Contribution of proliferation and DNA damage repair to alveolar epithelial type 2 cell recovery from hyperoxia

Abstract

. Contribution of proliferation and DNA damage repair to alveolar epithelial type 2 cell recovery from hyperoxia. Am J Physiol Lung Cell Mol Physiol 290: L685-L694, 2006. First published November 18, 2005 doi:10.1152/ajplung.00020.2005In this study, C57BL/6J mice were exposed to hyperoxia and allowed to recover in room air. The sublethal dose of hyperoxia for C57BL/6J was 48 h. Distal lung cellular isolates from treated animals were characterized as 98% epithelial, with minor fibroblast and endothelial cell contaminants. Cells were then verified as 95% pure alveolar epithelial type II cells (AEC2) by surfactant protein C (SP-C) expression. After hyperoxia exposure in vivo, fresh, uncultured AEC2 were analyzed for proliferation by cell yield, cell cycle, PCNA expression, and telomerase activity. DNA damage was assessed by TdT-dUTP nick-end labeling, whereas induction of DNA repair was evaluated by GADD-153 expression. A baseline level for proliferation and damage was observed in cells from control animals that did not alter significantly during acute hyperoxia exposure. However, a rise in these markers was observed 24 h into recovery. Over 72 h of recovery, markers for proliferation remained elevated, whereas those for DNA damage and repair peaked at 48 h and then returned back to baseline. The expression of GADD-153 followed a distinct course, rising significantly during acute exposure and peaking at 48 h recovery. These data demonstrate that in healthy, adult male C57BL/6J mice, AEC2 proliferation, damage, and repair follow separate courses during hyperoxia recovery and that both proliferation and efficient repair may be required to ensure AEC2 survival. C57BL/6J; GADD-153; telomerase IN LATE GESTATION OF MICE and rats, the alveolar epithelial cell (AEC) lineage develops from a multipotent population of stem cells that line the primitive respiratory tract (15). Alveolar epithelial type 2 cells (AEC2) manufacture surfactant and can differentiate, as required, into alveolar epithelial type 1 cells (AEC1), which regulate the gas exchange function of the organ (2, 14). To replace damaged cells throughout the life span of any animal, a particular subpopulation within the total population must retain the ability to divide. In the alveolar epithelium, this progenitor cell-like function has been ascribed to AEC2 (13,31,36). AEC2 proliferate during embryonic and fetal life but, in the adult lung, in the absence of injury, are highly differentiated and do not normally divide (9, 37). However, in response to environmental insult, some AEC2 become both hypertrophic and hyperplastic, such that cells undergo phenotypic and functional changes (17, 24). Regenerating rat AEC2 exhibit elevated cyclin and cyclin-dependent kinase (cdk) expression and activity during recovery following injury, indicating the regain of proliferative function (10, 39). During this period, the number of proliferating AEC2 has been reported to increase severalfold in rats (10, 36), mice (2), and humans (4). In human patients, this phase of recovery fr...

Oxidative Stress and Inflammation Modulate Rev-erbα Signaling in the Neonatal Lung and Affect Circadian Rhythmicity

“…Hyperoxia enhances the production of reactive oxygen species (3,12), leading to DNA strand breaks, chromosomal aberrations (5,40), and inhibition of cell cycle progression in the lung (7,54). In the neonatal period, this injury could have long-lasting consequences, because alveolarization continues for several weeks postnatally (48).…”

Combined effects of maternal inflammation and neonatal hyperoxia on lung fibrosis and RAGE expression in newborn rats

“…During recovery from sublethal hyperoxia, lung cells may proliferate to replace terminally damaged cells, and failure to impede this proliferation is associated with fibrosis (20). The formation of reactive oxygen species is thought to result in the production of cytokines.…”

Partial pneumonectomy of telomerase null mice carrying shortened telomeres initiates cell growth arrest resulting in a limited compensatory growth response

“…Following THX or PNX, animals were euthanized by use of Nembutal at 200 mg/kg ip and weighed. Lung tissue was harvested according to our standard procedure (34), with the exception that perfusion to complete exsanguination utilized only 3 ml of sterile, normal saline. Right lung was sharply separated from the bronchus, heart, thymic tissue, trachea, surgical clip if present, and any other adherent clot or fibrinous exudate.…”

“…Lungs were fixed and paraffin embedded according to protocols previously described (34). SP-C expression in situ was determined by using a specific rabbit antibody from Seven Hills Bioreagents (Cincinnati, OH).…”