In vivo gene transfer study for pathogenesis of lung injury. Endothelin and development of obliterative bronchiolitis

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Background. Obliterative bronchiolitis (OB) is a lesion that results when injury to small conducting airways is repaired by a proliferation of fibrous granulation tissue. OB has emerged as a main cause of morbidity and mortality in the setting of lung and heart-lung transplantation. Endothelin-1 (ET-1) initially discovered as a vasoconstrictive peptide, has a mitogenic activity on vascular smooth cells and airway epithelial cells. Overproduction of endothelin has been reported in patients with OB or chronic rejection after lung transplantation. It is still undetermined whether locally overexpressed ET-1 has a potential impact in the pathogenesis of OB. Methods. We locally overexpressed ET-1 using ultraviolet irradiation-inactivated hemagglitinating virus of Japan (HVJ)-liposome-mediated in vivo gene transfer. Plasmid DNA of prepro-ET-1 and high mobility group 1 (HMG1) protein were co-encapsulated in liposomes, and were introduced into airway epithelial cells by HVJ-mediated membrane fu … More sion. Control animals received instillation of HVJ-liposome with an empty expression cassette. To confirm the efficiency of transfection, HVJ liposome with β-galactosidase gene was introduced. The expression of ET-1 and β-galactosidase was assessed by histochemistry. Results. Bronchial epithelium alveolar cells and alveolar macrophage were stained blue (X-Gal) 1 week after in vivo gene transfer of β-gene, indicating β-gal activity. In animals 1 to 2 weeks after in vivo transfection of prepro-ET-1 gene, hyperplastic connective tissue plaque was seen in the alveolar duet and small conducting airway, indicating histologically distinctive bronchiolitis obliterans. Strong ET-1 like immunoactivies were seen in the airway epithelial, hyperplastic connective tissue and alveolar cells. No histopathologic changes were seen in the control animals. Summary and Future Direction. This result first suggests that ET-1 may have an important role in pathogenesis of OB presumably in the "common final pathway". However, the mechanism of mitogenic signaling by ET-1, its regulation of fibroblast proliferation, and its interaction with other cytokines or growth factors remained to be clarified at present. Further studies are needed to ascertain the specific role of ET-1 in the progression of OB. In summary, we conclude that local overexpression of ET-1 has a key role in the pathogenesis of OB. This evidence suggests the potential clinical implication that a pharmacological antagonist or inhibitor may be able to control the progression of this disease in patients with OB. Less