Critically ill patients are commonly treated with high levels of oxygen, hyperoxia, for prolonged periods of time. Unfortunately, extended exposure to hyperoxia can exacerbate respiratory failure and lead to a high mortality rate. Mitochondrial A-kinase anchoring protein (Akap) has been shown to regulate mitochondrial function. It has been reported that, under hypoxic conditions, Akap121 undergoes proteolytic degradation and promotes cardiac injury. However, the role of Akap1 in hyperoxia-induced acute lung injury (ALI) is largely unknown. To address this gap in our understanding of Akap1, we exposed wild-type ( wt) and Akap1 mice to 100% oxygen for 48 h, a time point associated with lung damage in the murine model of ALI. We found that under hyperoxia, Akap1 mice display increased levels of proinflammatory cytokines, immune cell infiltration, and protein leakage in lungs, as well as increased alveolar capillary permeability compared with wt controls. Further analysis revealed that Akap1 deletion enhances lung NF-κB p65 activity as assessed by immunoblotting and DNA-binding assay and mitochondrial autophagy-related markers, PINK1 and Parkin. Ultrastructural analysis using electron microscopy revealed that Akap1 deletion was associated with remarkably aberrant mitochondria and lamellar bodies in type II alveolar epithelial cells. Taken together, these results demonstrate that Akap1 genetic deletion increases the severity of hyperoxia-induced acute lung injury in mice.
Acute lung injury (ALI) is a major cause of morbidity and mortality worldwide, especially in aged populations. Mitochondrial damage is one of the key features of ALI. Hyperoxia-induced lung injury model in mice has been widely used for ALI study because it features many ALI phenotypes including, but not limited to, mitochondrial and vascular endothelial cell damage. Recently, accumulating evidence has shown that mitochondrial aldehyde dehydrogenase 2 (ALDH2) has a protective effect against oxidative stress mediated cell damage in epithelial cells. However, it is not known whether ALDH2 protects against oxidative stress in vascular endothelial cells. In this current study, we attempted to find the capacity of Alda-1 [(N-(1,3benzodioxol-5-ylmethyl)-2,6- dichloro-benzamide), an ALDH2 activator] to protect against oxidative stress in human microvascular endothelial cells (HMVEC). HMVEC pretreated with Alda-1 prior to hyperoxic exposure vs non-treated controls showed i) lower 4-hydroxynonenal (4-HNE) levels, ii) significantly decreased expressions of Bax and Cytochrome C, iii) partially restored activity and expression of ALDH2 and iv) significantly improved mitochondrial membrane potential. These results suggest that ALDH2 protein in lung vascular endothelial cells is a promising therapeutic target for the treatment of ALI and that Alda-1 is a potential treatment option.
Acute lung injury (ALI), a milder form of acute respiratory distress syndrome (ARDS), is a leading cause of mortality in older adults with an increasing prevalence. Oxygen therapy, is a common treatment for ALI, involving exposure to a high concentration of oxygen. Unfortunately, hyperoxia induces the formation of reactive oxygen species which can cause an increase in 4-HNE (4-hydroxy 2 nonenal), a toxic byproduct of lipid peroxidation. Mitochondrial aldehyde dehydrogenase 2 (ALDH2) serves as an endogenous shield against oxidative stress-mediated damage by clearing 4-HNE. Alda-1 [(N-(1, 3 benzodioxol-5-ylmethyl)-2, 6- dichloro-benzamide)], a small molecular activator of ALDH2, protects against reactive oxygen species-mediated oxidative stress by promoting ALDH2 activity. As a result, Alda-1 shields against ischemic reperfusion injury, heart failure, stroke, and myocardial infarction. However, the mechanisms of Alda-1 in hyperoxia-induced ALI remains unclear. C57BL/6 mice implanted with Alzet pumps received Alda-1 in a sustained fashion while being exposed to hyperoxia for 48 h. The mice displayed suppressed immune cell infiltration, decreased protein leakage and alveolar permeability compared to controls. Mechanistic analysis shows that mice pretreated with Alda-1 also experience decreased oxidative stress and enhanced levels of p-Akt and mTOR pathway associated proteins. These results show that continuous delivery of Alda-1 protects against hyperoxia-induced lung injury in mice.
Aging is a key contributor for subclinical progression of late-onset lung diseases. Basal, club, and type II alveolar epithelial cells (AECs) are lung epithelial progenitors whose capacities of differentiation are extensively studied. The timely transition of these cells in response to environmental changes helps maintain the intricate organization of lung structure. However, it remains unclear how aging affects their behavior. This paper demonstrates that the protein expression profiles of a type II AEC marker, prosurfactant protein C (pro-SPC), and a basal cell marker, p63, are altered in the lungs of 14-mo-old versus 7- to 9-wk-old mice. Expression of NH2-terminal-truncated forms of p63 (ΔNp63), a basal cell marker, and claudin-10, a club cell marker, in cytoplasmic extracts of lungs of 14-mo-old mice was upregulated. In contrast, nuclear expression of full-length forms of p63 (TAp63) decreases with age. These alterations in protein expression profiles coincide with dramatic changes in lung functions including compliance. Whole tissue lysates of middle-aged versus aged rhesus monkey lungs display similar age-associated alterations in pro-SPC expression. An age-associated decrease of TAp63 in nuclear lysates was observed in aged monkey group. Moreover, the lungs of 14-mo-old versus 7- to 9-wk-old mice display a wider spreading of ΔNp63-positive CCSP-positive bronchiolar epithelial cells. This expansion did not involve upregulation of Ki67, a representative proliferation marker. Collectively, it is postulated that 1) this expansion is secondary to a transition of progenitor cells committed to club cells from ΔNp63-negative to ΔNp63-positive status, and 2) high levels of cytoplasmic ΔNp63 expression trigger club cell migration.
Adenosine deaminase acting on RNA 2 (ADAR2), an RNA editing enzyme is involved in a site‐selective modification of adenosine (A) to inosine (I) in double‐stranded RNA (dsRNA). Its role in the lungs is unknown. The phenotypic characterization of Adarb1 mice that lacked ADAR2 auto‐regulation due to the deletion of editing complementary sequence (ΔECS mice) determined the functional role of ADAR2 in the lungs. ADAR2 protein expression increased in the ΔECS mice. These mice display immune cell infiltration and alveolar disorganization. The lung wet by dry ratio indicates there is no lung edema in ΔECS mice. Bronchoalveolar lavage (BAL) analysis of ΔECS mice reveals a significant increase in neutrophils. Interestingly, ΔECS mice spontaneously develop lung fibrosis as indicated by Sirius red staining of collagen fibers in the lung sections and a significant increase in hydroxyproline level in their lungs. ADAR2 expression increased significantly in a bleomycin mouse model, implicating a role of ADAR2 in lung fibrosis. Furthermore, there is a likely possibility that the genetically modified ΔECS mice does not model the physiological or pathophysiological process of lung fibrosis. Nevertheless, this model is useful in interrogating the role of ADAR2 in the lungs. The Ctgf mRNA and connective tissue growth factor (CTGF) protein significantly increased in ΔECS lungs and occurs in bronchial epithelial cells. There is a significant increase in Human antigen R (ELAVL1; HuR) protein levels in ΔECS lungs and suggests a role in stabilizing Ctgf mRNA. Lung mechanics such as total respiratory resistance, Newtonian resistance and tissue damping were increased, whereas inspiratory capacity was decreased in the ΔECS mice. Taken together, these data indicate that overexpression of ADAR2 causes spontaneous lung fibrosis via HuR‐mediated CTGF signaling and implicate a role for ADAR2 auto‐regulation in lung homeostasis. The identification of ADAR2 target genes in ΔECS mice would facilitate a mechanistic understanding of the role of ADAR2 in the lungs and provide a therapeutic strategy for lung fibrosis.
Acute lung injury (ALI) and its severe manifestation, acute respiratory distress syndrome (ARDS), are treated with high concentrations of supplementary oxygen. However, prolonged exposure to high oxygen concentrations stimulates the production of reactive oxygen species (ROS), which damages the mitochondria and accumulates misfolded proteins in the endoplasmic reticulum (ER). The mitochondrial protein A-kinase anchoring protein 1 (Akap1) is critical for mitochondrial homeostasis. It is known that Akap1 deficiency results in heart damage, neuronal development impairment, and mitochondrial malfunction in preclinical studies. Our laboratory recently revealed that deleting Akap1 increases the severity of hyperoxia-induced ALI in mice. To assess the role of Akap1 deletion in ER stress in lung injury, wild-type and Akap1−/− mice were exposed to hyperoxia for 48 h. This study indicates that Akap1−/− mice exposed to hyperoxia undergo ER stress, which is associated with an increased expression of BiP, JNK phosphorylation, eIF2α phosphorylation, ER stress-induced cell death, and autophagy. This work demonstrates that deleting Akap1 results in increased ER stress in the lungs of mice and that hyperoxia exacerbates ER stress-related consequences.
Abnormalities in airway epithelia and lung parenchyma are found in Atp8b1 mutant mice, which develop pulmonary fibrosis after hyperoxic insult. Microarray and ingenuity pathway analysis (IPA) show numerous transcripts involved in ciliogenesis are downregulated in 14-month (14M) -old Atp8b1 mouse lung compared with wild-type C57BL/6. Lung epithelium of Atp8b1 mice demonstrate apical abnormalities of ciliated and club cells in the bronchial epithelium on transmission electron microscopy (TEM). Matrix metalloproteinase 7 (MMP7) regulates of ciliogenesis and is a biomarker for idiopathic pulmonary fibrosis (IPF) in humans. Mmp7 transcript and protein expression are significantly upregulated in 14M Atp8b1 mutant mouse lung. MMP7 expression is also increased in bronchoalveolar lavage fluid (BAL). Immunohistochemistry is localized MMP7 to bronchial epithelial cells in the Atp8b1 mutant. In conclusion, MMP7 is upregulated in the aged Atp8b1 mouse model, which displays abnormal ciliated cell and club cell morphology. This mouse model can facilitate the exploration of the role of MMP7 in epithelial integrity and ciliogenesis in IPF. The Atp8b1 mutant mouse is proposed as a model for IPF.
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