Quercetin Enhances Ligand-induced Apoptosis in Senescent Idiopathic Pulmonary Fibrosis Fibroblasts and Reduces Lung Fibrosis In Vivo

Wound healing: cellular mechanisms and pathological outcomes

Wound healing is a complex, dynamic process supported by a myriad of cellular events that must be tightly coordinated to efficiently repair damaged tissue. Derangement in wound-linked cellular behaviours, as occurs with diabetes and ageing, can lead to healing impairment and the formation of chronic, non-healing wounds. These wounds are a significant socioeconomic burden due to their high prevalence and recurrence. Thus, there is an urgent requirement for the improved biological and clinical understanding of the mechanisms that underpin wound repair. Here, we review the cellular basis of tissue repair and discuss how current and emerging understanding of wound pathology could inform future development of efficacious wound therapies.

Insights into the Role of Bioactive Food Ingredients and the Microbiome in Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic disease mainly associated with aging and, to date, its causes are still largely unknown. It has been shown that dietary habits can accelerate or delay the occurrence of aging-related diseases; however, their potential role in IPF development has been underestimated so far. The present review summarizes the evidence regarding the relationship between diet and IPF in humans, and in animal models of pulmonary fibrosis, in which we discuss the bioactivity of specific dietary food ingredients, including fatty acids, peptides, amino acids, carbohydrates, vitamins, minerals and phytochemicals. Interestingly, many animal studies reveal preventive and therapeutic effects of particular compounds. Furthermore, it has been recently suggested that the lung and gut microbiota could be involved in IPF, a relationship which may be linked to changes in immunological and inflammatory factors. Thus, all the evidence so far puts forward the idea that the gut-lung axis could be modulated by dietary factors, which in turn have an influence on IPF development. Overall, the data reviewed here support the notion of identifying food ingredients with potential benefits in IPF, with the ultimate aim of designing nutritional approaches as an adjuvant therapeutic strategy.

Impaired Myofibroblast Dedifferentiation Contributes to Nonresolving Fibrosis in Aging

Idiopathic pulmonary fibrosis (IPF) is a fatal age-associated disease with no cure. Although IPF is widely regarded as a disease of aging, the cellular mechanisms that contribute to this age-associated predilection remain elusive. In this study, we sought to evaluate the consequences of senescence on myofibroblast cell fate and fibrotic responses to lung injury in the context of aging. We demonstrated that nonsenescent lung myofibroblasts maintained the capacity for dedifferentiation, whereas senescent/IPF myofibroblasts exhibited an impaired capacity for dedifferentiation. We previously demonstrated that the transcription factor MyoD acts as a critical switch in the differentiation and dedifferentiation of myofibroblasts. Here, we demonstrate that decreased levels of MyoD preceded myofibroblast dedifferentiation and apoptosis susceptibility in nonsenescent cells, whereas MyoD expression remained elevated in senescent/IPF myofibroblasts, which failed to undergo dedifferentiation and demonstrated resistance to apoptosis. Genetic strategies to silence MyoD restored the susceptibility of IPF myofibroblasts to undergo apoptosis and led to a partial reversal of age-associated persistent fibrosis in vivo. The capacity for myofibroblast dedifferentiation and subsequent apoptosis may be critical for normal physiologic responses to tissue injury, whereas restricted dedifferentiation and apoptosis resistance in senescent cells may underlie the progressive nature of age-associated human fibrotic disorders. These studies support the concept that senescence may promote profibrotic effects via impaired myofibroblast dedifferentiation and apoptosis resistance, which contributes to myofibroblast accumulation and ultimately persistent fibrosis in aging.

Quercetin alleviates kidney fibrosis by reducing renal tubular epithelial cell senescence through the SIRT1/PINK1/mitophagy axis

Emerging evidence implicates accelerated renal tubular epithelial cell (RTEC) senescence in renal fibrosis progression. Mitophagy protects against kidney injury. However, the mechanistic interplay between cell senescence and mitophagy in RTECs is not clearly defined. The purpose of this study was to evaluate the inhibition of RTEC senescence and renal fibrosis by quercetin and explore the underlying mechanisms. We found that quercetin attenuated RTEC senescence induced by angiotensin II (AngII) in vitro and unilateral ureteral obstruction in vivo. Moreover, we demonstrated that mitochondrial abnormalities such as elevated reactive oxygen species, decreased membrane potential, and fragmentation and accumulation of mitochondrial mass, occurred in AngII-treated RTECs. Quercetin treatment reversed these effects. Furthermore, quercetin enhanced mitophagy in AngII-treated RTECs, which was markedly reduced by treatment with mitophagy-specific inhibitors. Sirtuin-1 (SIRT1) was involved in quercetin-mediated PTEN-induced kinase 1 (PINK1)/Parkin-associated mitophagy activation. Pharmacological antagonism of SIRT1 in AngII-treated RTECs blocked the effects of quercetin on mitophagy and cellular senescence. Finally, quercetin alleviated kidney fibrosis by reducing RTEC senescence via mitophagy. Collectively, the antifibrotic effect of quercetin involved inhibition of RTEC senescence, possibly through activation of SIRT1/PINK1/Parkin-mediated mitophagy. These findings suggest that pharmacological elimination of senescent cells and stimulation of mitophagy represent effective therapeutic strategies to prevent kidney fibrosis.

The ageing lung under stress

Healthy ageing of the lung involves structural changes but also numerous cell-intrinsic and cell-extrinsic alterations. Among them are the age-related decline in central cellular quality control mechanisms such as redox and protein homeostasis. In this review, we would like to provide a conceptual framework of how impaired stress responses in the ageing lung, as exemplified by dysfunctional redox and protein homeostasis, may contribute to onset and progression of COPD and idiopathic pulmonary fibrosis (IPF). We propose that age-related imbalanced redox and protein homeostasis acts, amongst others (e.g.cellular senescence), as a “first hit” that challenges the adaptive stress-response pathways of the cell, increases the level of oxidative stress and renders the lung susceptible to subsequent injury and disease. In both COPD and IPF, additional environmental insults such as smoking, air pollution and/or infections then serve as “second hits” which contribute to persistently elevated oxidative stress that overwhelms the already weakened adaptive defence and repair pathways in the elderly towards non-adaptive, irremediable stress thereby promoting development and progression of respiratory diseases. COPD and IPF are thus distinct horns of the same devil, “lung ageing”.

Dr AFC: drug repositioning through anti-fibrosis characteristic

Fibrosis is a key component in the pathogenic mechanism of a variety of diseases. These diseases involving fibrosis may share common mechanisms and therapeutic targets, and therefore common intervention strategies and medicines may be applicable for these diseases. For this reason, deliberately introducing anti-fibrosis characteristics into predictive modeling may lead to more success in drug repositioning. In this study, anti-fibrosis knowledge base was first built by collecting data from multiple resources. Both structural and biological profiles were then derived from the knowledge base and used for constructing machine learning models including Structural Profile Prediction Model (SPPM) and Biological Profile Prediction Model (BPPM). Three external public data sets were employed for validation purpose and further exploration of potential repositioning drugs in wider chemical space. The resulting SPPM and BPPM models achieve area under the receiver operating characteristic curve (area under the curve) of 0.879 and 0.972 in the training set, and 0.814 and 0.874 in the testing set. Additionally, our results also demonstrate that substantial amount of multi-targeting natural products possess notable anti-fibrosis characteristics and might serve as encouraging candidates in fibrosis treatment and drug repositioning. To leverage our methodology and findings, we developed repositioning prediction platform, drug repositioning based on anti-fibrosis characteristic that is freely accessible via https://www.biosino.org/drafc.

The dietary antioxidant quercetin reduces hallmarks of bleomycin-induced lung fibrogenesis in mice

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) is a chronic, lethal disease of which the etiology is still not fully understood. Current treatment comprises two FDA-approved drugs that can slow down yet not stop or reverse the disease. As IPF pathology is associated with an altered redox balance, adding a redox modulating component to current therapy might exert beneficial effects. Quercetin is a dietary antioxidant with strong redox modulating capacities that is suggested to exert part of its antioxidative effects via activation of the redox-sensitive transcription factor Nrf2 that regulates endogenous antioxidant levels. Therefore, the aim of the present study was to investigate if the dietary antioxidant quercetin can exert anti-fibrotic effects in a mouse model of bleomycin-induced pulmonary fibrogenesis through Nrf2-dependent restoration of redox imbalance.

METHODS

Homozygous Nrf2 deficient mice and their wildtype littermates were fed a control diet without or with 800 mg quercetin per kg diet from 7 days prior to a single 1 μg/2 μl per g BW bleomycin challenge until they were sacrificed 14 days afterwards. Lung tissue and plasma were collected to determine markers of fibrosis (expression of extracellular matrix genes and histopathology), inflammation (pulmonary gene expression and plasma levels of tumor necrosis factor-α (TNFα) and keratinocyte chemoattrachtant (KC)), and redox balance (pulmonary gene expression of antioxidants and malondialdehyde-dG (MDA)- DNA adducts).

RESULTS

Mice fed the enriched diet for 7 days prior to the bleomycin challenge had significantly enhanced plasma and pulmonary quercetin levels (11.08 ± 0.73 μM versus 7.05 ± 0.2 μM) combined with increased expression of Nrf2 and Nrf2-responsive genes compared to mice fed the control diet in lung tissue. Upon bleomycin treatment, quercetin-fed mice displayed reduced expression of collagen (COL1A2) and fibronectin (FN1) and a tendency of reduced inflammatory lesions (2.8 ± 0.7 versus 1.9 ± 0.8). These beneficial effects were accompanied by reduced pulmonary gene expression of TNFα and KC, but not their plasma levels, and enhanced Nrf2-induced pulmonary antioxidant defences. In Nrf2 deficient mice, no effect of the dietary antioxidant on either histology or inflammatory lesions was observed.

CONCLUSION

Quercetin exerts anti-fibrogenic and anti-inflammatory effects on bleomycin-induced pulmonary damage in mice possibly through modulation of the redox balance by inducing Nrf2. However, quercetin could not rescue the bleomycin-induced pulmonary damage indicating that quercetin alone cannot ameliorate the progression of IPF.

NADPH oxidases: Pathophysiology and therapeutic potential in age-associated pulmonary fibrosis

Oxidative stress has been associated with a number of human fibrotic diseases, including idiopathic pulmonary fibrosis (IPF). Although oxidative stress is associated with both fibrosis and aging, the precise cellular sources(s) of reactive oxygen species (ROS) that contribute to the disease pathogenesis remain poorly understood. NADPH oxidase (Nox) enzymes are an evolutionarily conserved family, where their only known function is the production of ROS. A growing body of evidence supports a link between excessive Nox-derived ROS and numerous chronic diseases (including fibrotic disease), which is most prevalent among the elderly population. In this review, we examine the evidence for Nox isoforms in the pathogenesis of IPF, and the potential to target this enzyme family for the treatment of IPF and related fibrotic disorders. A better understanding of the Nox-mediated redox imbalance in aging may be critical to the development of more effective therapeutic strategies for age-associated fibrotic disorders. Strategies aimed at specifically blocking the source(s) of ROS through Nox inhibition may prove to be more effective as anti-fibrotic therapies, as compared to antioxidant approaches. This review also discusses the potential of Nox-targeting therapeutics currently in development.

Anti-fibrosis activity of quercetin attenuates rabbit tracheal stenosis via the TGF-β/AKT/mTOR signaling pathway

AIMS

This study aimed to explore the possible mechanism of trauma-induced laryngotracheal stenosis and potential protective and therapeutic efficacy of quercetin on trauma-induced laryngotracheal stenosis.

MAIN METHODS

The expression and activity of fibrotic factors [interleukin (IL)-6, IL-8, autophagy related 5 (ATG5), collagen (COL)-1, tumor growth factor (TGF)-β COL-3, microtubule-associated proteins 1A/1B light chain 3A (LC3), and vascular endothelial growth factor (VEGF)] and fibrotic signaling mediators [mammalian target of rapamycin (mTOR) and phosphorylated AKT (pAKT)] were detected by real-time quantitative PCR (qRT-PCR), ELISA, Western blot, and immunohistochemical staining, respectively, in the lipopolysaccharide (LPS)-induced WI-38 (a human embryonic lung fibroblast cell line) cellular fibrotic model and a trauma-induced rabbit tracheal stenosis model, with and without quercetin treatment.

KEY FINDINGS

Pre-treatment with quercetin significantly reversed the LPS-induced upregulation of pro-fibrotic factors (IL-6, IL-8, COL-1, COL-3, LC3) and fibrotic signaling mediators (mTOR and AKT), and it induced the downregulation of ATG5 in the WI-38 cells. Furthermore, the anti-fibrotic activity of quercetin was confirmed in the trauma-induced rabbit tracheal stenosis model. Thus, the nasogastric administration of quercetin attenuated the tracheal stenosis of the rabbit tracheal stenosis model, in addition to effectively reversing an increase in pro-fibrotic factors (VEGF, IL-6, TGF-β, COL-1, and COL-3) and fibrotic signaling mediators (mTOR and AKT), as well as downregulating ATG5 of the rabbit tracheal stenosis model.

SIGNIFICANCE

Quercetin exhibits anti-fibrotic activity by inhibiting pro-fibrotic factors and AKT/mTOR signaling pathway, in addition to activating autophagy activity. This study provided experimental evidence supporting the application of quercetin in tracheal stenosis, clinically.

Cellular Senescence as a Mechanism and Target in Chronic Lung Diseases

Cellular senescence is now considered an important driving mechanism for chronic lung diseases, particularly chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrosis. Cellular senescence is due to replicative and stress-related senescence with activation of p53 and p16^INK4a, respectively, leading to activation of p21^CIP1 and cell cycle arrest. Senescent cells secrete multiple inflammatory proteins known as the senescence-associated secretory phenotype, leading to low-grade chronic inflammation, which further drives senescence. Loss of key antiaging molecules sirtuin-1 and sirtuin-6 may be important in acceleration of aging and arises from oxidative stress reducing phosphatase PTEN (phosphatase tensin homolog), thereby activating PI3K (phosphoinositide-3-kinase) and mTOR (mammalian target of rapamycin). MicroRNA-34a (miR-34a), which is regulated by PI3K-mTOR signaling, plays a pivotal role in reducing sirtuin-1/6, and its inhibition with an antagomir results in their restoration, reducing markers of senescence, reducing senescence-associated secretory phenotype, and reversing cell cycle arrest in epithelial cells from peripheral airways of patients with COPD. miR-570 is also involved in reduction of sirtuin-1 and cellular senescence and is activated by p38 mitogen-activated protein kinase. These miRNAs may be released from cells in extracellular vesicles that are taken up by other cells, thereby spreading senescence locally within the lung but also outside the lung through the circulation; this may account for comorbidities of COPD and other lung diseases. Understanding the mechanisms of cellular senescence may result in new treatments for chronic lung disease, either by inhibiting PI3K-mTOR signaling, by inhibiting specific miRNAs, or by deletion of senescent cells with senolytic therapies, already shown to be effective in experimental lung fibrosis.

Targeting defective pulmonary innate immunity - A new therapeutic option?

Chronic pulmonary conditions now account for 1 in 15 deaths in the US and mortality is increasing. Chronic obstructive pulmonary disease (COPD) is due to become the 3rd largest cause of mortality by 2030 and mortality from other respiratory conditions such as asthma, idiopathic pulmonary fibrosis and cystic fibrosis are not reducing. There is an urgent need for novel therapies to address this problem as many of the current strategies targeting inflammation are not sufficient. The innate immune system of the lung is an important defence against invading pathogens, but in many chronic pulmonary diseases, this system mounts an inappropriate response. In COPD, macrophages are increased in number, but fail to clear pathogens correctly and become highly activated. This leads to increased damage and remodelling of the airways. In idiopathic fibrosis, there is a switch of macrophage phenotype to a cell that promotes abnormal repair. Neutrophils also display dysfunction in COPD where aberrant migratory profiles may lead to increased damage to lung tissue and emphysema; while in cystic fibrosis the proteolytic lung environment damages neutrophil receptors leading to ineffective phagocytosis and migration. Targeting the innate immune system to restore 'normal function' could have enormous benefits. Improving phagocytosis of pathogens could reduce exacerbations and hence the associated decline in lung function, and novel therapeutics such as sulforaphane appear to do this in vitro. Other natural products such as resveratrol and derivatives also have anti-inflammatory properties. Statins have traditionally been used to manage cholesterol levels in hypercholesterolaemia, however these molecules also have beneficial effects on the innate immune cells. Statins have been shown to be anti-inflammatory and restore aberrant neutrophil chemotaxis in aged cells. Other possible agents that may be efficacious are senolytics. These compounds include natural products such as quercetin which have anti-inflammatory properties but can also suppress viral replication. As viruses have been shown to suppress phagocytosis of macrophages, it is possible that these compounds could have benefit during viral exacerbations to protect this innate response. These compounds demonstrate that it is possible to address defective innate responses in the lung but a better understanding of the mechanisms driving defective innate immunity in pulmonary disease may lead to improved therapeutics.

Cellular Senescence: The Trojan Horse in Chronic Lung Diseases

Senescence is a cell fate decision characterized by irreversible arrest of proliferation accompanied by a senescence-associated secretory phenotype. Traditionally, cellular senescence has been recognized as a beneficial physiological mechanism during development and wound healing and in tumor suppression. However, in recent years, evidence of negative consequences of cellular senescence has emerged, illuminating its role in several chronic pathologies. In this context, senescent cells persist or accumulate and have detrimental consequences. In this review, we discuss the possibility that in chronic obstructive pulmonary disease, persistent senescence impairs wound healing in the lung caused by secretion of proinflammatory senescence-associated secretory phenotype factors and exhaustion of progenitor cells. In contrast, in idiopathic pulmonary fibrosis, chronic senescence in alveolar epithelial cells exacerbates the accumulation of senescent fibroblasts together with production of extracellular matrix. We review how cellular senescence may contribute to lung disease pathology.

Evasion of apoptosis by myofibroblasts: a hallmark of fibrotic diseases

Organ fibrosis is a lethal outcome of autoimmune rheumatic diseases such as systemic sclerosis. Myofibroblasts are scar-forming cells that are ultimately responsible for the excessive synthesis, deposition and remodelling of extracellular matrix proteins in fibrosis. Advances have been made in our understanding of the mechanisms that keep myofibroblasts in an activated state and control myofibroblast functions. However, the mechanisms that help myofibroblasts to persist in fibrotic tissues remain poorly understood. Myofibroblasts evade apoptosis by activating molecular mechanisms in response to pro-survival biomechanical and growth factor signals from the fibrotic microenvironment, which can ultimately lead to the acquisition of a senescent phenotype. Growing evidence suggests that myofibroblasts and senescent myofibroblasts, rather than being resistant to apoptosis, are actually primed for apoptosis owing to concomitant activation of cell death signalling pathways; these cells are poised to apoptose when survival pathways are inhibited. This knowledge of apoptotic priming has paved the way for new therapies that trigger apoptosis in myofibroblasts by blocking pro-survival mechanisms, target senescent myofibroblast for apoptosis or promote the reprogramming of myofibroblasts into scar-resolving cells. These novel strategies are not only poised to prevent progressive tissue scarring, but also have the potential to reverse established fibrosis and to regenerate chronically injured tissues.

Respiratory

Lung disease rivals the position for the top cause of death worldwide. Causes and pathology of the myriad lung diseases are varied, yet nutrition can either affect the outcome or support treatment in the majority of cases. This chapter explores the modifiable risk factors, from lifestyle changes to dietary intake to specific nutrients, anti-nutrients, and toxins helpful for the nutritionist or dietitian working with lung disease patients. General lung health is discussed, and three major disease states are explored in detail, including alpha-1 antitrypsin deficiency, asthma, and idiopathic pulmonary fibrosis. Although all lung diseases have diverse causes, many integrative and functional medical nutrition therapies are available and are not being utilized in practice today. This chapter begins the path toward better nutrition education for the integrative and functional medicine professional.

Senotherapeutics: Targeting senescence in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a fatal chronic lung disease characterized by progressive scarring of the lung tissue, leading to respiratory failure. There is no cure for IPF, and current anti-fibrotic treatments modestly arrest its further progression. IPF prevalence and incidence increase with age, which is a recognized risk factor. Intense clinical and basic research over the last fifteen years has shown that hallmarks of accelerated aging are present in the lungs of patients with IPF. Different cell types in IPF lungs exhibit premature hallmarks of aging, including telomere attrition and cellular senescence. In this Review, we discuss recent insights into the mechanisms behind these age-related alterations and their contribution to the development of lung fibrosis. We focus on the genetic and molecular basis of telomere attrition in alveolar type II epithelial cells, which promote cellular senescence and lung fibrosis. Mechanistically, senescent cells secrete pro-fibrotic factors that activate scar-forming myofibroblasts. Ultimately, senescent alveolar epithelial cells lose their regenerative capacity, impeding fibrosis resolution. In addition, mitochondrial dysfunction is strongly associated with the appearance of senescent epithelial cells and senescent myofibroblasts in IPF, which persist in the fibrotic tissue by adapting their metabolic pathways and becoming resistant to apoptosis. We discuss emerging novel therapeutic strategies to treat IPF by targeting cellular senescence with the so-called senotherapeutics.

Redox Imbalance in Idiopathic Pulmonary Fibrosis: A Role for Oxidant Cross-Talk Between NADPH Oxidase Enzymes and Mitochondria

Significance: Idiopathic pulmonary fibrosis (IPF) is a progressive age-related lung disease with a median survival of only 3 years after diagnosis. The pathogenic mechanisms behind IPF are not clearly understood, and current therapeutic approaches have not been successful in improving disease outcomes. Recent Advances: IPF is characterized by increased production of reactive oxygen species (ROS), primarily by NADPH oxidases (NOXes) and mitochondria, as well as altered antioxidant defenses. Recent studies have identified the NOX isoform NOX4 as a key player in various important aspects of IPF pathology. In addition, mitochondrial dysfunction is thought to enhance pathological features of IPF, in part by increasing mitochondrial ROS (mtROS) production and altering cellular metabolism. Recent findings indicate reciprocal interactions between NOX enzymes and mitochondria, which affect regulation of NOX activity as well as mitochondrial function and mtROS production, and collectively promote epithelial injury and profibrotic signaling. Critical Issues and Future Directions: The precise molecular mechanisms by which ROS from NOX or mitochondria contribute to IPF pathology are not known. This review summarizes the current knowledge with respect to the various aspects of ROS imbalance in the context of IPF and its proposed roles in disease development, with specific emphasis on the importance of inappropriate NOX activation, mitochondrial dysfunction, and the emerging evidence of NOX-mitochondria cross-talk as important drivers in IPF pathobiology.

Pharmacotherapy and adjunctive treatment for idiopathic pulmonary fibrosis (IPF)

Idiopathic pulmonary fibrosis (IPF) is an advancing and fatal lung disease with increasing incidence and prevalence. Nintedanib and pirfenidone were approved by the FDA for the treatment of IPF in 2014 based on positive phase 3 trials, and both of these antifibrotic drugs are conditionally recommended in the 2015 ATS/ERS/JRS/ALAT Clinical Practice Guideline. Although an improvement over previously suggested therapies, their capacity to reduce, but not completely arrest or improve, lung function over time presents an opportunity for novel or add-on pharmacologic agents. The purpose of this review is to deliver a brief overview of the results of phase 3/4 IPF trials with pirfenidone and nintedanib, as well as highlight encouraging results of phase 1/2 trials with novel therapies. Long-term studies indicate that pirfenidone and nintedanib are effective IPF treatments, with acceptable safety and tolerability. The combination of pirfenidone and nintedanib appear safe. Promising results have recently been made public for several phase 2 trials with novel targets, including the autotaxin-lysophosphatidic acid (ATX/LPA) pathway, connective tissue growth factor (CTGF), pentraxin-2, G protein-coupled receptor agonists/antagonists, αvβ6 integrin, and galectin-3. Results of treatments directed at gastro-esophageal reflux in patients with IPF have also been published. Currently, monotherapy with pirfenidone or nintedanib is the mainstay of pharmacological treatment for IPF. Innovative therapies along with combinations of pharmacological agents hold great promise for the future.

DNA-PKcs modulates progenitor cell proliferation and fibroblast senescence in idiopathic pulmonary fibrosis

BACKGROUND

Recent studies have highlighted the contribution of senescent mesenchymal and epithelial cells in Idiopathic Pulmonary Fibrosis (IPF), but little is known regarding the molecular mechanisms that regulate the accumulation of senescent cells in this disease. Therefore, we addressed the hypothesis that the loss of DNA repair mechanisms mediated by DNA protein kinase catalytic subunit (DNA-PKcs) in IPF, promoted the accumulation of mesenchymal progenitors and progeny, and the expression of senescent markers by these cell types.

METHODS

Surgical lung biopsy samples and lung fibroblasts were obtained from patients exhibiting slowly, rapidly or unknown progressing IPF and lung samples lacking any evidence of fibrotic disease (i.e. normal; NL). The expression of DNA-Pkcs in lung tissue was assessed by quantitative immunohistochemical analysis. Chronic inhibition of DNA-PKcs kinase activity was mimicked using a highly specific small molecule inhibitor, Nu7441. Proteins involved in DNA repair (stage-specific embryonic antigen (SSEA)-4⁺ cells) were determined by quantitative Ingenuity Pathway Analysis of transcriptomic datasets (GSE103488). Lastly, the loss of DNA-PKc was modeled in a humanized model of pulmonary fibrosis in NSG SCID mice genetically deficient in PRKDC (the transcript for DNA-PKcs) and treated with Nu7441.

RESULTS

DNA-PKcs expression was significantly reduced in IPF lung tissues. Chronic inhibition of DNA-PKcs by Nu7441 promoted the proliferation of SSEA4⁺ mesenchymal progenitor cells and a significant increase in the expression of senescence-associated markers in cultured lung fibroblasts. Importantly, mesenchymal progenitor cells and their fibroblast progeny derived from IPF patients showed a loss of transcripts encoding for DNA damage response and DNA repair components. Further, there was a significant reduction in transcripts encoding for PRKDC (the transcript for DNA-PKcs) in SSEA4⁺ mesenchymal progenitor cells from IPF patients compared with normal lung donors. In SCID mice lacking DNA-PKcs activity receiving IPF lung explant cells, treatment with Nu7441 promoted the expansion of progenitor cells, which was observed as a mass of SSEA4⁺ CgA⁺ expressing cells.

CONCLUSIONS

Together, our results show that the loss of DNA-PKcs promotes the expansion of SSEA4⁺ mesenchymal progenitors, and the senescence of their mesenchymal progeny.

The Future of Pharmacological Treatment in Idiopathic Pulmonary Fibrosis

The therapeutic approach in idiopathic pulmonary fibrosis has changed substantially over the past 5 years. National and international guidelines for the pharmacological treatment of IPF recommend 2antifibrotic drugs, nintedanib and pirfenidone. The use of both these drugs is supported by high-level evidence, with benefits including not only slower disease progression but also a reduction in the annual risk of death. Currently, the therapeutic management of these patients prioritizes both the use of drugs that act on the pathogenic mechanisms of the disease, and the positive effect of improving quality of life with integrated multidisciplinary support, including nutrition, physical activity, education, emotional support, and palliation of symptoms. The overall aim is to ensure that the patient remains as well as possible for as long as possible after diagnosis. However, the goal of the new antifibrotic combinations that are currently under evaluation in clinical trials is to use the potential antifibrotic synergy to enhance the therapeutic benefit or completely halt disease progression, by acting simultaneously on different pathogenic pathways. Another line of investigation involves markers that might be useful for identifying patients who may benefit more from certain antifibrotics than from others, which would make it possible to optimize resources and take the first steps toward precision medicine in pulmonary fibrosis. Below, we review the main potential areas for improvement in the pharmacological treatment of idiopathic pulmonary fibrosis in the short, medium, and long term.

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.

Mechanisms for the Resolution of Organ Fibrosis

Fibrosis is a dynamic process with the potential for reversibility and restoration of near-normal tissue architecture and organ function. Herein, we review mechanisms for resolution of organ fibrosis, in particular that involving the lung, with an emphasis on the critical roles of myofibroblast apoptosis and clearance of deposited matrix.

Activation of the mTORC1/PGC-1 axis promotes mitochondrial biogenesis and induces cellular senescence in the lung epithelium

Cellular senescence is a biological process by which cells lose their capacity to proliferate yet remain metabolically active. Although originally considered a protective mechanism to limit the formation of cancer, it is now appreciated that cellular senescence also contributes to the development of disease, including common respiratory ailments such as chronic obstructive pulmonary disease and idiopathic pulmonary fibrosis. While many factors have been linked to the development of cellular senescence, mitochondrial dysfunction has emerged as an important causative factor. In this study, we uncovered that the mitochondrial biogenesis pathway driven by the mammalian target of rapamycin/peroxisome proliferator-activated receptor-γ complex 1α/β (mTOR/PGC-1α/β) axis is markedly upregulated in senescent lung epithelial cells. Using two different models, we show that activation of this pathway is associated with other features characteristic of enhanced mitochondrial biogenesis, including elevated number of mitochondrion per cell, increased oxidative phosphorylation, and augmented mitochondrial reactive oxygen species (ROS) production. Furthermore, we found that pharmacological inhibition of the mTORC1 complex with rapamycin not only restored mitochondrial homeostasis but also reduced cellular senescence to bleomycin in lung epithelial cells. Likewise, mitochondrial-specific antioxidant therapy also effectively inhibited mTORC1 activation in these cells while concomitantly reducing mitochondrial biogenesis and cellular senescence. In summary, this study provides a mechanistic link between mitochondrial biogenesis and cellular senescence in lung epithelium and suggests that strategies aimed at blocking the mTORC1/PGC-1α/β axis or reducing ROS-induced molecular damage could be effective in the treatment of senescence-associated lung diseases.