Sex-specific airway hyperreactivity and sex-specific transcriptome remodeling in neonatal piglets challenged with intra-airway acid

Abstract

Acute airway acidification is a potent stimulus of sensory nerves and occurs commonly with gastroesophageal reflux disease, cystic fibrosis, and asthma. In infants and adults, airway acidification can acutely precipitate asthma-like symptoms, and treatment-resistant asthma can be associated with gastroesophageal reflux disease. Airway protective behaviors, such as mucus secretion and airway smooth muscle contraction, are often exaggerated in asthma. These behaviors are manifested through activation of neural circuits. In some populations, the neural response to acid might be particularly important. For example, the immune response in infants is relatively immature compared with adults. Infants also have a high frequency of gastroesophageal reflux. Thus, in the current study, we compared the transcriptomes of an airway-nervous system circuit (e.g., tracheal epithelia, nodose ganglia, and brain stem) in neonatal piglets challenged with intra-airway acid. We hypothesized that the identification of parallel changes in the transcriptomes of two neutrally connected tissues might reveal the circuit response, and, hence, molecules important for the manifestation of asthma-like features. Intra-airway acid induced airway hyperreactivity and airway obstruction in male piglets. In contrast, female piglets displayed airway obstruction without airway hyperreactivity. Pairwise comparisons revealed parallel changes in genes directly implicated in airway hyperreactivity ( scn10a) in male acid-challenged piglets, whereas acid-challenged females exhibited parallel changes in genes associated with mild asthma ( stat 1 and isg15). These findings reveal sex-specific responses to acute airway acidification and highlight distinct molecules within a neural circuit that might be critical for the manifestation of asthma-like symptoms in pediatric populations.

Acid exposure impairs mucus secretion and disrupts mucus transport in neonatal piglet airways

“…We previously reported that intra-airway acid induces mucus obstruction in the small airways (22). Similar to our previous studies, we found that intra-airway acid induced airway obstruction under both basal ( Figure 3A-3D) and methacholine-stimulated conditions ( Figure 3E-H).…”

“…Studies were performed by individuals blinded to treatment; only an animal ID was associated with post-mortem samples. Our previous work for histological scoring indicated a "n" of 8 per sex was required to achieve statistical significance (22,35). We observed no sex differences in airway obstruction induced by acid and therefore combined male and female data.…”

“…We previously examined inflammation extensively in acid-challenged piglets using inflammatory-directed gene arrays and ELISAs, but only found evidence for transcriptional inflammation (22). Thus, although it is possible that airway acidification induces mucus abnormalities through local inflammatory-mediated mechanisms, it is unlikely that large-scale and active inflammation is a major driver of acid-induced mucus abnormalities.…”

“…For animals that received methacholine in vivo, we performed a smaller study on saline and acid-challenged animals prior to investigating the effects of diminazene aceturate (n = 3 saline-challenged, 3 acid-challenged). For ELISA analysis, we previously reported a n of 6 was required (22). Prospective exclusion criteria established included any piglet that required antibiotics or anti-inflammatories due to gastrointestinal illness.…”

“…Our previous data suggested that neonatal piglets challenged with intra-airway acid exhibit airway obstruction (22), suggesting defects in mucus secretion, production and/or transport. Here we tested the hypothesis that transient airway acidification is sufficient to induce defects in mucus secretion and mucociliary transport in neonatal piglets.…”