Mechanical ventilation uncouples synthesis and assembly of elastin and increases apoptosis in lungs of newborn mice.

Abstract

Prolonged mechanical ventilation (MV) with O2-rich gas inhibits lung growth and causes excess, disordered accumulation of lung elastin in preterm infants, often resulting in chronic lung disease (CLD). Using newborn mice, in which alveolarization occurs postnatally, we designed studies to determine how MV with either 40% O2 or air might lead to dysregulated elastin production and impaired lung septation. MV of newborn mice for 8 h with either 40% O2 or air increased lung mRNA for tropoelastin and lysyl oxidase, relative to unventilated controls, without increasing lung expression of genes that regulate elastic fiber assembly (lysyl oxidase-like-1, fibrillin-1, fibrillin-2, fibulin-5, emilin-1). Serine elastase activity in lung increased fourfold after MV with 40% O2, but not with air. We then extended MV with 40% O2 to 24 h and found that lung content of tropoelastin protein doubled, whereas lung content of elastin assembly proteins did not change (lysyl oxidases, fibrillins) or decreased (fibulin-5, emilin-1). Quantitative image analysis of lung sections showed that elastic fiber density increased by 50% after MV for 24 h, with elastin distributed throughout the walls of air spaces, rather than at septal tips, as in control lungs. Dysregulation of elastin was associated with a threefold increase in lung cell apoptosis (TUNEL and caspase-3 assays), which might account for the increased air space size previously reported in this model. Our findings of increased elastin synthesis, coupled with increased elastase activity and reduced lung abundance of proteins that regulate elastic fiber assembly, could explain altered lung elastin deposition, increased apoptosis, and defective septation, as observed in CLD.

Lysyl Oxidase Activity Is Dysregulated during Impaired Alveolarization of Mouse and Human Lungs

“…For example, soon after parturition, lox 2/2 pups exhibit ruptured arterial aneurysms and ruptured diaphragms (25), whereas adult loxl1 2/2 mice develop pelvic organ and rectal prolapse and excessive skin laxity (41). In addition to the induction of lysyl oxidase gene expression by hyperoxia reported in this study, mechanical ventilation of mice with room air or with 40% oxygen gas mixtures for 8 hours was also able to increase lox, but not loxl1 mRNA expression (13); however, a similar modulation of lysyl oxidase gene expression has not been observed in premature lambs mechanically ventilated with high (FIO 2 0.26) levels of oxygen (42). Variable responses of elastin gene expression to oxygen levels has also been reported.…”

“…For example, in the injured lungs of premature lambs, increased deposition of elastic fibers has been associated with thickened walls of the terminal respiratory units (12). In addition, in the injured lungs of mouse pups with BPD, increased elastin synthesis has also been reported (13,14). These observations are important, because the ECM plays a pivotal role in late lung development, and any perturbations to the formation and remodeling of matrix structures would affect the development of the immature lung (15).…”

Bronchopulmonary dysplasia and emphysema: in search of common therapeutic targets

“…By contrast, elastic lamellae of blood vessels appear normal [36]. Mechanical ventilation, a triggering factor of BPD, has been found to uncouple synthesis and assembly of elastin in newborn mice, which might in turn participate to septation failure [37].…”

“…), and better understanding these represents a challenge to optimize the therapeutic use of retinoids. [107,108] Mechanical injury + ± [1,4] Infections ± - [1] Directly associated genetic disorders -+ [3] Risk-associated gene polymorphisms + + [2] Histological features Airspace enlargement + + [1][2][3][4] Elastic fiber destruction/ disrupted assembly + + [37][38][39][40][41] Extracellular matrix remodeling + + [1][2][3][4] Diminished microvasular bed ± + [52][53][54] Dysmorphic capillary vessels + -…”

Inhibition of Transforming Growth Factor β Worsens Elastin Degradation in a Murine Model of Kawasaki Disease

“…23 Cross sections of the large coronary arteries under ϫ40 magnification were evaluated in a blinded fashion, and the number of visible breaks was measured per 1000-m length of vessel wall. The amount of medial elastin was quantified by determining the total amount of stained elastin versus total medial area using a commercially available system (Bioquant True Color Windows Image Analysis system; R & M Biometrics, Nashville, TN) in cross sections of the large and medium coronary branches in a blinded fashion.…”