Original articleHyperoxia induces epigenetic changes in newborn mice lungs
Graphical abstract
Introduction
Supplemental oxygen administered to premature babies might injure the lungs [1] and, consequently, contribute to the development of bronchopulmonary dysplasia (BPD). However, the pathogenesis of BPD, which is a serious complication of prematurity, is complex and includes a range of external risk factors, as well as genetic susceptibility. Functional alterations of genomic pathways related to several genes encoding important growth factors, such as vascular endothelial growth factor (VEGF), transforming growth factor-β (TGF-β), and insulin-like growth factor (IGF), are among key factors responsible for such susceptibility [2]. VEGF regulates endothelial cell differentiation and angiogenesis and plays a central role in the formation of embryonic vasculature [3]. TGF-β is involved in inhibition of branching morphogenesis and alveolarization in embryonic lung development [4]. IGF is also involved in growth and injury repair processes in many organs, including the lungs [5].
It is well known that oxidative stress due to reactive oxygen species (ROS) and reactive nitrogen species (RNS) can (chemically) damage lung tissue. However, hyperoxia also has the potential to alter the genome activity in lung cells by inducing DNA modifications. ROS/RNS modify cytosine with the oxidative conversion of 5-methylcytosine (5-mC) to 5-hydroxymethylcytosine. Peroxides can also modify cytosine to 5-chlorocytosine, which mimics 5-mC [6], [7]. The above changes induce improper DNA methylation by inhibiting the binding of DNA methyltransferase 1 (Dnmt1) to DNA [8], [9]. The subsequent alteration of the methylation pattern within the CpG sequences can, in turn, result in gene silencing [10]. The above processes might serve as an example of epigenetic regulation of genome activity.
Understanding the epigenetic potential of hyperoxic lung injury might enable further improvement of therapeutic strategies. Therefore, in this study, we aimed at identifying specific, hyperoxia-related alterations of DNA methylation, which could affect the activity of crucial genetic pathways involved in the development of hyperoxic newborn lung injury. To achieve this, we used an established model with newborn mice exposed to long-term hyperoxia [11] and performed whole-genome methylation analysis with complementary expression assessment of specific genes of interest in lung tissue.
Section snippets
Animal experiment
A total of 24 newborn mice (C57Bl/6Tac) were randomized to hyperoxia (85% O2; 12 animals) or normoxia (21% O2; 12 animals) groups for 14 days, followed by normoxia conditions for all animals for the subsequent 14 days. All mice had free access to food and water and were kept under standard conditions in A-Chambers (O2 – monitor ProOX110, CO2 – monitor ProCO2 P120, BioSpherix). Lung tissue was harvested on day 28 after euthanasia with a zolazepam/tiletamine/xylazine/fentanyl cocktail. Tissue
Results
Histological assessment of lung tissue samples confirmed the presence of oxygen-related lung damage in the hyperoxia group. Fig. 1 shows arrested alveolarization with enlarged alveolar spaces and simplified alveolar structure resulting from prolonged hyperoxia.
The mean methylation level of all microarray probes was increased in the hyperoxia group compared to the normoxia group (average values for mean combined Z-scores 0.57 and − 0.31, respectively). This suggests the presence of an overall
Discussion
Hyperoxia-related alterations of cell signaling and genome expression have been thoroughly described and reviewed in the literature [14], [15], [16], [17]. It was shown that the immaturity of the antioxidant defense system, especially in extremely preterm infants [18], [19], may be a predisposing factor to BPD, as the use of high oxygen concentrations, and positive pressure ventilation upon resuscitation and in the neonatal intensive care unit. However, less is known about the influence of
Declaration of interest
None.
Funding
The work was funded by South and Eastern Norway Regional Health Authority; Source number: 6051, Project no.: 39570 and, partially, by the Polish-Norwegian Research Program, operated by the National Centre for Research and Development under the Norwegian Financial Mechanism 2009–2014 in the frame of Project Contract no. Pol-Nor/196065/54/2013.
References (28)
- et al.
Transfer of the active form of transforming growth factor-beta 1 gene to newborn rat lung induces changes consistent with bronchopulmonary dysplasia
Am. J. Pathol.
(2003) - et al.
Genomic imprinting: cis-acting sequences and regional control
Int. Rev. Cytol.
(2005) - et al.
Gene expression profile and histopathology of experimental bronchopulmonary dysplasia induced by prolonged oxidative stress
Free Radic. Biol. Med.
(2004) - et al.
Pathways of cell signaling in hyperoxia
Free Radic. Biol. Med.
(2003) - et al.
L-cysteine and glutathione metabolism are impaired in premature infants due to cystathionase deficiency
Am. J. Clin. Nutr.
(1995) - et al.
Oxidative stress induces DNA demethylation and histone acetylation in SH-SY5Y cells: potential epigenetic mechanisms in gene transcription in Aβ production
Neurobiol. Aging
(2013) - et al.
Genomic imprinting: cis-acting sequences and regional control
Int. Rev. Cytol.
(2005) Oxygen and oxidative stress in bronchopulmonary dysplasia
J. Perinat. Med.
(2010)- et al.
Genetic risk factors of bronchopulmonary dysplasia
Pediatr. Res.
(2008) - et al.
Enhancement of angiogenic effectors through hypoxia-inducible factor in preterm primate lung in vivo
Am. J. Physiol. Lung Cell. Mol. Physiol.
(2006)
Insulin-like growth factor-1 (IGF-1) and IGF-1 receptor (IGF-1R) expression in human lung in RDS and BPD
Pediatr. Pulmonol.
Inflammation-mediated cytosine damage: a mechanistic link between inflammation and the epigenetic alterations in human cancers
Cancer Res.
Incorporation of 5-chlorocytosine into mammalian DNA results in heritable gene silencing and altered cytosine methylation patterns
Carcinogenesis
Hypothesis: environmental regulation of 5-hydroxymethylcytosine by oxidative stress
Epigenetics
Cited by (27)
Effects of DNA methylase inhibitors in a murine model of severe BPD
2023, Respiratory Physiology and NeurobiologyMicroRNAs and epigenetic signatures in Down syndrome
2022, Genetics and Neurobiology of Down SyndromeEpigenetic response to hyperoxia in the neonatal lung is sexually dimorphic
2020, Redox BiologyCitation Excerpt :The interplay between epigenomic and transcriptomic changes is complex. Previous studies examining the role of epigenetic modifications in neonatal hyperoxic lung injury have focused mainly on DNA methylation [32–34]. Cuna et al. studied alterations in gene expression and DNA methylation in normal murine and human BPD and control lung samples.
Oxygen metabolism and oxygenation of the newborn
2020, Seminars in Fetal and Neonatal MedicineCitation Excerpt :These hypermethylated genes included Tgfbr1, Crebbp, and Creb1, which play central roles in the TGF-β signaling pathway and cell cycle regulation. In the normoxia control group no significant methylation differences were observed for specific genomic pathways [71]. A statistically significant enrichment of especially the TGF-beta signaling pathway was found.
Oxygen radical disease in the newborn, revisited: Oxidative stress and disease in the newborn period
2019, Free Radical Biology and MedicineCitation Excerpt :Hyperoxic treatment of newborn mice in a BPD model resulted in lasting global hypermethylation of lung tissue homogenates. In this hyperoxic lung injury model, significant global DNA hypermethylation was present in oxygen-exposed animals, as well as enrichment of the TGF-β pathways [136]. Recently, epigenetic data from newborn infants show that the amount of oxygen provided during postnatal stabilization changes the DNA methylome in preterm infants.
IRF4-mediated Treg phenotype switching can aggravate hyperoxia-induced alveolar epithelial cell injury
2024, BMC Pulmonary Medicine
- 1
The authors contributed equally to this study.