Ferroptosis is a necrotic form of regulated cell death (RCD) mediated by phospholipid peroxidation in association with free iron-mediated Fenton reactions. Disrupted iron homeostasis resulting in excessive oxidative stress has been implicated in the pathogenesis of chronic obstructive pulmonary disease (COPD). Here, we demonstrate the involvement of ferroptosis in COPD pathogenesis. Our in vivo and in vitro models show labile iron accumulation and enhanced lipid peroxidation with concomitant non-apoptotic cell death during cigarette smoke (CS) exposure, which are negatively regulated by GPx4 activity. Treatment with deferoxamine and ferrostatin-1, in addition to GPx4 knockdown, illuminate the role of ferroptosis in CS-treated lung epithelial cells. NCOA4-mediated ferritin selective autophagy (ferritinophagy) is initiated during ferritin degradation in response to CS treatment. CS exposure models, using both GPx4-deficient and overexpressing mice, clarify the pivotal role of GPx4-regulated cell death during COPD. These findings support a role for cigarette smoke-induced ferroptosis in the pathogenesis of COPD.

Extracellular vesicles (EVs), such as exosomes and microvesicles, encapsulate proteins and microRNAs (miRNAs) as new modulators of both intercellular crosstalk and disease pathogenesis. The composition of EVs is modified by various triggers to maintain physiological homeostasis. In response to cigarette smoke exposure, the lungs develop emphysema, myofibroblast accumulation and airway remodelling, which contribute to chronic obstructive pulmonary disease (COPD). However, the lung disease pathogenesis through modified EVs in stress physiology is not understood. Here, we investigated an EV‐mediated intercellular communication mechanism between primary human bronchial epithelial cells (HBECs) and lung fibroblasts (LFs) and discovered that cigarette smoke extract (CSE)‐induced HBEC‐derived EVs promote myofibroblast differentiation in LFs. Thorough evaluations of the modified EVs and COPD lung samples showed that cigarette smoke induced relative upregulation of cellular and EV miR‐210 expression of bronchial epithelial cells. Using co‐culture assays, we showed that HBEC‐derived EV miR‐210 promotes myofibroblast differentiation in LFs. Surprisingly, we found that miR‐210 directly regulates autophagy processes via targeting ATG7, and expression levels of miR‐210 are inversely correlated with ATG7 expression in LFs. Importantly, autophagy induction was significantly decreased in LFs from COPD patients, and silencing ATG7 in LFs led to myofibroblast differentiation. These findings demonstrate that CSE triggers the modification of EV components and identify bronchial epithelial cell‐derived miR‐210 as a paracrine autophagy mediator of myofibroblast differentiation that has potential as a therapeutic target for COPD. Our findings show that stressor exposure changes EV compositions as emerging factors, potentially controlling pathological disorders such as airway remodelling in COPD.

Cigarette smoke (CS)-induced accumulation of mitochondrial damage has been widely implicated in chronic obstructive pulmonary disease (COPD) pathogenesis. Mitophagy plays a crucial role in eliminating damaged mitochondria, and is governed by the PINK1 (PTEN induced putative protein kinase 1)-PRKN (parkin RBR E3 ubiquitin protein ligase) pathway. Although both increased PINK1 and reduced PRKN have been implicated in COPD pathogenesis in association with mitophagy, there are conflicting reports for the role of mitophagy in COPD progression. To clarify the involvement of PRKN-regulated mitophagy in COPD pathogenesis, prkn knockout (KO) mouse models were used. To illuminate how PINK1 and PRKN regulate mitophagy in relation to CS-induced mitochondrial damage and cellular senescence, overexpression and knockdown experiments were performed in airway epithelial cells (AEC). In comparison to wild-type mice, prkn KO mice demonstrated enhanced airway wall thickening with emphysematous changes following CS exposure. AEC in CS-exposed prkn KO mice showed accumulation of damaged mitochondria and increased oxidative modifications accompanied by accelerated cellular senescence. In vitro experiments showed PRKN overexpression was sufficient to induce mitophagy during CSE exposure even in the setting of reduced PINK1 protein levels, resulting in attenuation of mitochondrial ROS production and cellular senescence. Conversely PINK1 overexpression failed to recover impaired mitophagy caused by PRKN knockdown, indicating that PRKN protein levels can be the rate-limiting factor in PINK1-PRKN-mediated mitophagy during CSE exposure. These results suggest that PRKN levels may play a pivotal role in COPD pathogenesis by regulating mitophagy, suggesting that PRKN induction could mitigate the progression of COPD. Abbreviations: AD: Alzheimer disease; AEC: airway epithelial cells; BALF: bronchoalveolar lavage fluid; AKT: AKT serine/threonine kinase; CALCOCO2/NDP52: calcium binding and coiled-coil domain 2; CDKN1A: cyclin dependent kinase inhibitor 1A; CDKN2A: cyclin dependent kinase inhibitor 2A; COPD: chronic obstructive pulmonary disease; CS: cigarette smoke; CSE: CS extract; CXCL1: C-X-C motif chemokine ligand 1; CXCL8: C-X-C motif chemokine ligand 8; HBEC: human bronchial epithelial cells; 4-HNE: 4-hydroxynonenal; IL: interleukin; KO: knockout; LF: lung fibroblasts; LPS: lipopolysaccharide; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MTOR: mechanistic target of rapamycin kinase; 8-OHdG: 8-hydroxy-2ʹ-deoxyguanosine; OPTN: optineurin; PRKN: parkin RBR E3 ubiquitin protein ligase; PCD: programmed cell death; PFD: pirfenidone; PIK3C: phosphatidylinositol-4:5-bisphosphate 3-kinase catalytic subunit; PINK1: PTEN induced putative kinase 1; PTEN: phosphatase and tensin homolog; RA: rheumatoid arthritis; ROS: reactive oxygen species; SA-GLB1/β-Gal: senescence-associated-galactosidase, beta 1; SASP: senescence-associated secretory phenotype; SNP: single nucleotide polymorphism; TNF: tumor necrosis factor.

Accumulation of profibrotic myofibroblasts in fibroblastic foci (FF) is a crucial process for development of fibrosis during idiopathic pulmonary fibrosis (IPF) pathogenesis, and transforming growth factor (TGF)-β plays a key regulatory role in myofibroblast differentiation. Reactive oxygen species (ROS) has been proposed to be involved in the mechanism for TGF-β-induced myofibroblast differentiation. Metformin is a biguanide antidiabetic medication and its pharmacological action is mediated through the activation of AMP-activated protein kinase (AMPK), which regulates not only energy homeostasis but also stress responses, including ROS. Therefore, we sought to investigate the inhibitory role of metformin in lung fibrosis development via modulating TGF-β signaling. TGF-β-induced myofibroblast differentiation in lung fibroblasts (LF) was used for in vitro models. The anti-fibrotic role of metfromin was examined in a bleomycin (BLM)-induced lung fibrosis model. We found that TGF-β-induced myofibroblast differentiation was clearly inhibited by metformin treatment in LF. Metformin-mediated activation of AMPK was responsible for inhibiting TGF-β-induced NOX4 expression. NOX4 knockdown and N-acetylcysteine (NAC) treatment illustrated that NOX4-derived ROS generation was critical for TGF-β-induced SMAD phosphorylation and myofibroblast differentiation. BLM treatment induced development of lung fibrosis with concomitantly enhanced NOX4 expression and SMAD phosphorylation, which was efficiently inhibited by metformin. Increased NOX4 expression levels were also observed in FF of IPF lungs and LF isolated from IPF patients. These findings suggest that metformin can be a promising anti-fibrotic modality of treatment for IPF affected by TGF-β.

Aging is a major risk factor for the development of chronic lung diseases such as chronic obstructive pulmonary disease (COPD), idiopathic pulmonary fibrosis (IPF), and lung cancer. A main aspect of aging is the impaired function of maintaining homeostasis in the organs and body, which is associated with cellular senescence. Cellular senescence is recognized as the state of irreversible cell cycle arrest in response to a variety of cellular stresses. Senescent cells are not simply cell cycle-arrested cells; they also affect bystander cells through the secretion of bioactive molecules, termed the senescence-associated secretory phenotype (SASP). Many studies strongly indicate that senescent cells in the lungs are associated with the pathogenesis of age-related lung diseases by releasing SASP factors. Extracellular vesicles (EVs), including exosomes, microvesicles, and apoptotic bodies, are released from almost all cell types and are recognized as important mediators of intercellular communication. They have been shown to carry and transfer a wide variety of molecules, such as microRNAs, messenger RNAs, DNA, and proteins, which can contribute to physiological functions and the pathology of various diseases. Increasing evidence suggests that EVs secreted from senescent cells have unique characteristics and contribute to modulating the phenotype of recipient cells similar to SASP factors. Thus, the EVs secreted from senescent cells, namely, senescence-associated EVs, appear to be a novel SASP factor. In this review, we summarize the current knowledge linking senescence-associated EVs to the SASP factor and discuss the roles of these EVs in age-related lung diseases.

It is currently thought that extracellular vesicles (EVs), such as exosomes and microvesicles, play an important autocrine/paracrine role in intercellular communication. EVs package proteins, mRNA and microRNA (miRNA), which have the ability to transfer biological information to recipient cells in the lungs. Depending on their origin, EVs fulfil different functions. EVs derived from mesenchymal stem cells (MSCs) have been found to promote therapeutic activities that are comparable to MSCs themselves. Recent animal model-based studies suggest that MSC-derived EVs have significant potential as a novel alternative to whole-cell therapies. Compared to their parent cells, EVs may have a superior safety profile and can be stored without losing function. It has been observed that MSC-derived EVs suppress pro-inflammatory processes and reduce oxidative stress, pulmonary fibrosis and remodeling in a variety of in vivo inflammatory lung disease models by transferring their components. However, there remain significant challenges to translate this therapy to the clinic. From this view point, we will summarize recent studies on EVs produced by MSCs in preclinical experimental models of inflammatory lung diseases. We will also discuss the most relevant issues in bringing MSC-derived EV-based therapeutics to the clinic for the treatment of inflammatory lung diseases.