Hydrolysis of extracellular ATP by ectonucleoside triphosphate diphosphohydrolase (ENTPD) establishes the set point for fibrotic activity of cardiac fibroblasts

P2 X 7 receptor is a critical regulator of extracellular ATP-induced profibrotic genes expression in rat kidney: implication of transforming growth factor-β/Smad signaling pathway

This study was designed to investigate the potential of extracellular adenosine 5'-triphosphate (ATP) via the P2 X 7 receptor to activate the renal fibrotic processes in rats. The present study demonstrates that administration of ATP rapidly activated transforming growth factor-β (TGF-β) to induce phosphorylation of Smad-2/3. Renal connective tissue growth factor (CTGF) and tissue inhibitor of metalloproteinase-1 (TIMP-1) mRNA and protein expressions were also increased following ATP administration. A decrease in TGF-β amount in serum as well as renal Smad-2/3 phosphorylation was noticed in animals pre-treated with the specific antagonist of P2 X 7 receptor, A 438,079. In addition, a significant reduction in mRNA and protein expression of CTGF and TIMP-1were also observed in the kidneys of those animals. Collectively, the current findings demonstrate that ATP has the ability to augment TGF-β-mediated Smad-2/3 phosphorylation and enhance the expression of the pro-fibrotic genes, CTGF and TIMP-1, an effect that is largely mediated via P2 X 7 receptor.

Investigation of coagulation and proteomics profiles in symptomatic feline hypertrophic cardiomyopathy and healthy control cats

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is a crucial heart disease in cats. The clinical manifestations of HCM comprise pulmonary edema, dyspnea, syncope, arterial thromboembolism (ATE), and sudden cardiac death. D-dimer and prothrombin time (PT) are powerful biomarkers used to assess coagulation function. Dysregulation in these two biomarkers may be associated with HCM in cats. This study aims to assess D-dimer levels, PT, and proteomic profiling in healthy cats in comparison to cats with symptomatic HCM.

RESULTS

Twenty-nine client-owned cats with HCM were enrolled, including 15 healthy control and 14 symptomatic HCM cats. The D-dimer concentration and PT were examined. Proteomic analysis was conducted by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry and liquid chromatography-tandem mass spectrometry (LC-MS/MS). In symptomatic cats, D-dimer levels were statistically significantly higher (mean ± SEM: 372.19 ng/ml ± 58.28) than in healthy cats (mean ± SEM: 208.54 ng/ml ± 10.92) with P-value of less than 0.01, while PT was statistically significantly lower in symptomatic cats (mean ± SEM: 9.8 s ± 0.15) compared to healthy cats (mean ± SEM: 11.08 s ± 0.23) with P-value of less than 0.0001. The proteomics analysis revealed upregulation of integrin subunit alpha M (ITGAM), elongin B (ELOB), and fibrillin 2 (FBN2) and downregulation of zinc finger protein 316 (ZNF316) and ectonucleoside triphosphate diphosphohydrolase 8 (ENTPD8) in symptomatic HCM cats. In addition, protein-drug interaction analysis identified the Ras signaling pathway and PI3K-Akt signaling pathway.

CONCLUSIONS

Cats with symptomatic HCM have higher D-dimer and lower PT than healthy cats. Proteomic profiles may be used as potential biomarkers for the detection and management of HCM in cats. The use of D-dimer as a biomarker for HCM detection and the use of proteomic profiling for a better understanding of disease mechanisms remain to be further studied in cats.

Blockage of the adenosine A2B receptor prevents cardiac fibroblasts overgrowth in rats with pulmonary arterial hypertension

Sustained pressure overload and fibrosis of the right ventricle (RV) are the leading causes of mortality in pulmonary arterial hypertension (PAH). Although the role of adenosine in PAH has been attributed to the control of pulmonary vascular tone, cardiac reserve, and inflammatory processes, the involvement of the nucleoside in RV remodelling remains poorly understood. Conflicting results exist on targeting the low-affinity adenosine A2B receptor (A2BAR) for the treatment of PAH mostly because it displays dual roles in acute vs. chronic lung diseases. Herein, we investigated the role of the A2BAR in the viability/proliferation and collagen production by cardiac fibroblasts (CFs) isolated from RVs of rats with monocrotaline (MCT)-induced PAH. CFs from MCT-treated rats display higher cell viability/proliferation capacity and overexpress A2BAR compared to the cells from healthy littermates. The enzymatically stable adenosine analogue, 5'-N-ethylcarboxamidoadenosine (NECA, 1-30 μM), concentration-dependently increased growth, and type I collagen production by CFs originated from control and PAH rats, but its effects were more prominent in cells from rats with PAH. Blockage of the A2BAR with PSB603 (100 nM), but not of the A2AAR with SCH442416 (100 nM), attenuated the proliferative effect of NECA in CFs from PAH rats. The A2AAR agonist, CGS21680 (3 and 10 nM), was virtually devoid of effect. Overall, data suggest that adenosine signalling via A2BAR may contribute to RV overgrowth secondary to PAH. Therefore, blockage of the A2AAR may be a valuable therapeutic alternative to mitigate cardiac remodelling and prevent right heart failure in PAH patients.

Interference mechanism of benzo[a]pyrene exposure on the taste substance metabolisms in Ruditapes philippinarum

Aquatic animals are popular for their unique umami and high-quality protein. However, under the realistic background of increasing marine pollution, whether it affects the aquatic animal tastes, and what the interference mechanism is still remains unknown. Benzo[a]pyrene (B[a]P) is a typical Polycyclic aromatic hydrocarbons (PAHs) with high toxicity. In this study, we investigated the effects of B[a]P (0, 0.8, 4 and 20 μg/L) on the content and taste evaluation of Ruditapes philippinarum taste substances, and clarified the interference mechanism of B[a]P on taste substance metabolisms with transcriptome analysis. The results demonstrated that B[a]P significantly altered the contents and taste activity values (TAVs) of free amino acids (FAAs), 5'-nucleotides, organic acids, flavor peptides, organic bases, sugars and inorganic ions, as well as the gene expressions within their synthesis and decomposition, indicating that B[a]P affected these taste substance contents by interfering with their metabolisms, thereby changing the clam tastes (decreases of umami and sweetness, and increase of bitter taste). This study provided scientific basis for quality assurance of bivalve cultivation and control of marine pollution.

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.

Ectonucleoside triphosphate diphosphohydrolase-1 (CD39) impacts TGF-β1 responses: insights into cardiac fibrosis and function following myocardial infarction

Extracellular purine nucleotides and nucleosides released from activated or injured cells influence multiple aspects of cardiac physiology and pathophysiology. Ectonucleoside triphosphate diphosphohydrolase-1 (ENTPD1; CD39) hydrolyzes released nucleotides and thereby regulates the magnitude and duration of purinergic signaling. However, the impact of CD39 activity on post-myocardial infarction (MI) remodeling is incompletely understood. We measured the levels and activity of ectonucleotidases in human left ventricular samples from control and ischemic cardiomyopathy (ICM) hearts and examined the impact of ablation of Cd39 expression on post-myocardial infarction remodeling in mice. We found that human CD39 levels and activity are significantly decreased in ICM hearts (n = 5) compared with control hearts (n = 5). In mice null for Cd39, cardiac function and remodeling are significantly compromised in Cd39-/- mice following myocardial infarction. Fibrotic markers including plasminogen activator inhibitor-1 (PAI-1) expression, fibrin deposition, α-smooth muscle actin (αSMA), and collagen expression are increased in Cd39-/- hearts. Importantly, we found that transforming growth factor β1 (TGF-β1) stimulates ATP release and induces Cd39 expression and activity on cardiac fibroblasts, constituting an autocrine regulatory pathway not previously appreciated. Absence of CD39 activity on cardiac fibroblasts exacerbates TGF-β1 profibrotic responses. Treatment with exogenous ectonucleotidase rescues this profibrotic response in Cd39-/- fibroblasts. Together, these data demonstrate that CD39 has important interactions with TGF-β1-stimulated autocrine purinergic signaling in cardiac fibroblasts and dictates outcomes of cardiac remodeling following myocardial infarction. Our results reveal that ENTPD1 (CD39) regulates TGF-β1-mediated fibroblast activation and limits adverse cardiac remodeling following myocardial infarction.NEW & NOTEWORTHY We show that CD39 is a critical modulator of TGF-β1-mediated fibroblast activation and cardiac remodeling following myocardial infarction via modulation of nucleotide signaling. TGF-β1-induced CD39 expression generates a negative feedback loop that attenuates cardiac fibroblast activation. In the absence of CD39 activity, collagen deposition is increased, elastin expression is decreased, and diastolic dysfunction is worsened. Treatment with ecto-apyrase attenuates the TGF-β1-induced profibrotic cardiac fibroblast phenotype, revealing a novel approach to combat post-myocardial infarction cardiac fibrosis.

Adenosine and Adenosine Receptors: Advances in Atrial Fibrillation

Atrial fibrillation (AF) is the most common arrhythmia in the world. Because the key to developing innovative therapies that limit the onset and the progression of AF is to fully understand the underlying molecular mechanisms of AF, the aim of the present narrative review is to report the most recent advances in the potential role of the adenosinergic system in the pathophysiology of AF. After a comprehensive approach describing adenosinergic system signaling and the mechanisms of the initiation and maintenance of AF, we address the interactions of the adenosinergic system's signaling with AF. Indeed, adenosine release can activate four G-coupled membrane receptors, named A₁, A_2A, A_2B and A₃. Activation of the A_2A receptors can promote the occurrence of delayed depolarization, while activation of the A₁ receptors can shorten the action potential's duration and induce the resting membrane's potential hyperpolarization, which promote pulmonary vein firing, stabilize the AF rotors and allow for functional reentry. Moreover, the A_2B receptors have been associated with atrial fibrosis homeostasis. Finally, the adenosinergic system can modulate the autonomous nervous system and is associated with AF risk factors. A question remains regarding adenosine release and the adenosine receptors' activation and whether this would be a cause or consequence of AF.

MIG-23 is involved in sperm migration by modulating extracellular ATP levels in Ascaris suum

In nematodes, spermiogenesis is a process of sperm activation in which nonmotile spermatids are transformed into crawling spermatozoa. Sperm motility acquisition during this process is essential for successful fertilization, but the underlying mechanisms remain to be clarified. Herein, we have found that extracellular adenosine-5′-triphosphate (ATP) level regulation by MIG-23, which is a homolog of human ecto-nucleoside triphosphate diphosphohydrolase (E-NTPDase), was required for major sperm protein (MSP) filament dynamics and sperm motility in the nematode Ascaris suum. During sperm activation, a large amount of ATP was produced in mitochondria and was stored in refringent granules (RGs). Some of the produced ATP was released to the extracellular space through innexin channels. MIG-23 was localized in the sperm plasma membrane and contributed to the ecto-ATPase activity of spermatozoa. Blocking MIG-23 activity resulted in a decrease in the ATP hydrolysis activity of spermatozoa and an increase in the depolymerization rate of MSP filaments in pseudopodia, which eventually affected sperm migration. Overall, our data suggest that MIG-23, which contributes to the ecto-ATPase activity of spermatozoa, regulates sperm migration by modulating extracellular ATP levels.

P2Y2 promotes fibroblasts activation and skeletal muscle fibrosis through AKT, ERK, and PKC

BACKGROUND

Skeletal muscle atrophy and fibrosis are pathological conditions that contribute to morbidity in numerous conditions including aging, cachexia, and denervation. Muscle atrophy is characterized as reduction of muscle fiber size and loss of muscle mass while muscle fibrosis is due to fibroblasts activation and excessive production of extracellular matrix. Purinergic receptor P2Y2 has been implicated in fibrosis. This study aims to elucidate the roles of P2Y2 in sleketal muscle atrophy and fibrosis.

METHODS

Primary muscle fibroblasts were isolated from wild type and P2Y2 knockout (KO) mice and their proliferating and migrating abilities were assessed by CCK-8 and Transwell migration assays respectively. Fibroblasts were activated with TGF-β1 and assessed by western blot of myofibroblast markers including α-SMA, CTGF, and collagen I. Muscle atrophy and fibrosis were induced by transection of distal sciatic nerve and assessed using Masson staining.

RESULTS

P2Y2 KO fibroblasts proliferated and migrated significantly slower than WT fibroblasts with or without TGF-β1.The proliferation and ECM production were enhanced by P2Y2 agonist PSB-1114 and inhibited by antagonist AR-C118925. TGF-β1 induced fibrotic activation was abolished by P2Y2 ablation and inhibited by AKT, ERK, and PKC inhibitors. Ablation of P2Y2 reduced denervation induced muscle atrophy and fibrosis.

CONCLUSIONS

P2Y2 is a promoter of skeletal muscle atrophy and activation of fibroblasts after muscle injury, which signaling through AKT, ERK and PKC. P2Y2 could be a potential intervention target after muscle injury.

Danegaptide Prevents TGFβ1-Induced Damage in Human Proximal Tubule Epithelial Cells of the Kidney

Chronic kidney disease (CKD) is a global health problem associated with a number of comorbidities. Recent evidence implicates increased hemichannel-mediated release of adenosine triphosphate (ATP) in the progression of tubulointerstitial fibrosis, the main underlying pathology of CKD. Here, we evaluate the effect of danegaptide on blocking hemichannel-mediated changes in the expression and function of proteins associated with disease progression in tubular epithelial kidney cells. Primary human proximal tubule epithelial cells (hPTECs) were treated with the beta1 isoform of the pro-fibrotic cytokine transforming growth factor (TGFβ1) ± danegaptide. qRT-PCR and immunoblotting confirmed mRNA and protein expression, whilst a cytokine antibody array assessed the expression/secretion of proinflammatory and profibrotic cytokines. Carboxyfluorescein dye uptake and ATP biosensing measured hemichannel activity and ATP release, whilst transepithelial electrical resistance was used to assess paracellular permeability. Danegaptide negated carboxyfluorescein dye uptake and ATP release and protected against protein changes associated with tubular injury. Blocking Cx43-mediated ATP release was paralleled by partial restoration of the expression of cell cycle inhibitors, adherens and tight junction proteins and decreased paracellular permeability. Furthermore, danegaptide inhibited TGFβ1-induced changes in the expression and secretion of key adipokines, cytokines, chemokines, growth factors and interleukins. The data suggest that as a gap junction modulator and hemichannel blocker, danegaptide has potential in the future treatment of CKD.

Blocking Connexin-43 mediated hemichannel activity protects against early tubular injury in experimental chronic kidney disease

BACKGROUND

Tubulointerstitial fibrosis represents the key underlying pathology of Chronic Kidney Disease (CKD), yet treatment options remain limited. In this study, we investigated the role of connexin43 (Cx43) hemichannel-mediated adenosine triphosphate (ATP) release in purinergic-mediated disassembly of adherens and tight junction complexes in early tubular injury.

METHODS

Human primary proximal tubule epithelial cells (hPTECs) and clonal tubular epithelial cells (HK2) were treated with Transforming Growth Factor Beta1 (TGF-β1) ± apyrase, or ATPγS for 48 h. For inhibitor studies, cells were co-incubated with Cx43 mimetic Peptide 5, or purinergic receptor antagonists Suramin, A438079 or A804598. Immunoblotting, single-cell force spectroscopy and trans-epithelial electrical resistance assessed protein expression, cell-cell adhesion and paracellular permeability. Carboxyfluorescein uptake and biosensing measured hemichannel activity and real-time ATP release, whilst a heterozygous Cx43+/- mouse model with unilateral ureteral obstruction (UUO) assessed the role of Cx43 in vivo.

RESULTS

Immunohistochemistry of biopsy material from patients with diabetic nephropathy confirmed increased expression of purinergic receptor P2X7. TGF-β1 increased Cx43 mediated hemichannel activity and ATP release in hPTECs and HK2 cells. The cytokine reduced maximum unbinding forces and reduced cell-cell adhesion, which translated to increased paracellular permeability. Changes were reversed when cells were co-incubated with either Peptide 5 or P2-purinoceptor inhibitors. Cx43+/- mice did not exhibit protein changes associated with early tubular injury in a UUO model of fibrosis.

CONCLUSION

Data suggest that Cx43 mediated ATP release represents an initial trigger in early tubular injury via its actions on the adherens and tight junction complex. Since Cx43 is highly expressed in nephropathy, it represents a novel target for intervention of tubulointerstitial fibrosis in CKD. Video Abstract In proximal tubular epithelial cells (PTECs), tight junction proteins, including zona occuludens-1 (ZO-1), contribute to epithelial integrity, whilst the adherens junction protein epithelial (E)-cadherin (ECAD) maintains cell-cell coupling, facilitating connexin 43 (Cx43) gap junction-mediated intercellular communication (GJIC) and the direct transfer of small molecules and ions between cells. In disease, such as diabetic nephropathy, the pro-fibrotic cytokine transforming growth factor beta1 (TGF-β1) binds to its receptor and recruits SMAD2/3 signalling ahead of changes in gene transcription and up-regulation of Cx43-mediated hemichannels (HC). Uncoupled hemichannels permit the release of adenosine triphosphate (ATP) in to the extracellular space (↑[ATP]e), where ATP binds to the P2X7 purinoreceptor and activates the nucleotide-binding domain and leucine-rich repeat containing (NLR) protein-3 (NLRP3) inflammasome. Inflammation results in epithelial-to-mesenchymal transition (EMT), fibrosis and tubular injury. A major consequence is further loss of ECAD and reduced stickiness between cells, which can be functionally measured as a decrease in the maximum unbinding force needed to uncouple two adherent cells (Fmax). Loss of ECAD feeds forward to further lessen cell-cell coupling exacerbating the switch from GJIC to HC-mediated release of ATP. Reduction in ZO-1 impedes tight junction effectiveness and decreases trans-epithelial resistance (↓TER), resulting in increased paracellular permeability.

Inhibition of P2X7 Purinergic Receptor Ameliorates Cardiac Fibrosis by Suppressing NLRP3/IL-1β Pathway

P2X7 purinergic receptor (P2X7R) has been implicated in several cardiovascular diseases. However, whether it regulates cardiac fibrosis remains elusive. Herein, its involvement in the development of cardiac fibrosis was examined using a transverse aortic constriction (TAC) mice model and cardiac fibroblasts (CFs) hyperstimulated by TGF-β1 for 48 hours. Results showed that TAC and TGF-β1 treatment increased the expression of P2X7R. Silencing of P2X7R expression with siP2X7R ameliorated TGF-β1 effects on fibroblasts activation. Similarly, P2X7R inhibition by Brilliant Blue G (BBG) reduced mRNA and protein levels of profibrosis markers, while the P2X7R agonist BzATP accelerated the TGF-β1-induced CFs activation. Moreover, it was found that TGF-β1-induced CFs activation was mediated by the NLRP3/IL-1β inflammasome pathway. BBG or siP2X7R treatment suppressed NLRP3/IL-1β pathway signaling. In vivo, BBG significantly alleviated TAC-induced cardiac fibrosis, cardiac dysfunction, and NLRP3/IL-1β activation. Collectively, our findings imply that suppressing P2X7R may limit cardiac fibrosis and abnormal activation of CFs.

Enhanced clinical phenotyping by mechanistic bioprofiling in heart failure with preserved ejection fraction: insights from the MEDIA-DHF study (The Metabolic Road to Diastolic Heart Failure)

Background: Heart failure with preserved ejection fraction (HFpEF) is a heterogeneous syndrome for which clear evidence of effective therapies is lacking. Understanding which factors determine this heterogeneity may be helped by better phenotyping. An unsupervised statistical approach applied to a large set of biomarkers may identify distinct HFpEF phenotypes.Methods: Relevant proteomic biomarkers were analyzed in 392 HFpEF patients included in Metabolic Road to Diastolic HF (MEDIA-DHF). We performed an unsupervised cluster analysis to define distinct phenotypes. Cluster characteristics were explored with logistic regression. The association between clusters and 1-year cardiovascular (CV) death and/or CV hospitalization was studied using Cox regression.Results: Based on 415 biomarkers, we identified 2 distinct clusters. Clinical variables associated with cluster 2 were diabetes, impaired renal function, loop diuretics and/or betablockers. In addition, 17 biomarkers were higher expressed in cluster 2 vs. 1. Patients in cluster 2 vs. those in 1 experienced higher rates of CV death/CV hospitalization (adj. HR 1.93, 95% CI 1.12-3.32, p = 0.017). Complex-network analyses linked these biomarkers to immune system activation, signal transduction cascades, cell interactions and metabolism.Conclusion: Unsupervised machine-learning algorithms applied to a wide range of biomarkers identified 2 HFpEF clusters with different CV phenotypes and outcomes. The identified pathways may provide a basis for future research.Clinical significanceMore insight is obtained in the mechanisms related to poor outcome in HFpEF patients since it was demonstrated that biomarkers associated with the high-risk cluster were related to the immune system, signal transduction cascades, cell interactions and metabolismBiomarkers (and pathways) identified in this study may help select high-risk HFpEF patients which could be helpful for the inclusion/exclusion of patients in future trials.Our findings may be the basis of investigating therapies specifically targeting these pathways and the potential use of corresponding markers potentially identifying patients with distinct mechanistic bioprofiles most likely to respond to the selected mechanistically targeted therapies.

Targeting Purinergic Signaling and Cell Therapy in Cardiovascular and Neurodegenerative Diseases

Extracellular purines exert several functions in physiological and pathophysiological mechanisms. ATP acts through P2 receptors as a neurotransmitter and neuromodulator and modulates heart contractility, while adenosine participates in neurotransmission, blood pressure, and many other mechanisms. Because of their capability to differentiate into mature cell types, they provide a unique therapeutic strategy for regenerating damaged tissue, such as in cardiovascular and neurodegenerative diseases. Purinergic signaling is pivotal for controlling stem cell differentiation and phenotype determination. Proliferation, differentiation, and apoptosis of stem cells of various origins are regulated by purinergic receptors. In this chapter, we selected neurodegenerative and cardiovascular diseases with clinical trials using cell therapy and purinergic receptor targeting. We discuss these approaches as therapeutic alternatives to neurodegenerative and cardiovascular diseases. For instance, promising results were demonstrated in the utilization of mesenchymal stem cells and bone marrow mononuclear cells in vascular regeneration. Regarding neurodegenerative diseases, in general, P2X7 and A_2A receptors mostly worsen the degenerative state. Stem cell-based therapy, mainly through mesenchymal and hematopoietic stem cells, showed promising results in improving symptoms caused by neurodegeneration. We propose that purinergic receptor activity regulation combined with stem cells could enhance proliferative and differentiation rates as well as cell engraftment.

Kinetics of MSC-based enzyme therapy for immunoregulation

BACKGROUND

Mesenchymal stromal cells (MSC) demonstrate innate and regulatory immunologic functions and have been widely explored for cell therapy applications. Mechanisms by which MSCs achieve therapeutic effects are theorized, though appropriate dosing and duration of these mechanisms in vivo warrant deeper investigation. One, rapid immunosuppressive function of MSCs is through ectoenzyme expression of CD73 and CD39 which cooperatively hydrolyze inflammatory, extracellular adenosine triphosphate (ATP) to anti-inflammatory adenosine. Extracellular ATP has a key role in autoimmune and inflammatory diseases, which administered MSCs have the potential to modulate in a timescale that is befitting of shorter acting therapeutic function.

METHODS

In vitro experiments were performed to determine the hydrolysis rates of ATP by MSCs. Through kinetic modeling from experimental results, the rate at which a single cell can metabolize ATP was determined. Based on these rates, the ability of MSCs to downregulate inflammatory signaling pathways was prospectively validated using model system parameters with respect to two different mechanisms: extracellular ATP stimulates lymphocytes to suppress proliferation and induce apoptosis and with co-stimulation, it stimulates monocytes to release pro-inflammatory IL-1β. MSCs were co-cultured with immune cells using transwell inserts and compared to immune cell only groups.

RESULTS

Hydrolysis of ATP was efficiently modeled by first-order enzyme kinetics. For in vitro culture, the rate at which a single cell can hydrolyize ATP is 8.9 nmol/min. In the presence of extracellular ATP, cocultures of MSCs reduced cytotoxicity and allows for proliferation of lymphocytes while limiting IL-1β secretion from monocytes.

CONCLUSIONS

Such use of these models may allow for better dosing predictions for MSCs to be used therapeutically for chronic inflammatory diseases such as rheumatoid arthritis, diabetes, pancreatitis, and other systemic inflammatory response syndromes. For the first time, the effect of MSCs on ATP hydrolysis in immune cell response is quantitatively analyzed on a cell-molecule basis by modeling the hydrolysis as an enzyme-substrate reaction. The results also give insight into MSCs' dynamic response mechanisms to ameliorate effects of extracellular ATP whether it be through positive or negative regulation.

N6-(2-Hydroxyethyl) Adenosine From Cordyceps cicadae Ameliorates Renal Interstitial Fibrosis and Prevents Inflammation via TGF-β1/Smad and NF-κB Signaling Pathway

Renal interstitial fibrosis is characterized by inflammation and an excessive accumulation of extracellular matrix, which leads to end-stage renal failure. Our previous studies have shown that a natural product from Cordyceps cicadae can ameliorate chronic kidney diseases. N6-(2-Hydroxyethyl) adenosine (HEA), a physiologically active compound in C. cicadae, has been identified as a Ca²⁺ antagonist and an anti-inflammatory agent in pharmacological tests. However, its role in renal interstitial fibrosis and the underlying mechanism remains unclear. Here, unilateral ureteral obstruction (UUO) was used to induce renal interstitial fibrosis in male C57BL/6 mice. Different doses of HEA (2.5, 5, and 7.5 mg/kg) were given by intraperitoneal injection 24 h before UUO, and the treatment was continued for 14 days post-operatively. Histologic changes were examined by hematoxylin & eosin, Masson’s trichrome, and picrosirius red stain. Quantitative real-time PCR analysis, enzyme-linked immunosorbent assays, immunohistochemistry, and western blot analysis were used to evaluate proteins levels. And the results showed that HEA significantly decreased UUO-induced renal tubular injury and fibrosis. In vivo, HEA apparently decreased UUO-induced inflammation and renal fibroblast activation by suppression of the NF-κB and TGF-β1/Smad signaling pathway. In vitro, HEA also obviously decreased lipopolysaccharide-induced inflammatory cytokine level in RAW 264.7 cells and TGF-β1-induced fibroblast activation in NRK-49F cells by modulating NF-κB and TGF-β1/Smad signaling. In general, our findings indicate that HEA has a beneficial effect on UUO-induced tubulointerstitial fibrosis by suppression of inflammatory and renal fibroblast activation, which may be a potential therapy in chronic conditions such as renal interstitial fibrosis.

Stimulation of P2Y11 receptor modulates cardiac fibroblasts secretome toward immunomodulatory and protective roles after Hypoxia/Reoxygenation injury

Cardiac fibroblasts are important regulators of myocardial structure and function. Their implications in pathological processes such as Ischemia/Reperfusion are well characterized. Cardiac fibroblasts respond to stress by excessive proliferation and secretion of pro-inflammatory cytokines and other factors, e.g. ATP, leading to purinergic receptors activation. P2Y11 receptor (P2Y11R) is an ATP-sensitive GPCR playing an immunomodulatory role in human dendritic cells (DC). We hypothesized that P2Y11R stimulation modulated the pro-inflammatory responses of human cardiac fibroblasts (HCF) to Hypoxia/Reoxygenation (H/R) mainly by acting on their secretome. P2Y11R stimulation in HCF at the onset of reoxygenation significantly limited H/R-induced proliferation (-19%) and pro-inflammatory cytokines and ATP secretion (-44% and -83% respectively). Exposure of DC to HCF secretome increased their expression of CD83, CD25 and CD86, suggesting a switch from immature to mature phenotype. Under LPS stimulation, DC had a pro-inflammatory profile (high IL-12/IL-10 ratio) that was decreased by HCF secretome (-3,8-fold), indicating induction of a tolerogenic profile. Moreover, P2Y11R inhibition in HCF led to high IL-12 secretion in DC, suggesting that the immunomodulatory effect of HCF secretome is P2Y11R-dependant. HCF secretome reduced H/R-induced cardiomyocytes death (-23%) through RISK pathway activation. P2Y11R inhibition in HCF induced a complete loss of HCF secretome protective effect, highlighting the cardioprotective role of P2Y11R. Our data demonstrated paracrine interactions between HCF, cardiomyocytes and DC following H/R, suggesting a key role of HCF in the cellular responses to reperfusion. These results also demonstrated a beneficial role of P2Y11R in HCF during H/R and strongly support the hypothesis that P2Y11R is a modulator of I/R injury.

ATP triggers a robust intracellular [Ca2+ ]-mediated signalling pathway in human synovial fibroblasts

NEW FINDINGS

What is the central question of this study? What are the main [Ca²⁺ ]_i signalling pathways activated by ATP in human synovial fibroblasts? What is the main finding and its importance? In human synovial fibroblasts ATP acts through a linked G-protein (G_q ) and phospholipase C signalling mechanism to produce IP₃ , which then markedly enhances release of Ca²⁺ from the endoplasmic reticulum. These results provide new information for the detection of early pathophysiology of arthritis.

ABSTRACT

In human articular joints, synovial fibroblasts (HSFs) have essential physiological functions that include synthesis and secretion of components of the extracellular matrix and essential articular joint lubricants, as well as release of paracrine substances such as ATP. Although the molecular and cellular processes that lead to a rheumatoid arthritis (RA) phenotype are not fully understood, HSF cells exhibit significant changes during this disease progression. The effects of ATP on HSFs were studied by monitoring changes in intracellular Ca²⁺ ([Ca²⁺ ]_i ), and measuring electrophysiological properties. ATP application to HSF cell populations that had been enzymatically released from 2-D cell culture revealed that ATP (10-100 μm), or its analogues UTP or ADP, consistently produced a large transient increase in [Ca²⁺ ]_i . These changes (i) were initiated by activation of the P₂ Y purinergic receptor family, (ii) required G_q -mediated signal transduction, (iii) did not involve a transmembrane Ca²⁺ influx, but instead (iv) arose almost entirely from activation of endoplasmic reticulum (ER)-localized inositol 1,4,5-trisphosphate (IP₃ ) receptors that triggered Ca²⁺ release from the ER. Corresponding single cell electrophysiological studies revealed that these ATP effects (i) were insensitive to [Ca²⁺ ]_o removal, (ii) involved an IP₃ -mediated intracellular Ca²⁺ release process, and (iii) strongly turned on Ca²⁺ -activated K⁺ current(s) that significantly hyperpolarized these cells. Application of histamine produced very similar effects in these HSF cells. Since ATP is a known paracrine agonist and histamine is released early in the inflammatory response, these findings may contribute to identification of early steps/defects in the initiation and progression of RA.

Cell-subtype-specific changes in adenosine pathways in schizophrenia

Prior work in animal models implicates abnormalities of adenosine metabolism in astrocytes as a possible pathophysiological mechanism underlying the symptoms of schizophrenia. In the present study, we sought to reverse-translate these findings back to the human brain in schizophrenia, focusing on the following questions: (1) Which components of the adenosine system are dysregulated in schizophrenia, and (2) are these changes limited to astrocytes? To address these questions, we captured enriched populations of DLPFC pyramidal neurons and astrocytes from schizophrenia and control subjects using laser capture microdissection and assessed expression of adenosine system components using qPCR. Interestingly, we found changes in enriched populations of astrocytes and neurons spanning metabolic and catabolic pathways. Ectonucleoside triphosphate diphosphohydrolase-1 (ENTPD1) and ENTPD2 mRNA levels were significantly decreased (p < 0.05, n = 16 per group) in enriched populations of astrocytes; in pyramidal neurons equilibrative nucleoside transporter 1 (ENT1) and adenosine A₁ receptor mRNA levels were significantly decreased, with an increase in adenosine deaminase (ADA) (p < 0.05, n = 16 per group). Rodent studies suggest that some of our findings (A₁R and ENTPD2) may be due to treatment with antipsychotics. Our findings suggest changes in expression of genes involved in regulating metabolism of ATP in enriched populations of astrocytes, leading to lower availability of substrates needed to generate adenosine. In pyramidal neurons, changes in ENT1 and ADA mRNA may suggest increased catabolism of adenosine. These results offer new insights into the cell-subtype-specific pathophysiology of the adenosine system in this illness.

ATP increases [Ca2+ ]i and activates a Ca2+ -dependent Cl- current in rat ventricular fibroblasts

NEW FINDINGS

What is the central question of this study? Although electrophysiological and biophysical characteristics of heart fibroblasts have been studied in detail, their responses to prominent paracrine agents in the myocardium have not been addressed adequately. Our experiments characterize changes in cellular electrophysiology and intracellular calcium in response to ATP. What is the main finding and its importance? In rat ventricular fibroblasts maintained in cell culture, we find that ATP activates a specific subset of Ca²⁺ -activated Cl^- channels as a consequence of binding to P2Y purinoceptors and then activating phospholipase C. This response is not dependent on [Ca²⁺ ]_o but requires an increase in [Ca²⁺ ]_i and is modulated by the type of nucleotide that is the purinergic agonist.

ABSTRACT

Effects of ATP on enzymatically isolated rat ventricular fibroblasts maintained in short-term (36-72 h) cell culture were examined. Immunocytochemical staining of these cells revealed that a fibroblast, as opposed to a myofibroblast, phenotype was predominant. ATP, ADP or uridine 5'-triphosphate (UTP) all produced large increases in [Ca²⁺ ]_i . Voltage-clamp studies (amphotericin-perforated patch) showed that ATP (1-100 μm) activated an outwardly rectifying current, with a reversal potential very close to the Nernst potential for Cl^- . In contrast, ADP was much less effective, and UTP produced no detectable current. The non-selective Cl^- channel blockers niflumic acid, DIDS and NPPB (each at 100 μm), blocked the responses to 100 μm ATP. An agonist for P2Y purinoceptors, 2-MTATP, activated a very similar outwardly rectifying C1^- current. The P2Y receptor antagonists, suramin and PPADS (100 μm each), significantly inhibited the Cl^- current produced by 100 μm ATP. ATP was able to activate this Cl^- current when [Ca²⁺ ]_o was removed, but not when [Ca²⁺ ]_i was buffered with BAPTA-AM. In the presence of the phospholipase C inhibitor U73122, this Cl^- current could not be activated. PCR analysis revealed strong signals for a number of P2Y purinoceptors and for the Ca²⁺ -activated Cl^- channel, TMEM16F (also denoted ANO6). In summary, these results demonstrate that activation of P2Y receptors by ATP causes a phospholipase C-dependent increase in [Ca²⁺ ]_i , followed by activation of a Ca²⁺ -dependent Cl^- current in rat ventricular fibroblasts.

Acute In Vivo Analysis of ATP Release in Rat Kidneys in Response to Changes of Renal Perfusion Pressure

Background

ATP and derivatives are recognized to be essential agents of paracrine signaling. It was reported that ATP is an important regulator of the pressure‐natriuresis mechanism. Information on the sources of ATP, the mechanisms of its release, and its relationship to blood pressure has been limited by the inability to precisely measure dynamic changes in intrarenal ATP levels in vivo.

Methods and Results

Newly developed amperometric biosensors were used to assess alterations in cortical ATP concentrations in response to changes in renal perfusion pressure (RPP) in anesthetized Sprague–Dawley rats. RPP was monitored via the carotid artery; ligations around the celiac/superior mesenteric arteries and the distal aorta were used for manipulation of RPP. Biosensors were acutely implanted in the renal cortex for assessment of ATP. Rise of RPP activated diuresis/natriuresis processes, which were associated with elevated ATP. The increases in cortical ATP concentrations were in the physiological range (1–3 μmol/L) and would be capable of activating most of the purinergic receptors. There was a linear correlation with every 1‐mm Hg rise in RPP resulting in a 70‐nmol/L increase in ATP. Furthermore, this elevation of RPP was accompanied by a 2.5‐fold increase in urinary H₂O₂.

Conclusions

Changes in RPP directly correlate with renal sodium excretion and the elevation of cortical ATP. Given the known effects of ATP on regulation of glomerular filtration and tubular transport, the data support a role for ATP release in the rapid natriuretic responses to acute increases in RPP.

Stimulation of Adenosine A2B Receptor Inhibits Endothelin-1-Induced Cardiac Fibroblast Proliferation and α-Smooth Muscle Actin Synthesis Through the cAMP/Epac/PI3K/Akt-Signaling Pathway

Background and Purpose: Cardiac fibrosis is characterized by an increase in fibroblast proliferation, overproduction of extracellular matrix proteins, and the formation of myofibroblast that express α-smooth muscle actin (α-SMA). Endothelin-1 (ET-1) is involved in the pathogenesis of cardiac fibrosis. Overstimulation of endothelin receptors induced cell proliferation, collagen synthesis, and α-SMA expression in cardiac fibroblasts. Although adenosine was shown to have cardioprotective effects, the molecular mechanisms by which adenosine A₂ receptor inhibit ET-1-induced fibroblast proliferation and α-SMA expression in cardiac fibroblasts are not clearly identified.

Experimental Approach: This study aimed at evaluating the mechanisms of cardioprotective effects of adenosine receptor agonist in rat cardiac fibroblast by measurement of cell proliferation, and mRNA and protein levels of α-SMA.

Key results: Stimulation of adenosine subtype 2B (A_2B) receptor resulted in the inhibition of ET-1-induced fibroblast proliferation, and a reduction of ET-1-induced α-SMA expression that is dependent on cAMP/Epac/PI3K/Akt signaling pathways in cardiac fibroblasts. The data in this study confirm a critical role for Epac signaling on A_2B receptor-mediated inhibition of ET-1-induced cardiac fibrosis via PI3K and Akt activation.

Conclusion and Implications: This is the first work reporting a novel signaling pathway for the inhibition of ET-1-induced cardiac fibrosis mediated through the A_2B receptor. Thus, A_2B receptor agonists represent a promising perspective as therapeutic targets for the prevention of cardiac fibrosis.

Adenosine A2a Receptor Blockade Diminishes Wnt/β-Catenin Signaling in a Murine Model of Bleomycin-Induced Dermal Fibrosis

Adenosine A_2a receptor (A_2aR) stimulation promotes the synthesis of collagens I and III, and we have recently demonstrated that there is crosstalk between the A_2aR and WNT/β-catenin signaling pathway. In in vitro studies, A_2aR signaling for collagen III expression was mediated by WNT/β-catenin signaling in human dermal fibroblasts; we further verified whether the crosstalk between A_2aR and Wnt/β-catenin signaling was involved in diffuse dermal fibrosis in vivo. Wnt-signaling reporter mice (Tcf/Lef:H2B-GFP) were challenged with bleomycin and treated with the selective A_2aR antagonist istradefylline (KW6002) or vehicle. Dermal fibrosis was quantitated and nuclear translocation of β-catenin in fibroblasts was assessed by double-staining for Green fluorescent protein or dephosphorylated β-catenin or β-catenin phosphorylated at Ser552, and vimentin. KW6002 significantly reduced skin thickness, skinfold thickness, breaking tension, dermal hydroxyproline content, myofibroblast accumulation, and collagen alignment in bleomycin-induced dermal fibrosis. Also, there was increased expression of Tcf/Lef:H2B-GFP reporter in bleomycin-induced dermal fibrosis, an effect that was diminished by treatment with KW6002. Moreover, KW6002 significantly inhibited nuclear translocation of Tcf/Lef:H2B-GFP reporter, as well as dephosphorylated β-catenin and β-catenin phosphorylated at Ser552. Our work supports the hypothesis that pharmacologic blockade of A_2aR inhibits the WNT/β-catenin signaling pathway, contributing to its capacity to inhibit dermal fibrosis in diseases such as scleroderma.

Ectonucleotidase CD39-driven control of postinfarction myocardial repair and rupture

Mechanical complications of myocardial infarction (MI) are often fatal. Little is known about endogenous factors that predispose to myocardial rupture after MI. Ectonucleoside triphosphate diphosphohydrolase (CD39) could be a critical mediator of propensity to myocardial rupture after MI due to its role in modulating inflammation and thrombosis. Using a model of permanent coronary artery ligation, rupture was virtually abrogated in cd39-/- mice versus cd39+/+ controls, with elevated fibrin and collagen deposition and marked neutrophil and macrophage influx. Macrophages were found to display increased surface expression of CD301 and CD206, marking a reparative phenotype, driven by increased extracellular ATP and IL-4 in the infarcted myocardium of cd39-/- mice. A myeloid-specific CD39-knockout mouse also demonstrated protection from rupture, with an attenuated rupture phenotype, suggesting that complete ablation of CD39 provides the greatest degree of protection in this model. Absence of CD39, either globally or in a myeloid lineage-restricted fashion, skews the phenotype toward alternatively activated (reparative) macrophage infiltration following MI. These studies reveal a previously unrecognized and unexpected role of endogenous CD39 to skew macrophage phenotype and promote a propensity to myocardial rupture after MI.

Purinergic signaling in kidney disease

Nucleotides are key subunits for nucleic acids and provide energy for intracellular metabolism. They can also be released from cells to act physiologically as extracellular messengers or pathologically as danger signals. Extracellular nucleotides stimulate membrane receptors in the P2 and P1 family. P2X are ATP-activated cation channels; P2Y and P1 are G-protein coupled receptors activated by ATP, ADP, UTP, and UDP in the case of P2 or adenosine for P1. Renal P2 receptors influence both vascular contractility and tubular function. Renal cells also express ectonucleotidases that rapidly hydrolyze extracellular nucleotides. These enzymes integrate this multireceptor purinergic-signaling complex by determining the nucleotide milieu to titrate receptor activation. Purinergic signaling also regulates immune cell function by modulating the synthesis and release of various cytokines such as IL1-β and IL-18 as part of inflammasome activation. Abnormal or excessive stimulation of this intricate paracrine system can be pro- or anti-inflammatory, and is also linked to necrosis and apoptosis. Kidney tissue injury causes a localized increase in ATP concentration, and sustained activation of P2 receptors can lead to renal glomerular, tubular, and vascular cell damage. Purinergic receptors also regulate the activity and proliferation of fibroblasts, promoting both inflammation and fibrosis in chronic disease. In this short review we summarize some of the recent findings related to purinergic signaling in the kidney. We focus predominantly on the P2X7 receptor, discussing why antagonists have so far disappointed in clinical trials and how advances in our understanding of purinergic signaling might help to reposition these compounds as potential treatments for renal disease.

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

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

Purinergic signaling in scarring

Adenosine (ADO) and nucleotides such as ATP, ADP, and uridine 5'-triphosphate (UTP), among others, may serve as extracellular signaling molecules. These mediators activate specific cell-surface receptors-namely, purinergic 1 and 2 (P1 and P2)-to modulate crucial pathophysiological responses. Regulation of this process is maintained by nucleoside and nucleotide transporters, as well as the ectonucleotidases ectonucleoside triphosphate diphosphohydrolase [ENTPD; cluster of differentiation (CD)39] and ecto-5'-nucleotidase (5'-NT; CD73), among others. Cells involved in tissue repair, healing, and scarring respond to both ADO and ATP. Our recent investigations have shown that modulation of purinergic signaling regulates matrix deposition during tissue repair and fibrosis in several organs. Cells release adenine nucleotides into the extracellular space, where these mediators are converted by CD39 and CD73 into ADO, which is anti-inflammatory in the short term but may also promote dermal, heart, liver, and lung fibrosis with repetitive signaling under defined circumstances. Extracellular ATP stimulates cardiac fibroblast proliferation, lung inflammation, and fibrosis. P2Y2 (UTP/ATP) and P2Y6 [ADP/UTP/uridine 5'-diphosphate (UDP)] have been shown to have profibrotic effects, as well. Modulation of purinergic signaling represents a novel approach to preventing or diminishing fibrosis. We provide an overview of the current understanding of purinergic signaling in scarring and discuss its potential to prevent or decrease fibrosis.

Mechanisms of epithelial wound detection

Efficient wound healing requires the coordinated responses of various cell types within an injured tissue. To react to the presence of a wound, cells have to first detect it. Judging from their initial biochemical and morphological responses, many cells including leukocytes, epithelial cells, and endothelial cells detect wounds from over hundreds of micrometers within seconds-to-minutes. Wound detection involves the conversion of an injury-induced homeostatic perturbation, such as cell lysis, an unconstrained epithelial edge, or permeability barrier breakdown, into a chemical or physical signal. The signal is spatially propagated through the tissue to synchronize protective responses of cells near the wound site and at a distance. This review summarizes the triggers and mechanisms of wound detection in animals.

Cardiac purinergic signalling in health and disease

This review is a historical account about purinergic signalling in the heart, for readers to see how ideas and understanding have changed as new experimental results were published. Initially, the focus is on the nervous control of the heart by ATP as a cotransmitter in sympathetic, parasympathetic, and sensory nerves, as well as in intracardiac neurons. Control of the heart by centers in the brain and vagal cardiovascular reflexes involving purines are also discussed. The actions of adenine nucleotides and nucleosides on cardiomyocytes, atrioventricular and sinoatrial nodes, cardiac fibroblasts, and coronary blood vessels are described. Cardiac release and degradation of ATP are also described. Finally, the involvement of purinergic signalling and its therapeutic potential in cardiac pathophysiology is reviewed, including acute and chronic heart failure, ischemia, infarction, arrhythmias, cardiomyopathy, syncope, hypertrophy, coronary artery disease, angina, diabetic cardiomyopathy, as well as heart transplantation and coronary bypass grafts.

Cardiac myocyte-secreted cAMP exerts paracrine action via adenosine receptor activation

Acute stimulation of cardiac β-adrenoceptors is crucial to increasing cardiac function under stress; however, sustained β-adrenergic stimulation has been implicated in pathological myocardial remodeling and heart failure. Here, we have demonstrated that export of cAMP from cardiac myocytes is an intrinsic cardioprotective mechanism in response to cardiac stress. We report that infusion of cAMP into mice averted myocardial hypertrophy and fibrosis in a disease model of cardiac pressure overload. The protective effect of exogenous cAMP required adenosine receptor signaling. This observation led to the identification of a potent paracrine mechanism that is dependent on secreted cAMP. Specifically, FRET-based imaging of cAMP formation in primary cells and in myocardial tissue from murine hearts revealed that cardiomyocytes depend on the transporter ABCC4 to export cAMP as an extracellular signal. Extracellular cAMP, through its metabolite adenosine, reduced cardiomyocyte cAMP formation and hypertrophy by activating A1 adenosine receptors while delivering an antifibrotic signal to cardiac fibroblasts by A2 adenosine receptor activation. Together, our data reveal a paracrine role for secreted cAMP in intercellular signaling in the myocardium, and we postulate that secreted cAMP may also constitute an important signal in other tissues.

Cellular mechanisms of tissue fibrosis. 6. Purinergic signaling and response in fibroblasts and tissue fibrosis

Tissue fibrosis occurs as a result of the dysregulation of extracellular matrix (ECM) synthesis. Tissue fibroblasts, resident cells responsible for the synthesis and turnover of ECM, are regulated via numerous hormonal and mechanical signals. The release of intracellular nucleotides and their resultant autocrine/paracrine signaling have been shown to play key roles in the homeostatic maintenance of tissue remodeling and in fibrotic response post-injury. Extracellular nucleotides signal through P2 nucleotide and P1 adenosine receptors to activate signaling networks that regulate the proliferation and activity of fibroblasts, which, in turn, influence tissue structure and pathologic remodeling. An important component in the signaling and functional responses of fibroblasts to extracellular ATP and adenosine is the expression and activity of ectonucleotideases that attenuate nucleotide-mediated signaling, and thereby integrate P2 receptor- and subsequent adenosine receptor-initiated responses. Results of studies of the mechanisms of cellular nucleotide release and the effects of this autocrine/paracrine signaling axis on fibroblast-to-myofibroblast conversion and the fibrotic phenotype have advanced understanding of tissue remodeling and fibrosis. This review summarizes recent findings related to purinergic signaling in the regulation of fibroblasts and the development of tissue fibrosis in the heart, lungs, liver, and kidney.