Sequential Exposure to Antenatal Microbial Triggers Attenuates Alveolar Growth and Pulmonary Vascular Development and Impacts Pulmonary Epithelial Stem/Progenitor Cells.

Helene Widowski,John P Newnham,Tammo Delhaas,Jack P M Cleutjens,Peter G J Nikkels,Matthias C Hütten,Niki L Reynaert,Daan R M G Ophelders,Tim G A M Wolfs,Matthew S Payne,Matthew W Kemp,Alan H Jobe,Boris W Kramer,Carmen A H Severens-Rijvers,Masatoshi Saito,Haruo Usuda

doi:10.3389/fmed.2021.614239

Abstract

Perinatal inflammatory stress is strongly associated with adverse pulmonary outcomes after preterm birth. Antenatal infections are an essential perinatal stress factor and contribute to preterm delivery, induction of lung inflammation and injury, pre-disposing preterm infants to bronchopulmonary dysplasia. Considering the polymicrobial nature of antenatal infection, which was reported to result in diverse effects and outcomes in preterm lungs, the aim was to examine the consequences of sequential inflammatory stimuli on endogenous epithelial stem/progenitor cells and vascular maturation, which are crucial drivers of lung development. Therefore, a translational ovine model of antenatal infection/inflammation with consecutive exposures to chronic and acute stimuli was used. Ovine fetuses were exposed intra-amniotically to Ureaplasma parvum 42 days (chronic stimulus) and/or to lipopolysaccharide 2 or 7 days (acute stimulus) prior to preterm delivery at 125 days of gestation. Pulmonary inflammation, endogenous epithelial stem cell populations, vascular modulators and morphology were investigated in preterm lungs. Pre-exposure to UP attenuated neutrophil infiltration in 7d LPS-exposed lungs and prevented reduction of SOX-9 expression and increased SP-B expression, which could indicate protective responses induced by re-exposure. Sequential exposures did not markedly impact stem/progenitors of the proximal airways (P63+ basal cells) compared to single exposure to LPS. In contrast, the alveolar size was increased solely in the UP+7d LPS group. In line, the most pronounced reduction of AEC2 and proliferating cells (Ki67+) was detected in these sequentially UP + 7d LPS-exposed lambs. A similar sensitization effect of UP pre-exposure was reflected by the vessel density and expression of vascular markers VEGFR-2 and Ang-1 that were significantly reduced after UP exposure prior to 2d LPS, when compared to UP and LPS exposure alone. Strikingly, while morphological changes of alveoli and vessels were seen after sequential microbial exposure, improved lung function was observed in UP, 7d LPS, and UP+7d LPS-exposed lambs. In conclusion, although sequential exposures did not markedly further impact epithelial stem/progenitor cell populations, re-exposure to an inflammatory stimulus resulted in disturbed alveolarization and abnormal pulmonary vascular development. Whether these negative effects on lung development can be rescued by the potentially protective responses observed, should be examined at later time points.

Highlights

Perinatal inflammatory stress, including sepsis and mechanical ventilation are strongly associated with adverse pulmonary outcomes after preterm birth [1, 2]
Considering the increasing importance of aberrant vascular development in neonatal lung diseases [14], and recent findings of endogenous epithelial stem/progenitor cells playing a key role in the adverse pulmonary development [7, 15], our aim was to examine the consequences of sequential inflammatory stimuli on inflammatory read outs and on these crucial developmental aspects
There is increasing evidence that structural and functional abnormalities of the developing lungs that are provoked during pregnancy by inflammatory triggers, can contribute to postnatal lung pathology [25, 26]

Summary

Introduction

Perinatal inflammatory stress, including sepsis and mechanical ventilation are strongly associated with adverse pulmonary outcomes after preterm birth [1, 2]. BPD results from a demand of respiratory support and supplemental oxygen after preterm birth and histologically manifests as a delay in alveolar growth and an impairment in vascular maturation [3, 4]. Antenatal infections are an essential factor of perinatal stress and associated with preterm delivery and induction of lung inflammation and injury, thereby pre-disposing to BPD [5, 6]. We showed that timing of antenatal infection/inflammation and its duration of determine the extent and location of adverse effects in the preterm lungs [7]. We reported attenuated levels of endogenous stem/progenitor populations and their potential consequences, including altered surfactant protein expression and reduced alveolar differentiation in the course of antenatal inflammation [7]

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Conclusion