Endothelial to mesenchymal transition in neonatal hyperoxic lung injury: role of sex as a biological variable

BMAL1 sex-specific effects in the neonatal mouse airway exposed to moderate hyperoxia

Supplemental O2 (hyperoxia) is a critical intervention for premature infants (<34 weeks) but consequently is associated with development of bronchial airway hyperreactivity (AHR) and asthma. Clinical practice shifted toward the use of moderate hyperoxia (<60% O2), but risk for subsequent airway disease remains. In mouse models of moderate hyperoxia, neonatal mice have increased AHR with effects on airway smooth muscle (ASM), a cell type involved in airway tone, bronchodilation, and remodeling. Understanding mechanisms by which moderate O2 during the perinatal period initiates sustained airway changes is critical to drive therapeutic advancements toward treating airway diseases. We propose that cellular clock factor BMAL1 is functionally important in developing mouse airways. In adult mice, cellular clocks target pathways highly relevant to asthma pathophysiology and Bmal1 deletion increases inflammatory response, worsens lung function, and impacts survival outcomes. Our understanding of BMAL1 in the developing lung is limited, but our previous findings show functional relevance of clocks in human fetal ASM exposed to O2. Here, we characterize Bmal1 in our established mouse neonatal hyperoxia model. Our data show that Bmal1 KO deleteriously impacts the developing lung in the context of O2 and these data highlight the importance of neonatal sex in understanding airway disease.

Impact of different tissue dissociation protocols on endothelial cell recovery from developing mouse lungs

Flow cytometry and fluorescence-activated cell sorting are widely used to study endothelial cells, for which the generation of viable single-cell suspensions is an essential first step. Two enzymatic approaches, collagenase A and dispase, are widely employed for endothelial cell isolation. In this study, the utility of both enzymatic approaches, alone and in combination, for endothelial cell isolation from juvenile and adult mouse lungs was assessed, considering the number, viability, and subtype composition of recovered endothelial cell pools. Collagenase A yielded an 8-12-fold superior recovery of viable endothelial cells from lung tissue from developing mouse pups, compared to dispase, although dispase proved superior in efficiency for epithelial cell recovery. Single-cell RNA-Seq revealed that the collagenase A approach yielded a diverse endothelial cell subtype composition of recovered endothelial cell pools, with broad representation of arterial, capillary, venous, and lymphatic lung endothelial cells; while the dispase approach yielded a recovered endothelial cell pool highly enriched for one subset of general capillary endothelial cells, but poor representation of other endothelial cells subtypes. These data indicate that tissue dissociation markedly influences the recovery of endothelial cells, and the endothelial subtype composition of recovered endothelial cell pools, as assessed by single-cell RNA-Seq.

Recent progress in neonatal hyperoxic lung injury

With the progress in neonatal intensive care, there has been an increase in the survival rates of premature infants. However, this has also led to an increased incidence of neonatal hyperoxia lung injury and bronchopulmonary dysplasia (BPD), whose pathogenesis is believed to be influenced by various prenatal and postnatal factors, although the exact mechanisms remain unclear. Recent studies suggest that multiple mechanisms might be involved in neonatal hyperoxic lung injury and BPD, with sex also possibly playing an important role, and numerous drugs have been proposed and shown promise for improving the treatment outcomes of hyperoxic lung injury. Therefore, this paper aims to analyze and summarize sex differences in neonatal hyperoxic lung injury, potential pathogenesis and treatment progress to provide new ideas for basic and clinical research in this field.

Exogenous hydrogen sulfide attenuates hyperoxia effects on neonatal mouse airways

Supplemental O2 remains a necessary intervention for many premature infants (<34 wk gestation). Even moderate hyperoxia (<60% O2) poses a risk for subsequent airway disease, thereby predisposing premature infants to pediatric asthma involving chronic inflammation, airway hyperresponsiveness (AHR), airway remodeling, and airflow obstruction. Moderate hyperoxia promotes AHR via effects on airway smooth muscle (ASM), a cell type that also contributes to impaired bronchodilation and remodeling (proliferation, altered extracellular matrix). Understanding mechanisms by which O2 initiates long-term airway changes in prematurity is critical for therapeutic advancements for wheezing disorders and asthma in babies and children. Immature or dysfunctional antioxidant systems in the underdeveloped lungs of premature infants thereby heightens susceptibility to oxidative stress from O2. The novel gasotransmitter hydrogen sulfide (H2S) is involved in antioxidant defense and has vasodilatory effects with oxidative stress. We previously showed that exogenous H2S exhibits bronchodilatory effects in human developing airway in the context of hyperoxia exposure. Here, we proposed that exogenous H2S would attenuate effects of O2 on airway contractility, thickness, and remodeling in mice exposed to hyperoxia during the neonatal period. Using functional [flexiVent; precision-cut lung slices (PCLS)] and structural (histology; immunofluorescence) analyses, we show that H2S donors mitigate the effects of O2 on developing airway structure and function, with moderate O2 and H2S effects on developing mouse airways showing a sex difference. Our study demonstrates the potential applicability of low-dose H2S toward alleviating the detrimental effects of hyperoxia on the premature lung.NEW & NOTEWORTHY Chronic airway disease is a short- and long-term consequence of premature birth. Understanding effects of O2 exposure during the perinatal period is key to identify targetable mechanisms that initiate and sustain adverse airway changes. Our findings show a beneficial effect of exogenous H2S on developing mouse airway structure and function with notable sex differences. H2S donors alleviate effects of O2 on airway hyperreactivity, contractility, airway smooth muscle thickness, and extracellular matrix deposition.