P2Y6 receptor: A promising therapeutic target for atherosclerosis

Atherosclerosis is induced by lipid accumulation, inflammation, and endothelial dysfunction, and is the leading cause of death from cardiovascular disease worldwide. The P2Y6 receptor can be activated by the extracellular release of UDP. The evidence from the last decade has highlighted its critical therapeutic effect in atherosclerosis, yet with unclear mechanisms. This review introduced the P2Y6 receptor in atherosclerosis, and its mechanisms of atherosclerosis-promoting in macrophages, endothelial cells, and vascular smooth muscle cells. Finally, we discussed the development and potential of P2Y6 receptor antagonists in treating atherosclerosis.

New LFA-1 inhibitor Orientin reduces angiotensin II-induced vascular remodeling

BACKGROUND

The interaction between monocytes and vascular endothelium often leads to inflammatory reactions and vascular remodeling. The lymphocyte function-associated antigen 1 (LFA1) plays a crucial role in promoting leukocyte adhesion and migration during inflammatory diseases. However, the role of LFA1 in angiotensin II (Ang II)-induced hypertension and vascular remodeling is not clear. Orientin (Ori) has antioxidant, anti-inflammatory, anticancer, and resistance to myocardial remodeling. However, the role of Orientin remains unclear in angiotensin II (Ang II)-induced hypertension and vascular remodeling.

METHODS

In this study, Ang II was used to induce hypertension in mice. We employed various techniques including blood pressure monitoring, pathological staining, Immunofluorescent and Immunohistochemical staining, real time-PCR, vasodilation analysis and other methods to study whether LFA1 antibody and Orientin can regulate vascular remoding.

RESULTS

Our results showed that LFA1 significantly improved Ang II-induced hypertension, inflammation, fibrosis, and oxidative stress. Furthermore, in vitro experiments have substantiated that the use of neutralizing antibodies targeting LFA1 can effectively hinder the migration of macrophages to endothelial cells, which is triggered by Ang II. Additionally, the antibodies also reduce the extent of DNA damage and oxidative stress. Orientin can interact with LFA-1. Then, it was proved by pathological staining that Orientin can inhibit Ang II-induced vascular remodeling.

CONCLUSION

Here, we identified Orientin as a small molecule inhibitor of LFA-1 with anti-vascular remodeling function. These findings not only suggest that Orientin is a promising compound for the clinical treatment of vascular injury and hypertension, but also provide strategies for the treatment of cardiovascular diseases.

Attributes novel drug candidate: Constitutive GPCR signal bias mediated by purinergic receptors

G protein-coupled receptors (GPCRs) can transmit signals via G protein-dependent or independent pathways due to the conformational changes of receptors and ligands, which is called biased signaling. This concept posits that ligands can selectively activate a specific signaling pathway after receptor activation, facilitating downstream signaling along a preferred pathway. Biased agonism enables the development of ligands that prioritize therapeutic signaling pathways while mitigating on-target undesired effects. As a class of GPCRs located on the surface of cell membranes, the discovery and clinical implementation of adenosine and P2Y receptors purinergic signaling modulators have progressed dramatically. However, many preclinical drug candidates targeting purinergic receptors have failed in clinical trials due to limited efficacy and/or severe on-target undesired effects. To overcome the key barriers typically encountered when transitioning ligands into the clinic, the renewed impetus has focused on the modulation of purinergic receptor function by exogenous agonists/antagonists and allosteric modulators to exploit biased agonism. This article provides a brief overview of the research progress on the mechanism of purinergic biased signal transduction from the conformational changes of purinergic GPCRs and biased ligands primarily, and highlights therapeutically relevant biased agonism at purinergic receptors.

TRPC6-Mediated Zn2+ Influx Negatively Regulates Contractile Differentiation of Vascular Smooth Muscle Cells

Vascular smooth muscle cells (VSMCs) can dynamically change their phenotype between contractile and synthetic forms in response to environmental stress, which is pivotal in maintaining vascular homeostasis and mediating pathological remodeling of blood vessels. We previously reported that suppression of canonical transient receptor potential 6 (TRPC6) channel-mediated cation entry sustains VSMCs contractile phenotype and promotes the blood flow recovery after hindlimb ischemia in mice. We also reported that Zn2+, a metal biomolecule mobilized by TRPC6 channel activation, exerts potential beneficial effects on cardiac contractility and remodeling. Therefore, we hypothesized that TRPC6-mediated Zn2+ influx participates in phenotype switching of VSMCs and vascular remodeling. We established rat aortic smooth muscle cells (RAoSMCs) stably expressing wild type (WT) and Zn2+ only impermeable TRPC6 (KYD) mutant. Although the resting phenotypes were similar in both RAoSMCs, pharmacological TRPC6 activation by PPZ2 prevented the transforming growth factor (TGF) β-induced reduction in the intracellular Zn2+ amount and contractile differentiation in RAoSMCs (WT), but failed to prevent them in RAoSMCs (KYD). There were no significant differences in TRPC6-dependent cation currents among all RAoSMCs pretreated with or without TGFβ and/or PPZ2, suggesting that TRPC6 channels are functionally expressed in RAoSMCs regardless of their phenotype. Treatment of mice with PPZ2 attenuated the progression of vascular remodeling caused by chronic angiotensin II infusion. These results suggest that Zn2+ influx through TRPC6 channels negatively regulates the TGFβ-induced contractile differentiation of VSMCs and the progression of vascular remodeling in rodents.

Ligand-Independent Spontaneous Activation of Purinergic P2Y6 Receptor Under Cell Culture Soft Substrate

G protein-coupled receptors (GPCRs) exist in the conformational equilibrium between inactive state and active state, where the proportion of active state in the absence of a ligand determines the basal activity of GPCRs. Although many GPCRs have different basal activity, it is still unclear whether physiological stresses such as substrate stiffness affect the basal activity of GPCRs. In this study, we identified that purinergic P2Y6 receptor (P2Y6R) induced spontaneous Ca2+ oscillation without a nucleotide ligand when cells were cultured in a silicon chamber. This P2Y6R-dependent Ca2+ oscillation was absent in cells cultured in glass dishes. Coating substrates, including collagen, laminin, and fibronectin, did not affect the P2Y6R spontaneous activity. Mutation of the extracellular Arg-Gly-Asp (RGD) motif of P2Y6R inhibited spontaneous activity. Additionally, extracellular Ca2+ was required for P2Y6R-dependent spontaneous Ca2+ oscillation. The GPCR screening assay identified cells expressing 10 GPCRs, including purinergic P2Y1R, P2Y2R, and P2Y6R, that exhibited spontaneous Ca2+ oscillation under cell culture soft substrate. Our results suggest that stiffness of the cell adhesion surface modulates spontaneous activities of several GPCRs, including P2Y6R, through a ligand-independent mechanism.

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

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

The P2Y6 Receptor as a Potential Keystone in Essential Hypertension

Essential hypertension (HT) is a highly prevalent cardiovascular disease of unclear physiopathology. Pharmacological studies suggest that purinergic P2Y6 receptors (P2ry6) play important roles in cardiovascular function and may contribute to angiotensin II (AgtII) pathophysiological effects. Here, we tested the hypothesis that functional coupling between P2ry6 and AgtII receptors mediates altered vascular reactivity in HT. For this, a multipronged approach was implemented using mesenteric vascular smooth muscle cells (VSMCs) and arteries from Blood Pressure Normal (BPN) and Blood Pressure High (BPH) mice. Differential transcriptome profiling of mesenteric artery VSMCs identified P2ry6 purinergic receptor mRNA as one of the top upregulated transcripts in BPH. P2Y receptor activation elicited distinct vascular responses in mesenteric arteries from BPN and BPH mice. Accordingly, 10 µm UTP produced a contraction close to half-maximal activation in BPH arteries but no response in BPN vessels. AgtII-induced contraction was also higher in BPH mice despite having lower AgtII receptor type-1 (Agtr1) expression and was sensitive to P2ry6 modulators. Proximity ligation assay and super-resolution microscopy showed closer localization of Agtr1 and P2ry6 at/near the membrane of BPH mice. This proximal association was reduced in BPN mice, suggesting a functional role for Agtr1-P2ry6 complexes in the hypertensive phenotype. Intriguingly, BPN mice were resistant to AgtII-induced HT and showed reduced P2ry6 expression in VSMCs. Altogether, results suggest that increased functional coupling between P2ry6 and Agtr1 may contribute to enhanced vascular reactivity during HT. In this regard, blocking P2ry6 could be a potential pharmacological strategy to treat HT.

Potential of dapagliflozin to prevent vascular remodeling in the rat carotid artery following balloon injury

BACKGROUND AND AIMS

Sodium-glucose co-transporter 2 (SGLT2) inhibitors have been shown to reduce the risk of cardiovascular events independently of glycemic control. However, the possibility that SGLT2 inhibitors improve vascular restenosis is unknown. The aim of this study was to examine whether dapagliflozin could prevent neointima thickening following balloon injury and, if so, to determine the underlying mechanisms.

METHODS

Saline, dapagliflozin (1.5 mg/kg/day), or losartan (30 mg/kg/day) was administered orally for five weeks to male Wistar rats. Balloon injury of the left carotid artery was performed a week after starting the treatment and rats were sacrificed 4 weeks later. The extent of neointima was assessed by histomorphometric and immunofluorescence staining analyses. Vascular reactivity was assessed on injured and non-injured carotid artery rings, changes of target factors by immunofluorescence, RT-qPCR, and histochemistry.

RESULTS

Dapagliflozin and losartan treatments reduced neointima thickening by 32 % and 27 %, respectively. Blunted contractile responses to phenylephrine and relaxations to acetylcholine and down-regulation of eNOS were observed in the injured arteries. RT-qPCR investigations indicated an increased in gene expression of inflammatory (IL-1beta, VCAM-1), oxidative (p47phox, p22phox) and fibrotic (TGF-beta1) markers in the injured carotid. While these changes were not affected by dapagliflozin, increased levels of AT1R and NTPDase1 (CD39) and decreased levels of ENPP1 were observed in the restenotic carotid artery of the dapagliflozin group.

CONCLUSIONS

Dapagliflozin effectively reduced neointimal thickening. The present data suggest that dapagliflozin prevents restenosis through interfering with angiotensin and/or extracellular nucleotides signaling. SGLT2 represents potential new target for limiting vascular restenosis.

Unraveling the crosstalk between renin-angiotensin system receptors

The renin-angiotensin system (RAS) plays a key role in blood pressure regulation. The RAS is a complex interconnected system composed of two axes with opposite effects. The pressor arm, represented by angiotensin (Ang) II and the AT1 receptor (AT1R), mediates the vasoconstrictor, proliferative, hypertensive, oxidative, and pro-inflammatory effects of the RAS, while the depressor/protective arm, represented by Ang-(1-7), its Mas receptor (MasR) and the AT2 receptor (AT2R), opposes the actions elicited by the pressor arm. The AT1R, AT2R, and MasR belong to the G-protein-coupled receptor (GPCR) family. GPCRs operate not only as monomers, but they can also function in dimeric (homo and hetero) or higher-order oligomeric states. Due to the interaction with other receptors, GPCR properties may change: receptor affinity, trafficking, signaling, and its biological function may be altered. Thus, heteromerization provides a newly recognized means of modulation of receptor function, as well as crosstalk between GPCRs. This review is focused on angiotensin receptors, and how their properties are influenced by crosstalk with other receptors, adding more complexity to an already complex system and potentially opening up new therapeutic approaches.

The role of P2Y6 receptor in the pathogenesis of cardiovascular and inflammatory diseases

The purinergic receptor P2Y6 receptor (P2Y6R) is a member of the G protein-coupled receptors (GPCR) family. P2Y6R is widely expressed in various cell types and plays a critical role in physiological processes, where it is activated by extracellular uridine diphosphate (UDP) and mobilizes Ca2+ via the Gαq/11 protein pathway. We have recently discovered the pathophysiological role of P2Y6R in cardiovascular and inflammatory diseases, including inflammatory bowel disease and non-alcoholic fatty liver disease. Furthermore, we uncovered the redox-dependent internalization of P2Y6R. In this review, we provide a comprehensive overview of the pathophysiological activity of P2Y6R in cardiovascular and inflammatory diseases. Additionally, we discuss the concept of atypical internalization control of GPCRs, which may be applied in the prevention and treatment of intestinal inflammation and cardiovascular remodeling.

Interaction of Angiotensin II AT1 Receptors with Purinergic P2X Receptors in Regulating Renal Afferent Arterioles in Angiotensin II-Dependent Hypertension

In angiotensin II (Ang II)-dependent hypertension, Ang II activates angiotensin II type 1 receptors (AT1R) on renal vascular smooth muscle cells, leading to renal vasoconstriction with eventual glomerular and tubular injury and interstitial inflammation. While afferent arteriolar vasoconstriction is initiated by the increased intrarenal levels of Ang II activating AT1R, the progressive increases in arterial pressure stimulate the paracrine secretion of adenosine triphosphate (ATP), leading to the purinergic P2X receptor (P2XR)-mediated constriction of afferent arterioles. Thus, the afferent arteriolar tone is maintained by two powerful systems eliciting the co-existing activation of P2XR and AT1R. This raises the conundrum of how the AT1R and P2XR can both be responsible for most of the increased renal afferent vascular resistance existing in angiotensin-dependent hypertension. Its resolution implies that AT1R and P2XR share common receptor or post receptor signaling mechanisms which converge to maintain renal vasoconstriction in Ang II-dependent hypertension. In this review, we briefly discuss (1) the regulation of renal afferent arterioles in Ang II-dependent hypertension, (2) the interaction of AT1R and P2XR activation in regulating renal afferent arterioles in a setting of hypertension, (3) mechanisms regulating ATP release and effect of angiotensin II on ATP release, and (4) the possible intracellular pathways involved in AT1R and P2XR interactions. Emerging evidence supports the hypothesis that P2X1R, P2X7R, and AT1R actions converge at receptor or post-receptor signaling pathways but that P2XR exerts a dominant influence abrogating the actions of AT1R on renal afferent arterioles in Ang II-dependent hypertension. This finding raises clinical implications for the design of therapeutic interventions that will prevent the impairment of kidney function and subsequent tissue injury.

MicroRNA: Crucial modulator in purinergic signalling involved diseases

Both microRNAs (miRNAs) and purinergic signalling are widely and respectively expressed in various tissues of different organisms and play vital roles in a variety of physiological and pathological processes. Here, we reviewed the current publications contributed to the relationship of miRNAs and purinergic signalling in cardiovascular diseases, gastrointestinal diseases, neurological diseases, and ophthalmic diseases. We tried to decode the miRNAs-purinergic signalling network of purinergic signalling involved diseases. The evidence indicated that more than 30 miRNAs (miR-22, miR-30, miR-146, miR-150, miR-155, miR-187, etc.) directly or indirectly modulate P1 receptors (A₁, A_2A, A_2B, A₃), P2 receptors (P2X1, P2X3, P2X4, P2X7, P2Y2, P2Y6, P2Y12), and ecto-enzymes (CD39, CD73, ADA2); P2X7 and CD73 could be modulated by multiple miRNAs (P2X7: miR-21, miR-22, miR-30, miR-135a, miR-150, miR-186, miR-187, miR-216b; CD73: miR-141, miR-101, miR-193b, miR-340, miR-187, miR-30, miR-422a); miR-187 would be the common miRNA to modulate P2X7 and CD73.

The Pleiotropic Role of Extracellular ATP in Myocardial Remodelling

Myocardial remodelling is a molecular, cellular, and interstitial adaptation of the heart in response to altered environmental demands. The heart undergoes reversible physiological remodelling in response to changes in mechanical loading or irreversible pathological remodelling induced by neurohumoral factors and chronic stress, leading to heart failure. Adenosine triphosphate (ATP) is one of the potent mediators in cardiovascular signalling that act on the ligand-gated (P2X) and G-protein-coupled (P2Y) purinoceptors via the autocrine or paracrine manners. These activations mediate numerous intracellular communications by modulating the production of other messengers, including calcium, growth factors, cytokines, and nitric oxide. ATP is known to play a pleiotropic role in cardiovascular pathophysiology, making it a reliable biomarker for cardiac protection. This review outlines the sources of ATP released under physiological and pathological stress and its cell-specific mechanism of action. We further highlight a series of cardiovascular cell-to-cell communications of extracellular ATP signalling cascades in cardiac remodelling, which can be seen in hypertension, ischemia/reperfusion injury, fibrosis, hypertrophy, and atrophy. Finally, we summarize current pharmacological intervention using the ATP network as a target for cardiac protection. A better understanding of ATP communication in myocardial remodelling could be worthwhile for future drug development and repurposing and the management of cardiovascular diseases.

Knockout of Purinergic P2Y6 Receptor Fails to Improve Liver Injury and Inflammation in Non-Alcoholic Steatohepatitis

Nonalcoholic steatohepatitis (NASH) is a disease that progresses from nonalcoholic fatty liver (NAFL) and which is characterized by inflammation and fibrosis. The purinergic P2Y₆ receptor (P2Y₆R) is a pro-inflammatory G_q/G₁₂ family protein-coupled receptor and reportedly contributes to intestinal inflammation and cardiovascular fibrosis, but its role in liver pathogenesis is unknown. Human genomics data analysis revealed that the liver P2Y₆R mRNA expression level is increased during the progression from NAFL to NASH, which positively correlates with inductions of C-C motif chemokine 2 (CCL2) and collagen type I α1 chain (Col1a1) mRNAs. Therefore, we examined the impact of P2Y₆R functional deficiency in mice crossed with a NASH model using a choline-deficient, L-amino acid-defined, high-fat diet (CDAHFD). Feeding CDAHFD for 6 weeks markedly increased P2Y₆R expression level in mouse liver, which was positively correlated with CCL2 mRNA induction. Unexpectedly, the CDAHFD treatment for 6 weeks increased liver weights with severe steatosis in both wild-type (WT) and P2Y₆R knockout (KO) mice, while the disease marker levels such as serum AST and liver CCL2 mRNA in CDAHFD-treated P2Y₆R KO mice were rather aggravated compared with those of CDAHFD-treated WT mice. Thus, P2Y₆R may not contribute to the progression of liver injury, despite increased expression in NASH liver.

Mechanisms of sympathoexcitation via P2Y6 receptors

Many drugs used in cardiovascular therapy, such as angiotensin receptor antagonists and beta-blockers, may exert at least some of their actions through effects on the sympathetic nervous system, and this also holds true for e.g., P2Y12 antagonists. A new target at the horizon of cardiovascular drugs is the P2Y6 receptor which contributes to the development of arteriosclerosis and hypertension. To learn whether P2Y6 receptors in the sympathetic nervous system might contribute to actions of respective receptor ligands, responses of sympathetic neurons to P2Y6 receptor activation were analyzed in primary cell culture. UDP in a concentration dependent manner caused membrane depolarization and enhanced numbers of action potentials fired in response to current injections. The excitatory action was antagonized by the P2Y6 receptor antagonist MRS2578, but not by the P2Y2 antagonist AR-C118925XX. UDP raised intracellular Ca2+ in the same range of concentrations as it enhanced excitability and elicited inward currents under conditions that favor Cl- conductances, and these were reduced by a blocker of Ca2+-activated Cl- channels, CaCCInh-A01. In addition, UDP inhibited currents through KV7 channels. The increase in numbers of action potentials caused by UDP was not altered by the KV7 channel blocker linopirdine, but was enhanced in low extracellular Cl- and was reduced by CaCCInh-A01 and by an inhibitor of phospholipase C. Moreover, UDP enhanced release of previously incorporated [3H] noradrenaline, and this was augmented in low extracellular Cl- and by linopirdine, but attenuated by CaCCInh-A01. Together, these results reveal sympathoexcitatory actions of P2Y6 receptor activation involving Ca2+-activated Cl- channels.

Myocardial TRPC6-mediated Zn2+ influx induces beneficial positive inotropy through β-adrenoceptors

Baroreflex control of cardiac contraction (positive inotropy) through sympathetic nerve activation is important for cardiocirculatory homeostasis. Transient receptor potential canonical subfamily (TRPC) channels are responsible for α₁-adrenoceptor (α₁AR)-stimulated cation entry and their upregulation is associated with pathological cardiac remodeling. Whether TRPC channels participate in physiological pump functions remains unclear. We demonstrate that TRPC6-specific Zn²⁺ influx potentiates β-adrenoceptor (βAR)-stimulated positive inotropy in rodent cardiomyocytes. Deletion of trpc6 impairs sympathetic nerve-activated positive inotropy but not chronotropy in mice. TRPC6-mediated Zn²⁺ influx boosts α₁AR-stimulated βAR/G_s-dependent signaling in rat cardiomyocytes by inhibiting β-arrestin-mediated βAR internalization. Replacing two TRPC6-specific amino acids in the pore region with TRPC3 residues diminishes the α₁AR-stimulated Zn²⁺ influx and positive inotropic response. Pharmacological enhancement of TRPC6-mediated Zn²⁺ influx prevents chronic heart failure progression in mice. Our data demonstrate that TRPC6-mediated Zn²⁺ influx with α₁AR stimulation enhances baroreflex-induced positive inotropy, which may be a new therapeutic strategy for chronic heart failure.

Drug repurposing for the treatment of COVID-19

Coronavirus disease 2019 (COVID-19) remains prevalent worldwide since its onset was confirmed in Wuhan, China in 2019. Vaccines against the causative virus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), have shown a preventive effect against the onset and severity of COVID-19, and social and economic activities are gradually recovering. However, the presence of vaccine-resistant variants has been reported, and the development of therapeutic agents for patients with severe COVID-19 and related sequelae remains urgent. Drug repurposing, also called drug repositioning or eco-pharma, is the strategy of using previously approved and safe drugs for a therapeutic indication that is different from their original indication. The risk of severe COVID-19 and mortality increases with advancing age, cardiovascular disease, hypertension, diabetes, and cancer. We have reported three protein-protein interactions that are related to heart failure, and recently identified that one mechanism increases the risk of SARS-CoV-2 infection in mammalian cells. This review outlines the global efforts and outcomes of drug repurposing research for the treatment of severe COVID-19. It also discusses our recent finding of a new protein-protein interaction that is common to COVID-19 aggravation and heart failure.

Knockout of the P2Y6 Receptor Prevents Peri-Infarct Neuronal Loss after Transient, Focal Ischemia in Mouse Brain

After stroke, there is a delayed neuronal loss in brain areas surrounding the infarct, which may in part be mediated by microglial phagocytosis of stressed neurons. Microglial phagocytosis of stressed or damaged neurons can be mediated by UDP released from stressed neurons activating the P2Y6 receptor on microglia, inducing microglial phagocytosis of such neurons. We show evidence here from a small trial that the knockout of the P2Y6 receptor, required for microglial phagocytosis of neurons, prevents the delayed neuronal loss after transient, focal brain ischemia induced by endothelin-1 injection in mice. Wild-type mice had neuronal loss and neuronal nuclear material within microglia in peri-infarct areas. P2Y6 receptor knockout mice had no significant neuronal loss in peri-infarct brain areas seven days after brain ischemia. Thus, delayed neuronal loss after stroke may in part be mediated by microglial phagocytosis of stressed neurons, and the P2Y6 receptor is a potential treatment target to prevent peri-infarct neuronal loss.

Redox-dependent internalization of the purinergic P2Y6 receptor limits colitis progression

[Figure: see text].

Vascular Smooth Muscle Cells Mechanosensitive Regulators and Vascular Remodeling

Blood vessels are subjected to mechanical loads of pressure and flow, inducing smooth muscle circumferential and endothelial shear stresses. The perception and response of vascular tissue and living cells to these stresses and the microenvironment they are exposed to are critical to their function and survival. These mechanical stimuli not only cause morphological changes in cells and vessel walls but also can interfere with biochemical homeostasis, leading to vascular remodeling and dysfunction. However, the mechanisms underlying how these stimuli affect tissue and cellular function, including mechanical stimulation-induced biochemical signaling and mechanical transduction that relies on cytoskeletal integrity, are unclear. This review focuses on signaling pathways that regulate multiple biochemical processes in vascular mesangial smooth muscle cells in response to circumferential stress and are involved in mechanosensitive regulatory molecules in response to mechanotransduction, including ion channels, membrane receptors, integrins, cytoskeletal proteins, nuclear structures, and cascades. Mechanoactivation of these signaling pathways is closely associated with vascular remodeling in physiological or pathophysiological states.

Neuronal Loss after Stroke Due to Microglial Phagocytosis of Stressed Neurons

After stroke, there is a rapid necrosis of all cells in the infarct, followed by a delayed loss of neurons both in brain areas surrounding the infarct, known as 'selective neuronal loss', and in brain areas remote from, but connected to, the infarct, known as 'secondary neurodegeneration'. Here we review evidence indicating that this delayed loss of neurons after stroke is mediated by the microglial phagocytosis of stressed neurons. After a stroke, neurons are stressed by ongoing ischemia, excitotoxicity and/or inflammation and are known to: (i) release "find-me" signals such as ATP, (ii) expose "eat-me" signals such as phosphatidylserine, and (iii) bind to opsonins, such as complement components C1q and C3b, inducing microglia to phagocytose such neurons. Blocking these factors on neurons, or their phagocytic receptors on microglia, can prevent delayed neuronal loss and behavioral deficits in rodent models of ischemic stroke. Phagocytic receptors on microglia may be attractive treatment targets to prevent delayed neuronal loss after stroke due to the microglial phagocytosis of stressed neurons.

Structure-activity relationships of pyrimidine nucleotides containing a 5'-α,β-methylene diphosphonate at the P2Y6 receptor

The Gq-coupled P2Y6 receptor (P2Y6R) is a component of the purinergic signaling system and functions in inflammatory, cardiovascular and metabolic processes. UDP, the native P2Y6R agonist and P2Y14R partial agonist, is subject to hydrolysis by ectonucleotidases. Therefore, we have synthesized UDP/CDP analogues containing a stabilizing α,β-methylene bridge as P2Y6R agonists and identified compatible affinity-enhancing pyrimidine modifications. A distal binding region on the receptor was explored with 4-benzyloxyimino cytidine 5'-diphosphate analogues and their potency determined in a calcium mobilization assay. A 4-trifluoromethyl-benzyloxyimino substituent in 25 provided the highest human P2Y6R potency (MRS4554, 0.57 µM), and a 5-fluoro substitution of the cytosine ring in 28 similarly enhanced potency, with >175- and 39-fold selectivity over human P2Y14R, respectively. However, 3-alkyl (31-33, 37, 38), β-d-arabinofuranose (39) and 6-aza (40) substitution prevented P2Y6R activation. Thus, we have identified new α,β-methylene bridged N4-extended CDP analogues as P2Y6R agonists that are highly selective over the P2Y14R.

G protein-coupled purinergic P2Y receptor oligomerization: Pharmacological changes and dynamic regulation

P2Y receptors (P2YRs) are a δ group of rhodopsin-like G protein-coupled receptors (GPCRs) with many essential functions in physiology and pathology, such as platelet aggregation, immune responses, neuroprotective effects, inflammation, and cellular proliferation. Thus, they are among the most researched therapeutic targets used for the clinical treatment of diseases (e.g., the antithrombotic drug clopidogrel and the dry eye treatment drug diquafosol). GPCRs transmit signals as dimers to increase the diversity of signalling pathways and pharmacological activities. Many studies have frequently confirmed dimerization between P2YRs and other GPCRs due to their functions in cardiovascular and cerebrovascular processes in vivo and in vitro. Recently, some P2YR dimers that dynamically balance physiological functions in the body were shown to be involved in effective signal transduction and exert pathological responses. In this review, we summarize the types, pharmacological changes, and active regulators of P2YR-related dimerization, and delineate new functions and pharmacological activities of P2YR-related dimers, which may be a novel direction to improve the effectiveness of medications.

Blocking FcγRIIB in Smooth Muscle Cells Reduces Hypertension

[Figure: see text].

Extracellular Uridine Nucleotides-Induced Contractions Were Increased in Femoral Arteries of Spontaneously Hypertensive Rats

INTRODUCTION

Femoral arterial dysfunction including abnormal vascular responsiveness to endogenous ligands was often seen in arterial hypertension. Extracellular nucleotides including uridine 5'-diphosphate (UDP) and uridine 5'-triphosphate (UTP) play important roles for homeostasis in the vascular system including controlling the vascular tone. However, responsiveness to UDP and UTP in femoral arteries under arterial hypertension remains unclear. The aim of this study was to investigate if hypertension has an effect of vasoconstrictive responsiveness to UDP and UTP in femoral arteries of spontaneously hypertensive rats (SHRs) and Wistar-Kyoto rats (WKYs) after 7 and 12 months old.

METHODS

Organ baths were conducted to determine vascular reactivity in isolated femoral arterial rings.

RESULTS

In femoral arteries obtained from 12-month-old rats, augmented contractile responses to UDP and UTP were seen in femoral arteries of SHR than in those of WKY under situations not only intact but also nitric oxide synthase inhibition, whereas no difference of extracellular potassium-induced vasocontraction was seen in both SHR and WKY groups. Similar contraction trends occurred in femoral arteries obtained from 7-month-old rats. Moreover, contractions induced by UDP and UTP were increased in endothelium-denuded arteries. Cyclooxygenase inhibition decreased the contractions induced by these nucleotides and abolished the differences in responses between the SHR and WKY groups.

CONCLUSIONS

This study demonstrates the importance of regulation of extracellular uridine nucleotides-induced contractions in hypertension-associated peripheral arterial diseases.

Diabetes and hypertension: Pivotal involvement of purinergic signaling

Diabetes mellitus (DM) and hypertension are highly prevalent worldwide health problems and frequently associated with severe clinical complications, such as diabetic cardiomyopathy, nephropathy, retinopathy, neuropathy, stroke, and cardiac arrhythmia, among others. Despite all existing research results and reasonable speculations, knowledge about the role of purinergic system in individuals with DM and hypertension remains restricted. Purinergic signaling accounts for a complex network of receptors and extracellular enzymes responsible for the recognition and degradation of extracellular nucleotides and adenosine. The main components of this system that will be presented in this review are: P1 and P2 receptors and the enzymatic cascade composed by CD39 (NTPDase; with ATP and ADP as a substrate), CD73 (5'-nucleotidase; with AMP as a substrate), and adenosine deaminase (ADA; with adenosine as a substrate). The purinergic system has recently emerged as a central player in several physiopathological conditions, particularly those linked to inflammatory responses such as diabetes and hypertension. Therefore, the present review focuses on changes in both purinergic P1 and P2 receptor expression as well as the activities of CD39, CD73, and ADA in diabetes and hypertension conditions. It can be postulated that the manipulation of the purinergic axis at different levels can prevent or exacerbate the insurgency and evolution of diabetes and hypertension working as a compensatory mechanism.

RAGE ligands stimulate angiotensin II type I receptor (AT1) via RAGE/AT1 complex on the cell membrane

The receptor for advanced glycation end-products (RAGE) and the G protein-coupled angiotensin II (AngII) type I receptor (AT1) play a central role in cardiovascular diseases. It was recently reported that RAGE modifies AngII-mediated AT1 activation via the membrane oligomeric complex of the two receptors. In this study, we investigated the presence of the different directional crosstalk in this phenomenon, that is, the RAGE/AT1 complex plays a role in the signal transduction pathway of RAGE ligands. We generated Chinese hamster ovary (CHO) cells stably expressing RAGE and AT1, mutated AT1, or AT2 receptor. The activation of two types of G protein α-subunit, Gq and Gi, was estimated through the accumulation of inositol monophosphate and the inhibition of forskolin-induced cAMP production, respectively. Rat kidney epithelial cells were used to assess RAGE ligand-induced cellular responses. We determined that RAGE ligands activated Gi, but not Gq, only in cells expressing RAGE and wildtype AT1. The activation was inhibited by an AT1 blocker (ARB) as well as a RAGE inhibitor. ARBs inhibited RAGE ligand-induced ERK phosphorylation, NF-κB activation, and epithelial-mesenchymal transition of rat renal epithelial cells. Our findings suggest that the activation of AT1 plays a central role in RAGE-mediated cellular responses and elucidate the role of a novel molecular mechanism in the development of cardiovascular diseases.

That was then, this is now: the development of our knowledge and understanding of P2 receptor subtypes

P2 receptors are present in virtually all tissues and cell types in the human body, and they mediate the physiological and pharmacological actions of extracellular purine and pyrimidine nucleotides. They were first characterised and named by Geoff Burnstock in 1978, then subdivided into P2X and P2Y purinoceptors in 1985 on the basis of pharmacological criteria in functional studies on native receptors. Molecular cloning of receptors in the 1990s revealed P2X receptors to comprise seven different subunits that interact to produce functional homo- and heterotrimeric ligand-gated cation channels. A family of eight P2Y G protein-coupled receptors were also cloned, which can form homo- and heterodimers. Deep insight into the molecular mechanisms of agonist and antagonist action has been provided by more recent determination of the tertiary and quaternary structures of several P2X and P2Y receptor subtypes. Agonists and antagonists that are highly selective for individual subtypes are now available and some are in clinical use. This has all come about because of the intelligence, insight and drive of the force of nature that was Geoff Burnstock.

The endocytosis of oxidized LDL via the activation of the angiotensin II type 1 receptor

Arrestin-dependent activation of a G-protein-coupled receptor (GPCR) triggers endocytotic internalization of the receptor complex. We analyzed the interaction between the pattern recognition receptor (PRR) lectin-like oxidized low-density lipoprotein (oxLDL) receptor (LOX-1) and the GPCR angiotensin II type 1 receptor (AT1) to report a hitherto unidentified mechanism whereby internalization of the GPCR mediates cellular endocytosis of the PRR ligand. Using genetically modified Chinese hamster ovary cells, we found that oxLDL activates Gαi but not the Gαq pathway of AT1 in the presence of LOX-1. Endocytosis of the oxLDL-LOX-1 complex through the AT1-β-arrestin pathway was demonstrated by real-time imaging of the membrane dynamics of LOX-1 and visualization of endocytosis of oxLDL. Finally, this endocytotic pathway involving GPCR kinases (GRKs), β-arrestin, and clathrin is relevant in accumulating oxLDL in human vascular endothelial cells. Together, our findings indicate that oxLDL activates selective G proteins and β-arrestin-dependent internalization of AT1, whereby the oxLDL-LOX-1 complex undergoes endocytosis.

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The binding of oxidized LDL (oxLDL) to LOX-1 induces selective activation of AT1

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oxLDL and angiotensin II additively or competitively activate AT1 in different cells

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oxLDL promotes β-arrestin-dependent internalization of oxLDL-LOX-1-AT1 complex

Differential Contractile Reactivity to Nucleotides in Femoral Arteries of OLETF and LETO Rats

Extracellular nucleotides play an important role in the regulation of vascular function, and an abnormal vascular function is an important participant in the development and progression of diabetic vascular complications. The purpose of this study was to determine whether contractile responses induced by extracellular nucleotides and a dinucleotide, uridine adenosine tetraphosphate (Up₄A), in femoral arteries would be altered at the chronic stage of type 2 diabetes. We determined the changes in contractile reactivity induced by ATP, uridine triphosphate (UTP), uridine diphosphate (UDP), and Up₄A in the femoral arteries of Otsuka Long-Evans Tokushima Fatty (OLETF) rats (aged male type 2 diabetic rats) and, Long-Evans Tokushima Otsuka (LETO) rats (controls for OLETF rats). ATP-induced contractions were greater in OLETF rats than in LETO rats. UTP-induced contractions were lower in OLETF rats than in LETO rats. UDP- and Up₄A-induced contractions were similar between OLETF and LETO rats. The femoral artery contractile changes induced by the extracellular nucleotides and dinucleotide were similar when nitric oxide synthase was inhibited. These results suggest that the extent of femoral artery contractile reactivity to nucleotides/dinucleotides differs during long-term duration of type 2 diabetes.

[Risks of progression of cerebrovascular pathology associated with the activity of the brain purinergic system]

Until now, there is no understanding of the relationship between risk factors and the progression of cerebrovascular pathology. The review presents facts that confirm the involvement of various subtypes of purine P2 receptors in neuron activation, growth and myelination of axons, migration and microglia phagocytosis, astrogliosis, regulation of vascular tone, thrombosis and angiogenesis, neuroinflammation and immune responses. The data suggest the possibility of the activation of purinergic system of the brain during the development of main risk factors for cerebrovascular pathology (age, arterial hypertension, diabetes), as a stereotypical mechanism that can affect the homeostasis of the ensemble "neuron-glia-capillary". Purinergic P2 receptors may be a potential target for the development of pharmacological methods to limit the progression of cerebrovascular pathology.

P2Y Purinergic Receptors, Endothelial Dysfunction, and Cardiovascular Diseases

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

Angiotensin Receptors Heterodimerization and Trafficking: How Much Do They Influence Their Biological Function?

G-protein–coupled receptors (GPCRs) are targets for around one third of currently approved and clinical prescribed drugs and represent the largest and most structurally diverse family of transmembrane signaling proteins, with almost 1000 members identified in the human genome. Upon agonist stimulation, GPCRs are internalized and trafficked inside the cell: they may be targeted to different organelles, recycled back to the plasma membrane or be degraded. Once inside the cell, the receptors may initiate other signaling pathways leading to different biological responses. GPCRs’ biological function may also be influenced by interaction with other receptors. Thus, the ultimate cellular response may depend not only on the activation of the receptor from the cell membrane, but also from receptor trafficking and/or the interaction with other receptors. This review is focused on angiotensin receptors and how their biological function is influenced by trafficking and interaction with others receptors.

Modulation of P2Y6R expression exacerbates pressure overload-induced cardiac remodeling in mice

Cardiac tissue remodeling caused by hemodynamic overload is a major clinical outcome of heart failure. Uridine-responsive purinergic P2Y₆ receptor (P2Y₆R) contributes to the progression of cardiovascular remodeling in rodents, but it is not known whether inhibition of P2Y₆R prevents or promotes heart failure. We demonstrate that inhibition of P2Y₆R promotes pressure overload-induced sudden death and heart failure in mice. In neonatal cardiomyocytes, knockdown of P2Y₆R significantly attenuated hypertrophic growth and cell death caused by hypotonic stimulation, indicating the involvement of P2Y₆R in mechanical stress-induced myocardial dysfunction. Unexpectedly, compared with wild-type mice, deletion of P2Y₆R promoted pressure overload-induced sudden death, as well as cardiac remodeling and dysfunction. Mice with cardiomyocyte-specific overexpression of P2Y₆R also exhibited cardiac dysfunction and severe fibrosis. In contrast, P2Y₆R deletion had little impact on oxidative stress-mediated cardiac dysfunction induced by doxorubicin treatment. These findings provide overwhelming evidence that systemic inhibition of P2Y₆R exacerbates pressure overload-induced heart failure in mice, although P2Y₆R in cardiomyocytes contributes to the progression of cardiac fibrosis.

Gα12/13 signaling in metabolic diseases

As the key governors of diverse physiological processes, G protein-coupled receptors (GPCRs) have drawn attention as primary targets for several diseases, including diabetes and cardiovascular disease. Heterotrimeric G proteins converge signals from ~800 members of the GPCR family. Among the members of the G protein α family, the Gα₁₂ family members comprising Gα₁₂ and Gα₁₃ have been referred to as gep oncogenes. Gα_12/13 levels are altered in metabolic organs, including the liver and muscles, in metabolic diseases. The roles of Gα_12/13 in metabolic diseases have been investigated. In this review, we highlight findings demonstrating Gα_12/13 amplifying or dampening regulators of phenotype changes. We discuss the molecular basis of G protein biology in the context of posttranslational modifications to heterotrimeric G proteins and the cell signaling axis. We also highlight findings providing insights into the organ-specific, metabolic and pathological roles of G proteins in changes associated with specific cells, energy homeostasis, glucose metabolism, liver fibrosis and the immune and cardiovascular systems. This review summarizes the currently available knowledge on the importance of Gα_12/13 in the physiology and pathogenesis of metabolic diseases, which is presented according to the basic understanding of their metabolic actions and underlying cellular and molecular bases.

Understanding the activities of two members of a vital category of proteins called G proteins, which initiate metabolic changes when signaling molecules bind to cells, could lead to new therapies for many diseases. Researchers in South Korea and Japan, led by Sang Geon Kim at Seoul National University, review the significance of the Gα12 and Gα13 proteins in diseases characterised by significant changes in metabolism, including liver conditions and disorders of the cardiovascular and immune systems. Specific roles for the proteins have been identified by a variety of methods, including studying the effect of disabling the genes that code for them in mice. Recent insights suggest that drugs interfering with the activity of these Gα proteins might help treat many conditions in which the molecular signalling networks involving the proteins are disrupted.

The Role of a Selective P2Y6 Receptor Antagonist, MRS2578, on the Formation of Angiotensin II-Induced Abdominal Aortic Aneurysms

Objective

The P2Y₆ receptor has been shown to be involved in many cardiovascular diseases, including hypertension and atherosclerosis. The study is aimed at exploring the role of the P2Y₆ receptor in Ang II-induced abdominal aortic aneurysm (AAA) formation in apolipoprotein E-deficient (apoE^−/−) mice by using its selective antagonist.

Methods

Male apoE^−/− mice were fed with high-fat diet and infused with angiotensin (Ang) II (1000 ng/kg/min) for 4 weeks to induce AAA or saline as controls. Mice were divided into four groups: normal saline (NS, placebo control) group (n = 8), Ang II+vehicle (Ang II) group (n = 14), Ang II-low dose MRS2578 (Ang II+MRS-16 mg) group (n = 14), and Ang II-high dose MRS2578 (Ang II+MRS-32 mg) group (n = 14). Daily intraperitoneal injection with vehicle or MRS2578 was pretreated one week before Ang II infusion. On postoperative day 10, aorta imaging of each group was taken by ultrasonography. After 4 weeks of Ang II infusion, the excised aortas were processed for diameter measurement and quantification of aneurysm severity and tissue characteristics; the blood samples were collected for measurement of the lipid profile and levels of cytokines. Verhoeff's Van Gieson (EVG) staining and immunochemistry staining were performed to evaluate disruption of the extracellular matrix (ECM) and infiltration of macrophages. Expression and activity of matrix metalloproteinases (MMPs) was measured by gelatin zymography.

Results

Treatment with MRS2578 made no significant difference in AAA formation, and maximal aortic diameter yet caused higher AAA rupture-induced mortality from 7% (Ang II) to 21.4% (Ang II+MRS-16 mg) or 42.9% (Ang II+MRS-32 mg), respectively (p < 0.05). Consistently, the severity of aneurysm tended to be more deteriorated in MRS2578-treated groups, especially the high-dosage group. The ratios of type III and IV aneurysm were much higher in the MRS2578-coadministered groups (p < 0.05). Furthermore, histological analyses showed that administration of MRS2578 significantly increased infiltration of macrophages, expression of monocyte chemotactic protein 1 (MCP-1) and vascular cell adhesion molecule-1 (VCAM-1), and activities of MMP-2 and MMP-9 followed by aggravating degradation elastin in vivo (p < 0.05). However, the multiple effects of MRS2578 on the development of AAA are independent of changes in systolic blood pressure and lipid profiles.

Conclusions

The present study demonstrated that administration of MRS2578 exacerbated the progression and rupture of experimental AAA through promoting proinflammatory response and MMP expression and activity, which indicated a crucial role of the P2Y₆ receptor in AAA development. Clinical Relevance. Purinergic P2Y receptors have attracted much attention since the P2Y₁₂ receptor antagonist had been successfully applied in clinical practice. Elucidating the underlying mechanisms of AAA and exploring potential therapeutic strategies are essential to prevent its progression and reduce the mortality rate.

The role of P2Y6R in cardiovascular diseases and recent development of P2Y6R antagonists

As a member of the P2Y receptor family with a typical 7-transmembrane structure, P2Y₆ purinergic receptor (P2Y₆R) belongs to the G-protein-coupled nucleotide receptor activating the phospholipase-C signaling pathway. P2Y₆R is widely involved in a range of human diseases, including atherosclerosis and other cardiovascular diseases, gradually attracting attention owing to its inappropriate or excessive activation. In addition, it was reported that P2Y₆R might regulate inflammatory responses by governing the maturation and secretion of proinflammatory cytokines. Hence, several P2Y₆R antagonists have been subjected to evaluation as new therapeutic strategies in recent years. This review was aimed at summarizing the role of P2Y₆R in the pathogenesis of cardiovascular diseases, with an insight into the recent progress on discovery of P2Y₆R antagonists.

Purinergic Signaling During Hyperglycemia in Vascular Smooth Muscle Cells

The activation of purinergic receptors by nucleotides and/or nucleosides plays an important role in the control of vascular function, including modulation of vascular smooth muscle excitability, and vascular reactivity. Accordingly, purinergic receptor actions, acting as either ion channels (P2X) or G protein-coupled receptors (GCPRs) (P1, P2Y), target diverse downstream effectors, and substrates to regulate vascular smooth muscle function and vascular reactivity. Both vasorelaxant and vasoconstrictive effects have been shown to be mediated by different purinergic receptors in a vascular bed- and species-specific manner. Purinergic signaling has been shown to play a key role in altering vascular smooth muscle excitability and vascular reactivity following acute and short-term elevations in extracellular glucose (e.g., hyperglycemia). Moreover, there is evidence that vascular smooth muscle excitability and vascular reactivity is severely impaired during diabetes and that this is mediated, at least in part, by activation of purinergic receptors. Thus, purinergic receptors present themselves as important candidates mediating vascular reactivity in hyperglycemia, with potentially important clinical and therapeutic potential. In this review, we provide a narrative summarizing our current understanding of the expression, function, and signaling of purinergic receptors specifically in vascular smooth muscle cells and discuss their role in vascular complications following hyperglycemia and diabetes.

Amplification of the COX/TXS/TP receptor pathway enhances uridine diphosphate-induced contraction by advanced glycation end products in rat carotid arteries

Advanced glycation end products (AGEs) play a pivotal role in vascular functions under various pathophysiological conditions. Although uridine diphosphate (UDP) is an important extracellular nucleotide, the relationship between AGEs and UDP regarding their effect on vascular functions remains unclear. Therefore, we investigated the effects of AGE-bovine serum albumin (AGE-BSA) on UDP-mediated responses in rat thoracic aorta and carotid arteries. In rat thoracic aorta, UDP-induced relaxation was observed and this relaxation was similar between control (1.0 v/v% PBS) and AGE-BSA-treated (0.1 mg/mL for 60 min) groups. In contrast, contraction but not relaxation was obtained following UDP application to carotid arteries with and without endothelia; contraction was greater in the AGE-BSA-treated group than in the control group. The difference in UDP-induced contraction between the two groups was not abolished by the use of a nitric oxide synthase (NOS) inhibitor, whereas it was abolished by the use of cyclooxygenase (COX), thromboxane synthase (TXS), and thromboxane-prostanoid (TP) receptor antagonist. Further, the difference in UDP-induced contraction was not abolished by the use of a cPLA₂ inhibitor, whereas it was abolished by the use of an iPLA₂ inhibitor. UDP increased TXA₂ release in both groups, and its level was similar in both groups. Moreover, the release of PGE₂, PGF_2α, and PGI₂ was similar among the groups. Under NOS inhibition, TP receptor agonist-induced contraction increased in the AGE-BSA-treated group (vs. control group). In conclusion, the increase in UDP-induced carotid arterial contraction by AGE-BSA can be attributed to an increase in the COX/TXS/TP receptor pathway, particularly, TP receptor signaling.

Ibudilast attenuates doxorubicin-induced cytotoxicity by suppressing formation of TRPC3 channel and NADPH oxidase 2 protein complexes

BACKGROUND AND PURPOSE

Doxorubicin is a highly effective anticancer agent but eventually induces cardiotoxicity associated with increased production of ROS. We previously reported that a pathological protein interaction between TRPC3 channels and NADPH oxidase 2 (Nox2) contributed to doxorubicin-induced cardiac atrophy in mice. Here we have investigated the effects of ibudilast, a drug already approved for clinical use and known to block doxorubicin-induced cytotoxicity, on the TRPC3-Nox2 complex. We specifically sought evidence that this drug attenuated doxorubicin-induced systemic tissue wasting in mice.

EXPERIMENTAL APPROACH

We used the RAW264.7 macrophage cell line to screen 1,271 clinically approved chemical compounds, evaluating functional interactions between TRPC3 channels and Nox2, by measuring Nox2 protein stability and ROS production, with and without exposure to doxorubicin. In male C57BL/6 mice, samples of cardiac and gastrocnemius muscle were taken and analysed with morphometric, immunohistochemical, RT-PCR and western blot methods. In the passive smoking model, cells were exposed to DMEM containing cigarette sidestream smoke.

KEY RESULTS

Ibudilast, an anti-asthmatic drug, attenuated ROS-mediated muscle toxicity induced by doxorubicin treatment or passive smoking, by inhibiting the functional interactions between TRPC3 channels and Nox2, without reducing TRPC3 channel activity.

CONCLUSIONS AND IMPLICATIONS

These results indicate a common mechanism underlying induction of systemic tissue wasting by doxorubicin. They also suggest that ibudilast could be repurposed to prevent muscle toxicity caused by anticancer drugs or passive smoking.

TRPC6 regulates phenotypic switching of vascular smooth muscle cells through plasma membrane potential-dependent coupling with PTEN

Vascular smooth muscle cells (VSMCs) play critical roles in the stability and tonic regulation of vascular homeostasis. VSMCs can switch back and forth between highly proliferative synthetic and fully differentiated contractile phenotypes in response to changes in the vessel environment. Although abnormal phenotypic switching of VSMCs is a hallmark of vascular disorders such as atherosclerosis and restenosis after angioplasty, how control of VSMC phenotypic switching is dysregulated in pathologic conditions remains obscure. We found that inhibition of canonical transient receptor potential 6 (TRPC6) channels facilitated contractile differentiation of VSMCs through plasma membrane hyperpolarization. TRPC6-deficient VSMCs exhibited more polarized resting membrane potentials and higher protein kinase B (Akt) activity than wild-type VSMCs in response to TGF-β1 stimulation. Ischemic stress elicited by oxygen-glucose deprivation suppressed TGF-β1-induced hyperpolarization and VSMC differentiation, but this effect was abolished by TRPC6 deletion. TRPC6-mediated Ca²⁺ influx and depolarization coordinately promoted the interaction of TRPC6 with lipid phosphatase and tensin homolog deleted from chromosome 10 (PTEN), a negative regulator of Akt activation. Given the marked up-regulation of TRPC6 observed in vascular disorders, our findings suggest that attenuation of TRPC6 channel activity in pathologic VSMCs could be a rational strategy to maintain vascular quality control by fine-tuning of VSMC phenotypic switching.-Numaga-Tomita, T., Shimauchi, T., Oda, S., Tanaka, T., Nishiyama, K., Nishimura, A., Birnbaumer, L., Mori, Y., Nishida, M. TRPC6 regulates phenotypic switching of vascular smooth muscle cells through plasma membrane potential-dependent coupling with PTEN.

A Gs-coupled purinergic receptor boosts Ca2+ influx and vascular contractility during diabetic hyperglycemia

Elevated glucose increases vascular reactivity by promoting L-type CaV1.2 channel (LTCC) activity by protein kinase A (PKA). Yet, how glucose activates PKA is unknown. We hypothesized that a Gs-coupled P2Y receptor is an upstream activator of PKA mediating LTCC potentiation during diabetic hyperglycemia. Experiments in apyrase-treated cells suggested involvement of a P2Y receptor underlying the glucose effects on LTTCs. Using human tissue, expression for P2Y11, the only Gs-coupled P2Y receptor, was detected in nanometer proximity to CaV1.2 and PKA. FRET-based experiments revealed that the selective P2Y11 agonist NF546 and elevated glucose stimulate cAMP production resulting in enhanced PKA-dependent LTCC activity. These changes were blocked by the selective P2Y11 inhibitor NF340. Comparable results were observed in mouse tissue, suggesting that a P2Y11-like receptor is mediating the glucose response in these cells. These findings established a key role for P2Y11 in regulating PKA-dependent LTCC function and vascular reactivity during diabetic hyperglycemia.

Uridine adenosine tetraphosphate and purinergic signaling in cardiovascular system: An update

Uridine adenosine tetraphosphate (Up4A), biosynthesized by activation of vascular endothelial growth factor receptor (VEGFR) 2, was initially identified as a potent endothelium-derived vasoconstrictor in perfused rat kidney. Subsequently, the effect of Up4A on vascular tone regulation was intensively investigated in arteries isolated from different vascular beds in rodents including rat pulmonary arteries, aortas, mesenteric and renal arteries as well as mouse aortas, in which Up4A produces vascular contraction. In contrast, Up4A produces vascular relaxation in porcine coronary small arteries and rat aortas. Intravenous infusion of Up4A into conscious rats or mice decreases blood pressure, and intravenous bolus injection of Up4A into anesthetized mice increases coronary blood flow, indicating an overall vasodilator influence in vivo. Although Up4A is the first dinucleotide described that contains both purine and pyrimidine moieties, its cardiovascular effects are exerted mainly through activation of purinergic receptors. These effects not only encompass regulation of vascular tone, but also endothelial angiogenesis, smooth muscle cell proliferation and migration, and vascular calcification. Furthermore, this review discusses a potential role for Up4A in cardiovascular pathophysiology, as plasma levels of Up4A are elevated in juvenile hypertensive patients and Up4A-mediated vascular purinergic signaling changes in cardiovascular disease such as hypertension, diabetes, atherosclerosis and myocardial infarction. Better understanding the vascular effect of the novel dinucleotide Up4A and the purinergic signaling mechanisms mediating its effects will enhance its potential as target for treatment of cardiovascular disease.

Receptor-Receptor Interactions as a Widespread Phenomenon: Novel Targets for Drug Development?

The discovery of receptor-receptor interactions (RRI) has expanded our understanding of the role that G protein-coupled receptors (GPCRs) play in intercellular communication. The finding that GPCRs can operate as receptor complexes, and not only as monomers, suggests that several different incoming signals could already be integrated at the plasma membrane level via direct allosteric interactions between the protomers that form the complex. Most research in this field has focused on neuronal populations and has led to the identification of a large number of RRI. However, RRI have been seen to occur not only in neurons but also in astrocytes and, outside the central nervous system, in cells of the cardiovascular and endocrine systems and in cancer cells. Furthermore, RRI involving the formation of macromolecular complexes are not limited to GPCRs, being also observed in other families of receptors. Thus, RRI appear as a widespread phenomenon and oligomerization as a common mechanism for receptor function and regulation. The discovery of these macromolecular assemblies may well have a major impact on pharmacology. Indeed, the formation of receptor complexes significantly broadens the spectrum of mechanisms available to receptors for recognition and signaling, which may be implemented through modulation of the binding sites of the adjacent protomers and of their signal transduction features. In this context, the possible appearance of novel allosteric sites in the receptor complex structure may be of particular relevance. Thus, the existence of RRI offers the possibility of new therapeutic approaches, and novel pharmacological strategies for disease treatment have already been proposed. Several challenges, however, remain. These include the accurate characterization of the role that the receptor complexes identified so far play in pathological conditions and the development of ligands specific to given receptor complexes, in order to efficiently exploit the pharmacological properties of these complexes.

The Role of β-Arrestin Proteins in Organization of Signaling and Regulation of the AT1 Angiotensin Receptor

AT1 angiotensin receptor plays important physiological and pathophysiological roles in the cardiovascular system. Renin-angiotensin system represents a target system for drugs acting at different levels. The main effects of ATR1 stimulation involve activation of Gq proteins and subsequent IP3, DAG, and calcium signaling. It has become evident in recent years that besides the well-known G protein pathways, AT1R also activates a parallel signaling pathway through β-arrestins. β-arrestins were originally described as proteins that desensitize G protein-coupled receptors, but they can also mediate receptor internalization and G protein-independent signaling. AT1R is one of the most studied receptors, which was used to unravel the newly recognized β-arrestin-mediated pathways. β-arrestin-mediated signaling has become one of the most studied topics in recent years in molecular pharmacology and the modulation of these pathways of the AT1R might offer new therapeutic opportunities in the near future. In this paper, we review the recent advances in the field of β-arrestin signaling of the AT1R, emphasizing its role in cardiovascular regulation and heart failure.

Angiotensin II Signal Transduction: An Update on Mechanisms of Physiology and Pathophysiology

The renin-angiotensin-aldosterone system plays crucial roles in cardiovascular physiology and pathophysiology. However, many of the signaling mechanisms have been unclear. The angiotensin II (ANG II) type 1 receptor (AT₁R) is believed to mediate most functions of ANG II in the system. AT₁R utilizes various signal transduction cascades causing hypertension, cardiovascular remodeling, and end organ damage. Moreover, functional cross-talk between AT₁R signaling pathways and other signaling pathways have been recognized. Accumulating evidence reveals the complexity of ANG II signal transduction in pathophysiology of the vasculature, heart, kidney, and brain, as well as several pathophysiological features, including inflammation, metabolic dysfunction, and aging. In this review, we provide a comprehensive update of the ANG II receptor signaling events and their functional significances for potential translation into therapeutic strategies. AT₁R remains central to the system in mediating physiological and pathophysiological functions of ANG II, and participation of specific signaling pathways becomes much clearer. There are still certain limitations and many controversies, and several noteworthy new concepts require further support. However, it is expected that rigorous translational research of the ANG II signaling pathways including those in large animals and humans will contribute to establishing effective new therapies against various diseases.

P2Y2 and P2Y6 receptor activation elicits intracellular calcium responses in human adipose-derived mesenchymal stromal cells

Adipose tissue contains self-renewing multipotent cells termed mesenchymal stromal cells. In situ, these cells serve to expand adipose tissue by adipogenesis, but their multipotency has gained interest for use in tissue regeneration. Little is known regarding the repertoire of receptors expressed by adipose-derived mesenchymal stromal cells (AD-MSCs). The purpose of this study was to undertake a comprehensive analysis of purinergic receptor expression. Mesenchymal stromal cells were isolated from human subcutaneous adipose tissue and confirmed by flow cytometry. The expression profile of purinergic receptors was determined by quantitative real-time PCR and immunocytochemistry. The molecular basis for adenine and uracil nucleotide-evoked intracellular calcium responses was determined using Fura-2 measurements. All the known subtypes of P2X and P2Y receptors, excluding P2X2, P2X3 and P2Y₁₂ receptors, were detected at the mRNA and protein level. ATP, ADP and UTP elicited concentration-dependent calcium responses in mesenchymal cells (N = 7–9 donors), with a potency ranking ADP (EC₅₀ 1.3 ± 1.0 μM) > ATP (EC₅₀ 2.2 ± 1.1 μM) = UTP (3.2 ± 2.8 μM). Cells were unresponsive to UDP (< 30 μM) and UDP-glucose (< 30 μM). ATP responses were attenuated by selective P2Y₂ receptor antagonism (AR-C118925XX; IC₅₀ 1.1 ± 0.8 μM, 73.0 ± 8.5% max inhibition; N = 7 donors), and UTP responses were abolished. ADP responses were attenuated by the selective P2Y₆ receptor antagonist, MRS2587 (IC₅₀ 437 ± 133nM, 81.0 ± 8.4% max inhibition; N = 6 donors). These data demonstrate that adenine and uracil nucleotides elicit intracellular calcium responses in human AD-MSCs with a predominant role for P2Y₂ and P2Y₆ receptor activation. This study furthers understanding about how human adipose-derived mesenchymal stromal cells can respond to external signalling cues.

Proinflammatory Arterial Stiffness Syndrome: A Signature of Large Arterial Aging

Age-associated structural and functional remodeling of the arterial wall produces a productive environment for the initiation and progression of hypertension and atherosclerosis. Chronic aging stress induces low-grade proinflammatory signaling and causes cellular proinflammation in arterial walls, which triggers the structural phenotypic shifts characterized by endothelial dysfunction, diffuse intimal-medial thickening, and arterial stiffening. Microscopically, aged arteries exhibit an increase in arterial cell senescence, proliferation, invasion, matrix deposition, elastin fragmentation, calcification, and amyloidosis. These characteristic cellular and matrix alterations not only develop with aging but can also be induced in young animals under experimental proinflammatory stimulation. Interestingly, these changes can also be attenuated in old animals by reducing low-grade inflammatory signaling. Thus, mitigating age-associated proinflammation and arterial phenotype shifts is a potential approach to retard arterial aging and prevent the epidemic of hypertension and atherosclerosis in the elderly.

Oligomerization and cooperativity in GPCRs from the perspective of the angiotensin AT1 and dopamine D2 receptors

G Protein-Coupled Receptors (GPCRs) can form homo- and heterodimers or constitute higher oligomeric clusters with other heptahelical GPCRs. In this article, multiscale molecular modeling approaches as well as experimental techniques which are used to study oligomerization of GPCRs are reviewed. In particular, the effect of dimerization/oligomerization to the ligand binding affinity of individual protomers and also on the efficacy of the oligomer are discussed by including diverse examples from the literature. In addition, possible allosteric effects that may emerge upon interaction of GPCRs with membrane components, like cholesterol, is also discussed. Investigation of these above-mentioned interactions may greatly contribute to the candidate molecule screening studies and development of novel therapeutics with fewer adverse effects.

The Dynamics of GPCR Oligomerization and Their Functional Consequences

The functional importance of G protein-coupled receptor (GPCR) oligomerization remains controversial. Although obligate dimers of class C GPCRs are well accepted, the generalizability of this phenomenon is still strongly debated with respect to other classes of GPCRs. In this review, we focus on understanding the organization and dynamics between receptor equivalents and their signaling partners in oligomeric receptor complexes, with a view toward integrating disparate viewpoints into a unified understanding. We discuss the nature of functional oligomeric entities, and how asymmetries in receptor structure and function created by oligomers might have implications for receptor function as allosteric machines and for future drug discovery.