[PMNDTR mice: a new model to study neutrophils in vivo]

Characterization of a flexible AAV-DTR/DT mouse model of acute epithelial lung injury

Animal models are important to mimic certain pathways or biological aspects of human pathologies including acute and chronic pulmonary diseases. We developed a novel and flexible mouse model of acute epithelial lung injury based on adeno-associated virus (AAV) variant 6.2 mediated expression of the human diphtheria toxin receptor (DTR). Following intratracheal administration of diphtheria toxin (DT), a cell-specific death of bronchial and alveolar epithelial cells can be observed. In contrast to other lung injury models, the here described mouse model provides the possibility of targeted injury using specific tropisms of AAV vectors or cell type specific promotors to drive the human DTR expression. Also, generation of cell specific mouse lines is not required. Detailed characterization of the AAV-DTR/DT mouse model including titration of viral genome (vg) load and administered DT amount revealed increasing cell numbers in bronchoalveolar lavage (BAL; macrophages, neutrophils, and unspecified cells) and elevation of degenerated cells and infiltrated leukocytes in lung tissue, dependent of vg load and DT dose. Cytokine levels in BAL fluid showed different patterns with higher vg load, e.g. IFNγ, TNFα, and IP10 increasing and IL-5 and IL-6 decreasing, while lung function was not affected. Additionally, laser-capture microdissection (LCM)-based proteomics of bronchial epithelium and alveolar tissue revealed upregulated immune and inflammatory response in all regions and extracellular matrix deposition in infiltrated alveoli. Overall, our novel AAV-DTR/DT model allows investigation of repair mechanisms following epithelial injury and resembles specific mechanistic aspects of acute and chronic pulmonary diseases.

Neutrophils and IL-1α Regulate Surfactant Homeostasis during Cigarette Smoking

Cigarette smoke exposure induces inflammation marked by rapid and sustained neutrophil infiltration, IL-1α, release and altered surfactant homeostasis. However, the extent to which neutrophils and IL-1α contribute to the maintenance of pulmonary surfactant homeostasis is not well understood. We sought to investigate whether neutrophils play a role in surfactant clearance as well as the effect of neutrophil depletion and IL-1α blockade on the response to cigarette smoke exposure. In vitro and in vivo administration of fluorescently labeled surfactant phosphatidylcholine was used to assess internalization of surfactant by lung neutrophils and macrophages during or following cigarette smoke exposure in mice. We also depleted neutrophils using anti-Ly-6G or anti-Gr-1 Abs, or we neutralized IL-1α using a blocking Ab to determine their respective roles in regulating surfactant homeostasis during cigarette smoke exposure. We observed that neutrophils actively internalize labeled surfactant both in vitro and in vivo and that IL-1α is required for smoke-induced elevation of surfactant protein (SP)-A and SP-D levels. Neutrophil depletion during cigarette smoke exposure led to a further increase in SP-A levels in the bronchoalveolar lavage and increased IL-1α, CCL2, GM-CSF, and G-CSF release. Finally, macrophage expression of Mmp12, a protease linked to emphysema, was increased in neutrophil-depleted groups and decreased following IL-1α blockade. Taken together, our results indicate that neutrophils and IL-1α signaling are actively involved in surfactant homeostasis and that the absence of neutrophils in the lungs during cigarette smoke exposure leads to an IL-1α-dependent exacerbation of the inflammatory response.

[Mice, rats and men: how rodent models are still required to produce knowledge]

La recherche biomédicale est considérée par nos sociétés comme une nécessité et les réflexions sur les moyens à mettre en œuvre pour la développer s’accordent sur le constat que : « à défaut de pouvoir expérimenter sur l’homme, l’expérimentation animale est indispensable » [1]. Celle-ci, pour être légitime, doit respecter la fameuse règle des 3R (Raffiner, Remplacer, Réduire) énoncée dès 1959 par Russell et Burch [2]. En effet, bien que permettant certaines approches moléculaires, expérimentales ou modélisées, les méthodes alternatives conservent un caractère réducteur et ne permettent pas d’appréhender l’ensemble d’un organisme au sein de son environnement. À ce jour, il reste donc encore indispensable d’utiliser des modèles animaux pour générer des connaissances valides en recherche fondamentale et appliquée. La recherche fait ainsi appel à une grande variété d’organismes-modèles, parmi lesquels les rongeurs (rats et souris) sont les plus utilisés : en France, en 2016, 59,6 % des animaux utilisés pour la recherche étaient des souris et 8,9 % étaient des rats [3]. Le propos de cet article est de montrer en quoi les rongeurs sont des modèles expérimentaux importants et de donner quelques exemples des connaissances nouvelles qu’ils ont apportés.