P2Y2 receptor-mediated lymphotoxin-α secretion regulates intercellular cell adhesion molecule-1 expression in vascular smooth muscle cells

Structural Remodeling of the Extracellular Matrix in Arteriogenesis: A Review

Lower extremity arterial occlusive disease (AOD) results in significant morbidity and mortality for the population, with up to 10% of patients ultimately requiring amputation. An alternative method for non-surgical revascularization which is yet to be fully understood is the optimization of the body's own natural collateral arterial network in a process known as arteriogenesis. Under conditions of conductance vessel stenosis or occlusion resulting in increased flow, shear forces, and pressure gradients within collaterals, positive remodeling occurs to increase the diameter and capacity of these vessels. The creation of a distal arteriovenous fistula (AVF) will drive increased arteriogenesis as compared to collateral formation with the occlusion of a conductance vessel alone by further increasing flow through these arterioles, demonstrating the capacity for arteriogenesis to form larger, more efficient collaterals beyond what is spontaneously achieved after arterial occlusion. Arteries rely on an extracellular matrix (ECM) composed of elastic fibers and collagens that provide stability under hemodynamic stress, and ECM remodeling is necessary to allow for increased diameter and flow conductance in mature arterial structures. When positive remodeling occurs, digestion of lamella and the internal elastic lamina (IEL) by matrix metalloproteinases (MMPs) and other elastases results in the rearrangement and thinning of elastic structures and may be replaced with disordered elastin synthesis without recovery of elastic function. This results in transmission of wall strain to collagen and potential for aneurysmal degeneration along collateral networks, as is seen in the pancreaticoduodenal artery (PDA) after celiac occlusion and inferior mesenteric artery (IMA) with concurrent celiac and superior mesenteric artery (SMA) occlusions. Further understanding into the development of collaterals is required to both better understand aneurysmal degeneration and optimize collateral formation in AOD.

Filamin A Regulates Cardiovascular Remodeling

Filamin A (FLNA) is a large actin-binding cytoskeletal protein that is important for cell motility by stabilizing actin networks and integrating them with cell membranes. Interestingly, a C-terminal fragment of FLNA can be cleaved off by calpain to stimulate adaptive angiogenesis by transporting multiple transcription factors into the nucleus. Recently, increasing evidence suggests that FLNA participates in the pathogenesis of cardiovascular and respiratory diseases, in which the interaction of FLNA with transcription factors and/or cell signaling molecules dictate the function of vascular cells. Localized FLNA mutations associate with cardiovascular malformations in humans. A lack of FLNA in experimental animal models disrupts cell migration during embryogenesis and causes anomalies, including heart and vessels, similar to human malformations. More recently, it was shown that FLNA mediates the progression of myocardial infarction and atherosclerosis. Thus, these latest findings identify FLNA as an important novel mediator of cardiovascular development and remodeling, and thus a potential target for therapy. In this update, we summarized the literature on filamin biology with regard to cardiovascular cell function.

P2 Receptors as Therapeutic Targets in the Salivary Gland: From Physiology to Dysfunction

Although often overlooked in our daily lives, saliva performs a host of necessary physiological functions, including lubricating and protecting the oral cavity, facilitating taste sensation and digestion and maintaining tooth enamel. Therefore, salivary gland dysfunction and hyposalivation, often resulting from pathogenesis of the autoimmune disease Sjögren's syndrome or from radiotherapy of the head and neck region during cancer treatment, severely reduce the quality of life of afflicted patients and can lead to dental caries, periodontitis, digestive disorders, loss of taste and difficulty speaking. Since their initial discovery in the 1970s, P2 purinergic receptors for extracellular nucleotides, including ATP-gated ion channel P2X and G protein-coupled P2Y receptors, have been shown to mediate physiological processes in numerous tissues, including the salivary glands where P2 receptors represent a link between canonical and non-canonical saliva secretion. Additionally, extracellular nucleotides released during periods of cellular stress and inflammation act as a tissue alarmin to coordinate immunological and tissue repair responses through P2 receptor activation. Accordingly, P2 receptors have gained widespread clinical interest with agonists and antagonists either currently undergoing clinical trials or already approved for human use. Here, we review the contributions of P2 receptors to salivary gland function and describe their role in salivary gland dysfunction. We further consider their potential as therapeutic targets to promote physiological saliva flow, prevent salivary gland inflammation and enhance tissue regeneration.

P2Y2 R deletion ameliorates sialadenitis in IL-14α-transgenic mice

OBJECTIVE

Interleukin-14α-transgenic (IL-14αTG) mice develop an autoimmune exocrinopathy with characteristics similar to Sjögren's syndrome, including sialadenitis and hyposalivation. The P2Y₂ receptor (P2Y₂ R) for extracellular ATP and UTP is upregulated during salivary gland inflammation (i.e., sialadenitis) where it regulates numerous inflammatory responses. This study investigated the role of P2Y₂ Rs in autoimmune sialadenitis in the IL-14αTG mouse model of Sjögren's syndrome.

MATERIALS AND METHODS

IL-14αTG mice were bred with P2Y₂ R^-/- mice to generate IL-14αTG × P2Y₂ R^-/- mice. P2Y₂ R expression, lymphocytic focus scores, B- and T-cell accumulation, and lymphotoxin-α expression were evaluated in the submandibular glands (SMG) along with carbachol-stimulated saliva secretion in IL-14αTG, IL-14αTG × P2Y₂ R^-/- , and C57BL/6 control mice at 9 and 12 months of age.

RESULTS

Genetic ablation of P2Y₂ Rs in IL-14αTG mice significantly reduced B and T lymphocyte infiltration of SMGs. However, reduced sialadenitis did not restore saliva secretion in IL-14αTG × P2Y₂ R^-/- mice. Decreased sialadenitis in IL-14αTG × P2Y₂ R^-/- mice correlated with decreased lymphotoxin-α levels, a critical proinflammatory cytokine associated with autoimmune pathology in IL-14αTG mice.

CONCLUSIONS

The results of this study suggest that P2Y₂ Rs contribute to the development of salivary gland inflammation in IL-14αTG mice and may also contribute to autoimmune sialadenitis in humans.

The P2Y2 nucleotide receptor is an inhibitor of vascular calcification

BACKGROUND AND AIMS

Mutations in the 5'-nucleotidase ecto (NT5E) gene that encodes CD73, a nucleotidase that converts AMP to adenosine, are linked to arterial calcification. However, the role of purinergic receptor signaling in the pathology of intimal calcification is not well understood. In this study, we examined whether extracellular nucleotides acting via P2Y₂ receptor (P2Y₂R) modulate arterial intimal calcification, a condition highly correlated with cardiovascular morbidity.

METHODS

Apolipoprotein E, P2Y₂R double knockout mice (ApoE^-/-P2Y₂R^-/-) were used to determine the effect of P2Y₂R deficiency on vascular calcification in vivo. Vascular smooth muscle cells (VSMC) isolated from P2Y₂R^-/- mice grown in high phosphate medium were used to assess the role of P2Y₂R in the conversion of VSMC into osteoblasts. Luciferase-reporter assays were used to assess the effect of P2Y₂R on the transcriptional activity of Runx2.

RESULTS

P2Y₂R deficiency in ApoE^-/- mice caused extensive intimal calcification despite a significant reduction in atherosclerosis and macrophage plaque content. The ectoenzyme apyrase that degrades nucleoside di- and triphosphates accelerated high phosphate-induced calcium deposition in cultured VSMC. Expression of P2Y₂R inhibits calcification in vitro inhibited the osteoblastic trans-differentiation of VSMC. Mechanistically, expression of P2Y₂R inhibited Runx2 transcriptional activation of an osteocalcin promoter driven luciferase reporter gene.

CONCLUSIONS

This study reveals a role for vascular P2Y₂R as an inhibitor of arterial intimal calcification and provides a new mechanistic insight into the regulation of the osteoblastic trans-differentiation of SMC through P2Y₂R-mediated Runx2 antagonism. Given that calcification of atherosclerotic lesions is a significant clinical problem, activating P2Y₂R may be an effective therapeutic approach for treatment or prevention of vascular calcification.

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.

Deletion of P2Y2 receptor reveals a role for lymphotoxin-α in fatty streak formation

Background

Lymphotoxin alpha (LTα) is expressed in human atherosclerotic lesions and genetic variations in the LTα pathway have been linked to myocardial infarction. Activation of the P2Y₂ nucleotide receptor (P2Y₂R) regulates the production of LTα. in vitro. We aimed to uncover a potential pathway linking purinergic receptor to LTα-mediated inflammatory processes pivotal to the early stages of atherosclerosis in apolipoprotein E (ApoE^−/−) deficient mice.

Methods and results

En face immunostaining revealed that P2Y₂R and VCAM-1 are preferentially expressed in the atherosclerosis prone site of the mouse aortic sinus. Deletion of the P2Y₂R gene suppresses VCAM-1 expression. Compared with ApoE^−/−mice, ApoE^−/−mice lacking the P2Y₂R gene (ApoE^−/−/P2Y₂R^−/−) did not develop fatty streak lesions when fed a standard chow diet for 15 weeks. Systemic and CD4⁺ T cell production of the pro-inflammatory cytokine lymphotoxin-alpha (LTα) were specifically inhibited in ApoE^−/−/P2Y₂R^−/− mice. Anti-LTα preventive treatment was initiated in ApoE^−/− mice with intraperitoneal administration of recombinant human tumor necrosis factor receptor 1 fusion protein (TNFR1-Fc) on 5 consecutive days before the disease onset. Remarkably, none of the TNFR1:Fc-treated ApoE^−/− mice exhibited atherosclerotic lesions at any developmental stage.

Significance

ApoE^−/− mice deficient in P2Y₂R exhibit low endothelial cell VCAM-1 levels, decreased production of LTα and delayed onset of atherosclerosis. These data suggest that targeting this nucleotide receptor could be an effective therapeutic approach in atherosclerosis.

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.

A Novel Function for P2Y2 in Myeloid Recipient-Derived Cells during Graft-versus-Host Disease

Acute graft-versus-host disease (GvHD) is a life-threatening complication of allogeneic hematopoietic cell transplantation. During the initiation phase of acute GvHD, endogenous danger signals such as ATP are released and inform the innate immune system via activation of the purinergic receptor P2X7 that a noninfectious damage has occurred. A second ATP-activated purinergic receptor involved in inflammatory diseases is P2Y2. In this study, we used P2y2(-/-) mice to test the role of this receptor in GvHD. P2y2(-/-) recipients experienced reduced GvHD-related mortality, IL-6 levels, enterocyte apoptosis, and histopathology scores. Chimeric mice with P2y2 deficiency restricted to hematopoietic tissues survived longer after GvHD induction than did wild-type mice. P2y2 deficiency of the recipient was connected to lower levels of myeloperoxidase in the intestinal tract of mice developing GvHD and a reduced myeloid cell signature. Selective deficiency of P2Y2 in inflammatory monocytes decreased GvHD severity. Mechanistically, P2y2(-/-) inflammatory monocytes displayed defective ERK activation and reactive oxygen species production. Compatible with a role of P2Y2 in human GvHD, the frequency of P2Y2(+) cells in inflamed GvHD lesions correlated with histopathological GvHD severity. Our findings indicate a novel function for P2Y2 in ATP-activated recipient myeloid cells during GvHD, which could be exploited when targeting danger signals to prevent GvHD.

P2Y2 nucleotide receptor mediates arteriogenesis in a murine model of hind limb ischemia

OBJECTIVE

Arteriogenesis represents the maturation of preformed vascular connections in response to flow changes and shear stress. These collateral vessels can restore up to 60% of the native blood flow. Shear stress and vascular injury can induce the release of nucleotides from vascular smooth muscle cells and platelets that can serve as signaling ligands, suggesting they may be involved in mediating arteriogenesis. The P2Y2 nucleotide receptor (P2Y2R) has also been shown to mediate smooth muscle migration and arterial remodeling. Thus, we hypothesize that P2Y2R mediates arteriogenesis in response to ischemia.

METHODS

Hind limb ischemia was induced by femoral artery ligation (FAL) in C57Bl/6NJ or P2Y2R negative mice (P2Y2(-/-)). Hind limb perfusion was measured with laser Doppler perfusion imaging and compared with the sham-operated contralateral limb immediately and at 3, 7, 14, 21, and 28 days after ligation. Collateral vessel size was measured by Microfil casting. Muscle specimens were harvested and analyzed with immunohistochemistry for Ki67, vascular cell adhesion molecule, macrophages, and muscle viability by hematoxylin and essoin stain.

RESULTS

Hind limb ischemia induced by FAL in C57Bl/6NJ mice resulted in significant ischemia as measured by laser Doppler perfusion imaging. There was rapid recovery to nearly normal levels of perfusion by 2 weeks. FAL in P2Y2(-/-) mice resulted in severe ischemia with greater tissue loss. Recovery of perfusion was impaired, achieving only 40% compared with wild-type mice by 28 days. Collateral vessels in the P2Y2(-/-) mice were underdeveloped, with reduced vascular cell proliferation and smaller vessel size. The collaterals were ∼65% the size of wild-type collateral vessels (P = .011). Angiogenesis at 28 days in the ischemic muscle, however, was greater in the P2Y2(-/-) mice (P < .001), possibly related to persistent ischemia leading and angiogenic drive. Early macrophage recruitment was reduced by nearly 70% in P2Y2(-/-) despite significantly more myocyte necrosis. However, inflammation was greater at 28 days in the P2Y2(-/-) mice.

CONCLUSIONS

P2Y2R deficiency does not alter baseline collateral vessel formation but does significantly impair collateral maturation, with resultant persistent limb ischemia despite enhanced angiogenesis. These findings reinforce the importance of arteriogenesis in the recovery of perfusion in ischemic tissues compared with angiogenesis. They also support the role of P2Y2R in mediating this process. The mechanism by which P2Y2R mediates arteriogenesis may involve the recruitment of inflammatory cells to the ischemic tissues, which is essential to arteriogenesis. Approaches to target P2Y2R may yield new therapeutic strategies for the treatment of arterial occlusive disease.

The inhibitory effects of extracellular ATP on the growth of nasopharyngeal carcinoma cells via P2Y2 receptor and osteopontin

Background

Nasopharyngeal carcinoma (NPC) is a common malignant tumor observed in the populations of southern China and Southeast Asia. However, little is known about the effects of purinergic signal on the behavior of NPC cells. This study analyzed the effects of ATP on the growth and migration of NPC cells, and further investigated the potential mechanisms during the effects.

Methods

Cell viability was estimated by MTT assay. Transwell assay was utilized to assess the motility of NPC cells. Cell cycle and apoptosis were detected by flow cytometry analysis. Changes in OPN, P2Y2 and p65 expression were assessed by western blotting analysis or immunofluorescence. The effects of ATP and P2Y2 on promoter activity of OPN were analyzed by luciferase activity assay. The binding of p65 to the promoter region of OPN was examined by ChIP assay.

Results

An MTT assay indicated that ATP inhibited the proliferation of NPC cells in time- and dose-dependent manners, and a Transwell assay showed that extracellular ATP inhibited the motility of NPC cells. We further investigated the potential mechanisms involved in the inhibitory effect of extracellular ATP on the growth of NPC cells and found that extracellular ATP could reduce Bcl-2 and p-AKT levels while elevating Bax and cleaved caspase-3 levels in NPC cells. Decreased levels of p65 and osteopontin were also detected in the ATP-treated NPC cells. We demonstrated that extracellular ATP inhibited the growth of NPC cells via p65 and osteopontin and verified that P2Y2 overexpression elevated the inhibitory effect of extracellular ATP on the proliferation of NPC cells. Moreover, a dual luciferase reporter assay showed that the level of osteopontin transcription was inhibited by extracellular ATP and P2Y2. ATP decreased the binding of p65 to potential sites in the OPN promoter region in NPC cells.

Conclusion

This study indicated that extracellular ATP inhibited the growth of NPC cells via P2Y2, p65 and OPN. ATP could be a promising agent serving as an adjuvant in the treatment of NPC.

Role of the Lymphotoxin/LIGHT System in the Development and Maintenance of Reticular Networks and Vasculature in Lymphoid Tissues

Lymphoid organs are meeting zones where lymphocytes come together and encounter antigens present in the blood and lymph or as delivered by cells migrating from the draining tissue bed. The exquisite efficiency of this process relies heavily on highly specialized anatomy to direct and position the various players. Gated entry and exit control access to these theaters and reticular networks and associated chemokines guide cells into the proper sections. Lymphoid tissues are remarkably plastic, being able to expand dramatically and then involute upon resolution of the danger. All of the reticular scaffolds and vascular and lymphatic components adapt accordingly. As such, the lymph node (LN) is a wonderful example of a physiologic remodeling process and is potentially a guide to study such elements in pathological settings such as fibrosis, chronic infection, and tumor metastasis. The lymphotoxin/LIGHT axis delivers critical differentiation signals that direct and hone differentiation of both reticular networks and the vasculature. Considerable progress has been made recently in understanding the mesenchymal differentiation pathways leading to these specialized networks and in the remodeling that occurs in reactive LNs. In this article, we will review some new advances in the area in terms of developmental, differentiation, and maintenance events mediated by this axis.

The P2Y2 Receptor Interacts with VE-Cadherin and VEGF Receptor-2 to Regulate Rac1 Activity in Endothelial Cells

Vascular endothelial cadherin (VE-cadherin) mediates homophylic adhesion between endothelial cells and is an important regulator of angiogenesis, blood vessel permeability and leukocyte trafficking. Rac1, a member of the Rho family of GTPases, controls VE-cadherin adhesion by acting downstream of several growth factors, including angiopoietin-1 and vascular endothelial growth factor (VEGF). Here we show that UTP-induced activation of the G_q protein-coupled P2Y₂ nucleotide receptor (P2Y₂R) in human coronary artery endothelial cells (HCAECs) activated Rac1 and caused a transient complex to form between P2Y₂R, VE-cadherin and VEGF receptor-2 (VEGFR-2). Knockdown of VE-cadherin expression with siRNA did not affect UTP-induced activation of extracellular signal-regulated kinases 1/2 (ERK1/2) but led to a loss of UTP-induced Rac1 activation and tyrosine phosphorylation of p120 catenin, a cytoplasmic protein known to interact with VE-cadherin. Activation of the P2Y₂R by UTP also caused a prolonged interaction between p120 catenin and vav2 (a guanine nucleotide exchange factor for Rac) that correlated with the kinetics of UTP-induced tyrosine phosphorylation of p120 catenin and VE-cadherin. Inhibitors of VEGFR-2 (SU1498) or Src (PP2) significantly diminished UTP-induced Rac1 activation, tyrosine phosphorylation of p120 catenin and VE-cadherin, and association of the P2Y₂R with VE-cadherin and p120 catenin with vav2. These findings suggest that the P2Y₂R uses Src and VEGFR-2 to mediate association of the P2Y₂R with VE-cadherin complexes in endothelial adherens junctions to activate Rac1.