Regulation of ecto-5′-nucleotidase (CD73) in cultured cortical astrocytes by different inflammatory factors

Expression of functionally distinct ecto-5'-nucleotidase/CD73 glycovariants in reactive astrocytes in experimental autoimmune encephalomyelitis and neuroinflammatory conditions in vitro

Ecto-5'-nucleotidase/CD73 (eN/CD73) is a membrane-bound enzyme involved in extracellular production of adenosine and a cell adhesion molecule involved in cell-cell interactions. In neuroinflammatory conditions such as experimental autoimmune encephalomyelitis (EAE), reactive astrocytes occupying active demyelination areas significantly upregulate eN/CD73 and express additional eN/CD73 variants. The present study investigated whether the different eN/CD73 variants represent distinct glycoforms and the functional consequences of their expression in neuroinflammatory states. The study was performed in animals at different stages of EAE and in primary astrocyte cultures treated with a range of inflammatory cytokines. Upregulation at the mRNA, protein, and functional levels, as well as the appearance of multiple eN/CD73 glycovariants were detected in the inflamed spinal cord tissue. At the peak of the disease, eN/CD73 exhibited higher AMP turnover and lower enzyme-substrate affinity than the control group, which was attributed to altered glycosylation under neuroinflammatory conditions. A subsequent in vitro study showed that primary astrocytes upregulated eN/CD73 and expressed the multiple glycovariants upon stimulation with TNFα, IL-1β, IL-6, and ATP, with the effect occurring at least in part via induction of JAK/STAT3 signaling. Experimental removal of glycan moieties from membrane glycoproteins by PNGaseF decreased eN/CD73 activity but had no effect on the enzyme's involvement in astrocyte migration. Our results suggest that neuroinflammatory states are associated with the appearance of functionally distinct eN/CD73 glycovariants, which may play a role in the development of the reactive astrocyte phenotype.

Accelerated Extracellular Nucleotide Metabolism in Brain Microvascular Endothelial Cells in Experimental Hypercholesterolemia

Hypercholesterolemia affects the neurovascular unit, including the cerebral blood vessel endothelium. Operation of this system, especially in the context of energy metabolism, is controlled by extracellular concentration of purines, regulated by ecto-enzymes, such as e-NTPDase-1/CD39, ecto-5'-NT/CD73, and eADA. We hypothesize that hypercholesterolemia, via modulation of the activity of nucleotide metabolism-regulating ecto-enzymes, deteriorates glycolytic efficiency and energy metabolism of endothelial cells, which may potentially contribute to development of neurodegenerative processes. We aimed to determine the effect of hypercholesterolemia on the concentration of purine nucleotides, glycolytic activity, and activity of ecto-enzymes in the murine brain microvascular endothelial cells (mBMECs). We used 3-month-old male LDLR-/-/Apo E-/- double knockout mice to model hypercholesterolemia and atherosclerosis. The age-matched wild-type C57/BL6 mice were a control group. The intracellular concentration of ATP and NAD and extracellular activity of the ecto-enzymes were measured by HPLC. The glycolytic function of mBMECs was assessed by means of the extracellular acidification rate (ECAR) using the glycolysis stress test. The results showed an increased activity of ecto-5'-NT and eADA in mBMECs of the hypercholesterolemic mice, but no differences in intracellular concentration of ATP, NAD, and ECAR between the hypercholesterolemic and control groups. The changed activity of ecto-5'-NT and eADA leads to increased purine nucleotides turnover and a shift in their concentration balance towards adenosine and inosine in the extracellular space. However, no changes in the energetic metabolism of the mBMECs are reported. Our results confirm the influence of hypercholesterolemia on regulation of purine nucleotides metabolism, which may impair the function of the cerebral vascular endothelium. The effect of hypercholesterolemia on the murine brain microvascular endothelial cells (mBMECs). An increased activity of ecto-5'-NT and eADA in mBMECs of the LDLR-/-/Apo E-/- mice leads to a shift in the concentration balance towards adenosine and inosine in the extracellular space with no differences in intracellular concentration of ATP. Figure was created with Biorender.com.

Anti-inflammatory potency of novel ecto-5'-nucleotidase/CD73 inhibitors in astrocyte culture model of neuroinflammation

Three novel cytosine-derived α,β-methylene diphosphonates designated MRS4598, MRS4552, and MRS4602 were tested in the range of 1 × 10-9 to 1 × 10-3 M for their efficacy and potency in inhibiting membrane-bound ecto-5'-nucleotidase/CD73 activity in primary astrocytes in vitro. The compounds were also tested for their ability to attenuate the reactive astrocyte phenotype induced by proinflammatory cytokines. The main findings are as follows: A) The tested compounds induced concentration-dependent inhibition of CD73 activity, with maximal inhibition achieved at ∼1 × 10-3M; B) All compounds showed high inhibitory potency, as reflected by IC50 values in the submicromolar range; C) All compounds showed high binding capacity, as reflected by Ki values in the low nanomolar range; D) Among the tested compounds, MRS4598 showed the highest inhibitory efficacy and potency, as reflected by IC50 and Ki values of 0.11 μM and 18.2 nM; E) Neither compound affected astrocyte proliferation and cell metabolic activity at concentrations near to IC50; E) MRS4598 was able to inhibit CD73 activity in reactive astrocytes stimulated with TNF-α and to induce concentration-dependent inhibition of CD73 in reactive astrocytes stimulated with IL-1β, with an order of magnitude higher IC50 value; F) MRS4598 was the only compound tested that was able to induce shedding of the CD73 from astrocyte membranes and to enhance astrocyte migration in the scratch wound migration assay, albeit at concentration well above its IC50 value. Given the role of CD73 in neurodegenerative diseases, MRS4598, MRS4552, and MRS4602 are promising pharmacological tools for the treatment of neurodegeneration and neuroinflammation.

Proteolytic regulation of CD73 by TRIM21 orchestrates tumor immunogenicity

Despite the rapid utilization of immunotherapy, emerging challenges to the current immune checkpoint blockade need to be resolved. Here, we report that elevation of CD73 levels due to its aberrant turnover is correlated with poor prognosis in immune-cold triple-negative breast cancers (TNBCs). We have identified TRIM21 as an E3 ligase that governs CD73 destruction. Disruption of TRIM21 stabilizes CD73 that in turn enhances CD73-catalyzed production of adenosine, resulting in the suppression of CD8+ T cell function. Replacement of lysine 133, 208, 262, and 321 residues by arginine on CD73 attenuated CD73 ubiquitylation and degradation. Diminishing of CD73 ubiquitylation remarkably promotes tumor growth and impedes antitumor immunity. In addition, a TRIM21high/CD73low signature in a subgroup of human breast malignancies was associated with a favorable immune profile. Collectively, our findings uncover a mechanism that governs CD73 proteolysis and point to a new therapeutic strategy by modulating CD73 ubiquitylation.

Current Strategies for Promoting the Large-scale Production of Exosomes

Exosomes, as nanoscale biological vesicles, have been shown to have great potential for biomedical applications. However, the low yield of exosomes limits their application. In this review, we focus on methods to increase exosome yield. Two main strategies are used to increase exosome production, one is based on genetic manipulation of the exosome biogenesis and release pathway, and the other is by pretreating parent cells, changing the culture method or adding different components to the medium. By applying these strategies, exosomes can be produced on a large scale to facilitate their practical application in the clinic.

Effect of Thiazolidin-4-one Against Lipopolysaccharide-Induced Oxidative Damage, and Alterations in Adenine Nucleotide Hydrolysis and Acetylcholinesterase Activity in Cultured Astrocytes

Astrocytes play multiple important roles in brain physiology. However, depending on the stimuli, astrocytes may exacerbate inflammatory reactions, contributing to the development and progression of neurological diseases. Therefore, therapies targeting astrocytes represent a promising area for the development of new brain drugs. Thiazolidinones are heterocyclic compounds that have a sulfur and nitrogen atom and a carbonyl group in the ring and represent a class of compounds of great scientific interest due to their pharmacological properties. The aim of this study was to investigate the effect of 3-(3-(diethylamino)propyl)-2-(4-(methylthio)phenyl)thiazolidin-4-one (DS27) on cell proliferation and morphology, oxidative stress parameters, activity of the enzymes ectonucleotidases and acetylcholinesterase (AChE) and interleukin 6 (IL-6) levels in primary astrocyte cultures treated with lipopolysaccharide (LPS), to model neuroinflammation. The astrocyte culture was exposed to LPS (10 μg/ml) for 3 h and subsequently treated with compound DS27 for 24 and 48 h (concentrations ranging to 10-100 μM). LPS induced an increase in astrocyte proliferation, AChE activity, IL-6 levels, oxidative damage, ATP and ADP and a reduction in AMP hydrolysis in rat primary astrocyte cultures. DS27 treatment was effective in reversing these alterations induced by LPS. Our findings demonstrated that DS27 is able to modulate cholinergic and purinergic signaling, redox status, and the levels of pro-inflammatory cytokines in LPS-induced astrocyte damage. These glioprotective effects of DS27 may be very important for improving neuroinflammation, which is associated with many brain diseases.

The Effects of CD73 on Gastrointestinal Cancer Progression and Treatment

Gastrointestinal (GI) cancer is a common and deadly malignant tumor. CD73, a cell-surface protein, acts as a switch of the adenosine-related signaling pathway that can cause significant immunosuppression. Recent evidence has emerged that CD73 is a promising immunotherapy target for regaining immune cell function and restraining tumorigenesis, and a growing stream of research indicates that combining immunotherapy with other therapies can effectively improve the prognosis and survival of GI cancer patients. Several immune checkpoint inhibitors have been approved for use in GI cancer recently; however, they have demonstrated limited efficacy. Solving the problem of immunosuppression in GI cancer is the key to developing an effective therapeutic option and the modulation of CD73 expression may provide an answer. In this review, we discuss current research on CD73 in gastric, liver, pancreatic, and colorectal cancer to evaluate its therapeutic potential as an immunotherapy target in GI cancers.

Investigating genetic drivers of juvenile dermatomyositis pathogenesis using bioinformatics methods

Juvenile dermatomyositis (JDM) is a chronic autoimmune disease. The pathogenic mechanisms remain ill-defined. The purpose of this study was to identify key genes related to JDM. Microarray datasets were downloaded from the Gene Expression Omnibus database. The differentially expressed genes (DEG) were identified. Then, Gene Ontology, Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis, and protein-protein interaction (PPI) network were carried out. In addition, the hub genes were selected by cytoHubba. The expression profile and diagnostic capacity (receiver-operator curve [ROC]) of interested hub genes were verified. Gene set enrichment analysis (GSEA) was also carried out. Moreover, the signature of hub genes was then used as a search query to explore the Connectivity Map (CMAP). A total of 128 DEG were identified. The enriched functions and pathways of the DEG include response to virus, negative regulation of cell migration, cadmium ion transmembrane transport, defense response to Gram-negative bacterium, positive regulation of megakaryocyte differentiation, and negative regulation of angiogenesis. Twenty-one hub genes were identified. The expression levels of the interested genes were also confirmed. ROC analysis confirmed that the expression of these genes can distinguish JDM from controls. GSEA showed that these genes are mainly related to "inflammatory response", "complement", "interferon-α response", "IL6/JAK/STAT3 signaling", "TGF-β signaling", "IL2/STAT5 signaling" and "TNF-α signaling via NF-κB". The CMAP research found some compounds with the potential to counteract the effects of the dysregulated molecular signature in JDM. In this study, bioinformatics methods were used to identify DEG, which helps us understand the molecular mechanisms of JDM and provide candidate targets for diagnosis and treatment of JDM.

Exosomes from TNF-α-treated human gingiva-derived MSCs enhance M2 macrophage polarization and inhibit periodontal bone loss

Mesenchymal stem cell (MSC)–derived exosome plays a central role in the cell-free therapeutics involving MSCs and the contents can be customized under disease-associated microenvironments. However, optimal MSC-preconditioning to enhance its therapeutic potential is largely unknown. Here, we show that preconditioning of gingival tissue-derived MSCs (GMSCs) with tumor necrosis factor-alpha (TNF-α) is ideal for the treatment of periodontitis. TNF-α stimulation not only increased the amount of exosome secreted from GMSCs, but also enhanced the exosomal expression of CD73, thereby inducing anti-inflammatory M2 macrophage polarization. The effect of GMSC-derived exosomes on inflammatory bone loss were examined by ligature-induced periodontitis model in mice. Local injection of GMSC-derived exosomes significantly reduced periodontal bone resorption and the number of tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts, and these effects were further enhanced by preconditioning of GMSCs with TNF-α. Thus, GMSC-derived exosomes also exhibited anti-osteoclastogenic activity. Receptor activator of NF-κB ligand (RANKL) expression was regulated by Wnt5a in periodontal ligament cells (PDLCs), and exosomal miR-1260b was found to target Wnt5a-mediated RANKL pathway and inhibit its osteoclastogenic activity. These results indicate that significant ability of the TNF-α-preconditioned GMSC-derived exosomes to regulate inflammation and osteoclastogenesis paves the way for establishment of a therapeutic approach for periodontitis.

Immunometabolic Changes in Glia - A Potential Role in the Pathophysiology of Obesity and Diabetes

Chronic low-grade inflammation is a feature of the pathophysiology of obesity and diabetes in the CNS as well as peripheral tissues. Glial cells are critical mediators of the response to inflammation in the brain. Key features of glia include their metabolic flexibility, sensitivity to changes in the CNS microenvironment, and ability to rapidly adapt their function accordingly. They are specialised cells which cooperate to promote and preserve neuronal health, playing important roles in regulating the activity of neuronal networks across the brain during different life stages. Increasing evidence points to a role of glia, most notably astrocytes and microglia, in the systemic regulation of energy and glucose homeostasis in the course of normal physiological control and during disease. Inflammation is an energetically expensive process that requires adaptive changes in cellular metabolism and, in turn, metabolic intermediates can also have immunomodulatory actions. Such "immunometabolic" changes in peripheral immune cells have been implicated in contributing to disease pathology in obesity and diabetes. This review will discuss the evidence for a role of immunometabolic changes in glial cells in the systemic regulation of energy and glucose homeostasis, and how this changes in the context of obesity and diabetes.

Estrogen receptors modulate ectonucleotidases activity in hippocampal synaptosomes of male rats

Extracellular adenine nucleotides and nucleosides, such as adenosine-5'-triphosphate (ATP) and adenosine, are among least investigated signaling factors that participate in 17β-estradiol (E2)-mediated synaptic rearrangements in rodent hippocampus. Their levels in the extrasynaptic space are tightly controlled by ecto-nucleoside triphosphate diphosphohydrolases1-3 (NTPDase1-3)/ecto-5'-nucleotidase (eN) enzyme chain. Therefore, the aim of the present study was to get closer insight in the E2-induced decrease in NTPDase and eN activity in the hippocampal synaptic compartment of male rats and to identify estradiol receptors (ERs i.e. ERα, ERβ or GPER1) responsible for the observed effects of E2. In this study we show indiscriminate participation of estradiol receptor α (ERα), -β (ERβ) and G- protein coupled estrogen receptor 1 (GPER1) in the mediation of E2 actions in hippocampal synaptosomes of male rats. Synaptic NTPDase1-3 activities are modulated only through activation of ERβ, while activation of ERα, -β and/or non-classical GPER1 decreases synaptic eN activity. Since both ATP and adenosine function as neuromodulators in the hippocampal networks, influencing its function, profound knowledge of mechanisms by which ectonucleotidases are regulated/modulated is of great importance.

Cell type- and tissue-specific functions of ecto-5'-nucleotidase (CD73)

Ecto-5'-nucleotidase [cluster of differentiation 73 (CD73)] is a ubiquitously expressed glycosylphosphatidylinositol-anchored glycoprotein that converts extracellular adenosine 5'-monophosphate to adenosine. Anti-CD73 inhibitory antibodies are currently undergoing clinical testing for cancer immunotherapy. However, many protective physiological functions of CD73 need to be taken into account for new targeted therapies. This review examines CD73 functions in multiple organ systems and cell types, with a particular focus on novel findings from the last 5 years. Missense loss-of-function mutations in the CD73-encoding gene NT5E cause the rare disease "arterial calcifications due to deficiency of CD73." Aside from direct human disease involvement, cellular and animal model studies have revealed key functions of CD73 in tissue homeostasis and pathology across multiple organ systems. In the context of the central nervous system, CD73 is antinociceptive and protects against inflammatory damage, while also contributing to age-dependent decline in cortical plasticity. CD73 preserves barrier function in multiple tissues, a role that is most evident in the respiratory system, where it inhibits endothelial permeability in an adenosine-dependent manner. CD73 has important cardioprotective functions during myocardial infarction and heart failure. Under ischemia-reperfusion injury conditions, rapid and sustained induction of CD73 confers protection in the liver and kidney. In some cases, the mechanism by which CD73 mediates tissue injury is less clear. For example, CD73 has a promoting role in liver fibrosis but is protective in lung fibrosis. Future studies that integrate CD73 regulation and function at the cellular level with physiological responses will improve its utility as a disease target.

Generation and Function of Non-cell-bound CD73 in Inflammation

Extracellular adenine nucleotides participate in cell-to-cell communication and modulate the immune response. The concerted action of ectonucleotidases CD39 and CD73 plays a major role in the local production of anti-inflammatory adenosine, but both ectonucleotidases are rarely co-expressed by human T cells. The expression of CD39 on T cells increases upon T cell activation and is high at sites of inflammation. CD73, in contrast, disappears from the cellular membrane after activation. The possibility that CD73 could act in trans would resolve the conundrum of both enzymes being co-expressed for the degradation of ATP and the generation of adenosine. An enzymatically active soluble form of CD73 has been reported, and AMPase activity has been detected in body fluids of patients with inflammation and cancer. It is not yet clear how CD73, a glycosylphosphatidylinositol (GPI)-anchored protein, is released from the cell membrane, but plausible mechanisms include cleavage by metalloproteinases and shedding mediated by cell-associated phospholipases. Importantly, like many other GPI-anchored proteins, CD73 at the cell membrane is preferentially localized in detergent-resistant domains or lipid rafts, which often contribute to extracellular vesicles (EVs). Indeed, CD73-containing vesicles of different size and origin and with immunomodulatory function have been found in the tumor microenvironment. The occurrence of CD73 as non-cell-bound molecule widens the range of action of this enzyme at sites of inflammation. In this review, we will discuss the generation of non-cell-bound CD73 and its physiological role in inflammation.

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.

Substrate-independent immunomodulatory characteristics of mesenchymal stem cells in three-dimensional culture

Mesenchymal stem cells (MSCs) play important roles in tissue regeneration, and multi-lineage differentiation and immunomodulation are two major characteristics of MSCs that are utilized in stem cell therapy. MSCs in vivo have a markedly different three-dimensional (3D) niche compared to the traditional two-dimensional (2D) culture in vitro. A 3D scaffold is predicted to provide an artificial 3D environment similar to the in vivo environment. Significant changes in MSC differentiation are shown to be occurred when under 3D culture. However, the immunomodulatory characteristics of MSCs under 3D culture remain unknown. In this study, 3D culture systems were constructed using different substrates to evaluate the common immunomodulatory characteristics of MSCs. Compared to the MSCs under 2D culture, the MSCs under 3D culture, which had higher stemness and maintained cell phenotype, showed altered immunophenotypic pattern. Gene expression profile analysis at mRNA and protein level detected by gene chip and protein chip, respectively, further revealed the difference between 3D cultured MSCs and 2D cultured MSCs, which was mainly concentrated in the immunoregulation related aspects. Moreover, the immunoregulatory role of 3D culture was confirmed by our immunosuppressive experiments. These findings demonstrated that the immunomodulatory capacities of MSCs were enhanced by the 3D geometry of substrates.

Spatial Distribution and Expression of Ectonucleotidases in Rat Hippocampus After Removal of Ovaries and Estradiol Replacement

Purinergic signaling is the main synaptic and non-synaptic signaling system in brain. ATP acts as a fast excitatory transmitter, while adenosine sets a global inhibitory tone within hippocampal neuronal networks. ATP and adenosine are interconnected by ectonucleotidase enzymes, which convert ATP to adenosine. Existing data point to the converging roles of ovarian steroids and purinergic signaling in synapse formation and refinement and synapse activity in the hippocampus. Therefore, in the present study, we have used enzyme histochemistry and expression analysis to obtain data on spatial distribution and expression of ecto-enzymes NTPDase1, NTPDase2, and ecto-5'-nucleotidase (eN) after removal of ovaries (OVX) and estradiol replacement (E2) in female rat hippocampus. The results show that target ectonucleotidases are predominantly localized in synapse-rich hippocampal layers. The most represented NTPDase in the hippocampal tissue is NTPDase2, being at the same time the mostly affected ectonucleotidase by OVX and E2. Specifically, OVX decreases the expression of NTPDase2 and eN, whereas E2 restores their expression to control level. Impact of OVX and E2 on ectonucleotidase expression was also examined in purified synaptosome (SYN) and gliosome (GLIO) fractions. Data reveal that SYN expresses NTPDase1 and NTPDase2, both of which are reduced following OVX and restored with E2. GLIO exhibits NTPDase2-mediated ATP hydrolysis, which falls in OVX, and recovers by E2. These changes in the activity occur without parallel changes in NTPDase2-protein abundance. The same holds for eN. The lack of correlation between NTPDase2 and eN activities and their respective protein abundances suggest a non-genomic mode of E2 action, which is studied further in primary astrocyte culture. Since ovarian steroids shape hippocampal synaptic networks and regulate ectonucleotidase activities, it is possible that cognitive deficits seen after ovary removal may arise from the loss of E2 modulatory actions on ectonucleotidase expression in the hippocampus.

Unveiling the Role of Ecto-5'-Nucleotidase/CD73 in Astrocyte Migration by Using Pharmacological Tools

CD73 is a bifunctional glycosylphosphatidylinositol (GPI)-anchored membrane protein which functions as ecto-5′-nucleotidase and a membrane receptor for extracellular matrix protein (ECM). A large body of evidence demonstrates a critical involvement of altered purine metabolism and particularly, increased expression of CD73 in a number of human disorders, including cancer and immunodeficiency. Massive up-regulation of CD73 was also found in reactive astrocytes in several experimental models of human neuropathologies. In all the pathological contexts studied so far, the increased expression of CD73 has been associated with the altered ability of cells to adhere and/or migrate. Thus, we hypothesized that increased expression of CD73 in reactive astrocytes has a role in the process of astrocyte adhesion and migration. In the present study, the involvement of CD73 in astrocyte migration was investigated in the scratch wound assay (SW), using primary astrocyte culture prepared from neonatal rat cortex. The cultures were treated with one of the following pharmacological inhibitors which preferentially target individual functions of CD73: (a) α,β-methylene ADP (APCP), which inhibits the catalytic activity of CD73 (b) polyclonal anti-CD73 antibodies, which bind to the internal epitope of CD73 molecule and mask their surface exposure and (c) small interfering CD73-RNA (siCD73), which silences the expression of CD73 gene. It was concluded that approaches that reduce surface expression of CD73 increase migration velocity and promote wound closure in the scratch wound assay, while inhibition of the enzyme activity by APCP induces redistribution of CD73 molecules at the cell surface, thus indirectly affecting cell adhesion and migration. Application of anti-CD73 antibodies induces a decrease in CD73 activity and membrane expression, through CD73 molecules shedding and their release to the culture media. In addition, all applied pharmacological inhibitors differentially affect other aspects of astrocyte function in vitro, including reduced cell proliferation, altered expression of adenosine receptors and increased expression of ERK1/2. Altogether these data imply that CD73 participates in cell adhesion/migration and transmits extracellular signals through interactions with ECM.

17β-Estradiol-Induced Synaptic Rearrangements Are Accompanied by Altered Ectonucleotidase Activities in Male Rat Hippocampal Synaptosomes

17β-Estradiol (E2) rapidly, by binding to membrane estrogen receptors, activates cell signaling cascades which induce formation of new dendritic spines in the hippocampus of males as in females, but the interaction with other metabolic processes, such as extracellular adenine nucleotides metabolism, are currently unknown. Extracellular adenine nucleotides play significant roles, controlling excitatory glutamatergic synapses and development of neural circuits and synaptic plasticity. Their precise regulation in the synaptic cleft is tightly controlled by ecto-nucleoside triphosphate diphosphohydrolase (NTPDase)/ecto-5'-nucleotidase (eN) enzyme chain. Therefore, we sought to clarify whether a single systemic injection of E2 in male rats is accompanied by changes in the expression of the pre- and postsynaptic proteins and downstream kinases linked to E2-induced synaptic rearrangement as well as alterations in NTPDase/eN pathway in the hippocampal synaptosomes. Obtained data showed activation of mammalian target of rapamycin and upregulation of key synaptic proteins necessary for spine formation, 24 h after systemic E2 administration. In E2-mediated conditions, we found downregulation of NTPDase1 and NTPDase2 and attenuation of adenine nucleotide hydrolysis by NTPDase/eN enzyme chain, without changes in NTPDase3 properties and augmentation of synaptic tissue-nonspecific alkaline phosphatase (TNAP) activity. Despite reduced NTPDase activities, increased TNAP activity probably prevents toxic accumulation of ATP in the extracellular milieu and also hydrolyzes accumulated ADP due to unchanged NTPDase3 activity. Thus, our initial evaluation supports idea of specific roles of different ectonucleotidases and their coordinated actions in E2-mediated spine remodeling and maintenance.

Regional and sex-related differences in modulating effects of female sex steroids on ecto-5'-nucleotidase expression in the rat cerebral cortex and hippocampus

Ecto-5'-nucleotidase (eN), a membrane rate-limiting enzyme of the purine catabolic pathway, catalyzes the conversion of AMP to adenosine involved in the regulation of many brain physiological and pathological processes. Since gender fundamentally determines hormonal milieu in the body and brain, it is reasonable to assume that sex differences in the activity of various signaling systems, including adenosine, may be generated by gonadal steroids. Thus, we examined expression of eN as a component of adenosine signaling system in the basal state in cerebral cortex and hippocampus of male and female rats at gene, protein and functional level, as well as in the state of gonadal hormone deprivation, induced by ovariectomy (OVX), whereas impact of steroid hormones was explored after repeated administration of 17α-estradiol, 17β-estradiol and progesterone for seven consecutive days. Results showed regional and sex-related differences in basal eN activity level, with the highest AMP hydrolysis observed in the hippocampus of male rats. Furthermore, ovarian steroids do not contribute to basal gene eN expression or the activity in cortical and hippocampal region of female rats. However, protein eN expression was increased in OVX rats in both investigated region. Investigated exogenous steroids had no influence on eN expression in male brain, while in OVX females alterations in eN activity were induced. The observed effects in female rats were different between examined regions e.g. in cortex, applied treatments predominantly decreased whereas in hippocampus increased eN activity. Based on the presented results, eN exerts regional and sex-related response in basal state as well as after treatment with female gonadal hormones, however the exact mechanisms of sex steroids actions on eN remain unclear and should be fully explored.

Neurogenic Differentiation of Mesenchymal Stem Cells Induces Alterations in Extracellular Nucleotides Metabolism

The presented results show for the first time that the neurogenic transdifferentiation of hUC-MSCs considerably changes the elements of purinergic signaling profile. Although, it has been demonstrated in the literature that extracellular nucleotides and nucleosides determine the fate of mesenchymal and neural stem cells, there is lack of comprehensive studies on the activity of ecto-enzymes metabolizing nucleotides on the surface of neurogenically induced cells. Our study shows that human UC-MSCs sense the microenvironment and adjust their response to the environmental signals for example, adenine nucleotides and nucleosides. Nucleotides, and not adenosine, signaling alters the biological potential of MSCs-decreases their proliferation rate, increases the neurogenic transdifferentiation efficiency expressed as the number of positively labeled NCAM⁺ and A2B5⁺ cells and simultaneously increases the ecto-nucleotidases activity on neural- and glial-committed precursors. Purines implication in the proliferative and neurogenic potential of hUC-MSCs is of strong importance for the in vitro propagation of hUC-MSCs and for their successive therapeutic applications. J. Cell. Biochem. 118: 478-486, 2017. © 2016 Wiley Periodicals, Inc.

How does adenosine control neuronal dysfunction and neurodegeneration?

The adenosine modulation system mostly operates through inhibitory A₁ (A₁ R) and facilitatory A_2A receptors (A_2A R) in the brain. The activity-dependent release of adenosine acts as a brake of excitatory transmission through A₁ R, which are enriched in glutamatergic terminals. Adenosine sharpens salience of information encoding in neuronal circuits: high-frequency stimulation triggers ATP release in the 'activated' synapse, which is locally converted by ecto-nucleotidases into adenosine to selectively activate A_2A R; A_2A R switch off A₁ R and CB1 receptors, bolster glutamate release and NMDA receptors to assist increasing synaptic plasticity in the 'activated' synapse; the parallel engagement of the astrocytic syncytium releases adenosine further inhibiting neighboring synapses, thus sharpening the encoded plastic change. Brain insults trigger a large outflow of adenosine and ATP, as a danger signal. A₁ R are a hurdle for damage initiation, but they desensitize upon prolonged activation. However, if the insult is near-threshold and/or of short-duration, A₁ R trigger preconditioning, which may limit the spread of damage. Brain insults also up-regulate A_2A R, probably to bolster adaptive changes, but this heightens brain damage since A_2A R blockade affords neuroprotection in models of epilepsy, depression, Alzheimer's, or Parkinson's disease. This initially involves a control of synaptotoxicity by neuronal A_2A R, whereas astrocytic and microglia A_2A R might control the spread of damage. The A_2A R signaling mechanisms are largely unknown since A_2A R are pleiotropic, coupling to different G proteins and non-canonical pathways to control the viability of glutamatergic synapses, neuroinflammation, mitochondria function, and cytoskeleton dynamics. Thus, simultaneously bolstering A₁ R preconditioning and preventing excessive A_2A R function might afford maximal neuroprotection. The main physiological role of the adenosine modulation system is to sharp the salience of information encoding through a combined action of adenosine A_2A receptors (A_2A R) in the synapse undergoing an alteration of synaptic efficiency with an increased inhibitory action of A₁ R in all surrounding synapses. Brain insults trigger an up-regulation of A_2A R in an attempt to bolster adaptive plasticity together with adenosine release and A₁ R desensitization; this favors synaptotocity (increased A_2A R) and decreases the hurdle to undergo degeneration (decreased A₁ R). Maximal neuroprotection is expected to result from a combined A_2A R blockade and increased A₁ R activation. This article is part of a mini review series: "Synaptic Function and Dysfunction in Brain Diseases".

Adenosine signalling mediates the anti-inflammatory effects of the COX-2 inhibitor nimesulide

Extracellular adenosine formation from ATP is controlled by ecto-nucleoside triphosphate diphosphohydrolase (E-NTPDase/CD39) and ecto-5'-nucleotidase (e-5NT/CD73); the latter converts AMP to adenosine and inorganic phosphate, representing the rate limiting step controlling the ratio between extracellular ATP and adenosine. Evidence that cellular expression and activity of CD39 and CD73 may be subject to changes under pathophysiological conditions has identified this pathway as an endogenous modulator in several diseases and was shown to be involved in the molecular mechanism of drugs, such as methotrexate, salicylates , interferon-β. We evaluated whether CD73/adenosine/A2A signalling pathway is involved in nimesulide anti-inflammatory effect, in vivo and in vitro. We found that the adenosine A2A agonist, 4-[2-[[6-amino-9-(N-ethyl-β-d-ribofuranuronamidosyl)-9H-purin-2-yl]amino]ethyl]benzenepropanoic acid hydrochloride (CGS21680, 2mg/kg ip.), inhibited carrageenan-induced rat paw oedema and the effect was reversed by co-administration of the A2A antagonist -(2-[7-amino-2-[2-furyl][1,2,4]triazolo[2,3-a][1,3,5]triazin-5-yl-amino]ethyl)phenol (ZM241385; 3mg/kg i.p.). Nimesulide (5mg/kg i.p.) anti-inflammatory effect was inhibited by pre-treatment with ZM241385 (3mg/kg i.p.) and by local administration of the CD73 inhibitor, adenosine 5'-(α,β-methylene)diphosphate (APCP; 400μg/paw). Furthermore, we found increased activity of 5'-nucleotidase/CD73 in paws and plasma of nimesulide treated rats, 4h following oedema induction. In vitro, the inhibitory effect of nimesulide on nitrite and prostaglandin E2 production by lipopolysaccharide-activated J774 cell line was reversed by ZM241385 and APCP. Furthermore, nimesulide increased CD73 activity in J774 macrophages while it did not inhibit nitrite accumulation by lipopolysaccharide-activated SiRNA CD73 silenced J774 macrophages. Our data demonstrate that the anti-inflammatory effect of nimesulide in part is mediated by CD73-derived adenosine acting on A2A receptors.

17β-Estradiol upregulates ecto-5'-nucleotidase (CD73) in hippocampal synaptosomes of female rats through action mediated by estrogen receptor-α and -β

17β-Estradiol (E2) crucially affects several processes in the hippocampus of both sexes. E2 acts upon estradiol receptors ERα and ERβ, influencing target gene expression and/or modulates intracellular signaling cascades. Another potent modulator of hippocampal function is nucleoside adenosine, the final product of ectonucleotidase cascade, enzymes which hydrolyze extracellular ATP to adenosine. The last and rate-limiting step of the hydrolysis is catalyzed by membrane-bound ecto-5'-nucleotidase (eN). Previous findings obtained on adenosine metabolism in brain suggest that eN may be modulated by ovarian steroids. Therefore, the present study reports that the activity and protein abundance of membrane-bound eN fluctuates across the estrus cycle in the hippocampal synaptosomes of female rats. Further, we analyzed the role of E2 and its intracellular receptors on the expression of eN in ovariectomized females. We found that E2 upregulated eN activity and protein abundance in the hippocampal synaptosomes. Application of nonspecific ER antagonist, ICI 182,780 and selective ERα and ERβ agonists, PPT and DPN, respectively, demonstrated the involvement of both receptor subtypes in observed actions. Selective ERα receptor agonist, PPT, induced upregulation of both the protein level and activity of eN, while application of selective ERβ receptor agonist, DPN, increased only the activity of eN. In both cases, E2 entered into the intracellular compartment and activated ER(s), which was demonstrated by membrane impermeable E2-BSA conjugate. Together these results imply that E2-induced effects on connectivity and functional properties of the hippocampal synapses may be in part mediated through observed effect on eN.

Impaired oligodendrocyte maturation in preterm infants: Potential therapeutic targets

Preterm birth is an evolving challenge in neonatal health care. Despite declining mortality rates among extremely premature neonates, morbidity rates remain very high. Currently, perinatal diffuse white matter injury (WMI) is the most commonly observed type of brain injury in preterm infants and has become an important research area. Diffuse WMI is associated with impaired cognitive, sensory and psychological functioning and is increasingly being recognized as a risk factor for autism-spectrum disorders, ADHD, and other psychological disturbances. No treatment options are currently available for diffuse WMI and the underlying pathophysiological mechanisms are far from being completely understood. Preterm birth is associated with maternal inflammation, perinatal infections and disrupted oxygen supply which can affect the cerebral microenvironment by causing activation of microglia, astrogliosis, excitotoxicity, and oxidative stress. This intricate interplay of events negatively influences oligodendrocyte development, causing arrested oligodendrocyte maturation or oligodendrocyte cell death, which ultimately results in myelination failure in the developing white matter. This review discusses the current state in perinatal WMI research, ranging from a clinical perspective to basic molecular pathophysiology. The complex regulation of oligodendrocyte development in healthy and pathological conditions is described, with a specific focus on signaling cascades that may play a role in WMI. Furthermore, emerging concepts in the field of WMI and issues regarding currently available animal models are put forward. Novel insights into the molecular mechanisms underlying impeded oligodendrocyte maturation in diffuse WMI may aid the development of novel treatment options which are desperately needed to improve the quality-of-life of preterm neonates.

Extracellular ATP Selectively Upregulates Ecto-Nucleoside Triphosphate Diphosphohydrolase 2 and Ecto-5'-Nucleotidase by Rat Cortical Astrocytes In Vitro

Extracellular ATP (eATP) acts as a danger-associated molecular pattern which induces reactive response of astrocytes after brain insult, including morphological remodeling of astrocytes, proliferation, chemotaxis, and release of proinflammatory cytokines. The responses induced by eATP are under control of ecto-nucleotidases, which catalyze sequential hydrolysis of ATP to adenosine. In the mammalian brain, ecto-nucleotidases comprise three enzyme families: ecto-nucleoside triphosphate diphosphohydrolases 1-3 (NTPDase1-3), ecto-nucleotide pyrophosphatase/phospodiesterases 1-3 (NPP1-3), and ecto-5'-nucleotidase (eN), which crucially determine ATP/adenosine ratio in the pericellular milieu. Altered expression of ecto-nucleotidases has been demonstrated in several experimental models of human brain dysfunctions. In the present study, we have explored the pattern of NTPDase1-3, NPP1-3, and eN expression by cultured cortical astrocytes challenged with 1 mmol/L ATP (eATP). At the transcriptional level, eATP upregulated expression of NTPDase1, NTPDase2, NPP2, and eN, while, at translational and functional levels, these were paralleled only by the induction of NTPDase2 and eN. Additionally, eATP altered membrane topology of eN, from clusters localized in membrane domains to continuous distribution along the cell membrane. Our results suggest that eATP, by upregulating NTPDase2 and eN and altering the enzyme membrane topology, affects local kinetics of ATP metabolism and signal transduction that may have important roles in the process related to inflammation and reactive gliosis.

Different danger signals differently impact on microglial proliferation through alterations of ATP release and extracellular metabolism

Microglia rely on their ability to proliferate in the brain parenchyma to sustain brain innate immunity and participate in the reaction to brain damage. We now studied the influence of different danger signals activating microglia, both internal (typified by glutamate, associated with brain damage) and external (using a bacterial lipopolysaccharide, LPS), on the proliferation of microglia cells. We found that LPS (100 ng/mL) increased, whereas glutamate (0.5 mM) decreased proliferation. Notably, LPS decreased whereas glutamate increased the extracellular levels of ATP. In contrast, LPS increased whereas glutamate decreased the extracellular catabolism of ATP into adenosine through ecto-nucleotidases and ecto-5'-nucleotidase. Finally, apyrase (degrades extracellular ATP) abrogated glutamate-induced inhibition of microglia proliferation; conversely, inhibitors of ecto-nucleotidases (ARL67156 or α,β-methylene ADP) and adenosine deaminase (degrades extracellular adenosine) abrogated the LPS-induced increase of microglia proliferation, which was blocked by a selective A2A receptor antagonist, SCH58261 (50 nM). Overall, these results highlight the importance of the extracellular purinergic metabolism to format microglia proliferation and influence the spatio-temporal profile of neuroinflammation in different conditions of brain damage.

Ecto-5'-nucleotidase (CD73) is involved in chronic cerebral hypoperfusion-induced white matter lesions and cognitive impairment by regulating glial cell activation and pro-inflammatory cytokines

Recent studies have demonstrated that inflammatory and immune mechanisms play important roles in the progression of chronic cerebral hypoperfusion (CCH)-induced white matter lesions (WMLs). As an endogenous neuromodulator in the brain, the extracellular levels of adenosine represent a critical endogenous mechanism for the regulation of immune and inflammatory responses. Ecto-5'-nucleotidase (CD73), which dephosphorylates AMP to adenosine, is considered to catalyze the rate-limiting step in the generation of extracellular adenosine. However, the role of CD73 in the development of CCH-induced WMLs remains unclear. In the present study, we investigated the expression and activity of CD73 using immunohistochemistry, Western blot analysis and measurements of the rate of AMP hydrolysis in a mouse model of CCH via bilateral common carotid artery stenosis (BCAS) surgery. Moreover, C57BL/6-CD73 knockout (KO) and their wild-type littermates were subjected to BCAS surgery to further investigate the functional roles of CD73 in the WMLs. White matter (WM) changes, astrocyte and microglia proliferation, proinflammatory cytokine levels in the corpus callosum and cognitive function were assessed on the 30th day after BCAS. The results indicated that CD73 expression and activities significantly increased in the corpus callosum on the 30th day after BCAS. Moreover, CD73 deficiency exacerbated CCH-induced WMLs and cognitive impairment. More reactive astrocytes and microglia were observed in the corpus callosum in CD73-KO mice. CD73 deficiency significantly increased the levels of proinflammatory cytokines, including tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and interleukin-1β (IL-1β) in the BCAS model of CCH. These findings suggest that CD73 plays a protective role in the development of CCH-induced WMLs and cognitive impairment via the regulation of glial cell activation and proinflammatory cytokine expression.

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.

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.

CD73 expression in RPE cells is associated with the suppression of conventional CD4 cell proliferation

CD73 is intensively involved in the regulation of immune responses through the conversion of pro-inflammatory ATP to immunosuppressive adenosine. Herein, we clarified whether cells in the retina express CD73 and participate in the regulation of inflammatory eye diseases such as experimental autoimmune uveitis (EAU). First, immunofluorescence staining was performed to compare the distribution of CD73(+) cells in the retinas of EAU-induced and normal B10RIII mice. The results revealed that a layer of cells in the normal retina that was consistent with the location of retinal pigment epithelial (RPE) cells strongly expressing CD73, and the expression was markedly reduced in the presence of EAU. Thereafter, EAU was also induced in C57BL/6 mice by active immunization or adoptive transfer. CD73 expression in isolated RPE cells was assessed by real-time RT-PCR and western blotting, and the catalytic abilities of the cells to convert AMP to adenosine were determined using HPLC analyses. Compared to the normal control, significantly decreased CD73 expression and AMP catalytic ability were found in the RPE cells isolated from inflamed eyes. CD73 expression and activity were also studied in cultured RPE cells treated with different stimuli, such as Toll-like receptor ligands and cytokines. Highly varied functional CD73 expression was observed in RPE cells through cytokines or Toll-like receptor agonist treatments. Finally, whether RPE cells could regulate the immune response, particularly the proliferation of CD4 cells, through surface-expressed CD73 was determined using a two-chamber assay. The robust inhibition of conventional T-cell proliferation was uniquely observed when CD73(+) RPE cells in the upper chamber were in the presence of AMP. To further confirm the function of CD73 in RPE cells, Cd73(-/-) RPE cells were isolated, and CD73-rescued control cells were constructed. CD73(+)Cd73(-/-) RPE, not Cd73(-/-) RPE, significantly suppressed interacted CD4 cells proliferation and cytokine production. Taken together, these data suggest that naive RPE cells suppressed the immune response through their high expression of CD73. The expression of CD73 in RPE cells could be regulated through many factors, and down-regulated CD73 expression attenuated the suppressive effect of RPE on the proliferation of conventional CD4 cells.

Developmental increase in ecto-5'-nucleotidase activity overlaps with appearance of two immunologically distinct enzyme isoforms in rat hippocampal synaptic plasma membranes

Ecto-5'-nucleotidase (e-5NT), a glycosylphosphatidylinositol-linked membrane protein, catalyzes a conversion of AMP to adenosine, which influences nearly every aspect of brain physiology, including embryonic and postnatal brain development. The present study aimed to investigate a pattern of expression, activity and kinetic properties of e-5NT in the hippocampal formation and synaptic plasma membrane (SPM) preparations in rats at postnatal days (PDs) 7, 15, 20, 30 and 90. By combining gene expression analysis and enzyme histochemistry, we observed that e-5NT mRNA reached the adult level at PD20, while the enzyme activity continued to increase beyond this age. Further analysis revealed that hippocampal layers rich in synapses expressed the highest levels of e-5NT activity, while in layers populated with neuronal cell bodies, the enzyme activity was weak or absent. Therefore, activity and expression of e-5NT were analyzed in SPM preparations isolated from rats at different ages. The presence of two protein bands of about 65 and 68 kDa was determined by immunoblot analysis. The 65-kDa band was present at all ages, and its abundance increased from PD7 to PD20. The 68-kDa band appeared at PD15 and increased until PD30, coinciding with the increase of e-5NT activity, substrate affinity and enzymatic efficiency. Since distinct e-5NT isoforms may derive from different patterns of the enzyme protein N-glycosylation, we speculate that long-term regulation of e-5NT activity in adulthood may be effectuated at posttranslational level and without overall change in the gene and protein expression.

Astroglial redistribution of aquaporin 4 during spongy degeneration in a Canavan disease mouse model

Canavan disease is a spongiform leukodystrophy caused by an autosomal recessive mutation in the aspartoacylase gene. Deficiency of oligodendroglial aspartoacylase activity and a subsequent increase of its substrate N-acetylaspartate are the etiologic factors for the disease. N-acetylaspartate acts as a molecular water pump. Therefore, an osmotic-hydrostatic mechanism is thought to be involved in the development of the Canavan disease phenotype. Astrocytes express water transporters and are critically involved in regulating and maintaining water homeostasis in the brain. We used the ASPA(Nur7/Nur7) mouse model of Canavan disease to investigate whether a disturbance of water homeostasis might be involved in the disease's progression. Animals showed an age-dependent impairment of motor performance and spongy degeneration in various brain regions, among the basal ganglia, brain stem, and cerebellar white matter. Astrocyte activation was prominent in regions which displayed less tissue damage, such as the corpus callosum, cortex, mesencephalon, and stratum Purkinje of cerebellar lobe IV. Immunohistochemistry revealed alterations in the cellular distribution of the water channel aquaporin 4 in astrocytes of ASPA(Nur7/Nur7) mice. In control animals, aquaporin 4 was located exclusively in the astrocytic end feet. In contrast, in ASPA(Nur7/Nur7) mice, aquaporin 4 was located throughout the cytoplasm. These results indicate that astroglial regulation of water homeostasis might be involved in the partial prevention of spongy degeneration. These observations highlight aquaporin 4 as a potential therapeutic target for Canavan disease.

Expression of ecto-nucleoside triphosphate diphosphohydrolase1-3 (NTPDase1-3) by cortical astrocytes after exposure to pro-inflammatory factors in vitro

Nucleoside triphosphate diphosphohydrolases (NTPDases) are ecto-enzymes catalyzing the first step of sequential hydrolysis of extracellular ATP to adenosine, as the final product. Among eight members of NTPDase family, NTPDases1-3 have been shown to be expressed in the brain. Although altered NTPDase expression has been observed in relation to cell death and reactive gliosis in several experimentally induced neuropathologies, regulators of NTPDases expression and function are largely unknown. The present study explored the effects of several inflammatory factors (i.e., INF-γ, TNF-α, LPS, peroxide, and glutamate) on NTPDase1-3 activity and expression by cultured cortical astrocytes. We were able to demonstrate that INF-γ and TNF-α increased both ATP and ADP hydrolysis, while LPS specifically increased ATP hydrolysis. Consistent with the observed enhanced nucleotidase activity, INF-γ induced the upregulation of NTPDase1 at the mRNA and protein level. Furthermore, we were able to demonstrate that INF-γ and TNF-α decreased the relative abundance of dominant astrocytic NTPDase2 in favor of NTPDase1. In summary, these results suggest that INF-γ, TNF-α, and LPS may be relevant in vivo regulators of NTPDase expression in neuropathologies associated with neuroinflammation.