Calcitonin gene-related peptide ameliorates hyperoxia-induced lung injury in neonatal rats

AMPK/MTOR/TP53 Signaling Pathway Regulation by Calcitonin Gene-Related Peptide Reduces Oxygen-Induced Lung Damage in Neonatal Rats through Autophagy Promotion

Our previous studies indicated that calcitonin gene-related peptide (CGRP) alleviates hyperoxia-induced lung injury and suggested the possible involvement of autophagy in this process. Herein, we aimed to further explore the potential involvement of tumor protein p53 (TP53) and autophagy in the mode of action of CGRP against hyperoxia-induced lung injury in vitro and in vivo. The study conducted tests on type II alveolar epithelial cells (AECII) and rats that were subjected to hyperoxia treatment or combined treatment of hyperoxia with CGRP, CGRP inhibitor, rapamycin (an autophagy agonist), 3-methyladenine (3-MA, an autophagy inhibitor), TP53 silencing/inhibitor (pifithrin-α), or expression vector/activator (PRIMA-1 (2,2-bis(hydroxymethyl)-3-quinuclidinone)) and their corresponding controls. We found that oxidative stress, apoptosis, and autophagy were all increased by hyperoxia treatment in vitro. However, treating AECII cells with CGRP reversed hyperoxia-induced oxidative stress and apoptosis but further promoted autophagy. In addition, the combined treatment with rapamycin or TP53 silencing with CGRP promoted the effect of CGRP, while contrary results were obtained with combined therapy with 3-MA or TP53 overexpression. In vivo, the number of hyperoxia-induced autophagosomes was promoted in the lung tissue of neonatal rats. Furthermore, hyperoxia increased the expression levels of AMP-activated protein kinase (AMPK) alpha 1 (also known as protein kinase AMP-activated catalytic subunit alpha 1 (PRKAA1)) but inhibited TP53 and mechanistic target of rapamycin (MTOR); these expression trends were regulated by CGRP treatment. In conclusion, we showed that CGRP can attenuate hyperoxia-induced lung injury in neonatal rats by enhancing autophagy and regulating the TP53/AMPK/MTOR crosstalk axis.

Oxidative stress and bronchopulmonary dysplasia

With the progress of modern medicine, oxygen therapy has become a crucial measure for the treatment of premature infants. As an environmental stimulus, in the normal development of lungs, oxygen plays a very important regulatory role. However, the problem is that long-term exposure to hyperoxia can interfere with the development of lungs, leading to irreversible developmental abnormalities. Now, the incidence of bronchopulmonary dysplasia (BPD) is increasing year by year. The existing related research shows that although BPD is a multi-factor triggered disease, its main risk factors are the premature exposure to hyperoxia and the role of reactive oxygen species (ROS). As for premature infants, especially very premature babies and those with very low birth weight, prolonged exposure to high oxygen can affect and alter the normal developmental trajectories of lung tissue and vascular beds, triggering developmental disorders, such as BPD. In the relevant studies about human BPD, a large number of them support that ROS is associated with impaired lung development. Neonates, due to the damage in the development of alveolar, are specific to hyperoxia-induced inflammatory damage. This review while focusing on the role of oxidative stress in the pathogenesis of BPD, suggests that antioxidant measures may be effective to guard against BPD of preterm infants.

The Wnt7b/β-catenin signaling pathway is involved in the protective action of calcitonin gene-related peptide on hyperoxia-induced lung injury in premature rats

Background

Calcitonin gene-related peptide (CGRP) can protect against hyperoxia-induced lung injury, making the upregulation of CGRP a potential therapeutic approach for this type of injury. However, the effects of CGRP on the Wnt7b/β-catenin signaling pathway are unclear. In this study, we investigated the roles of CGRP and the Wnt7b/β-catenin signaling pathway in hyperoxia-induced lung injury.

Methods

Premature Sprague Dawley (SD) rats were exposed to 21, 40, 60 and 95% oxygen for 3, 7 and 14 days. The animals’ body weights, survival rates and endogenous CGRP levels were measured. Lung samples were harvested for histological analyses and measurements of malondialdehyde (MDA) concentration and total antioxidant capacity (TAOC). We also assessed the MDA concentration and TAOC in the lung tissues after administration of 200 nmol/kg CGRP_8–37 (a CGRP antagonist). Finally, alveolar epithelial type II (AEC II) cells were isolated from premature rats, exposed to 21 or 95% oxygen for 3, 7 and 14 days, and treated with 10^− 8 mol/l exogenous CGRP. The protein expressions of Wnt7b and β-catenin were assessed using western blotting, and TCF and c-myc mRNA expressions were assessed using qPCR.

Results

Rats exposed to 60 and 95% oxygen had significantly lower body weights and survival rates than the 21 and 40% groups, and the decrease was time dependent. Endogenous CGRP was elevated in the lung tissues of premature rats exposed to 95% oxygen. CGRP_8–37 induced apparent inflammation in the lung tissue and alveolar structural remodeling. In addition, the expression levels of Wnt7b and β-catenin were markedly increased after exposure for 3 days. They peaked at 7 days, then declined at 14 days. The levels of TCF/c-myc in AEC II cells increased significantly after CGRP treatment when compared with cells that had only undergone hyperoxia.

Conclusions

CGRP protected against hyperoxia-induced lung injury in premature rats. This process involves the Wnt7b/β-catenin signaling pathway.

Extrinsic Calcitonin Gene-Related Peptide Inhibits Hyperoxia-Induced Alveolar Epithelial Type II Cells Apoptosis, Oxidative Stress, and Reactive Oxygen Species (ROS) Production by Enhancing Notch 1 and Homocysteine-Induced Endoplasmic Reticulum Protein (HERP) Expression

Background

Lung alveolar epithelial type II cells (AEC II) are the most important stem cells in lung tissues, which are critical for wound repair of bronchopulmonary dysplasia (BPD). This study investigated the effects of calcitonin gene-related peptide (CGRP) on AEC II cells exposed to hyperoxia.

Material/Methods

Neonatal rat AEC II cells were isolated and identified by detecting surfactant protein C (SP-C). Three small interfering RNAs targeting Notch 1 were synthesized and transfected into AEC II. A hyperoxia-exposed AEC II cell injury model was established and was divided into 8 groups. MDA levels and SOD activity were examined using lipid peroxidation assay kits. Apoptosis and reactive oxygen species (ROS) production were evaluated using flow cytometry. Notch 1 mRNA expression was examined using RT-PCR. Homocysteine-induced endoplasmic reticulum protein (HERP) was examined using Western blot analysis.

Results

CGRP treatment significantly enhanced MDA levels and decreased SOD activity compared to hyperoxia-treated AEC II cells (P<0.05). CGRP treatment significantly inhibited hyperoxia-induced AEC II cell apoptosis, and significantly suppressed hyperoxia-induced ROS production compared to hyperoxia-treated AEC II cells (P<0.05) either undergoing γ secretase inhibitor or Notch RNA interference. CGRP significantly triggered Notch 1 mRNA expression and significantly enhanced HERP expression compared to hyperoxia-treated AEC II cells (P<0.05) either undergoing γ secretase inhibitor or Notch RNA interference.

Conclusions

In AEC II cells, extrinsic peptide CGRP suppressed hyperoxia-induced apoptosis, oxidative stress, and ROS production, which may be triggered by Notch 1 and HERP 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.

CGRP 8-37 enhances lipopolysaccharide-induced acute lung injury and regulating aquaporin 1 and 5 expressions in rats

Calcitonin gene-related peptide (CGRP) has been shown to play important roles in biological functions. However, there is very little evidence on the value of CGRP in lipopolysaccharide (LPS)-induced acute lung injury/acute respiratory distress syndrome (ALI/ARDS). Therefore, this study aimed to investigate the role of CGRP in LPS-induced ALI in rats. In the experiment, Sprague-Dawley (SD) rats were randomized into control, an antagonist of α-calcitonin gene-related peptide receptor (CGRP8-37), LPS groups, and CGRP8-37 + LPS groups. ALI model was prepared through retrograde injection of LPS (10 mg/kg). At 6 and 12 h, bronchoalveolar lavage was performed and used to assess total cell count and levels of tumor necrosis factor-α, interleukin-1β, -6, and -10 by enzyme-linked immunosorbent assay (ELISA). Lung tissue was collected for assessing wet-to-dry (W/D) ratio, hematoxylin and eosin staining. Aquaporin (AQP)-1 and -5 expressions in lung tissues were detected by quantitative PCR and Western blot. The results showed that histological injury, total cell count, and W/D ratio significantly reduced in LPS group after 6 h. The levels of inflammatory cytokines in CGRP8-37 + LPS-treated rats were higher than that in LPS-treated rats (all, P < 0.001). Real-time RT-PCR analysis showed that levels of AQP-1 in rats from CGRP8-37 + LPS group was lower than that in LPS-treated rats (P = 0.005 and P < 0.001). Western blotting analysis showed that AQP-1 protein levels at 6 h significantly decreased in CGRP8-37 + LPS rats. Together, our data suggest that CGRP antagonists, CGRP8-37 could enhance ALI induced by LPS in the rat model, and regulate the expression levels of AQP-1 and AQP-5 by affecting inflammatory cytokines. Thereby, regulating endogenous CGRP may be a potential treatment for ALI/ARDS.

Exogenous α-calcitonin gene-related peptide attenuates lipopolysaccharide-induced acute lung injury in rats

α-Calcitonin gene-related peptide (α-CGRP) is a 37 amino-acid neuropeptide that is primarily released from C-type sensory neurons. α-CGRP exerts multiple modulatory effects on immune responses and visceral organ function, but the role of exogenous α-CGRP in lipopolysaccharide (LPS)-induced acute lung injury (ALI) has remained to be elucidated. Forty-eight rats were randomized to receive continuous intraperitoneal infusion of α-CGRP (0.4 μg/kg/min) or normal saline for 30 min, followed by intratracheal injection of 0.5 mg/kg LPS or saline. There were four groups of animals: The saline-saline (S-S) group; the saline-α-CGRP (S-C) group; the LPS-saline (L-S) group and the LPS-α-CGRP (L-C) group. Mean arterial pressure and arterial blood gases were assessed prior to α-CGRP and LPS administration and every hour following LPS treatment. After 4 h, bronchoalveolar lavage was performed and used to assess total cell count and levels of tumor necrosis factor-α, interleukin-1β, intracellular cell adhesion molecule 1 and macrophage inflammatory protein 2. Lung tissue was also collected for assessing wet-to-dry (W/D) ratio, histology and Evans blue (EB) dye extravasation. Pulmonary α-CGRP concentration and α-CGRP receptor expression were also examined, and inducible cyclic adenosine monophosphate early repressor (ICER) and TNF-α mRNA expression levels were measured. Treatment with exogenous α-CGRP improved oxygenation during LPS-induced ALI. Correspondingly, histological injury, total cell count, inflammatory cytokine levels, W/D ratio and EB dye extravasation were also significantly reduced. α-CGRP receptor 1 expression was noted in pulmonary endothelial cells and alveolar macrophages and α-CGRP receptor expression levels were decreased during ALI, whereas pulmonary α-CGRP expression was continuously increased. Furthermore, exogenous α-CGRP induced upregulation of ICER during LPS-induced ALI. In conclusion, exogenous α-CGRP improved oxygenation and ameliorated lung damage in LPS-induced ALI, and these effects were associated with the upregulation of ICER.

Conditional overexpression of TGFβ1 promotes pulmonary inflammation, apoptosis and mortality via TGFβR2 in the developing mouse lung

Background

Earlier studies have reported that transforming growth factor beta 1(TGFβ1) is a critical mediator of hyperoxia-induced acute lung injury (HALI) in developing lungs, leading to impaired alveolarization and a pulmonary phenotype of bronchopulmonary dysplasia (BPD). However, the mechanisms responsible for the TGFβ1-induced inflammatory signals that lead to cell death and abnormal alveolarization are poorly understood. We hypothesized that TGFβ1 signaling via TGFβR2 is necessary for the pathogenesis of the BPD pulmonary phenotype resulting from HALI.

Methods

We utilized lung epithelial cell-specific TGFβ1 overexpressing transgenic and TGFβR2 null mutant mice to evaluate the effects on neonatal mortality as well as pulmonary inflammation and apoptosis in developing lungs. Lung morphometry was performed to determine the impaired alveolarization and multicolor flow cytometry studies were performed to detect inflammatory macrophages and monocytes in lungs. Apoptotic cell death was measured with TUNEL assay, immunohistochemistry and western blotting and protein expression of angiogenic mediators were also analyzed.

Results

Our data reveals that increased TGFβ1 expression in newborn mice lungs leads to increased mortality, macrophage and immature monocyte infiltration, apoptotic cell death specifically in Type II alveolar epithelial cells (AECs), impaired alveolarization, and dysregulated angiogenic molecular markers.

Conclusions

Our study has demonstrated the potential role of inhibition of TGFβ1 signaling via TGFβR2 for improved survival, reduced inflammation and apoptosis that may provide insights for the development of potential therapeutic strategies targeted against HALI and BPD.

Postnatal inflammation in the pathogenesis of bronchopulmonary dysplasia

Exposure to hyperoxia, invasive mechanical ventilation, and systemic/local sepsis are important antecedents of postnatal inflammation in the pathogenesis of bronchopulmonary dysplasia (BPD). This review will summarize information obtained from animal (baboon, lamb/sheep, rat and mouse) models that pertain to the specific inflammatory agents and signaling molecules that predispose a premature infant to BPD.