BACKGROUND Idiopathic pulmonary fibrosis (IPF) is a fatal lung disease with few treatment options. The poor success in developing anti-IPF strategies has impelled researchers to reconsider the importance of the choice of animal model and assessment methodologies. Currently, it is still not settled whether the bleomycin-induced lung fibrosis mouse model finally returns to resolution. METHODS This study aimed to follow the dynamic fibrotic features of bleomycin-treated mouse lungs over extended durations through a combination of the latest technologies (micro-computed tomography imaging and histological detection of degraded collagens) and traditional methods. In addition, we also applied immunohistochemistry to explore the distribution of all hydroxyproline-containing molecules. RESULTS As determined by classical biochemical methods, total lung hydroxyproline contents reached a peak at 4 weeks after bleomycin injury and maintained a steady high level thereafter until the end of the experiments (16 weeks). This result seemed to partially contradict with the changes of other fibrosis evaluation parameters, which indicated a gradual degradation of collagens and a recovery of lung aeration after the fibrosis peak. This inconsistency was well reconciled by our data from immunostaining against hydroxyproline and fluorescent peptide staining against degraded collagen, together showing large amounts of hydroxyproline-rich degraded collagen fragments detained and enriched within the intracellular regions at 10 or 16 weeks rather than at 4 weeks after bleomycin treatment. CONCLUSIONS Our present data not only offer respiratory researchers a new perspective towards the resolution nature of mouse lung fibrosis, but also remind them to be cautious when using the hydroxyproline content assay to evaluate the severity of fibrosis.

中文翻译：

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博莱霉素诱导的肺纤维化消退后的细胞内羟脯氨酸印记。

背景特发性肺纤维化（IPF）是一种致命的肺部疾病，几乎没有治疗选择。开发抗 IPF 策略的失败促使研究人员重新考虑选择动物模型和评估方法的重要性。目前，博来霉素诱导的肺纤维化小鼠模型是否最终恢复解决尚无定论。方法 本研究旨在通过结合最新技术（微型计算机断层扫描成像和降解胶原的组织学检测）和传统方法，长期跟踪博莱霉素处理的小鼠肺的动态纤维化特征。此外，我们还应用免疫组织化学来探索所有含羟脯氨酸分子的分布。结果 经经典生化方法测定，肺总羟脯氨酸含量在博来霉素损伤后4周达到峰值，此后一直保持稳定的高水平，直到实验结束（16周）。该结果似乎与其他纤维化评估参数的变化部分矛盾，这表明胶原蛋白逐渐降解，并且在纤维化高峰后肺通气恢复。我们对羟脯氨酸的免疫染色和对降解胶原蛋白的荧光肽染色的数据很好地调和了这种不一致，一起显示大量富含羟脯氨酸的降解胶原蛋白片段在博莱霉素后 10 或 16 周而不是 4 周时滞留在细胞内区域并富集治疗。