Mechanism of Action of IFN-beta in the Treatment of Multiple Sclerosis: A Special Reference to CD73 and Adenosine

Extracellular Purine Metabolism-Potential Target in Multiple Sclerosis

The purinergic signaling system comprises a complex network of extracellular purines and purine-metabolizing ectoenzymes, nucleotide and nucleoside receptors, ATP release channels, and nucleoside transporters. Because of its immunomodulatory function, this system is critically involved in the pathogenesis of multiple sclerosis (MS) and its best-characterized animal model, experimental autoimmune encephalomyelitis (EAE). MS is a chronic neuroinflammatory demyelinating and neurodegenerative disease with autoimmune etiology and great heterogeneity, mostly affecting young adults and leading to permanent disability. In MS/EAE, alterations were detected in almost all components of the purinergic signaling system in both peripheral immune cells and central nervous system (CNS) glial cells, which play an important role in the pathogenesis of the disease. A decrease in extracellular ATP levels and an increase in its downstream metabolites, particularly adenosine and inosine, were frequently observed at MS, indicating a shift in metabolism toward an anti-inflammatory environment. Accordingly, upregulation of the major ectonucleotidase tandem CD39/CD73 was detected in the blood cells and CNS of relapsing-remitting MS patients. Based on the postulated role of A2A receptors in the transition from acute to chronic neuroinflammation, the association of variants of the adenosine deaminase gene with the severity of MS, and the beneficial effects of inosine treatment in EAE, the adenosinergic system emerged as a promising target in neuroinflammation. More recently, several publications have identified ADP-dependent P2Y12 receptors and the major extracellular ADP producing enzyme nucleoside triphosphate diphosphohydrolase 2 (NTPDase2) as novel potential targets in MS.

A2AR antagonist treatment for multiple sclerosis: Current progress and future prospects

Emerging evidence suggests that both selective and non-selective Adenosine A2A receptor (A2AR) antagonists could effectively protect mice from experimental autoimmune encephalomyelitis (EAE), which is the most commonly used animal model for multiple sclerosis (MS) research. Meanwhile, the recent FDA approval of Nourianz® (istradefylline) in 2019 as an add-on treatment to levodopa in Parkinson's disease (PD) with "OFF" episodes, along with its proven clinical safety, has prompted us to explore the potential of A2AR antagonists in treating multiple sclerosis (MS) through clinical trials. However, despite promising findings in experimental autoimmune encephalomyelitis (EAE), the complex and contradictory role of A2AR signaling in EAE pathology has raised concerns about the feasibility of using A2AR antagonists as a therapeutic approach for MS. This review addresses the potential effect of A2AR antagonists on EAE/MS in both the peripheral immune system (PIS) and the central nervous system (CNS). In brief, A2AR antagonists had a moderate effect on the proliferation and inflammatory response, while exhibiting a potent anti-inflammatory effect in the CNS through their impact on microglia, astrocytes, and the endothelial cells/epithelium of the blood-brain barrier. Consequently, A2AR signaling remains an essential immunomodulator in EAE/MS, suggesting that A2AR antagonists hold promise as a drug class for treating MS.

Association study of promoter polymorphisms of interferon alpha and beta receptor subunit 1 (IFNAR1) gene and therapeutic response to interferon-beta in patients with multiple sclerosis

BACKGROUND

Multiple sclerosis (MS) is an autoimmune disease described by inflammatory neuronal losses and resultant failures. The disease could abate by interferon-beta (IFN-β) therapy in MS patients. However, the drug response productivity is changeable between patients, and the accurate mechanism of action of the IFN-β is not obvious. The present study aims to investigate the role of interferon alpha and beta receptor subunit 1 (IFNAR1) promoter polymorphisms towards IFN-β treatment response in MS patients.

METHODS

The subjects herein were separated into either responder (n = 57) or non-responder (n = 43) groups according to IFN-β treatment and Expanded Disability Status Scale score. The Sanger sequencing method was used for genotyping.

RESULTS

Among nearly 64 Single Nucleotide Polymorphisms (SNPs), we found a significant association between the rs2850015 polymorphism and the responders and non-responders to IFN-β treatment in the recessive model of inheritance (P = 0.02). The results also revealed a significant change in the two groups of responders and non-responders to the treatment for rs36158718 as an Insertion/Deletion (INDEL) (P = 0.02). Moreover, bioinformatic analyses predicted a remarkable role for both rs2850015 and rs36158718 related to the changes of binding affinity of transcription factors and alterations in their alleles.

CONCLUSION

The present study results suggest that the genetic heterogeneity in the promoter region of IFNAR1 could affect the response to IFN-β. However, further studies with a larger sample size are needed to further demonstrate this relationship.

Chronic Neurological Disorders: Genetic and Epigenetic Markers for Monitoring of Pharmacotherapy

Introduction

Chronic neurological diseases are a major cause of mortality and morbidity in the world. With increasing life expectancy in the developing world, the incidence and prevalence of these diseases are predicted to rise even further. This has also contributed to an increase in disability-adjusted life years (DALYs) for noncommunicable diseases. Treatment for such diseases also poses a challenge with multiple genetic and epigenetic factors leading to a varied outcome. Personalization of treatment is one way that treatment outcome/prognosis of disease can be improved, and pharmacogenomics plays a significant role in this context.

Methodology

This article reviewed the evidence pertaining to the association of genetic and epigenetic markers with major neurological disorders like multiple sclerosis (MS), Alzheimer's disease (AD), and Parkinson's disease (PD), which are a major source of burden among neurological disorders. Types of studies included are peer-reviewed original research articles from the PubMed database (1999-2018).

Results

This study compiled data regarding specific genetic and epigenetic markers with a significant correlation between the clinical diagnosis of the disease and prognosis of therapy from 65 studies. In a single platform, this review highlights the clues to some vital questions, such as why interferon beta (IFN-β) therapy fails to improve symptoms in all MS patients? why cholinesterase inhibitors fail to improve cognitive impairment in a subset of people suffering from AD? or why some individuals on levodopa (L-DOPA) for PD suffer from side-effects ranging from dyskinesia to hallucination while others do not?

Conclusion

This article summarizes the genetic and epigenetic factors that may either require monitoring or help in deciding future pharmacotherapy in a patient suffering from MS, AD, and PD. As the health care system develops and reaches newer heights, we expect more and more of these biomarkers to be used as pharmacotherapeutic outcome indicators.

The CD73/Ado System-A New Player in RT Induced Adverse Late Effects

Radiotherapy (RT) is a central component of standard treatment for many cancer patients. RT alone or in multimodal treatment strategies has a documented contribution to enhanced local control and overall survival of cancer patients, and cancer cure. Clinical RT aims at maximizing tumor control, while minimizing the risk for RT-induced adverse late effects. However, acute and late toxicities of IR in normal tissues are still important biological barriers to successful RT: While curative RT may not be tolerable, sub-optimal tolerable RT doses will lead to fatal outcomes by local recurrence or metastatic disease, even when accepting adverse normal tissue effects that decrease the quality of life of irradiated cancer patients. Technical improvements in treatment planning and the increasing use of particle therapy have allowed for a more accurate delivery of IR to the tumor volume and have thereby helped to improve the safety profile of RT for many solid tumors. With these technical and physical strategies reaching their natural limits, current research for improving the therapeutic gain of RT focuses on innovative biological concepts that either selectively limit the adverse effects of RT in normal tissues without protecting the tumor or specifically increase the radiosensitivity of the tumor tissue without enhancing the risk of normal tissue complications. The biology-based optimization of RT requires the identification of biological factors that are linked to differential radiosensitivity of normal or tumor tissues, and are amenable to therapeutic targeting. Extracellular adenosine is an endogenous mediator critical to the maintenance of homeostasis in various tissues. Adenosine is either released from stressed or injured cells or generated from extracellular adenine nucleotides by the concerted action of the ectoenzymes ectoapyrase (CD39) and 5′ ectonucleotidase (NT5E, CD73) that catabolize ATP to adenosine. Recent work revealed a role of the immunoregulatory CD73/adenosine system in radiation-induced fibrotic disease in normal tissues suggesting a potential use as novel therapeutic target for normal tissue protection. The present review summarizes relevant findings on the pathologic roles of CD73 and adenosine in radiation-induced fibrosis in different organs (lung, skin, gut, and kidney) that have been obtained in preclinical models and proposes a refined model of radiation-induced normal tissue toxicity including the disease-promoting effects of radiation-induced activation of CD73/adenosine signaling in the irradiated tissue environment. However, expression and activity of the CD73/adenosine system in the tumor environment has also been linked to increased tumor growth and tumor immune escape, at least in preclinical models. Therefore, we will discuss the use of pharmacologic inhibition of CD73/adenosine-signaling as a promising strategy for improving the therapeutic gain of RT by targeting both, malignant tumor growth and adverse late effects of RT with a focus on fibrotic disease. The consideration of the therapeutic window is particularly important in view of the increasing use of RT in combination with various molecularly targeted agents and immunotherapy to enhance the tumor radiation response, as such combinations may result in increased or novel toxicities, as well as the increasing number of cancer survivors.

Complex regulation of ecto-5'-nucleotidase/CD73 and A2AR-mediated adenosine signaling at neurovascular unit: A link between acute and chronic neuroinflammation

The review summarizes available data regarding the complex regulation of CD73 at the neurovascular unit (NVU) during neuroinflammation. Based on available data we propose the biphasic pattern of CD73 regulation at NVU, with an early attenuation and a postponed up-regulation of CD73 activity. Transient attenuation of CD73 activity on leukocyte/vascular endothelium and leukocyte/astrocyte surface, required for the initiation of a neuroinflammatory response, may be effectuated either by catalytic inhibition of CD73 and/or by shedding of the CD73 molecule from the cell surface, while postponed induction of CD73 is effectuated by transcriptional up-regulation of Nt5e and posttranslational modifications. Neuroinflammatory conditions are also associated with significant enhancement and gain-of-function of A_2AR-mediated adenosine signaling. However, in contrast to the temporary prevalence of A_2AR over A₁R signaling during an acute inflammatory response, prolonged induction of A_2AR and resulting perpetual CD73/A_2AR coupling may be a contributing factors in the transition between acute and chronic neuroinflammation. Thus, pharmacological targeting of the CD73/A_2AR axis may attenuate inflammatory response and ameliorate neurological deficits in chronic neuroinflammatory conditions.

Dys-regulation of peripheral transcript levels of ecto-5'-nucleotidase in multiple sclerosis patients

CD73, also entitled as ecto-5'-nucleotidase (NT5E), is an ecto-nucleotidase that contributes in the breakage of extracellular ATP to adenosine and the preservation of immune balance. In spite of acknowledged role for immune response imbalance in the pathogenesis of multiple sclerosis (MS), data regarding NT5E expression in MS patients are scarce. In the current study, we assessed expression of NT5E in peripheral blood of MS patients and healthy subjects to unravel its role in the pathogenesis of MS. Results of Multilevel Bayesian model showed no significant difference in NT5E expression between total MS patients and healthy subjects. However, its expression was significantly lower in male MS patients compared with male controls (P= 0.031, 95% credible intervals: [-6.93, -0.56]). No significant correlation was found between expression of NT5E and age in any study subgroups. Remarkably, NT5E transcript levels had 92.31% sensitivity and 80% specificity in diagnosis of MS disease. The diagnostic power of NT5E transcripts was 86.2% based on AUC values. Consequently, the current study indicates the role of NT5E in the pathogenesis of MS disease in male subjects. Moreover, expression level of this gene might be used as a putative marker especially in male MS patients.

Peripheral CD39-expressing T regulatory cells are increased and associated with relapsing-remitting multiple sclerosis in relapsing patients

CD39, an ectonucleotidase that hydrolyses pro-inflammatory ATP, is a marker of highly active and suppressive T regulatory cells (Tregs). Although CD39 has a role in Treg suppression and might be important in the control of neuroinflammation in relapsing-remitting multiple sclerosis (RR-MS), to date, there are contradictory reports concerning the Tregs expression of CD39 in RR-MS patients. Thus, our objectives were to assess the activity and expression of CD39, especially in Tregs from peripheral blood mononuclear cells (PBMCs) of relapsing RR-MS patients compared with control subjects and to evaluate the association of CD39+ Tregs with disability and the odds of RR-MS. The activity and expression of CD39 and the CD39⁺ Treg frequency were measured in PBMCs from 55 relapsing RR-MS patients (19 untreated and 36 receiving immunomodulatory treatment) and 55 age- and sex-paired controls. Moreover, the association between CD39⁺ Tregs and RR-MS was assessed by multivariate logistic regression. CD39 activity and the frequency of CD39-expressing Tregs were elevated in relapsing RR-MS patients. Moreover, CD39⁺ Tregs were significantly correlated with the EDSS score and were independently associated with the odds of RR-MS. Our results highlight the relevance of CD39⁺ Treg subset in the clinical outcomes of RR-MS.

Purinergic Receptors in Neurological Diseases With Motor Symptoms: Targets for Therapy

Since proving adenosine triphosphate (ATP) functions as a neurotransmitter in neuron/glia interactions, the purinergic system has been more intensely studied within the scope of the central nervous system. In neurological disorders with associated motor symptoms, including Parkinson's disease (PD), motor neuron diseases (MND), multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), Huntington's Disease (HD), restless leg syndrome (RLS), and ataxias, alterations in purinergic receptor expression and activity have been noted, indicating a potential role for this system in disease etiology and progression. In neurodegenerative conditions, neural cell death provokes extensive ATP release and alters calcium signaling through purinergic receptor modulation. Consequently, neuroinflammatory responses, excitotoxicity and apoptosis are directly or indirectly induced. This review analyzes currently available data, which suggests involvement of the purinergic system in neuro-associated motor dysfunctions and underlying mechanisms. Possible targets for pharmacological interventions are also discussed.

The Role of Extracellular Adenosine Generation in the Development of Autoimmune Diseases

Adenosine (ADO) is an immunosuppressive molecule, which suppresses the immune responses by interacting with specific receptors expressed by immune effector cells. ADO is produced from ATP through the enzymatic activities of CD39 and CD73. Alternatively, ADO can be generated starting from NAD⁺, which is metabolized by the concerted action of CD38, CD203a/PC-1, and CD73. The role of ADO in immunity has been characterized in the last years in physiology and in pathological settings. This review examines a panel of reports focused on the functions of ADO in the context of human autoimmune/inflammatory diseases and the selected animal models. The final aim is to consider the role of adenosinergic ectoenzymes and ADO receptors as novel therapeutic targets for selected diseases.

TANK-Binding Kinase 1-Dependent Responses in Health and Autoimmunity

The pathogenesis of autoimmune diseases, such as rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) is driven by genetic predisposition and environmental triggers that lead to dysregulated immune responses. These include the generation of pathogenic autoantibodies and aberrant production of inflammatory cytokines. Current therapies for RA and other autoimmune diseases reduce inflammation by targeting inflammatory mediators, most of which are innate response cytokines, resulting in generalized immunosuppression. Overall, this strategy has been very successful, but not all patients respond, responses can diminish over time and numerous side effects can occur. Therapies that target the germinal center (GC) reaction and/or antibody-secreting plasma cells (PC) potentially provide a novel approach. TANK-binding kinase 1 (TBK1) is an IKK-related serine/threonine kinase best characterized for its involvement in innate antiviral responses through the induction of type I interferons. TBK1 is also gaining attention for its roles in humoral immune responses. In this review, we discuss the role of TBK1 in immunological pathways involved in the development and maintenance of antibody responses, with particular emphasis on its potential relevance in the pathogenesis of humoral autoimmunity. First, we review the role of TBK1 in the induction of type I IFNs. Second, we highlight how TBK1 mediates inducible T cell co-stimulator signaling to the GC T follicular B helper population. Third, we discuss emerging evidence on the contribution of TBK1 to autophagic pathways and the potential implications for immune cell function. Finally, we discuss the therapeutic potential of TBK1 inhibition in autoimmunity.

In Vivo PET Imaging of Adenosine 2A Receptors in Neuroinflammatory and Neurodegenerative Disease

Adenosine receptors are G-protein coupled P1 purinergic receptors that are broadly expressed in the peripheral immune system, vasculature, and the central nervous system (CNS). Within the immune system, adenosine 2A (A_2A) receptor-mediated signaling exerts a suppressive effect on ongoing inflammation. In healthy CNS, A_2A receptors are expressed mainly within the neurons of the basal ganglia. Alterations in A_2A receptor function and expression have been noted in movement disorders, and in Parkinson's disease pharmacological A_2A receptor antagonism leads to diminished motor symptoms. Although A_2A receptors are expressed only at a low level in the healthy CNS outside striatum, pathological challenge or inflammation has been shown to lead to upregulation of A_2A receptors in extrastriatal CNS tissue, and this has been successfully quantitated using in vivo positron emission tomography (PET) imaging and A_2A receptor-binding radioligands. Several radioligands for PET imaging of A_2A receptors have been developed in recent years, and A_2A receptor-targeting PET imaging may thus provide a potential additional tool to evaluate various aspects of neuroinflammation in vivo. This review article provides a brief overview of A_2A receptors in healthy brain and in a selection of most important neurological diseases and describes the recent advances in A_2A receptor-targeting PET imaging studies.

Purinergic signalling links mechanical breath profile and alveolar mechanics with the pro-inflammatory innate immune response causing ventilation-induced lung injury

Severe pulmonary infection or vigorous cyclic deformation of the alveolar epithelial type I (AT I) cells by mechanical ventilation leads to massive extracellular ATP release. High levels of extracellular ATP saturate the ATP hydrolysis enzymes CD39 and CD73 resulting in persistent high ATP levels despite the conversion to adenosine. Above a certain level, extracellular ATP molecules act as danger-associated molecular patterns (DAMPs) and activate the pro-inflammatory response of the innate immunity through purinergic receptors on the surface of the immune cells. This results in lung tissue inflammation, capillary leakage, interstitial and alveolar oedema and lung injury reducing the production of surfactant by the damaged AT II cells and deactivating the surfactant function by the concomitant extravasated serum proteins through capillary leakage followed by a substantial increase in alveolar surface tension and alveolar collapse. The resulting inhomogeneous ventilation of the lungs is an important mechanism in the development of ventilation-induced lung injury. The high levels of extracellular ATP and the upregulation of ecto-enzymes and soluble enzymes that hydrolyse ATP to adenosine (CD39 and CD73) increase the extracellular adenosine levels that inhibit the innate and adaptive immune responses rendering the host susceptible to infection by invading microorganisms. Moreover, high levels of extracellular adenosine increase the expression, the production and the activation of pro-fibrotic proteins (such as TGF-β, α-SMA, etc.) followed by the establishment of lung fibrosis.

Adenosine receptor signaling: a key to opening the blood-brain door

The aim of this review is to outline evidence that adenosine receptor (AR) activation can modulate blood–brain barrier (BBB) permeability and the implications for disease states and drug delivery. Barriers of the central nervous system (CNS) constitute a protective and regulatory interface between the CNS and the rest of the organism. Such barriers allow for the maintenance of the homeostasis of the CNS milieu. Among them, the BBB is a highly efficient permeability barrier that separates the brain micro-environment from the circulating blood. It is made up of tight junction-connected endothelial cells with specialized transporters to selectively control the passage of nutrients required for neural homeostasis and function, while preventing the entry of neurotoxic factors. The identification of cellular and molecular mechanisms involved in the development and function of CNS barriers is required for a better understanding of CNS homeostasis in both physiological and pathological settings. It has long been recognized that the endogenous purine nucleoside adenosine is a potent modulator of a large number of neurological functions. More recently, experimental studies conducted with human/mouse brain primary endothelial cells as well as with mouse models, indicate that adenosine markedly regulates BBB permeability. Extracellular adenosine, which is efficiently generated through the catabolism of ATP via the CD39/CD73 ecto-nucleotidase axis, promotes BBB permeability by signaling through A₁ and A_2A ARs expressed on BBB cells. In line with this hypothesis, induction of AR signaling by selective agonists efficiently augments BBB permeability in a transient manner and promotes the entry of macromolecules into the CNS. Conversely, antagonism of AR signaling blocks the entry of inflammatory cells and soluble factors into the brain. Thus, AR modulation of the BBB appears as a system susceptible to tighten as well as to permeabilize the BBB. Collectively, these findings point to AR manipulation as a pertinent avenue of research for novel strategies aiming at efficiently delivering therapeutic drugs/cells into the CNS, or at restricting the entry of inflammatory immune cells into the brain in some diseases such as multiple sclerosis.

Early prediction of persistent organ failure by soluble CD73 in patients with acute pancreatitis*

OBJECTIVE

New biomarkers are needed to better predict the severity of acute pancreatitis. CD73/ecto-5'-nucleotidase is an enzyme that generates adenosine, which dampens inflammation and improves vascular barrier function in several disease models. CD73 also circulates in a soluble form in the blood. We studied whether levels of soluble form of CD73 predict the development of organ failure in acute pancreatitis.

DESIGN

A prospective cohort study of patients with acute pancreatitis from 2003 to 2007.

SETTING

Admissions to the biggest tertiary care hospital in Finland.

PATIENTS

One hundred sixty-one patients with acute pancreatitis, of which 107 were subclassified according to the revised Atlanta criteria into mild, 29 into moderately severe and 25 into severe.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Serum and blood cell samples were collected at admission. Protein levels of soluble form of CD73 in serum were determined using a novel enzyme-linked immunosorbent assay, activity of soluble form of CD73 using radioactive enzyme assays, and CD73 messenger RNA levels from leukocytes using quantitative polymerase chain reaction. Activity and protein concentration of soluble form of CD73, and messenger RNA level of CD73 all decreased along with the disease severity (p ≤ 0.01 for all). The activity of soluble form of CD73 at admission predicted the development of the severe pancreatitis in different groups of the patients. The area under the receiver-operating characteristic curve value for activity of soluble form of CD73 was 0.65 (95% CI, 0.51-0.80) among a subgroup of patients comprising moderately severe and severe disease, 0.79 (95% CI, 0.69-0.88) among all patients including mild pancreatitis, and 0.75 (95% CI, 0.60-0.89) among patients who had no signs of organ failure (modified Marshall score < 2) at admission. Especially, in the last-mentioned group, activity of soluble form of CD73 was better than C-reactive protein or creatinine in predicting the severe pancreat

CONCLUSIONS

: Activity of soluble form of CD73 at admission to hospital has prognostic value in predicting the development of the severe form of acute pancreatitis.

Expression of a second ecto-5'-nucleotidase variant besides the usual protein in symptomatic phase of experimental autoimmune encephalomyelitis

Ecto-5'-nucleotidase/cluster of differentiation 73 (CD73) (eN) is a 70-kDa glycoprotein expressed in several different mammalian tissues and cell types. It is the rate-limiting enzyme of the purine catabolic pathway, which catalyzes the hydrolysis of AMP to produce adenosine with known anti-inflammatory and immunosuppressive actions. There is strong evidence for lymphocyte and endothelial cell eN having a role in experimental autoimmune encephalomyelitis (EAE), but the role of eN in cell types within the central nervous system is less clear. We have previously shown that eN activity significantly increased in the lumbar spinal cord during EAE. The present study is aimed to explore molecular pattern of the eN upregulation over the course of the disease and cell type(s) accountable for the induction. EAE was induced in Dark Agouti (DA) rats by immunization with the spinal cord tissue homogenate and adjuvant. Animals were sacrificed 8, 15, and 28 days following immunization (D8, D15, and D28), i.e., at time points which corresponded to the presymptomatic, symptomatic, and postsymptomatic phases of the disease, respectively. Significant increase in eN activity and its upregulation at the gene and the protein levels were demonstrated at D15 and less prominently at D28 in comparison to control. Additionally, reactive astrocytes abundantly present in the lumbar spinal cord parenchyma were identified as principal cell type with significantly elevated eN expression. In all experimental groups, eN was expressed as a 71-kDa protein band of uniform abundance, whereas the overexpression of eN at D15 and D28 was associated with the expression of a second 75-kDa eN variant. The possible outcome of eN upregulation during EAE as a part of protective astrocyte repertoire contributing to the resolution of the disease is discussed.

Is there a need for emerging drugs for the acute respiratory distress syndrome?

The acute respiratory distress syndrome (ARDS) is a common and devastating syndrome of acute respiratory failure for which little effective pharmacotherapy exists. The authors describe some interventions that show promise as potential therapies for this condition, with particular reference to clinically relevant human models of ARDS. Aspirin, mesenchymal stromal (stem) cells, keratinocyte growth factor, IFN-β and oncostatin M inhibition are discussed.

The roles of CD73 in cancer

Purinergic signaling has emerged as an important player in cancer progression and is regulated by a series of nucleotidases. Among the enzyme cascade, CD73, which catelyzes AMP breakdown to adenosine, has been found to be overexpressed in many types of cancer. Various factors and mechanisms are employed to regulate expression of CD73. Accumulating studies have shown that CD73 is a key regulatory molecule of cancer cells proliferation, migration and invasion in vitro, tumor angiogenesis, and tumor immune escape in vivo. With such important roles in cancer, CD73 has become an appealing therapy target. Recent evidences in mice models demonstrated that targeted blockade of CD73 could be a favorable therapeutic approach for cancer patients in the future. In this review, we will summarize the multiple roles of CD73 in cancer development, including its clinical significance, its promotive effects on tumor growth, metastasis, and angiogenesis, and its suppressive effects on immune response, regulatory mechanisms of CD73 expression, and current situation of anti-CD73 cancer therapy.

Acetate supplementation modulates brain adenosine metabolizing enzymes and adenosine A₂A receptor levels in rats subjected to neuroinflammation

Background

Acetate supplementation reduces neuroglia activation and pro-inflammatory cytokine expression in rat models of neuroinflammation and Lyme neuroborreliosis. Because single-dose glyceryl triacetate (GTA) treatment increases brain phosphocreatine and reduces brain AMP levels, we postulate that GTA modulates adenosine metabolizing enzymes and receptors, which may be a possible mechanism to reduce neuroinflammation.

Methods

To test this hypothesis, we quantified the ability of GTA to alter brain levels of ecto-5’-nucleotidase (CD73), adenosine kinase (AK), and adenosine A_2A receptor using western blot analysis and CD73 activity by measuring the rate of AMP hydrolysis. Neuroinflammation was induced by continuous bacterial lipopolysaccharide (LPS) infusion in the fourth ventricle of the brain for 14 and 28 days. Three treatment strategies were employed, one and two where rats received prophylactic GTA through oral gavage with LPS infusion for 14 or 28 days. In the third treatment regimen, an interventional strategy was used where rats were subjected to 28 days of neuroinflammation, and GTA treatment was started on day 14 following the start of the LPS infusion.

Results

We found that rats subjected to neuroinflammation for 28 days had a 28% reduction in CD73 levels and a 43% increase in AK levels that was reversed with prophylactic acetate supplementation. CD73 activity in these rats was increased by 46% with the 28-day GTA treatment compared to the water-treated rats. Rats subjected to neuroinflammation for 14 days showed a 50% increase in levels of the adenosine A_2A receptor, which was prevented with prophylactic acetate supplementation. Interventional GTA therapy, beginning on day 14 following the induction of neuroinflammation, resulted in a 67% increase in CD73 levels and a 155% increase in adenosine A_2A receptor levels.

Conclusion

These results support the hypothesis that acetate supplementation can modulate brain CD73, AK and adenosine A_2A receptor levels, and possibly influence purinergic signaling.

CD39 and CD73 in immunity and inflammation

The enzymatic activities of CD39 and CD73 play strategic roles in calibrating the duration, magnitude, and chemical nature of purinergic signals delivered to immune cells through the conversion of ADP/ATP to AMP and AMP to adenosine, respectively. This drives a shift from an ATP-driven proinflammatory environment to an anti-inflammatory milieu induced by adenosine. The CD39/CD73 pathway changes dynamically with the pathophysiological context in which it is embedded. It is becoming increasingly appreciated that altering this catabolic machinery can change the course or dictate the outcome of several pathophysiological events, such as AIDS, autoimmune diseases, infections, atherosclerosis, ischemia-reperfusion injury, and cancer, suggesting these ectoenzymes are novel therapeutic targets for managing a variety of disorders.

[The role of ecto-purines in inflammation leading to demyelination - new means for therapies against multiple sclerosis]

Nucleotides released from activated and/or injured cells activate P2 receptors. Extracellular nucleotides serve as danger signals or damage-associated molecular patterns (DAMPs) that trigger various immune responses. Indeed, P2 receptors are highly expressed in the astrocytes, microglia and other immune cells such as T and B lymphocytes that migrate to the central nervous system. The activation of P2 receptors triggers the secretion of proinflammatory cytokines and chemokines as well as immune cell migration and proliferation that contribute to demyelination and axonal damage. The activation of P2 receptors is controlled by the ectonucleotidases which hydrolyze extracellular nucleotides. Ecto-NTPDases and ecto-5'-nucleotidase are expressed in the astrocytes, oligodendrocytes, microglia, endothelial cells and activated T cells. The hydrolysis of extracellular ATP and ADP by enzymes results in the generation of extracellular adenosine. This nucleoside interacts with P1 receptors and activates anti-inflammatory and immunosuppressive responses in the cells involved in MS.

Emerging role of extracellular nucleotides and adenosine in multiple sclerosis

Extracellular nucleotides and adenosine play important roles in inflammation. These signaling molecules interact with the cell-surface-located P2 and P1 receptors, respectively, that are widely distributed in the central nervous system and generally exert opposite effects on immune responses. Indeed, extracellular ATP, ADP, UTP, and UDP serve as alarmins or damage-associated molecular patterns that activate mainly proinflammatory mechanisms, whereas adenosine has potent anti-inflammatory and immunosuppressive effects. This review discusses the actual and potential role of extracellular nucleotides and adenosine in multiple sclerosis (MS).

Purinergic signalling at the plasma membrane: a multipurpose and multidirectional mode to deal with amyotrophic lateral sclerosis and multiple sclerosis

ATP is a widespread and multipurpose signalling molecule copiously released in the extracellular environment of the whole nervous system upon cell activation, stress, or damage. Extracellular ATP is also a multidirectional information molecule, given the concurrent presence at the plasma membrane of various targets for ATP. These include ectonucleotidases (metabolizing ATP down to adenosine), ATP/adenosine transporters, P2 receptors for purine/pyrimidine nucleotides (ligand-gated ion channels P2X receptors and G-protein-coupled P2Y receptors), in addition to metabotropic P1 receptors for nucleosides. All these targets rarely operate as single units, rather they associate with each other at the plasma membrane as multi-protein complexes. Altogether, they control the duration, magnitude and/or direction of the signals triggered and propagated by purine/pyrimidine ligands, and the impact that each single ligand has on a variety of short- and long-term functions. A strict control system allows assorted, even divergent, biological outcomes. Among these, we enumerate cell-to-cell communication, tropic, trophic, but also noxious actions causing the insurgence/progression of pathological conditions. Here, we show that purinergic signalling in the nervous system can be instrumental for instance to neurodegenerative and neuroinflammatory diseases such as amyotrophic lateral sclerosis and multiple sclerosis.

CD73 is required for efficient entry of lymphocytes into the central nervous system during experimental autoimmune encephalomyelitis

CD73 is a cell surface enzyme of the purine catabolic pathway that catalyzes the breakdown of AMP to adenosine. Because of the strong immunosuppressive and antiinflammatory properties of adenosine, we predicted that cd73(-/-) mice would develop severe experimental autoimmune encephalomyelitis (EAE), an animal model for the central nervous system (CNS) inflammatory disease, multiple sclerosis. Surprisingly, cd73(-/-) mice were resistant to EAE. However, CD4 T cells from cd73(-/-) mice secreted more proinflammatory cytokines than wild-type (WT) mice and were able to induce EAE when transferred into naïve cd73(+/+) T cell-deficient recipients. Therefore, the protection from EAE observed in cd73(-/-) mice was not caused by a deficiency in T cell responsiveness. Immunohistochemistry showed that cd73(-/-) mice had fewer infiltrating lymphocytes in their CNS compared with WT mice. Importantly, susceptibility to EAE could be induced in cd73(-/-) mice after the transfer of WT CD73(+)CD4(+) T cells, suggesting that CD73 must be expressed either on T cells or in the CNS for disease induction. In the search for the source of CD73 in the CNS that might facilitate lymphocyte migration, immunohistochemistry revealed a lack of CD73 expression on brain endothelial cells and high expression in the choroid plexus epithelium which regulates lymphocyte immunosurveillance between the blood and cerebrospinal fluid. Because blockade of adenosine receptor signaling with the A(2a) adenosine receptor-specific antagonist SCH58261 protected WT mice from EAE induction, we conclude that CD73 expression and adenosine receptor signaling are required for the efficient entry of lymphocytes into the CNS during EAE development.