Effects of different states of oxidative stress on fetal rat alveolar type II epithelial cells in vitro and ROS-induced changes in Wnt signaling pathway expression

ROS-Influenced Regulatory Cross-Talk With Wnt Signaling Pathway During Perinatal Development

Over a century ago, it was found that a rapid burst of oxygen is needed and produced by the sea urchin oocyte to activate fertilization and block polyspermy. Since then, scientific research has taken strides to establish that Reactive Oxygen Species (ROS), besides being toxic effectors of cellular damage and death, also act as molecular messengers in important developmental signaling cascades, thereby modulating them. Wnt signaling pathway is one such developmental pathway, which has significant effects on growth, proliferation, and differentiation of cells at the earliest embryonic stages of an organism, apart from being significant role-players in the instances of cellular transformation and cancer when this tightly-regulated system encounters aberrations. In this review, we discuss more about the Wnt and ROS signaling pathways, how they function, what roles they play overall in animals, and mostly about how these two major signaling systems cross paths and interplay in mediating major cellular signals and executing the predestined changes during the perinatal condition, in a systematic manner.

The Role of Sphingolipid Signaling in Oxidative Lung Injury and Pathogenesis of Bronchopulmonary Dysplasia

Premature infants are born with developing lungs burdened by surfactant deficiency and a dearth of antioxidant defense systems. Survival rate of such infants has significantly improved due to advances in care involving mechanical ventilation and oxygen supplementation. However, a significant subset of such survivors develops the chronic lung disease, Bronchopulmonary dysplasia (BPD), characterized by enlarged, simplified alveoli and deformed airways. Among a host of factors contributing to the pathogenesis is oxidative damage induced by exposure of the developing lungs to hyperoxia. Recent data indicate that hyperoxia induces aberrant sphingolipid signaling, leading to mitochondrial dysfunction and abnormal reactive oxygen species (ROS) formation (ROS). The role of sphingolipids such as ceramides and sphingosine 1-phosphate (S1P), in the development of BPD emerged in the last decade. Both ceramide and S1P are elevated in tracheal aspirates of premature infants of <32 weeks gestational age developing BPD. This was faithfully reflected in the murine models of hyperoxia and BPD, where there is an increased expression of sphingolipid metabolites both in lung tissue and bronchoalveolar lavage. Treatment of neonatal pups with a sphingosine kinase1 specific inhibitor, PF543, resulted in protection against BPD as neonates, accompanied by improved lung function and reduced airway remodeling as adults. This was accompanied by reduced mitochondrial ROS formation. S1P receptor1 induced by hyperoxia also aggravates BPD, revealing another potential druggable target in this pathway for BPD. In this review we aim to provide a detailed description on the role played by sphingolipid signaling in hyperoxia induced lung injury and BPD.

Claudin-18 expression under hyperoxia in neonatal lungs of bronchopulmonary dysplasia model rats

BACKGROUND

Bronchopulmonary dysplasia (BPD) is characterized by impaired alveolar and microvascular development. Claudin-18 is the only known lung-specific tight junction protein affecting the development and transdifferentiation of alveolar epithelium.

OBJECTIVE

We aimed to explore the changes in the expression of claudin-18, podoplanin, SFTPC, and the canonical WNT pathway, in a rat model of hyperoxia-induced BPD, and to verify the regulatory relationship between claudin-18 and the canonical WNT pathway by cell experiments.

METHODS

A neonatal rat and cell model of BPD was established by exposing to hyperoxia (85%). Hematoxylin and eosin (HE) staining was used to confirm the establishment of the BPD model. The mRNA levels were assessed using quantitative real-time polymerase chain reaction(qRT-PCR). Protein expression levels were determined using western blotting, immunohistochemical staining, and immunofluorescence.

RESULTS

As confirmed by HE staining, the neonatal rat model of BPD was successfully established. Compared to that in the control group, claudin-18 and claudin-4 expression decreased in the hyperoxia group. Expression of β-catenin in the WNT signaling pathway decreased, whereas that of p-GSK-3β increased. Expression of the AEC II marker SFTPC initially decreased and then increased, whereas that of the AEC I marker podoplanin increased on day 14 (P < 0.05). Similarly, claudin-18, claudin-4, SFTPC and β-catenin were decreased but podoplanin was increased when AEC line RLE-6TN exposed to 85% hyperoxia. And the expression of SFTPC was increased, the podoplanin was decreased, and the WNT pathway was upregulated when claudin-18 was overexpressed.

CONCLUSIONS

Claudin-18 downregulation during hyperoxia might affect lung development and maturation, thereby resulting in hyperoxia-induced BPD. Additionally, claudin-18 is associated with the canonical WNT pathway and AECs transdifferentiation.

The alveolar epithelial cells are involved in pulmonary vascular remodeling and constriction of hypoxic pulmonary hypertension

BACKGROUND

Hypoxic pulmonary hypertension (HPH) is a common type of pulmonary hypertension and characterized by pulmonary vascular remodeling and constriction. Alveolar epithelial cells (AECs) primarily sense alveolar hypoxia, but the role of AECs in HPH remains unclear. In this study, we explored whether AECs are involved in pulmonary vascular remodeling and constriction.

METHODS

In the constructed rat HPH model, hemodynamic and morphological characteristics were measured. By treating AECs with hypoxia, we further detected the levels of superoxide dismutase 2 (SOD2), catalase (CAT), reactive oxygen species (ROS) and hydrogen peroxide (H2O2), respectively. To detect the effects of AECs on pulmonary vascular remodeling and constriction, AECs and pulmonary artery smooth cells (PASMCs) were co-cultured under hypoxia, and PASMCs and isolated pulmonary artery (PA) were treated with AECs hypoxic culture medium. In addition, to explore the mechanism of AECs on pulmonary vascular remodeling and constriction, ROS inhibitor N-acetylcysteine (NAC) was used.

RESULTS

Hypoxia caused pulmonary vascular remodeling and increased pulmonary artery pressure, but had little effect on non-pulmonary vessels in vivo. Meanwhile, in vitro, hypoxia promoted the imbalance of SOD2 and CAT in AECs, leading to increased ROS and hydrogen peroxide (H2O2) production in the AECs culture medium. In addition, AECs caused the proliferation of co-cultured PASMCs under hypoxia, and the hypoxic culture medium of AECs enhanced the constriction of isolated PA. However, treatment with ROS inhibitor NAC effectively alleviated the above effects.

CONCLUSION

The findings of present study demonstrated that AECs were involved in pulmonary vascular remodeling and constriction under hypoxia by paracrine H2O2 into the pulmonary vascular microenvironment.

Polyphenols (S3) Isolated from Cone Scales of Pinus koraiensis Alleviate Decreased Bone Formation in Rat under Simulated Microgravity

In order to screen out an effective bone loss protectant from natural plant polyphenol and to elucidate the mechanism of the plant polyphenols that alleviate bone loss under simulated microgravity, the proliferation activities of 9 total polyphenol extracts from natural product (TPENP) on osteoblasts were measured. Polyphenols (S3) was isolated from total polyphenols of cone scales from pinus koraiensis (Korean pine). ALP activity in osteoblasts and MDA level in femur were measured. Mechanical properties and microstructure of the distal cancellous region of the femur in rat were tested. Various bone metabolism markers, enzymes activity and genes expression were also analyzed. The results showed that S3 has the highest activity of osteoblast proliferation. S3 promoted ALP activity in osteoblasts, enhanced mechanical properties and microstructure of the distal cancellous region of femur in rat, decreased MDA level, elevated the serum concentration of BALP, PINP and activities of SOD, CAT, GSH-Px in femur under simulated microgravity. In addition, S3 enhanced the expression of NRF-2, β-catenin, p-GSK3-β, OSX, RUNX2, Osteonectin, Osteocalcin, ALP and collagen I. These results indicated that S3 can alleviated bone loss induced by simulated microgravity through abate the inhibition of the oxidative stress on Wnt/β-catenin signaling pathway.

CGRP attenuates hyperoxia-induced oxidative stress-related injury to alveolar epithelial type II cells via the activation of the Sonic hedgehog pathway

The aim of this study was to examine the effect of calcitonin gene-related peptide (CGRP) on primary alveolar epithelial type II (AECII) cells and expression of Sonic hedgehog (SHH) signaling pathway components following exposure to hyperoxia. The AECII cells were isolated and purified from premature rats and exposed to air (21% oxygen), air + CGRP, hyperoxia (95% oxygen) or hyperoxia + CGRP. The production of intracellular reactive oxygen species (ROS) was determined using the 2',7'-dichlorofluorescin diacetate molecular probe. The levels of malondialdehyde (MDA) and superoxide dismutase (SOD) in the culture supernatant were detected by spectrophotometry. The apoptosis of AECII cells was assayed by flow cytometry, and the mRNA and protein expression levels of Shh and Ptc1 in the AECII cells were detected by reverse transcription-quantitative polymerase chain reaction (RT-qPCR), western blot analysis and immunofluorescence, respectively. The cellular pathological changes partly improved and apoptosis was markedly decreased upon treatment with CGRP under hyperoxic conditions. The levels of ROS in the hyperoxia + CGRP group were significantly lower than thoe in the hyperoxia group. In addition, the hyperoxia-induced increase in MDA levels and the decrease in SOD activity in the culture supernatant of the AECII cells were attenuated by CGRP. Compared with the cells exposed to air, hyperoxia markedly inhibited the mRNA and protein expression levels of Shh and Ptc1 in the AECII cells; however, this inhibition was partly attenuated by treatment with CGRP. On the whole, our data suggest that CGRP can partly protect AECII cells from hyperoxia-induced injury, and the upregulation of CGRP may be a potential therapeutic approach with which to combat hyperoxia-induced lung injury, which may be associated with the activation of the SHH signaling pathway.

Regulation of the angiotensin II-p22phox-reactive oxygen species signaling pathway, apoptosis and 8-oxoguanine-DNA glycosylase 1 retrieval in hyperoxia-induced lung injury and fibrosis in rats

The present study was designed to explore the impact of hyperoxia on lung injury and fibrosis via the angiotensin II (AngII)-p22phox-reactive oxygen species (ROS) signaling pathway, apoptosis and 8-oxoguanine-DNA glycosylase 1 (OGG1) repair enzyme. Newborn Sprague-Dawley rats were randomly divided in the newborn air group, newborn hyperoxia group and newborn intervention group, the latter of which was administered the chymotrypsin inhibitor, 2-(5-formylamino-6-oxo-2-phenyl-1, 6-dihydropyrimidine-1-yl)-N-[4-dioxo-1-phenyl-7-(2-pyridyloxy)] 2-heptyl-acetamide (NK3201). A group of adult rats also received hyperoxic treatment. Histomorphological changes in lung tissues were dynamically observed. AngII, ROS, angiotensin type 1 receptor (AT₁R) and p22phox messenger RNA (mRNA) levels, and OGG1 and peroxisome proliferator-activated receptor-γ (PPARγ) protein levels in the lung tissues were detected at various times after hyperoxia. Hyperoxia led to traumatic changes in the lungs of newborn rats that resulted in decreased viability, increased mortality, morphological changes and the apoptosis of alveolar type II epithelial cells (AT-II), as well as increased expression levels of AngII, AT₁R and p22phox, which would ultimately lead to secondary diseases. NK3201 significantly inhibited the hyperoxia-induced increased expression of AngII, AT₁R and p22phox and further promoted OGG1 and PPARγ protein expression, thus reducing the intrapulmonary ROS level, the apoptotic index and caspase-3 levels. However, the adult hyperoxia group only exhibited tachypnea and reduced viability. This study suggested that the AngII-p22phox-ROS signaling pathway, PPARγ and OGG1 together contributed to the hyperoxia-induced lung injury and that NK3201 was able to reverse the effects of hyperoxia.

Calcitonin gene-related peptide protects type II alveolar epithelial cells from hyperoxia-induced DNA damage and cell death

Hyperoxia therapy for acute lung injury (ALI) may unexpectedly lead to reactive oxygen species (ROS) production and cause additional ALI. Calcitonin gene-related peptide (CGRP) is a 37 amino acid neuropeptide that regulates inflammasome activation. However, the role of CGRP in DNA damage during hyperoxia is unclear. Therefore, the aim of the present study was to investigate the effects of CGRP on DNA damage and the cell death of alveolar epithelial type II cells (AEC II) exposed to 60% oxygen. AEC II were isolated from 19–20 gestational day fetal rat lungs and were exposed to air or to 60% oxygen during treatment with CGRP or the specific CGRP receptor antagonist CGRP_8–37. The cells were evaluated using immunofluorescence to examine surfactant protein-C and ROS levels were measured by probing with 2′,7′-dichlorofluorescin diacetate. The apoptosis rate and cell cycle of AEC II were analyzed by flow cytometry, and apoptosis was determined by western blotting analysis of activated caspase 3. The DNA damage was confirmed with immunofluorescence of H2AX via high-content analysis. The ROS levels, apoptotic cell number and the expression of γH2AX were markedly increased in the hyperoxia group compared with those in the air group. Concordantly, ROS levels, apoptotic cell number and the expression of γH2AX were significantly lower with a significant arrest of S and G2/M phases in the CGRP/O₂ group than in the hyperoxia or CGRP_8–37/O₂ groups. CGRP was concluded to protect lung epithelium cells against hyperoxic insult, and upregulation of CGRP may be a possible novel therapeutic target to treat hyperoxic lung injury.

Wnt5a reverses the inhibitory effect of hyperoxia on transdifferentiation of alveolar epithelial type II cells to type I cells

Transdifferentiation of alveolar epithelial type II cells (AECIIs) to type I cells (AECIs) is critical for reestablishment and maintenance of an intact alveolar epithelium. However, this process is frequently destroyed by hyperoxia treatment, which is commonly used in respiratory distress syndrome therapy in preterm infants. Wnt5a is considered to participate in this physiopathologic process, but the clear mechanisms still need to be further investigated. In this study, preterm rats and primary rat AECIIs were exposed to hyperoxia. Hematoxylin and eosin staining was used to examine the histological changes of the lungs. Real-time PCR and western blotting were used to examine Wnt5a expression and biomarkers of AECII and AECI expression. Immunohistochemistry and immunofluorescence were also used to determine the expression and location of selected biomarkers. Furthermore, AECIIs transfected with Wnt5a gene and exogenous Wnt5a were used to examine whether Wnt5a contributes to the transdifferentiation of AECIIs to AECIs. Results showed that hyperoxia inhibited the transdifferentiation of AECIIs to AECIs in vitro, which is represented by biomarkers of two types of cell that remained unchanged. In addition, Wnt5a protein expression was found to be decreased after hyperoxia exposure in vitro and in vivo. Furthermore, both the overexpression of Wnt5a and exogenous Wnt5a addition blocked the inhibitory effect of hyperoxia in vitro. In conclusion, our results suggest that the transdifferentiation of AECIIs to AECIs is impaired by hyperoxia, and this process may be associated with Wnt5a downregulation. Targeting Wnt5a may have the potential for the therapy of lung injury in preterm infants induced by hyperoxia.

Dishevelled-1 (Dvl-1) protein: a potential participant of oxidative stress induced by selenium deficiency

Oxidative stress induced by selenium deficiency has been shown to be associated with cardiovascular diseases. Nevertheless, the mechanism associated with oxidative stress induced by selenium deficiency is poorly understood. In the present study, 36 weaning C57BL/6 mice were randomly divided into 4 groups as follows: control (n =9), 4-week selenium deficiency (n =9), 8-week selenium deficiency (n = 9), and 12-week selenium deficiency (n =9). The levels of myocardial glutathione peroxidase (GPx), superoxide dismutase (SOD), and malondialdehyde (MDA) were determined by Western blotting or commercial kits. Real-time PCR was performed to detect the mRNA expression of dishevelled-1 (Dvl-1) protein. Western blotting was conducted to evaluate the protein expression levels of Dvl-1 and β-catenin. Our results demonstrated that the levels of GPx and SOD were significantly reduced, along with an increase in MDA in selenium-deficient mice. Importantly, Dvl-1 and β-catenin were clearly upregulated under oxidative stress. Collectively, our findings indicate that Dvl-1 may be an underlying participant of oxidative stress induced by selenium deficiency.