Localization of endothelin receptors in bleomycin-induced pulmonary fibrosis in the rat

Abstract

Pulmonary fibrosis is characterized by excessive extracellular matrix deposition with concomitant loss of gas exchange units, and endothelin-1 (ET-1) has been implicated in its pathogenesis. Increased levels of ET-1 from tissues and bronchoalveolar lavage have been reported in patients with pulmonary fibrosis and in animal models after intratracheal bleomycin. We characterized the cellular distribution of alveolar ET receptors by immunohistochemistry in bleomycin-induced pulmonary fibrosis in the rat and determined the regulation by bleomycin of ET receptor mRNA expression in isolated alveolar macrophages and rat lung fibroblasts. We found significant increases in the numbers of fibroblasts and macrophages at day 7 compared to day 28 and control animals. ET(B) receptor immunoreactivity was observed on fibroblasts and invading monocytes. Isolated fibroblasts expressed both ET(A) and ET(B) receptor mRNA, and ET(A) receptor mRNA was upregulated by bleomycin. Isolated resident alveolar macrophages expressed neither ET(A) nor ET(B) receptor mRNA which were also not induced by bleomycin. We conclude that, while ET(B) receptor stimulation of fibroblasts and monocytes recruited during bleomycin-induced lung injury exerts antagonistic effects on fibroblast collagen synthesis, the observed increase in the number of fibroblasts in vivo and upregulation of fibroblast ET(A) receptor mRNA by bleomycin in vitro point to a predominance of the profibrotic effects of ET receptor engagement.

Distribution of Endothelin Receptor Subtypes ETA and ETB in the Rat Kidney

“…For the ET B receptor antibody, we obtained bands of z34, 52, and 60 kDa. In a previous study we used the same antibody in rat lungs and obtained bands of z52 and 34 kDa (Wendel et al 2004) in accordance with the report by Kozuka et al (1991). In the present study we observed an additional band of z60 kDa.…”

Endothelin-1 and Transforming Growth Factor-β1 Independently Induce Fibroblast Resistance to Apoptosis via AKT Activation

“…Both cytokines have been shown to modulate pulmonary fibrosis in murine models, and both have been shown to be highly expressed in the lungs of patients with pulmonary fibrosis (4,(25)(26)(27)(28)(29). Moreover, both of these mediators induce fibroblast differentiation, ECM synthesis, and collagen gel contraction (7,10).…”

Endothelin-1 Induces Alveolar Epithelial–Mesenchymal Transition through Endothelin Type A Receptor–Mediated Production of TGF-β1

“…Previous results evaluating ET-A receptor and ET-B receptor expression in AEC have been variable. Wendel and colleagues were unable to detect ET-A or ET-B mRNA expression in type I or type II AEC in rat lung after bleomycin injury (40). In contrast, ET-A receptor expression has been demonstrated in an immortalized AEC line (32) and in the alveolar epithelium of normal and scleroderma lung tissue by immunohistochemistry (41).…”