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Idiopathic pulmonary fibrosis (IPF) is an age-related disease. Failure of the proteostasis network with age, including insufficient autophagy, contributes to the pathology of IPF. Mechanisms underlying autophagy disruption in IPF are unclear and may involve regulation of USP (ubiquitin-specific protease) by post-translational modifications. To expand our previous observation of low USP13 expression in IPF, this study evaluated the role of USP13 in age-related lung fibrosis. Here, we demonstrated that Usp13 -deficient aged mice exhibited impaired autophagic activity and increased vulnerability to bleomycin-induced fibrosis. Mechanistically, USP13 interacted with and deubiquitinated Beclin 1, and Beclin 1 overexpression abolished the effects of USP13 disruption. In addition, Beclin 1 inhibition resulted in insufficient autophagy and more severe lung fibrosis after bleomycin injury, consistent with the phenotype of aged Usp13 -deficient mice. Collectively, we show a protective role of USP13 in age-related pulmonary fibrosis. Aging-mediated USP13 loss impairs autophagic activity and facilitates lung fibrosis through Beclin 1 deubiquitination. Our findings support the notion that age-dependent dysregulation of autophagic regulators enhances vulnerability to lung fibrosis.

The dysfunction of type II alveolar epithelial cells (AECIIs), mainly manifested by apoptosis, has emerged as a major component of idiopathic pulmonary fibrosis (IPF) pathophysiology. A pivotal mechanism leading to AECIIs apoptosis is mitochondrial dysfunction. Recently, interleukin (IL)-17A has been demonstrated to have a pro-fibrotic role in IPF, though the mechanism is unclear. In this study, we report enhanced expression of IL-17 receptor A (IL-17RA) in AECIIs in lung samples of IPF patients, which may be related to the accumulation of mitochondria in AECIIs of IPF. Next, we investigated this relationship in bleomycin (BLM)-induced PF murine model. We found that IL-17A knockout (IL-17A -/- ) mice exhibited decreased apoptosis levels of AECIIs. This was possibly a result of the recovery of mitochondrial morphology from the improved mitochondrial dynamics of AECIIs, which eventually contributed to alleviating lung fibrosis. Analysis of in vitro data indicates that IL-17A impairs mitochondrial function and mitochondrial dynamics of mouse primary AECIIs, further promoting apoptosis. PTEN-induced putative kinase 1 (PINK1)/Parkin signal-mediated mitophagy is an important aspect of mitochondria homeostasis maintenance. Our data demonstrate that IL-17A inhibits mitophagy and promotes apoptosis of AECIIs by decreasing the expression levels of PINK1. We conclude that IL-17A exerts its pro-fibrotic effects by inducing mitochondrial dysfunction in AECIIs by disturbing mitochondrial dynamics and inhibiting PINK1-mediated mitophagy, thereby leading to apoptosis of AECIIs., (© 2022 The Authors. Journal of Cellular and Molecular Medicine published by Foundation for Cellular and Molecular Medicine and John Wiley & Sons Ltd.)

Background: Serum Krebs von den Lungen-6 (KL-6) has been reported to be elevated in patients with idiopathic pulmonary fibrosis (IPF)., Objective: The aim of this study was to evaluate the diagnostic value of KL-6 and whether the expression value of KL-6 could indicate the severity of the disease in IPF patients. To address this question, it is necessary to see whether the patients' physical characteristics and other clinical conditions could affect the baseline KL-6 level., Design: We conducted a study of 100 patients who were diagnosed with IPF. Lung function, computed tomography (CT), and serological lab tests data were analyzed., Results: The tests showed that there is a significant elevation of KL-6 in IPF patients compared with other interstitial lung disease (ILD) and healthy controls. It was noted that serum KL-6 is a stable biomarker not affected by lung infection and smoking, though IPF patients with antinuclear antibody (ANA) showed higher KL-6 levels. KL-6, in conjunction with poor pulmonary function and higher radiological fibrosis scores, indicates the severity of the disease but not poor survival., Conclusions: It is identified that serum KL-6 is a useful noninvasive biomarker to help improve the certainty of IPF diagnosis from other interstitial lung disease and assist evaluation of disease severity and prognosis., (© 2022 The Authors. The Clinical Respiratory Journal published by John Wiley & Sons Ltd.)