Alveolar epithelial type II cell apoptosis in vivo during resolution of keratinocyte growth factor-induced hyperplasia in the rat.
Keratinocyte growth factor (KGF) induces rapid and transient hyperplasia of alveolar epithelial type II cells. We sought to determine components of the apoptotic process involved in the resolution of this hyperplasia and the fate of the apoptotic cells. Rats received intrabronchial instillation of 5 mg KGF/kg body weight or diluent. Lungs were fixed 1, 2, 3, 5, and 7 days later. Apoptosis was identified by TdT-mediated dUTP nick-end labeling (TUNEL), double-labeling for TUNEL and the type II cell marker MNF116, and electron microscopy. Fas, FasL, Bax, Bcl-2, and pro- and active caspase-3 were studied by immunohistochemistry. Changes were quantified by stereology. Cell type specificity was investigated by immunofluorescence double staining. Type II cells exhibited Fas, FasL, Bcl-2, and procaspase-3 irrespective of treatment and time. Immunoelectron microscopy revealed Fas at the apical type II cell membrane. Bax staining was prominent in controls (45-95% of type II cell surface fraction), markedly decreased during hyperplasia at days 2 (20-40%) and 3 (0-10%), and reappeared at day 7 (25-45%) when apoptosis was prominent. Remnants of apoptotic type II cells were incorporated in membrane-bound vacuoles of type II cell neighbors as well as alveolar macrophages. The results indicate that type II cells can enter the Fas/FasL/caspase-3 pathway regulated by Bax and Bcl-2. High Bcl-2:Bax levels favor type II cell survival and a low rate of apoptosis during hyperplasia. Low Bcl-2:Bax levels favor type II cell apoptosis during resolution. Because of time-dependent changes that occur within a short time, the KGF-treated rat lung provides a useful in vivo model to investigate apoptosis in the context of tissue remodeling and repair.
Fehrenbach
H
H
Institute of Pathology, University Clinic Carl Gustav Carus, TU Dresden, Germany. hefeh@rcs.urz.tu-dresden.de
Kasper
M
M
Koslowski
R
R
Pan
T
T
Schuh
D
D
Müller
M
M
Mason
R J
RJ
D000818:Animals; D017209:Apoptosis; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism / Q000473:pathology*; D053222:Fas Ligand Protein; D051526:Fibroblast Growth Factor 10; D051523:Fibroblast Growth Factor 7; D005346:Fibroblast Growth Factors; D019084:Fluorescent Antibody Technique, Indirect; D006133:Growth Substances / Q000494:pharmacology*; D006965:Hyperplasia / Q000139:chemically induced; D020287:In Situ Nick-End Labeling; D008562:Membrane Glycoproteins / Q000378:metabolism; D016253:Microscopy, Immunoelectron; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D011650:Pulmonary Alveoli / Q000187:drug effects / Q000378:metabolism / Q000473:pathology*; D051381:Rats; D011916:Rats, Inbred F344; D011994:Recombinant Proteins / Q000494:pharmacology; D015398:Signal Transduction; D013997:Time Factors; D051028:bcl-2-Associated X Protein; D019014:fas Receptor / Q000378:metabolism
C494828:Bax protein, rat; D053222:Fas Ligand Protein; C505662:Faslg protein, rat; C496455:Fgf7 protein, rat; D051526:Fibroblast Growth Factor 10; D006133:Growth Substances; D008562:Membrane Glycoproteins; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D011994:Recombinant Proteins; D051028:bcl-2-Associated X Protein; D019014:fas Receptor; D051523:Fibroblast Growth Factor 7; D005346:Fibroblast Growth Factors; C505410:Casp3 protein, rat; D053148:Caspase 3; D020169:Caspases