p62 sequestosome 1/light chain 3b complex confers cytoprotection on lung epithelial cells after hyperoxia

Role of sirtuins in sepsis and sepsis-induced organ dysfunction: A review

Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection. Sepsis causes a high mortality rate and current treatment focuses on supportive therapies but lacks specific therapeutic targets. Notably, sirtuins (SIRTs) shows potential clinical application in the treatment of sepsis. It has been demonstrated that SIRTs, the nicotinamide adenine dinucleotide+(NAD+)-dependent deacetylases that regulate key signaling pathways in eukaryotes and prokaryotes, are involved in a variety of biological processes. To date, seven mammalian yeast Sir2 homologs have been identified. SIRTs can regulate inflammation, oxidative stress, apoptosis, autophagy, and other pathways that play important roles in sepsis-induced organ dysfunction. However, the existing studies on SIRTs in sepsis are too scattered, and there is no relevant literature to integrate them. This review innovatively summarizes the different mechanisms of SIRTs in sepsis organ dysfunction according to the different systems, and focuses on SIRT agonists, inhibitors, and targeted drugs that have been proved to be effective in the treatment of sepsis, so as to integrate the clinical research and basic research closely. We searched PubMed for all literature related to SIRTs and sepsis since its inception using the following medical subject headings: sirtuins, SIRTs, and sepsis. Data on the mechanisms of SIRTs in sepsis-induced organ damage and their potential as targets for disease treatment were extracted.

The interplay between mitophagy and mitochondrial ROS in acute lung injury

Mitochondria orchestrate the production of new mitochondria and the removal of damaged ones to dynamically maintain mitochondrial homeostasis through constant biogenesis and clearance mechanisms. Mitochondrial quality control particularly relies on mitophagy, defined as selective autophagy with mitochondria-targeting specificity. Most ROS are derived from mitochondria, and the physiological concentration of mitochondrial ROS (mtROS) is no longer considered a useless by-product, as it has been proven to participate in immune and autophagy pathway regulation. However, excessive mtROS appears to be a pathogenic factor in several diseases, including acute lung injury (ALI). The interplay between mitophagy and mtROS is complex and closely related to ALI. Here, we review the pathways of mitophagy, the intricate relationship between mitophagy and mtROS, the role of mtROS in the pathogenesis of ALI, and their effects and related progression in ALI induced by different conditions.

Methionine sulfoxide reductase 2 regulates Cvt autophagic pathway by altering the stability of Atg19 and Ape1 in Saccharomyces cerevisiae

The reversible oxidation of methionine plays a crucial role in redox regulation of proteins. Methionine oxidation in proteins causes major structural modifications that can destabilize and abrogate their function. The highly conserved methionine sulfoxide reductases protect proteins from oxidative damage by reducing their oxidized methionines, thus restoring their stability and function. Deletion or mutation in conserved methionine sulfoxide reductases leads to aging and several human neurological disorders and also reduces yeast growth on nonfermentable carbon sources. Despite their importance in human health, limited information about their physiological substrates in humans and yeast is available. For the first time, we show that Mxr2 interacts in vivo with two core proteins of the cytoplasm to vacuole targeting (Cvt) autophagy pathway, Atg19, and Ape1 in Saccharomyces cerevisiae. Deletion of MXR2 induces instability and early turnover of immature Ape1 and Atg19 proteins and reduces the leucine aminopeptidase activity of Ape1 without affecting the maturation process of Ape1. Additonally, Mxr2 interacts with the immature Ape1, dependent on Met17 present within the propeptide of Ape1 as a single substitution mutation of Met17 to Leu abolishes this interaction. Importantly, Ape1 M17L mutant protein resists oxidative stress-induced degradation in WT and mxr2Δ cells. By identifying Atg19 and Ape1 as cytosolic substrates of Mxr2, our study maps the hitherto unexplored connection between Mxr2 and the Cvt autophagy pathway and sheds light on Mxr2-dependent oxidative regulation of the Cvt pathway.

Caveolin-1 scaffolding domain peptide abrogates autophagy dysregulation in pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is the most common and fatal form of interstitial lung disease. IPF is characterized by irreversible scarring of the lungs leading to lung function decline. Although the etiology remains poorly understood, dysregulated autophagy in alveolar-epithelial cells (AECs) together with interplay between apoptotic-AECs and proliferative-myofibroblasts have been strongly implicated in IPF pathogenesis. Recent studies have revealed that a caveolin-1-derived 7-mer peptide, CSP7, mitigates established PF at least in part by improving AEC viability. In the present study, we aimed to determine whether and how CSP7 regulates autophagy in fibrotic-lung AECs. We found that p53 and autophagic proteins were markedly upregulated in AECs from mice with single/multi-doses of bleomycin—or silica-induced PF. This was abolished following treatment of PF-mice with CSP7. Further, CSP7 abrogated silica- or bleomycin-induced p53 and autophagy proteins in AECs. Immunoprecipitation further revealed that CSP7 abolishes the interaction of caveolin-1 with LC3BII and p62 in AECs. AEC-specific p53-knockout mice resisted silica- or bleomycin-induced changes in autophagy proteins, or CSP7 treatment. Our findings provide a novel mechanism by which CSP7 inhibits dysregulated autophagy in injured AECs and mitigates existing PF. These results affirm the potential of CSP7 for treating established PF, including IPF and silicosis.

Caveolin-1 Alleviates Crohn's Disease-induced Intestinal Fibrosis by Inhibiting Fibroblasts Autophagy Through Modulating Sequestosome 1

BACKGROUND

Intestinal fibrosis is a common complication of Crohn's disease (CD) and is characterized by the excessive accumulation of extracellular matrix produced by activated myofibroblasts. Caveolin-1 (CAV1) inhibits fibrosis. However, limited data show that CAV1 affects intestinal fibrosis.

METHODS

Human CD tissue samples were gained from patients with CD who underwent surgical resection of the intestine and were defined as stenotic or nonstenotic areas. A dextran sodium sulfate-induced mouse model of intestinal fibrosis was established. For in vitro experiments, we purchased CCD-18Co intestinal fibrosis cells and isolated and cultured human primary colonic fibroblasts. These fibroblasts were activated by transforming growth factor β administration for 48 hours. In the functional experiments, a specific small interfering RNA or overexpression plasmid was transfected into fibroblasts. The messenger RNA levels of fibrosis markers, such as α-smooth muscle actin, fibronectin, connective tissue growth factor, and collagen I1α, were determined using quantitative polymerase chain reaction. Western blot analysis was applied to detect the expression of CAV1, SQSTM1/p62 (sequestosome 1), and other fibrosis markers.

RESULTS

In human CD samples and the dextran sodium sulfate-induced mouse model of intestinal fibrosis, we observed a downregulation of CAV1 in fibrosis-activated areas. Mechanistically, CAV1 knockdown in both human primary colonic fibroblasts and CCD-18Co cells promoted fibroblast activation, while CAV1 overexpression inhibited fibroblast activation in vitro. We found that SQSTM1/p62 positively correlated with CAV1 expression levels in patients with CD and that it was indirectly modulated by CAV1 expression. Rescue experiments showed that CAV1 decreased primary human intestinal fibroblast activation by inhibiting fibroblast autophagy through the modulation of SQSTM1/p62.

CONCLUSIONS

Our data demonstrate that CAV1 deficiency induces fibroblast activation by indirectly regulating SQSTM1/p62 to promote fibroblast autophagy. CAV1 or SQSTM1/p62 may be potential therapeutic targets for intestinal fibrosis.

TBHQ alleviates pyroptosis and necroptosis in chicken alveolar epithelial cells induced by fine particulate matter from broiler houses

Fine particulate matter (PM2.5) from poultry houses has adverse effects on the health of animals and workers. Tert-butylhydroquinone (TBHQ), an antioxidant, is widely used in feed additives. The present study investigated the effects of TBHQ on broiler house PM2.5-induced damage in chicken primary alveolar epithelial cells (AECII) extracted from 16-day-old chicken embryos using the method of differential adhesion. AECII were exposed to PM2.5 and TBHQ alone or in combination, and then, cell membrane integrity, pyroptosis, and necroptosis were detected. Our results showed that PM2.5 from broiler houses caused cell rupture and loss of cell membrane integrity. This result was confirmed by the obvious increases in lactate dehydrogenase (LDH) release and propidium iodide (PI)-positive cells compared to the control group. In addition, the intracellular reactive oxygen species (ROS) levels and the expression levels of pyroptosis-related genes (NLRP3, IL-18, IL-1β) and necroptosis-related genes (RIPK3) were also significantly enhanced. However, TBHQ significantly inhibited intracellular ROS, improved cell viability, and reduced the release of LDH and the number of PI-positive cells compared to those in the PM2.5 group. The expression levels of pyroptosis-related genes (Caspase-1, NLRP3, IL-18, IL-1β) and necroptosis-related genes (RIPK3) were also significantly decreased in the co-treatment group. In summary, these results indicated that TBHQ can alleviate PM2.5-mediated cell pyroptosis and necroptosis in chicken AECII and provide a basis for overcoming the danger that air pollutants from broiler houses pose to the health of chickens.

DIM-C-pPhtBu induces lysosomal dysfunction and unfolded protein response - mediated cell death via excessive mitophagy

Despite technological advances in cancer treatment, the survival rate of patients with head and neck cancer (HNC) has not improved significantly. Many studies have shown that endoplasmic reticulum (ER) stress-related signals are associated with mitochondrial damage and that these signals determine whether cells maintain homeostasis or activate cell death programs. The unfolded protein response (UPR) is regulated by ER membrane proteins such as double-stranded RNA-activated protein kinase R(PKR)-like ER kinase (PERK), which directly activate transcription of chaperones or genes that function in redox homeostasis, protein secretion, or cell death programs. In this study, we focused on the role of mitophagy and ER stress-mediated cell death induced by DIM-C-pPhtBu in HNC cancer. We found that DIM-C-pPhtBu, a compound that activates ER stress in many cancers, induced lysosomal dysfunction, excessive mitophagy, and cell death in HNC cells. Moreover, DIM-C-pPhtBu strongly inhibited HNC progression in a xenograft model by altering mitophagy related protein expression. Taken together, the results demonstrate that DIM-C-pPhtBu induces excessive mitophagy and eventually UPR-mediated cell death in HNC cells, suggesting that new anti-cancer drugs could be developed based on the connection between mitophagy and cancer cell death.

Autophagy markers as mediators of lung injury-implication for therapeutic intervention

Lung injury is characterized by inflammatory processes demonstrated as loss of function of the pulmonary capillary endothelial and alveolar epithelial cells. Autophagy is an intracellular digestion system that work as an inducible adaptive response to lung injury which is a resultant of exposure to various stress agents like hypoxia, ischemia-reperfusion and xenobiotics which may be manifested as acute lung injury (ALI), acute respiratory distress syndrome (ARDS), chronic lung injury (CLI), bronchopulmonary dysplasia (BPD), chronic obstructive pulmonary disease (COPD), asthma, ventilator-induced lung injury (VILI), ventilator-associated lung injury (VALI), pulmonary fibrosis (PF), cystic fibrosis (CF) and radiation-induced lung injury (RILI). Numerous regulators like LC3B-II, Beclin 1, p62, HIF1/BNIP3 and mTOR play pivotal role in autophagy induction during lung injury possibly for progression/inhibition of the disease state. The present review focuses on the critical autophagic mediators and their potential cross talk with the lung injury pathophysiology thereby bringing to limelight the possible therapeutic interventions.

DR5 related autophagy can promote apoptosis in gliomas after irradiation

As a cancer treatment strategy, irradiation therapy is widely used that can cause DNA breakage and increase free radicals, which leads to different types of cell death. Among them, apoptosis and autophagy are the most important and the most studied cell death processes. Although the exploration of the relationship between apoptosis and autophagy has been a major area of focus, still the molecular mechanisms of autophagy on apoptosis remain unclear. Here, we have revealed that apoptosis was enhanced by the death receptor 5 (DR5) pathway, and the effect of autophagy on apoptosis was promoted by DR5 interacting with LC3B as well as Caspase8 in gliomas after irradiation. Interestingly, we observed that the addition of four different autophagy inducers, rapamycin (RAP), CCI779, ABT737 and temozolomide (TMZ), induced the differences of DR5 expression and cell apoptosis after irradiation. Unlike RAP and CCI779, ABT737 and TMZ were able to increase DR5 expression and further induce cell death. Therefore, we have concluded that DR5 plays a novel and indispensable role in promoting cell apoptosis under irradiation and suggest a potential therapeutic approach for glioblastoma treatment.

miR‑21‑5p ameliorates hyperoxic acute lung injury and decreases apoptosis of AEC II cells via PTEN/AKT signaling in rats

Inhibiting apoptosis of type II alveolar epithelial cells (AEC II) is an effective way to decrease hyperoxic acute lung injury (HALI); however, the specific underlying molecular mechanisms have not yet been fully elucidated. Although miRNA‑21‑5p has previously been reported to decrease H2O2‑induced AEC II apoptosis by targeting PTEN in vitro, whether miR‑21‑5p can decrease HALI in vivo and the downstream molecular mechanisms remain unclear. In the present study, rats were endotracheally administered with an miR‑21‑5p‑encoding (AAV‑6‑miR‑21‑5p) or a negative control adenovirus vector, and then a HALI model was established by exposure to hyperoxia. At 3 weeks following the administration of AAV‑6‑miR‑21‑5p, the severity of HALI was decreased, as evidenced by the improved outcome of the oxygenation index, respiratory index, wet/dry weight ratio and pathological scores of the HALI lungs. To further investigate the underlying mechanisms, AEC II cells were isolated from the lungs of the experimental rats and cultured. The expression levels of miR‑21‑5p and its target gene, PTEN, were detected, as well as the levels of phosphorylated and total AKT. In addition, the apoptosis rate of AEC II was detected by flow cytometry. The results demonstrated that AAV‑6‑miR‑21‑5p administration increased the miR‑21‑5p levels in primary AEC II cells, while it decreased the expression levels of PTEN. miR‑21‑5p overexpression also increased AKT phosphorylation in AEC II cells from the HALI lungs compared with that of the HALI alone group and the control virus group. The present study indicated that miR‑21‑5p ameliorated HALI in vivo, which may have resulted from the inhibition of PTEN/AKT‑induced apoptosis of AEC II cells. These findings suggest that miR‑21‑5p and PTEN/AKT signaling might serve as potential targets for HALI treatment.

Caveolin-1 selectively regulates microRNA sorting into microvesicles after noxious stimuli

Emerging evidence suggests that extracellular vesicle (EV)-containing miRNAs mediate intercellular communications in response to noxious stimuli. It remains unclear how a cell selectively sorts the cellular miRNAs into EVs. We report that caveolin-1 (cav-1) is essential for sorting of selected miRNAs into microvesicles (MVs), a main type of EVs generated by outward budding of the plasma membrane. We found that cav-1 tyrosine 14 (Y14)-phosphorylation leads to interactions between cav-1 and hnRNPA2B1, an RNA-binding protein. The cav-1/hnRNPA2B1 complex subsequently traffics together into MVs. Oxidative stress induces O-GlcNAcylation of hnRNPA2B1, resulting in a robustly altered hnRNPA2B1-bound miRNA repertoire. Notably, cav-1 pY14 also promotes hnRNPA2B1 O-GlcNAcylation. Functionally, macrophages serve as the principal recipient of epithelial MVs in the lung. MV-containing cav-1/hnRNPA2B1 complex-bound miR-17/93 activate tissue macrophages. Collectively, cav-1 is the first identified membranous protein that directly guides RNA-binding protein into EVs. Our work delineates a novel mechanism by which oxidative stress compels epithelial cells to package and secrete specific miRNAs and elicits an innate immune response.

Protective Features of Autophagy in Pulmonary Infection and Inflammatory Diseases

Autophagy is a highly conserved catabolic process involving autolysosomal degradation of cellular components, including protein aggregates, damaged organelles (such as mitochondria, endoplasmic reticulum, and others), as well as various pathogens. Thus, the autophagy pathway represents a major adaptive response for the maintenance of cellular and tissue homeostasis in response to numerous cellular stressors. A growing body of evidence suggests that autophagy is closely associated with diverse human diseases. Specifically, acute lung injury (ALI) and inflammatory responses caused by bacterial infection or xenobiotic inhalation (e.g., chlorine and cigarette smoke) have been reported to involve a spectrum of alterations in autophagy phenotypes. The role of autophagy in pulmonary infection and inflammatory diseases could be protective or harmful dependent on the conditions. In this review, we describe recent advances regarding the protective features of autophagy in pulmonary diseases, with a focus on ALI, idiopathic pulmonary fibrosis (IPF), chronic obstructive pulmonary disease (COPD), tuberculosis, pulmonary arterial hypertension (PAH) and cystic fibrosis.

Identification of miRNA-rich vesicles in bronchoalveolar lavage fluid: Insights into the function and heterogeneity of extracellular vesicles

Despite emerging interest in the role of extracellular vesicle (EV)-containing microRNAs (EV-miRNAs), the existence of functional EV-miRNAs under patho-physiological conditions has been viewed with skepticism. Due to the heterogenicity of EVs, several barriers related to EV-miRNA research are to be explored before the in vivo function of EV-miRNAs can be thoroughly delineated. For example, it has been reported that far less than one copy of a given miRNA can be detected per exosome. In this study, we demonstrated that miRNA-rich-EVs exist and can be consistently isolated using differential centrifugation & density-gradient fractionation from bronchoalveolar lavage fluid (BALF) in vivo. The absolute number of this 'miRNA-rich'-EV population is only about 7.05 × 10⁹ per mouse (6% of total EVs). However, the RNA amount detected in this population of EVs represents approximately 39% of the total EV RNAs in the BALF. In contrast, the remaining populations of BALF EVs (76% of total EVs) contain extremely low concentrations of RNAs and miRNAs. The miRNA-rich-EVs in BALF are likely derived from alveolar epithelial type-I cells (ATIs). Notably, caveolin-1, a lipid raft protein, is exclusively detected in the miRNA-rich-EVs, suggesting the lipid raft protein as a biomarker of EV-miRNA enrichment. We further demonstrated that miRNAs contained in the ATI-EVs are actively delivered into alveolar macrophages, subsequently promoting inflammasome activation, neutrophil recruitment, and M1-macrophage polarization in response to P. aeruginosa pneumonia in vitro and in vivo. Collectively, we are the first to identify and characterize the miRNA-rich-EVs in BALF. These miRNA-rich EVs endorse pro-inflammatory responses in bacterial lung infection. Our study provides a novel insight into the development of biomarkers, therapeutic strategies and underlying mechanisms for lung pathology.

Oxidative stress, autophagy and airway ion transport

Mucociliary clearance is critically important in protecting the airways from infection and from the harmful effects of smoke and various inspired substances known to induce oxidative stress and persistent inflammation. An essential feature of the clearance mechanism involves regulation of the periciliary liquid layer on the surface of the airway epithelium, which is necessary for normal ciliary beating and maintenance of mucus hydration. The underlying ion transport processes associated with airway surface hydration include epithelial Na⁺ channel-dependent Na⁺ absorption occurring in parallel with CFTR and Ca²⁺-activated Cl^- channel-dependent anion secretion, which are coordinately regulated to control the depth of the periciliary liquid layer. Oxidative stress is known to cause both acute and chronic effects on airway ion transport function, and an increasing number of studies in the past few years have identified an important role for autophagy as part of the physiological response to the damaging effects of oxidation. In this review, recent studies addressing the influence of oxidative stress and autophagy on airway ion transport pathways, along with results showing the potential of autophagy modulators in restoring the function of ion channels involved in transepithelial electrolyte transport necessary for effective mucociliary clearance, are presented.

Autophagy inducers restore impaired autophagy, reduce apoptosis, and attenuate blunted alveolarization in hyperoxia-exposed newborn rats

AIM

Autophagy is a common process during development. Abnormal autophagy can impact cell apoptosis. Previous studies have shown that apoptosis is present during bronchopulmonary dysplasia (BPD). However, there is no consensus on the level of coexisting autophagy. This study was designed to investigate the role of autophagy and the effects of autophagy inducers in a BPD model.

METHOD

A total of 100 newborn Sprague-Dawley rats were randomly assigned to model and control groups. BPD models were established by hyperoxic induction(FiO₂ 0.80). Some of them were treated with autophagy-inducing agents.

RESULT

As compared to the control group, more autophagic bodies were found within Type II alveolar epithelial cells (AT-II cells) under transmission electron microscopy (TEM) in the model group at 3 d . These autophagic bodies were also accompanied by apoptotic bodies and expression of both bodies peaked at 7 d. As shown by TdT-mediated dUTP nick end labeling (TUNEL), there were more apoptotic cells in the model group than in the control group. Protein expression levels of LC3B-II, p62, Lamp1, and cleaved Caspase-3 increased with increased hyperoxic exposure time. No significant differences were observed in the mRNA expression levels of LC3B, p62, and Lamp1. After introducing an autophagy inducer, either rapamycin or lithium chloride, the radial alveolar count (RAC) value of BPD model group increased as compared with placebo group, the thickness of alveolar septum decreased, while apoptosis decreased.

CONCLUSION

Reduced autophagy resulting from blocked autophagy flow may be a key link in the pathogenesis of BPD. By enhancing repressed autophagy, apoptosis could be reduced and alveolar development improved.

Factors that influence adult neurogenesis as potential therapy

Adult neurogenesis involves persistent proliferative neuroprogenitor populations that reside within distinct regions of the brain. This phenomenon was first described over 50 years ago and it is now firmly established that new neurons are continually generated in distinct regions of the adult brain. The potential of enhancing the neurogenic process lies in improved brain cognition and neuronal plasticity particularly in the context of neuronal injury and neurodegenerative disorders. In addition, adult neurogenesis might also play a role in mood and affective disorders. The factors that regulate adult neurogenesis have been broadly studied. However, the underlying molecular mechanisms of regulating neurogenesis are still not fully defined. In this review, we will provide critical analysis of our current understanding of the factors and molecular mechanisms that determine neurogenesis. We will further discuss pre-clinical and clinical studies that have investigated the potential of modulating neurogenesis as therapeutic intervention in neurodegeneration.

miR‑21‑5p regulates type II alveolar epithelial cell apoptosis in hyperoxic acute lung injury

Hyperoxia-induced acute lung injury (HALI) as one of the most common complications in patents on mechanical ventilation, and there are no efficient methods to overcome this at present. It was hypothesized that microRNA 21-5p(miR-21-5p) can promote the survival of type II alveolar epithelial cells (AECII), alleviating HALI. The present study aimed to combine gene chip analysis with the overexpression miR-21-5p to develop a novel therapeutic option for HALI. It was found that AECII apoptosis was an important pathogenic event in the development of HALI, and the overexpression of miR-21-5p prevented HALI, associated with reducing AECII apoptosis. These results were obtained using adenoviral/lentiviral vectors, which overexpressed miR-21-5p, to transfect AECII cells in vitro and in vivo. It was found that the overexpression of miR-21-5p reduced the apoptotic rate of the AECII cells. In addition, miR-21-5p decreased the ratio of B-cell lymphoma 2 (Bcl-2)-associated X protein/Bcl-2 and the expression of caspase-3. It was also revealed that the overexpression of miR-21-5p alleviated acute lung injury in adult rats exposed to a hyperoxic environment. These results suggest that miR-21-5p may become a novel therapeutic option for patients with HALI, by protecting AECII cells from apoptosis.

Lung Epithelial Cell-Derived Microvesicles Regulate Macrophage Migration via MicroRNA-17/221-Induced Integrin β1 Recycling

Robust lung inflammation is one of the prominent features in the pathogenesis of acute lung injury (ALI). Macrophage migration and recruitment are often seen at the early stage of lung inflammatory responses to noxious stimuli. Using an acid inhalation-induced lung injury model, we explored the mechanisms by which acid exposure initiates macrophage recruitment and migration during development of ALI. The lung epithelium comprises a large surface area and functions as a first-line defense against noxious insults. We found that acid exposure induced a remarkable microvesicle (MV) release from lung epithelium as detected in bronchoalveolar lavage fluid. Significantly elevated RNA, rather than protein, was found in these epithelium-derived MVs after acid and included several highly elevated microRNAs, including microRNA (miR)-17 and miR-221. Acid-induced epithelial MV release promoted macrophage migration in vitro and recruitment into the lung in vivo and required, in part, MV shuttling of miR-17 and/or miR-221. Mechanistically, acid-induced epithelial MV miR-17/221 promoted β₁ integrin recycling and presentation back onto the surface of macrophages, in part via a Rab11-mediated pathway. Integrin β₁ is known to play an essential role in regulating macrophage migration. Taken together, acid-induced ALI results in epithelial MV shuttling of miR-17/221 that in turn modulates macrophage β₁ integrin recycling, promoting macrophage recruitment and ultimately contributing to lung inflammation.

Inhibition of Regulatory-Associated Protein of Mechanistic Target of Rapamycin Prevents Hyperoxia-Induced Lung Injury by Enhancing Autophagy and Reducing Apoptosis in Neonatal Mice

Administration of supplemental oxygen remains a critical clinical intervention for survival of preterm infants with respiratory failure. However, prolonged exposure to hyperoxia can augment pulmonary damage, resulting in developmental lung diseases embodied as hyperoxia-induced acute lung injury and bronchopulmonary dysplasia (BPD). We sought to investigate the role of autophagy in hyperoxia-induced apoptotic cell death in developing lungs. We identified increased autophagy signaling in hyperoxia-exposed mouse lung epithelial-12 cells, freshly isolated fetal type II alveolar epithelial cells, lungs of newborn wild-type mice, and human newborns with respiratory distress syndrome and evolving and established BPD. We found that hyperoxia exposure induces autophagy in a Trp53-dependent manner in mouse lung epithelial-12 cells and in neonatal mouse lungs. Using pharmacological inhibitors and gene silencing techniques, we found that the activation of autophagy, upon hyperoxia exposure, demonstrated a protective role with an antiapoptotic response. Specifically, inhibiting regulatory-associated protein of mechanistic target of rapamycin (RPTOR) in hyperoxia settings, as evidenced by wild-type mice treated with torin2 or mice administered (Rptor) silencing RNA via intranasal delivery or Rptor^+/-, limited lung injury by increased autophagy, decreased apoptosis, improved lung architecture, and increased survival. Furthermore, we identified increased protein expression of phospho-beclin1, light chain-3-II and lysosomal-associated membrane protein 1, suggesting altered autophagic flux in the lungs of human neonates with established BPD. Collectively, our study unveils a novel demonstration of enhancing autophagy and antiapoptotic effects, specifically through the inhibition of RPTOR as a potentially useful therapeutic target for the treatment of hyperoxia-induced acute lung injury and BPD in developing lungs.

Hyperoxia-mediated LC3B activation contributes to the impaired transdifferentiation of type II alveolar epithelial cells (AECIIs) to type I cells (AECIs)

Life-saving mechanical ventilation can also cause lung injury through the overproduction of reactive oxygen species (ROS), leading to bronchopulmonary dysplasia (BPD)-like symptoms in preterm infants. It is reported that the autophagic protein microtubule-associated protein-1 light chain (LC)-3B can confer protection against hyperoxia-induced DNA damage in lung alveolar epithelium. However, its role in the transdifferentiation of type II alveolar epithelial cells (AECIIs) to type I cells (AECIs) is unclear and requires further investigation. In this study, newborn Sprague-Dawley rats were exposed to 90% oxygen for up to 14 days to mimic BPD in human infants, with neonatal pups exposed to room air (21% oxygen) as controls. Primary rat AECIIs were cultured under hyperoxic conditions for up to 24 hours to further investigate the underlying mechanisms. This study found that hyperoxia promoted a significant and time-dependent increase of AECII marker surfactant protein (SP)-C in the lung. The increase of AECI marker T1α was repressed by hyperoxia during lung development. These results indicated an impaired AECII transdifferentiation. Pulmonary ROS concentration and expression of autophagic protein LC-3B were increased gradually in response to hyperoxia exposure. Furthermore, AECIIs produced more ROS when cultured under hyperoxic conditions in vitro. Both the LC3B expression and the conversion from LC3BI to LC3BII were enhanced in hyperoxic AECs. Interestingly, inhibition of LC3B either by ROS inhibitor N-acetyl-l-cysteine (NAC) or adenovirus-mediated LC3B shRNA could partly restore AECII transdifferentiation under hyperoxia condition. In summary, the current study reveals a novel role of activated LC3B induced by hyperoxia in AECII transdifferentiation.

Sclareol inhibits cell proliferation and sensitizes cells to the antiproliferative effect of bortezomib via upregulating the tumor suppressor caveolin-1 in cervical cancer cells

The anticancer effect of sclareol has long been reported, however, the exact mechanisms underlying the antitumorigenic effect of sclareol in cervical carcinoma remain to be fully elucidated. The present study analyzed cell proliferation and cell apoptosis by MTT and FITC-Annexin V assays. The protein levels of caveolin-1 (Cav-1) and copper-zinc superoxide dismutase (SOD)1 were determined by western blotting, and the interaction of Cav1 and HSC70 was investigated by co-immunoprecipitation experiments. The present study found that sclareol inhibited cell proliferation and induced apoptosis in HeLa cells. Two cancer-associated proteins, Cav1 and SOD1 were identified as potential targets of sclareol in HeLa cells. The expression of Cav1 increased when the cells were treated with sclareol, and the protein level of SOD1 was negatively correlated with Cav1. The overexpression of Cav1 enhanced the sensitivity of the HeLa cells to sclareol treatment and downregulated the protein level of SOD1, which exhibited potential associations between Cav1 and SOD1. In addition, sclareol significantly sensitized several cancer cells to the anticancer effect of bortezomib by targeting Cav1 and SOD1. Taken together, the results of the present study demonstrated that sclareol inhibited tumor cell growth through the upregulation of Cav1, and provides a potential therapeutic target for human cancer.

Relevance of FXR-p62/SQSTM1 pathway for survival and protection of mouse hepatocytes and liver, especially with steatosis

Background

Liver injury and regeneration involve complicated processes and are affected by various physio-pathological conditions. Surgically, severe liver injury after surgical resection often leads to fatal liver failure, especially with some underlying pathological conditions such as steatosis. Therefore, protection from the injury of hepatocytes and liver is a serious concern in various clinical settings.

Methods

We studied the effects of the farnesoid X receptor (FXR) on cell survival and steatosis in mouse hepatocytes (AML12 mouse liver cells) and investigated their molecular mechanisms. We next studied whether or not FXR improves liver injury, regeneration and steatosis in a mouse model of partial hepatectomy (PH) with steatosis.

Results

An FXR-specific agonist, GW4064, induced expressions of the p62/SQSTM1 gene and protein in AML12 mouse liver cells. Because we previously reported p62/SQSTM1 as a key molecule for antioxidation and cell survival in hepatocytes, we next examined the activation of nuclear factor erythroid 2-related factor-2 (Nrf2) and induction of the antioxidant molecules by GW4064. GW4064 activated Nrf2 and subsequently induced antioxidant molecules (Nrf2, catalase, HO-1, and thioredoxin). We also examined expressions of pro-survival and cell protective molecules associated with p62/SQSTM1. Expectedly, GW4064 induced phosphorylation of Akt, expression of the anti-apoptotic molecules (Bcl-xL and Bcl-2), and reduced harmful hepatic molecules (Fas ligand and Fas). GW4064 promoted hepatocyte survival, which was cancelled by p62/SQSTM1 siRNA. These findings suggest the potential relevance of the FXR-p62/SQSTM1 pathway for the survival and protection of hepatocytes. Furthermore, GW4064 induced the expression of small heterodimer partners (SHP) and suppressed liver X receptor (LXR)-induced steatosis in hepatocytes, expecting the in vivo protective effect of FXR on liver injury especially with steatosis. In the hepatectomy model of db/db mice with fatty liver, pre-treatment by GW4064 significantly reduced post-PH liver injury (serum levels of LDH, AST & ALT and histological study) and improved steatosis. The key molecules, p62/SQSTM1, Nrf2 and SHP were upregulated in fatty liver tissue by GW4064 treatment.

Conclusions

The present study is the first to demonstrate the relevance of FXR-p62/SQSTM1 and -SHP in the protection against injury of hepatocytes and post-PH liver, especially with steatosis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12876-016-0568-3) contains supplementary material, which is available to authorized users.

Epithelial cell-derived microvesicles activate macrophages and promote inflammation via microvesicle-containing microRNAs

Intercellular communications between lung epithelial cells and alveolar macrophages play an essential role in host defense against acute lung injury. Hyperoxia-induced oxidative stress is an established model to mimic human lung injury. We show that after hyperoxia-associated oxidative stress, a large amount of extracellular vesicles (EVs) are detectable in bronchoalveolar lavage fluid (BALF) and culture medium of lung epithelial cells. Microvesicles (MVs), but not exosomes (Exos) or apoptotic bodies (Abs), are the main type of EVs found in the early stages after hyperoxia. Among all the MV compositions, small RNAs are altered the most significantly after hyperoxia-associated oxidative stress. We further confirmed that hyperoxia up-regulates the levels of certain specific miRNAs in the epithelial cell-derived MVs, such as the miR-320a and miR-221. Functionally, the hyperoxia-induced epithelial MVs promote macrophage activation in vitro and facilitate the recruitment of immunomodulatory cells in vivo detected in BALF. Using MV as a cargo, delivery of the specific miRNA-enriched epithelial MVs (miR-221 and/or miR-320a) also triggers macrophage-mediated pro-inflammatory effects. Collectively, epithelial cell-derived MVs promote macrophage-regulated lung inflammatory responses via MV-shuttling miRNAs.

Differential regulation of autophagy and mitophagy in pulmonary diseases

Lysosomal-mediated degradation of intracellular lipids, proteins and organelles, known as autophagy, represents a inducible adaptive response to lung injury resulting from exposure to insults, such as hypoxia, microbes, inflammation, ischemia-reperfusion, pharmaceuticals (e.g., bleomycin), or inhaled xenobiotics (i.e., air pollution, cigarette smoke). This process clears damaged or toxic cellular constituents and facilitates cell survival in stressful environments. Autophagic degradation of dysfunctional or damaged mitochondria is termed mitophagy. Enhanced mitophagy is usually an early response to promote survival. However, overwhelming or prolonged mitochondrial damage can induce excessive/pathological levels of mitophagy, thereby promoting cell death and tissue injury. Autophagy/mitophagy is therefore an important modulator in human pulmonary diseases and a potential therapeutic target. This review article will summarize the most recent studies highlighting the role of autophagy/mitophagy and its molecular pathways involved in stress response in pulmonary pathologies.

MiR-15a/16 Regulates Apoptosis of Lung Epithelial Cells after Oxidative Stress

Lung epithelial cell apoptosis is an important feature of hyperoxia-induced lung injury. Death receptor-associated extrinsic pathway and mitochondria-associated intrinsic pathway both mediate the development of lung epithelial cell apoptosis. Despite decades of research, molecular mechanisms of hyperoxia-induced epithelial cell apoptosis remain incompletely understood. Here we report a novel regulatory paradigm in response to hyperoxia-associated oxidative stress. Hyperoxia markedly up-regulated miR-15a/16 levels in lung epithelial cells, broncho-alveolar lavage fluid (BALF) and lung tissue. This effect was mediated by hyperoxia-induced reactive oxygen species (ROS). Functionally, miR-15a/16 inhibitors induced caspase 3-mediated lung epithelial cell apoptosis, in the presence of hyperoxia. MiR-15a/16 inhibitors robustly enhanced FADD level and down-regulated Bcl-2 expression. Consistently, cleaved caspase 8 and 9 were highly induced in the miR-15a/16 deficient cells, after hyperoxia. Using airway epithelial cell specific, miR-15a/16^-/- mice, we found that Bcl-2 significantly reduced in lung epithelial cells in vivo after hyperoxia. In contrast, caspase 3, 8 and Bcl-2 associated death promoter (BAD) were highly elevated in the miR-15a/16^-/- epithelial cells in vivo. Interestingly, in lung epithelial malignant cells, rather than benign cells, deletion of miR-15a/16 prevented apoptosis. Furthermore, deletion of miR-15a/16 in macrophages also prohibited apoptosis, opposite to what we have found in normal lung epithelial cells. Taken together, our data suggested that miR-15a/16 may exert differential roles in different cell types. MiR-15a/16 deficiency result in lung epithelial cell apoptosis in response to hyperoxia, via modulating both intrinsic and extrinsic apoptosis pathways.

miR-185 mediates lung epithelial cell death after oxidative stress

Lung epithelial cell death is a prominent feature involved in the development of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). Hyperoxia-induced ALI is an established animal model mimicking human ARDS. Small noncoding RNAs such as microRNAs (miRNAs) have potent physiological and pathological functions involving multiple disease processes. Emerging interests focus on the potential of miRNAs to serve as novel therapeutic targets and diagnostic biomarkers. We found that hyperoxia highly induces miR-185 and its precursor in human lung epithelial cells in a time-dependent manner, and this observation is confirmed using mouse primary lung epithelial cells. The hyperoxia-induced miR-185 is mediated by reactive oxygen species. Furthermore, histone deacetylase 4 (HDAC4) locates in the promoter region of miR-185. We found that hyperoxia suppresses HDAC4 specifically in a time-dependent manner and subsequently affects histone deacetylation, resulting in an elevated miR-185 transcription. Using MC1586, an inhibitor of class IIa HDACs, we showed that inhibition of class IIa HDACs upregulates the expression of miR-185, mimicking the effects of hyperoxia. Functionally, miR-185 promotes hyperoxia-induced lung epithelial cell death through inducing DNA damage. We confirmed functional roles of miR-185 using both the loss- and gain-of-function approaches. Moreover, multiple 14-3-3δ pathway proteins are highly attenuated by miR-185 in the presence of hyperoxia. Taken together, hyperoxia-induced miR-185 in lung epithelial cells contributes to oxidative stress-associated epithelial cell death through enhanced DNA damage and modulation of 14-3-3δ pathways.

Enhanced Resolution of Hyperoxic Acute Lung Injury as a result of Aspirin Triggered Resolvin D1 Treatment

Acute lung injury (ALI), which presents as acute respiratory failure, is a major clinical problem that requires aggressive care, and patients who require prolonged oxygen exposure are at risk of developing this disease. Although molecular determinants of ALI have been reported, the molecules involved in disease catabasis associated with oxygen toxicity have not been well studied. It has been reported that lung mucosa is rich in omega-3 fatty acid dicosahexanoic acid (DHA), which has antiinflammatory properties. Aspirin-triggered resolvin D1 (AT-RvD1) is a potent proresolution metabolite of DHA that can curb the inflammatory effects in various acute injuries, yet the effect of AT-RvD1 on hyperoxic acute lung injury (HALI) or in the oxygen toxicity setting in general has not been investigated. The effects of AT-RvD1 on HALI were determined for the first time in 8- to 10-week-old C57BL/6 mice that were exposed to hyperoxia (≥95% O2) for 48 hours. Mice were given AT-RvD1 (100 ng) in saline or a saline vehicle for 24 hours in normoxic (≈21% O2) conditions after hyperoxia. Lung tissue and bronchoalveolar lavage (BAL) fluid were collected for analysis associated with proinflammatory signaling and lung inflammation. AT-RvD1 treatment resulted in reduced oxidative stress, increased glutathione production, and significantly decreased tissue inflammation. AT-RvD1 treatment also significantly reduced the lung wet/dry ratio, protein in BAL fluid, and decreased apoptotic and NF-κB signaling. These results show that AT-RvD1 curbs oxygen-induced lung edema, permeability, inflammation, and apoptosis and is thus an effective therapy for prolonged hyperoxia exposure in this murine model.

p62/SQSTM1 plays a protective role in oxidative injury of steatotic liver in a mouse hepatectomy model

AIMS

Liver injury and regeneration involve complicated processes and are affected by various physio-pathological factors. We investigated the mechanisms of steatosis-associated liver injury and delayed regeneration in a mouse model of partial hepatectomy.

RESULTS

Initial regeneration of the steatotic liver was significantly delayed after hepatectomy. Although hepatocyte proliferation was not significantly suppressed, severe liver injury with oxidative stress (OS) occurred immediately after hepatectomy in the steatotic liver. Fas-ligand (FasL)/Fas expression was upregulated in the steatotic liver, whereas the expression of antioxidant and anti-apoptotic molecules (catalase/MnSOD/Ref-1 and Bcl-2/Bcl-xL/FLIP, respectively) and p62/SQSTM1, a steatosis-associated protein, was downregulated. Interestingly, pro-survival Akt was not activated in response to hepatectomy, although it was sufficiently expressed even before hepatectomy. Suppression of p62/SQSTM1 increased FasL/Fas expression and reduced nuclear factor erythroid 2-related factor-2 (Nrf-2)-dependent antioxidant response elements activity and antioxidant responses in steatotic and nonsteatotic hepatocytes. Exogenously added FasL induced severe cellular OS and necrosis/apoptosis in steatotic hepatocytes, with only the necrosis being inhibited by pretreatment with antioxidants, suggesting that FasL/Fas-induced OS mainly leads to necrosis. Furthermore, p62/SQSTM1 re-expression in the steatotic liver markedly reduced liver injury and improved liver regeneration.

INNOVATION

This study is the first which demonstrates that reduced expression of p62/SQSTM1 plays a crucial role in posthepatectomy acute injury and delayed regeneration of steatotic liver, mainly via redox-dependent mechanisms.

CONCLUSION

In the steatotic liver, reduced expression of p62/SQSTM1 induced FasL/Fas overexpression and suppressed antioxidant genes, mainly through Nrf-2 inactivation, which, along with the hypo-responsiveness of Akt, caused posthepatectomy necrotic/apoptotic liver injury and delayed regeneration, both mainly via a redox-dependent mechanism.

Co-localization of iron binding on silica with p62/sequestosome1 (SQSTM1) in lung granulomas of mice with acute silicosis

The cellular mechanisms involved in the development of silicosis have not been fully elucidated. This study aimed to examine influence of silica-induced lung injury on autophagy. Suspensions of crystalline silica particles were administered transnasally to C57BL/6j mice. Immunohistochemical examination for Fas and p62 protein expression was performed using lung tissue specimens. Two-dimensional and quantitative analysis of silica deposits in the lungs were performed in situ using lung tissue sections by an in-air microparticle induced X-ray emission (in-air micro-PIXE) analysis system, which was based on irrradiation of specimens with a proton ion microbeam. Quantitative analysis showed a significant increase of iron levels on silica particles (assessed as the ratio of Fe relative to Si) on day 56 compared with day 7 (p<0.05). Fas and p62 were expressed by histiocytes in granulomas on day 7, and the expressions persisted for day 56. Fas- and p62-expressing histiocytes were co-localized in granulomas with silica particles that showed an increase of iron levels on silica particles in mouse lungs. Iron complexed with silica induces apoptosis, and may lead to dysregulations of autophagy in histiocytes of granulomas, and these mechanisms may contribute to granuloma development and progression in silicosis.

Emerging role of selective autophagy in human diseases

Autophagy was originally described as a highly conserved system for the degradation of cytosol through a lysosome-dependent pathway. In response to starvation, autophagy degrades organelles and proteins to provide metabolites and energy for its pro-survival effects. Autophagy is recognized as playing a role in the pathogenesis of disease either directly or indirectly, through the regulation of vital processes such as programmed cell death, inflammation, and adaptive immune mechanisms. Recent studies have demonstrated that autophagy is not only a simple metabolite recycling system, but also has the ability to degrade specific cellular targets, such as mitochondria, cilia, and invading bacteria. In addition, selective autophagy has also been implicated in vesicle trafficking pathways, with potential roles in secretion and other intracellular transport processes. Selective autophagy has drawn the attention of researchers because of its potential importance in clinical diseases. Therapeutic strategies to target selective autophagy rather than general autophagy may maximize clinical benefit by enhancing selectivity. In this review, we outline the principle components of selective autophagy processes and their emerging importance in human disease, with an emphasis on pulmonary diseases.

Cross-talk between apoptosis and autophagy in lung epithelial cell death

As an essential organ for gas exchange, the lungs are constantly exposed to the external environment and are simulated by toxicants and pathogens. The integrity of lung epithelium and epithelial cells is crucial for fulfilling the physiological functions of the lung. The homeostasis of lung epithelial cells is maintained by a complex network by which survival and death are tightly regulated. Upon noxious stimulation, lung epithelium attempts to maintain its normal structure and function. Savage of injured cells and clearance of unsalvageable dying cells or unwanted proliferated cells constantly occur in the lung epithelium. Apoptosis, or programmed cell death, functions as a primary mechanism to discard unsalvageable cells or unwanted overgrowth. Autophagy, on the other hand, initially attempts to save and repair the injured cells. However, when the noxious stimulation is too strong and cell survival becomes unfeasible, autophagy behaves oppositely and cooperates with apoptosis, subsequently accelerates cell death. The imbalance between autophagy and apoptosis potentially leads to tumorigenesis or devastating cell death/lung injury. Therefore, the cross-talk between apoptosis and autophagy in lung epithelial cells is critical in determining the fate of epithelial cells and its balance of death/survival in response to environmental stimuli. In this review, we will focus on the current understandings of the communications between apoptosis and autophagy in lung epithelial cells. We will review multiple key regulators and their underlying mechanisms involved in the cross-talk between apoptosis and autophagy. The autophagic factors, such as the Beclin-1, ATG5, Fap-1, p62 and concentration-dependent LC3B, all closely interact with multiple apoptosis pathways. Understanding these regulations of apoptosis/autophagy cross-talk potentially provides novel targets for developing diagnostic and therapeutic strategies for many lung diseases, including lung injuries and malignancies.