Fas/FasL-mediated apoptosis in perinatal murine lungs

Abstract

I. Luks. Fas/FasL-mediated apoptosis in perinatal murine lungs. Am J Physiol Lung Cell Mol Physiol 287: L730 -L742, 2004; 10.1152/ajplung.00120.2004.-Postcanalicular lung development is characterized by a time-specific increase in alveolar epithelial type II cell apoptosis. We have previously demonstrated that, in fetal rabbits, developmental type II cell apoptosis coincides with transient upregulation of the cell death regulator Fas ligand (FasL). The aims of this study were 1) to determine the spatiotemporal patterns of pulmonary apoptosis and Fas/FasL gene expression in the murine model [embryonic day 17 (E17) through postnatal day 5 (P5)], and 2) to investigate the functional involvement of the Fas/FasL system by determining the effect of Fas activation and inhibition on perinatal pulmonary apoptosis. The apoptotic activity of alveolar epithelial type II cells, determined by combined TUNEL labeling and anti-surfactant protein B immunohistochemistry, showed a dramatic increase during the perinatal transition (type II cell apoptotic index Ͻ0.1% at E17, 1.5% at P1-P3, and 0.3% at P5). This timing of enhanced type II cell apoptosis coincided with a robust 14-fold increase in Fas mRNA and protein levels and a threefold increase in FasL protein levels; both Fas and FasL immunolocalized to type II and bronchial epithelial cells. In vitro and in vivo exposure of fetal and postnatal murine type II cells to anti-Fas antibody induced a fourfold increase in apoptotic activity that was prevented by administration of a broad-spectrum caspase inhibitor; the pulmonary apoptotic activity of Fas-deficient lpr mice remained unchanged. Conversely, administration of a caspase inhibitor to newborn mice (P1) resulted in marked diminution of pulmonary apoptotic activity. These combined findings strongly implicate the Fas/FasL system as a critical regulator of perinatal type II cell apoptosis. The developmental time dependence of apoptosis-related events in the murine model should facilitate investigations of the regulation of perinatal pulmonary apoptotic gene expression.programmed cell death; lpr; CD95; lung development DURING PERINATAL development, the distal lung parenchyma undergoes a series of orchestrated morphological and functional changes required for optimizing postnatal gas exchange. This process is initiated in utero during the transition from the pseudoglandular to the canalicular and saccular stages of lung development and is completed after birth during the alveolar stage. Postcanalicular lung development is characterized by a coordinated thinning of the interstitium, expansion of the alveolar septa, and a significant reduction in the number of alveolar type II cells (6,22).The loss of alveolar type II cells in postcanalicular lungs traditionally has been attributed to terminal differentiation of type II cells into type I cells, but recent observations suggest that apoptosis (programmed cell death) may be an important contributor to perinatal type II cell homeostasis as well (reviewed in Ref. 14). We previously demon...

Fas-Ligand-Induced Apoptosis of Respiratory Epithelial Cells Causes Disruption of Postcanalicular Alveolar Development

“…10 Briefly, type II cells were isolated by protease digestion and differential adherence to CD45-and CD32-coated dishes. After isolation and purification, the cells were resuspended in culture medium (HEPESbuffered Dulbecco's modified Eagle's medium, 10% fetal bovine serum, 100 U/ml penicillin, 100 g/ml streptomycin).…”

“…First, we previously demonstrated that perinatal murine respiratory epithelial cells are exquisitely sensitive to Fasmediated apoptosis in vitro and in vivo. 10,22 Furthermore, the Fas/FasL signaling pathway lends itself better to experimental manipulation than other, in particular intrinsic (mitochondrial-dependent) pathways. Finally, the Fas/ FasL system has been implicated as critical regulator of alveolar type II cell apoptosis in physiological alveolar remodeling 10,11 and in various clinical and experimental models of adult lung injury.…”

“…10,22 Furthermore, the Fas/FasL signaling pathway lends itself better to experimental manipulation than other, in particular intrinsic (mitochondrial-dependent) pathways. Finally, the Fas/ FasL system has been implicated as critical regulator of alveolar type II cell apoptosis in physiological alveolar remodeling 10,11 and in various clinical and experimental models of adult lung injury. [23][24][25][26][27][28][29][30][31][32][33] It is therefore conceivable that Fas/FasL signaling may play an important role in BPD-associated apoptosis as well.…”

“…10 This approach allowed us to demonstrate that perinatal alveolar epithelial cells are susceptible to Fas-mediated apoptosis. 10 However, systemic Fas activation resulted in rapid death from liver failure before the effects of exaggerated alveolar apoptosis on alveolar remodeling could be ascertained.…”

“…10 This approach allowed us to demonstrate that perinatal alveolar epithelial cells are susceptible to Fas-mediated apoptosis. 10 However, systemic Fas activation resulted in rapid death from liver failure before the effects of exaggerated alveolar apoptosis on alveolar remodeling could be ascertained. To circumvent the deleterious effects of prolonged and systemic FasL exposure, we generated a tetracycline-inducible (tet-on) lung epithelial-specific FasL-overexpressing mouse, adapted from the Tet system of Gossen and colleagues, 34 to target apoptosis to respiratory epithelial cells during perinatal lung development.…”