Cellular Senescence in Chronic Obstructive Pulmonary Disease: Multifaceted and Multifunctional

Aging, brain-derived neurotrophic factor, and allergen-induced pulmonary responses in mice

Asthma in the elderly is being recognized as more severe, resistant to standard therapies, and having greater morbidity. Therefore, it becomes important to understand the impact of aging-associated airway structure and functional changes toward pathogenesis of asthma in the elderly. Here, airway smooth muscle plays important roles in airway hyperreactivity and structural remodeling. The role of smooth muscle in asthma can be modulated by growth factors [including neurotrophins such as brain-derived neurotrophic factor (BDNF)] and proinflammatory senescence factors. In this study, we investigated aging effects on airway hyperreactivity, structural remodeling, inflammation, and senescence in a mouse model of allergic asthma. C57BL/6J wild-type mice or smooth muscle-specific BDNF knockout mice at 4, 18, and 24 mo of age were intranasally exposed to mixed allergens (MAs, ovalbumin, Aspergillus, Alternaria, and house dust mite) over 4 wk. Assessing lung function by flexiVent, we found that compared with 4-mo-old mice, 18- and 24-mo-old C57BL/6J mice showed decreased airway resistance and increased airway compliance after PBS or MA treatment. Deletion of smooth muscle BDNF blunted airway hyperreactivity in aged mice. Lung histology analysis revealed that aging increased bronchial airway thickness and decreased lung inflammation. Multiplex assays showed that aging largely reduced allergen-induced lung expression of proinflammatory chemokines and cytokines. By immunohistochemistry staining, we found that aging increased bronchial airway expression of senescence markers, including p21, phospho-p53, and phospho-γH2A.X. Our data suggest that aging-associated increase of airway senescence in the context of allergen exposure may contribute to asthma pathology in the elderly.NEW & NOTEWORTHY The pathogenesis of asthma in elderly is not well understood. Using a mouse model of asthma, we show that aging results in decreased lung function and less responsiveness to allergen exposure, impacted by locally produced brain-derived neurotrophic factor. Aging also decreases allergen-induced inflammation but increases airway remodeling and senescence. Our results suggest that senescence pathways may contribute to asthma pathogenesis in elderly.

Cortex Mori Radicis[Morus Alba L. (Moraceae)] extract alleviates senescence via PI3K/Akt signaling in COPD fibroblasts

BACKGROUND

Chronic obstructive pulmonary disease (COPD) is marked by prolonged exposure to cigarette smoke, which accelerates senescence in lung fibroblasts and contributes to lung fibrosis. Cortex Mori Radicis [Morus albal. (Moraceae)], a traditional Chinese medicinal herb known for its antitussive properties, has emerged as a potential therapeutic agent for COPD. This study aims to elucidate the immunological mechanisms by which Cortex Mori Radicis mitigates COPD progression, utilizing a mouse model and the MRC-5 cell line.

METHODS AND RESULTS

COPD mouse models were established through chronic cigarette smoke (CS) exposure, followed by isolation of lung fibroblasts. Senescence markers and inflammatory mediators were assessed in both the isolated cells and the mice. Lung fibroblasts and bleomycin (Bleomycin)-treated MRC-5 cells exhibited elevated expression of senescence markers, including senescence-associated beta-galactosidase activity, p16INK4A, p21, p38 MAPK, and p53, along with increased levels of senescence-associated secretory phenotype (SASP) mRNA, such as IL-6 and IL-8. Treatment with Cortex Mori Radicis significantly attenuated the protein levels of these senescence markers and reduced SASP mRNA expression. Furthermore, integration of transcriptomic data from lung tissues and primary fibroblasts, combined with network pharmacology analysis, indicated that Cortex Mori Radicis inhibits fibroblast senescence via the PI3K/Akt pathway, thereby ameliorating lung pathology in COPD mice.

CONCLUSION

Through the application of transcriptomics and network analysis, this study identifies that Cortex Mori Radicis suppresses cigarette smoke-induced senescence in pulmonary tissues and bleomycin (Bleomycin)-exposed MRC-5 cells by targeting the PI3K/Akt signaling pathway. These findings underscore the therapeutic potential of Cortex Mori Radicis as a novel intervention for COPD.

MicroRNA-377-3p exacerbates chronic obstructive pulmonary disease through suppressing ZFP36L1 expression and inducing lung fibroblast senescence

Chronic obstructive pulmonary disease (COPD) is a leading aging related cause of global mortality. Small airway narrowing is recognized as an early and significant factor for COPD development. Senescent fibroblasts were observed to accumulate in lung of COPD patients and promote COPD progression through aberrant extracellular matrix (ECM) deposition and senescence-associated secretory phenotype (SASP). On the basis of our previous study, we further investigated the the causes for the increased levels of miR-377-3p in the blood of COPD patients, as well as its regulatory function in the pathological progression of COPD. We found that the majority of up-regulated miR-377-3p was localized in lung fibroblasts. Inhibition of miR-377-3p improved chronic smoking-induced COPD in mice. Mechanistically, miR-377-3p promoted senescence of lung fibroblasts, while knockdown of miR-377-3p attenuated bleomycin-induced senescence in lung fibroblasts. We also identified ZFP36L1 as a direct target for miR-377-3p that likely mediated its pro senescence activity in lung fibroblasts. Our data reveal that miR-377-3p is crucial for COPD pathogenesis, and may serve as a potential target for COPD therapy.

The lung mesenchyme in development, regeneration, and fibrosis

Mesenchymal cells are uniquely located at the interface between the epithelial lining and the stroma, allowing them to act as a signaling hub among diverse cellular compartments of the lung. During embryonic and postnatal lung development, mesenchyme-derived signals instruct epithelial budding, branching morphogenesis, and subsequent structural and functional maturation. Later during adult life, the mesenchyme plays divergent roles wherein its balanced activation promotes epithelial repair after injury while its aberrant activation can lead to pathological remodeling and fibrosis that are associated with multiple chronic pulmonary diseases, including bronchopulmonary dysplasia, idiopathic pulmonary fibrosis, and chronic obstructive pulmonary disease. In this Review, we discuss the involvement of the lung mesenchyme in various morphogenic, neomorphogenic, and dysmorphogenic aspects of lung biology and health, with special emphasis on lung fibroblast subsets and smooth muscle cells, intercellular communication, and intrinsic mesenchymal mechanisms that drive such physiological and pathophysiological events throughout development, homeostasis, injury repair, regeneration, and aging.

Cellular senescence is increased in airway smooth muscle cells of elderly persons with asthma

Senescent cells can drive age-related tissue dysfunction partially via a senescence-associated secretory phenotype (SASP) involving proinflammatory and profibrotic factors. Cellular senescence has been associated with a structural and functional decline during normal lung aging and age-related diseases such as chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrosis (IPF). Asthma in the elderly (AIE) represents a major healthcare burden. AIE is associated with bronchial airway hyperresponsiveness and remodeling, which involves increased cell proliferation and higher rates of fibrosis, and resistant to standard therapy. Airway smooth muscle (ASM) cells play a major role in asthma such as remodeling via modulation of inflammation and the extracellular matrix (ECM) environment. Whether senescent ASM cells accumulate in AIE and contribute to airway structural or functional changes is unknown. Lung tissues from elderly persons with asthma showed greater airway fibrosis compared with age-matched elderly persons with nonasthma and young age controls. Lung tissue or isolated ASM cells from elderly persons with asthma showed increased expression of multiple senescent markers including phospho-p53, p21, telomere-associated foci (TAF), as well as multiple SASP components. Senescence and SASP components were also increased with aging per se. These data highlight the presence of cellular senescence in AIE that may contribute to airway remodeling.

Impaired regenerative capacity contributes to skeletal muscle dysfunction in chronic obstructive pulmonary disease

Locomotor skeletal muscle dysfunction is a relevant comorbidity of chronic obstructive pulmonary disease (COPD) and is strongly associated with worse clinical outcomes including higher mortality. Over the last decades, a large body of literature helped characterize the process, defining the disruptive muscle phenotype caused by COPD that involves reduction in muscle mass, force-generation capacity, fatigue-tolerance, and regenerative potential following injury. A major limitation in the field has been the scarcity of well-calibrated animal models to conduct mechanistic research based on loss- and gain-of-function studies. This article provides an overall description of the process, the tools available to mechanistically investigate it, and the potential role of mitochondrially driven metabolic signals on the regulation muscle regeneration after injury in COPD. Finally, a description of future avenues to further expand on the area is proposed based on very recent evidence involving mitochondrial metabolic cues affecting myogenesis.

Role of mTOR in the development of asthma in mice with cigarette smoke-induced cellular senescence

The role of cellular senescence in the development of asthma is not well known. We aimed to evaluate the susceptibility of mice with cellular senescence to asthma development and determine whether the mTOR pathway played an important role in this process. Cellular senescence was induced in mice by intranasal instillation of 2% cigarette smoke extract (CSE). Subsequently, a low dose (0.1 μg) of house dust mite (HDM) allergens, which cause no inflammation and airway hyperresponsiveness (AHR) in mice without cellular senescence, was administered intranasally. To evaluate the role of the mTOR pathway in this model, rapamycin (TORC1 inhibitor) was injected intraperitoneally before CSE instillation. CSE significantly increased senescence-associated β-gal activity in lung homogenate and S100A8/9+ p-mTOR+ population in lung cells. Moreover, S100A8/9+ or HMGB1+ populations in airway epithelial cells with p-mTOR activity increased remarkably. Rapamycin attenuated all changes. Subsequent administration of low-dose HDM allergen induced murine asthma characterized by increased AHR, serum HDM-specific immunoglobulin E, and eosinophilic airway inflammation; these asthma characteristics disappeared after rapamycin injection. In vitro experiments showed significant activation of bone marrow-derived cells cocultured with S100A9 or HMGB1 overexpressing MLE-12 cells treated with HDM allergen, compared to those treated with HDM allergen only. CSE increased the levels of senescence markers (S100A8/9 and HMGB1) in airway epithelial cells, making the mice susceptible to asthma development due to low-dose HDM allergens by activating dendritic cells. Because rapamycin significantly attenuated asthma characteristics, the mTOR pathway may be important in this murine model.

Autophagy in major human diseases

Autophagy is a core molecular pathway for the preservation of cellular and organismal homeostasis. Pharmacological and genetic interventions impairing autophagy responses promote or aggravate disease in a plethora of experimental models. Consistently, mutations in autophagy-related processes cause severe human pathologies. Here, we review and discuss preclinical data linking autophagy dysfunction to the pathogenesis of major human disorders including cancer as well as cardiovascular, neurodegenerative, metabolic, pulmonary, renal, infectious, musculoskeletal, and ocular disorders.

Role of p53 in the Regulation of Cellular Senescence

The p53 transcription factor plays a critical role in cellular responses to stress. Its activation in response to DNA damage leads to cell growth arrest, allowing for DNA repair, or directs cellular senescence or apoptosis, thereby maintaining genome integrity. Senescence is a permanent cell-cycle arrest that has a crucial role in aging, and it also represents a robust physiological antitumor response, which counteracts oncogenic insults. In addition, senescent cells can also negatively impact the surrounding tissue microenvironment and the neighboring cells by secreting pro-inflammatory cytokines, ultimately triggering tissue dysfunction and/or unfavorable outcomes. This review focuses on the characteristics of senescence and on the recent advances in the contribution of p53 to cellular senescence. Moreover, we also discuss the p53-mediated regulation of several pathophysiological microenvironments that could be associated with senescence and its development.

Critical Challenges and Compelling Questions for Chronic Obstructive Pulmonary Disease. Moving the Field Forward: A National Heart, Lung, and Blood Institute Perspective

Although the National Heart, Lung, and Blood Institute (NHLBI) supports an active and varied portfolio of research pertaining to chronic obstructive pulmonary disease (COPD), there remain several research gaps that, when filled, could significantly help ease the burden of this disease. I use the NHLBI Strategic Vision in this article to identify opportunities for COPD research over the next decade. Filling these gaps will require collaboration between NHLBI, funded investigators, and various other stakeholders. Recent advances, including the development of powerful research technologies and the completion of the COPD National Action Plan, offer new tools that will one day improve the lives of patients with COPD and their families.

Mesenchymal Regulation of the Microvascular Niche in Chronic Lung Diseases

The adult lung is comprised of diverse vascular, epithelial, and mesenchymal progenitor cell populations that reside in distinct niches. Mesenchymal progenitor cells (MPCs) are intimately associated with both the epithelium and the vasculature, and new evidence is emerging to describe their functional roles in these niches. Also emerging, following lineage analysis and single cell sequencing, is a new understanding of the diversity of mesenchymal cell subpopulations in the lung. However, several gaps in knowledge remain, including how newly defined MPC lineages interact with cells in the vascular niche and the role of adult lung MPCs during lung repair and regeneration following injury, especially in chronic lung diseases. Here we summarize how the current evidence on MPC regulation of the microvasculature during tissue homeostasis and injury may inform studies on understanding their role in chronic lung disease pathogenesis or repair. © 2019 American Physiological Society. Compr Physiol 9:1431-1441, 2019.

Cellular senescence in the lung across the age spectrum

Cellular senescence results in cell cycle arrest with secretion of cytokines, chemokines, growth factors, and remodeling proteins (senescence-associated secretory phenotype; SASP) that have autocrine and paracrine effects on the tissue microenvironment. SASP can promote remodeling, inflammation, infectious susceptibility, angiogenesis, and proliferation, while hindering tissue repair and regeneration. While the role of senescence and the contributions of senescent cells are increasingly recognized in the context of aging and a variety of disease states, relatively less is known regarding the portfolio and influences of senescent cells in normal lung growth and aging per se or in the induction or progression of lung diseases across the age spectrum such as bronchopulmonary dysplasia, asthma, chronic obstructive pulmonary disease, or pulmonary fibrosis. In this review, we introduce concepts of cellular senescence, the mechanisms involved in the induction of senescence, and the SASP portfolio that are relevant to lung cells, presenting the potential contribution of senescent cells and SASP to inflammation, hypercontractility, and remodeling/fibrosis: aspects critical to a range of lung diseases. The potential to blunt lung disease by targeting senescent cells using a novel class of drugs (senolytics) is discussed. Potential areas for future research on cellular senescence in the lung are identified.