70 - Role of fatty acid oxidation in hyperoxia-induced endothelial-to-mesenchymal transition in lung endothelial cells

Abstract

Bronchopulmonary dysplasia (BPD) is a chronic lung disease, which is characterized by alveolar dysplasia and impaired vascularization in premature infants. BPD can develop pulmonary hypertension (PH) in adolescence and adulthood. This is corroborated by previous reports showing that hyperoxic exposure in newborn mice caused PH in adult mice. Endothelial-to-mesenchymal cells (EndoMT), a biological process where endothelial cells (ECs) progressively lose their specific markers and gain mesenchymal phenotype, is one of the contributing factors for development of PH. It has been shown that inhibition of fatty acid oxidation (FAO) augments the magnitude of EndoMT in ECs. This was attenuated by enhancing FAO via overexpression of carnitine palmitoyltransferase 1a (Cpt1a), a rate-limiting step of the carnitine shuttle. However, no information is available on whether hyperoxic exposure reduces FAO, resulting in EndoMT in lung ECs. We hypothesized that hyperoxic exposure causes EndoMT by modulating FAO in lung ECs. To test this hypothesis, mouse fetal lung EC line (MFLM-91U) and primary lung microvascular endothelial cells (LMVECs) were exposed to hyperoxia (95% O2/5% CO2) for 24 h. Some cultures were placed in air for 1, 3, or 7 days post exposure (air recovery). We found that hyperoxic exposure followed by air recovery reduced FAO as determined by the Seahorse XF24 Analyzer. The levels of markers for mesenchymal cells (i.e., vimentin, CD44, Snail1, Snug, Twist1, and α-SMA) were increased, while the EC markers (i.e., vWF, PECAM-1/CD31 and CD34) were reduced in lung ECs exposed to hyperoxia followed by air recovery. Surprisingly, gene deletion of Cpt1a attenuated hyperoxia-induced reduction of CD34 and CD31 gene expression. In conclusion, hyperoxic exposure followed by air recovery causes EndoMT in lung ECs, and inhibition of FAO rescues this phenotype. These findings may provide therapeutic approach targeting Cpt1a to preventing PH in BPD patients.