Role of CXC chemokine receptor-2 in a murine model of bronchopulmonary dysplasia.

The contribution of neutrophils and CXC chemokines to the pathogenesis of bronchopulmonary dysplasia is not well defined. The transgenic expression of IL-1ß in the pulmonary epithelium causes lung inflammation and disrupts alveolar development in infant mice. To study the hypothesis that CXC chemokine receptor-2 (CXCR2) is a mediator of inflammatory lung injury, we compared lung development in IL-1ß-expressing mice with wild-type (IL-1ß/CXCR2(+/+)) or null (IL-1ß/CXCR2(-/-)) CXCR2 loci. CXCR2 deficiency abolished the transmigration of neutrophils into the alveolar lumen in IL-1ß-expressing mice, but did not alter the number of neutrophils in the parenchyma. The deletion of CXCR2 increased the alveolar chord length and reduced the survival of mice when IL-1ß was expressed from the pseudoglandular to the alveolar stages. The capillary configuration was highly abnormal in both IL-1ß/CXCR2(+/+) and IL-1ß/CXCR2(-/-) lungs, but in very different ways. The cellular area of the parenchyma and the total capillary area of IL-1ß/CXCR2(+/+) and IL-1ß/CXCR2(-/-) mice were smaller than those of control/CXCR2(+/+) and control/CXCR2(-/-) mice, but the ratio of capillary area to cellular area was similar in all four genotypes. When IL-1ß was expressed during the saccular stage, IL-1ß/CXCR2(-/-) mice had smaller alveolar chord lengths and better survival than did IL-1ß/CXCR2(+/+) mice. Independent of the timing of IL-1ß expression, IL-1ß increased alveolar septal thickness in mice with wild-type CXCR2 loci, but not in CXCR2 null mice. Depending on the developmental stage at the time of the inflammatory insult, inhibition of the CXCR2 pathway may exert opposite effects on alveolar septation in the neonatal lung.

Angiotensin II receptor inhibition prevents pneumocyte apoptosis in surfactant-depleted rat lungs.

Pneumocyte apoptosis is implicated in the pathophysiology of acute inflammatory lung injuries in newborns and adults. Pulmonary angiotensin (ANG) II contributes to lung epithelial apoptosis in vitro, but its role in acute lung injury in vivo is unclear. We therefore studied the effects of ANG II receptor action on the pulmonary inflammatory and apoptotic changes in surfactant-depleted lungs in rats. Lung injury was induced by repeated lung lavage with saline, and the rats were then ventilated with 60% oxygen for 1, 3, or 5 hr. Separate groups of rats were pretreated with a nonspecific ANG II receptor inhibitor saralasin, the specific ANG II type 1 receptor antagonist losartan, or ANG II type 2 receptor inhibitor PD123319, and were similarly studied. Lungs were studied histologically for tissue injury, and with terminal deoxynucleodityl transferase-mediated dUTP nick end-labeling (TUNEL) and cleaved caspase 3 antibody staining, and by electron microscopy for apoptotic cell death. Surfactant-depleted lungs showed an increased number of TUNEL-positive epithelial cells throughout the study, and intrapulmonary leukocyte migration and histological tissue injury scores were similarly elevated, compared to controls, from 1-5 hr of ventilation. Pretreatment with saralasin or losartan significantly prevented the increase of TUNEL positivity in pneumocytes, but had no effect on the amount of neutrophil influx or total injury score in lavaged lungs. In contrast, administration of PD123319 did not affect the number of TUNEL-positive epithelial cells or histological injury . The results suggest that increased epithelial apoptosis in surfactant-deficient lungs is mediated by ANG II receptor (specifically, subtype 1) action.

Lung epithelial cells undergo apoptosis in neonatal respiratory distress syndrome.

For studying the presence of programmed cell death in the lungs of infants with fatal respiratory distress syndrome (RDS) and the possible contribution of postnatal glucocorticoid administration on this cell destruction, lung tissue samples from autopsies of 16 premature infants with fatal RDS were studied. The infants had neither been exposed to antenatal steroids nor received surfactant therapy, but seven of these infants had been subjected to postnatal dexamethasone treatment. Lung autopsy samples of seven term and two preterm neonates without any obvious lung disease served as controls. Lungs were studied histologically, and apoptotic cell death was identified using DNA nick end-labeling assay and caspase-related M30 antibody staining (CytoDeath). Lung tissue from the RDS infants showed elevated leukocyte infiltration, histologic injury score, and number of apoptotic cells, located mainly in the respiratory epithelium, when compared with controls. In contrast, lungs from infants who had RDS and received dexamethasone demonstrated markedly reduced tissue leukocyte accumulation and injury score and lower rates of epithelial apoptosis than the lungs of infants who had RDS and did not receive dexamethasone. These results suggest that significant epithelial apoptosis is present in the lungs of newborn infants with fatal RDS and that this apoptosis may be attenuated by steroid administration.