Koloko Ngassie, Maunick Lefin

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.

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 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.

Mechanical stretch associated with respiratory support can impair airway development and function in neonates, but the mechanisms are not fully understood. Using developing human airway smooth muscle cells exposed to cyclic forces with static stretch to mimic continuous positive airway pressure, we found that stretch dysregulates long-term cell proliferation and inflammatory cytokine production, and mechanosensitive Piezo ion channels may play a role in the proliferation response.

Supplemental O 2 (hyperoxia) in premature infants detrimentally affects bronchial airways leading to increased senescence. Understanding the mechanisms by which hyperoxia initiates senescence in developing airways is critical for future therapeutic strategies. The current study showed that hyperoxia-induced senescence is mediated through increased mitochondrial reactive oxygen species and endoplasmic reticulum (ER) stress. ER stress inhibitors or mitochondria-targeted antioxidants may represent future therapies to blunt detrimental effects of supplemental oxygen in developing lungs.

Our previous study suggests that glial-derived neurotrophic factor (GDNF) is involved in allergen-induced airway hyperreactivity and remodeling in vivo. Here, we show that GDNF has no direct effects in remodeling of human airway smooth muscle (ASM) but GDNF dysregulates mitochondrial morphology in human ASM in the context of asthma.

Our study identified chronic obstructive pulmonary disease (COPD)-associated differences in the lung extracellular matrix (ECM) composition. We highlight the compartmental differences in the ECM landscape in different subtypes of COPD. The most prominent differences were observed for severe-early onset COPD. Moreover, we identified unique ECM signatures that describe airway walls and parenchyma providing insight into the intertwined nature and complexity of ECM changes in COPD that together drive ECM remodeling and may contribute to disease pathogenesis.

Mechanical forces on the airway can contribute to altered contractility and remodeling in airway diseases, but the mechanisms are not clearly understood. Using human airway smooth muscle cells exposed to cyclic forces with static stretch to mimic breathing and static pressure, we found that the effects of stretch are mediated through STIM1, resulting in the activation of multiple pathways, including Piezo channels and the inflammasome, with potential downstream influences on contractility and remodeling.