Biomedical subjects

Michael R Blackburn

Publications and source records attributed to Michael R Blackburn.

At least 19 recordsLinked to original sources

PubMed2007

Enhanced CXCL1 production and angiogenesis in adenosine-mediated lung disease.

Angiogenesis is a feature of chronic lung diseases such as asthma and pulmonary fibrosis; however, the pathways controlling pathological angiogenesis during lung disease are not completely understood. Adenosine is a signaling molecule that has been implicated in the exacerbation of chronic lung disease and in the regulation of angiogenesis; however, the relationship between these factors has not been investigated. The current study utilized adenosine deaminase (ADA)-deficient mice to determine whether chronic elevations in adenosine in vivo result in pulmonary angiogenesis. Results demonstrate substantial angiogenesis in the tracheas of ADA-deficient mice in association with adenosine elevations. ADA replacement enzyme therapy resulted in a lowering of adenosine levels and reversal of tracheal angiogenesis, indicating that the increases in vessel number are dependent on adenosine elevations. Levels of the angiogenic chemokine CXCL1 (mouse functional homologue of human IL-8) were found to be elevated in an adenosine-dependent manner in the lungs of ADA-deficient mice. Neutralization of CXCL1 and its receptor, CXCR2, resulted in the inhibition of angiogenic activity, which suggests that CXCL1 signaling through the CXCR2 receptor mediated the observed increases in angiogenesis. Our findings suggest that adenosine plays an important role, via CXCL1, in the induction of pulmonary angiogenesis.

Adenosine↗

PubMed2006

Modulation of ischaemic contracture in mouse hearts: a 'supraphysiological' response to adenosine.

While inhibition of ischaemic contracture was one of the first documented cardioprotective actions of exogenously applied adenosine, it is not known whether this is a normal function of endogenous adenosine generated during ischaemic stress. Additionally, the relevance of delayed contracture to postischaemic outcome is unclear. We tested the ability of endogenous versus exogenous adenosine to modify contracture (and postischaemic outcomes) in C57/Bl6 mouse hearts. During ischaemia, untreated hearts developed peak contracture (PC) of 85 +/- 5 mmHg at 8.9 +/- 0.8 min, with time to reach 20 mmHg (time to onset of contracture; TOC) of 4.4 +/- 0.3 min. Adenosine (50 microm) delayed TOC to 6.7 +/- 0.6 min, as did pretreatment with 10 microm 2-chloroadenosine (7.2 +/- 0.5 min) or 50 nm of A(1) adenosine receptor (AR) agonist N(6)-cyclohexyladenosine (CHA) (6.7 +/- 0.3 min), but not A(2A)AR or A(3)AR agonists (20 nm 2-[4-(2-carboxyethyl) phenethylamino]-5' N-methylcarboxamidoadenosine (CGS21680) or 150 nm 2-chloro-N(6)-(3-iodobenzyl)-adenosine-5'-N-methyluronamide (Cl-IB-MECA), respectively). Adenosinergic contracture inhibition was eliminated by A(1)AR gene knockout (KO), mimicked by A(1)AR overexpression, and was associated with preservation of myocardial [ATP]. This adenosine-mediated inhibition of contracture was, however, only evident after prolonged (10 or 15 min) and not brief (3 min) pretreatment. Ischaemic contracture was also insensitive to endogenously generated adenosine, since A(1)AR KO, and non-selective and A(1)AR-selective antagonists (50 microm 8-sulphophenyltheophylline and 150 nm 8-cyclopentyl-1, 3-dipropylxanthine (DPCPX), respectively), all failed to alter intrinsic contracture development. Finally, delayed contracture with A(1)AR agonism/overexpression or ischaemic 2,3-butanedione monoxime (BDM; 5 microm to target Ca(2+) cross-bridge formation) was linked to enhanced postischaemic outcomes. In summary, adenosinergic inhibition of contracture is solely A(1)AR mediated; the response is 'supraphysiological', evident only with significant periods of pre-ischaemic AR agonism (or increased A(1)AR density); and ischaemic contracture appears insensitive to locally generated adenosine, potentially owing to the rapidity of contracture development versus the finite time necessary for expression of AR-mediated cardioprotection.

2-Chloroadenosine↗

PubMed2006

A3 adenosine receptor signaling contributes to airway mucin secretion after allergen challenge.

Mucin hypersecretion is a prominent feature of obstructive airway diseases such as asthma. Clara cells conditionally produce mucin in response to inflammatory signals in a process termed mucous metaplasia. This can be followed by mucin secretion stimulated by various signaling molecules. The cellular and molecular mechanisms that regulate mucin production and secretion are not well understood. Adenosine is a signaling nucleoside that has been implicated in airway diseases in which mucus obstruction is prominent. Furthermore, the A(3) adenosine receptor (A(3)AR) is upregulated in mucin-producing goblet cells of the airway, thereby implicating it in processes involved in mucous cell biology. Here we use genetic approaches to investigate the contribution of A(3)AR signaling to mucus production and secretion in a mouse model of allergen-induced pulmonary disease. We found that the degree of mucin production in response to allergen is similar in wild-type and A(3)AR-deficient mice, and that overexpression of this receptor in Clara cells neither induces mucin production itself, nor enhances mucin production in response to allergen challenge. Collectively, these experiments demonstrate that the A(3)AR is neither necessary nor sufficient for mucous cell metaplasia. In contrast to the lack of effect on mucin production, agonist-induced mucin secretion was increased in goblet cells overexpressing the A(3)AR, and was absent in A(3)AR-deficient mice. Thus, the A(3)AR contributes to mucin secretion in allergen-induced metaplasia. Signaling through this receptor may contribute to mucus airway obstruction seen in pulmonary disorders in which adenosine levels are elevated.

Animals↗

PubMed2006

Further differentiation of murine double-positive thymocytes is inhibited in adenosine deaminase-deficient murine fetal thymic organ culture.

Murine fetal thymic organ culture (FTOC) was used to investigate the mechanism by which a lack of adenosine deaminase (ADA) leads to a failure of T cell production in the thymus. We previously showed that T cell development was inhibited beginning at the CD4(-)CD8(-)CD25(+)CD44(low) stage in ADA-deficient FTOC initiated at day 15 of gestation when essentially all thymocytes are CD4(-)CD8(-). In the present study, we asked whether thymocytes at later stages of differentiation would also be sensitive to ADA inhibition by initiating FTOC when substantial numbers of CD4(+)CD8(+) thymocytes were already present. dATP was highly elevated in ADA-deficient cultures, and the recovery of alphabeta TCR(+) thymocytes was inhibited by 94%, indicating that the later stages of thymocyte differentiation are also dependent upon ADA. ADA-deficient cultures were partially rescued by the pan-caspase inhibitor carbobenzoxy-Val-Ala-Asp-fluoromethyl ketone or by the use of apoptotic protease-activating factor-1-deficient mice. Rescue was even more dramatic, with 60- to >200-fold increases in the numbers of CD4(+)CD8(+) cells, when FTOC were performed with an inhibitor of adenosine kinase, the major thymic deoxyadenosine phosphorylating enzyme, or with bcl-2 transgenic mice. dATP levels were normalized by treatment with either carbobenzoxy-Val-Ala-Asp-fluoromethyl ketone or an adenosine kinase inhibitor, but not in cultures with fetal thymuses from bcl-2 transgenic mice. These data suggest that ADA deficiency leads to the induction of mitochondria-dependent apoptosis as a consequence of the accumulation of dATP derived from thymocytes failing the positive/negative selection checkpoint.

Adenosine Deaminase↗

PubMed2006

In vivo transduction by intravenous injection of a lentiviral vector expressing human ADA into neonatal ADA gene knockout mice: a novel form of enzyme replacement therapy for ADA deficiency.

Using a mouse model of adenosine deaminase-deficient severe combined immune deficiency syndrome (ADA-deficient SCID), we have developed a noninvasive method of gene transfer for the sustained systemic expression of human ADA as enzyme replacement therapy. The method of delivery is a human immunodeficiency virus 1-based lentiviral vector given systemically by intravenous injection on day 1 to 2 of life. In this article we characterize the biodistribution of the integrated vector, the expression levels of ADA enzyme activity in various tissues, as well as the efficacy of systemic ADA expression to correct the ADA-deficient phenotype in this mouse model. The long-term expression of enzymatically active ADA achieved by this method, primarily from transduction of liver and lung, restored immunologic function and significantly extended survival. These studies illustrate the potential for sustained in vivo production of enzymatically active ADA, as an alternative to therapy by frequent injection of exogenous ADA protein.

Adenosine Deaminase↗

PubMed2006

Ecto-5'-nucleotidase (CD73)-mediated adenosine production is tissue protective in a model of bleomycin-induced lung injury.

Adenosine signaling has diverse actions on inflammation and tissue injury. Levels of adenosine are rapidly elevated in response to tissue injury; however, the mechanisms responsible for adenosine production in response to injury are not well understood. In this study, we found that adenosine levels are elevated in the lungs of mice injured by the drug bleomycin. In addition, increased activity of ecto-5'-nucleotidase (CD73) was found in the lungs in conjunction with adenosine elevations. To determine the contribution of CD73 to the generation of adenosine in the lung, CD73(-/-) mice were subjected to bleomycin challenges. Results demonstrated that CD73(-/-) mice challenged with bleomycin no longer accumulated adenosine in their lungs, suggesting that the primary means of adenosine production following bleomycin injury resulted from the release and subsequent dephosphorylation of adenine nucleotides. CD73(-/-) mice challenged with bleomycin exhibited enhanced pulmonary inflammation and fibrosis as well as exaggerated expression of proinflammatory and profibrotic mediators in the lung. Intranasal instillations of exogenous nucleotidase restored the ability of lungs of CD73(-/-) mice to accumulate adenosine following bleomycin challenge. Furthermore, these treatments were associated with a decrease in pulmonary inflammation and fibrosis. CD73(+/+) animals challenged with bleomycin and supplemented with exogenous nucleotidase also exhibited reduced inflammation. Together, these findings suggest that CD73-dependent adenosine production contributes to anti-inflammatory pathways in bleomycin-induced lung injury.

5'-Nucleotidase↗

PubMed2006

Effects of adenosine deaminase and A1 receptor deficiency in normoxic and ischaemic mouse hearts.

OBJECTIVE: Adenosine deaminase (ADA) may be multifunctional, regulating adenosine levels and adenosine receptor (AR) agonism, and potentially modifying AR functionality. Herein we assess effects of ADA (and A1AR) deficiency on AR-mediated responses and ischaemic tolerance. METHODS: Normoxic function and responses to 20 or 25 min ischaemia and 45 min reperfusion were studied in isolated hearts from wild-type mice and from mice deficient in ADA and/or A1ARs. RESULTS: Neither ADA or A1AR deficiency significantly modified basal contractility, although ADA deficiency reduced resting heart rate (an effect abrogated by A1AR deficiency). Bradycardia and vasodilation in response to AR agonism (2-chloroadenosine) were unaltered by ADA deficiency, while A1AR deficiency eliminated the heart rate response. Adenosine efflux increased 10- to 20-fold with ADA deficiency (at the expense of inosine). Deletion of ADA improved outcome from 25 min ischaemia, reducing ventricular diastolic pressure (by 45%; 21+/-4 vs. 38+/-3mm Hg) and lactate dehydrogenase (LDH) efflux (by 40%; 0.12+/-0.01 vs. 0.21+/-0.02 U/g/min ischaemia), and enhancing pressure development (by 35%; 89+/-6 vs. 66+/-5mm Hg). Similar protection was evident after 20 min ischaemia, and was mimicked by the ADA inhibitor EHNA (5 microM). Deletion of ADA also enhanced tolerance in A1AR deficient hearts, though effects on diastolic pressure were eliminated. CONCLUSIONS: Deficiency of ADA does not alter sensitivities of cardiovascular A1 or A2ARs (despite markedly elevated [adenosine]), but significantly improves ischaemic tolerance. Conversely, A1AR deficiency impairs ischaemic tolerance. Effects of ADA deficiency on diastolic pressure appear solely A1AR-dependent while other ARs or processes additionally contribute to improved contractile recovery and reduced cell death.

2-Chloroadenosine↗

PubMed2006

Constant darkness is a circadian metabolic signal in mammals.

Environmental light is the 'zeitgeber' (time-giver) of circadian behaviour. Constant darkness is considered a 'free-running' circadian state. Mammals encounter constant darkness during hibernation. Ablation of the master clock synchronizer, the suprachiasmatic nucleus, abolishes torpor, a hibernation-like state, implicating the circadian clock in this phenomenon. Here we report a mechanism by which constant darkness regulates the gene expression of fat catabolic enzymes in mice. Genes for murine procolipase (mClps) and pancreatic lipase-related protein 2 (mPlrp2) are activated in a circadian manner in peripheral organs during 12 h dark:12 h dark (DD) but not light-dark (LD) cycles. This mechanism is deregulated in circadian-deficient mPer1-/-/mPer2m/m mice. We identified circadian-regulated 5'-AMP, which is elevated in the blood of DD mice, as a key mediator of this response. Synthetic 5'-AMP induced torpor and mClps expression in LD animals. Torpor induced by metabolic stress was associated with elevated 5'-AMP levels in DD mice. Levels of glucose and non-esterified fatty acid in the blood are reversed in DD and LD mice. Induction of mClps expression by 5'-AMP in LD mice was reciprocally linked to blood glucose levels. Our findings uncover a circadian metabolic rhythm in mammals.

Adenosine Monophosphate↗

PubMed2006

Adenosine signaling in asthma and chronic obstructive pulmonary disease.

PURPOSE OF REVIEW: The chronic lung diseases, asthma and chronic obstructive pulmonary disease, are pulmonary disorders in which persistent inflammation and alterations in lung structure contribute to a progressive loss of lung function. Although the exact type of inflammation and damage in each disease is distinct, they share the common feature that they are chronic in nature. Despite efforts, little is known about the cellular and molecular mechanisms that drive the chronicity of these two diseases. This review will summarize important findings regarding the role of adenosine, a signaling nucleoside implicated in the pathogenesis of these two disorders. RECENT FINDINGS: Aerosolized adenosine induces bronchoconstriction in patients with asthma and chronic obstructive pulmonary disease primarily through the release of mast cell mediators. In this setting it can not only be used to aid in diagnosis but also to monitor patient responses to steroid therapy. Adenosine levels are elevated in the lungs of asthma patients, indicating greater flux through adenosine receptor signaling pathways. In-vitro studies have shown adenosine to access pathways leading to the genesis of chronic inflammation via the release of proinflammatory cytokines and chemokines. Animal studies demonstrate that merely elevating adenosine levels in the mouse is sufficient to induce a pulmonary phenotype with features of asthma and chronic obstructive pulmonary disease. SUMMARY: Identifying mediators regulating the chronic nature of asthma and chronic obstructive pulmonary disease is critical towards advancements in treatment options. Adenosine has been implicated in promoting the inflammation and airway remodeling seen in chronic lung disease and thus makes an attractive therapeutic target.

Adenosine↗

PubMed2006

Adenosine metabolism and murine strain-specific IL-4-induced inflammation, emphysema, and fibrosis.

To define the factors that control the tissue effects of IL-4, we compared the effects of Tg IL-4 in Balb/c and C57BL/6 mice. In the former, IL-4 caused modest eosinophilic inflammation and mild airway fibrosis and did not shorten survival. In C57BL/6 mice, IL-4 caused profound eosinophilic inflammation, airway fibrosis, emphysematous alveolar destruction, and premature death. These differences could not be accounted for by changes in Th2 or Th1 cytokines, receptor components, STAT6 activation, MMPs, or cathepsins. In contrast, in C57BL/6 mice, alveolar remodeling was associated with decreased levels of tissue inhibitors of metalloproteinase 2, -3, and -4 and alpha1-antitrypsin, and fibrosis was associated with increased levels of total and bioactive TGF-beta1. Impressive differences in adenosine metabolism were also appreciated, with increased tissue adenosine levels and A(1), A(2B), and A(3) adenosine receptor expression and decreased adenosine deaminase (ADA) activity in C57BL/6 animals. Treatment with ADA also reduced the inflammation, fibrosis, and emphysematous destruction and improved the survival of C57BL/6 Tg animals. These studies demonstrate that genetic influences control IL-4 effector pathways in the murine lung. They also demonstrate that IL-4 has different effects on adenosine metabolism in Balb/c and C57BL/6 mice and that these differences contribute to the different responses that IL-4 induces in these inbred animals.

Adenosine↗

PubMed2006

Role of A2B adenosine receptor signaling in adenosine-dependent pulmonary inflammation and injury.

Adenosine has been implicated in the pathogenesis of chronic lung diseases such as asthma and chronic obstructive pulmonary disease. In vitro studies suggest that activation of the A2B adenosine receptor (A2BAR) results in proinflammatory and profibrotic effects relevant to the progression of lung diseases; however, in vivo data supporting these observations are lacking. Adenosine deaminase-deficient (ADA-deficient) mice develop pulmonary inflammation and injury that are dependent on increased lung adenosine levels. To investigate the role of the A2BAR in vivo, ADA-deficient mice were treated with the selective A2BAR antagonist CVT-6883, and pulmonary inflammation, fibrosis, and airspace integrity were assessed. Untreated and vehicle-treated ADA-deficient mice developed pulmonary inflammation, fibrosis, and enlargement of alveolar airspaces; conversely, CVT-6883-treated ADA-deficient mice showed less pulmonary inflammation, fibrosis, and alveolar airspace enlargement. A2BAR antagonism significantly reduced elevations in proinflammatory cytokines and chemokines as well as mediators of fibrosis and airway destruction. In addition, treatment with CVT-6883 attenuated pulmonary inflammation and fibrosis in wild-type mice subjected to bleomycin-induced lung injury. These findings suggest that A2BAR signaling influences pathways critical for pulmonary inflammation and injury in vivo. Thus in chronic lung diseases associated with increased adenosine, antagonism of A2BAR-mediated responses may prove to be a beneficial therapy.

Adenosine↗

PubMed2005

Partially adenosine deaminase-deficient mice develop pulmonary fibrosis in association with adenosine elevations.

Adenosine, a signaling nucleoside, exhibits tissue-protective and tissue-destructive effects. Adenosine levels in tissues are controlled in part by the enzyme adenosine deaminase (ADA). ADA-deficient mice accumulate adenosine levels in multiple tissues, including the lung, where adenosine contributes to the development of pulmonary inflammation and chronic airway remodeling. The present study describes the development of pulmonary fibrosis in mice that have been genetically engineered to possess partial ADA enzyme activity and, thus, accumulate adenosine over a prolonged period of time. These partially ADA-deficient mice live for up to 5 mo and die from apparent respiratory distress. Detailed investigations of the lung histopathology of partially ADA-deficient mice revealed progressive pulmonary fibrosis marked by an increase in the number of pulmonary myofibroblasts and an increase in collagen deposition. In addition, in regions of the distal airways that did not exhibit fibrosis, an increase in the number of large foamy macrophages and a substantial enlargement of the alveolar air spaces suggest emphysemic changes. Furthermore, important proinflammatory and profibrotic signaling pathways, including IL-13 and transforming growth factor-beta1, were activated. Increases in tissue fibrosis were also seen in the liver and kidneys of these mice. These changes occurred in association with pronounced elevations of lung adenosine concentrations and alterations in lung adenosine receptor levels, supporting the hypothesis that elevation of endogenous adenosine is a proinflammatory and profibrotic signal in this model.

Adenosine↗

PubMed2005

Adenosine-dependent pulmonary fibrosis in adenosine deaminase-deficient mice.

Pulmonary fibrosis is a common feature of numerous lung disorders, including interstitial lung diseases, asthma, and chronic obstructive pulmonary disease. Despite the prevalence of pulmonary fibrosis, the molecular mechanisms governing inflammatory and fibroproliferative aspects of the disorder are not clear. Adenosine is a purine-signaling nucleoside that is generated in excess during cellular stress and damage. This signaling molecule has been implicated in the regulation of features of chronic lung disease; however, the impact of adenosine on pulmonary fibrosis is not well understood. The goal of this study was to explore the impact of endogenous adenosine elevations on pulmonary fibrosis. To accomplish this, adenosine deaminase (ADA)-deficient mice were treated with various levels of ADA enzyme replacement therapy to regulate endogenous adenosine levels in the lung. Maintaining ADA-deficient mice on low dosages of ADA enzyme therapy led to chronic elevations in lung adenosine levels that were associated with pulmonary inflammation, expression of profibrotic molecules, collagen deposition, and extreme alteration in airway structure. These features could be blocked by preventing elevations in lung adenosine. Furthermore, lowering lung adenosine levels after the establishment of pulmonary fibrosis resulted in a resolution of fibrosis. These findings demonstrate that chronic adenosine elevations are associated with pulmonary fibrosis in ADA-deficient mice and suggest that the adenosine functions as a profibrotic signal in the lung.

Adenosine↗

PubMed2005

Genetic deletion of the A1 adenosine receptor limits myocardial ischemic tolerance.

Adenosine receptors may be important determinants of intrinsic ischemic tolerance. Genetically modified mice were used to examine effects of global A1 adenosine receptor (A1AR) knockout (KO) on function and ischemic tolerance in perfused mouse hearts. Baseline contractile function and heart rate were unaltered by A1AR KO, which was shown to abolish the negative chronotropic effects of 2-chloroadenosine (A1AR-mediated) without altering A2 adenosine receptor-mediated coronary dilation. Tolerance to 25 minutes global normothermic ischemia (followed by 45 minutes reperfusion) was significantly limited by A1AR KO, with impaired contractile recovery (reduced by 25%) and enhanced lactate dehydrogenase (LDH) efflux (increased by 100%). Functional effects of A1AR KO involved worsened systolic pressure development with little to no change in diastolic dysfunction. In contrast, cardiac specific A1AR overexpression enhanced ischemic tolerance with a primary action on diastolic dysfunction. Nonselective receptor agonism (10 micromol/L 2-chloroadenosine) protected wild-type and also A1AR KO hearts (albeit to a lesser extent), implicating protection via subtypes additional to A1ARs. However, A1AR KO abrogated effects of 2-chloroadenosine on ischemic contracture and diastolic dysfunction. These data are the first demonstrating global deletion of the A1AR limits intrinsic myocardial resistance to ischemia. Data indicate the function of intrinsically activated A1ARs appears primarily to be enhancement of postischemic contractility and limitation of cell death.

Animals↗

PubMed2005

Adenosine deaminase deficiency: metabolic basis of immune deficiency and pulmonary inflammation.

Genetic deficiencies in the purine catabolic enzyme adenosine deaminase (ADA) in humans results primarily in a severe lymphopenia and immunodeficiency that can lead to the death of affected individuals early in life. The metabolic basis of the immunodeficiency is likely related to the sensitivity of lymphocytes to the accumulation of the ADA substrates adenosine and 2'-deoxyadenosine. Investigations using ADA-deficient mice have provided compelling evidence to support the hypothesis that T and B cells are sensitive to increased concentrations of 2'-deoxyadenosine that kill cells through mechanisms that involve the accumulation of dATP and the induction of apoptosis. In addition to effects on the developing immune system, ADA-deficient humans exhibit phenotypes in other physiological systems including the renal, neural, skeletal, and pulmonary systems. ADA-deficient mice develop similar abnormalities that are dependent on the accumulation of adenosine and 2'-deoxyadenosine. Detailed analysis of the pulmonary insufficiency seen in ADA-deficient mice suggests that the accumulation of adenosine in the lung can directly access cellular signaling pathways that lead to the development and exacerbation of chronic lung disease. The ability of adenosine to regulate aspects of chronic lung disease is likely mediated by specific interactions with adenosine receptor subtypes on key regulatory cells. Thus, the examination of ADA deficiency has identified the importance of purinergic signaling during lymphoid development and in the regulation of aspects of chronic lung disease.

Adenosine Deaminase↗

PubMed2005

A protective role for the A1 adenosine receptor in adenosine-dependent pulmonary injury.

Adenosine is a signaling nucleoside that has been implicated in the regulation of asthma and chronic obstructive pulmonary disease. Adenosine signaling can serve both pro- and anti-inflammatory functions in tissues and cells. In this study we examined the contribution of A(1) adenosine receptor (A(1)AR) signaling to the pulmonary inflammation and injury seen in adenosine deaminase-deficient (ADA-deficient) mice, which exhibit elevated adenosine levels. Experiments revealed that transcript levels for the A(1)AR were elevated in the lungs of ADA-deficient mice, in which expression was localized predominantly to alveolar macrophages. Genetic removal of the A(1)AR from ADA-deficient mice resulted in enhanced pulmonary inflammation along with increased mucus metaplasia and alveolar destruction. These changes were associated with the exaggerated expression of the Th2 cytokines IL-4 and IL-13 in the lungs, together with increased expression of chemokines and matrix metalloproteinases. These findings demonstrate that the A(1)AR plays an anti-inflammatory and/or protective role in the pulmonary phenotype seen in ADA-deficient mice, which suggests that A(1)AR signaling may serve to regulate the severity of pulmonary inflammation and remodeling seen in chronic lung diseases by controlling the levels of important mediators of pulmonary inflammation and damage.

Adenosine↗

PubMed2004

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.

Adenosine Deaminase↗

PubMed2004

Mucin is produced by clara cells in the proximal airways of antigen-challenged mice.

Airway mucus hypersecretion is a prominent feature of many obstructive lung diseases. We thus determined the ontogeny and exocytic phenotype of mouse airway mucous cells. In naive mice, ciliated (approximately 40%) and nonciliated (approximately 60%) epithelial cells line the airways, and > 95% of the nonciliated cells are Clara cells that contain Clara cell secretory protein (CCSP). Mucous cells comprise < 5% of the nonciliated cells. After sensitization and a single aerosol antigen challenge, alcian blue-periodic acid Schiff's positive mucous cell numbers increase dramatically, appearing 6 h after challenge (21% of nonciliated/nonbasal cells), peaking from Days 1-7 (99%), and persisting at Day 28 (65%). Throughout the induction and resolution of mucous metaplasia, ciliated and Clara cell numbers identified immunohistochemically change only slightly. Intracellular mucin content peaks at Day 7, and mucin expression is limited specifically to a Clara cell subset in airway generations 2-4 that continue to express CCSP. Functionally, Clara cells are secretory cells that express the regulated exocytic marker Rab3D and, in antigen-challenged mice, rapidly secrete mucin in response to inhaled ATP in a dose-dependent manner. Thus, Clara cells show great plasticity in structure and secretory products, yet have molecular and functional continuity in their identity as specialized apical secretory cells.

Adenosine Triphosphate↗