Background Azithromycin (Azm) is a macrolide recognized for its disease-modifying effects and reduction in exacerbation of chronic airway diseases. It is not clear whether the beneficial effects of Azm are due to its anti-microbial activity or other pharmacological actions. We have shown that Azm affects the integrity of the bronchial epithelial barrier measured by increased transepithelial electrical resistance. To better understand these effects of Azm on bronchial epithelia we have investigated global changes in gene expression. Methods VA10 bronchial epithelial cells were treated with Azm and cultivated in air-liquid interface conditions for up to 22 days. RNA was isolated at days 4, 10 and 22 and analyzed using high-throughput RNA sequencing. qPCR and immunostaining were used to confirm key findings from bioinformatic analyses. Detailed assessment of cellular changes was done using microscopy, followed by characterization of the lipidomic profiles of the multivesicular bodies present. Results Bioinformatic analysis revealed that after 10 days of treatment genes encoding effectors of sterol and cholesterol metabolism were prominent. Interestingly, expression of genes associated with epidermal barrier differentiation, KRT1, CRNN, SPINK5 and DSG1 , increased significantly at day 22. Together with immunostaining, these results suggest an epidermal differentiation pattern. We also found that Azm induced the formation of multivesicular and lamellar bodies in two different airway epithelial cell lines. Lipidomic analysis revealed that Azm was entrapped in multivesicular bodies linked to different types of lipids, most notably palmitate and stearate. Furthermore, targeted analysis of lipid species showed accumulation of phosphatidylcholines, as well as ceramide derivatives. Conclusions Taken together, we demonstrate how Azm might confer its barrier enhancing effects, via activation of epidermal characteristics and changes to intracellular lipid dynamics. These effects of Azm could explain the unexpected clinical benefit observed during Azm-treatment of patients with various lung diseases affecting barrier function. Electronic supplementary material The online version of this article (10.1186/s12931-019-1101-3) contains supplementary material, which is available to authorized users.

with oxidative stress, may lead to activation of resident immune cells in the distal lungs to secrete inflammatory mediators resulting in edema and fibrosis, collectively referred to as biotrauma (Beitler et al., 2016).All mechanically ventilated patients are at risk for VILI, especially when it becomes challenging to ventilate the patient due to pathology in the lungs, as in acute respiratory distress syndrome (ARDS) (Carrasco Loza et al., 2015). VILI can cause, or augment substantially, damage of lung tissue in ARDS while being a necessary part of its treatment. The onset of ARDS is associated with the activation of the resident alveolar macrophages as a response to an insult or injury. The ensuing secretion of inflammatory mediators attracts neutrophils and monocytes from nearby capillaries, which secrete mediators harmful to endothelium and alveolar epithelium, causing increased permeability of the alveolar-capillary membrane, facilitating edema in the interstitium and air spaces. The following collapse of alveoli, increased dead space, worsening gas exchange and reduced lung compliance necessitate mechanical ventilation (Slutsky and Ranieri, 2013). AR-DS is a common and lethal or disabling syndrome that 10% of

Ventilator-induced lung injury (VILI) is a serious acute injury to the lung tissue that can develop during mechanical ventilation of patients. Due to the mechanical strain of ventilation, damage can occur in the bronchiolar and alveolar epithelium resulting in a cascade of events that may be fatal to the patients. Patients requiring mechanical ventilation are often critically ill, which limits the possibility of obtaining patient samples, making VILI research challenging. In vitro models are very important for VILI research, but the complexity of the cellular interactions in multi-organ animals, necessitates in vivo studies where the mouse model is a common choice. However, the settings and duration of ventilation used to create VILI in mice vary greatly, causing uncertainty in interpretation and comparison of results. This review examines approaches to induce VILI in mouse models for the last 10 years, to our best knowledge, summarizing methods and key parameters presented across the studies. The results imply that a more standardized approach is warranted.