Divergent roles for Clusterin in Lung Injury and Repair

Cell Proliferation and Apoptosis-Key Players in the Lung Aging Process

Currently, the global lifespan has increased, resulting in a higher proportion of the population over 65 years. Changes that occur in the lung during aging increase the risk of developing acute and chronic lung diseases, such as acute respiratory distress syndrome, chronic obstructive pulmonary disease, idiopathic pulmonary fibrosis, and lung cancer. During normal tissue homeostasis, cell proliferation and apoptosis create a dynamic balance that constitutes the physiological cell turnover. In basal conditions, the lungs have a low rate of cell turnover compared to other organs. During aging, changes in the rate of cell turnover in the lung are observed. In this work, we review the literature that evaluates the role of molecules involved in cell proliferation and apoptosis in lung aging and in the development of age-related lung diseases. The list of molecules that regulate cell proliferation, apoptosis, or both processes in lung aging includes TNC, FOXM1, DNA-PKcs, MicroRNAs, BCL-W, BCL-XL, TCF21, p16, NOX4, NRF2, MDM4, RPIA, DHEA, and MMP28. However, despite the studies carried out to date, the complete signaling pathways that regulate cell turnover in lung aging are still unknown. More research is needed to understand the changes that lead to the development of age-related lung diseases.

Proteomic analysis of lung responses to SARS-CoV-2 infection in aged non-human primates: clinical and research relevance

With devastating health and socioeconomic impact worldwide, much work is left to understand the Coronavirus Disease 2019 (COVID-19), with emphasis in the severely affected elderly population. Here, we present a proteomics study of lung tissue obtained from aged vs. young rhesus macaques (Macaca mulatta) and olive baboons (Papio Anubis) infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Using age as a variable, we identified common proteomic profiles in the lungs of aged infected non-human primates (NHPs), including key regulators of immune function, as well as cell and tissue remodeling, and discuss the potential clinical relevance of such parameters. Further, we identified key differences in proteomic profiles between both NHP species, and compared those to what is known about SARS-CoV-2 in humans. Finally, we explored the translatability of these animal models in the context of aging and the human presentation of the COVID-19.

Multifaceted immune dysregulation characterizes individuals at-risk for rheumatoid arthritis

Molecular markers of autoimmunity, such as antibodies to citrullinated protein antigens (ACPA), are detectable prior to inflammatory arthritis (IA) in rheumatoid arthritis (RA) and may define a state that is 'at-risk' for future RA. Here we present a cross-sectional comparative analysis among three groups that include ACPA positive individuals without IA (At-Risk), ACPA negative individuals and individuals with early, ACPA positive clinical RA (Early RA). Differential methylation analysis among the groups identifies non-specific dysregulation in peripheral B, memory and naïve T cells in At-Risk participants, with more specific immunological pathway abnormalities in Early RA. Tetramer studies show increased abundance of T cells recognizing citrullinated (cit) epitopes in At-Risk participants, including expansion of T cells reactive to citrullinated cartilage intermediate layer protein I (cit-CILP); these T cells have Th1, Th17, and T stem cell memory-like phenotypes. Antibody-antigen array analyses show that antibodies targeting cit-clusterin, cit-fibrinogen and cit-histone H4 are elevated in At-Risk and Early RA participants, with the highest levels of antibodies detected in those with Early RA. These findings indicate that an ACPA positive at-risk state is associated with multifaceted immune dysregulation that may represent a potential opportunity for targeted intervention.

Investigation of a UPR-Related Gene Signature Identifies the Pro-Fibrotic Effects of Thrombospondin-1 by Activating CD47/ROS/Endoplasmic Reticulum Stress Pathway in Lung Fibroblasts

Unfolded protein response (UPR) signaling and endoplasmic reticulum (ER) stress have been linked to pulmonary fibrosis. However, the relationship between UPR status and pulmonary function and prognosis in idiopathic pulmonary fibrosis (IPF) patients remains largely unknown. Through a series of bioinformatics analyses, we established a correlation between UPR status and pulmonary function in IPF patients. Furthermore, thrombospondin-1 (TSP-1) was identified as a potential biomarker for prognostic evaluation in IPF patients. By utilizing both bulk RNA profiling and single-cell RNA sequencing data, we demonstrated the upregulation of TSP-1 in lung fibroblasts during pulmonary fibrosis. Gene set enrichment analysis (GSEA) results indicated a positive association between TSP-1 expression and gene sets related to the reactive oxygen species (ROS) pathway in lung fibroblasts. TSP-1 overexpression alone induced mild ER stress and pulmonary fibrosis, and it even exacerbated bleomycin-induced ER stress and pulmonary fibrosis. Mechanistically, TSP-1 promoted ER stress and fibroblast activation through CD47-dependent ROS production. Treatment with either TSP-1 inhibitor or CD47 inhibitor significantly attenuated BLM-induced ER stress and pulmonary fibrosis. Collectively, these findings suggest that the elevation of TSP-1 during pulmonary fibrosis is not merely a biomarker but likely plays a pathogenic role in the fibrotic changes in the lung.

The Ins and Outs of Clusterin: Its Role in Cancer, Eye Diseases and Wound Healing

Clusterin (CLU) is a glycoprotein originally discovered in 1983 in ram testis fluid. Rapidly observed in other tissues, it was initially given various names based on its function in different tissues. In 1992, it was finally named CLU by consensus. Nearly omnipresent in human tissues, CLU is strongly expressed at fluid-tissue interfaces, including in the eye and in particular the cornea. Recent research has identified different forms of CLU, with the most prominent being a 75-80 kDa heterodimeric protein that is secreted. Another truncated version of CLU (55 kDa) is localized to the nucleus and exerts pro-apoptotic activities. CLU has been reported to be involved in various physiological processes such as sperm maturation, lipid transportation, complement inhibition and chaperone activity. CLU was also reported to exert important functions in tissue remodeling, cell-cell adhesion, cell-substratum interaction, cytoprotection, apoptotic cell death, cell proliferation and migration. Hence, this protein is sparking interest in tissue wound healing. Moreover, CLU gene expression is finely regulated by cytokines, growth factors and stress-inducing agents, leading to abnormally elevated levels of CLU in many states of cellular disturbance, including cancer and neurodegenerative conditions. In the eye, CLU expression has been reported as being severely increased in several pathologies, such as age-related macular degeneration and Fuch's corneal dystrophy, while it is depleted in others, such as pathologic keratinization. Nevertheless, the precise role of CLU in the development of ocular pathologies has yet to be deciphered. The question of whether CLU expression is influenced by these disorders or contributes to them remains open. In this article, we review the actual knowledge about CLU at both the protein and gene expression level in wound healing, and explore the possibility that CLU is a key factor in cancer and eye diseases. Understanding the expression and regulation of CLU could lead to the development of novel therapeutics for promoting wound healing.

Impaired Extracellular Proteostasis in Patients with Heart Failure

BACKGROUND

Proteostasis impairment and the consequent increase of amyloid burden in the myocardium have been associated with heart failure (HF) development and poor prognosis. A better knowledge of the protein aggregation process in biofluids could assist the development and monitoring of tailored interventions.

AIM

To compare the proteostasis status and protein's secondary structures in plasma samples of patients with HF with preserved ejection fraction (HFpEF), patients with HF with reduced ejection fraction (HFrEF), and age-matched individuals.

METHODS

A total of 42 participants were enrolled in 3 groups: 14 patients with HFpEF, 14 patients with HFrEF, and 14 age-matched individuals. Proteostasis-related markers were analyzed by immunoblotting techniques. Fourier Transform Infrared (FTIR) Spectroscopy in Attenuated Total Reflectance (ATR) was applied to assess changes in the protein's conformational profile.

RESULTS

Patients with HFrEF showed an elevated concentration of oligomeric proteic species and reduced clusterin levels. ATR-FTIR spectroscopy coupled with multivariate analysis allowed the discrimination of HF patients from age-matched individuals in the protein amide I absorption region (1700-1600 cm^-1), reflecting changes in protein conformation, with a sensitivity of 73 and a specificity of 81%. Further analysis of FTIR spectra showed significantly reduced random coils levels in both HF phenotypes. Also, compared to the age-matched group, the levels of structures related to fibril formation were significantly increased in patients with HFrEF, whereas the β-turns were significantly increased in patients with HFpEF.

CONCLUSION

Both HF phenotypes showed a compromised extracellular proteostasis and different protein conformational changes, suggesting a less efficient protein quality control system.

Clusterin Plasma Concentrations Are Decreased in Sepsis and Inversely Correlated with Established Markers of Inflammation

Clusterin is a multifunctional protein that is recognized to mediate cellular stress response associated with organ failure, systemic inflammation, and metabolic alterations. The aim of this study was to determine the value of clusterin as a clinical biomarker in critical ill patients with or without sepsis. We analyzed clusterin plasma concentrations in 200 critically ill patients (133 with sepsis, 67 without sepsis) on admission to the medical intensive care unit (ICU). The results were compared with 66 healthy controls. Clusterin plasma concentration was significantly elevated in critically ill patients compared to healthy subjects. Clusterin levels were significantly higher in non-septic ICU patients than in patients with sepsis. Clusterin correlated inversely with routinely used biomarkers of inflammatory response. Furthermore, clusterin levels were higher in ICU patients with pre-existing obesity and type 2 diabetes. Clusterin was not associated with disease severity, organ failure, or mortality in the ICU. This study highlights significantly elevated clusterin levels in critically ill patients, predominantly in non-sepsis conditions, and associates circulating clusterin to inflammatory and metabolic dysfunctions.

The Role of DNA Damage and Repair in Idiopathic Pulmonary Fibrosis

The mortality rate of idiopathic pulmonary fibrosis (IPF) increases yearly due to ineffective treatment. Given that the lung is exposed to the external environment, it is likely that oxidative stress, especially the stimulation of DNA, would be of particular importance in pulmonary fibrosis. DNA damage is known to play an important role in idiopathic pulmonary fibrosis initiation, so DNA repair systems targeting damage are also crucial for the survival of lung cells. Although many contemporary reports have summarized the role of individual DNA damage and repair pathways in their hypotheses, they have not focused on idiopathic pulmonary fibrosis. This review, therefore, aims to provide a concise overview for researchers to understand the pathways of DNA damage and repair and their roles in IPF.

BRCA mutational status shapes the stromal microenvironment of pancreatic cancer linking clusterin expression in cancer associated fibroblasts with HSF1 signaling

Tumors initiate by mutations in cancer cells, and progress through interactions of the cancer cells with non-malignant cells of the tumor microenvironment. Major players in the tumor microenvironment are cancer-associated fibroblasts (CAFs), which support tumor malignancy, and comprise up to 90% of the tumor mass in pancreatic cancer. CAFs are transcriptionally rewired by cancer cells. Whether this rewiring is differentially affected by different mutations in cancer cells is largely unknown. Here we address this question by dissecting the stromal landscape of BRCA-mutated and BRCA Wild-type pancreatic ductal adenocarcinoma. We comprehensively analyze pancreatic cancer samples from 42 patients, revealing different CAF subtype compositions in germline BRCA-mutated vs. BRCA Wild-type tumors. In particular, we detect an increase in a subset of immune-regulatory clusterin-positive CAFs in BRCA-mutated tumors. Using cancer organoids and mouse models we show that this process is mediated through activation of heat-shock factor 1, the transcriptional regulator of clusterin. Our findings unravel a dimension of stromal heterogeneity influenced by germline mutations in cancer cells, with direct implications for clinical research.

Inhibition of Clusterin Represses Proliferation by Inducing Cellular Senescence in Pancreatic Cancer

BACKGROUND

The outcome of pancreatic ductal adenocarcinoma (PDAC) is unsatisfactory, and the identification of novel therapeutic targets is urgently needed. Clinical studies on the antisense oligonucleotide that targets clusterin (CLU) expression have been conducted and have shown efficacy in other cancers. We aimed to investigate the effects of CLU in PDAC and the underlying mechanisms with a view to the clinical application of existing drugs.

METHODS

We knocked down CLU in PDAC cells and evaluated changes in cell proliferation. To elucidate the mechanism responsible for these changes, we performed western blot analysis, cell cycle assay, and senescence-associated β-galactosidase (SA-β-gal) staining. To evaluate the clinical significance of CLU, immunohistochemistry was performed, and CLU expression was analyzed in specimens resected from PDAC patients not treated with preoperative chemotherapy.

RESULTS

Knockdown of CLU significantly decreased cell proliferation and did not induce apoptosis, but did induce cellular senescence by increasing the percentage of G1-phase and SA-β-gal staining-positive cells. A marker of DNA damage such as γH2AX and factors related to cellular senescence, such as p21 and the senescence-associated secretory phenotype, were upregulated by knockdown of CLU. CLU expression in resected PDAC specimens was located in the cytoplasm of tumor cells and revealed significantly better recurrence-free survival and overall survival in the CLU-low group than in the CLU-high group.

CONCLUSIONS

We identified that CLU inhibition leads to cellular senescence in PDAC. Our findings suggest that CLU is a novel therapeutic target that contributes to the prognosis of PDAC by inducing cellular senescence.

Single-Cell RNA-Seq Analysis Reveals Lung Epithelial Cell Type-Specific Responses to HDM and Regulation by Tet1

Tet1 protects against house dust mite (HDM)-induced lung inflammation in mice and alters the lung methylome and transcriptome. In order to explore the role of Tet1 in individual lung epithelial cell types in HDM-induced inflammation, we established a model of HDM-induced lung inflammation in Tet1 knockout and littermate wild-type mice, then studied EpCAM+ lung epithelial cells using single-cell RNA-seq analysis. We identified eight EpCAM+ lung epithelial cell types, among which AT2 cells were the most abundant. HDM challenge altered the relative abundance of epithelial cell types and resulted in cell type-specific transcriptomic changes. Bulk and cell type-specific analysis also showed that loss of Tet1 led to the altered expression of genes linked to augmented HDM-induced lung inflammation, including alarms, detoxification enzymes, oxidative stress response genes, and tissue repair genes. The transcriptomic regulation was accompanied by alterations in TF activities. Trajectory analysis supports that HDM may enhance the differentiation of AP and BAS cells into AT2 cells, independent of Tet1. Collectively, our data showed that lung epithelial cells had common and unique transcriptomic signatures of allergic lung inflammation. Tet1 deletion altered transcriptomic networks in various lung epithelial cells, which may promote allergen-induced lung inflammation.

Clusterin as a serum biomarker candidate contributes to the lung fibroblasts activation in chronic obstructive pulmonary disease

BACKGROUND

Fibrosis in the peripheral airways contributes to airflow limitation in patients with chronic obstructive pulmonary disease (COPD). However, the key proteins involved in its development are still poorly understood. Thus, we aimed to identify the differentially expressed proteins (DEPs) between smoker patients with and without COPD and elucidate the molecular mechanisms involved by investigating the effects of the identified biomarker candidate on lung fibroblasts.

METHODS

The potential DEPs were identified by isobaric tags for relative and absolute quantitation (iTRAQ)-based proteomic analysis. The messenger RNA and protein levels of clusterin (CLU) in COPD patients and 12% cigarette smoke extract (CSE)-treated human bronchial epithelial cells were determined at the indicated time points. Furthermore, an in vitro COPD model was established via the administration of 8% CSE to normal human lung fibroblasts (NHLFs) at indicated time points. The effects of CSE treatment and CLU silencing on proliferation and activation of lung fibroblasts were analyzed.

RESULTS

A total of 144 DEPs were identified between COPD patients and normal smokers. The iTRAQ-based proteomics and bioinformatics analyses identified CLU as a serum biomarker candidate. We also discovered that CLU levels were significantly increased ( P   <  0.0001) in Global Initiative for Obstructive Lung Disease II, III, and IV patients and correlated ( P   <  0.0001) with forced expiratory volume in 1 s ( R  = -0.7705), residual volume (RV) ( R  = 0.6281), RV/total lung capacity ( R  = 0.5454), and computerized tomography emphysema ( R  = 0.7878). Similarly, CLU levels were significantly increased in CSE-treated cells at indicated time points ( P  < 0.0001). The CSE treatment significantly inhibited the proliferation, promoted the inflammatory response, differentiation of NHLFs, and collagen matrix deposition, and induced the apoptosis of NHLFs; however, these effects were partially reversed by CLU silencing.

CONCLUSION

Our findings suggest that CLU may play significant roles during airway fibrosis in COPD by regulating lung fibroblast activation.

Lung tumor MHCII immunity depends on in situ antigen presentation by fibroblasts

A key unknown of the functional space in tumor immunity is whether CD4 T cells depend on intratumoral MHCII cancer antigen recognition. MHCII-expressing, antigen-presenting cancer-associated fibroblasts (apCAFs) have been found in breast and pancreatic tumors and are considered to be immunosuppressive. This analysis shows that antigen-presenting fibroblasts are frequent in human lung non-small cell carcinomas, where they seem to actively promote rather than suppress MHCII immunity. Lung apCAFs directly activated the TCRs of effector CD4 T cells and at the same time produced C1q, which acted on T cell C1qbp to rescue them from apoptosis. Fibroblast-specific MHCII or C1q deletion impaired CD4 T cell immunity and accelerated tumor growth, while inducing C1qbp in adoptively transferred CD4 T cells expanded their numbers and reduced tumors. Collectively, we have characterized in the lungs a subset of antigen-presenting fibroblasts with tumor-suppressive properties and propose that cancer immunotherapies might be strongly dependent on in situ MHCII antigen presentation.

Conditioned Media of Adipose-Derived Stem Cells Suppresses Sidestream Cigarette Smoke Extract Induced Cell Death and Epithelial-Mesenchymal Transition in Lung Epithelial Cells

The role of the epithelial-mesenchymal transition (EMT) in lung epithelial cells is increasingly being recognized as a key stage in the development of COPD, fibrosis, and lung cancers, which are all highly associated with cigarette smoking and with exposure to second-hand smoke. Using the exposure of human lung cancer epithelial A549 cells and non-cancerous Beas-2B cells to sidestream cigarette smoke extract (CSE) as a model, we studied the protective effects of adipose-derived stem cell-conditioned medium (ADSC-CM) against CSE-induced cell death and EMT. CSE dose-dependently induced cell death, decreased epithelial markers, and increased the expression of mesenchymal markers. Upstream regulator analysis of differentially expressed genes after CSE exposure revealed similar pathways as those observed in typical EMT induced by TGF-β1. CSE-induced cell death was clearly attenuated by ADSC-CM but not by other control media, such as a pass-through fraction of ADSC-CM or A549-CM. ADSC-CM effectively inhibited CSE-induced EMT and was able to reverse the gradual loss of epithelial marker expression associated with TGF-β1 treatment. CSE or TGF-β1 enhanced the speed of A549 migration by 2- to 3-fold, and ADSC-CM was effective in blocking the cell migration induced by either agent. Future work will build on the results of this in vitro study by defining the molecular mechanisms through which ADSC-CM protects lung epithelial cells from EMT induced by toxicants in second-hand smoke.

Sensitization of the UPR by loss of PPP1R15A promotes fibrosis and senescence in IPF

The unfolded protein response (UPR) is a direct consequence of cellular endoplasmic reticulum (ER) stress and a key disease driving mechanism in IPF. The resolution of the UPR is directed by PPP1R15A (GADD34) and leads to the restoration of normal ribosomal activity. While the role of PPP1R15A has been explored in lung epithelial cells, the role of this UPR resolving factor has yet to be explored in lung mesenchymal cells. The objective of the current study was to determine the expression and role of PPP1R15A in IPF fibroblasts and in a bleomycin-induced lung fibrosis model. A survey of IPF lung tissue revealed that PPP1R15A expression was markedly reduced. Targeting PPP1R15A in primary fibroblasts modulated TGF-β-induced fibroblast to myofibroblast differentiation and exacerbated pulmonary fibrosis in bleomycin-challenged mice. Interestingly, the loss of PPP1R15A appeared to promote lung fibroblast senescence. Taken together, our findings demonstrate the major role of PPP1R15A in the regulation of lung mesenchymal cells, and regulation of PPP1R15A may represent a novel therapeutic strategy in IPF.

Cellular Senescence: Pathogenic Mechanisms in Lung Fibrosis

Pulmonary fibrosis is a chronic and fatal lung disease that significantly impacts the aging population globally. To date, anti-fibrotic, immunosuppressive, and other adjunct therapy demonstrate limited efficacies. Advancing our understanding of the pathogenic mechanisms of lung fibrosis will provide a future path for the cure. Cellular senescence has gained substantial interest in recent decades due to the increased incidence of fibroproliferative lung diseases in the older age group. Furthermore, the pathologic state of cellular senescence that includes maladaptive tissue repair, decreased regeneration, and chronic inflammation resembles key features of progressive lung fibrosis. This review describes regulatory pathways of cellular senescence and discusses the current knowledge on the senescence of critical cellular players of lung fibrosis, including epithelial cells (alveolar type 2 cells, basal cells, etc.), fibroblasts, and immune cells, their phenotypic changes, and the cellular and molecular mechanisms by which these cells contribute to the pathogenesis of pulmonary fibrosis. A few challenges in the field include establishing appropriate in vivo experimental models and identifying senescence-targeted signaling molecules and specific therapies to target senescent cells, known collectively as "senolytic" or "senotherapeutic" agents.

Clusterin Deficiency Exacerbates Hyperoxia-Induced Acute Lung Injury

Exposure to high oxygen concentrations leads to generation of excessive reactive oxygen species, causing cellular injury and multiple organ dysfunctions and is associated with a high mortality rate. Clusterin (CLU) is a heterodimeric glycoprotein that mediates several intracellular signaling pathways, including cell death and inflammation. However, the role of CLU in the pathogenesis of hyperoxic acute lung injury (HALI) is unknown. Wild-type (WT) and CLU-deficient mice and cultured human airway epithelial cells were used. Changes in cell death- and inflammation-related molecules with or without hyperoxia exposure in cells and animals were determined. Hyperoxia induced an increase in CLU expression in mouse lungs and human airway epithelial cells. Mice lacking CLU had increased HALI and mortality rate compared with WT mice. In vitro, CLU-disrupted cells showed enhanced release of cytochrome c, Bax translocation, cell death and inflammatory cytokine expression. However, treatment with recombinant CLU attenuated hyperoxia-induced apoptosis. Moreover, the Kyoto Encyclopedia of Genes and Genomes and Gene Ontology analyses revealed metabolic pathways, hematopoietic cell lineage, response to stress and localization and regulation of immune system that were differentially regulated between WT and CLU-/- mice. These results demonstrate that prolonged hyperoxia-induced lung injury is associated with CLU expression and that CLU replenishment may alleviate hyperoxia-induced cell death.

Clusterin as modulator of carcinogenesis: A potential avenue for targeted cancer therapy

Clusterin (CLU) is an evolutionary conserved molecular chaperone present in different human tissues and fluids and established to be a significant cancer regulator. It controls several cancer-associated cellular events, including cancer cell proliferation, stemness, survival, metastasis, epithelial-mesenchymal transition, therapy resistance, and inhibition of programmed cell death to support cancer growth and recurrence. This multifunctional role of CLU makes it an ideal target for cancer control. More importantly, genetic and antisense-mediated (OGX-011) inhibition of CLU enhances the anticancer potential of different FDA-approved chemotherapeutic drugs at the clinical level, improving patient's survival. In this review, we have discussed the detailed mechanism of CLU-mediated modulation of different cancer-associated signaling pathways. We have also provided updated information on the current preclinical and clinical findings that drive trials in various cancer types for potential targeted cancer therapy.

Proteomic profiling of biomarkers by MALDI-TOF mass spectrometry for the diagnosis of tracheobronchial stenosis after tracheobronchial tuberculosis

Tracheobronchial tuberculosis (TB) leads to airway stenosis, irreversible airway damage and even death. The present study aimed to identify biomarkers for the diagnosis of tracheobronchial stenosis (TBS) secondary to tracheobronchial TB. A cohort was recruited, including patients with TBS after tracheobronchial TB, TBS after tracheal intubation or tracheotomy (TIT) and no stenosis of early-stage lung cancer,. Proteomic profiling was performed to gain insight into the mechanisms of the pathological processes. Differentially expressed proteins in the serum and bronchial alveolar lavage fluid (BALF) from patients were detected by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). Subsequently, ELISA was performed to validate the changes of protein levels in an additional cohort. MALDI-TOF MS revealed that 8 peptides in the serum, including myeloid-associated differentiation marker, keratin type I cytoskeletal 18, fibrinogen α-chain, angiotensinogen (AGT), apolipoprotein A-I (APOAI), clusterin and two uncharacterized peptides, and nine peptides in BALF, including argininosuccinate lyase, APOAI, AGT and five uncharacterized peptides, were differentially expressed (molecular-weight range, 1,000-10,000 Da) in the TB group compared with the TIT group. The ELISA results indicated that the changes in the protein levels had a similar trend as those identified by proteomic profiling. In conclusion, the present study identified proteins that may serve as potential biomarkers and provide novel insight into the molecular mechanisms underlying TBS after tracheobronchial TB.

Mitochondrial 8-oxoguanine DNA glycosylase mitigates alveolar epithelial cell PINK1 deficiency, mitochondrial DNA damage, apoptosis, and lung fibrosis

Alveolar epithelial cell (AEC) apoptosis, arising from mitochondrial dysfunction and mitophagy defects, is important in mediating idiopathic pulmonary fibrosis (IPF). Our group established a role for the mitochondrial (mt) DNA base excision repair enzyme, 8-oxoguanine-DNA glycosylase 1 (mtOGG1), in preventing oxidant-induced AEC mtDNA damage and apoptosis and showed that OGG1-deficient mice have increased lung fibrosis. Herein, we determined whether mice overexpressing the mtOGG1 transgene (mtOgg1^tg) are protected against lung fibrosis and whether AEC mtOGG1 preservation of mtDNA integrity mitigates phosphatase and tensin homolog-induced putative kinase 1 (PINK1) deficiency and apoptosis. Compared with wild type (WT), mtOgg1^tg mice have diminished asbestos- and bleomycin-induced pulmonary fibrosis that was accompanied by reduced lung and AEC mtDNA damage and apoptosis. Asbestos and H₂O₂ promote the MLE-12 cell PINK1 deficiency, as assessed by reductions in the expression of PINK1 mRNA and mitochondrial protein expression. Compared with WT, Pink1-knockout (Pink1-KO) mice are more susceptible to asbestos-induced lung fibrosis and have increased lung and alveolar type II (AT2) cell mtDNA damage and apoptosis. AT2 cells from Pink1-KO mice and PINK1-silenced (siRNA) MLE-12 cells have increased mtDNA damage that is augmented by oxidative stress. Interestingly, mtOGG1 overexpression attenuates oxidant-induced MLE-12 cell mtDNA damage and apoptosis despite PINK1 silencing. mtDNA damage is increased in the lungs of patients with IPF as compared with controls. Collectively, these findings suggest that mtOGG1 maintenance of AEC mtDNA is crucial for preventing PINK1 deficiency that promotes apoptosis and lung fibrosis. Given the key role of AEC apoptosis in pulmonary fibrosis, strategies aimed at preserving AT2 cell mtDNA integrity may be an innovative target.

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.

Profiling of apoptosis- and autophagy-associated molecules in human lung cancer A549 cells in response to cisplatin treatment using stable isotope labeling with amino acids in cell culture

Cis‑diammine‑dichloro‑platinum II‑based adjuvant chemotherapy provides an alternative therapy to improve the survival of patients with lung tumors, especially those with non‑small cell lung cancer (NSCLC). However, drug resistance is a large clinical problem and its underlying mechanism remains unclear. In the present study, NSCLC A549 cells were treated with a low concentration of cisplatin in order to observe and determine the development of chemoresistance, via growth curves, colony forming assays and apoptosis assays. Then the induction of autophagy was examined in the cisplatin‑treated A549 cells with a fluorescence reporter. Profiled proteins in the cisplatin‑treated A549 cells were also assessed using the stable isotope labeling by amino acids in cell culture (SILAC) method, and then the differentially expressed molecules were verified. The results demonstrated that A549 cells became less sensitive to cisplatin [resistant A549 cells (A549R)] following 20 passages in the medium containing a low concentration of cisplatin, with less apoptotic cells post‑cisplatin treatment. A549R cells grew more efficiently in the cisplatin medium, with more colony formation and more cells migrating across the baseline. In addition, NSCLC results demonstrated that more autophagy‑related proteins (ATGs) were expressed in the A549R cells. Furthermore, the western blotting results confirmed this upregulation of ATGs in A549R cells. In addition, two repeated SILAC screening experiments recognized 15 proteins [glucose‑regulated protein, 78 kDa (GRP78), heat shock protein 71, pre‑mRNA processing factor 19, polypyrimidine tract binding protein 1, translationally controlled tumor protein, Cathepsin D, Cytochrome c, thioredoxin domain containing 5, MutS homolog (MSH) 6, Annexin A2 (ANXA2), BRCA2 and Cyclin dependent kinase inhibitor 1A interacting protein, MSH2, protein phosphatase 2A 55 kDa regulatory subunit Bα, Rho glyceraldehyde‑3‑phosphate‑dissociation inhibitor 1 and ANXA4] that were upregulated by >1.5‑fold in heavy (H)‑ and light (L)‑labeled A549R cells. In addition, 16 and 14 proteins were downregulated by >1.5‑fold in the H‑ and L‑labeled A549R cells, respectively. The majority of the downregulated proteins were associated with apoptosis. In conclusion, the present study isolated a cisplatin‑resistant human lung cancer A549 cell clone, with reduced apoptosis and high levels of autophagy, in response to cisplatin treatment. In cisplatin‑resistant A549R cells, SILAC proteomics recognized the high expression of GRP78 and other proteins that are associated with anti‑apoptosis and/or autophagy promotion.

The mitochondria in lung fibrosis: friend or foe?

Idiopathic pulmonary fibrosis (IPF) and other forms of lung fibrosis are age-associated diseases with increased deposition of mesenchymal collagen that promotes respiratory malfunction and eventual death from respiratory failure. Our understanding of the pathobiology underlying pulmonary fibrosis is incomplete and current therapies available to slow or treat lung fibrosis are limited. Evidence reviewed herein demonstrates key involvement of mitochondrial dysfunction in diverse pulmonary cell populations, including alveolar epithelial cells (AEC), fibroblasts, and macrophages and/or immune cells that collectively advances the development of pulmonary fibrosis. The mitochondria have an important role in regulating whether fibrogenic stimuli results in the return of normal healthy function ("friend") or the development of pulmonary fibrosis ("foe"). In particular, we summarize the evidence suggesting that AEC mitochondrial dysfunction is important in mediating lung fibrosis signaling via mechanisms involving imbalances in the levels of reactive oxygen species, endoplasmic reticulum stress response, mitophagy, apoptosis and/or senescence, and inflammatory signaling. Further, we review the emerging evidence suggesting that dysfunctional mitochondria in AECs and other cell types play crucial roles in modulating nearly all aspects of the 9 hallmarks of aging in the context of pulmonary fibrosis as well as some novel molecular pathways that have recently been identified. Finally, we discuss the potential translational aspects of these studies as well as the key knowledge gaps necessary for better informing our understanding of the pathobiology of the mitochondria in mediating pulmonary fibrosis. We reason that targeting deficient mitochondria-derived pathways may provide innovative future treatment strategies that are urgently needed for lung fibrosis.