Lung metabolism in the nitrofen model of congenital diaphragmatic hernia

Resumen

Infants born with a congenital diaphragmatic hernia (CDH) have a developmental abnormality of the diaphragm, with defect of closure, leading to lung compression by herniated contents from the abdomen. This compression causes changes in the structure and blood vessels of the lungs and alters the development of the heart. While the causes of CDH are not fully understood, genetic and environmental factors have been suggested as contributing to its genesis. Moreover, the pathogenesis leading to lung hypoplasia and pulmonary arterial hypertension in CDH is still poorly understood. During fetal development, the lungs grow and develop in a low-oxygen environment. However, in CDH, compression from the abdominal contents, particularly a more compact viscera such the liver, can lead to decreased blood flow to the lungs, reducing oxygen and nutrient delivery. As a result, fetal lung cells may switch to predominantly anaerobic metabolism to produce sufficient energy without generating harmful free radicals. However, if the cells are unable to produce enough energy, they may not be able to function properly, going to a standby status and leading to a developmental arrest, lung hypoplasia, and pulmonary hypertension in CDH. The project's overall objective was to determine if metabolic and energetic changes can play a role in the pathogenesis of CDH. We integrated an in-depth metabolic study with an understanding of the gene and protein expression of enzymes involved in glycolysis and energy regulation in CDH fetal lungs. I used the nitrofen model of CDH because it is the most commonly used and preferred method for investigating the etiopathogenic mechanisms of the disease. First, I performed a metabolomic analysis using nuclear magnetic resonance (NMR) spectroscopy to identify changes in the metabolites of fetal CDH lungs. The analysis revealed changes related to oxidative stress, nucleotide synthesis, amino acid metabolism, glycerophospholipid metabolism, and glucose metabolism in fetal CDH lungs. The highest variable importance in projection score metabolites were lactate, glutamate, and adenosinetriphosphate (ATP). Second, I found that fetal CDH lungs are chronically hypoxic, which affects cell metabolism and bioenergetics, and impacts normal lung development. I observed an increase in hypoxiainducible factor 1alfa (HIF-1alfa) and the main fetal glucose transporter in nitrofen-exposed lungs. Further analyses showed upregulation of glycolysis and a decrease in oxidative phosphorylation, as well as severe depletion of adenosine triphosphate (ATP), adenosine diphosphate (ADP), and increased adenosine monophosphate (AMP) in CDH fetal lungs, with an inverted AMP:ATP and ADP:ATP ratios and a depleted energy cellular charge. Third, transcription levels and protein expression confirmed the cell attempt to prevent energy collapse, with an increase in lactate dehydrogenase C, pyruvate dehydrogenase kinase 1 and 2, adenosine monophosphate deaminase, AMP-activated protein kinase, calcium/calmodulin-dependent protein kinase 2, liver kinase B1, and a decrease in ATP synthase. These findings suggest that the changes in lung metabolism and bioenergetics may have a role in CDH pathogenesis, providing new insights into the molecular mechanisms behind CDH pathophysiology and could lead to the development of novel treatment targets for CDH patients. These studies demonstrate the importance of understanding lung metabolism and bioenergetics in CDH pathogenesis and the potential for novel therapies to target these processes to improve outcomes for CDH patients.