Novel effects of adenosine receptors on pericellular hyaluronan matrix: implications for human smooth muscle cell phenotype and interactions with monocytes during atherosclerosis

Adenosine A3 Receptor: From Molecular Signaling to Therapeutic Strategies for Heart Diseases

Cardiovascular diseases (CVDs), particularly heart failure, are major contributors to early mortality globally. Heart failure poses a significant public health problem, with persistently poor long-term outcomes and an overall unsatisfactory prognosis for patients. Conventionally, treatments for heart failure have focused on lowering blood pressure; however, the development of more potent therapies targeting hemodynamic parameters presents challenges, including tolerability and safety risks, which could potentially restrict their clinical effectiveness. Adenosine has emerged as a key mediator in CVDs, acting as a retaliatory metabolite produced during cellular stress via ATP metabolism, and works as a signaling molecule regulating various physiological processes. Adenosine functions by interacting with different adenosine receptor (AR) subtypes expressed in cardiac cells, including A1AR, A2AAR, A2BAR, and A3AR. In addition to A1AR, A3AR has a multifaceted role in the cardiovascular system, since its activation contributes to reducing the damage to the heart in various pathological states, particularly ischemic heart disease, heart failure, and hypertension, although its role is not as well documented compared to other AR subtypes. Research on A3AR signaling has focused on identifying the intricate molecular mechanisms involved in CVDs through various pathways, including Gi or Gq protein-dependent signaling, ATP-sensitive potassium channels, MAPKs, and G protein-independent signaling. Several A3AR-specific agonists, such as piclidenoson and namodenoson, exert cardioprotective impacts during ischemia in the diverse animal models of heart disease. Thus, modulating A3ARs serves as a potential therapeutic approach, fueling considerable interest in developing compounds that target A3ARs as potential treatments for heart diseases.

Hyaluronan synthesis inhibition normalizes ethanol-enhanced hepatic stellate cell activation

BACKGROUND

Chronic ethanol overconsumption promotes alcohol-associated liver disease (ALD), characterized by hepatocyte injury, inflammation, hepatic stellate cell (HSC) activation, and fibrosis. Hyaluronan (HA) concentration is greater in livers and blood from advanced ALD patients than patients with advanced non-ALD. In the liver, HSCs are the major HA producers. The relationship between ethanol, HA, and HSC activation is incompletely understood. Thus, here, we tested the hypothesis that ethanol enhances HSC activation in a HA-dependent manner.

METHODS

Liver tissue microarrays (TMAs) containing steatotic livers from donors with or without a history of alcohol consumption were used to measure HA and collagen content. Mice were fed a moderate (2%, v/v) ethanol-containing diet or pair-fed control diet for 2 days, after which they were given a single carbon tetrachloride (CCl4 ) injection. To inhibit HA synthesis, we provided 4-methylumbelliferone (4MU) daily. We used LX2 cells, a human HSC cell line, to determine the impact ethanol had on LPS responses, with or without concurrent 4MU exposure.

RESULTS

CCl4 induced liver injury, but it did not differ between ethanol or control diet fed mice with or without 4MU treatment. Ethanol feeding enhanced CCl4 -induced hepatic HA content, which was paralleled by HA synthase (Has)2 transcript abundance; 4MU treatment normalized both. Consistently, HSC activation, assessed by measuring αSMA mRNA and protein, was induced by CCl4 exposure, enhanced by ethanol feeding, and normalized by 4MU. Hepatic transcripts, but not protein, for Ccl2 were enhanced by ethanol feeding and normalized by 4MU exposure. Finally, ethanol-exposed LX2 cells made more LPS-stimulated CCL2 mRNA and protein than cells not exposed to ethanol; 4MU prevented this.

CONCLUSION

These data show that ethanol augments HSC activation through HA synthesis and enhances hepatic profibrogenic features. Therefore, targeting HSC HA production could potentially attenuate liver disease in ALD patients.

ROLE OF HYALURONAN IN PATHOPHYSIOLOGY OF VASCULAR1 ENDOTHELIAL AND SMOOTH MUSCLE CELLS

One of the main components of the extracellular matrix (ECM) of the blood vessel is hyaluronic acid or hyaluronan (HA). It is a ubiquitous polysaccharide belonging to the family of glycosaminoglycans, but, differently from other proteoglycan-associated glycosaminoglycans, it is synthesized on the plasma membrane by a family of three HA synthases (HAS). HA can be released as a free polymer in the extracellular space or remain associated with the membrane in the pericellular space via HAS or via binding proteins. In fact, several cell surface proteins can interact with HA working as HA receptors like CD44, RHAMM, and LYVE-1. In physiological conditions, HA is localized in the glycocalyx and in the adventitia and is responsible for the loose and hydrated vascular structure favoring flexibility and allowing the stretching of vessels in response to mechanical forces. During atherogenesis, ECM undergoes dramatic alterations which have a crucial role in lipoprotein retention and in triggering multiple signaling cascades that wake up cells from their quiescent status. HA becomes highly present in the media and neointima favoring smooth muscle cells dedifferentiation, migration, and proliferation that strongly contribute to vessel wall thickening. Further, HA is able to modulate immune cell recruitment both within the vessel wall and on the endothelial cell layer. This review is focused on the effects of HA on vascular cell behavior.

Helix-Loop-Helix Factor Id3 (Inhibitor of Differentiation 3): A Novel Regulator of Hyaluronan-Mediated Adipose Tissue Inflammation

OBJECTIVE

The aim of this study was to unravel mechanisms whereby deficiency of the transcription factor Id3 (inhibitor of differentiation 3) leads to metabolic dysfunction in visceral obesity. We investigated the impact of loss of Id3 on hyaluronic acid (HA) production by the 3 HAS isoenzymes (HA synthases; -1, -2, and -3) and on obesity-induced adipose tissue (AT) accumulation of proinflammatory B cells. Approach and Results: Male Id3-/- mice and respective wild-type littermate controls were fed a 60% high-fat diet for 4 weeks. An increase in inflammatory B2 cells was detected in Id3-/- epididymal AT. HA accumulated in epididymal AT of high-fat diet-fed Id3-/- mice and circulating levels of HA were elevated. Has2 mRNA expression was increased in epididymal AT of Id3-/- mice. Luciferase promoter assays showed that Id3 suppressed Has2 promoter activity, while loss of Id3 stimulated Has2 promoter activity. Functionally, HA strongly promoted B2 cell adhesion in the AT and on cultured vascular smooth muscle cells of Id3-/- mice, an effect sensitive to hyaluronidase.

CONCLUSIONS

Our data demonstrate that loss of Id3 increases Has2 expression in the epididymal AT, thereby promoting HA accumulation. In turn, elevated HA content promotes HA-dependent binding of B2 cells and an increase in the B2 cells in the AT, which contributes to AT inflammation.

Focusing on Adenosine Receptors as a Potential Targeted Therapy in Human Diseases

Adenosine is involved in a range of physiological and pathological effects through membrane-bound receptors linked to G proteins. There are four subtypes of adenosine receptors, described as A1AR, A2AAR, A2BAR, and A3AR, which are the center of cAMP signal pathway-based drug development. Several types of agonists, partial agonists or antagonists, and allosteric substances have been synthesized from these receptors as new therapeutic drug candidates. Research efforts surrounding A1AR and A2AAR are perhaps the most enticing because of their concentration and affinity; however, as a consequence of distressing conditions, both A2BAR and A3AR levels might accumulate. This review focuses on the biological features of each adenosine receptor as the basis of ligand production and describes clinical studies of adenosine receptor-associated pharmaceuticals in human diseases.

G-Protein-Coupled Receptors in Heart Disease

GPCRs (G-protein [guanine nucleotide-binding protein]-coupled receptors) play a central physiological role in the regulation of cardiac function in both health and disease and thus represent one of the largest class of surface receptors targeted by drugs. Several antagonists of GPCRs, such as βARs (β-adrenergic receptors) and Ang II (angiotensin II) receptors, are now considered standard of therapy for a wide range of cardiovascular disease, such as hypertension, coronary artery disease, and heart failure. Although the mechanism of action for GPCRs was thought to be largely worked out in the 80s and 90s, recent discoveries have brought to the fore new and previously unappreciated mechanisms for GPCR activation and subsequent downstream signaling. In this review, we focus on GPCRs most relevant to the cardiovascular system and discuss traditional components of GPCR signaling and highlight evolving concepts in the field, such as ligand bias, β-arrestin-mediated signaling, and conformational heterogeneity.

Versican is differentially regulated in the adventitial and medial layers of human vein grafts

Changes in extracellular matrix proteins may contribute significantly to the adaptation of vein grafts to the arterial circulation. We examined the production and distribution of versican and hyaluronan in intact human vein rings cultured ex vivo, veins perfused ex vivo, and cultured venous adventitial and smooth muscle cells. Immunohistochemistry revealed higher levels of versican in the intima/media compared to the adventitia, and no differences in hyaluronan. In the vasa vasorum, versican and hyaluronan associated with CD34⁺ progenitor cells. Culturing the vein rings for 14 days revealed increased versican immunostaining of 30–40% in all layers, with no changes in hyaluronan. Changes in versican accumulation appear to result from increased synthesis in the intima/media and decreased degradation in the adventitia as versican transcripts were increased in the intima/media, but unchanged in the adventitia, and versikine (the ADAMTS-mediated cleavage product of versican) was increased in the intima/media, but decreased in the adventitia. In perfused human veins, versican was specifically increased in the intima/media in the presence of venous pressure, but not with arterial pressure. Unexpectedly, cultured adventitial cells express and accumulate more versican and hyaluronan than smooth muscle cells. These data demonstrate a differential regulation of versican and hyaluronan in human venous adventitia vs. intima/media and suggest distinct functions for these extracellular matrix macromolecules in these venous wall compartments during the adaptive response of vein grafts to the arterial circulation.

Extracellular ATP activates hyaluronan synthase 2 (HAS2) in epidermal keratinocytes via P2Y2, Ca2+ signaling, and MAPK pathways

Extracellular nucleotides are used as signaling molecules by several cell types. In epidermis, their release is triggered by insults such as ultraviolet radiation, barrier disruption, and tissue wounding, and by specific nerve terminals firing. Increased synthesis of hyaluronan, a ubiquitous extracellular matrix glycosaminoglycan, also occurs in response to stress, leading to the attractive hypothesis that nucleotide signaling and hyaluronan synthesis could also be linked. In HaCaT keratinocytes, ATP caused a rapid and strong but transient activation of hyaluronan synthase 2 (HAS2) expression via protein kinase C-, Ca²⁺/calmodulin-dependent protein kinase II-, mitogen-activated protein kinase-, and calcium response element-binding protein-dependent pathways by activating the purinergic P2Y₂ receptor. Smaller but more persistent up-regulation of HAS3 and CD44, and delayed up-regulation of HAS1 were also observed. Accumulation of peri- and extracellular hyaluronan followed 4-6 h after stimulation, an effect further enhanced by the hyaluronan precursor glucosamine. AMP and adenosine, the degradation products of ATP, markedly inhibited HAS2 expression and, despite concomitant up-regulation of HAS1 and HAS3, inhibited hyaluronan synthesis. Functionally, ATP moderately increased cell migration, whereas AMP and adenosine had no effect. Our data highlight the strong influence of adenosinergic signaling on hyaluronan metabolism in human keratinocytes. Epidermal insults are associated with extracellular ATP release, as well as rapid up-regulation of HAS2/3, CD44, and hyaluronan synthesis, and we show here that the two phenomena are linked. Furthermore, as ATP is rapidly degraded, the opposite effects of its less phosphorylated derivatives facilitate a rapid shut-off of the hyaluronan response, providing a feedback mechanism to prevent excessive reactions when more persistent signals are absent.

The CD44-HA axis and inflammation in atherosclerosis: A temporal perspective

Cardiovascular disease (CVD) due to atherosclerosis is a disease of chronic inflammation at both the systemic and the tissue level. CD44 has previously been implicated in atherosclerosis in both humans and mice. This multi-faceted receptor plays a critical part in the inflammatory response during the onset of CVD, though little is known of CD44's role during the latter stages of the disease. This review focuses on the role of CD44-dependent HA-dependent effects on inflammatory cells in several key processes, from disease initiation throughout the progression of atherosclerosis. Understanding how CD44 and HA regulate inflammation in atherogenesis is key in determining the utility of the CD44-HA axis as a therapeutic target to halt disease and potentially promote disease regression.

Intracellular cAMP Sensor EPAC: Physiology, Pathophysiology, and Therapeutics Development

This review focuses on one family of the known cAMP receptors, the exchange proteins directly activated by cAMP (EPACs), also known as the cAMP-regulated guanine nucleotide exchange factors (cAMP-GEFs). Although EPAC proteins are fairly new additions to the growing list of cAMP effectors, and relatively "young" in the cAMP discovery timeline, the significance of an EPAC presence in different cell systems is extraordinary. The study of EPACs has considerably expanded the diversity and adaptive nature of cAMP signaling associated with numerous physiological and pathophysiological responses. This review comprehensively covers EPAC protein functions at the molecular, cellular, physiological, and pathophysiological levels; and in turn, the applications of employing EPAC-based biosensors as detection tools for dissecting cAMP signaling and the implications for targeting EPAC proteins for therapeutic development are also discussed.

Role of hyaluronan in atherosclerosis: Current knowledge and open questions

Hyaluronan (HA), HA synthases (HAS) and HA receptors are expressed during the progression of atherosclerotic plaques. HA is thought to promote the activated phenotype of local vascular smooth muscle cells characterized by increased migration, proliferation and matrix synthesis. Furthermore, HA may modulate the immune response by increasing macrophage retention and by promoting the polarization of Th1 cells that enhance macrophage driven inflammation as well. The pro-atherosclerotic functions of HA are opposed by the presence of HA in the glycocalyx where it critically contributes to anti-thrombotic and anti-inflammatory function of the glycocalyx. Patients with atherosclerosis often are affected by comorbidities among them diabetes mellitus type 2 and inflammatory comorbidities. Diabetes mellitus type 2 likely has close interrelations to HA synthesis in atherosclerosis because the activity and transcription of HA synthases are sensitive to the intracellular glucose metabolism, which determines the substrate availability and the posttranslational modifications of HA synthases. The pro-inflammatory comorbidities aggravate the course of atherosclerosis and will affect the expression of the genes related to HA biosynthesis, -degradation, HA-matrix assembly or signaling. One example being the induction of HAS3 by interleukin-1β and other cytokines. Furthermore complications of atherosclerosis such as the healing after myocardial infarction also involve HA responses.

Hyaluronan synthase 3 promotes plaque inflammation and atheroprogression

OBJECTIVE

Hyaluronan (HA) is a prominent component of the provisional extracellular matrix (ECM) present in the neointima of atherosclerotic plaques. Here the role of HA synthase 3 (HAS3) in atheroprogression was studied.

APPROACH AND RESULTS

It is demonstrated here that HAS isoenzymes 1, -2 and -3 are expressed in human atherosclerotic plaques of the carotid artery. In Apolipoprotein E (Apoe)-deficient mice Has3 expression is increased early during lesion formation when macrophages enter atherosclerotic plaques. Importantly, HAS3 expression in vascular smooth muscle cells (VSMC) was found to be regulated by interleukin 1 β (IL-1β) in an NFkB dependent manner and blocking antibodies to IL-1β abrogate Has3 expression in VSMC by activated macrophages. Has3/Apoe double deficient mice developed less atherosclerosis characterized by decreased Th1-cell responses, decreased IL-12 release, and decreased macrophage-driven inflammation.

CONCLUSIONS

Inhibition of HAS3-dependent synthesis of HA dampens systemic Th1 cell polarization and reduces plaque inflammation. These data suggest that HAS3 might be a promising therapeutic target in atherosclerosis. Moreover, because HAS3 is regulated by IL-1β, our results suggest that therapeutic anti-IL-1β antibodies, recently tested in human clinical trials (CANTOS), may exert their beneficial effects on inflammation in post-myocardial infarction patients in part via effects on HAS3. TOC categorybasic study TOC subcategoryarteriosclerosis.

Surface Modification of Poly(dimethylsiloxane) with Polydopamine and Hyaluronic Acid To Enhance Hemocompatibility for Potential Applications in Medical Implants or Devices

Poly(dimethylsiloxane) (PDMS) has been widely utilized in micro-electromechanical systems (MEMS) and implantable devices. To improve the hemocompatibility of a PDMS-based implant, a facile technique was developed by modifying PDMS with a hyaluronic acid (HA) and polydopamine (PDA) composite (HA/PDA). Under appropriate ratio of HA to PDA, platelet adhesion and activation were considerably reduced on modified PDMS substrates, indicating an enhanced hemocompatibility compared to native PDMS or those coated with HA or PDA solely. HA/PDA coating also posed minimal cytotoxicity on the adhesion and proliferation of endothelial cells (HUVECs). The anti-inflammation effect of the modified PDMS surface was characterized based on the expression of critical cytokines in adherent macrophages. This study revealed that the hemocompatibility, cytotoxicity, and anti-inflammation properties could be tailored conveniently by adjusting the ratio of HA and PDA composite on the modified PDMS surface, which has an exceptional potential as the core or packaging material for constructing implantable devices in biomedical applications.

Exchange proteins directly activated by cAMP (EPACs): Emerging therapeutic targets

Exchange proteins directly activated by cAMP (EPACs) are critical cAMP-dependent signaling pathway mediators. The discovery of EPAC proteins has significantly facilitated understanding on cAMP-dependent signaling pathway and efforts along this line open new avenues for developing novel therapeutics for cancer, diabetes, heart failure, inflammation, infections, neurological disorders and other human diseases. Over the past decade, important progress has been made in the identification of EPAC agonists, antagonists and their biological and pharmacological applications. In this review, we briefly summarize recently reported novel functions of EPACs and the discovery of their small molecule modulators. The challenges and future perspectives are also discussed.

Human Keratinocytes Respond to Extracellular UTP by Induction of Hyaluronan Synthase 2 Expression and Increased Hyaluronan Synthesis

The release of nucleotides into extracellular space is triggered by insults like wounding and ultraviolet radiation, resulting in stimulatory or inhibitory signals via plasma membrane nucleotide receptors. As similar insults are known to activate hyaluronan synthesis we explored the possibility that extracellular UTP or its breakdown products UDP and UMP act as mediators for hyaluronan synthase (HAS) activation in human epidermal keratinocytes. UTP increased hyaluronan both in the pericellular matrix and in the culture medium of HaCaT cells. 10-100 μm UTP strongly up-regulated HAS2 expression, although the other hyaluronan synthases (HAS1, HAS3) and hyaluronidases (HYAL1, HYAL2) were not affected. The HAS2 response was rapid and transient, with the maximum stimulation at 1.5 h. UDP exerted a similar effect, but higher concentrations were required for the response, and UMP showed no stimulation at all. Specific siRNAs against the UTP receptor P2Y₂, and inhibitors of UDP receptors P2Y₆ and P2Y₁₄, indicated that the response to UTP was mediated mainly through P2Y₂ and to a lesser extent via UDP receptors. UTP increased the phosphorylation of p38, ERK, CREB, and Ser-727 of STAT3 and induced nuclear translocation of pCaMKII. Inhibitors of PKC, p38, ERK, CaMKII, STAT3, and CREB partially blocked the activation of HAS2 expression, confirming the involvement of these pathways in the UTP-induced HAS2 response. The present data reveal a selective up-regulation of HAS2 expression by extracellular UTP, which is likely to contribute to the previously reported rapid activation of hyaluronan metabolism in response to tissue trauma or ultraviolet radiation.

Adenosine-generating ovarian cancer cells attract myeloid cells which differentiate into adenosine-generating tumor associated macrophages - a self-amplifying, CD39- and CD73-dependent mechanism for tumor immune escape

BACKGROUND

Ovarian cancer (OvCA) tissues show abundant expression of the ectonucleotidases CD39 and CD73 which generate immunomodulatory adenosine, thereby inhibiting cytotoxic lymphocytes. Little, however, is known about the effect of adenosine on myeloid cells. Considering that tumor associated macrophages (TAM) and myeloid-derived suppressor cells (MDSC) constitute up to 20 % of OvCA tissue, we investigated the effect of adenosine on myeloid cells and explored a possible contribution of myeloid cells to adenosine generation in vitro and ex vivo.

METHODS

Monocytes were used as human blood-derived myeloid cells. After co-incubation with SK-OV-3 or OAW-42 OvCA cells, monocyte migration was determined in transwell assays. For conversion into M2-polarized "TAM-like" macrophages, monocytes were co-incubated with OAW-42 cells. Ex vivo TAMs were obtained from OvCA ascites. Macrophage phenotypes were investigated by intracellular staining for IL-10 and IL-12. CD39 and CD73 expression were assessed by FACS analysis both on in vitro-induced TAM-like macrophages and on ascites-derived ex situ-TAMs. Myeloid cells in solid tumor tissue were analyzed by immunohistochemistry. Generation of biologically active adenosine by TAM-like macrophages was measured in luciferase-based reporter assays. Functional effects of adenosine were investigated in proliferation-experiments with CD4(+) T cells and specific inhibitors.

RESULTS

When CD39 or CD73 activity on OvCA cells were blocked, the migration of monocytes towards OvCA cells was significantly decreased. In vivo, myeloid cells in solid ovarian cancer tissue were found to express CD39 whereas CD73 was mainly detected on stromal fibroblasts. Ex situ-TAMs and in vitro differentiated TAM-like cells, however, upregulated the expression of CD39 and CD73 compared to monocytes or M1 macrophages. Expression of ectonucleotidases also translated into increased levels of biologically active adenosine. Accordingly, co-incubation with these TAMs suppressed CD4(+) T cell proliferation which could be rescued via blockade of CD39 or CD73.

CONCLUSION

Adenosine generated by OvCA cells likely contributes to the recruitment of TAMs which further amplify adenosine-dependent immunosuppression via additional ectonucleotidase activity. In solid ovarian cancer tissue, TAMs express CD39 while CD73 is found on stromal fibroblasts. Accordingly, small molecule inhibitors of CD39 or CD73 could improve immune responses in ovarian cancer.

Identification of A3 adenosine receptor agonists as novel non-narcotic analgesics

Chronic pain negatively impacts the quality of life in a variety of patient populations. The current therapeutic repertoire is inadequate in managing patient pain and warrants the development of new therapeutics. Adenosine and its four cognate receptors (A1 , A2A , A2B and A3 ) have important roles in physiological and pathophysiological states, including chronic pain. Preclinical and clinical studies have revealed that while adenosine and agonists of the A1 and A2A receptors have antinociceptive properties, their therapeutic utility is limited by adverse cardiovascular side effects. In contrast, our understanding of the A3 receptor is only in its infancy, but exciting preclinical observations of A3 receptor antinociception, which have been bolstered by clinical trials of A3 receptor agonists in other disease states, suggest pain relief without cardiovascular side effects and with sufficient tolerability. Our goal herein is to briefly discuss adenosine and its receptors in the context of pathological pain and to consider the current data regarding A3 receptor-mediated antinociception. We will highlight recent findings regarding the impact of the A3 receptor on pain pathways and examine the current state of selective A3 receptor agonists used for these studies. The adenosine-to-A3 receptor pathway represents an important endogenous system that can be targeted to provide safe, effective pain relief from chronic pain.

Multifunctional Coating Based on Hyaluronic Acid and Dopamine Conjugate for Potential Application on Surface Modification of Cardiovascular Implanted Devices

Surface modification by conjugating biomolecules has been widely proved to enhance biocompatibility of cardiovascular implanted devices. Here, we aimed at developing a multifunctional surface that not only provides good hemocompatibility but also functions well in inducing desirable vascular cell-material interaction. In the present work, the multicoatings of hyaluronic acid (HA) and dopamine (PDA) were prepared onto 316L stainless steel (316L SS) via chemical conjugation (Michael addition, Schiff base reaction, and electrostatic adsorption). The results of platelet adhesion and activation and the whole blood tests indicated that the HA/PDA coatings obtained better hemocompatibility compared with the bare 316L SS and HA or PDA immobilized on 316L SS. The HA/PDA coatings also inhibited the proliferation of smooth muscle cells and adhesion/activation of macrophages effectively, whereas not all the HA/PDA coatings improved surface endothelialization rapidly and the effects of the multifunctional coatings on endothelial cell growth depend on the HA amounts (1.0, 2.0, and 5.0 mg/mL, labeled as PDA-HA-1, PDA-HA-2, and PDA-HA-5 respectively). Herein the PDA-HA-1 and PDA-HA-2 coatings were found to improve endothelial cell adhesion and proliferation significantly. The tissue compatibility of the HA/PDA coatings also depends on the HA amounts, and the PDA-HA-2 coating was proved to cause milder in vivo tissue response. Additionally, the mechanism of the HA molecular weight change and in vivo tissue response was also explored. These results effectively suggested that the HA/PDA coating might be promising when serving as a cardiovascular implanted device coating.

Deletion of Hyaluronan Synthase 3 Inhibits Neointimal Hyperplasia in Mice

OBJECTIVE

Hyaluronan (HA) is a polymeric glucosaminoglycan that forms a provisional extracellular matrix in diseased vessels. HA is synthesized by 3 different HA synthases (HAS1, HAS2, and HAS3). Aim of this study was to unravel the role of the HAS3 isoenzyme during experimental neointimal hyperplasia.

APPROACH AND RESULTS

Neointimal hyperplasia was induced in Has3-deficient mice by ligation of the carotid artery. HA in the media of Has3-deficient mice was decreased 28 days after ligation, and neointimal hyperplasia was strongly inhibited. However, medial and luminal areas were unaffected. Cell density, proliferation, and apoptosis were not altered, suggesting a proportional decrease of both, the number of cells and extracellular matrix. In addition, endothelial function as determined by acetylcholine-induced relaxation of aortic rings, immunoblotting of endothelial nitric oxide synthase, and arterial blood pressure were not affected. Furthermore, the oxidative stress response was not affected as determined in total protein extracts from aortae. Transcriptome analysis comparing control versus ligated carotid arteries hinted toward a mitigated differential regulation of various signaling pathways in Has3-deficient mice in response to ligation that were related to vascular smooth muscle cell (VSMC) migration, including focal adhesions, integrins, mitogen-activated protein kinase, and phosphatidylinositol signaling system. Lentiviral overexpression of HAS3 in VSMC supported the migratory phenotype of VSMC in response to platelet-derived growth factor BB in vitro. Accordingly, knockdown of HAS3 reduced the migratory response to platelet-derived growth factor BB and in addition decreased the expression of PDGF-B mRNA.

CONCLUSIONS

HAS3-mediated HA synthesis after vessel injury supports seminal signaling pathways in activation of VSMC, increases platelet-derived growth factor BB-mediated migration, and in turn enhances neointimal hyperplasia in vivo.

CD73 regulates vascular smooth muscle cell functions and facilitates atherosclerotic plaque formation

Extracellular adenosine, generated by ecto-5'-nucleotidase (CD73) via enzymatic catalyzation, has been found to facilitate atherosclerosis (AS). Thus, suppressing CD73 may attenuate AS. In this study, we evaluated the role of CD73 during AS development and further explored cellular and molecular mechanism in smooth muscle cells (SMCs). In a mouse model of carotid artery ligation, inactivation of CD73 inhibited migration and proliferation of vascular SMCs. In in vitro experiments, RNA interference of CD73 inhibited migration, proliferation, and foam cell transformation of human umbilical artery smooth muscle cells. Further, we established an atherosclerotic model using ApoE-/- mice fed with a western diet for 16 weeks. Inactivation of CD73-attenuated AS and hyperlipidemia in ApoE-/- mice. In conclusion, our data suggest that CD73 facilitates AS by promoting migration, proliferation, and foam cell transformation of vascular SMCs and elevating serum lipid levels. Thus, inhibition of CD73 may be beneficial for prevention and treatment of AS.

The A3 adenosine receptor: history and perspectives

By general consensus, the omnipresent purine nucleoside adenosine is considered a major regulator of local tissue function, especially when energy supply fails to meet cellular energy demand. Adenosine mediation involves activation of a family of four G protein-coupled adenosine receptors (ARs): A(1), A(2)A, A(2)B, and A(3). The A(3) adenosine receptor (A(3)AR) is the only adenosine subtype to be overexpressed in inflammatory and cancer cells, thus making it a potential target for therapy. Originally isolated as an orphan receptor, A(3)AR presented a twofold nature under different pathophysiologic conditions: it appeared to be protective/harmful under ischemic conditions, pro/anti-inflammatory, and pro/antitumoral depending on the systems investigated. Until recently, the greatest and most intriguing challenge has been to understand whether, and in which cases, selective A(3) agonists or antagonists would be the best choice. Today, the choice has been made and A(3)AR agonists are now under clinical development for some disorders including rheumatoid arthritis, psoriasis, glaucoma, and hepatocellular carcinoma. More specifically, the interest and relevance of these new agents derives from clinical data demonstrating that A(3)AR agonists are both effective and safe. Thus, it will become apparent in the present review that purine scientists do seem to be getting closer to their goal: the incorporation of adenosine ligands into drugs with the ability to save lives and improve human health.

Interactions between Hyaluronan and Its Receptors (CD44, RHAMM) Regulate the Activities of Inflammation and Cancer

The glycosaminoglycan hyaluronan (HA), a major component of extracellular matrices, and cell surface receptors of HA have been proposed to have pivotal roles in cell proliferation, migration, and invasion, which are necessary for inflammation and cancer progression. CD44 and receptor for HA-mediated motility (RHAMM) are the two main HA-receptors whose biological functions in human and murine inflammations and tumor cells have been investigated comprehensively. HA was initially considered to be only an inert component of connective tissues, but is now known as a “dynamic” molecule with a constant turnover in many tissues through rapid metabolism that involves HA molecules of various sizes: high molecular weight HA (HMW HA), low molecular weight HA, and oligosaccharides. The intracellular signaling pathways initiated by HA interactions with CD44 and RHAMM that lead to inflammatory and tumorigenic responses are complex. Interestingly, these molecules have dual functions in inflammations and tumorigenesis. For example, the presence of CD44 is involved in initiation of arthritis, while the absence of CD44 by genetic deletion in an arthritis mouse model increases rather than decreases disease severity. Similar dual functions of CD44 exist in initiation and progression of cancer. RHAMM overexpression is most commonly linked to cancer progression, whereas loss of RHAMM is associated with malignant peripheral nerve sheath tumor growth. HA may similarly perform dual functions. An abundance of HMW HA can promote malignant cell proliferation and development of cancer, whereas antagonists to HA-CD44 signaling inhibit tumor cell growth in vitro and in vivo by interfering with HMW HA-CD44 interaction. This review describes the roles of HA interactions with CD44 and RHAMM in inflammatory responses and tumor development/progression, and how therapeutic strategies that block these key inflammatory/tumorigenic processes may be developed in rodent and human diseases.

The infarct-sparing effect of IB-MECA against myocardial ischemia/reperfusion injury in mice is mediated by sequential activation of adenosine A3 and A 2A receptors

Conflicting results exist regarding the role of A3 adenosine receptors (A3ARs) in mediating cardioprotection during reperfusion following myocardial infarction. We hypothesized that the effects of the A3AR agonist IB-MECA to produce cardioprotection might involve activation of other adenosine receptor subtypes. C57Bl/6 (B6), A3AR KO, A2AAR KO, and A2AAR KO/WT bone marrow chimeric mice were assigned to 12 groups undergoing either hemodynamic studies or 45 min of LAD occlusion and 60 min of reperfusion. IB-MECA (100 μg/kg) or vehicle was administered by iv bolus 5 min before reperfusion. Radioligand binding assays showed that IB-MECA has high affinity for the mouse A3AR (K i = 0.17 ± 0.05 nM), but also can bind with lower affinity to the A1AR (9.0 ± 2.4 nM) or the A2AAR (56.5 ± 10.2 nM). IB-MECA caused bi-phasic hemodynamic changes, which were completely absent in A3AR KO mice and were modified by A2AAR blockade or deletion. IB-MECA stimulated histamine release, increased heart rate, and significantly reduced IF size in B6 mice from 61.5 ± 1.4 to 48.6 ± 2.4% of risk region (RR; 21% reduction, p < 0.05) but not in A3AR KO mice. Compared to B6, A3AR KO mice had significantly reduced IF size (p < 0.05). In B6/B6 bone marrow chimeras, IB-MECA caused a 47% reduction of IF size (from 47.3 ± 3.9 to 24.7 ± 4.5, p < 0.05). However, no significant cardioprotective effect of IB-MECA was observed in A2AARKO/B6 mice, which lacked A2AARs only on their bone marrow-derived cells. Activation of A3ARs induces a bi-phasic hemodynamic response, which is partially mediated by activation of A2AARs. The cardioprotective effect of IB-MECA is due to the initial activation of A3AR followed by activation of A2AARs in bone marrow-derived cells.

cAMP signalling in the vasculature: the role of Epac (exchange protein directly activated by cAMP)

The second messenger cAMP plays a central role in mediating vascular smooth muscle relaxation in response to vasoactive transmitters and in strengthening endothelial cell-cell junctions that regulate the movement of solutes, cells and macromolecules between the blood and the surrounding tissue. The vasculature expresses three cAMP effector proteins: PKA (protein kinase A), CNG (cyclic-nucleotide-gated) ion channels, and the most recently discovered Epacs (exchange proteins directly activated by cAMP). Epacs are a family of GEFs (guanine-nucleotide-exchange factors) for the small Ras-related GTPases Rap1 and Rap2, and are being increasingly implicated as important mediators of cAMP signalling, both in their own right and in parallel with the prototypical cAMP target PKA. In the present paper, we review what is currently known about the role of Epac within blood vessels, particularly with regard to the regulation of vascular tone, endothelial barrier function and inflammation.

Immunoregulatory effects of adenosine

Adenosine, a purine nucleoside, is involved in local and systemic inflammatory responses. Adenosine plays a pivotal role in the modulation of differentiation, maturation and migration of immune cells (neutrophils, macrophages, dendritic cells, lymphocytes, etc.), as well as in the secretion of cytokines and chemokines by activating four G protein-coupled receptors (A1, A2A, A2B, and A3) which are expressed by a variety of immune cells. The development of selective agonists and antagonists of adenosine receptors has advanced the current understanding on the multiple functions of adenosine in immunologic responses and related diseases. This article reviews the metabolism of adenosine and its effects on immune cells and inflammatory diseases via adenosine receptors.