Loss of Nrf2 promotes alveolar type 2 cell loss in irradiated, fibrotic lung

Discussion of the material basis for prevention and treatment of pulmonary fibrosis using naturally medicinal and edible homologous herbs based on the dynamic process of Nrf2, NF-κB and TGF-β in PF

Pulmonary fibrosis (PF) is a progressive chronic lung disease with a high incidence and poor prognosis. Despite extensive research into the mechanisms that initiate and drive the progression of pulmonary fibrosis, developing effective treatments remains challenging due to the multiple etiologies, pathogenic links, and signaling pathways involved in PF. Indeed, nuclear factor erythroid 2-related factor 2 (Nrf2), nuclear factor kappa-B (NF-κB), and transforming growth factor-beta (TGF-β) are central players in the pathogenesis of pulmonary fibrosis, and each of these factors influences distinct yet interconnected processes that collectively contribute to disease progression: Nrf2 upregulates antioxidants to mitigate oxidative stress, NF-κB modulates inflammatory responses, and TGF-β promotes fibroblast activation and extracellular matrix (ECM) deposition, leading to fibrosis. Targeting these pathways may offer therapeutic strategies, uncover new insights and provide potential therapeutic targets for PF. Absolutely, the interactions between Nrf2, NF-κB, and TGF-β pathways are complex and can significantly influence the progression of PF, which indicated that targeting a single pathway may show poor efficacy in managing the condition. Moreover, few therapies that effectively intervene in these pathways have been approved. This review focused on the molecular mechanisms of Nrf2, NF-κB, and TGF-β involving in PF and the material basis of the naturally medicinal and edible homologous herbs, which provides a solid foundation for understanding the disease's pathogenesis, and supports the development of therapeutic drugs or treatments for addressing the complex nature of PF.

Targeting the AMPK/Nrf2 Pathway: A Novel Therapeutic Approach for Acute Lung Injury

ALI(acute lung injury) is a severe respiratory dysfunction caused by various intrapulmonary and extrapulmonary factors. It is primarily characterized by oxidative stress and affects the integrity of the pulmonary barrier. In severe cases, ALI can progress to ARDS(acute respiratory distress syndrome), a condition that poses a serious threat to the lives of affected patients. To date, the etiological mechanisms underlying ALI remain elusive, and available therapeutic options are quite limited. AMPK(AMP-activated protein kinase), an essential serine/threonine protein kinase, performs a pivotal function in the regulation of cellular energy levels and cellular regulatory mechanisms, including the detection of redox signals and mitigating oxidative stress. Meanwhile, Nrf2(nuclear factor erythroid 2-related factor 2), a critical transcription factor, alleviates inflammation and oxidative responses by interacting with multiple signaling pathways and contributing to the modulation of oxidative enzymes associated with inflammation and programmed cell death. Indeed, AMPK induces the dissociation of Nrf2 from Keap1(kelch-like ECH-associated protein-1) and facilitates its translocation into the nucleus to trigger the transcription of downstream antioxidant genes, ultimately suppressing the expression of inflammatory cells in the lungs. Given their roles, AMPK and Nrf2 hold promise as novel treatment targets for ALI. This study aimed to summarise the current status of research on the AMPK/Nrf2 signaling pathway in ALI, encompassing recently reported natural compounds and drugs that can activate the AMPK/Nrf2 signaling pathway to alleviate lung injury, and provide a theoretical reference for early intervention in lung injury and future research on lung protection.

Nrf-2 as a novel target in radiation induced lung injury

Radiation-induced lung injury (RILI) is a common and fatal complication of chest radiotherapy. The underlying mechanisms include radiation-induced oxidative stress caused by damage to the deoxyribonucleic acid (DNA) and production of reactive oxygen species (ROS), resulting in apoptosis of lung and endothelial cells and recruitment of inflammatory cells and myofibroblasts expressing NADPH oxidase to the site of injury, which in turn contribute to oxidative stress and cytokine production. Nuclear factor erythroid 2-related factor 2 (Nrf-2) is a vital transcription factor that regulates oxidative stress and inhibits inflammation. Studies have shown that Nrf-2 protects against radiation-induced lung inflammation and fibrosis. This review discusses the protective role of Nrf-2 in RILI and its possible mechanisms.

Activation of Nrf2/ARE pathway by Anisodamine (654-2) for Inhibition of cellular aging and alleviation of Radiation-Induced lung injury

BACKGROUND

Radiation-induced lung injury (RILI) is a common side effect of thoracic tumor radiotherapy, including early-stage radiation-induced lung injury (RP) and late-stage radiation-induced pulmonary fibrosis (RIPF). Currently, it is urgently needed to clarify the pathogenesis of RILI and find safe and effective RILI treatment methods. Irradiation causes DNA damage and oxidative stress in tissues and cells, induces cellular senescence, and promotes the occurrence and development of RILI. In recent years, Anisodamine (654-2) has shown potential therapeutic value in acute lung injury, acute kidney injury, chlamydial pneumonia, and COVID-19. However, there is currently no research on the mechanism of 654-2-mediated cellular senescence and its preventive and therapeutic effects on RILI.

PURPOSE

This study aimed to investigate the protective effect and mechanism of 654-2 on X-ray-induced RILI.

METHODS

In vivo experiments involved a mouse RILI model with 18 Gy X-ray irradiation. Mice were divided into control, model, medication (control + 654-2), and treatment (model + 654-2) groups. And mice in medication and treatment groups were intraperitoneal injection of 5 mg/kg 654-2 every other day until being sacrificed at week 6. In vitro experiments used MLE-12 cells irradiated with 16 Gy and divided into control, model, and model + 654-2（2 μM and 10 μM） groups. Various assays were performed to evaluate lung tissue morphology, fibrosis, apoptosis, cytokine expression, cellular senescence, protein expression, and antioxidant capacity.

RESULTS

654-2 mitigated pulmonary pathological damage, inflammation, DNA damage, cellular senescence, and apoptosis in RILI mice and MLE-12 cells. It restored epithelial cell proliferation ability and enhanced antioxidant capacity. Additionally, 654-2 activated the Nrf2/ARE pathway, increased Nrf2 phosphorylation, and upregulated antioxidant gene expression. Inhibition of Nrf2 reversed the effects of 654-2 on ROS production, antioxidant capacity, and cell senescence.

CONCLUSION

654-2 can activate the Nrf2/ARE pathway, enhance cellular antioxidant capacity, and inhibit cellular senescence, thereby exerting a protective effect against RILI.

From Basic Research to Clinical Practice: Considerations for Treatment Drugs for Silicosis

Silicosis, characterized by irreversible pulmonary fibrosis, remains a major global public health problem. Nowadays, cumulative studies are focusing on elucidating the pathogenesis of silicosis in order to identify preventive or therapeutic antifibrotic agents. However, the existing research on the mechanism of silica-dust-induced pulmonary fibrosis is only the tip of the iceberg and lags far behind clinical needs. Idiopathic pulmonary fibrosis (IPF), as a pulmonary fibrosis disease, also has the same problem. In this study, we examined the relationship between silicosis and IPF from the perspective of their pathogenesis and fibrotic characteristics, further discussing current drug research and limitations of clinical application in silicosis. Overall, this review provided novel insights for clinical treatment of silicosis with the hope of bridging the gap between research and practice in silicosis.

An interactive murine single-cell atlas of the lung responses to radiation injury

Radiation Induced Lung Injury (RILI) is one of the main limiting factors of thorax irradiation, which can induce acute pneumonitis as well as pulmonary fibrosis, the latter being a life-threatening condition. The order of cellular and molecular events in the progression towards fibrosis is key to the physiopathogenesis of the disease, yet their coordination in space and time remains largely unexplored. Here, we present an interactive murine single cell atlas of the lung response to irradiation, generated from C57BL6/J female mice. This tool opens the door for exploration of the spatio-temporal dynamics of the mechanisms that lead to radiation-induced pulmonary fibrosis. It depicts with unprecedented detail cell type-specific radiation-induced responses associated with either lung regeneration or the failure thereof. A better understanding of the mechanisms leading to lung fibrosis will help finding new therapeutic options that could improve patients' quality of life.

Targeting NRF2 to promote epithelial repair

The transcription factor NRF2 is well known as a master regulator of the cellular stress response. As such, activation of NRF2 has gained widespread attention for its potential to prevent tissue injury, but also as a possible therapeutic approach to promote repair processes. While NRF2 activation affects most or even all cell types, its effect on epithelial cells during repair processes has been particularly well studied. In response to tissue injury, these cells proliferate, migrate and/or spread to effectively repair the damage. In this review, we discuss how NRF2 governs repair of epithelial tissues, and we highlight the increasing number of NRF2 targets with diverse roles in regulating epithelial repair.

NMN ameliorated radiation induced damage in NRF2-deficient cell and mice via regulating SIRT6 and SIRT7

Risk of cancer often increases with aging, and radiotherapy is an essential component of treatment. As for abdominal and pelvic cancer, radiotherapy always inevitably causes injury to intestines through direct DNA damage or overload of reactive oxygen species (ROS). Nuclear factor erythroid 2-related factor 2 (NRF2) has been identified as a key protective factor against ionizing-radiation induced damage through promoting DNA damage repair and antioxidant modulation. However, the level of NRF2 always decreases with aging. Here, we demonstrated that NRF2 deficiency aggravated cellular DNA damage and the intestinal pathological lesion. Overexpression of SIRT6 or SIRT7 could improve cell proliferation and protect against radiation injury in NRF2 knock-out (KO) cells by modulating oxidative-stress and DNA damage repair. Consistently, supplement of nicotinamide mononucleotide (NMN), the agonist of sirtuins, increased the level of SIRT6 and SIRT7 in NRF2 KO cells, concomitant with reduced cellular ROS level and ameliorated DNA damage. In vivo, long-term oral administration of NMN attenuated the radiation-induced injury of jejunum, increased the number of intestinal stem cells, and promoted the ability of intestinal proliferation in NRF2-/- mice. Together, our results indicated that SIRT6 and SIRT7 had involved in scavenging ROS and repairing DNA damage, and NMN could be a promising candidate for preventing radiation damage when NRF2 is lacking.

Thromboxane-Prostanoid Receptor Signaling Drives Persistent Fibroblast Activation in Pulmonary Fibrosis

Rationale: Although persistent fibroblast activation is a hallmark of idiopathic pulmonary fibrosis (IPF), mechanisms regulating persistent fibroblast activation in the lungs have not been fully elucidated. Objectives: On the basis of our observation that lung fibroblasts express TBXA2R (thromboxane-prostanoid receptor) during fibrosis, we investigated the role of TBXA2R signaling in fibrotic remodeling. Methods: We identified TBXA2R expression in lungs of patients with IPF and mice and studied primary mouse and human lung fibroblasts to determine the impact of TBXA2R signaling on fibroblast activation. We used TBXA2R-deficient mice and small-molecule inhibitors to investigate TBXA2R signaling in preclinical lung fibrosis models. Measurements and Main Results: TBXA2R expression was upregulated in fibroblasts in the lungs of patients with IPF and in mouse lungs during experimental lung fibrosis. Genetic deletion of TBXA2R, but not inhibition of thromboxane synthase, protected mice from bleomycin-induced lung fibrosis, thereby suggesting that an alternative ligand activates profibrotic TBXA2R signaling. In contrast to thromboxane, F2-isoprostanes, which are nonenzymatic products of arachidonic acid induced by reactive oxygen species, were persistently elevated during fibrosis. F2-isoprostanes induced TBXA2R signaling in fibroblasts and mediated a myofibroblast activation profile due, at least in part, to potentiation of TGF-β (transforming growth factor-β) signaling. In vivo treatment with the TBXA2R antagonist ifetroban reduced profibrotic signaling in the lungs, protected mice from lung fibrosis in three preclinical models (bleomycin, Hermansky-Pudlak mice, and radiation-induced fibrosis), and markedly enhanced fibrotic resolution after bleomycin treatment. Conclusions: TBXA2R links oxidative stress to fibroblast activation during lung fibrosis. TBXA2R antagonists could have utility in treating pulmonary fibrosis.

The Role of Nrf2 in Pulmonary Fibrosis: Molecular Mechanisms and Treatment Approaches

Pulmonary fibrosis is a chronic, progressive, incurable interstitial lung disease with high mortality after diagnosis and remains a global public health problem. Despite advances and breakthroughs in understanding the pathogenesis of pulmonary fibrosis, there are still no effective methods for the prevention and treatment of pulmonary fibrosis. The existing treatment options are imperfect, expensive, and have considerable limitations in effectiveness and safety. Hence, there is an urgent need to find novel therapeutic targets. The nuclear factor erythroid 2-related factor 2 (Nrf2) is a central regulator of cellular antioxidative responses, inflammation, and restoration of redox balance. Accumulating reports reveal that Nrf2 activators exhibit potent antifibrosis effects and significantly attenuate pulmonary fibrosis in vivo and in vitro. This review summarizes the current Nrf2-related knowledge about the regulatory mechanism and potential therapies in the process of pulmonary fibrosis. Nrf2 orchestrates the activation of multiple protective genes that target inflammation, oxidative stress, fibroblast–myofibroblast differentiation (FMD), and epithelial–mesenchymal transition (EMT), and the mechanisms involve Nrf2 and its downstream antioxidant, Nrf2/HO−1/NQO1, Nrf2/NOX4, and Nrf2/GSH signaling pathway. We hope to indicate potential for Nrf2 system as a therapeutic target for pulmonary fibrosis.

Activation of the P62-Keap1-NRF2 Pathway Protects against Ferroptosis in Radiation-Induced Lung Injury

Radiation-induced lung injury (RILI) is one of the most common, serious, and dose-limiting toxicities of thoracic radiotherapy. A primary cause for this is the radiation-induced cell death. Ferroptosis is a recently recognized form of regulated cell death, characterized by the accumulation of lipid peroxidation products and lethal reactive oxygen species (ROS). The ROS generated by irradiation might be the original trigger of ferroptosis in RILI. In addition, activation of the P62-Kelch-like ECH-associated protein 1 (Keap1)-nuclear factor erythroid 2-related factor 2 (NRF2) pathway has been shown to blunt ferroptosis and thus acts as a protective factor. Therefore, this study aimed to explore the protective effect of the P62-Keap1-NRF2 pathway against radiation-induced ferroptosis in alveolar epithelial cells. First, we found that radiation induced ferroptosis in vitro using a RILI cell model, which could be significantly reduced by ferrostatin-1 (Fer-1), a specific ferroptosis inhibitor. Additionally, overexpression of P62 interacted with Keap1 to facilitate the translocation of NRF2 into the nucleus and promote the expression of its target proteins, including quinone oxidoreductase 1 (NQO1), heme oxygenase 1 (HO1), and ferritin heavy chain 1 (FTH1). In summary, our results demonstrated that the activation of the P62-Keap1-NRF2 pathway prevents radiation-induced ferroptosis in RILI cells, providing a theoretical basis of finding a potential therapeutic approach for RILI.

Crossed Pathways for Radiation-Induced and Immunotherapy-Related Lung Injury

Radiation-induced lung injury (RILI) is a form of radiation damage to normal lung tissue caused by radiotherapy (RT) for thoracic cancers, which is most commonly comprised of radiation pneumonitis (RP) and radiation pulmonary fibrosis (RPF). Moreover, with the widespread utilization of immunotherapies such as immune checkpoint inhibitors as first- and second-line treatments for various cancers, the incidence of immunotherapy-related lung injury (IRLI), a severe immune-related adverse event (irAE), has rapidly increased. To date, we know relatively little about the underlying mechanisms and signaling pathways of these complications. A better understanding of the signaling pathways may facilitate the prevention of lung injury and exploration of potential therapeutic targets. Therefore, this review provides an overview of the signaling pathways of RILI and IRLI and focuses on their crosstalk in diverse signaling pathways as well as on possible mechanisms of adverse events resulting from combined radiotherapy and immunotherapy. Furthermore, this review proposes potential therapeutic targets and avenues of further research based on signaling pathways. Many new studies on pyroptosis have renewed appreciation for the value and importance of pyroptosis in lung injury. Therefore, the authors posit that pyroptosis may be the common downstream pathway of RILI and IRLI; discussion is also conducted regarding further perspectives on pyroptosis as a crucial signaling pathway in lung injury treatment.

Role of Nrf2 in Disease: Novel Molecular Mechanisms and Therapeutic Approaches - Pulmonary Disease/Asthma

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a major transcription factor involved in redox homeostasis and in the response induced by oxidative injury. Nrf2 is present in an inactive state in the cytoplasm of cells. Its activation by internal or external stimuli, such as infections or pollution, leads to the transcription of more than 500 elements through its binding to the antioxidant response element. The lungs are particularly susceptible to factors that generate oxidative stress such as infections, allergens and hyperoxia. Nrf2 has a crucial protective role against these ROS. Oxidative stress and subsequent activation of Nrf2 have been demonstrated in many human respiratory diseases affecting the airways, including asthma and chronic obstructive pulmonary disease (COPD), or the pulmonary parenchyma such as acute respiratory distress syndrome (ARDS) and pulmonary fibrosis. Several compounds, both naturally occurring and synthetic, have been identified as Nrf2 inducers and enhance the activation of Nrf2 and expression of Nrf2-dependent genes. These inducers have proven particularly effective at reducing the severity of the oxidative stress-driven lung injury in various animal models. In humans, these compounds offer promise as potential therapeutic strategies for the management of respiratory pathologies associated with oxidative stress but there is thus far little evidence of efficacy through human trials. The purpose of this review is to summarize the involvement of Nrf2 and its inducers in ARDS, COPD, asthma and lung fibrosis in both human and in experimental models.

Identification and Integrated Analysis of circRNA and miRNA of Radiation-Induced Lung Injury in a Mouse Model

Background

Radiation-induced lung injury (RILI) is a main threat to patients who received thoracic radiotherapy. Thus, understanding the molecular mechanism of RILI is of great importance. Circular RNAs (circRNAs) have been found to act as a regulator of multiple biological processes, and the circRNA-microRNA (miRNA)-mRNA axis could play an important role in the signaling pathway of many human diseases including radiation injury.

Methods

First, the circRNA and miRNA of RILI in a mouse model were investigated. The mice received 12 Gy of thoracic irradiation, and the irradiated lung tissues at 48 hours after irradiation were analyzed by RNA sequencing (RNA-seq) compared with normal lung tissues. Then, Gene Ontology analysis of the target mRNAs of the significantly differently expressed circRNAs was performed.

Results

In the irradiated group, inflammatory changes in lungs were observed; 21 significantly up-regulated and 33 down-regulated significantly miRNAs were identified (p < 0.05). Among 27 differentially expressed circRNAs, 10 were down-regulated and 17 were up-regulated in the irradiated group [log2 (fold change) > 1 or < −1, p<0.05]. These differentially expressed miRNAs took part in a series of cellular processes, such as positive regulation of alpha-beta T-cell proliferation, interstitial matrix, collagen fibril organization, chemokine receptor activity, cellular defense response, and B-cell receptor signaling pathway. The differentially expressed circRNAs were related to Th1 and Th2 differentiation pathways, and the predicted mRNAs were verified.

Conclusion

This study revealed immune-related molecular pathways play an important role in the early response after radiotherapy. In the future, research on the target mechanism and early intervention of circRNAs with associated miRNAs such as circRNA5229, circRNA544, and circRNA3340, could benefit the treatment of RILI.

Pterocarpus santalinus L. extract mitigates gamma radiation-inflicted derangements in BALB/c mice by Nrf2 upregulation

Plant-based natural extracts contain several nutrients and bioactive compounds, such as phenolics and flavonoids, that possess various health-promoting activities. This study investigated the effects of polyphenols from Pterocarpus santalinus hydroalcoholic extract (PSHE) against gamma radiation-induced derangements via the upregulation of Nrf2. Ultra High Performance Liquid Chromatography Coupled to High Resolution Mass Spectrometry (UHPLC-HRMS/MS) analysis was performed to identify the possible radioprotectors. In vivo and in vitro studies, namely Real-Time-PCR (RT-PCR) analysis, Reactive Oxygen Species (ROS) scavenging activity, lipid peroxidation and GSH levels, DNA damage and cell death studies, anti-inflammatory (Sandwich ELISA), immunomodulatory studies (antibody staining), and model free radical scavenging assays, were performed. Vanillic acid, protocatechuic acid, para-hydroxybenzoic acid, chlorogenic acid, TNF-α inhibitor (Eudesmin), isoflavone (Daidzein 7-o-glucoside), astragalin (Kaempferol 3-o-glycoside), and other polyphenols were identified in PSHE using UHPLC-HRMS/MS analysis. Prophylactic administration of PSHE (-1 h) rendered more than 33% survival in mice exposed to 8 Gy whole-body-irradiation with increased mice survival and recovery of bone marrow and spleen cellularity. Real-time RT-PCR analysis showed that PSHE treatment (50 µg/mL) upregulated Nrf2, HO-1, and GPX-1 in mice splenocytes. At 50 µg/mL, PSHE reduced ROSscavenging activity, mitochondrial and spleen membrane lipid peroxidation levels, DNA damage, and cell death, and increased GSH levels. At 10 µg/mL, PSHE treatment diminished the content of IL-6 and TNF-α. At 50 µg/mL, PSHE suppressed lymphocyte proliferation. These findings indicate that polyphenols of PSHE possess marked antioxidant, anti-inflammatory, and immunomodulatory capacities, which play important roles in the prevention of radiation damage.

Protective Effect of Sirt1 against Radiation-Induced Damage

Radiotherapy is an important method for the treatment of malignant tumors. It can directly or indirectly lead to the formation of free radicals and DNA damage, resulting in a series of biological effects, including tumor cell death and normal tissue damage. These radiation effects are typically accompanied by the abnormal expression of sirtuin 1 (Sirt1), which deacetylates histones and non-histones. These Sirt1 substrates, including transcription factors and some catalytic enzymes, play a crucial role in anti-oxidative stress, DNA damage repair, autophagy regulation, anti-senescence, and apoptosis, which are closely related to triggering cell defense and survival in radiation-induced damage. In this article, we review the mechanisms underlying cellular responses to ionizing radiation and the role of Sirt1 in the process, with the aim of providing a theoretical basis for protection against radiation by Sirt1 as well as novel targets for developing radioprotective agents.

The role of natural products in the prevention and treatment of pulmonary fibrosis: a review

Pulmonary fibrosis is an incurable end-stage lung disease and remains a global public health problem. Although there have been some breakthroughs in understanding the pathogenesis of pulmonary fibrosis, effective intervention methods are still limited. Natural products have the advantages of multiple biological activities and high levels of safety, which are important factors for preventing and treating pulmonary fibrosis. In this review, we summarized the mechanisms and health benefits of natural products against pulmonary fibrosis. These natural products target oxidative stress, inflammatory injury, epithelial-mesenchymal transition (EMT), fibroblast activation, extracellular matrix accumulation and metabolic regulation, and the mechanisms involve the NF-κB, TGF-β1/Smad, PI3K/Akt, p38 MAPK, Nrf2-Nox4, and AMPK signaling pathways. We hope to provide new ideas for pulmonary fibrosis prevention and treatment strategies.

Interaction of the NRF2 and p63 transcription factors promotes keratinocyte proliferation in the epidermis

Epigenetic regulation of cell and tissue function requires the coordinated action of transcription factors. However, their combinatorial activities during regeneration remain largely unexplored. Here, we discover an unexpected interaction between the cytoprotective transcription factor NRF2 and p63- a key player in epithelial morphogenesis. Chromatin immunoprecipitation combined with sequencing and reporter assays identifies enhancers and promoters that are simultaneously activated by NRF2 and p63 in human keratinocytes. Modeling of p63 and NRF2 binding to nucleosomal DNA suggests their chromatin-assisted interaction. Pharmacological and genetic activation of NRF2 increases NRF2–p63 binding to enhancers and promotes keratinocyte proliferation, which involves the common NRF2–p63 target cyclin-dependent kinase 12. These results unravel a collaborative function of NRF2 and p63 in the control of epidermal renewal and suggest their combined activation as a strategy to promote repair of human skin and other stratified epithelia.

The role of Nrf2/PIWIL2/purine metabolism axis in controlling radiation-induced lung fibrosis

NF-E2-related factor 2 (Nrf2) is a key transcription factor recently implicated in the control of radiation-induced lung fibrosis (RILF). However, the molecular mechanism of Nrf2 in the pathogenesis of RILF is still unclear. The purpose of this study was to evaluate the regulatory effect and mechanism of Nrf2 in the pathogenesis of RILF. The effects of different Nrf2 expression levels on RILF were explored in vitro and in vivo. The RILF model of Nrf2 knockout mice was established for in vivo study. In the study of the mechanism of action, ChIP-seq assay and metabolomics analysis were performed. The discovered mechanism of Nrf2-mediated RILF alleviation was further validated in vitro and in vivo. We found that overexpression of Nrf2 significantly alleviated the fibrosis caused by irradiation in vivo and in vitro. Conversely, Nrf2 silencing strongly aggravated the development of RILF. Mechanistically, Nrf2 signaling increased the expression of piwi-like RNA-mediated gene silencing 2 (PIWIL2), leading to the alteration of purine metabolism and contributing to the relief of RILF. These results suggest that Nrf2 promotes the attenuation of RILF in vivo and in vitro by directly targeting PIWIL2 and activating purine metabolism.

Oxidative Stress in Pulmonary Fibrosis

Oxidative stress has been linked to various disease states as well as physiological aging. The lungs are uniquely exposed to a highly oxidizing environment and have evolved several mechanisms to attenuate oxidative stress. Idiopathic pulmonary fibrosis (IPF) is a progressive age-related disorder that leads to architectural remodeling, impaired gas exchange, respiratory failure, and death. In this article, we discuss cellular sources of oxidant production, and antioxidant defenses, both enzymatic and nonenzymatic. We outline the current understanding of the pathogenesis of IPF and how oxidative stress contributes to fibrosis. Further, we link oxidative stress to the biology of aging that involves DNA damage responses, loss of proteostasis, and mitochondrial dysfunction. We discuss the recent findings on the role of reactive oxygen species (ROS) in specific fibrotic processes such as macrophage polarization and immunosenescence, alveolar epithelial cell apoptosis and senescence, myofibroblast differentiation and senescence, and alterations in the acellular extracellular matrix. Finally, we provide an overview of the current preclinical studies and clinical trials targeting oxidative stress in fibrosis and potential new strategies for future therapeutic interventions. © 2020 American Physiological Society. Compr Physiol 10:509-547, 2020.

The roles of Nrf2 and autophagy in modulating inflammation mediated by TLR4 - NFκB in A549 cell exposed to layer house particulate matter 2.5 (PM2.5)

Particulate matter (PM) from layer house has adverse effect on people and chicken respiratory health, which can further influence animal performance and reduce production efficiency. However, little study focus on the respiratory inflammation induced by PM_2.5 from layer house and the underlying mechanism also unclear. In this study, human adenocarcinoma alveolar basal epithelial cells (A549 cell) was subjected to the PM_2.5 from layer house to evaluate the inflammation reaction caused by PM_2.5 and explore the role of Nrf2 and autophagy in regulating the inflammation. Results showed that the viability of A549 cell decreased in a time - and concentration - dependent manner after PM_2.5 treatment. TNFα, IL6, and IL8 increased significantly treated with PM_2.5 at 12 h. RNA sequencing indicated differentially expressed genes were enriched in immune system process, oxidative stress (OS), endoplasmic reticulum stress (ERS), and autophagy. Further studies showed TLR4 - NFκB p65 signal pathway involved in the inflammation reaction caused by PM_2.5. The overexpression of Nrf2 decreased the level of TNFα, IL6, IL8 markedly as well as the level of NFκB p65 and NFκB pp65. OS and ERS were also limited under overactivation of Nrf2 in PM_2.5 treated cells. Autophagy induced by PM_2.5 promoted the inflammation through increasing the level of NFκB p65 and NFκB pp65. Autophagy deficient strengthened the expression of Nrf2. Collectively, our study revealed Nrf2 prevents inflammation caused by layer house PM_2.5 stimulation, however, autophagy exerts a promotive role in TLR4 - NFκB p65 mediating inflammation in A549 cell.

Mitochondrial biology in airway pathogenesis and the role of NRF2

A constant improvement in understanding of mitochondrial biology has provided new insights into mitochondrial dysfunction in human disease pathogenesis. Impaired mitochondrial dynamics caused by various stressors are characterized by structural abnormalities and leakage, compromised turnover, and reactive oxygen species overproduction in mitochondria as well as increased mitochondrial DNA mutation frequency, which leads to modified energy production and mitochondria-derived cell signaling. The mitochondrial dysfunction in airway epithelial, smooth muscle, and endothelial cells has been implicated in diseases including chronic obstructive lung diseases and acute lung injury. Increasing evidence indicates that the NRF2-antioxidant response element (ARE) pathway not only enhances redox defense but also facilitates mitochondrial homeostasis and bioenergetics. Identification of functional or potential AREs further supports the role for Nrf2 in mitochondrial dysfunction-associated airway disorders. While clinical reports indicate mixed efficacy, NRF2 agonists acting on respiratory mitochondrial dynamics are potentially beneficial. In lung cancer, growth advantage provided by sustained NRF2 activation is suggested to be through increased cellular antioxidant defense as well as mitochondria reinforcement and metabolic reprogramming to the preferred pathways to meet the increased energy demands of uncontrolled cell proliferation. Further studies are warranted to better understand NRF2 regulation of mitochondrial functions as therapeutic targets in airway disorders.

Protective Role of Nuclear Factor-Erythroid 2-Related Factor 2 Against Radiation-Induced Lung Injury and Inflammation

Radiation-induced lung injury (RILI) is one of the most common and fatal complications of thoracic radiotherapy. Inflammatory cell infiltration, imbalance of inflammatory cytokines, and oxidative damage were reported to be involved during RILI pathogenesis, especially in the early phase of RILI. Nuclear factor-erythroid 2-related factor 2 (Nrf2) is a key transcriptional regulator of antioxidative cascades, and regulates life span of mice after administration of thoracic irradiation. We investigated the effects of Nrf2 on RILI and inflammation using Nrf2-knockout, Nrf2-overexpression and wild-type mice with or without 15 Gy ionizing radiation to thorax. Our results showed that Nrf2 deficiency aggravated radiation-induced histopathological changes, macrophage and neutrophil infiltration, serum levels of pro-inflammatory cytokines (IL-6, MCP-1, IFN-γ, TNF, and IL-12p70), and the levels of peroxidation products in the mouse lung. Moreover, loss of Nrf2 reduced radiation-induced serum levels of anti-inflammatory cytokine, IL-10, and antioxidative proteins. Nrf2 overexpression significantly alleviated radiation-induced histopathological changes, macrophages and neutrophils infiltration, serum levels of pro-inflammatory cytokines, and the levels of peroxidation products in lung tissues. Nrf2 overexpression also increased the serum levels of IL-10 and antioxidative proteins. These results indicated that Nrf2 had a protective role against radiation-induced acute lung injury and inflammation, and that antioxidative therapy might be a promising treatment for RILI.

NRF2 Activation Inhibits Both TGF-β1- and IL-13-Mediated Periostin Expression in Fibroblasts: Benefit of Cinnamaldehyde for Antifibrotic Treatment

Systemic fibrosing or sclerotic disorders are life-threatening, but only very limited treatment modalities are available for them. In recent years, periostin (POSTN), a major extracellular matrix component, was established by several studies as a novel key player in the progression of systemic fibrotic disease. In this research, we revealed the involvement of oxidative stress in the expression of POSTN induced by TGF-β1 and IL-13 in dermal fibroblasts. We found that the antioxidant cinnamaldehyde activated the NRF2/HMOX1 pathway. Cinnamaldehyde also alleviated TGF-β1- and IL-13-mediated production of reactive oxygen species and subsequent POSTN upregulation in dermal fibroblasts. In contrast, NRF2 silencing abolished the cinnamaldehyde-mediated downregulation of POSTN. These results suggest that cinnamaldehyde is a broad inhibitor of POSTN expression covering both TGF-β1 and IL-13 signaling. Cinnamaldehyde may thus be beneficial for the treatment of systemic fibrotic diseases.

The Role of Nrf2 in the Response to Normal Tissue Radiation Injury

The transcription factor Nrf2 is an important modulator of antioxidant and drug metabolism, carbohydrate and lipid metabolism, as well as heme and iron metabolism. Regulation of Nrf2 expression occurs transcriptionally and post-transcriptionally. Post-transcriptional regulation entails ubiquitination followed by proteasome-dependent degradation. Additionally, Nrf2-mediated gene expression is subject to negative regulation by ATF3, Bach1 and cMyc. Nrf2-mediated gene expression is an important regulator of a cell's response to radiation. Although a majority of studies have shown that Nrf2 deficient cells are radiosensitized and Nrf2 over expression confers radioresistance, Nrf2's role in mediating the radiation response of crypt cells is controversial. The Nrf2 activator CDDO attenuates radiation-mediated crypt injury, whereas intestinal crypts in Nrf2 null mice are radiation resistant. Further investigation is needed in order to define the relationship between Nrf2 and radiation sensitivity in Lgr5+ and Bmi1+ cells that regulate regeneration of crypt stem cells. In hematopoietic compartments Nrf2 promotes the survival of irradiated osteoblasts that support long-term hematopoietic stem cell (LT-HSC) niches. Loss of Nrf2 in LT-HSCs increases stem cell intrinsic radiosensitivity, with the consequence of lowering the LD50₃₀. An Nrf2 deficiency drives LT-HSCs from a quiescent to a proliferative state. This results in hematopoietic exhaustion and reduced engraftment after myoablative irradiation. The question of whether induction of Nrf2 in LT-HSC enhances hematopoietic reconstitution after bone marrow transplantation is not yet resolved. Irradiation of the lung induces pulmonary pneumonitis and fibrosis. Loss of Nrf2 promotes TGF-β/Smad signaling that induces ATF3 suppression of Nrf2-mediated target gene expression. This, in turn, results in elevated reactive oxygen species (ROS) and isolevuglandin adduction of protein that impairs collagen degradation, and may contribute to radiation-induced chronic cell injury. Loss of Nrf2 impairs ΔNp63 stem/progenitor cell mobilization after irradiation, while promoting alveolar type 2 cell epithelial-mesenchymal transitions into myofibroblasts. These studies identify Nrf2 as an important factor in the radiation response of normal tissue.