Effect of A2B adenosine receptor gene ablation on proinflammatory adenosine signaling in mast cells

Pharmacological studies suggest that A(2B) adenosine receptors mediate proinflammatory effects of adenosine in human mast cells in part by up-regulating production of Th2 cytokines and angiogenic factors. This concept has been recently challenged by the finding that mast cells cultured from bone marrow-derived mast cells (BMMCs) of A(2B) knockout mice display an enhanced degranulation in response to FcepsilonRI stimulation. This finding was interpreted as evidence of anti-inflammatory functions of A(2B) receptors and it was suggested that antagonists with inverse agonist activity could promote activation of mast cells. In this report, we demonstrate that genetic ablation of the A(2B) receptor protein has two distinct effects on BMMCs, one is the previously reported enhancement of Ag-induced degranulation, which is unrelated to adenosine signaling; the other is the loss of adenosine signaling via this receptor subtype that up-regulates IL-13 and vascular endothelial growth factor secretion. Genetic ablation of A(2B) receptors had no effect on A(3) adenosine receptor-dependent potentiation of Ag-induced degranulation in mouse BMMCs, but abrogated A(2B) adenosine receptor-dependent stimulation of IL-13 and vascular endothelial growth factor secretion. Adenosine receptor antagonists MRS1706 and DPCPX with known inverse agonist activity at the A(2B) subtype inhibited IL-13 secretion induced by the adenosine analog NECA, but did not mimic the enhanced Ag-induced degranulation observed in A(2B) knockout BMMCs. Thus, our study confirmed the proinflammatory role of adenosine signaling via A(2B) receptors and the anti-inflammatory actions of A(2B) antagonists in mouse BMMCs.     

Differential effect of adenosine on tumor and normal cell growth: focus on the A3 adenosine receptor

Adenosine is an ubiquitous nucleoside present in all body cells. It is released from metabolically active or stressed cells and subsequently acts as a regulatory molecule through binding to specific A1, A2A, A2B and A3 cell surface receptors. The synthesis of agonists and antagonists to the adenosine receptors and their cloning enabled the exploration of their physiological functions. As nearly all cells express specific adenosine receptors, adenosine serves as a physiological regulator and acts as a cardioprotector, neuroprotector, chemoprotector, and as an immunomodulator. At the cellular level, activation of the receptors by adenosine initiates signal transduction mechanisms through G-protein associated receptors. Adenosine's unique characteristic is to differentially modulate normal and transformed cell growth, depending upon its extracellular concentration, the expression of adenosine cell surface receptors, and the physiological state of the target cell. Stimulation of cell proliferation following incubation with adenosine has been demonstrated in a variety of normal cells in the range of low micromolar concentrations, including mesangial and thymocyte cells, Swiss mouse 3T3 fibroblasts, and bone marrow cells. Induction of apoptosis in tumor or normal cells was shown at higher adenosine concentrations (>100 microM) such as in leukemia HL-60, lymphoma U-937, A431 epidermoid cells, and GH3 tumor pituitary cell lines. It was further noted that the A3 adenosine receptor (A3AR) plays a key role in the inhibitory and stimulatory growth activities of adenosine. Modulation of the A3AR was found to affect cell growth either positively or negatively depending on the concentration of the agonist, similar to the effect described for adenosine. At nanomolar concentrations, the A3AR agonists possess dual activity, i.e., antiproliferative activity toward tumor cells and stimulatory effect on bone marrow cells. In vivo, these agonists exerted anti-cancer effects, and when given in combination with chemotherapy, they enhanced the chemotherapeutic index and acted as chemoprotective agents. Taken together, activation of the A3AR, by minute concentrations of its natural ligand or synthetic agonists, may serve as a new approach for cancer therapy.     

(3)H]Adenosine uptake in brainstem membranes of CD-1 mice lacking the adenosine A(2a) receptor

Previous studies in our laboratory have demonstrated a decrease in [(3)H]nitrobenzylthioinosine binding sites in the brainstem of adenosine A(2a) receptor knockout mice, particularly in the brain nuclei involved in central control of cardiovascular function [Brain Research 877 (2000) 160]. The present study aimed to correlate this decrease, shown using autoradiography, with a functional change using a previously described method of [(3)H]adenosine uptake in a membrane preparation from the brainstem of wildtype CD - 1 and homozygous mutant mice lacking the adenosine A(2a) receptor. A statistically significant decrease was shown in the mean V(MAX) value obtained from homozygous mutant preparations (4.7 +/- 1.3 fmol/mg protein/20 s, P < 0.05, n = 4) compared to that obtained from wildtype controls (51.6 +/- 4.2 fmol/mg protein/20 s, n = 4). Competition studies using nucleoside uptake inhibitors showed a statistically significant increase in the log IC(50) values for dipyridamole (Wildtype: -4.3 +/- 0.2, Homozygous mutant: -8.3 +/- 0.4, n=5, P < 0.05) and dilazep (Wildtype: -3.9 +/- 0.8, Homozygous mutant: -8.3 +/- 0.8, n=5, P < 0.05) in the preparations using homozygous mutant tissue. The present study, in conjunction with the results of previous studies [Brain Research 877 (2000) 160], indicates that components of purinergic neurotransmission system have apparently adjusted in compensation for the lack of the A(2a) receptor.     

Changes of adenosine and its A(1) receptor in hypoxic preconditioning.

Effects of hypoxic preconditioning on adenosine (ADO) and its A(1) receptor were studied in Kunming mice. The ADO content and its metabolites in the brain were measured by a specific enzymatic method; a radioligand binding method was used to study the ADO A(1) receptor. The ADO content of the hippocampus in group C (exposure to 4 runs of hypoxia) was markedly higher than that in group A (control, without exposure to hypoxia and B (exposure to 1 run of hypoxia), showing that the ADO content could be cumulatively increased in the hippocampus, which was more sensitive to ischemia and hypoxia, during acute and repeated exposure to hypoxia. A(1) receptor density in group C was significantly lower than in group A and no difference was seen between groups B and C; A(1) receptor affinity in the hippocampus, pons and medula oblongata in group C was significantly higher than in group A, implying that during hypoxic preconditioning there might be some mechanisms preventing A(1) receptor density from decreasing further and making A(1) receptor affinity increase in some brain regions. These results indicate that cumulatively increased ADO in the hippocampus via A(1) receptor may play a neuroprotective role in the CNS as an inhibitory neuromodulator and thus contribute to the formation and development of acute hypoxic adaptation or tolerance.     

A3 adenosine receptor signaling contributes to airway inflammation and mucus production in adenosine deaminase-deficient mice

Adenosine signaling has been implicated in chronic lung diseases such as asthma and chronic obstructive pulmonary disease; however, the specific roles of the various adenosine receptors in processes central to these disorders are not well understood. In this study, we have investigated the role(s) of the A(3) adenosine receptor in adenosine-dependent pulmonary inflammation observed in adenosine deaminase (ADA)-deficient mice. The A(3) receptor (A(3)R) was found to be expressed in eosinophils and mucus-producing cells in the airways of ADA-deficient mice. Treatment of ADA-deficient mice with MRS 1523, a selective A(3)R antagonist, prevented airway eosinophilia and mucus production. Similar findings were seen in the lungs of ADA/A(3) double knockout mice. Although eosinophils were decreased in the airways of ADA-deficient mice following antagonism or removal of the A(3)R, elevations in circulating and lung interstitial eosinophils persisted, suggesting signaling through the A(3)R is needed for the migration of eosinophils into the airways. These findings identify an important role for the A(3)R in regulating lung eosinophilia and mucus production in an environment of elevated adenosine.     

Disruption of the kinin B1 receptor gene affects potentiating effect of captopril on BK-induced contraction in mice stomach fundus

A transgenic mouse model, deficient in kinin B₁ receptor (B₁^−/−) was used to evaluate the role of B₂ receptor in the smooth muscle stomach fundus. The results showed that the potency of bradykinin (BK) to induce contraction in the gastric tissue was maintained whereas the efficacy was markedly reduced. The angiotensin converting enzyme (ACE) inhibitor captopril potentiated BK-induced effect in wild type (WT) but not in B₁^−/− fundus. However, ACE activity detected by the convertion of Ang I to Ang II was inhibited by captopril in both types of gastric tissues. Taking into account the hypothesis that captopril and ACE bind to the B₂ receptor, we suggest that this complex was not formed in the stomach deficient in B₁ receptor. Therefore, our finding strongly support the hypothesis that in smooth muscles that constitutively express the kinin B₁ and B₂ receptors, an interaction between captopril and ACE, B₁ and B₂ receptors should occur forming a complex protein interaction for the potentiating effect of ACE on kinin receptors.     

A(3) adenosine receptor deficiency does not influence atherogenesis

Atherosclerosis is a multifactorial disease, the progression of which is modulated by several factors, including inflammation and hypercholesterolemia. The A(3) adenosine receptor (A(3)AR) has been reported to affect mast cell degranulation leading to inflammation, as well as to influence cardiovascular homeostasis. Here, we show that its deletion can also impact vascular smooth muscle cell (VSMC) proliferation in vitro. Based on these observations, we hypothesized that A(3)AR deficiency would affect atheromatous lesion development in vivo. Our results indicate that the expression of the matrix enzyme lysyl oxidase (LO) is increased while the proliferation potential of VSMC is decreased in A(3)AR-null aortas. This is in accordance with the previously reported inverse correlation between LO level and proliferation. Nevertheless, we found that A(3)-deficiency does not protect vessels against atherogenesis. This was demonstrated in mouse models of high fat diet-induced atherosclerosis and guidewire-induced femoral artery injury. We conclude that the contributions of the A(3)AR to inflammation and to modulating LO levels are not significant enough to control vascular response to injury.     

Molecular modeling study on potent and selective adenosine A(3) receptor agonists

Adenosine A(3) receptor (A(3)AR) is involved in a variety of key physio-pathological processes and its agonists are potential therapeutic agents for the treatment of rheumatoid arthritis, dry eye disorders, asthma, as anti-inflammatory agents, and in cancer therapy. Recently reported MECA (5'-N-methylcarboxamidoadenosine) derivatives bearing a methyl group in N(6)-position and an arylethynyl substituent in 2-position demonstrated to possess sub-nanomolar affinity and remarkable selectivity for the human A(3)AR, behaving as full agonists of this receptor. In this study, we made an attempt to get a rationalization of the high affinities and selectivities of these molecules for the human A(3)AR, by using adenosine receptor (AR) structural models based on the A(2A)AR crystal structure and molecular docking analysis. Post-docking analysis allowed to evaluate the ability of modeling tools in predicting AA(3)R affinity and in providing interpretation of compound substituents effect on the A(3)AR affinity and selectivity.     

Disruption of nuclear vitamin D receptor gene causes enhanced thrombogenicity in mice

Vitamin D metabolites influence the expression of various genes involved in calcium homeostasis, cell differentiation, and regulation of the immune system. Expression of these genes is mediated by the activation of the nuclear vitamin D receptor (VDR). Previous studies have shown that a hormonally active form of vitamin D, 1alpha,25-dihydroxyvitamin D3, exerts anticoagulant effects in cultured monocytic cells. To clarify whether activation of VDR plays any antithrombotic actions in vivo, hemostatic/thrombogenic systems were examined in normocalcemic VDR knock-out (KO) mice on a high calcium diet and compared with wild type and hypocalcemic VDRKO mice that were fed a regular diet. Platelet aggregation was enhanced significantly in normocalcemic VDRKO mice compared with wild type and hypocalcemic VDRKO mice. Aortic endothelial nitric-oxide (NO) synthase expression and urinary NOx excretions were reduced in hypocalcemic VDRKO mice, but not in normocalcemic VDRKO mice. Northern blot and RT-PCR analyses revealed that the gene expression of antithrombin in the liver as well as that of thrombomodulin in the aorta, liver and kidney was down-regulated in hypo- and normocalcemic VDRKO mice. Whereas tissue factor mRNA expression in the liver and kidney was up-regulated in VDRKO mice regardless of plasma calcium level. Furthermore, VDRKO mice manifested an exacerbated multi-organ thrombus formation after exogenous lipopolysaccharide injection regardless of the calcemic conditions. These results demonstrate that activation of nuclear VDR elicits antithrombotic effects in vivo, and suggest that the VDR system may play a physiological role in the maintenance of antithrombotic homeostasis.     

Activation of murine lung mast cells by the adenosine A3 receptor

Adenosine has been implicated to play a role in asthma in part through its ability to influence mediator release from mast cells. Most physiological roles of adenosine are mediated through adenosine receptors; however, the mechanisms by which adenosine influences mediator release from lung mast cells are not understood. We established primary murine lung mast cell cultures and used real-time RT-PCR and immunofluorescence to demonstrate that the A(2A), A(2B), and A(3) adenosine receptors are expressed on murine lung mast cells. Studies using selective adenosine receptor agonists and antagonists suggested that activation of A(3) receptors could induce mast cell histamine release in association with increases in intracellular Ca(2+) that were mediated through G(i) and phosphoinositide 3-kinase signaling pathways. The function of A(3) receptors in vivo was tested by exposing mice to the A(3) receptor agonist, IB-MECA. Nebulized IB-MECA directly induced lung mast cell degranulation in wild-type mice while having no effect in A(3) receptor knockout mice. Furthermore, studies using adenosine deaminase knockout mice suggested that elevated endogenous adenosine induced lung mast cell degranulation by engaging A(3) receptors. These results demonstrate that the A(3) adenosine receptor plays an important role in adenosine-mediated murine lung mast cell degranulation.     

Putative role of the adenosine A3 receptor in the antiproliferative action of N 6-(2-isopentenyl)adenosine

We tested a panel of naturally occurring nucleosides for their affinity towards adenosine receptors. Both N ⁶-(2-isopentenyl)adenosine (IPA) and racemic zeatin riboside were shown to be selective human adenosine A₃ receptor (hA₃R) ligands with affinities in the high nanomolar range (K _i values of 159 and 649 nM, respectively). These values were comparable to the observed K _i value of adenosine on hA₃R, which was 847 nM in the same radioligand binding assay. IPA also bound with micromolar affinity to the rat A₃R. In a functional assay in Chinese hamster ovary cells transfected with hA₃R, IPA and zeatin riboside inhibited forskolin-induced cAMP formation at micromolar potencies. The effect of IPA could be blocked by the A₃R antagonist VUF5574. Both IPA and reference A₃R agonist 2-chloro-N ⁶-(3-iodobenzyl)adenosine-5′-N-methylcarboxamide (Cl-IB-MECA) have known antitumor effects. We demonstrated strong and highly similar antiproliferative effects of IPA and Cl-IB-MECA on human and rat tumor cell lines LNCaP and N1S1. Importantly, the antiproliferative effect of low concentrations of IPA on LNCaP cells could be fully blocked by the selective A₃R antagonist MRS1523. At higher concentrations, IPA appeared to inhibit cell growth by an A₃R-independent mechanism, as was previously reported for other A₃R agonists. We used HPLC to investigate the presence of endogenous IPA in rat muscle tissue, but we could not detect the compound. In conclusion, the antiproliferative effects of the naturally occurring nucleoside IPA are at least in part mediated by the A₃R.     

Inhibitory effect of KW-3902, an adenosine A(1) receptor antagonist, on p-aminohippurate transport in OK cells.

KW-3902 (8-(noradamantan-3-yl)-1,3-dipropylxanthine) is a novel potent and selective adenosine A(1) receptor antagonist. We examined the effect of KW-3902 on p-aminohippurate (PAH) transport in opossum kidney (OK) epithelial cells. Pretreatment for 3 h with KW-3902 inhibited the transcellular transport of PAH across OK cell monolayers from the basal to the apical side. The uptake of PAH across the basolateral membrane of OK cells was inhibited by KW-3902 pretreatment in a time- and concentration-dependent manner. A kinetic analysis revealed that the inhibitory effect of KW-3902 on the basolateral PAH uptake was due to an increase in the Michaelis constant (K(m)) as well as a decrease in the maximum uptake rate (V(max)), showing that the inhibition was a mixed type. Pretreatment with adenosine deaminase or 8-cyclopentyl-1,3-dipropylxanthine, another selective adenosine A(1) receptor antagonist, also decreased the basolateral PAH uptake. KW-3902 pretreatment had no effect on the concentration of intracellular alpha-ketoglutarate which exchanges for PAH across the basolateral membrane of OK cells. These results suggest that KW-3902 has an inhibitory effect on PAH transport in OK epithelial cells.     

腺苷A2a受体在博莱霉素诱导的小鼠肺纤维化中的作用

目的：观察腺苷A_2a受体（A_2aR）在小鼠肺纤维化形成中的调控作用。方法：30只雄性SPF级野生型BALB/C小鼠和20只A_2aR基因敲除BALB/C小鼠,随机分为以下5组：野生型小鼠对照组（A组）、野生型小鼠纤维化组（B组）、A_2aR基因敲除小鼠对照组（C组）、A_2aR基因敲除小鼠纤维化组（D组）、野生型小鼠纤维化+A_2aR激动剂（CGS21680）组（E组）,每组各10只。纤维化组小鼠气管内注入博莱霉素（bleomycin,BLM）溶液50μl （5 mg/kg体重）,对照组在气管内注入等体积生理盐水,注射后立即将小鼠直立旋转3~5 min,使其均匀分布于两肺。A、B、C、D各组每天腹腔注射生理盐水0.5 ml,E组每天腹腔注射A_2aR激动剂（CGS21680）0.5 ml （0.25 mg/kg体重）,连续28 d。第29天取血检测血清转化生长因子β1（TGF-β1）含量;检测肺组织中羟脯氨酸（hydroxyproline,Hyp）、TGF-β1和A_2aR蛋白质含量,TGF-β1 mRNA、A_2aR mRNA的表达,并观察肺组织光镜和超微结构。结果：①光镜和超微结构提示,B组肺泡壁增厚破坏,肺泡腔狭窄或部分陷闭,纤维增生,炎细胞浸润,I型、Ⅱ型肺泡上皮细胞明显空泡化,D组较B组明显,E组表现较B组减轻。Masson染色提示B组、D组小鼠肺组织纤维增生明显,E组明显减少,提示基因缺失加重了小鼠肺纤维化的形成。②与A组比较,B组血清TGF-β1含量,肺组织Hyp含量,TGF-β1、A_2aR蛋白质含量和TGF-β1 mRNA、A_2aR mRNA的表达均明显增高（P<0.01,P<0.05）。与C组比较,D组血清TGF-β1含量、肺组织Hyp、TGF-β1含量和TGF-β1 mRNA表达明显增高（P<0.01,P<0.05）,提示肺纤维化小鼠肺组织Hyp含量增高,TGF-β1表达上调。③与B组相比,D组血清TGF-β1、肺组织Hyp、TGF-β1含量和TGF-β1 mRNA表达明显增高（P<0.01）。与B组比较,E组A_2aR蛋白质含量和A_2aR mRNA的表达均增高（P<0.01）,而血清TGF-β1、肺组织Hyp和TGF-β1蛋白含量及TGF-β1 mRNA表达较B组明显下降（P<0.01,P<0.05）,提示A_2aR基因敲除小鼠肺组织Hyp含量增高、TGF-β1表达上调;A_2aR激动剂可使A_2aR表达上调、TGF-β1表达下降。结论：A_2aR基因敲除小鼠的肺纤维化明显增加。A_2aR在肺纤维化形成中反应性增高,可通过降低TGF-β1的表达而抑制肺纤维化形成。     

双酚A(BPA)与黑腹果蝇雌激素相关受体(dERR)的结合模式及对其基因表达的影响

【目的】雌激素相关受体(estrogen-related receptors, ERRs)属于核受体(nuclear receptor, NR)超家族,在昆虫新陈代谢和能量转换调节中发挥重要作用。双酚A(bisphenol A, BPA)与昆虫生殖和神经系统疾病有关。本研究旨在探究BPA影响黑腹果蝇Drosophila melanogaster ERR(dERR)的作用机理。【方法】通过AutoDock Vina模拟小分子BPA与Modeller 9.25构建的dERR蛋白的分子对接,使用Gromacs 5.1.9进行分子动力学模拟,并结合自由能的计算探究BPA与dERR的结合模式。利用qRT-PCR方法检测3种浓度(0.1, 1和10 μg/L) BPA处理6, 12和24 h对黑腹果蝇成虫和2龄幼虫中dERR基因转录水平的影响。【结果】通过分子对接和极性溶剂化能发现,Phe370及Leu334等侧链氨基酸是BPA与dERR结合的关键氨基酸。qRT-PCR分析显示,不同浓度的BPA处理6和12 h时黑腹果蝇成虫和2龄幼虫中dERR基因转录水平均发生显著变化,而0.1 μg/L BPA处理24 h时的几乎接近对照。【结论】BPA能够影响黑腹果蝇体内dERR的表达,作用机理可能跟BPA与dERR的潜在特异性结合有关。     

Genetic inactivation of the adenosine A(2A) receptor exacerbates brain damage in mice with experimental autoimmune encephalomyelitis

Studies with multiple sclerosis patients and animal models of experimental autoimmune encephalomyelitis (EAE) implicate adenosine and adenosine receptors in modulation of neuroinflammation and brain injury. Although the involvement of the A(1) receptor has been recently demonstrated, the role of the adenosine A(2A) receptor (A(2A) R) in development of EAE pathology is largely unknown. Using mice with genetic inactivation of the A(2A) receptor, we provide direct evidence that loss of the A(2A) R exacerbates EAE pathology in mice. Compared with wild-type mice, A(2A) R knockout mice injected with myelin oligodendroglia glycoprotein peptide had a higher incidence of EAE and exhibited higher neurological deficit scores and greater decrease in body weight. A(2A) R knockout mice displayed increased inflammatory cell infiltration and enhanced microglial cell activation in cortex, brainstem, and spinal cord. In addition, demyelination and axonal damage in brainstem were exacerbated, levels of Th1 cytokines increased, and Th2 cytokines decreased. Collectively, these findings suggest that extracellular adenosine acting at A(2A) Rs triggers an important neuroprotective mechanism. Thus, the A(2A) receptor is a potential target for therapeutic approaches to multiple sclerosis.     

Disruption of the gene encoding 3beta-hydroxysterol Delta-reductase (Tm7sf2) in mice does not impair cholesterol biosynthesis

Tm7sf2 gene encodes 3beta-hydroxysterol Delta(14)-reductase (C14SR, DHCR14), an endoplasmic reticulum enzyme acting on Delta(14)-unsaturated sterol intermediates during the conversion of lanosterol to cholesterol. The C-terminal domain of lamin B receptor, a protein of the inner nuclear membrane mainly involved in heterochromatin organization, also possesses sterol Delta(14)-reductase activity. The subcellular localization suggests a primary role of C14SR in cholesterol biosynthesis. To investigate the role of C14SR and lamin B receptor as 3beta-hydroxysterol Delta(14)-reductases, Tm7sf2 knockout mice were generated and their biochemical characterization was performed. No Tm7sf2 mRNA was detected in the liver of knockout mice. Neither C14SR protein nor 3beta-hydroxysterol Delta(14)-reductase activity were detectable in liver microsomes of Tm7sf2((-/-)) mice, confirming the effectiveness of gene inactivation. C14SR protein and its enzymatic activity were about half of control levels in the liver of heterozygous mice. Normal cholesterol levels in liver membranes and in plasma indicated that, despite the lack of C14SR, Tm7sf2((-/-)) mice are able to perform cholesterol biosynthesis. Lamin B receptor 3beta-hydroxysterol Delta(14)-reductase activity determined in liver nuclei showed comparable values in wild-type and knockout mice. These results suggest that lamin B receptor, although residing in nuclear membranes, may contribute to cholesterol biosynthesis in Tm7sf2((-/-)) mice. Affymetrix microarray analysis of gene expression revealed that several genes involved in cell-cycle progression are downregulated in the liver of Tm7sf2((-/-)) mice, whereas genes involved in xenobiotic metabolism are upregulated.