Extracellular ATP and ADP stimulate proliferation of porcine aortic smooth muscle cells

Purinergic Receptor Antagonists: A Complementary Treatment for Hypertension

The treatment of hypertension has improved in the last century; attention has been directed to restoring several altered pathophysiological mechanisms. However, regardless of the current treatments, it is difficult to control blood pressure. Uncontrolled hypertension is responsible for several cardiovascular complications, such as chronic renal failure, which is frequently observed in hypertensive patients. Therefore, new approaches that may improve the control of arterial blood pressure should be considered to prevent serious cardiovascular disorders. The contribution of purinergic receptors has been acknowledged in the pathophysiology of hypertension; this review describes the participation of these receptors in the alteration of kidney function in hypertension. Elevated interstitial ATP concentrations are essential for the activation of renal purinergic receptors; this becomes a fundamental pathway that leads to the development and maintenance of hypertension. High ATP levels modify essential mechanisms implicated in the long-term control of blood pressure, such as pressure natriuresis, the autoregulation of the glomerular filtration rate and renal blood flow, and tubuloglomerular feedback responses. Any alteration in these mechanisms decreases sodium excretion. ATP stimulates the release of vasoactive substances, causes renal function to decline, and induces tubulointerstitial damage. At the same time, a deleterious interaction involving angiotensin II and purinergic receptors leads to the deterioration of renal function.

Hypothesis: can transfer of primary neoplasm-derived extracellular vesicles and mitochondria contribute to the development of donor cell-derived hematologic neoplasms after allogeneic hematopoietic cell transplantation?

Allogeneic hematopoietic cell transplantation (allo-HCT) is an essential treatment option for various neoplastic and non-neoplastic hematologic diseases. Although its efficacy is modest, a significant proportion of patients experience relapse, graft-versus-host disease, infection or impaired hematopoiesis. Among these, the most frequent cause of post-transplant mortality is relapse, whereas the development of de novo hematologic neoplasms from donor cells after allo-HCT occurs on some occasion as a rare complication. The mechanisms involved in the pathogenesis of the de novo hematologic neoplasms from donor cells are complex, and a multifactorial process contributes to the development of this complication. Recently, extracellular vesicles, particularly exosomes, and mitochondria have been shown to play crucial roles in intercellular communication through the transfer of specific constituents, such as deoxyribonucleic acids, ribonucleic acids, lipids, metabolites and cytosolic and cell-surface proteins. Here, I discuss the potential causative roles of these subcellular components in the development of de novo hematologic neoplasms from donor cells after allo-HCT, in addition to other etiologies.

Transcriptome Analysis Reveals That Alfalfa Promotes Rumen Development Through Enhanced Metabolic Processes and Calcium Transduction in Hu Lambs

A healthy gut is very important for young animal development. The rumen of ruminants expands in size with the colonization of microbiota by 2 months of age. This process is promoted by alfalfa intervention. To elucidate the mechanism of this promotion, we performed transcriptomic analyses using a cohort of 23 lambs to evaluate the effects of starter diets plus alfalfa on the development of the rumen wall from the pre- to the postweaning period. The quantitative PCR analyses were used to validate selected genes that were differentially expressed in the transcriptome mapping. We found that several metabolic processes associated with rumen tissue development were affected by solid feed intake, with genes linked to the calcium signaling transduction pathway and the metabolism of pteridine-containing compounds and homocysteine metabolic process being upregulated in the group with alfalfa intervention. The results suggest that the pteridine-containing compounds and calcium signaling are targets for precise regulation of rumen development.

Integration of purinergic and angiotensin II receptor function in renal vascular responses and renal injury in angiotensin II-dependent hypertension

Glomerular arteriolar vasoconstriction and tubulointerstitial injury are observed before glomerular damage occurs in models of hypertension. High interstitial ATP concentrations, caused by the increase in arterial pressure, alter renal mechanisms involved in the long-term control of blood pressure, autoregulation of glomerular filtration rate and blood flow, tubuloglomerular feedback (TGF) responses, and sodium excretion. Elevated ATP concentrations and augmented expression of P2X receptors have been demonstrated under a genetic background or induction of hypertension with vasoconstrictor peptides. In addition to the alterations of the microcirculation in the hypertensive kidney, the vascular actions of elevated intrarenal angiotensin II levels may be mitigated by the administration of broad purinergic P2 antagonists or specific P2Y12, P2X1, and P2X7 receptor antagonists. Furthermore, the prevention of tubulointerstitial infiltration with immunosuppressor compounds reduces the development of salt-sensitive hypertension, indicating that tubulointerstitial inflammation is essential for the development and maintenance of hypertension. Inflammatory cells also express abundant purinergic receptors, and their activation by ATP induces cytokine and growth factor release that in turn contributes to augment tubulointerstitial inflammation. Collectively, the evidence suggests a pathophysiological activation of purinergic P2 receptors in angiotensin-dependent hypertension. Coexistent increases in intrarenal angiotensin II and activates Ang II AT1 receptors, which interacts with over-activated purinergic receptors in a complex manner, suggesting convergence of their post-receptor signaling processes.

ENPP1-Fc prevents neointima formation in generalized arterial calcification of infancy through the generation of AMP

Generalized arterial calcification of infancy (GACI) is associated with widespread arterial calcification and stenoses and is caused by mutations in ENPP1. ENPP1 encodes for ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1), which cleaves ATP to generate inorganic pyrophosphate (PP_i) and adenosine monophosphate (AMP) extracellularly. The current study was designed to define the prevalence of arterial stenoses in GACI individuals and to identify the mechanism through which ENPP1 deficiency causes intimal proliferation. Furthermore, we aimed to effectively prevent and treat neointima formation in an animal model of GACI through the systemic administration of recombinant human (rh)ENPP1-Fc protein. Based on a literature review, we report that arterial stenoses are present in at least 72.4% of GACI cases. We evaluated the effect of rhENPP1-Fc on ENPP1-silenced human vascular smooth muscle cells (VSMCs) and on induced intimal proliferation in Enpp1-deficient ttw/ttw mice treated with carotid ligation. We demonstrate that silencing ENPP1 in VSMCs resulted in a tenfold increase in proliferation relative to that of cells transfected with negative control siRNA. The addition of rhENPP1-Fc, AMP or adenosine restored the silenced ENPP1-associated proliferation. In contrast, neither PP_i nor etidronate, a current off-label treatment for GACI, had an effect on VSMC proliferation. Furthermore, subcutaneous rhENPP1-Fc protein replacement was effective in preventing and treating intimal hyperplasia induced by carotid ligation in an animal model of GACI. We conclude that ENPP1 inhibits neointima formation by generating  AMP. RhENPP1-Fc may serve as an approach for the effective prevention and treatment of arterial stenoses in GACI.

A protein replacement therapy may prove useful in tackling calcification and narrowing of the arteries in babies with a severe genetic disorder. Generalized Arterial Calcification of Infancy (GACI) is a rare condition in which infants’ arteries become calcified and their blood vessels internally scarred. It often leads to congestive heart failure. The ENPP1 gene encodes a protein that is crucial to preventing excess calcium build-up in the body. Mutations in the ENPP1 gene lead to GACI, but no therapies for the condition exist. Now, Frank Rutsch at Muenster University Children’s Hospital in Germany and co-workers have shown that administering a protein replacement can inhibit blood vessel scarring and arterial clogging in GACI mice models and in human stem cell cultures. The protein replacement boosts production of a key metabolic molecule called adenosine monophosphate.

Defining the momiome: Promiscuous information transfer by mobile mitochondria and the mitochondrial genome

Mitochondria are complex intracellular organelles that have long been identified as the powerhouses of eukaryotic cells because of the central role they play in oxidative metabolism. A resurgence of interest in the study of mitochondria during the past decade has revealed that mitochondria also play key roles in cell signaling, proliferation, cell metabolism and cell death, and that genetic and/or metabolic alterations in mitochondria contribute to a number of diseases, including cancer. Mitochondria have been identified as signaling organelles, capable of mediating bidirectional intracellular information transfer: anterograde (from nucleus to mitochondria) and retrograde (from mitochondria to nucleus). More recently, evidence is now building that the role of mitochondria extends to intercellular communication as well, and that the mitochondrial genome (mtDNA) and even whole mitochondria are indeed mobile and can mediate information transfer between cells. We define this promiscuous information transfer function of mitochondria and mtDNA as "momiome" to include all mobile functions of mitochondria and the mitochondrial genome. Herein, we review the "momiome" and explore its role in cancer development, progression, and treatment.

Recombinant soluble apyrase APT102 inhibits thrombosis and intimal hyperplasia in vein grafts without adversely affecting hemostasis or re-endothelialization

Essentials New strategies are needed to inhibit thrombosis and intimal hyperplasia (IH) in vein grafts (VG). We studied effects of apyrase (APT102) on VGs and smooth muscle and endothelial cells (SMC/EC). APT102 inhibited thrombosis, SMC migration, and IH without impairing hemostasis or EC recovery. Apyrase APT102 is a single-drug approach to inhibit multiple processes that cause VG failure.

SUMMARY

Background Occlusion of vein grafts (VGs) after bypass surgery, owing to thrombosis and intimal hyperplasia (IH), is a major clinical problem. Apyrases are enzymes that scavenge extracellular ATP and ADP, and promote adenosine formation at sites of vascular injury, and hence have the potential to inhibit VG pathology. Objectives To examine the effects of recombinant soluble human apyrase, APT102, on platelets, smooth muscle cells (SMCs) and endothelial cells (ECs) in vitro, and on thrombosis and IH in murine VGs. Methods SMC and EC proliferation and migration were studied in vitro. Inferior vena cava segments from donor mice were grafted into carotid arteries of recipient mice. Results APT102 potently inhibited ADP-induced platelet aggregation and VG thrombosis, but it did not impair surgical hemostasis. APT102 did not directly inhibit SMC or EC proliferation, but significantly attenuated the effects of ATP on SMC and EC proliferation. APT102 significantly inhibited SMC migration, but did not inhibit EC migration, which may be mediated, at least in part, by inhibition of SMC, but not EC, migration by adenosine. At 4 weeks after surgery, there was significantly less IH in VGs of APT102-treated mice than in control VGs. APT102 significantly inhibited cell proliferation in VGs, but did not inhibit re-endothelialization. Conclusions Systemic administration of a recombinant human apyrase inhibits thrombosis and IH in VGs without increasing bleeding or compromising re-endothelialization. These results suggest that APT102 has the potential to become a novel, single-drug treatment strategy to prevent multiple pathologic processes that drive early adverse remodeling and occlusion of VGs.

Direct Evidence for P2Y2 Receptor Involvement in Vascular Response to Injury

OBJECTIVES

Extracellular nucleotide release at the site of arterial injury mediates the proliferation and migration of vascular smooth muscle cells. Our aim was to investigate the role of the P2Y2 nucleotide receptor (P2Y2R) in neointimal hyperplasia. Approach and Results: Vascular injury was induced by the implantation of a polyethylene cuff around the femoral artery in wild-type and P2Y2R-deficient mice (P2Y2R-/-). Electron microscopy was used to analyze monocyte and lymphocyte influx to the intima 36 h after injury. Compared to wild-type littermates, P2Y2R-/- mice exhibited a 3-fold decreased number of mononuclear leukocytes invading the intima (p < 0.05). Concomitantly, the migration of smooth muscle cells was decreased by more than 60% (p < 0.05), resulting in a sharp inhibition of intimal thickening formation in P2Y2R-/- mice (n = 15) 14 days after cuff placement. In vitro, loss of P2Y2R significantly impaired monocyte migration in response to nucleotide agonists. Furthermore, transgenic rats overexpressing the P2Y2R developed accelerated intimal lesions resulting in more than 95% luminal stenosis (p < 0.05, n = 10).

CONCLUSIONS

Loss- and gain-of-function approaches established direct evidence for P2Y2R involvement in neointimal hyperplasia. Specific anti-P2Y2R therapies may be used against restenosis and bypass graft failure.

Adenosine Triphosphate Regresses Endometrial Explants in a Rat Model of Endometriosis

The aim of this study was to determine the effects of adenosine triphosphate (ATP) in a rat endometriosis model. After surgical induction of endometriosis, 3 rats were killed, and explants were measured in the remaining 19 rats, which were then randomly assigned to 4 groups. Group 1 (n = 4) received normal saline (2 mL/d intragastric [IG]), group 2 (n = 4) gestrinone (0.5 mg/kg/d IG), group 3 (n = 5) ATP (3.4 mg/kg/d IG), and group 4 (n = 6) ATP (1.0 mg/kg/d; intramuscularly), respectively. Four weeks after medication, they were euthanized to evaluate histological features of explants and eutopic uterine tissues. To test the effect of ATP on the growth of eutopic endometrium stromal cells, proliferation rates of hEM15A cells at 24, 48, and 72 hours after treatment with different concentrations of ATP and vehicle control were detected with the Cell Counting Kit-8 (CCK-8) method. There was a significant difference between pretreatment and posttreatment volumes within group 2 (positive control; P = .048) and group 4 (P = .044). On condition that pretreatment implant size was similar in both groups (P = .516), regression of explants in group 4 was significantly higher than that in group 1 (negative control; P = .035). Epithelial cells were significantly better preserved in group 1 than in group 3 (P = .008) and group 4 (P = .037). The CCK-8 assay showed no significant difference in proliferation among hEM15A cells treated with ATP and controls. These results suggest that ATP regresses endometriotic tissues in a rat endometriosis model but has no impact on the growth of eutopic endometrium stromal cells.

Purinergic receptors in tubulointerstitial inflammatory cells: a pathophysiological mechanism of salt-sensitive hypertension

Recent studies have suggested that both the tubulointerstitial inflammatory cells and the activation of purinergic receptors integrate common mechanisms that result in salt-sensitive hypertension. The basis of this hypothesis is that renal endothelial cells release ATP in response to shear stress in the setting of hypertension. It has been demonstrated that the over-expression and activation of the P2X7, P2Y12 and P2X1 receptors favour the elevation of blood pressure induced by high-salt intake. In addition, the release of interleukins and inflammatory mediators in the tubulointerstitial area appears to be related to the activation of these receptors. Renal vasoconstriction and tubulointerstitial injury develop as a result, which increase sodium reabsorption by epithelial cells. Consistent with these effects, the reduction of tubulointerstitial inflammation caused by immunosuppressants, such as mycophenolate mofetil, prevents the development of salt-sensitive hypertension. Also, P2X7-receptor knockout mice develop minor renal injury when hypertension is induced via the administration of deoxycorticosterone acetate and a high-salt diet. In the setting of angiotensin II-induced hypertension, which is an early stage in the development of salt-sensitive hypertension, an acute blockade with the specific, non-selective P2 antagonist pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid prevented the renal vasoconstriction induced by angiotensin II. In addition, it normalized glomerular haemodynamics and restored sodium excretion to control values. These findings suggest that chronic administration of P2 purinergic antagonists may prevent the deleterious effects of purinergic receptors during the development of salt-sensitive hypertension.

Purinergic transmission in blood vessels

There are nineteen different receptor proteins for adenosine, adenine and uridine nucleotides, and nucleotide sugars, belonging to three families of G protein-coupled adenosine and P2Y receptors, and ionotropic P2X receptors. The majority are functionally expressed in blood vessels, as purinergic receptors in perivascular nerves, smooth muscle and endothelial cells, and roles in regulation of vascular contractility, immune function and growth have been identified. The endogenous ligands for purine receptors, ATP, ADP, UTP, UDP and adenosine, can be released from different cell types within the vasculature, as well as from circulating blood cells, including erythrocytes and platelets. Many purine receptors can be activated by two or more of the endogenous ligands. Further complexity arises because of interconversion between ligands, notably adenosine formation from the metabolism of ATP, leading to complex integrated responses through activation of different subtypes of purine receptors. The enzymes responsible for this conversion, ectonucleotidases, are present on the surface of smooth muscle and endothelial cells, and may be coreleased with neurotransmitters from nerves. What selectivity there is for the actions of purines/pyrimidines comes from differential expression of their receptors within the vasculature. P2X1 receptors mediate the vasocontractile actions of ATP released as a neurotransmitter with noradrenaline (NA) from sympathetic perivascular nerves, and are located on the vascular smooth muscle adjacent to the nerve varicosities, the sites of neurotransmitter release. The relative contribution of ATP and NA as functional cotransmitters varies with species, type and size of blood vessel, neuronal firing pattern, the tone/pressure of the blood vessel, and in ageing and disease. ATP is also a neurotransmitter in non-adrenergic non-cholinergic perivascular nerves and mediates vasorelaxation via smooth muscle P2Y-like receptors. ATP and adenosine can act as neuromodulators, with the most robust evidence being for prejunctional inhibition of neurotransmission via A1 adenosine receptors, but also prejunctional excitation and inhibition of neurotransmission via P2X and P2Y receptors, respectively. P2Y2, P2Y4 and P2Y6 receptors expressed on the vascular smooth muscle are coupled to vasocontraction, and may have a role in pathophysiological conditions, when purines are released from damaged cells, or when there is damage to the protective barrier that is the endothelium. Adenosine is released during hypoxia to increase blood flow via vasodilator A2A and A2B receptors expressed on the endothelium and smooth muscle. ATP is released from endothelial cells during hypoxia and shear stress and can act at P2Y and P2X4 receptors expressed on the endothelium to increase local blood flow. Activation of endothelial purine receptors leads to the release of nitric oxide, hyperpolarising factors and prostacyclin, which inhibits platelet aggregation and thus ensures patent blood flow. Vascular purine receptors also regulate endothelial and smooth muscle growth, and inflammation, and thus are involved in the underlying processes of a number of cardiovascular diseases.

Suppression of endothelial CD39/ENTPD1 is associated with pulmonary vascular remodeling in pulmonary arterial hypertension

Endothelial cell (EC) dysfunction plays a role in the pathobiology of occlusive vasculopathy in pulmonary arterial hypertension (PAH). Purinergic signaling pathways, which consist of extracellular nucleotide and nucleoside-mediated cell signaling through specific receptors, are known to be important regulators of vascular tone and remodeling. Therefore, we hypothesized that abnormalities in the vascular purinergic microenvironment are associated with PAH. Enzymatic clearance is crucial to terminate unnecessary cell activation; one of the most abundantly expressed enzymes on the EC surface is E-NTPDase1/CD39, which hydrolyzes ATP and ADP to AMP. we used histological samples from patients and healthy donors, radioisotope-labeled substrates to measure ectoenzyme activity, and a variety of in vitro approaches to study the role of CD39 in PAH. Immunohistochemistry on human idiopathic PAH (IPAH) patients' lungs demonstrated that CD39 was significantly downregulated in the endothelium of diseased small arteries. Similarly, CD39 expression and activity were decreased in cultured pulmonary ECs from IPAH patients. Suppression of CD39 in vitro resulted in EC phenotypic switch that gave rise to apoptosis-resistant pulmonary arterial endothelial cells and promoted a microenvironment that induced vascular smooth muscle cell migration. we also identified that the ATP receptor P2Y11 is essential for ATP-mediated EC survival. Furthermore, we report that apelin, a known regulator of pulmonary vascular homeostasis, can potentiate the activity of CD39 both in vitro and in vivo. we conclude that sustained attenuation of CD39 activity through ATP accumulation is tightly linked to vascular dysfunction and remodeling in PAH and could represent a novel target for therapy.

Nucleolin down-regulation is involved in ADP-induced cell cycle arrest in S phase and cell apoptosis in vascular endothelial cells

High concentration of extracellular ADP has been reported to induce cell apoptosis, but the molecular mechanisms remain not fully elucidated. In this study, we found by serendipity that ADP treatment of human umbilical vein endothelial cells (HUVEC) and human aortic endothelial cells (HAEC) down-regulated the protein level of nucleolin in a dose- and time-dependent manner. ADP treatment did not decrease the transcript level of nucloelin, suggesting that ADP might induce nucleolin protein degradation. HUVEC and HAEC expressed ADP receptor P2Y13 receptor, but did not express P2Y1 or P2Y12 receptors. However, P2Y1, 12, 13 receptor antagonists MRS2179, PSB0739, MRS2211 did not inhibit ADP-induced down-regulation of nucleolin. Moreover, MRS2211 itself down-regulated nucleolin protein level. In addition, 2-MeSADP, an agonist for P2Y1, 12 and 13 receptors, did not down-regulate nucleolin protein. These results suggested that ADP-induced nucleolin down-regulation was not due to the activation of P2Y1, 12, or 13 receptors. We also found that ADP treatment induced cell cycle arrest in S phase, cell apoptosis and cell proliferation inhibition via nucleolin down-regulation. The over-expression of nucleolin by gene transfer partly reversed ADP-induced cell cycle arrest, cell apoptosis and cell proliferation inhibition. Furthermore, ADP sensitized HUVEC to cisplatin-induced cell death by the down-regulation of Bcl-2 expression. Taken together, we found, for the first time to our knowledge, a novel mechanism by which ADP regulates cell proliferation by induction of cell cycle arrest and cell apoptosis via targeting nucelolin.

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.

Nano-nutrition of chicken embryos. The effect of silver nanoparticles and ATP on expression of chosen genes involved in myogenesis

It has been suggested that the quantity and quality of nutrients stored in the egg might not be optimal for the fast rate of chicken embryo development in modern broilers, and embryos could be supplemented with nutrients by in ovo injection. Recent experiments showed that in ovo feeding reduces post-hatch mortality and skeletal disorders and increases muscle growth and breast meat yield. Adenosine triphosphate (ATP) is a "ready for use" energetic molecule, while nanoparticles of silver (Nano-Ag) may penetrate tissues as well as cells and localise inside cells. In this investigation, we hypothesised that silver nanoparticles could be used as a protective carrier for ATP as well as an active agent. ATP and/or an ATP complex with Nano-Ag would be delivered to the muscle cells as a gene expression regulator and promoter of growth and development of embryo breast muscle. A collection of 160 broiler eggs was randomly divided into a Control group without injection and injected groups with hydrocolloids of Nano-Ag, ATP or a complex of Nano-Ag and ATP (Nano-Ag/ATP). The embryos were evaluated on day 20 of incubation. The results indicate that the application of ATP to chicken embryos increases expression of fibroblast growth factor 2 (FGF2), vascular endothelial growth factor (VEGF) and Na(+)/K(+) transporting ATPase (ATP1A1), which may indicate that an extra energy source can enhance molecular mechanisms of muscle cell proliferation. Nano-Ag also up-regulated expression of FGF2, VEGF, ATP1A1 and, also up-regulated expression of myogenic differentiation 1(MyoD1), affecting cell differentiation. The results indicate that ATP and Nano-Ag may accelerate growth and maturation of muscle cells.

BRMS1 Sensitizes Breast Cancer Cells to ATP-Induced Growth Suppression

Purinergic signaling may represent an effective target in cancer therapy because the expression of purinergic receptors is altered in many forms of cancer and extracellular nucleotides modulate cancer cell growth. We examined the effect of extracellular ATP on the growth of the metastatic breast carcinoma cell line MDA-MB-435 relative to an immortalized breast epithelial cell line, hTERT-HME1. We also investigated whether the metastasis suppressor gene BRMS1 alters the sensitivity of breast cancer cells to ATP. Exposure to ATP for 24 h decreased proliferation and induced apoptosis in hTERT-HME1. However, exposure to ATP did not decrease proliferation or induce apoptosis in MDA-MD-435 cells until 48 h of exposure and only at higher doses than were effective with hTERT-HME1, suggesting MDA-MB-435 cells were resistant to the antiproliferative and apoptosis-inducing effects of ATP. Exposure to ATP for 24 h induced a decrease in proliferation of MDA-MB-435 cells expressing BRMS1, similar to hTERT-HME1, but did not induce an increase in apoptosis. MDA-MB-435 cells expressed low levels of the purinergic receptor P2Y₂, as well as decreased ATP-induced cytosolic calcium mobilization, relative to hTERT-HME1. However, expressing BRMS1 in MDA-MB-435 cells restored P2Y₂ levels and ATP-induced cytosolic calcium mobilization such that they were similar to hTERT-HME1. These data suggest that BRMS1 increases the sensitivity of breast cancer cells to the antiproliferative, but not apoptosis-inducing effects of ATP and that this is at least partly mediated by increased expression of the P2Y₂ receptor.

Adenosine-5'-triphosphate up-regulates proliferation of human cardiac fibroblasts

BACKGROUND AND PURPOSE

ATP is a potent signalling molecule that regulates biological activities including increasing or decreasing proliferation in different types of cells. The aim of the present study was to investigate how ATP regulates the proliferation of human cardiac fibroblasts.

EXPERIMENTAL APPROACH

Reverse transcription (RT)-PCR, Western blot analysis, cell proliferation and migration assays were employed to investigate the effects of ATP on human adult ventricular fibroblasts.

KEY RESULTS

ATP increased cell proliferation in a concentration-dependent manner. Similarly, the P2X receptor agonist α,β-methylene ATP and P2Y receptor agonist ATP-γS also up-regulated cell proliferation. The P2 receptor antagonists suramin and reactive blue-2 prevented the ATP-induced increase in proliferation and RT-PCR and Western blot analysis revealed that mRNAs of P2X(4/7) and P2Y(2) are abundant in cardiac fibroblasts. ATP increased phosphorylated PKB (Akt) and ERK1/2 levels; an effect antagonized by suramin, reactive blue-2, the PI3-kinase inhibitor, wortmannin, PKB inhibitor, API-2, and MAPK inhibitor, PD98059. These kinase inhibitors also prevented the ATP-induced increase in proliferation. In addition, ATP enhanced the progression of cells from the G0/G1 phase to the S phase by increasing the expression of proteins for cyclin D1 and cyclin E. Silencing the P2X(4/7) and P2Y(2) receptors with siRNA targeting the corresponding receptor diminished ATP-stimulated proliferation and migration of the cardiac fibroblasts.

CONCLUSION AND IMPLICATION

ATP activates P2X(4/7) and P2Y(2) receptors and up-regulates the proliferation of human cardiac fibroblasts by promoting cell cycling progression. It also increases the migration of these cells. These effects of ATP may be involved in cardiac remodelling of injured hearts.

Expression of pannexin isoforms in the systemic murine arterial network

AIMS

Pannexins (Panx) form ATP release channels and it has been proposed that they play an important role in the regulation of vascular tone. However, distribution of Panx across the arterial vasculature is not documented.

METHODS

We tested antibodies against Panx1, Panx2 and Panx3 on human embryonic kidney cells (which do not endogenously express Panx proteins) transfected with plasmids encoding each Panx isoform and Panx1(-/-) mice. Each of the Panx antibodies was found to be specific and was tested on isolated arteries using immunocytochemistry.

RESULTS

We demonstrated that Panx1 is the primary isoform detected in the arterial network. In large arteries, Panx1 is primarily in endothelial cells, whereas in small arteries and arterioles it localizes primarily to the smooth muscle cells. Panx1 was the predominant isoform expressed in coronary arteries, except in arteries less than 100 µm where Panx3 became detectable. Only Panx3 was expressed in the juxtaglomerular apparatus and cortical arterioles. The pulmonary artery and alveoli had expression of all 3 Panx isoforms. No Panx isoforms were detected at the myoendothelial junctions.

CONCLUSION

We conclude that the specific localized expression of Panx channels throughout the vasculature points towards an important role for these channels in regulating the release of ATP throughout the arterial network.

Mechanisms of ATP release and signalling in the blood vessel wall

The nucleotide adenosine 5'-triphosphate (ATP) has classically been considered the cell's primary energy currency. Importantly, a novel role for ATP as an extracellular autocrine and/or paracrine signalling molecule has evolved over the past century and extensive work has been conducted to characterize the ATP-sensitive purinergic receptors expressed on almost all cell types in the body. Extracellular ATP elicits potent effects on vascular cells to regulate blood vessel tone but can also be involved in vascular pathologies such as atherosclerosis. While the effects of purinergic signalling in the vasculature have been well documented, the mechanism(s) mediating the regulated release of ATP from cells in the blood vessel wall and circulation are now a key target of investigation. The aim of this review is to examine the current proposed mechanisms of ATP release from vascular cells, with a special emphasis on the transporters and channels involved in ATP release from vascular smooth muscle cells, endothelial cells, circulating red blood cells, and perivascular sympathetic nerves, including vesicular exocytosis, plasma membrane F(1)/F(0)-ATP synthase, ATP-binding cassette (ABC) transporters, connexin hemichannels, and pannexin channels.

Signaling mechanisms mediating uridine adenosine tetraphosphate-induced proliferation of human vascular smooth muscle cells

Proliferation of vascular smooth muscle cells (SMCs) plays an important role in the development of atherosclerosis and restenosis. Extracellular mononucleotides, such as adenosine triphosphate and uridine-5'-triphosphate stimulate SMC proliferation. However, the effects of dinucleotides on SMC proliferation and their underlying signaling mechanisms are less well defined. Recently, increasing evidence suggests that the dinucleotide, uridine adenosine tetraphosphate (Up4A) plays a role in the regulation of cardiovascular function. We have previously demonstrated that Up4A stimulates DNA synthesis and proliferation of human SMCs. This study investigated the signaling mechanisms underlying the proliferative effect of Up4A. Up4A-induced increase in bromodeoxyuridine incorporation was blocked by the mammalian target of rapamycin inhibitor, rapamycin, and the MEK inhibitor, PD98059. Up4A-stimulated phosphorylation and kinase activity of S6 kinase (S6K) and Erk1/2 were inhibited by PD98059, whereas phosphorylation and kinase activity of S6K, but not Erk1/2, were inhibited by rapamycin. Up4A also increased the phosphorylation of Akt, which was blocked by the PI3-kinase inhibitor, LY294002. Up4A-stimulated activation of S6K, but not Erk1/2, was also prevented by LY294002. Furthermore, Up4A-stimulated phosphorylation and kinase activity of S6K and Erk1/2 were inhibited by the P2 receptor antagonist, suramin, but not by the P2X receptor antagonist, Ip5I. Up4A also stimulated an increase in the protein expression of cycle-dependent kinase 2, which was prevented by rapamycin, PD98059, and suramin. These results suggest that the signaling mechanisms underlying the Up4A-stimulated proliferation of SMCs are mediated by P2Y receptors and involve the PI3-K/Akt and mitogen-activated protein kinase pathways, leading to the independent activation of S6K and an increase in cycle-dependent kinase 2 expression. This work stresses the concept that dinucleotides, like mononucleotides, play potentially important roles in the regulation of vascular function.

Transactivation of EGFR/PI3K/Akt involved in ATP-induced inflammatory protein expression and cell motility

Phenotype transition of vascular smooth muscle cells (VSMCs) is important in vascular diseases, such as atherosclerosis and restenosis. Once released, ATP may promote activation of VSMCs by stimulating cyclooxygenase-2 (COX-2), cytosolic phospholipase A(2) (cPLA(2)) expression and prostaglandin (PG)E(2) synthesis via activation of MAPKs and NF-κB. However, whether alternative signaling pathways participated in regulating COX-2 and cPLA(2) expression associated with cell migration were investigated in rat VSMCs. Western blot analysis, RT-PCR, promoter assay and PGE(2) ELISA were used to determine expression of COX-2, cPLA(2) and PGE(2). Specific inhibitors and siRNAs against various protein kinases or transcription factors were used to investigate the related signaling components in inflammatory protein induction by ATPγS. We found that ATPγS-induced COX-2 and cPLA(2) expression and PGE(2) release was attenuated by the pharmacological inhibitors or transfection with siRNA against PKCδ, c-Src, EGFR, PI3-K, Akt, p44/p42 MAPK or Elk-1. Moreover, ATPγS-stimulated phosphorylation of PKCδ, c-Src, EGFR, Akt, p42/p44 MAPK and Elk-1, suggesting the participation of PKCδ/c-Src/EGFR/PI3-K/Akt/p42/p44 MAPK cascade in mediating Elk-1 activities in VSMCs. In addition, migration assay revealed that ATPγS promoted cell mobility through up-regulation of COX-2 and cPLA(2) expression and PGE(2) release, which was attenuated by pretreatment with PGE(2) receptor antagonists. Taken together, these data showed that ATPγS up-regulated the expression of COX-2 and cPLA(2) through transactivation of PKCδ/c-Src/EGFR/PI3K/Akt/Elk-1 pathway. Newly synthesized PGE(2) acted on its receptors to promote cell motility of ATPγS-stimulated VSMCs.

20-Hydroxyeicosatetraenoic acid inhibits ATP-induced COX-2 expression via peroxisome proliferator activator receptor-α in vascular smooth muscle cells

BACKGROUND AND PURPOSE

20-Hydroxyeicosatetraenoic acid (20-HETE), formed from arachidonate by cytochrome P450, regulates vascular smooth muscle cell (VSMC) function. Because 20-HETE may activate peroxisome proliferator activator receptors (PPARs) and may participate in inflammatory responses, we asked whether 20-HETE may inhibit cyclooxygenase 2 (COX-2) expression by activating PPARs in VSMC.

EXPERIMENTAL APPROACH

Quiescent neonatal VSMC (R22D cell line), were incubated with 20-HETE, synthetic ligands of PPARs, or inhibitors of the extracellular signal regulated kinase (ERK1/2), c-jun N-terminal kinase and the transcription factor activated protein-1 before adding ATPγS. mRNA and protein expression of COX-2 and the promoter luciferase activity of COX-2 and PPAR response element were determined.

KEY RESULTS

Pretreatment with 20-HETE (5-10 µM) significantly inhibited ATPγS-induced COX-2 mRNA and protein expression in VSMC. The inhibitory effect of 20-HETE on COX-2 expression was mimicked by WY14643, a PPARα ligand and inhibited by MK886, a PPARα inhibitor or by transfection of shRNA for PPARα. Both 20-HETE and WY14643 significantly increased the PPAR-response element luciferase activity. Furthermore, ATPγS-induced activation of the COX-2 promoter containing the activated protein-1 site was also inhibited by pretreatment with 20-HETE, which was reversed by MK886 or by transfection with shRNA for PPARα.

CONCLUSIONS AND IMPLICATIONS

The PPARα may mediate the inhibitory effects of 20-HETE on COX-2 expression through a negative cross-talk between PPARα and the COX-2 promoter.

Vascular smooth muscle cell expression of ectonucleotidase CD39 (ENTPD1) is required for neointimal formation in mice

Vascular smooth muscle cell (VSMC) migration and proliferation are critical steps in the pathogenesis of atherosclerosis, post-angioplasty restenosis, neointimal hyperplasia, and chronic allograft rejection. Extracellular nucleotides are known to influence both migration and proliferation of VSMC. Although it is well established that vascular endothelial Cd39/ENTPD1 regulates blood nucleotide concentrations, whether Cd39 associated with VSMC also impacts vascular wall pathology has not been investigated. The objective of this paper is to determine levels of expression of Cd39 on VSMC and functional consequences of gene deletion in vitro and in vivo. Cd39 is the major ectonucleotidase in VSMC, as shown by substantive decreases in ecto-ATPase and -ADPase activity in Cd39-null cells compared to wild type. Significant decreases in neointimal lesion formation are observed in Cd39-null mice at 21 days post arterial balloon injury. Stimulated Cd39-null VSMC have pronounced proliferative responses in vitro. However, using Transwell systems, we show that Cd39-null VSMC fail to migrate in response to ATP, UTP, and PDGF. Cd39 is the dominant ectonucleotidase expressed by VSMC. Deletion of Cd39 in mice results in decreased neointimal formation after vascular injury and is associated with impaired VSMC migration responses in vitro.

Overexpression of CD39/nucleoside triphosphate diphosphohydrolase-1 decreases smooth muscle cell proliferation and prevents neointima formation after angioplasty

BACKGROUND

Growing evidence implicates the involvement of extracellular nucleotides in the regulation of platelet, leukocyte, endothelial cell (EC) and vascular smooth muscle cell (VSMC) phenotype and function. Within the quiescent vasculature, extracellular nucleotides are rapidly hydrolyzed by CD39, the dominant endothelial nucleoside triphosphate diphosphohydrolase (NTPDase-1). However, vascular CD39/NTPDase-1 activity is lost in EC activated by oxidative stress or proinflammatory mediators, and upon denudation of the endothelium following balloon injury. The consequent increase in extracellular nucleotide concentrations triggers signaling events leading to prothrombotic responses and increased VSMC proliferation.

OBJECTIVES

To investigate the effect of overexpressed CD39/NTPDase-1 in injured aorta.

METHODS

Using adenoviral-mediated gene transfer we expressed CD39/NTPDase-1 in mechanically denudated rat aortas. We measured intima formation by morphometry and VSMC proliferation by the [(3)H]-thymidine incorporation assay.

RESULTS

Targeted expression of CD39 in injured vessels increased NTPDase activity (from 2.91 +/- 0.31 to 22.07 +/- 6.7 nmols Pi mg(-1) protein, 4 days after exposure to the adenovirus) and prevented the formation of neointima. The thickness of the intimal layer in injured aortas exposed to Ad-CD39 was 26.2 +/- 3.9 microm vs. 51.8 +/- 6.1 microm and 64.4 +/- 22.2 microm (P < 0.001) in vessels treated with Ad-beta-gal and saline, respectively. Moreover, targeted expression of CD39/NTPDase-1 caused a 70% (P < 0.01) decrease in proliferation of VSMC isolated from transduced rat aortas as compared with VSMC derived from control vessels.

CONCLUSIONS

The presented data suggest that increasing CD39/NTPDase-1 activity in VSMC could represent a novel therapeutic approach for the prevention of stenosis associated with angioplasty and other occlusive vascular diseases.

Phosphorylation of beta-catenin by PKA promotes ATP-induced proliferation of vascular smooth muscle cells

Extracellular ATP stimulates proliferation of vascular smooth muscle cells (VSMC) through activation of G protein-coupled P2Y purinergic receptors. We have previously shown that ATP stimulates a transient activation of protein kinase A (PKA), which, together with the established mitogenic signaling of purinergic receptors, promotes proliferation of VSMC (Hogarth DK, Sandbo N, Taurin S, Kolenko V, Miano JM, Dulin NO. Am J Physiol Cell Physiol 287: C449-C456, 2004). We also have shown that PKA can phosphorylate beta-catenin at two novel sites (Ser552 and Ser675) in vitro and in overexpression cell models (Taurin S, Sandbo N, Qin Y, Browning D, Dulin NO. J Biol Chem 281: 9971-9976, 2006). beta-Catenin promotes cell proliferation by activation of a family of T-cell factor (TCF) transcription factors, which drive the transcription of genes implicated in cell cycle progression including cyclin D1. In the present study, using the phosphospecific antibodies against phospho-Ser552 or phospho-Ser675 sites of beta-catenin, we show that ATP can stimulate PKA-dependent phosphorylation of endogenous beta-catenin at both of these sites without affecting its expression levels in VSMC. This translates to a PKA-dependent stimulation of TCF transcriptional activity through an increased association of phosphorylated (by PKA) beta-catenin with TCF-4. Using the PKA inhibitor PKI or dominant negative TCF-4 mutant, we show that ATP-induced cyclin D1 promoter activation, cyclin D1 protein expression, and proliferation of VSMC are all dependent on PKA and TCF activities. In conclusion, we show a novel mode of regulation of endogenous beta-catenin through its phosphorylation by PKA, and we demonstrate the importance of this mechanism for ATP-induced proliferation of VSMC.

Nucleotide P2Y1 receptor regulates EGF receptor mitogenic signaling and expression in epithelial cells

Epidermal growth factor receptor (EGFR) function is transregulated by a variety of stimuli, including agonists of certain G-protein-coupled receptors (GPCRs). One of the most ubiquitous GPCRs is the P2Y(1) receptor (P2RY1, hereafter referred to as P2Y(1)R) for extracellular nucleotides, mainly ADP. Here, we show in tumoral HeLa cells and normal FRT epithelial cells that P2Y(1)R broadcasts mitogenic signals by transactivating the EGFR. The pathway involves PKC, Src and cell surface metalloproteases. Stimulation of P2Y(1)R for as little as 15-60 minutes triggers mitogenesis, mirroring the half-life of extracellular ADP. Apyrase degradation of extracellular nucleotides and drug inhibition of P2Y(1)R, both reduced basal cell proliferation of HeLa and FRT cells, but not MDCK cells, which do not express P2Y(1)R. Thus, cell-released nucleotides constitute strong mitogenic stimuli, which act via P2Y(1)R. Strikingly, MDCK cells ectopically expressing P2Y(1)R display a highly proliferative phenotype that depends on EGFR activity associated with an increased level of EGFR, thus disclosing a novel aspect of GPCR-mediated regulation of EGFR function. These results highlight a role of P2Y(1)R in EGFR-dependent epithelial cell proliferation. P2Y(1)R could potentially mediate both trophic stimuli of basally released nucleotides and first-line mitogenic stimulation upon tissue damage. It could also contribute to carcinogenesis and serve as target for antitumor therapies.

Purinergic receptors contribute to early mesangial cell transformation and renal vessel hypertrophy during angiotensin II-induced hypertension

Chronic ANG II infusions lead to increases in intrarenal ANG II levels, hypertension, and tissue injury. Increased blood pressure also elicits increases in renal interstitial fluid (RIF) ATP concentrations that stimulate cell proliferation. We evaluated the contribution of purinergic receptor activation to ANG II-induced renal injury in rats by treating with clopidogrel, a P2Y12 receptor blocker, or with PPADS, a nonselective P2 receptor blocker. alpha-Actin expression in mesangial cells, afferent arteriolar wall thickness (AAWT), cortical cell proliferation, and macrophage infiltration were used as early markers of renal injury. Clopidogrel and PPADS did not alter blood pressure, renin or kidney ANG II content. alpha-Actin expression increased from control of 0.6 +/- 0.4% of mesangial area to 6.3 +/- 1.9% in ANG II-infused rats and this response was prevented by clopidogrel (0.4 +/- 0.2%) and PPADS. The increase in AAWT from 4.7 +/- 0.1 to 6.0 +/- 0.1 mm in ANG II rats was also prevented by clopidogrel (4.8 +/- 0.1 mm) and PPADS. ANG II infusion led to interstitial macrophage infiltration (105 +/- 16 vs. 62 +/- 4 cell/mm(2)) and tubular proliferation (71 +/- 15 vs. 20 +/- 4 cell/mm(2)) and these effects were prevented by clopidogrel (52 +/- 4 and 36 +/- 3 cell/mm(2)) and PPADS. RIF ATP levels were higher in ANG II-infused rats than in control rats (11.8 +/- 1.9 vs. 5.6 +/- 0.6 nmol/l, P < 0.05). The results suggest that activation of vascular and glomerular purinergic P2 receptors may contribute to the mesangial cell transformation, renal inflammation, and vascular hypertrophy observed in ANG II-dependent hypertension.

P2 receptors in cardiovascular regulation and disease

The role of ATP as an extracellular signalling molecule is now well established and evidence is accumulating that ATP and other nucleotides (ADP, UTP and UDP) play important roles in cardiovascular physiology and pathophysiology, acting via P2X (ion channel) and P2Y (G protein-coupled) receptors. In this article we consider the dual role of ATP in regulation of vascular tone, released as a cotransmitter from sympathetic nerves or released in the vascular lumen in response to changes in blood flow and hypoxia. Further, purinergic long-term trophic and inflammatory signalling is described in cell proliferation, differentiation, migration and death in angiogenesis, vascular remodelling, restenosis and atherosclerosis. The effects on haemostasis and cardiac regulation is reviewed. The involvement of ATP in vascular diseases such as thrombosis, hypertension and diabetes will also be discussed, as well as various heart conditions. The purinergic system may be of similar importance as the sympathetic and renin-angiotensin-aldosterone systems in cardiovascular regulation and pathophysiology. The extracellular nucleotides and their cardiovascular P2 receptors are now entering the phase of clinical development.

P2 receptors in atherosclerosis and postangioplasty restenosis

Atherosclerosis is an immunoinflammatory process that involves complex interactions between the vessel wall and blood components and is thought to be initiated by endothelial dysfunction [Ross (Nature 362:801–09, 1993); Fuster et al. (N Engl J Med 326:242–50, 1992); Davies and Woolf (Br Heart J 69:S3–S11, 1993)]. Extracellular nucleotides that are released from a variety of arterial and blood cells [Di Virgilio and Solini (Br J Pharmacol 135:831–42, 2002)] can bind to P2 receptors and modulate proliferation and migration of smooth muscle cells (SMC), which are known to be involved in intimal hyperplasia that accompanies atherosclerosis and postangioplasty restenosis [Lafont et al. (Circ Res 76:996–002, 1995)]. In addition, P2 receptors mediate many other functions including platelet aggregation, leukocyte adherence, and arterial vasomotricity. A direct pathological role of P2 receptors is reinforced by recent evidence showing that upregulation and activation of P2Y₂ receptors in rabbit arteries mediates intimal hyperplasia [Seye et al. (Circulation 106:2720–726, 2002)]. In addition, upregulation of functional P2Y receptors also has been demonstrated in the basilar artery of the rat double-hemorrhage model [Carpenter et al. (Stroke 32:516–22, 2001)] and in coronary artery of diabetic dyslipidemic pigs [Hill et al. (J Vasc Res 38:432–43, 2001)]. It has been proposed that upregulation of P2Y receptors may be a potential diagnostic indicator for the early stages of atherosclerosis [Elmaleh et al. (Proc Natl Acad Sci U S A 95:691–95, 1998)]. Therefore, particular effort must be made to understand the consequences of nucleotide release from cells in the cardiovascular system and the subsequent effects of P2 nucleotide receptor activation in blood vessels, which may reveal novel therapeutic strategies for atherosclerosis and restenosis after angioplasty.

Alterations in Purinoceptor Expression in Human Long Saphenous Vein during Varicose Disease

OBJECTIVES

Varicose veins are dilated tortuous veins of varying tone. Purinergic signalling is important in the control of tone and in mediating trophic changes in blood vessels. The expression of P2 receptors in control and varicose veins will be examined.

METHODS

Purinergic signalling in circular and longitudinal smooth muscle of the human long saphenous vein was studied in control and varicose tissues using immunohistochemistry, organ bath pharmacology and electron microscopy.

RESULTS

P2X1, P2Y1, P2Y2, P2Y4 and P2Y6 receptors were present on circular and longitudinal smooth muscle. Purine-mediated circular and longitudinal muscle contractions were weaker in varicose veins. Electron microscopy and immunohistochemistry findings support the view that smooth muscle cells change from the contractile to synthetic phenotype in varicose veins, associated with an upregulation of P2Y1 and P2Y2 receptors and a down regulation of P2X1 receptors.

CONCLUSIONS

Down regulation of P2X1 receptors on the smooth muscle of varicose veins is associated with loss of contractile activity. Upregulation of P2Y1 and P2Y2 receptors is associated with a shift from contractile to synthetic and/or proliferative roles. The phenotype change in smooth muscle is associated with weakening of vein walls and may be a causal factor in the development of varicose veins.

Diguanosine pentaphosphate: an endogenous activator of Rho-kinase possibly involved in blood pressure regulation

OBJECTIVE

Rho-kinase activity is increased in cardiovascular disease and in the pathophysiology of hypertension. Few endogenous factors are known that activate the Rho-kinase pathway. Stimulation of P2Y receptors activates the Rho-kinase pathway. Recently identified diguanosine pentaphosphate (Gp5G) possibly activates P2Y receptors. In this study, Gp5G was identified and quantified in human plasma. The influence of Gp5G on vascular tone was studied.

METHODS

Gp5G in human plasma was purified to homogeneity by several steps. Gp5G was quantified and identified by matrix-assisted laser desorption/ionization mass spectrometry and enzymatic analysis. The vasoactive effects of Gp5G were studied in the isolated perfused rat kidney and after intra-aortic application. Activation of Rho-kinase was measured using western blot analysis.

RESULTS

The plasma level of Gp5G in healthy donors is 9.47 +/- 4.97 nmol/l. Gp5G increases contractile responses induced by angiotensin II in a dose-dependent way [ED50 (-log mol) angiotensin II: 10.9 +/- 0.1; angiotensin II plus Gp5G (100 nmol/l): 11.5 +/- 0.1]. P2 receptor antagonists inhibited the Gp5G-induced increase in angiotensin II vasoconstriction. MRS2179, a selective P2Y1 receptor antagonist, had no effect on Gp5G-mediated angiotensin II potentiation. Rho-kinase inhibition by Y27632 abolished the Gp5G-induced increase of contractile responses to angiotensin II. Concentrations of 10 nmol/l Gp5G activated the translocation of RhoA from the cytosolic to the membranous fraction indicating the activation of Rho-kinase. The intra-aortic application of 100 pmol Gp5G significantly increased mean arterial blood pressure by 13.5 +/- 4.2 mmHg.

CONCLUSION

Gp5G is an endogenous activator of Rho-kinase, which might affect vascular tone control by Rho-kinase at physiological levels. Gp5G activates P2Y4&6 receptors, and might play a role in physiological and pathophysiological vascular tone control.

Purinergic signaling regulates neural progenitor cell expansion and neurogenesis

Neural stem and progenitor cells typically exhibit a density-dependent survival and expansion, such that critical densities are required below which clonogenic progenitors are lost. This suggests that short-range autocrine factors may be critical for progenitor cell maintenance. We report here that purines drive the expansion of ventricular zone neural stem and progenitor cells, and that purine receptor activation is required for progenitor cells to be maintained as such. Neural progenitors expressed P2Y purinergic receptors and mobilized intracellular calcium in response to agonist. Receptor antagonists suppressed proliferation and permitted differentiation into neurons and glia in vitro, while subsequent removal of purinergic inhibition restored progenitor cell expansion. Real-time bioluminescence imaging of extracellular ATP revealed that the source of extracellular nucleotides are the progenitor cells themselves, which appear to release ATP in episodic burst events. Enzyme histochemistry of the adult rat brain for ectonucleotidase activity revealed that NTDPase, which acts to degrade active ATP and thereby clears it from areas of active purinergic transmission, was selectively localized to the subventricular zone and the dentate gyrus, regions in which neuronal differentiation proceeds from the progenitor cell pool. These data suggest that purine nucleotides act as proliferation signals for neural progenitor cells, and thereby serve as negative regulators of terminal neuronal differentiation. As a result, progenitor cell-derived neurogenesis is thus associated with regions of both active purinergic signaling and modulation thereof.

Imaging of cortical astrocytes using 2-photon laser scanning microscopy in the intact mouse brain

A number of studies over the past decade have shown that astrocytes, the supportive cells of the brain, play important roles in synaptic transmission including regulating the strength of both excitatory and inhibitory synapses. A major challenge for the future is to define the role of astrocytes in complex tasks, such as functional hyperemia and sensory processing, as well as their contribution to acute and degenerative diseases of the nervous system. Multiphoton imaging approaches are ideally suited to study electrically non-excitable astrocytes. We here discuss novel in vivo studies aimed at defining the role of astrocytes in normal and pathological brain function. With a better understanding of the role astrocytes play in information processing and regulation of the brain microenvironment in vivo, and the understanding that astrocytes are heavily implicated in the pathology of many diseases such as epilepsy, Alzheimer's and Parkinson's diseases, astrocytes provide a promising target for future drug therapy approaches.

P2 receptors in atherosclerosis and postangioplasty restenosis

Atherosclerosis is an immunoinflammatory process that involves complex interactions between the vessel wall and blood components and is thought to be initiated by endothelial dysfunction [1-3]. Extracellular nucleotides that are released from a variety of arterial and blood cells [4] can bind to P2 receptors and modulate proliferation and migration of smooth muscle cells (SMC), which is known to be involved in intimal hyperplasia that accompanies atherosclerosis and postangioplasty restenosis [5]. In addition, P2 receptors mediate many other functions, including platelet aggregation, leukocyte adherence, and arterial vasomotoricity. A direct pathological role of P2 receptors is reinforced by recent evidence showing that up-regulation and activation of P2Y(2) receptors in rabbit arteries mediates intimal hyperplasia [6]. In addition, up-regulation of functional P2Y receptors also has been demonstrated in the basilar artery of the rat double-hemorrhage model [7] and in coronary arteries of diabetic dyslipidemic pigs [8]. It has been proposed that up-regulation of P2Y receptors may be a potential diagnostic indicator for the early stages of atherosclerosis [9]. Therefore, particular effort must be made to understand the consequences of nucleotide release from cells in the cardiovascular system and the subsequent effects of P2 nucleotide receptor activation in blood vessels, which may reveal novel therapeutic strategies for atherosclerosis and restenosis after angioplasty.

Mechanisms for inhibition of P2 receptors signaling in neural cells

Trophic factors are required to ensure neuronal viability and regeneration after neural injury. Although abundant information is available on the factors that cause the activation of astrocytes, little is known about the molecular mechanisms underlying the regulation of this process. Nucleotides released into the extracellular space from injured or dying neural cells can activate astrocytes via P2 nucleotide receptors. After a brief historical review and update of novel P2 receptor antagonists, this article focuses on recent advancements toward understanding molecular mechanisms that regulate G protein-coupled P2Y receptor signaling. Among P2Y receptor subtypes, the heptahelical P2Y2 nucleotide receptor interacts with vitronectin receptors via an RGD sequence in the first extracellular loop, and this interaction is required for effective signal transduction to activate mitogen-activated protein kinases ERK1/2, to mobilize intracellular calcium stores via activation of phospholipase C, protein kinase C isoforms, and to activate focal adhesion kinase and other signaling events. Ligation of vitronectin receptors with specific antibodies caused an inhibition of P2Y2 receptor-induced ERK1/2 and p38 phosphorylation and P2Y2 receptor-induced cytoskeleton rearrangement and DNA synthesis. Structure-function studies have identified agonist-induced phosphorylation of the C-terminus of the P2Y2 receptor, an important mechanism for receptor desensitization. Understanding selective mechanisms for regulating P2Y2 receptor signaling could provide novel targets for therapeutic strategies in the management of brain injury, synaptogenesis, and neurological disorders.

Adenosine and deoxyadenosine induces apoptosis in oestrogen receptor-positive and -negative human breast cancer cells via the intrinsic pathway

In this study we have examined the cytotoxic effects of different concentrations of adenosine (Ado) and deoxyadenosine (dAdo) on human breast cancer cell lines. Ado and dAdo alone had little effect on cell cytotoxicity. However, in the presence of adenosine deaminase (ADA) inhibitor, EHNA, adenosine and deoxyadenosine led to significant growth inhibition of cells of the lines tested. Ado/EHNA and dAdo/EHNA-induced cell death was significantly inhibited by NBTI, an inhibitor of nucleoside transport, and 5'-amino-5'-deoxyadenosine, an inhibitor of adenosine kinase, but the effects were not affected by 8-phenyltheophylline, a broad inhibitor of adenosine receptors. The Ado/EHNA combination brought about morphological changes consistent with apoptosis. Caspase-9 activation was observed in MCF-7 and MDA-MB468 human breast cancer cell lines on treatment with Ado/EHNA or dAdo/EHNA, but, as expected, caspase-3 activation was only observed in MDA-MB468 cells. The results of the study, thus, suggest that extracellular adenosine and deoxyadenosine induce apoptosis in both oestrogen receptor-positive (MCF-7) and also oestrogen receptor-negative (MDA-MB468) human breast cancer cells by its uptake into the cells and conversion to AMP (dAMP) followed by activation of nucleoside kinase, and finally by the activation of the mitochondrial/intrinsic apoptotic pathway.

Enhanced P2X7 activity in human fibroblasts from diabetic patients: a possible pathogenetic mechanism for vascular damage in diabetes

OBJECTIVE

We have investigated expression and function of the P2X7 receptor in fibroblasts from healthy subjects and patients with type 2 diabetes.

METHODS AND RESULTS

Fibroblasts were isolated from skin biopsies. P2X7 receptor expression in both cell populations was measured by functional assays, RT-PCR, fluorescence-activated cell sorter, and immunoblotting. We found that fibroblasts from diabetic subjects are characterized by enhanced P2X7-mediated responses as indicated by increased shape changes, microvesiculation, enhanced fibronectin and interleukin 6 secretion, and accelerated apoptosis. These responses were blocked by preincubation with the P2X blockers KN-62, oxidized ATP, or pyridoxal phosphate-6-azo(benzene-2,4-disulfonic acid). Furthermore, we also found a higher level of spontaneous fibronectin secretion and of apoptosis in fibroblasts from diabetic compared with healthy subjects. Both higher basal level of fibronectin secretion and spontaneous rate of apoptosis were likely attributable to the increased pericellular concentration of ATP because fibroblasts from diabetic subjects released 3x as much ATP into the supernatants compared with fibroblasts from healthy subjects.

CONCLUSIONS

We conclude that fibroblasts from type 2 diabetes patients are characterized by a hyperactive purinergic loop based either on a higher level of ATP release or on increased P2X7 reactivity.

Dual role of PKA in phenotypic modulation of vascular smooth muscle cells by extracellular ATP

Extracellular ATP is released from activated platelets and endothelial cells and stimulates proliferation of vascular smooth muscle cells (VSMC). We found that ATP stimulates a profound but transient activation of protein kinase A (PKA) via purinergic P2Y receptors. The specific inhibition of PKA by adenovirus-mediated transduction of the PKA inhibitor (PKI) attenuates VSMC proliferation in response to ATP, suggesting a positive role for transient PKA activation in VSMC proliferation. By contrast, isoproterenol and forskolin, which stimulate a more sustained PKA activation, inhibit VSMC growth as expected. On the other hand, the activity of serum response factor (SRF) and the SRF-dependent expression of smooth muscle (SM) genes, such as SM-alpha-actin and SM22, are extremely sensitive to regulation by PKA, and even transient PKA activation by ATP is sufficient for their downregulation. Analysis of the dose responses of PKA activation, VSMC proliferation, SRF activity, and SM gene expression to ATP, with or without PKI overexpression, suggests the following model for the phenotypic modulation of VSMC by ATP, in which the transient PKA activation plays a critical role. At low micromolar doses, ATP elicits a negligible effect on DNA synthesis but induces profound SRF activity and SM gene expression, thus promoting the contractile VSMC phenotype. At high micromolar doses, ATP inhibits SRF activity and SM gene expression and promotes VSMC growth in a manner dependent on transient PKA activation. Transformation of VSMC by high doses of ATP can be prevented and even reversed by inhibition of PKA activity.

Extracellular ATP-mediated signaling for survival in hyperoxia-induced oxidative stress

Respiratory failure is a serious consequence of lung cell injury caused by treatment with high inhaled oxygen concentrations. Human lung microvascular endothelial cells (HLMVEC) are a principal target of hyperoxic injury (hyperoxia). Cell stress can cause release of ATP, and this extracellular nucleotide can activate purinoreceptors and mediate responses essential for survival. In this investigation, exposure of endothelial cells to an oxidative stress, hyperoxia, caused rapid but transient ATP release (20.03 +/- 2.00 nm/10(6) cells in 95% O(2) versus 0.08 +/- 0.01 nm/10(6) cells in 21% O2 at 30 min) into the extracellular milieu without a concomitant change in intracellular ATP. Endogenously produced extracellular ATP-enhanced mTOR-dependent uptake of glucose (3467 +/- 102 cpm/mg protein in 95% oxygen versus 2100 +/- 112 cpm/mg protein in control). Extracellular addition of ATP-activated important cell survival proteins like PI 3-kinase and extracellular-regulated kinase (ERK-1/2). These events were mediated primarily by P2Y receptors, specifically the P2Y2 and/or P2Y6 subclass of receptors. Extracellular ATP was required for the survival of HLMVEC in hyperoxia (55 +/- 10% surviving cells with extracellular ATP scavengers [apyrase + adenosine deaminase] versus 95 +/- 12% surviving cells without ATP scavengers at 4 d of hyperoxia). Incubation with ATP scavengers abolished ATP-dependent ERK phosphorylation stimulated by hyperoxia. Further, ERK activation also was found to be important for cell survival in hyperoxia, as treatment with PD98059 enhanced hyperoxia-mediated cell death. These findings demonstrate that ATP release and subsequent ATP-mediated signaling events are vital for survival of HLMVEC in hyperoxia.

Cellular Distribution and Functions of P2 Receptor Subtypes in Different Systems

This review is aimed at providing readers with a comprehensive reference article about the distribution and function of P2 receptors in all the organs, tissues, and cells in the body. Each section provides an account of the early history of purinergic signaling in the organ?cell up to 1994, then summarizes subsequent evidence for the presence of P2X and P2Y receptor subtype mRNA and proteins as well as functional data, all fully referenced. A section is included describing the plasticity of expression of P2 receptors during development and aging as well as in various pathophysiological conditions. Finally, there is some discussion of possible future developments in the purinergic signaling field.

Extracellular ATP as a signaling molecule for epithelial cells

The charge of this invited review is to present a convincing case for the fact that cells release their ATP for physiological reasons. Many of our "purinergic" colleagues as well as ourselves have experienced resistance to this concept, because it is teleologically counter-intuitive. This review serves to integrate the three main tenets of extracellular ATP signaling: ATP release from cells, ATP receptors on cells, and ATP receptor-driven signaling within cells to affect cell or tissue physiology. First principles will be discussed in the Introduction concerning extracellular ATP signaling. All possible cellular mechanisms of ATP release will then be presented. Use of nucleotide and nucleoside scavengers as well as broad-specificity purinergic receptor antagonists will be presented as a method of detecting endogenous ATP release affecting a biological endpoint. Innovative methods of detecting released ATP by adapting luciferase detection reagents or by using "biosensors" will be presented. Because our laboratory has been primarily interested in epithelial cell physiology and pathophysiology for several years, the role of extracellular ATP in regulation of epithelial cell function will be the focus of this review. For ATP release to be physiologically relevant, receptors for ATP are required at the cell surface. The families of P2Y G protein-coupled receptors and ATP-gated P2X receptor channels will be introduced. Particular attention will be paid to P2X receptor channels that mediate the fast actions of extracellular ATP signaling, much like neurotransmitter-gated channels versus metabotropic heptahelical neurotransmitter receptors that couple to G proteins. Finally, fascinating biological paradigms in which extracellular ATP signaling has been implicated will be highlighted. It is the goal of this review to convert and attract new scientists into the exploding field of extracellular nucleotide signaling and to convince the reader that extracellular ATP is indeed a signaling molecule.

P2Y-receptors stimulating the proliferation of human mesangial cells through the MAPK42/44 pathway

1. Mesangial cell proliferation is observed in a number of kidney diseases. The sympathetic cotransmitter ATP is suspected to play a major role in proliferative processes. Therefore, the effects of exogenous ATP on human mesangial cells in culture were studied. 2. Fresh human kidney cortex was processed to obtain mesangial cells in culture. Effects of nucleotides on [(3)H]thymidine incorporation, the activation of mitogen-activated protein kinase and the cell number were studied. The involved P2-receptors were characterized pharmacologically. In addition, we searched for mRNA for P2Y- and P2X-receptors by RT-PCR. 3. ATP (0.1-300 micro M) and related nucleotides induced a significant increase in [(3)H]thymidine incorporation up to 220% of control. The adenine nucleotides ATP and ADP were about equally effective. Also ATP-gamma-S, UTP, ADP-beta-S and 2-m-thio-ADP induced a weaker response. UDP and alpha-beta-methylene-ATP failed to induce an effect on [(3)H]thymidine uptake. 4. ATP (100 micro M) induced a fast activation of the MAPK(42/44) pathway. The effects of ATP on MAPK(42/44) activation and [(3)H]thymidine incorporation were reduced by the MAPK inhibitor PD 98059. Platelet-derived growth factor (PDGF 5 ng ml(-1)) increased the cell number to more than 122% of control. ATP (10 micro M) on top of PDGF amplified PDGF induced cell proliferation to 136% of control. 5. RT-PCR products for P2Y(1,2,4,6,11,12)- and P2X(1,2,4,5,6,7)-receptor subtypes were detected in human mesangial cells. 6. ATP has mitogenic effects on human mesangial cells. DNA synthesis is increased by the activation of the MAPK(42/44) pathway. ATP amplifies PDGF-induced cell hyperplasia.

Activation of P2Y2 receptor induces c-FOS protein through a pathway involving mitogen-activated protein kinases and phosphoinositide 3-kinases in HeLa cells

The effects of P2Y2 purinoceptor activation on c-Fos expression and the signaling pathways evoked by extracellular ATP/UTP in HeLa cells were investigated. We found that P2Y2 activation induced c-Fos protein and phosphorylated the extracellular signal-regulated kinases 1 and 2 (ERK1/2). The P2Y2-stimulated c-Fos induction was partly blocked (a) by U73122, a phospholipase C inhibitor, (b) by Gö6976, a conventional PKC inhibitor, (c) by PD098059, a mitogen-activated protein kinase kinase inhibitor, and, moreover, (d) by the inhibitors of phosphoinositide 3-kinases (PI3K), LY294002 and wortmannin. When Gö6976 and PD098059, or Gö6976 and wortmannin, were combined there was a totally inhibition of P2Y2-induced c-Fos increase. Either U73122 or Gö6976 did not inhibit ERK1/2 phosphorylation induced by ATP/UTP, while it was inhibited by LY294002 (or wortmannin) and by staurosporine. Additionally, wortmannin inhibited the cytosol-to-membrane translocation of PKC- epsilon induced by ATP/UTP. These data indicated that agonist-induced PI3K and downstream PKC- epsilon activation mediated the effect of ATP/UTP on ERK1/2 activation. To test the biological consequences of ERK1/2 activation, the effect of P2Y2 on cell functions were examined. P2Y2 stimulation increased cell proliferation and this effect was attenuated by PD098059 in a dose-dependent manner, thereby indicating that the ERK pathway mediates mitogenic signaling by P2Y2. In conclusion, the activation of conventional PKCs through P2Y2 receptor acts in concert with ERK and PI3K/PKC- epsilon pathways to induce c-Fos protein and HeLa cell proliferation.