Comprehensive Pneumology Center, Institute of Lung Biology and Disease, Helmholtz Zentrum München; Member of the German Center for Lung Research (DZL), Munich, Germany.
Division of Pulmonary Sciences and Critical Care Medicine, University of Colorado, Anschutz Medical Campus, Aurora, CO, USA.
Eur Respir J. 2021 May 13;57(5). doi: 10.1183/13993003.01416-2020. Print 2021 May.
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 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 orthotopic left LTx mouse model. Mechanistic studies were performed 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.
闭塞性细支气管炎综合征（BOS）是肺移植（LTx）后的主要并发症。BOS 的特征是广泛的支气管周围纤维化，导致空气陷闭引起的肺功能障碍。组织蛋白酶 B 是一种溶酶体半胱氨酸蛋白酶，已被证明在几种疾病中增强纤维化途径。然而，组织蛋白酶 B 在 BOS 进展中的相关性尚未得到解决。本研究旨在阐明组织蛋白酶 B 在 BOS 发病机制中的作用。我们测定了健康供体（HD）和 BOS LTx 患者支气管肺泡灌洗液（BALF）和肺组织中的组织蛋白酶 B 水平。使用荧光共振能量转移（FRET）基于测定法评估组织蛋白酶 B 活性，并使用 Western blot、ELISA 和免疫染色测定蛋白表达。为了研究组织蛋白酶 B 在 BOS 病理生理学中的影响，我们使用了原位左侧 LTx 小鼠模型。使用巨噬细胞和成纤维细胞系进行了机制研究。我们发现 BOS 患者的 BALF 和肺组织以及我们的淋巴细胞性细支气管炎小鼠模型中组织蛋白酶 B 活性显著增加。此外，组织蛋白酶 B 活性与胶原蛋白生物合成增加有关，并对肺功能产生负面影响。我们观察到组织蛋白酶 B 主要表达在浸润大量胶原沉积的区域的巨噬细胞中。在机制上，巨噬细胞衍生的组织蛋白酶 B 有助于转化生长因子-β1 依赖性成纤维细胞激活，其抑制逆转了表型。浸润的巨噬细胞释放活性组织蛋白酶 B，从而促进成纤维细胞的激活和随后的胶原沉积，从而导致 BOS。组织蛋白酶 B 是预防 BOS 进展的有前途的治疗靶点。
