Citations

Iron is an essential element for cellular homeostasis and functionality. Increased iron in the lung is associated with aging and asthma in the elderly (AIE). Using human airway smooth muscle cells from young versus elderly versus AIE patients, we found that dysregulated iron metabolism (more than iron accumulation), resulting in activation of antioxidant systems and increased susceptibility to ferroptosis, occurs in AIE, contributing to cell hyperplasia and matrix remodeling of aging and AIE.

Iron is an important metal element regulating biological processes such as gene expression, electron transport, cell proliferation, differentiation and division, and cellular respiration. Regulation of iron levels is therefore critical, with excess iron accumulation leading to iron-dependent lipid peroxidation and cell death (ferroptosis). Factors such as aging and environmental exposures (e.g., high/low oxygen, particulate iron) can disrupt iron homeostasis. Iron-dependent processes influence downstream pathways such as inflammation, mitochondrial energetics, and remodeling (proliferation, fibrosis), pathways involved in lung diseases particularly at the extremes of age, from hyperoxic lung injury in neonates to chronic diseases such as asthma, chronic obstructive pulmonary disease (COPD), and pulmonary fibrosis (PF) that increase with age. Although these diseases involve structural and functional changes in bronchial versus alveolar compartments, including airway hyperreactivity, altered mucus production, cell proliferation and migration, increased extracellular matrix (ECM) remodeling, senescence, and metabolic dysregulation, the casual or consequential links between iron dysregulation and disease pathology, particularly with aging, are still being investigated. The aim of this topical review is to 1) highlight current knowledge regarding iron regulation in normal lung versus lung diseases, 2) identify known roles of iron in lung homeostasis and the contribution of iron dysregulation in lung diseases with aging, and 3) explore the potential benefit of targeting iron regulation and/or ferroptosis in lung diseases.

Abstract Introduction Pulmonary fibrosis is characterized by excessive fibroblast activation and alveolar remodeling, leading to progressive lung dysfunction. Osteoglycin (OGN), a small leucine-rich proteoglycan, and its functional fragment MC002 have been identified as regulators of alveolar epithelial regeneration, a process that is impaired in fibrotic lung disease. This study investigates the effects of OGN and MC002 on TGF-β-induced fibrotic responses in lung fibroblasts, organoids, and an in vivo fibrosis model. Methods Human lung fibroblasts (MRC5) were treated with OGN or MC002 for 48 hours, with or without transforming growth factor-beta (TGF-β; 2 ng/mL). Expression of the myofibroblast marker α-smooth muscle actin (ACTA2) and matrix markers collagen 1a1 (COL1A1) and fibronectin (FN1) was assessed by RT-PCR and Western blotting. Global transcriptomic changes were analyzed by RNA sequencing. Myofibroblast differentiation was evaluated by phalloidin staining and quantified using the phalloidin/DAPI ratio. Murine lung organoids were generated by co-culturing epithelial progenitor cells with fibroblasts and treated with TGF-β (2 ng/mL) in the presence or absence of OGN or MC002. Organoid number, size, and alveolar differentiation were quantified after 14 days. In vivo, pulmonary fibrosis was induced in mice using intratracheal bleomycin. MC002 was administered at different doses (6.75 µg or 20.25 µg) every other day starting from day 7 post-bleomycin, and lung weight and pressure-volume (PV) loops were assessed to evaluate fibrotic burden and lung mechanics. Osteoglycin expression in human lung tissue from 13 non-smokers, 11 ex-smokers, and 12 IPF patients was analyzed by immunostaining. Results TGF-β induced pro-fibrotic gene expression in fibroblasts, while OGN and MC002 alone had no pro-fibrotic effects. MC002 fully reversed TGF-β-induced ACTA2, COL1A1, and FN1 expression, whereas OGN selectively attenuated COL1A1. RNA-sequencing revealed broad suppression of fibrosis- and ECM-associated gene programs by MC002. At the protein level, TGF-β-induced ACTA2 expression was reversed by MC002 but not by OGN. Both compounds reduced TGF-β-induced stress fiber formation. In lung organoids, TGF-β impaired organoid formation and alveolar differentiation, effects that were restored by OGN and MC002 in a concentration-dependent manner. In the bleomycin model, MC002 significantly reduced lung weight and improved PV loop profiles, indicating attenuation of fibrotic stiffening and improved lung compliance. Osteoglycin protein expression was significantly diminished in IPF whole lung tissue and parenchyma compared to controls. Conclusion OGN, and particularly MC002, counteract TGF-β-driven fibroblast activation and myofibroblast differentiation while promoting alveolar preservation. The superior efficacy of MC002 supports its potential as a therapeutic candidate for pulmonary fibrosis. This abstract is funded by: Lung Foundation Netherlands 10.1.23.021PPS

Recognizing that antioxidant systems are impaired in the airways of premature infants, we used human fetal airway cells to explore the impact of oxygen on iron regulation and iron-mediated cell death (ferroptosis). We find moderate hyperoxia impairs antioxidant systems that prevent ferroptosis and dysregulates iron metabolism, while severe hyperoxia has a negative effect on mechanisms driving the early onset of ferroptosis. Inhibitors of ferroptosis decrease iron and lipid peroxidation, demonstrating links between oxygen and iron regulation in developing airways.

Abstract As an intrinsically mechanosensitive organ, the lung experiences a range of mechanical forces. Chronic obstructive pulmonary disease (COPD) involves abnormal macroscopic cellular and extracellular matrix (ECM) changes that impact mechanical properties of the lung. Mechanosensitive Piezo1/2 channels are expressed in the lung including on airway smooth muscle cells (ASM) that mediate cellular responses to stretch and ECM biomechanics. The expression and roles of Piezos in COPD lung ASM are not known. We hypothesized that Piezo expression and activation are altered in COPD lung ASM influencing ECM regulation. Distribution of Piezo proteins in ASM and epithelium of small airways of COPD stage II and IV vs. non-COPD controls was assessed using immunohistochemistry and ImageJ (n=10-17/group). Isolated ASM cells from control (n=6) vs. COPD stage II and IV patients (n=3 each stage) were exposed to stretch or the Piezo1 agonist Yoda1 followed by measurement of ECM gene and protein expression. Less Piezo2 staining was observed in COPD IV patients compared to controls, with lesser area and intensity of staining in the epithelial layer, and lower intensity of staining in ASM and small airways as a whole. Fura-2-based imaging of ASM Ca 2+ showed lower influx after Yoda1 exposure in COPD II compared to control and COPD IV. Gene expression of Piezo1 increased upon stretching in controls but not in COPD ASM, while Piezo2 protein expression decreased with stretching in all groups. Yoda1 treatment resulted in decreased collagen1 , fibulin1 and periostin gene and collagen 1 and periostin protein expression in ASM. Overall, these results support a role for Piezo activation in abnormal ECM-ASM cell crosstalk in COPD.

Abstract Rationale Premature birth necessitates interventions such as supplemental O2 (hyperoxia, typically <60% O2) with or without respiratory support primarily using nasal CPAP. The static stretch of CPAP can induce sustained airway hyperresponsiveness (AHR) and airway thickening (remodeling) even after CPAP is stopped - effects that contribute to a wheezing phenotype and predispose to asthma, major sources of respiratory morbidity in former “preemies.” Effects of CPAP can impact airway smooth muscle (ASM), a key cell type in asthma. We sought to find out if mechanosensitive Piezo (PZ) channels in developing ASM contribute to CPAP-induced AHR and remodeling. In other cell systems, PZ affects the Wnt/β-catenin (β-cat) pathway, but there is currently little information on how stretch influences this pathway and its downstream role in developing ASM. Our overall hypothesis is that in developing airways, PZ channels and downstream Wnt/β-cat pathway are linked in the context of stretch effects, leading to AHR and remodeling. Methods Fetal ASM (fASM) cells were isolated from lungs of 18-20-week fetuses (Mayo IRB exempt). Neonatal mice (comparable to late gestation humans) were also used; lung tissue was harvested following IACUC protocols. Western blot (WB), qRT-PCR, immunofluorescence imaging (IF), extracellular matrix (ECM) deposition assay, proliferation assay, and precision cut lung slice (PCLS) imaging were performed. Stretch conditions used were “non-stretch” (0% static strain imposed on 5% cyclic strain representing normal breathing) or “stretch” (5-10% static strain imposed on 5% cyclic strain, representing superimposed CPAP). Compounds used were Yoda1 (PZ1 agonist), GsMTx4 (PZ inhibitor), DKK1 (Wnt pathway inhibitor), and Wnt3a ligand. Results PZ1 and PZ2 are expressed in fASM and stretch increased expression of both, shown by qRT-PCR and WB. In neonatal mice exposed to CPAP, lumen area of PCLS were decreased compared to control; GsMTx4 alleviated this effect. Stretch increased ECM in fASM, however the effect was blunted by GsMTx4. Stretch increased mRNA for canonical Wnt pathway elements and decreased negative regulatory elements. Stretch increased GSK3β protein phosphorylation and β-cat protein nuclear translocation; effects blunted by DKK1. Wnt3a ligand increased proliferation and ECM in fASM. Stretch increased Wnt3a mRNA and β-cat protein nuclear translocation, with effects blunted by GsMTx4. Stretch alone or in combination with Wnt3a ligand, as well as Yoda1 alone, increased nuclear β-cat, shown qualitatively by IF. Conclusions Our study showed that Wnt/β-cat may be a novel, important, and conceivably targetable pathway (e.g. with PZ modulators) in alleviating potentially long-term, detrimental airway responses to CPAP. This abstract is funded by: NIH R01 HL056470 (Prakash), R01 HL177837 (Pabelick)

Abstract Rationale Premature infants exposed to supplemental oxygen are at increased risk of developing airway diseases such as bronchopulmonary dysplasia (BPD) and asthma, making it important to understand how oxygen detrimentally impacts developing airways. Even in moderation, hyperoxia promotes bronchial airway hyperresponsiveness (AHR) through effects on fetal airway smooth muscle (fASM), a cell type involved in impaired bronchodilation and remodeling. Iron dysregulation has been implicated in adult airway diseases such as asthma, COPD, and hyperoxic lung injury (HLI). Immature antioxidant systems in neonates and their increased susceptibility to iron-induced oxidative stress may lead to ferroptosis, contributing to pathologies observed in subsequent airway disease. The role of impaired iron metabolism, mediated by hyperoxia, remains largely unexplored in fetal airways. This study investigated the effects of increasing oxygen levels on antioxidant systems, iron metabolism, and lipid peroxidation in human fASM. Methods fASM from 18-20 week gestational age (canalicular stage; Mayo IRB exempt) were isolated and exposed to normoxia (21% O2) or increasing levels of hyperoxia (50%, 70%, and 90% O2) and treated with iron chelator, deferoxamine (DFO) [100uM] or reactive oxygen species (ROS) scavenger ferrostatin (Fer-1) [10uM] for 48h. Levels of intracellular iron (Fe2+) were determined using ferroOrange. Cell lysates were examined for protein expression of antioxidant markers (GPX4, SLC7A11, CBS, NRF2, KEAP1, and FSP1) and iron metabolism markers (TfR1, FTH1, and NCOA4). 4-HNE (lipid radical) expression was determined by immunofluorescence staining. Results Hyperoxia decreased SLC7A11, CBS, NRF2, KEAP1 (redox regulators), and iron storage (FTH1) at all concentrations. Iron influx (TfR1) increased under 50% and 70% O2 but not 90% O2. Cytosolic iron levels increased under hyperoxia in a dose-dependent manner and decreased with iron chelator, DFO. DFO further decreased FTH1 expression under 90% O2. 4-HNE (lipid radical) increased under 90% O2 and was reduced by ROS scavenger, Fer-1. Conclusion Our findings suggest that hyperoxia simultaneously impairs antioxidant systems and iron metabolism in fASM. Specifically, hyperoxia dose-dependently increases the labile iron pool which exhausts anti-ferroptotic mechanisms: effects which can be reduced by DFO and Fer-1. This implies the presence of a redox threshold tightly regulating iron accumulation in fASM. Overall, antioxidant impairment and iron metabolism dysfunction synergistically can contribute to pediatric airway disease: mechanisms which allow for the development of targetable strategies to blunt the impact of supplemental oxygen in the premature lung. This abstract is funded by: National Institutes of Health

Abstract Rationale Pulmonary Fibrosis (PF) is a fibroproliferative disease characterized by increased proliferation, constant extracellular matrix (ECM) deposition, and dysfunctional antioxidant systems. In PF, an emerging initiator is abnormal iron regulation and lipid peroxidation: consequences of iron catalyzed cell death, i.e. ferroptosis (FP). Abnormal iron regulation and lipid peroxidation lead to diminished glutathione (GSH)/glutathione peroxidase 4 (GPX4) antioxidant systems which promote ECM signaling in fibroblasts. Accordingly, inhibiting ferroptosis and/or correcting iron dysregulation via increasing GSH can help with early PF intervention. We hypothesize that enhanced hydrogen sulfide (H2S) signaling through exogenous H2S donors GYY4137 (slow-releasing) and AP39 (mitochondrial-specific), can blunt FP/lipid peroxidation leading to reduced ECM deposition in the context of PF. Methodsand Results Human fibroblasts were isolated from lung tissue of patients with PF and healthy patients (Mayo IRB approved) and were treated with exogenous H2S donors. Prussian blue staining of FFPE lung sections from patients with PF revealed increased ferric iron in alveolar regions. Immunostaining of PF human lung tissue showed lower expression of H2S generating enzyme, CBS, and higher expression of the lipid peroxidation enzyme, ACSL4, compared to non-PF patients. At the cellular level, Western blot was performed in fibroblasts to understand the effect of PF on Fe regulation. PF fibroblasts showed higher expression of transferrin receptor (TfR1) and ferritin, as well as higher expression of ACSL4. The impact of exogenous H2S donors on PF fibroblasts was tested. While H2S donors did not impact TfR1 or ferritin, they did blunt lipid peroxidation as determined using live cell BDP 581/591 C11- fluorescent imaging and ACSL4 protein expression. Furthermore, GYY4137 increased the cysteine transport protein xCT(SLC7A11; part of xC), the H2S synthesis enzyme CBS and GPX4, overall showing an antioxidant effect. This was further substantiated though measuring GSH/GSSG ratios via luminescence assay. In PF fibroblasts, GSH/GSSG levels were low comparatively to normal fibroblasts. However, with exogenous H2S, PF fibroblasts showed increased GSH/GSSG levels indicating a restoration of antioxidant function. Deposition of collagen-1 was higher in PF fibroblasts, and was blunted by GYY4137, which was more potent than the FP inhibitor ferrostatain-1. Conclusion Our data suggests ferroptosis/impaired antioxidant systems are significant factors in PF and that exogeneous H2S can be leveraged to replenish antioxidant systems and blunt FP, thus potentially reducing fibrotic activity. This abstract is funded by: NIH T32 HL 176414 (Ravi), R01 HL160570 (Pabelick, Prakash), R01 HL158532 (Prakash)

Abstract Rationale Bronchial airways are exposed to continual mechanical forces such as normal breathing, sighs, and clinically applied pressures such as CPAP that influence airway smooth muscle mechanics. Asthmatic airways experience exaggerated mechanical stress due to bronchoconstriction and airway wall thickening (remodeling) which contributes to lung injury. Mechanical stress is known to alter redox balance and ion channel signaling, yet its impact on iron homeostasis in asthmatic human airway smooth muscle cells (hASMs) remain unclear. Ferroptosis and iron dysregulation have emerged as significant factors in epithelial damage and airway inflammation in asthmatic models. In addition, recently discovered mechanosensitive Piezo (PZ) channels play a critical role in calcium influx upon mechanical stimulation and have been shown to contribute to iron dysregulation. In this study, we used hASMs to test the hypothesis that asthmatic patients experience iron dysregulation in the presence of mechanical stimulation. Methods hASMs and lung tissues from adult male and female patients with/without asthma were used (approved by Mayo IRB). Cells were pretreated with either PZ inhibitor GsMTx4 [1 µM] or PZ1 agonist Yoda1 [10 µM] 45 minutes before stretch. Cells were exposed to normal breathing stretch conditions on a FlexCell System at a 5% cyclic strain (15 cycles/minute) or 10% static stretch superimposed onto normal breathing for 24 hours. Cell lysates were examined for iron accumulation and antioxidant and lipid peroxidation markers (FTH1, TfR1, GPX4, and SLC7A11). Levels of intracellular ferrous iron (Fe2+) were determined using the fluorescent dye FerroOrange in non-stretched samples. Results In healthy airways PZ inhibition decreased iron uptake while activation increased intracellular iron uptake. In healthy airways, mechanical stretch upregulated SLC7A11 expression in a PZ1 independent manner, while mechanical stretch in asthmatic patients displayed no increase in the cysteine transporter. Transferrin levels remained unchanged under mechanical stimulation but displayed upregulation in asthmatic cells. In healthy cells, ferritin showed no changes in response to stretch, however, asthmatic cells showed lower baseline expression and increased its expression in response to stretch in a PZ1 independent manner. GPX4 showed no changes in expression between healthy and asthmatic groups or in response to stretch. Conclusions Our findings suggest that PZ and mechanical stretch play a role in iron regulation in hASMs. Additionally, iron regulation is impaired in asthmatic populations, suggesting a resultant increased iron import, decreased capacity to sequester iron, and decreased defensive cysteine import. This abstract is funded by: NIH R01HL171915 (CMP), R01HL056470 (YSP) 24POST1241979 (NAB)

ABSTRACT Supplemental oxygen (hyperoxia), often provided to premature infants, can disrupt lung growth and contribute to development of neonatal and pediatric lung diseases, necessitating understanding of underlying mechanisms. We previously showed that even moderate hyperoxia (< 60% O 2 ) induces detrimental cellular senescence in 18–22 weeks human fetal airway smooth muscle (fASM), a key cell type in airway contractility and remodeling. In this study, we examined the ability of senotherapeutics Fucoidan and Dasatinib (D) + Quercetin (Q) (D + Q) to mitigate adverse effects of hyperoxia and assessed the preventive effect of mitochondrial antioxidants (MitoQ). fASM cells exposed to normoxia (21% O 2 ) or hyperoxia (50% O 2 ) were treated with Fucoidan [100 μg/mL], D + Q [250 nM + 375 nM] or MitoQ [100 nM] and assessed for senescence markers, senescence‐associated secretory profile (SASP), extracellular matrix (ECM) deposition, and cell viability. Our results showed that moderate hyperoxia increases senescence markers and SASP. Fucoidan decreased p21 expression and inhibited SASP release without inducing cell death, while D + Q decreased β‐galactosidase (β‐Gal) activity, p21 and plasminogen activator inhibitor‐1 (PAI‐1) expression, and caused cell death without affecting SASP in hyperoxia‐induced senescent fASM. MitoQ prevented increases in senescence markers and SASP in hyperoxia‐exposed fASM. These findings demonstrate distinct and viable strategies to counter hyperoxia‐induced fASM senescence. Fucoidan (senomorphic), D + Q (senolytic), and MitoQ (prophylactic antioxidant) represent promising, mechanistically different approaches to alleviate detrimental effects of moderate hyperoxia in developing airways towards limiting perinatal lung disease.