Bubble Trouble: Epithelial Extracellular Vesicles and Their microRNA Mischief in Chronic Obstructive Pulmonary Disease

Cellular senescence, a hallmark of lung aging, plays a crucial role in the progression of chronic obstructive pulmonary disease (COPD) (1). Emerging evidence suggests that microRNAs (miRNAs, miRs) are novel regulators of cellular processes, including senescence, in COPD (2). Notably, miR-34a promotes oxidative stress and cellular senescence by suppressing antiaging molecules such as sirtuin 1 (SIRT1) and SIRT6 in the airway epithelial cells of COPD patients (3). Previous studies have indicated that SIRT1, an antiinflammatory and antiaging protein, is reduced in the serum, lungs, and macrophages of smokers and patients with COPD (4, 5). This reduction is associated with post-translational modifications, such as the formation of nitrotyrosine and aldehyde carbonyl adducts, driven by components of cigarette smoke (4). Further evidence supports the notion that the reduction in SIRT1 also contributes to disruption of the circadian clock and abnormal inflammatory response in smokers and patients with COPD and in in vivo mouse models of cigarette smoke exposure (6, 7).

Extracellular vesicles (EVs) are tiny membrane-bound structures released by various cell types, including epithelial cells, and they play a crucial role in mediating intercellular communication (8, 9). A previous study identified specific miRNA signatures in EVs derived from the plasma of smokers and patients with COPD (10). These findings were further validated by examining EVs originating from BEAS-2B epithelial cells treated with cigarette smoke extract in comparison with untreated controls (10). Another study demonstrated that human bronchial epithelial cells exposed to serum from patients with COPD exhibit increased expression of cellular senescence markers, including senescence-associated β-galactosidase, histone γ-H2A.X, and p21, compared with those treated with serum from healthy control subjects (11). However, this study did not investigate the secretory factors or miRNAs in the serum of patients with COPD and healthy control subjects.

In this issue of the Journal, Devulder and colleagues (pp. 210–220) present compelling findings which demonstrate that EVs enriched with miR-34a can amplify the cellular senescence phenotype in small airway epithelial cells (SAECs), thereby contributing to COPD pathophysiology (12). The study revealed that SAECs from patients with COPD produce larger EVs (10-fold higher) than those from healthy control subjects. Both small and large EVs from COPD-derived SAECs were highly enriched with miR-34a compared with EVs from healthy control subjects. Uptake studies confirmed that COPD-derived EVs were internalized by healthy SAECs as early as 3 hours post-incubation. Functionally, large EVs from COPD SAECs transferred miR-34a to healthy SAECs, leading to a reduction in SIRT1 mRNA and protein concentrations. This reduction in SIRT1 expression was associated with increased senescence markers, including p21^CIP1 and p16^INK4a, elevated secretion of the proinflammatory cytokine IL-6, and enhanced senescence-associated β-galactosidase activity after 48 hours post-treatment.

To confirm the role of miR-34a, antagomirs (molecules that inhibit miRNA) targeting miR-34a were used. Treatment with these miR-34a antagomirs effectively prevented the reduction in SIRT1 levels and mitigated the increase in p21^CIP1 expression, although the effect on p16^INK4a was less pronounced. These findings highlight the importance of miR-34a–enriched EVs from COPD SAECs in driving senescence-associated secretory phenotypes (SASPs), which can be counteracted by miR-34a inhibition. This study contributes to the growing evidence that miRNA cargo in EVs plays an important role in promoting cellular senescence in neighboring cells within the lung microenvironment. Unlike soluble SASP factors, EVs offer a targeted delivery system for senescence signals, potentially explaining the localized progression of lung tissue dysfunction in COPD. Furthermore, the ability of EVs to travel systemically may provide a mechanistic explanation for the comorbidities often observed in patients with COPD, such as cardiovascular and musculoskeletal aging.

The study has several limitations worth noting. First, it lacked a detailed small RNA profile of small and large EV-enriched miRNAs and proteins from COPD and healthy control SAECs. Other members of the miR-34 family, additional miRNAs, or large EV-enriched proteins from COPD SAECs may have also contributed to the observed cellular senescence phenotype in recipient SAECs. Second, the sole focus on miR-34a’s target gene, SIRT1, and a limited set of cellular senescence and SASP mediators may not provide a comprehensive mechanistic understanding. Subsequent studies should explore additional miR-34a-specific target genes that directly influence cellular senescence and SASP signaling to strengthen the findings.

Future studies should focus on key areas to uncover mechanisms underlying cellular senescence in COPD. First, researchers should identify novel COPD-specific EV miRNA signatures and their target genes. This would provide valuable insights into the molecular pathways involved. Second, the feasibility of using EVs as delivery vehicles for therapeutic miRNAs or inhibitors, such as miR-34a antagomirs, should be investigated. Modulating disease-specific miRNAs holds promise for halting the progression of cellular senescence and other aging-related processes in COPD (13). In addition, comprehensive profiling of EV cargo, including miRNA and protein content, from patients with COPD versus healthy control subjects could further elucidate the interplay between EVs from various cell types and their contribution to COPD severity and progression. This systems-level understanding could inform the development of EV-based diagnostics and therapeutics.

This study highlights the critical role of EVs in propagating cellular senescence in COPD and age-related lung diseases. Moving forward, systematic and mechanistic investigations into EV cargo and their effects on target cells are essential to uncover novel biomarkers and therapeutic targets. The promise of liquid biopsy lies in integrated multiomics approaches, which offer a powerful avenue to explore the potential of EV cargo (e.g., miRNAs and proteins) from diverse biological sources (14). Such approaches could unravel the complex signaling networks underlying chronic lung diseases and could facilitate the identification of innovative diagnostic, prognostic, and therapeutic biomarkers (14, 15). A deeper understanding of EV signatures and their modulation may revolutionize the management of complex, age-related lung diseases such as COPD.