here we show for the first time that atorvastatin dose-dependently inhibited CXCR7 mRNA and protein expression in THP-1 macrophages, without affecting the other SDF-1 receptor, CXCR4. Pharmacotherapy relevant dose of atorvastatin affected neither cell viability nor macrophage differentiation. Suppression of CXCR7 expression was completely reversed by supplementation with mevalonate. Inhibition of squalene synthase, the enzyme committed to cholesterol biosynthesis, also decreased CXCR7 induction, albeit not as efficacious as atorvastatin. However, the geranylgeranyl transferase inhibitor, GGTI-286, the farnesyl transferase inhibitor, FTI-276, and the Rho kinase inhibitor, Y-27632, all failed to mimic the effect of atorvastatin, suggesting that the protein prenylation pathways are not critical for atorvastatin inhibition of CXCR7 induction. Interestingly, the dramatic effect of atorvastatin was only partially mimicked by other statins including pravastatin, fluvastatin, mevastatin, and simvastatin. Furthermore, activation of CXCR7 by SDF-1, TC14012, or I-TAC all prompted macrophage migration, which was significantly suppressed by atorvastatin treatment, but not by the CXCR4 antagonist. We conclude that atorvastatin modulates macrophage migration by down-regulating CXCR7 expression, suggesting a new CXCR7-dependent mechanism of atorvastatin to benefit atherosclerosis treatment beyond its lipid lowering effect.

Purinergic signaling and blood vessels in health and disease

Purinergic signaling plays important roles in control of vascular tone and remodeling. There is dual control of vascular tone by ATP released as a cotransmitter with noradrenaline from perivascular sympathetic nerves to cause vasoconstriction via P2X1 receptors, whereas ATP released from endothelial cells in response to changes in blood flow (producing shear stress) or hypoxia acts on P2X and P2Y receptors on endothelial cells to produce nitric oxide and endothelium-derived hyperpolarizing factor, which dilates vessels. ATP is also released from sensory-motor nerves during antidromic reflex activity to produce relaxation of some blood vessels. In this review, we stress the differences in neural and endothelial factors in purinergic control of different blood vessels. The long-term (trophic) actions of purine and pyrimidine nucleosides and nucleotides in promoting migration and proliferation of both vascular smooth muscle and endothelial cells via P1 and P2Y receptors during angiogenesis and vessel remodeling during restenosis after angioplasty are described. The pathophysiology of blood vessels and therapeutic potential of purinergic agents in diseases, including hypertension, atherosclerosis, ischemia, thrombosis and stroke, diabetes, and migraine, is discussed.

Uridine triphosphate increases proliferation of human cancerous pancreatic duct epithelial cells by activating P2Y2 receptor

OBJECTIVES

The aim of this study was to investigate the effect of uridine triphosphate (UTP) on the proliferation of human cancerous pancreatic duct epithelial cells.

METHODS

Proliferation was measured by immunoassay for bromodeoxyuridine incorporation into the pancreatic cell line PANC-1. Effect of UTP was assayed using selective P2 agonist and antagonist, small interfering RNA, intracellular signal inhibitors, and Western blot.

RESULTS

Incubation of PANC-1 cells with UTP or MRS2768, a selective P2Y2 receptor agonist, resulted in a dose- and time-dependent increase of proliferation. The messenger RNA transcript and protein of P2Y2 receptor were expressed in PANC-1 cells. P2 receptor antagonist suramin and small interfering RNA against P2Y2 receptor significantly decreased the proliferative effect of UTP and MRS2768. Activation of P2Y2 receptor by UTP transduced to phospholipase C, inositol 1,4,5-triphosphate (IP3), and protein kinase C. Uridine triphosphate-induced proliferation was mediated by protein kinase D, Src-family tyrosine kinase, Ca/calmodulin-dependent protein kinase II, phosphatidylinositol 3-kinase (PI3K), Akt, and phospholipase D. Uridine triphosphate increased phosphorylation of Akt through protein kinase C, Src-family tyrosine kinase, Ca/calmodulin-dependent protein kinase II, and PI3K.

CONCLUSIONS

Uridine triphosphate increases proliferation of human pancreatic duct epithelial cells by activation of P2Y2 receptor and PI3K/Akt pathway. This could be helpful for discovering the long-term roles of P2Y2 receptor in pancreatic cells.

The P2Y2/Src/p38/COX-2 pathway is involved in the resistance to ursolic acid-induced apoptosis in colorectal and prostate cancer cells

One of the hallmarks of cancer is resistance to apoptosis. Elucidating the mechanisms of how cancer cells evade or delay apoptosis should lead to novel therapeutic strategies. Previously, we showed that HT-29 colorectal cancer cells undergoing apoptosis overexpressed cyclooxygenase-2 (COX-2), in a p38 dependent pathway, to delay ursolic acid-induced apoptosis. Here, we focused on elucidating the upstream signaling pathways regulating this resistance mechanism. The role of ATP as an extracellular signaling molecule took a long time to be accepted. In recent years, ATP and its analogs, via the activation of specific purinergic receptors, have been implicated in many biological processes including cell proliferation, differentiation and apoptosis. In the present report, we have demonstrated a novel role involving purinergic receptors and particularly the P2Y(2) receptor in resistance to ursolic acid-induced apoptosis in both colorectal HT-29 and prostate DU145 cancer cells. We found that ursolic acid induced an increase in intracellular ATP and P2Y(2) transcript levels. Upon activation, P2Y(2) activated Src which in turn phosphorylated p38 leading to COX-2 overexpression which induced resistance to apoptosis in both HT-29 and DU145 cells. Furthermore, Ca(2+)-independent PLA(2) (iPLA(2)) and Ca(2+)-dependent secretory PLA(2) (sPLA(2)) were responsible for arachidonic acid release, the substrate of COX-2. Our findings document that apoptosis triggering was dependent on protein kinase C (PKC) activation in both cell lines after ursolic acid treatment.

Opposite regulation by PI3K/Akt and MAPK/ERK pathways of tissue factor expression, cell-associated procoagulant activity and invasiveness in MDA-MB-231 cells

Background

Tissue factor (TF), an initiator of blood coagulation, participates in cancer progression and metastasis. We recently found that inhibition of MAPK/ERK upregulated both full length TF (flTF) and soluble isoform TF (asTF) gene expression and cell-associated TF activity in breast cancer MDA-MB-231 cells. We explored the possible mechanisms, especially the possible interaction with EGFR and PI3K/Akt pathways.

Methods

A plasmid containing TF promoter −2174 ~ +128 plus luciferase reporter gene was introduced into MDA-MB-231 cells to evaluate TF promoter activity. In order to study the interaction of these pathways, ERK inhibitor (PD98059), PI3K inhibitors (LY294002, wortmannin), Akt inhibitor (A6730), and EGFR inhibitor (erlotinib) as well as the corresponding siRNAs were used to treat MDA-MB-231 cells, and ovarian cancer OVCAR-3 and SKOV-3 cells. Quantitative PCR and western blot were used to determine TF expression. One stage clotting assays were used to measure pro-coagulation activity of the MDA-MB-231 cells.

Results

We show that PI3K inhibitors LY294002, wortmannin and A6730 significantly inhibited TF promoter activity, and reduced TF mRNA and protein levels due to the inhibition of Akt phosphorylation. In contrast, ERK inhibitor PD98059 and ERK siRNA enhanced TF promoter activity by 2.5 fold and induced an increase in TF mRNA and protein levels in a dose dependent manner in these cells. The PI3K/Akt pathway was shown to be involved in PD98059-induced TF expression because the induction was inhibited by PI3K/Akt inhibitors. Most interestingly, the EGFR inhibitor erlotinib and EGFR siRNA also significantly suppressed PD98059- or ERK siRNA-induced TF promoter activity and TF protein expression. Similar results were found with ovarian cancer cells SKOV-3 and OVCAR-3. Furthermore, in MDA-MB-231, mRNA levels of asTF were regulated in a similar way to that of TF in response to the cell treatment.

Conclusions

This study showed a regulatory mechanism in which MAPK/ERK signals inhibit EGFR/PI3K/Akt-mediated TF expression in breast cancer MDA-MB-231 cells. The same regulation was observed in ovarian cancer OVCAR-3 and SKOV-3 cells. Interestingly, we observed that both flTF and asTF could be regulated in a parallel manner in MDA-MB-231. As the PI3K/Akt pathway and EGFR regulate TF expression in cancer cells, targeting these signaling components is expected to potentially inhibit TF expression-associated tumor progression.

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.

Phosphorylation of Sar1b protein releases liver fatty acid-binding protein from multiprotein complex in intestinal cytosol enabling it to bind to endoplasmic reticulum (ER) and bud the pre-chylomicron transport vesicle

Native cytosol requires ATP to initiate the budding of the pre-chylomicron transport vesicle from intestinal endoplasmic reticulum (ER). When FABP1 alone is used, no ATP is needed. Here, we test the hypothesis that in native cytosol FABP1 is present in a multiprotein complex that prevents FABP1 binding to the ER unless the complex is phosphorylated. We found on chromatography of native intestinal cytosol over a Sephacryl S-100 HR column that FABP1 (14 kDa) eluted in a volume suggesting a 75-kDa protein complex that contained four proteins on an anti-FABP1 antibody pulldown. The FABP1-containing column fractions were chromatographed over an anti-FABP1 antibody adsorption column. Proteins co-eluted from the column were identified as FABP1, Sar1b, Sec13, and small VCP/p97-interactive protein by immunoblot, LC-MS/MS, and MALDI-TOF. The four proteins of the complex had a total mass of 77 kDa and migrated on native PAGE at 75 kDa. When the complex was incubated with intestinal ER, there was no increase in FABP1-ER binding. However, when the complex member Sar1b was phosphorylated by PKCζ and ATP, the complex completely disassembled into its component proteins that migrated at their monomer molecular weight on native PAGE. FABP1, freed from the complex, was now able to bind to intestinal ER and generate the pre-chylomicron transport vesicle (PCTV). No increase in ER binding or PCTV generation was observed in the absence of PKCζ or ATP. We conclude that phosphorylation of Sar1b disrupts the FABP1-containing four-membered 75-kDa protein complex in cytosol enabling it to bind to the ER and generate PCTV.