Ablation of Arg1 in hematopoietic cells improves respiratory function of lung parenchyma, but not that of larger airways or inflammation in asthmatic mice

Abstract

Cloots RH, Sankaranarayanan S, de Theije CC, Poynter ME, Terwindt E, van Dijk P, Hakvoort TB, Lamers WH, Köhler SE. Ablation of Arg1 in hematopoietic cells improves respiratory function of lung parenchyma, but not that of larger airways or inflammation in asthmatic mice. Am J Physiol Lung Cell Mol Physiol 305: L364-L376, 2013. First published July 5, 2013; doi:10.1152/ajplung.00341.2012.-Asthma is a chronic inflammatory disease of the small airways, with airway hyperresponsiveness (AHR) and inflammation as hallmarks. Recent studies suggest a role for arginase in asthma pathogenesis, possibly because arginine is the substrate for both arginase and NO synthase and because NO modulates bronchial tone and inflammation. Our objective was to investigate the importance of increased pulmonary arginase 1 expression on methacholine-induced AHR and lung inflammation in a mouse model of allergic asthma. Arginase 1 expression in the lung was ablated by crossing Arg1 fl/fl with Tie2Cre tg/Ϫ mice. Mice were sensitized and then challenged with ovalbumin. Lung function was measured with the Flexivent. Adaptive changes in gene expression, chemokine and cytokine secretion, and lung histology were quantified with quantitative PCR, ELISA, and immunohistochemistry. Arg1 deficiency did not affect the allergic response in lungs and large-airway resistance, but it improved peripheral lung function (tissue elastance and resistance) and attenuated adaptive increases in mRNA expression of arginine-catabolizing enzymes Arg2 and Nos2, arginine transporters Slc7a1 and Slc7a7, chemokines Ccl2 and Ccl11, cytokines Tnfa and Ifng, mucus-associated epithelial markers Clca3 and Muc5ac, and lung content of IL-13 and CCL11. However, expression of Il4, Il5, Il10, and Il13 mRNA; lung content of IL-4, IL-5, IL-10, TNF-␣, and IFN-␥ protein; and lung pathology were not affected. Correlation analysis showed that Arg1 ablation disturbed the coordinated pulmonary response to ovalbumin challenges, suggesting arginine (metabolite) dependence of this response. Arg1 ablation in the lung improved peripheral lung function and affected arginine metabolism but had little effect on airway inflammation. airway hyperresponsiveness; arginine; inflammation ALLERGIC ASTHMA IS A CHRONIC inflammatory disorder of the lung that is characterized by a reversible limitation of the airflow due to an allergic reaction in the airways with the characteristics of a T H 2-predominant airway inflammation. The airway inflammation is initiated by the binding of inhaled allergens to complementary IgEs on IgE receptor-bearing cells. Upon activation, these cells release histamine, cytokines, and proteases, resulting in the activation of the inflammatory cascade with lung infiltration of eosinophils and mononuclear cells. Increased mucus production, mucosal edema, and a disproportionate smooth-muscle contraction lead to airway hyperresponsiveness (AHR). As a result of the recurring inflammation, airway remodeling develops as a consequence of fibrosis and airway wall thickening (2,3,6,36).Rec...

Deletion of endothelial arginase 1 does not improve vasomotor function in diabetic mice

“…In a model of allergic asthma in the same mouse strain, we did not find an effect of Arg1 ablation on pulmonary inflammation as determined by cytokine expression and histology (Cloots et al. ). We did, however, not investigate cytokine profiles, NO production or leukocyte adhesion to vessel walls in the current model and can, therefore, not exclude that some vascular inflammation was present that could have masked potential beneficial effects of endothelial Arg1 ablation.…”

“…In addition, Arg1‐KO Tie2 mice suffering from allergic asthma did not express ARG1 mRNA or protein in their lungs, even though this condition upregulates Arg1 expression >200‐fold in control mice (Cloots et al. ). These data underscore our claim that Arg1 expression was eliminated from the endothelium.…”

“…Endothelial ablation of ARG1 was achieved by crossing Arg1 fl/fl (Cloots et al. ) and Tie2Cre tg/− (Kisanuki et al. ) mice.…”

Arginase-1 Deficiency Regulates Arginine Concentrations and NOS2-Mediated NO Production during Endotoxemia

“…To investigate the role of arginase-1, Arg fl/fl /Tie2-Cre tg/− mice were generated in our laboratory as described in detail elsewhere [30], [32]. In brief, Arg1 exon 4 on chromosome 10 was surrounded by LoxP sites [32], as exon 4 is essential for the enzymatic activity of arginase1 [33] and deletion will result in a frame shift.…”

“…In brief, Arg1 exon 4 on chromosome 10 was surrounded by LoxP sites [32], as exon 4 is essential for the enzymatic activity of arginase1 [33] and deletion will result in a frame shift. The targeting vector (17.515 Kb) used consisted of Arg1 exons and introns 2 and 3 (4.6 Kb) at the 5′end, a Neo-TK selection cassette flanked by frt sites [34], exon 4 (160 bp) flanked by loxP sites [35], introns 4–7, exons 5–8, and a small fragment downstream of the gene (in total 4.3 Kb) at the 3′end.…”