Abstract
Bronchiolitis obliterans syndrome (BOS) is a major complication after lung transplantation (LTx). BOS is characterised by massive peribronchial fibrosis, leading to air trapping-induced pulmonary dysfunction. Cathepsin B, a lysosomal cysteine protease, has been shown to enforce fibrotic pathways in several diseases. However, the relevance of cathepsin B in BOS progression has not yet been addressed. The aim of the study was to elucidate the function of cathepsin B in BOS pathogenesis.
We determined cathepsin B levels in bronchoalveolar lavage fluid (BALF) and lung tissue from healthy donors (HD) and BOS LTx patients. Cathepsin B activity was assessed via a fluorescence resonance energy transfer-based assay and protein expression was determined using Western blotting, ELISA and immunostaining. To investigate the impact of cathepsin B in the pathophysiology of BOS, we used an in vivo orthotopic left LTx mouse model. Mechanistic studies were performed in vitro using macrophage and fibroblast cell lines.
We found a significant increase of cathepsin B activity in BALF and lung tissue from BOS patients, as well as in our murine model of lymphocytic bronchiolitis. Moreover, cathepsin B activity was associated with increased biosynthesis of collagen and had a negative effect on lung function. We observed that cathepsin B was mainly expressed in macrophages that infiltrated areas characterised by a massive accumulation of collagen deposition. Mechanistically, macrophage-derived cathepsin B contributed to transforming growth factor-β1-dependent activation of fibroblasts, and its inhibition reversed the phenotype.
Infiltrating macrophages release active cathepsin B, thereby promoting fibroblast activation and subsequent collagen deposition, which drive BOS. Cathepsin B represents a promising therapeutic target to prevent the progression of BOS.
Abstract
CatB is a new biomarker and therapeutic target for early bronchiolitis obliterans syndrome after lung transplantation https://bit.ly/36vOXHc
Footnotes
This article has an editorial commentary: https://doi.org/10.1183/13993003.04607-2020
This article has supplementary material available from erj.ersjournals.com
Author contributions: C. Morrone, N.F. Smirnova, O. Eickelberg and A.Ö. Yildirim designed the experiments; C. Morrone performed all the experiments and analysed the data; A. Jeridi provided feedback to figure 5; N.F. Smirnova and A.Ö. Yildirim oversaw all data analysis; N. Kneidinger provided human BALF and clinical information; C. Hollauer performed tissue staining; J.C. Schupp and N. Kaminski performed single-cell re-analysis; N.F. Smirnova performed the LTx murine surgeries; C. Morrone drafted the manuscript; C. Morrone, A. Jeridi, N.F. Smirnova and A.Ö. Yildirim corrected the manuscript. All authors have critically revised the manuscript. All authors have read, reviewed and approved the final manuscript as submitted and take public responsibility for it.
Conflict of interest: C. Morrone has nothing to disclose.
Conflict of interest: N.F. Smirnova has nothing to disclose.
Conflict of interest: A. Jeridi has nothing to disclose.
Conflict of interest: N. Kneidinger has nothing to disclose.
Conflict of interest: C. Hollauer has nothing to disclose.
Conflict of interest: J.C. Schupp has nothing to disclose.
Conflict of interest: N. Kaminski reports personal fees for consultancy and/or advisory board work from Biogen Idec, Boehringer Ingelheim, Third Rock, Samumed, NuMedii, Indaloo, Theravance, LifeMax, Three Lake Partners, RohBar, Pliant and AstraZeneca; non-financial support from Miragen, equity with Pliant and miRagen, and a grant from Veracyte, all outside the submitted work; has patents on New Therapies in Pulmonary Fibrosis and on Peripheral Blood Gene Expression that have been licensed to Biotech; and serves as deputy editor of Thorax.
Conflict of interest: D. Jenne has nothing to disclose.
Conflict of interest: O. Eickelberg has nothing to disclose.
Conflict of interest: A.Ö. Yildirim has nothing to disclose.
Support statement: This was supported by the German Center for Lung Research (DZL); by the European Union's Horizon 2020 Research and Innovation Program (668036, RELENT) and Max-Planck Society.
- Received April 26, 2020.
- Accepted November 8, 2020.
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