ABSTRACT
Limitations on tissue proliferation capacity determined by telomerase/apoptosis balance have been implicated in pathogenesis of idiopathic pulmonary fibrosis. In addition, collagen V shows promise as an inductor of apoptosis. We evaluated the quantitative relationship between the telomerase/apoptosis index, collagen V synthesis, and epithelial/fibroblast replication in mice exposed to butylated hydroxytoluene (BHT) at high oxygen concentration. Two groups of mice were analyzed: 20 mice received BHT, and 10 control mice received corn oil. Telomerase expression, apoptosis, collagen I, III, and V fibers, and hydroxyproline were evaluated by immunohistochemistry, in situ detection of apoptosis, electron microscopy, immunofluorescence, and histomorphometry. Electron microscopy confirmed the presence of increased alveolar epithelial cells type 1 (AEC1) in apoptosis. Immunostaining showed increased nuclear expression of telomerase in AEC type 2 (AEC2) between normal and chronic scarring areas of usual interstitial pneumonia (UIP). Control lungs and normal areas from UIP lungs showed weak green birefringence of type I and III collagens in the alveolar wall and type V collagen in the basement membrane of alveolar capillaries. The increase in collagen V was greater than collagens I and III in scarring areas of UIP. A significant direct association was found between collagen V and AEC2 apoptosis. We concluded that telomerase, collagen V fiber density, and apoptosis evaluation in experimental UIP offers the potential to control reepithelization of alveolar septa and fibroblast proliferation. Strategies aimed at preventing high rates of collagen V synthesis, or local responses to high rates of cell apoptosis, may have a significant impact in pulmonary fibrosis.
Subject(s)
Animals , Male , Apoptosis/physiology , Collagen Type V/biosynthesis , Idiopathic Pulmonary Fibrosis/pathology , Pulmonary Fibrosis/pathology , Telomerase/metabolism , Butylated Hydroxytoluene , Cell Proliferation , Collagen Type I/analysis , Collagen Type II/analysis , Collagen Type V/analysis , Disease Models, Animal , Epithelial Cells/metabolism , Epithelial Cells/pathology , Fluorescent Antibody Technique , Fibroblasts/metabolism , Fibroblasts/pathology , Hydroxyproline/analysis , Immunohistochemistry , In Situ Nick-End Labeling , Mice, Inbred BALB C , Microscopy, Electron , Pulmonary Alveoli/pathology , Pulmonary Alveoli/ultrastructure , Staining and Labeling , Telomerase/isolation & purificationABSTRACT
OBJECTIVE: The importance of type V collagen and its relationships with other types of collagen and with vascular and epithelial apoptosis were studied in a model of chemical carcinogenesis in the mouse lung. METHODS: Two groups of male Balb/c mice were studied: a) animals that received two intraperitoneal doses of 3 g/kg urethane carcinogen (urethane group = 24); and b) animals submitted to a sham procedure, comparable to the test group (control group = 7). Both groups were sacrificed after 120 days. In situ detection of apoptosis, immunohistochemistry, immunofluorescence and histomorphometry were used to evaluate the fraction occupied by the tumor, vascular and epithelial apoptosis, and type V, III and I collagen fibers in the lung parenchyma from both groups. RESULTS: The lung parenchyma from the urethane group showed low fractions of vascular and epithelial apoptosis as well as reduced type V collagen fibers when compared to the control group. A significant direct association was found between type V and III collagen fibers and epithelial apoptosis, type V collagen fibers and vascular apoptosis, and type V and type I collagen fibers. CONCLUSION: The results show that a direct link between low amounts of type V collagen and decreased cell apoptosis may favor cancer cell growth in the mouse lung after chemical carcinogenesis, suggesting that strategies aimed at preventing decreased type V collagen synthesis or local responses to reduced apoptosis may have a greater impact in lung cancer control.