Oligodendrocyte precursor cell maturation: role of adenosine receptors

Oligodendrocyte-formed myelin sheaths allow fast synaptic transmission in the brain and their degeneration leads to demyelinating diseases such as multiple sclerosis. Remyelination requires the differentiation of oligodendrocyte progenitor cells into mature oligodendrocytes but, in chronic neurodegenerative disorders, remyelination fails due to adverse environment. Therefore, a strategy to prompt oligodendrocyte progenitor cell differentiation towards myelinating oligodendrocytes is required. The neuromodulator adenosine, and its receptors(A1, A(2A), A(2B) and A3 receptors: A1R, A(2A)R, A(2B)R and A3R), are crucial mediators in remyelination processes. It is known that A1Rs facilitate oligodendrocyte progenitor cell maturation and migration whereas the A3Rs initiates apoptosis in oligodendrocyte progenitor cells. Our group of research contributed to the field by demonstrating that A(2A)R and A(2B)R inhibit oligodendrocyte progenitor cell maturation by reducing voltage-dependent K^+ currents necessary for cell differentiation. The present review summarizes the possible role of adenosine receptor ligands as potential therapeutic targets in demyelinating pathologies such as multiple sclerosis.

The seeming paradox of adenosine receptors as targets for the treatment of Alzheimer's disease: agonists or antagonists?

Alzheimer＇s disease （AD） is the most common neurodegenerative disorder, and its incidence is relatively high among elderly people, affecting about 1-2% of the population between 60-65 years old and rising dramatically （about 30%） in people aged 80 years or older （Selkoe, 2002）. Nowadays, considering the increasing mean lifespan of populations in developed countries, the disease is becoming more and more a health concern, and the search for an effective cure has turned into＂a real need＂.

Adenosine A_(2A)receptor blockade attenuates excitotoxicity in rat striatal medium spiny neurons during an ischemic-like insult

During brain ischemia,excitotoxicity and peri-infarct depolarization injuries occur and cause cerebral tissue damage.Indeed,anoxic depolarization,consisting of massive neuronal depolarization due to the loss of membrane ion gradients,occurs in vivo or in vitro during an energy failure.The neuromodulator adenosine is released in huge amounts during cerebral ischemia and exerts its effects by activating specific metabotropic receptors,namely:A_(1),A_(2A),A_(2B),and A_(3).The A_(2A)receptor subtype is highly expressed in striatal medium spiny neurons,which are particularly susceptible to ischemic damage.Evidence indicates that the A2Areceptors are upregulated in the rat striatum after stroke and the selective antagonist SCH58261 protects from exaggerated glutamate release within the first 4 hours from the insult and alleviates neurological impairment and histological injury in the following 24 hours.We recently added new knowledge to the mechanisms by which the adenosine A2Areceptor subtype participates in ischemia-induced neuronal death by performing patch-clamp recordings from medium spiny neurons in rat striatal brain slices exposed to oxygen and glucose deprivation.We demonstrated that the selective block of A2Areceptors by SCH58261 significantly reduced ionic imbalance and delayed the anoxic depolarization in medium spiny neurons during oxygen and glucose deprivation and that the mechanism involves voltage-gated K+channel modulation and a presynaptic inhibition of glutamate release by the A2Areceptor antagonist.The present review summarizes the latest findings in the literature about the possibility of developing selective ligands of A2Areceptors as advantageous therapeutic tools that may contribute to counteracting neurodegeneration after brain ischemia.

Unlocking antitumor immunity with adenosine receptorblockers

Tumors survive by creating a tumor microenvironment(TME)that suppresses antitumor immunity.The TME suppresses the immune system by limiting antigen presentation,inhibiting lymphocyte and natural killer(NK)cell activation,and facilitating T cell exhaustion.Checkpoint inhibitors like anti-PD-1 and anti-CTLA4 are immunostimulatory antibodies,and their blockade extends the survival of some but not all cancer patients.Extracellular adenosine triphosphate(ATP)is abundant in inflamed tumors,and its metabolite,adenosine(ADO),is a driver of immunosuppression mediated by adenosine A2A receptors(A2AR)and adenosine A2B receptors(A2BR)found on tumor-associated lymphoid and myeloid cells.This review will focus on adenosine as a key checkpoint inhibitor-like immunosuppressive player in the TME and how reducing adenosine production or blocking A2AR and A2BR enhances antitumor immunity.

Adenosine 2A receptor contributes to the facilitation of postinfectious irritable bowel syndrome by γδ T cells via the PKA/CREB/NF-κB signaling pathway

BACKGROUND Immunological dysfunction-induced low-grade inflammation is regarded as one of the predominant pathogenetic mechanisms in post-infectious irritable bowel syndrome(PI-IBS).γδT cells play a crucial role in innate and adaptive immunity.Adenosine receptors expressed on the surface ofγδT cells participate in intestinal inflammation and immunity regulation.AIM To investigate the role ofγδT cell regulated by adenosine 2A receptor(A2AR)in PI-IBS.METHODS The PI-IBS mouse model has been established with Trichinella spiralis(T.spiralis)infection.The intestinal A2AR and A2AR inγδT cells were detected by immunohistochemistry,and the inflammatory cytokines were measured by western blot.The role of A2AR on the isolatedγδT cells,including proliferation,apoptosis,and cytokine production,were evaluated in vitro.Their A2AR expression was measured by western blot and reverse transcription polymerase chain reaction(RT-PCR).The animals were administered with A2AR agonist,or A2AR antagonist.Besides,γδT cells were also injected back into the animals,and the parameters described above were examined,as well as the clinical features.Furthermore,the A2AR-associated signaling pathway molecules were assessed by western blot and RT-PCR.RESULTS PI-IBS mice exhibited elevated ATP content and A2AR expression(P<0.05),and suppression of A2AR enhanced PI-IBS clinical characteristics,indicated by the abdominal withdrawal reflex and colon transportation test.PI-IBS was associated with an increase in intestinal T cells,and cytokine levels of interleukin-1(IL-1),IL-6,IL-17A,and interferon-α(IFN-α).Also,γδT cells expressed A2AR in vitro and generated IL-1,IL-6,IL-17A,and IFN-α,which can be controlled by A2AR agonist and antagonist.Mechanistic studies demonstrated that the A2AR antagonist improved the function ofγδT cells through the PKA/CREB/NF-κB signaling pathway.CONCLUSION Our results revealed that A2AR contributes to the facilitation of PI-IBS by regulating the function ofγδT cells via the PKA/CREB/NF-κB signaling pathway.

Regulation of epithelial sodium channel ^-subunit expression by adenosine receptor A2a in alveolar epithelial ceils

Background The amiloride-sensitive epithelial sodium channel a-subunit （a-ENaC） is an important factor for alveolar fluid clearance during acute lung injury. The relationship between adenosine receptor A2a （A2aAR） expressed in alveolar epithelial cells and aα-ENaC is poorly understood. We targeted the A2aAR in this study to investigate its role in the expression of αa-ENaC and in acute lung injury.Methods A549 cells were incubated with different concentrations of A2aAR agonist CGS-21680 and with 100 μmol/L CGS-21680 for various times. Rats were treated with lipopolysaccharide （LPS） after CGS-21680 was injected. Animals were sacrificed and tissue was harvested for evaluation of lung injury by analysis of the lung wet-to-dry weight ratio, lung permeability and myeloperoxidase activity. RT-PCR and Western blotting were used to determine the mRNA and protein expression levels of α-ENaC in A549 cells and alveolar type II epithelial cells.Results Both mRNA and protein levels of α-ENaC were markedly higher from 4 hours to 24 hours after exposure to 100μmol/L CGS-21680. There were significant changes from 0.1 umol/L to 100 μmol/L CGS-21680, with a positive correlation between increased concentrations of CGS-21680 and expression of α-ENaC. Treatment with CGS-21680during LPS induced lung injury protected the lung and promoted α-ENaC expression in the alveolar epithelial cells.Conclusion Activation of A2aAR has a protective effect during the lung injury, which may be beneficial to the prognosis of acute lung injury

Hypoxia induces T-cell apoptosis by inhibiting chemokine C receptor 7 expression:the role of adenosine receptor A2

Hypoxia is a major characteristic of the tumor microenvironment,and its effects on immune cells are proposed to be important factors for the process of tumor immune escape.It has been reported that hypoxia affects the function of dendritic cells and the antitumor function of T cells.Here we discuss the effects of hypoxia on T-cell survival.Our results showed that hypoxia induced apoptosis of T cells.Adenosine and adenosine receptors(AR)are important to the hypoxia-related signaling pathway.Using AR agonists and antagonists,we demonstrated that hypoxia-induced apoptosis of T cells was mediated by A^(2a)and A^(2b)receptors.Furthermore,we are the first,to our knowledge,to report that hypoxia significantly inhibited the expression of chemokine C receptor 7(CCR7)of T cells via the A^(2)R signal pathway,perhaps representing a mechanism of hypoxia-induced apoptosis of T cells.Collectively,our research demonstrated that hypoxia induces T-cell apoptosis by the A^(2)R signaling pathway partly by suppressing CCR7.Blocking the A^(2)R signaling pathway and/or activation of CCR7 can increase the anti-apoptosis function of T cells and may become a new strategy to improve antitumor potential.

Expression of adenosine receptors in human retinal pigment epithelium cells in vitro

Background Adenosine receptors （ADORs） have been reported to play a role in experimental myopia. This study aimed to determine the distribution of ADORs in human retinal pigment epithelium （RPE） cells cultured in vitro.Methods Human RPE cells （cell line D407） were cultured in vitro. ADOR mRNA in RPE was detected by reverse transcription polymerase chain reaction. ADOR protein expression in RPE was confirmed by Western blotting analysis of cell lysates. Confocal fluorescence microscopy was used to study the subcellular distribution of ADORs.Results All four subtypes of ADORs mRNA and protein were expressed in human RPE. This was confirmed by Western blotting analysis. The ADOR subtypes were differently distributed within the cells. ADORA1 was expressed in nucleus, perinucleus and cytoplasm of RPE. ADORA2A was concentrated mainly in one side of the perinucleus and cytoplasm of RPE. ADORA2B was strongly expressed in the nucleus, perinucleus and the cytoplasm, and ADORA3 was expressed weakly in the cytoplasm of RPE.Conclusions ADORs are expressed in human RPE. The different distribution at the subcellular level suggests different functions of ADOR subtypes.

Motor Effects of 1,3-Disubstituted 8-Styrylxanthines as A_(1) and A_(2) Adenosine-Receptor Antagonists in Rats

A series of 1,3-substituted 8-styrylxanthines (11a-d) was synthesized, under chemo- and regioselective conditions, in a good overall yield. The compounds showed affinity towards both A1 and A2A-adenosine receptors by radioligand binding by means of in vitro assays. The (E)-3-ethyl-1-propyl-8-styrylxanthine (11a) showed the greatest affinity towards the A2A receptor, whereas (E)-3-pentyl-1-propyl-8-styrylxanthine (11d) showed the greatest affinity for the A1 receptor. When the 8-styrylxanthines 11a (A15Et) and 11c (A15Bu) were administrated in rats, which were previously injured with 6-hydroxydopamine at the substantia nigra pars compacta (SNc), the turning behavior decreased 50%. Based on these results we propose to A15Et as a potential compound to treat some symptoms of Parkinson’s disease.

Electroacupuncture-induced neuroprotection against focal cerebral ischemia in the rat is mediated by adenosine A1 receptors

The activation of adenosine A1 receptors is important for protecting against ischemic brain injury and pretreatment with electroacupuncture has been shown to mitigate ischemic brain insult. The aim of this study was to test whether the adenosine A1 receptor mediates electroacupuncture pretreatment-induced neuroprotection against ischemic brain injury. We first performed 30 minutes of electroacupuncture pretreatment at the Baihui acupoint（GV20）, delivered with a current of 1 mA, a frequency of 2/15 Hz, and a depth of 1 mm. High-performance liquid chromatography found that adenosine triphosphate and adenosine levels peaked in the cerebral cortex at 15 minutes and 120 minutes after electroacupuncture pretreatment, respectively. We further examined the effect of 15 or 120 minutes electroacupuncture treatment on ischemic brain injury in a rat middle cerebral artery-occlusion model. We found that at 24 hours reperfusion,120 minutes after electroacupuncture pretreatment, but not for 15 minutes, significantly reduced behavioral deficits and infarct volumes. Last, we demonstrated that the protective effect gained by 120 minutes after electroacupuncture treatment before ischemic injury was abolished by pretreatment with the A1-receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine（1 mg/kg, intraperitoneally）. Our results suggest that pretreatment with electroacupuncture at the Baihui acupoint elicits protection against transient cerebral ischemia via action at adenosine A1 receptors.

Upregulated adenosine 2A receptor accelerates post-infectious irritable bowel syndrome by promoting CD4+T cells’T helper 17 polarization

BACKGROUND Post-infectious irritable bowel syndrome(PI-IBS)is generally regarded as a functional disease.Several recent studies have reported the involvement of lowgrade inflammation and immunological dysfunction in PI-IBS.T helper 17(Th17)polarization occurs in IBS.Adenosine and its receptors participate in intestinal inflammation and immune regulation.AIM To investigate the role of Th17 polarization of CD4+T cells regulated by adenosine 2A receptor(A2AR)in PI-IBS.METHODS A PI-IBS model was established by infecting mice with Trichinella spiralis.The intestinal A2AR and CD4+T lymphocytes were detected by immunohistochemistry,and the inflammatory cytokines were detected by enzyme-linked immunoassay.CD4+T lymphocytes present in the animal’s spleen were separated and cultured with or without A2AR agonist and antagonist.Western blotting and real-time quantitative polymerase chain reaction were performed to determine the effect of A2AR on the cells and intestinal tissue.Cytokine production was determined.The protein and mRNA levels of A2AR associated signaling pathway molecules were also evaluated.Furthermore,A2AR agonist and antagonist were injected into the mouse model and the clinical features were observed.RESULTS The PI-IBS mouse model showed increased expression of ATP and A2AR(P<0.05),and inhibition of A2AR improved the clinical features in PI-IBS,including the abdominal withdrawal reflex and colon transportation test(P<0.05).The number of intestinal CD4+T cells and interleukin-17(IL-17)protein levels increased during PI-IBS,which was reversed by administration of the A2AR antagonist(P<0.05).CD4+T cells expressed A2AR and produced IL-17 in vitro,which was regulated by the A2AR agonist and antagonist.The A2AR antagonist increased the production of IL-17 by CD4+T cells via the Janus kinase-signal transducer and activator of transcriptionreceptor-related orphan receptorγsignaling pathway.CONCLUSION The results of the present study suggested that the upregulation of A2AR increases PI-IBS by promoting the Th17 polarization of CD4+T cells.

Structural insight into the dual-antagonistic mechanism of AB928 on adenosine A_(2)receptors

The adenosine subfamily G protein-coupled receptors A_(2A)R and A_(2B)R have been identified as promising cancer immunotherapy candidates.One of the A_(2A)R/A_(2B)R dual antagonists,AB928,has progressed to a phaseⅡclinical trial to treat rectal cancer.However,the precise mechanism underlying its dual-antagonistic properties remains elusive.Herein,we report crystal structures of the A_(2A)R complexed with AB928 and a selective A_(2A)R antagonist 2-118.The structures revealed a common binding mode on A_(2A)R,wherein the ligands established extensive interactions with residues from the orthosteric and secondary pockets.In contrast,the cAMP assay and A_(2A)R and A_(2B)R molecular dynamics simulations indicated that the ligands adopted distinct binding modes on A_(2B)R.Detailed analysis of their chemical structures suggested that AB928 readily adapted to the A_(2B)R pocket,while 2-118 did not due to intrinsic differences.This disparity potentially accounted for the difference in inhibitory efficacy between A_(2B)R and A_(2A)R.This study serves as a valuable structural template for the future development of selective or dual inhibitors targeting A_(2A)R/A_(2B)R for cancer therapy.

Brain-derived neurotrophic factor signaling in the neuromuscular junction during developmental axonal competition and synapse elimination

During the development of the nervous system,there is an overproduction of neurons and synapses.Hebbian competition between neighboring nerve endings and synapses performing different activity levels leads to their elimination or strengthening.We have extensively studied the involvement of the brain-derived neurotrophic factor-Tropomyosin-related kinase B receptor neurotrophic retrograde pathway,at the neuromuscular junction,in the axonal development and synapse elimination process versus the synapse consolidation.The purpose of this review is to describe the neurotrophic influence on developmental synapse elimination,in relation to other molecular pathways that we and others have found to regulate this process.In particular,we summarize our published results based on transmitter release analysis and axonal counts to show the different involvement of the presynaptic acetylcholine muscarinic autoreceptors,coupled to downstream serine-threonine protein kinases A and C(PKA and PKC)and voltage-gated calcium channels,at different nerve endings in developmental competition.The dynamic changes that occur simultaneously in several nerve terminals and synapses converge across a postsynaptic site,influence each other,and require careful studies to individualize the mechanisms of specific endings.We describe an activity-dependent balance(related to the extent of transmitter release)between the presynaptic muscarinic subtypes and the neurotrophin-mediated TrkB/p75NTR pathways that can influence the timing and fate of the competitive interactions between the different axon terminals.The downstream displacement of the PKA/PKC activity ratio to lower values,both in competing nerve terminals and at postsynaptic sites,plays a relevant role in controlling the elimination of supernumerary synapses.Finally,calcium entry through L-and P/Q-subtypes of voltage-gated calcium channels(both channels are present,together with the N-type channel in developing nerve terminals)contributes to reduce transmitter release and promote withdrawal of the most unfavorable nerve terminals during elimination(the weakest in acetylcholine release and those that have already become silent).The main findings contribute to a better understanding of punishment-rewarding interactions between nerve endings during development.Identifying the molecular targets and signaling pathways that allow synapse consolidation or withdrawal of synapses in different situations is important for potential therapies in neurodegenerative diseases.

Targeting the adenosine A2A receptor for neuroprotection and cognitive improvement in traumatic brain injury and Parkinson's disease

Adenosine exerts its dual functions of homeostasis and neuromodulation in the brain by acting at mainly 2 G-protein coupled receptors,called A1 and A2A receptors.The adenosine A2A receptor(A2AR)antagonists have been clinically pursued for the last 2 decades,leading to final approval of the istradefylline,an A2AR antagonist,for the treatment of OFF-Parkinson's disease(PD)patients.The approval paves the way to develop novel therapeutic methods for A2AR antagonists to address 2 major unmet medical needs in PD and traumatic brain injury(TBI),namely neuroprotection or improving cognition.In this review,we first consider the evidence for aberrantly increased adenosine signaling in PD and TBI and the sufficiency of the increased A2AR signaling to trigger neurotoxicity and cognitive impairment.We further discuss the increasing preclinical data on the reversal of cognitive deficits in PD and TBI by A2AR antagonists through control of degenerative proteins and synaptotoxicity,and on protection against TBI and PD pathologies by A2AR antagonists through control of neuroinflammation.Moreover,we provide the supporting evidence from multiple human prospective epidemiological studies which revealed an inverse relation between the consumption of caffeine and the risk of developing PD and cognitive decline in aging population and Alzheimer's disease patients.Collectively,the convergence of clinical,epidemiological and experimental evidence supports the validity of A2AR as a new therapeutic target and facilitates the design of A2AR antagonists in clinical trials for disease-modifying and cognitive benefit in PD and TBI patients.

The inhibitory effect of adenosine on tumor adaptive immunity and intervention strategies

Adenosine(Ado)is significantly elevated in the tumor microenvironment(TME)compared to normal tissues.It binds to adenosine receptors(AdoRs),suppressing tumor antigen presentation and immune cell activation,thereby inhibiting tumor adaptive immunity.Ado downregulates major histocompatibility complex II(MHC II)and co-stimulatory factors on dendritic cells(DCs)and macrophages,inhibiting antigen presentation.It suppresses anti-tumor cytokine secretion and T cell activation by disrupting T cell receptor(TCR)binding and signal transduction.Ado also inhibits chemokine secretion and KCa3.1 channel activity,impeding effector T cell trafficking and infiltration into the tumor site.Furthermore,Ado diminishes T cell cytotoxicity against tumor cells by promoting immune-suppressive cytokine secretion,upregulating immune checkpoint proteins,and enhancing immune-suppressive cell activity.Reducing Ado production in the TME can significantly enhance anti-tumor immune responses and improve the efficacy of other immunotherapies.Preclinical and clinical development of inhibitors targeting Ado generation or AdoRs is underway.Therefore,this article will summarize and analyze the inhibitory effects and molecular mechanisms of Ado on tumor adaptive immunity,as well as provide an overview of the latest advancements in targeting Ado pathways in anti-tumor immune responses.

Bone-derived MSCs encapsulated in alginate hydrogel prevent collagen-induced arthritis in mice through the activation of adenosine A_(2A/2B)receptors in tolerogenic dendritic cells

Tolerogenic dendritic cells(tol DCs)facilitate the suppression of autoimmune responses by differentiating regulatory T cells(Treg).The dysfunction of immunotolerance results in the development of autoimmune diseases,such as rheumatoid arthritis(RA).As multipotent progenitor cells,mesenchymal stem cells(MSCs),can regulate dendritic cells(DCs)to restore their immunosuppressive function and prevent disease development.However,the underlying mechanisms of MSCs in regulating DCs still need to be better defined.Simultaneously,the delivery system for MSCs also influences their function.Herein,MSCs are encapsulated in alginate hydrogel to improve cell survival and retention in situ,maximizing efficacy in vivo.The three-dimensional co-culture of encapsulated MSCs with DCs demonstrates that MSCs can inhibit the maturation of DCs and the secretion of pro-inflammatory cytokines.In the collagen-induced arthritis(CIA)mice model,alginate hydrogel encapsulated MSCs induce a significantly higher expression of CD39^(+)CD73^(+)on MSCs.These enzymes hydrolyze ATP to adenosine and activate A_(2A/2B)receptors on immature DCs,further promoting the phenotypic transformation of DCs to tol DCs and regulating naive T cells to Tregs.Therefore,encapsulated MSCs obviously alleviate the inflammatory response and prevent CIA progression.This finding clarifies the mechanism of MSCs-DCs crosstalk in eliciting the immunosuppression effect and provides insights into hydrogel-promoted stem cell therapy for autoimmune diseases.

Role of adenosine in tumor progression: focus on A_(2B) receptor as potential therapeutic target

Adenosine receptors are a family of G-coupled receptors which mediate the anti-inflammatory and immune-suppressive effects of adenosine in a damaged tissue.A large number of evidence indicate that the accumulation of adenosine under hypoxic conditions favors tumor progression,helping cancer cells to evade immune responses.Tumor cells and/or lymphoid and myeloid cells can express the adenosine-generating enzyme CD73 and/or A2A receptor,which in turn strongly suppresses an effective T-cell-mediated response,while promotes the activity of suppressive cells such as Treg and myeloid-derived suppressor cells.CD73 inhibitors and A2A antagonists,either as single agents,or in combination with immune-checkpoints inhibitors such as anti PD-1 monoclonal antibodies,are currently in Phase I clinical trial in cancer patients.Recent studies show that A2B receptor plays an important role in mediating the pro-tumor effects of adenosine,since its selective blockade can inhibit tumor growth in some murine tumor models.Targeting A2B receptor reduces immunosuppression induced by myeloid cells and inhibits the stromal cells activity within the tumor microenvironment,limiting tumor angiogenesis and metastatic processes.Here,the authors review the current data on involvement of A2B receptor in regulating tumor progression and discuss the development of A2B receptor inhibitors as potential therapeutic agents in cancer treatment.

Connexins in neurons and glia: targets for intervention in disease and injury

Both neurons and glia throughout the central nervous system are organized into networks by gap junctions. Among glia, gap junctions facilitate metabolic homeostasis and intercellular communication. Among neurons, gap junctions form electrical synapses that function primarily for communication. However, in neurodegenerative states due to disease or injury gap junctions may be detrimental to survival. Electrical synapses may facilitate hyperactivity and bystander killing among neurons, while gap junction hemichannels in glia may facilitate inflammatory signaling and scar formation. Advances in understanding mechanisms of plasticity of electrical synapses and development of molecular therapeutics to target glial gap junctions and hemichannels offer new hope to pharmacologically limit neuronal degeneration and enhance recovery.

Glycolysis in energy metabolism during seizures

Studies have shown that glycolysis increases during seizures, and that the glycolytic metabolite lactic acid can be used as an energy source. However, how lactic acid provides energy for seizures and how it can participate in the termination of seizures remains unclear. We reviewed possible mechanisms of glycolysis involved in seizure onset. Results showed that lactic acid was involved in seizure onset and provided energy at early stages. As seizures progress, lactic acid reduces the pH of tissue and induces metabolic acidosis, which terminates the seizure. The specific mechanism of lactic acid-induced acidosis involves several aspects, which include lactic acid-induced inhibition of the glycolytic enzyme 6-diphosphate kinase-1, inhibition of the N-methyl-D-aspartate receptor, activation of the acid-sensitive 1A ion channel, strengthening of the receptive mechanism of the inhibitory neurotransmitter Y-aminobutyric acid, and changes in the intra- and extracellular environment.

The plant hormone zeatin riboside inhibits T lymphocyte activity via adenosine A2A receptor activation

Cytokinins are plant hormones that play an integral role in multiple aspects of plant growth and development. The biological functions of cytokinins in mammalian systems are, however, largely uncharacterized. The naturally occurring cytokinin zeatin riboside has recently been demonstrated to activate the mammalian adenosine A2A receptor, which is broadly expressed by various cell types including immune system cells, with the activation of the A2AR playing a role in the regulation of cells involved in both innate and adaptive immunity. We show for the first time that zeatin riboside modulates mammalian immune system activity via an A2AR-dependent mechanism. Specifically, zeatin riboside treatment induces the production of cyclic adenosine monophosphate （cAMP） by T lymphocytes and inhibits the production by CD3^＋CD4^＋ T cells of interferon （IFN）-γ, IL-2, tumor-necrosis factor （TNF）-α, IL-4 and IL-13, and the production by CD3^＋CD8^＋ T cells of IFN-γ, IL-2 and TNF-α. Additionally, the upregulation of CD25, CD69 and CD40L by activated T lymphocytes is modulated by zeatin riboside. Zeatin riboside treatment also potently inhibits thioglycollate-induced peritoneal leukocytosis. The immunomodulatory activities of zeatin riboside are blocked by co-treatment with the selective A2AR antagonist ZM241385. These data suggest that zeatin riboside possesses therapeutic potential as a mammalian immunomodulatory agent.