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Cathepsin B, a new player in the progression of Bronchiolitis obliterans syndrome
Cathepsin B, a new player in the progression of Bronchiolitis obliterans syndrome
Bronchiolitis obliterans syndrome (BOS) is a major chronic complication after lung transplantation (LTx). BOS is characterized by massive fibrosis in areas surrounding small airways that leads to air trapping induced pulmonary dysfunction. Several cellular and molecular features of BOS have been described in the latest stage of the disease, however, triggers that promote airway fibroproliferation and the disease-progression have not yet been sufficiently investigated. Cathepsin-B (CatB), a lysosomal cysteine-protease, is able to exert its activity under acidic and neutral pH conditions, cleaving its targets intracellularly and extracellularly. CatB has been described in association with several fibrotic diseases and was shown to enforce fibrotic pathways in vitro conditions. Furthermore, the relevance of CatB in BOS progression has not yet been investigated. In this study, we aimed to elucidate the role of CatB as potential trigger of BOS pathogenesis and its contribution to the progression of the disease. CatB expression and its activity in lung tissue and bronchoalveolar lavage fluid (BALF) were determined using Western blotting, staining and a FRET-based activity assay, respectively. Pro-collagen levels were analysed in BALF samples via ELISA. To further investigate the impact of Cathepsin-B in the pathophysiology of BOS, we used an in vivo orthotopic left-lung transplantation mouse model of early-stage of BOS development, called lymphocytic bronchiolitis (LB). Mechanistical studies were performed in vitro using macrophage and fibroblast cell lines. With our study, we demonstrated that CatB protein levels were increased in BALF samples and in lung tissue of patients who developed BOS, as well as in our murine model of LB. Interestingly, CatB activity was increased in BALF from BOS patients, already at early stages of the disease. Remarkably, the activity of CatB negatively correlated with the lung function over the progression of BOS disease, and was associated with an increased biosynthesis of pro-collagen. We furthermore identified infiltrating pro-inflammatory macrophages being the main source of CatB in BOS. Mechanistically, we demonstrated that CatB contributed to TGF-β1-dependent activation of fibroblasts, and its inhibition prevented BOS phenotype. In conclusion, infiltrating macrophages, in areas surrounding airways, release CatB that promotes fibroblast-activation and subsequent collagen deposition, driving BOS progression. CatB may represent a potential therapeutic target to prevent BOS progression.
Not available
Morrone, Carmela
2020
English
Universitätsbibliothek der Ludwig-Maximilians-Universität München
Morrone, Carmela (2020): Cathepsin B, a new player in the progression of Bronchiolitis obliterans syndrome. Dissertation, LMU München: Faculty of Medicine
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Abstract

Bronchiolitis obliterans syndrome (BOS) is a major chronic complication after lung transplantation (LTx). BOS is characterized by massive fibrosis in areas surrounding small airways that leads to air trapping induced pulmonary dysfunction. Several cellular and molecular features of BOS have been described in the latest stage of the disease, however, triggers that promote airway fibroproliferation and the disease-progression have not yet been sufficiently investigated. Cathepsin-B (CatB), a lysosomal cysteine-protease, is able to exert its activity under acidic and neutral pH conditions, cleaving its targets intracellularly and extracellularly. CatB has been described in association with several fibrotic diseases and was shown to enforce fibrotic pathways in vitro conditions. Furthermore, the relevance of CatB in BOS progression has not yet been investigated. In this study, we aimed to elucidate the role of CatB as potential trigger of BOS pathogenesis and its contribution to the progression of the disease. CatB expression and its activity in lung tissue and bronchoalveolar lavage fluid (BALF) were determined using Western blotting, staining and a FRET-based activity assay, respectively. Pro-collagen levels were analysed in BALF samples via ELISA. To further investigate the impact of Cathepsin-B in the pathophysiology of BOS, we used an in vivo orthotopic left-lung transplantation mouse model of early-stage of BOS development, called lymphocytic bronchiolitis (LB). Mechanistical studies were performed in vitro using macrophage and fibroblast cell lines. With our study, we demonstrated that CatB protein levels were increased in BALF samples and in lung tissue of patients who developed BOS, as well as in our murine model of LB. Interestingly, CatB activity was increased in BALF from BOS patients, already at early stages of the disease. Remarkably, the activity of CatB negatively correlated with the lung function over the progression of BOS disease, and was associated with an increased biosynthesis of pro-collagen. We furthermore identified infiltrating pro-inflammatory macrophages being the main source of CatB in BOS. Mechanistically, we demonstrated that CatB contributed to TGF-β1-dependent activation of fibroblasts, and its inhibition prevented BOS phenotype. In conclusion, infiltrating macrophages, in areas surrounding airways, release CatB that promotes fibroblast-activation and subsequent collagen deposition, driving BOS progression. CatB may represent a potential therapeutic target to prevent BOS progression.