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

Prolonged intermittent theta burst stimulation restores the balance between A2AR- and A1R-mediated adenosine signaling in the 6-hydroxidopamine model of Parkinson's disease

JOURNAL/nrgr/04.03/01300535-202507000-00027/figure1/v/2024-09-09T124005Z/r/image-tiff An imbalance in adenosine-mediated signaling, particularly the increased A2AR-mediated signaling, plays a role in the pathogenesis of Parkinson's disease. Existing therapeutic approaches fail to alter disease progression, demonstrating the need for novel approaches in PD. Repetitive transcranial magnetic stimulation is a non-invasive approach that has been shown to improve motor and non-motor symptoms of Parkinson's disease. However, the underlying mechanisms of the beneficial effects of repetitive transcranial magnetic stimulation remain unknown. The purpose of this study is to investigate the extent to which the beneficial effects of prolonged intermittent theta burst stimulation in the 6-hydroxydopamine model of experimental parkinsonism are based on modulation of adenosine-mediated signaling. Animals with unilateral 6-hydroxydopamine lesions underwent intermittent theta burst stimulation for 3 weeks and were tested for motor skills using the Rotarod test. Immunoblot, quantitative reverse transcription polymerase chain reaction, immunohistochemistry, and biochemical analysis of components of adenosine-mediated signaling were performed on the synaptosomal fraction of the lesioned caudate putamen. Prolonged intermittent theta burst stimulation improved motor symptoms in 6-hydroxydopamine-lesioned animals. A 6-hydroxydopamine lesion resulted in progressive loss of dopaminergic neurons in the caudate putamen. Treatment with intermittent theta burst stimulation began 7 days after the lesion, coinciding with the onset of motor symptoms. After treatment with prolonged intermittent theta burst stimulation, complete motor recovery was observed. This improvement was accompanied by downregulation of the eN/CD73-A2AR pathway and a return to physiological levels of A1R-adenosine deaminase 1 after 3 weeks of intermittent theta burst stimulation. Our results demonstrated that 6-hydroxydopamine-induced degeneration reduced the expression of A1R and elevated the expression of A2AR. Intermittent theta burst stimulation reversed these effects by restoring the abundances of A1R and A2AR to control levels. The shift in ARs expression likely restored the balance between dopamine-adenosine signaling, ultimately leading to the recovery of motor control.

The association of caffeine and nandrolone decanoate modulates aversive memory and nociception in rats

Caffeine and anabolic-androgenic steroids (AAS) are commonly used to improve muscle mass and athletic performance. Nandrolone Decanoate (ND) is one of the most abused AAS worldwide, leading to behavioral changes in both humans and rodents. Caffeine, the most widely consumed psychostimulant globally, is present in various thermogenic and gym supplements. Low and moderate doses of caffeine antagonize adenosine receptors and have been linked to improved memory and pain relief. We have previously demonstrated that consuming caffeine prevents the risk-taking behavior triggered by nandrolone. In this study, we aimed to investigate the long-term effects of ND and caffeine, either alone or in combination, on passive avoidance memory and nociception. We used the step-down and hot-plate tasks in male and female Lister Hooded rats. Our results confirmed the antinociceptive effect of caffeine and indicated that chronic administration of the ND-caffeine association promotes the evocation of aversive memory in female rats.

Impaired olfactory performance and anxiety-like behavior in a rat model of multiple sclerosis are associated with enhanced adenosine signaling in the olfactory bulb via A1R, A2BR, and A3R

The present study shows that animals with experimental autoimmune encephalomyelitis (EAE) exhibit olfactory dysfunction and impaired general cognitive abilities, as well as anxiety-like behavior. Olfactory dysfunction occurs on average at 2 dpi, well before the onset of the first motor signs of EAE (8-10 dpi). After the initial olfactory dysfunction, the EAE animals show a fluctuation in olfactory performance that resembles the relapsing-remitting course of human MS. The study also shows severe neuroinflammation in the olfactory bulb (OB), with numerous infiltrated CD4+ T cells and peripheral macrophages in the superficial OB layers, marked microgliosis, and massive induction of TNF-α, IL-1β, and IL-6. Reduced tyrosine hydroxylase activity in the glomerular layer, pronounced granule cell atrophy, and reduced numbers of type B neuroblasts in the rostral migratory stream also indicate altered plasticity of the neuronal network in the OB. Considering the exceptionally high purinome expression in the OB, the possible involvement of purinergic signaling was also investigated. The study shows that macrophages infiltrating the OB overexpress A3R, while highly reactive microglia overexpress the adenosine-producing enzyme eN/CD73 as well as A2BR, A3R, and P2X4R. Given the simultaneous induction of complement component C3, the results suggest that the microglial cells develop a functional phenotype of phagocytizing microglia. The study also demonstrates transcriptional and translational upregulation of A1R in mitral and tufted cells, which likely influence resting network activity in OB and likely contribute to olfactory dysfunction in EAE. Overall, our study shows that olfactory dysfunction and altered social and cognitive behavior in EAE are associated with increased adenosine signaling via A1R, A2BR, and A3R.

Flaxseed Oil Alleviates Trimethyltin-Induced Cell Injury and Inhibits the Pro-Inflammatory Activation of Astrocytes in the Hippocampus of Female Rats

Exposure to the neurotoxin trimethyltin (TMT) selectively induces hippocampal neuronal injury and astrocyte activation accompanied with resultant neuroinflammation, which causes severe behavioral, cognitive, and memory impairment. A large body of evidence suggests that flaxseed oil (FSO), as one of the richest sources of essential omega-3 fatty acids, i.e., α-linolenic acids (ALA), displays neuroprotective properties. Here, we report the preventive effects of dietary FSO treatment in a rat model of TMT intoxication. The administration of FSO (1 mL/kg, orally) before and over the course of TMT intoxication (a single dose, 8 mg/kg, i.p.) reduced hippocampal cell death, prevented the activation of astrocytes, and inhibited their polarization toward a pro-inflammatory/neurotoxic phenotype. The underlying protective mechanism was delineated through the selective upregulation of BDNF and PI3K/Akt and the suppression of ERK activation in the hippocampus. Pretreatment with FSO reduced cell death and efficiently suppressed the expression of inflammatory molecules. These beneficial effects were accompanied by an increased intrahippocampal content of n-3 fatty acids. In vitro, ALA pretreatment prevented the TMT-induced polarization of cultured astrocytes towards the pro-inflammatory spectrum. Together, these findings support the beneficial neuroprotective properties of FSO/ALA against TMT-induced neurodegeneration and accompanied inflammation and hint at a promising preventive use of FSO in hippocampal degeneration and dysfunction.

Altered Topographic Distribution and Enhanced Neuronal Expression of Adenosine-Metabolizing Enzymes in Rat Hippocampus and Cortex from Early to late Adulthood

The present study demonstrates altered topographic distribution and enhanced neuronal expression of major adenosine-metabolizing enzymes, i.e. ecto-5'-nucleotidase (eN) and tissue non-specific alkaline phosphatase (TNAP), as well as adenosine receptor subtype A_2A in the hippocampus and cortex of male rats from early to late adulthood (3, 6, 12 and 15 months old males). The significant effect of age was demonstrated for the increase in the activity and the protein expression of eN and TNAP. At 15-m, enzyme histochemistry demonstrated enhanced expression of eN in synapse-rich hippocampal and cortical layers, whereas the upsurge of TNAP was observed in the hippocampal and cortical neuropil, rather than in cells and layers where two enzymes mostly reside in 3-m old brain. Furthermore, a dichotomy in A₁R and A_2AR expression was demonstrated in the cortex and hippocampus from early to late adulthood. Specifically, a decrease in A₁R and enhancement of A_2AR expression were demonstrated by immunohistochemistry, the latter being almost exclusively localized in hippocampal pyramidal and cortical superficial cell layers. We did not observe any glial upregulation of A_2AR, which was common for both advanced age and chronic neurodegeneration. Taken together, the results imply that the adaptative changes in adenosine signaling occurring in neuronal elements early in life may be responsible for the later prominent glial enhancement in A_2AR-mediated adenosine signaling, and neuroinflammation and neurodegeneration, which are the hallmarks of both advanced age and age-associated neurodegenerative diseases.

Expression of Ectonucleoside Triphosphate Diphosphohydrolase 2 (NTPDase2) Is Negatively Regulated Under Neuroinflammatory Conditions In Vivo and In Vitro

Ectonucleoside triphosphate diphosphohydrolase 2 (NTPDase2) hydrolyzes extracellular ATP to ADP, which is the ligand for P2Y1,12,13 receptors. The present study describes the distribution of NTPDase2 in adult rat brains in physiological conditions, and in hippocampal neurodegeneration induced by trimethyltin (TMT). The study also describes the regulation of NTPDase2 by inflammatory mediators in primary astrocytes and oligodendroglial cell line OLN93. In physiological conditions, NTPDase2 protein was most abundant in the hippocampus, where it was found in fibrous astrocytes and synaptic endings in the synaptic-rich hippocampal layers. In TMT-induced neurodegeneration, NTPDase2-mRNA acutely decreased at 2-dpi and then gradually recovered to the control level at 7-dpi and 21-dpi. As determined by immunohistochemistry and double immunofluorescence, the decrease was most pronounced in the dentate gyrus (DG), where NTPDase2 withdrew from the synaptic boutons in the polymorphic layer of DG, whereas the recovery of the expression was most profound in the subgranular layer. Concerning the regulation of NTPDase2 gene expression, proinflammatory cytokines IL-6, IL-1β, TNFα, and IFNγ negatively regulated the expression of NTPDase2 in OLN93 cells, while did not altering the expression in primary astrocytes. Different cell-intrinsic stressors, such as depletion of intracellular energy store, oxidative stress, endoplasmic reticulum stress, and activation of protein kinase C, also massively disturbed the expression of the NTPDase2 gene. Together, our results suggest that the expression and the activity of NTPDase2 transiently cease in neurodegeneration and brain injury, most likely as a part of the acute adaptive response designed to promote cell defense, survival, and recovery.

Ectonucleotidases in the hippocampus: Spatial distribution and expression after ovariectomy and estradiol replacement

Extracellular purine nucleotides, such as adenosine 5'-triphosphate (ATP), are important modulators of hippocampal function and plasticity. In the extracellular space, ATP is inherently short-lived molecule, which undergoes rapid enzymatic degradation to adenosine by ectonucleotidases. Given that ectonucleotidases have distinct and overlapping distribution in the hippocampus, and as ovarian hormones participate in a formation, maturation, and a refinement of synaptic contacts, both during development and in adulthood, the present chapter summarizes known data about spatial distribution of selected ecto-enzymes and estradiol-induced effects on ectonucleotidases in the rat hippocampus.

Microglial- and Astrocyte-Specific Expression of Purinergic Signaling Components and Inflammatory Mediators in the Rat Hippocampus During Trimethyltin-Induced Neurodegeneration

The present study examined the involvement of purinergic signaling components in the rat model of hippocampal degeneration induced by trimethyltin (TMT) intoxication (8 mg/kg, single intraperitoneal injection), which results in behavioral and neurological dysfunction similar to neurodegenerative disorders. We investigated spatial and temporal patterns of ecto-nucleoside triphosphate diphosphohydrolase 1 (NTPDase1/CD39) and ecto-5′ nucleotidase (eN/CD73) activity, their cell-specific localization, and analyzed gene expression pattern and/or cellular localization of purinoreceptors and proinflammatory mediators associated with reactive glial cells. Our study demonstrated that all Iba1+ cells at the injured area, irrespective of their morphology, upregulated NTPDase1/CD39, while induction of eN/CD73 has been observed at amoeboid Iba1+ cells localized within the hippocampal neuronal layers with pronounced cell death. Marked induction of P2Y₁₂R, P2Y₆R, and P2X₄-messenger RNA at the early stage of TMT-induced neurodegeneration might reflect the functional properties, migration, and chemotaxis of microglia, while induction of P2X₇R at amoeboid cells probably modulates their phagocytic role. Reactive astrocytes expressed adenosine A₁, A_2A, and P2Y₁ receptors, revealed induction of complement component C3, inducible nitric oxide synthase, nuclear factor-kB, and proinflammatory cytokines at the late stage of TMT-induced neurodegeneration. An increased set of purinergic system components on activated microglia (NTPDase1/CD39, eN/CD73, and P2X₇) and astrocytes (A₁R, A_2AR, and P2Y₁), and loss of homeostatic glial and neuronal purinergic pathways (P2Y₁₂ and A₁R) may shift purinergic signaling balance toward excitotoxicity and inflammation, thus favoring progression of pathological events. These findings may contribute to a better understanding of the involvement of purinergic signaling components in the progression of neurodegenerative disorders that could be target molecules for the development of novel therapies.

Effects of Tannic Acid on Antioxidant Activity and Ovarian Development in Adolescent and Adult Female Brandt's Voles

It is well known that tannins can influence the reproduction of animals, but there is little research published to elucidate the mechanics of this phenomenon. The purpose of this study was to investigate the role of antioxidation in the influence of tannic acid on the ovarian development of Brandt's voles (Lasiopodomys brandtii), which is a species of prairie animal that feeds on plants containing tannins. Postnatal 4-week-old female Brandt's voles were treated with 0 (control), 0.3% (low dose), or 0.6% (high dose) tannic acid for 4 or 9 weeks (i.e., when they reached puberty [8 weeks] or sexual maturity [13 weeks], respectively). The results showed that in both adolescent and adult Brandt's voles, firstly, treatment with tannic acid produced a higher ovary coefficient (ratio of the weight of ovaries to body weight), a greater proportion of mature follicles, and an increased follicular diameter. Secondly, tannic acid increased the serum contents of luteinizing hormone, follicle-stimulating hormone, and serum estradiol. Thirdly, tannic acid elevated the levels of antioxidant enzymes (superoxide dismutase, glutathione peroxidase, and catalase) and reduced the level of malondialdehyde. Therefore, it is suggested that tannic acid may promote the ovarian development of female Brant's voles by enhancing their antioxidant capacity.

Trimethyltin Increases Intracellular Ca2+ Via L-Type Voltage-Gated Calcium Channels and Promotes Inflammatory Phenotype in Rat Astrocytes In Vitro

Astrocytes are the first responders to noxious stimuli by undergoing cellular and functional transition referred as reactive gliosis. Every acute or chronic disorder is accompanied by reactive gliosis, which could be categorized as detrimental (A1) of beneficial (A2) for nervous tissue. Another signature of pathological astrocyte activation is disturbed Ca2+ homeostasis, a common denominator of neurodegenerative diseases. Deregulation of Ca+ signaling further contributes to production of pro-inflammatory cytokines and reactive oxygen species. Trimethyltin (TMT) intoxication is a widely used model of hippocampal degeneration, sharing behavioral and molecular hallmarks of Alzheimer's disease (AD), thus representing a useful model of AD-like pathology. However, the role of astrocyte in the etiopathology of TMT-induced degeneration as well as in AD is not fully understood. In an effort to elucidate the role of astrocytes in such pathological processes, we examined in vitro effects of TMT on primary cortical astrocytes. The application of a range of TMT concentrations (5, 10, 50, and 100 μM) revealed changes in [Ca2+]i in a dose-dependent manner. Specifically, TMT-induced Ca2+ transients were due to L-type voltage-gated calcium channels (VGCC). Additionally, TMT induced mitochondrial depolarization independent of extracellular Ca2+ and disturbed antioxidative defense of astrocyte in several time points (4, 6, and 24 h) after 10 μM TMT intoxication, inducing oxidative and nitrosative stress. Chronic exposure (24 h) to 10 μM TMT induced strong upregulation of main pro-inflammatory factors, components of signaling pathways in astrocyte activation, A1 markers, and VGCC. Taken together, our results provide an insight into cellular and molecular events of astrocyte activation in chronic neuroinflammation.

Effect of estradiol on enzymes of vascular extracellular nucleotide metabolism

PURPOSE

Estrogens have beneficial effects on the cardiovascular system, promoting vasodilation, endothelial cells growth, relaxation, and regulation of blood pressure. Some of these effects could be associated with the purinergic system known for the control of vasodilation, inflammation, and platelet function. The aim of our study was the evaluation of ATP, AMP, and adenosine extracellular catabolism, catalyzed by ectonucleoside triphosphate diphosphohydrolase-1 (CD39), ecto-5'-nucleotidase (CD73), and ecto-adenosine deaminase (eADA) in mouse aortas.

METHODS

Extracellular hydrolysis of ATP, AMP, and adenosine was estimated on the aortic surface of 3-month-old female and male C57BL/6 J wild-type (WT) mice, in female WT mouse aortas incubated for 48 h in the presence or absence of 100 nM estradiol, and in WT female mouse and ApoE-/-LDL-R-/- aortas. The conversion of substrates to products was analyzed by high-pressure liquid chromatography (HPLC).

RESULTS

We demonstrated significantly higher adenosine deamination rate in WT male vs. female mice (p = 0.041). We also noted the lower adenosine hydrolysis in aortas exposed to estradiol, as compared with the samples incubated in estradiol-free medium (p = 0.043). Finally, we observed that adenosine conversion to inosine was significantly higher on the surface of ApoE-/-LDL-R-/- aortas compared with WT mice (p = 0.001). No such effects were noted in ATP and AMP extracellular hydrolysis.

CONCLUSION

We conclude that estradiol inhibits the extracellular degradation of adenosine to inosine, which may be an element of its vascular protective effect, as it will lead to an increase in extracellular adenosine concentration. We can also assume that during the development of the atherosclerotic process, the protective role of estradiol in the regulation of adenosine degradation may be obscured by other pathogenic factors.

Response by the authors

Response to comments on Cui Q-Q et al: "Hippocampal CD 39/ENTPD 1 promotes mouse depression-like behavior through hydrolyzing extracellular ATP".

Estradiol induces synaptic rearrangements

17β-Estradiol (E2) is a potent steroid hormone of both gonadal and neuronal origin that exerts profound effects on neuroplasticity in several brain regions. Dendritic spine and synapse formation and rearrangements are modulated and mediated by estrogens. In this chapter, we highlighted the essential background concerning the effects of E2 on synaptic rearrangements accompanied by synaptic plasticity in E2-sensitive brain regions that mediate learning and memory, i.e., cortex and hippocampus. We also address details of the molecular mechanisms underlying E2 regulation of spine dynamics. The proposed models of action of E2 overlaps with that for well-established synaptic modulators, such as adenosine. Thus, the possible synergistic effects of those two molecules in respect to synaptic rearrangement and plasticity were presented.

Ectonucleoside Triphosphate Diphosphohydrolase-1/CD39 Affects the Response to ADP of Female Rat Platelets

There is evidence that an imbalance of extracellular purine levels may be associated with increased cardiovascular risk. Platelets play a pivotal role in vascular homeostasis and thrombosis and are important source of purine nucleotides and nucleosides. Hydrolysis of nucleotides ATP and ADP is regulated by two ectonucleotidases, triphosphate diphosphohydrolase-1 (NTPDase-1/CD39) and ecto-5’-nucleotidase (ecto-5’-NT/CD73). CD39 enzyme is expressed on the endothelium, circulating blood cells, and smooth muscle cells; there is evidence that changes in CD39 expression and activity affects the potential thrombogenic of a tissue. Gender difference in the cardiovascular risk has been extensively observed; however, while the age-dependent difference in the prevalence of cardiovascular events between men and women has been attributed to the loss of the protective effect of estrogens in the postmenopausal period, the physiological mechanism behind gender disparity is still unclear. Here, we evaluated comparatively male and female rat platelet reactivity and considered the possible role of CD39 at the basis of difference observed. We found a reduced in vitro response to ADP (1–30 µM) of female compared to male platelets, associated to increased platelet CD39 expression and activity. Platelet response to ADP was strongly increased by incubation (10 min) with the CD39 inhibitor, ARL67156 (100 µM), while male platelet response was unaffected. Rat treatment with clopidogrel (30 mg/kg, per os) inhibited ex vivo platelet aggregation. Bleeding time was prolonged in female compared to male. Taken together, our results suggest that platelet ATPase and ADPase activity might be a reliable predictor of platelet reactivity.