Fatty Acid Oxidation Protects against Hyperoxia-induced Endothelial Cell Apoptosis and Lung Injury in Neonatal Mice

Abstract

In neonates, hyperoxia or positive pressure ventilation causes continued lung injury characterized by simplified vascularization and alveolarization, which are the hallmarks of bronchopulmonary dysplasia. Although endothelial cells (ECs) have metabolic flexibility to maintain cell function under stress, it is unknown whether hyperoxia causes metabolic dysregulation in ECs, leading to lung injury. We hypothesized that hyperoxia alters EC metabolism, which causes EC dysfunction and lung injury. To test this hypothesis, we exposed lung ECs to hyperoxia (95% O 2 /5% CO 2) followed by air recovery (O 2 /rec). We found that O 2 /rec reduced mitochondrial oxidative phosphorylation without affecting mitochondrial DNA copy number or mitochondrial mass and that it specifically decreased fatty acid oxidation (FAO) in ECs. This was associated with increased ceramide synthesis and apoptosis. Genetic deletion of carnitine palmitoyltransferase 1a (Cpt1a), a rate-limiting enzyme for carnitine shuttle, further augmented O 2 /rec-induced apoptosis. O 2 /rec-induced ceramide synthesis and apoptosis were attenuated when the FAO was enhanced by L-carnitine. Newborn mice were exposed to hyperoxia (.95% O 2) between Postnatal Days 1 and 4 and were administered L-carnitine (150 and 300 mg/kg, i.p.) or etomoxir, a specific Cpt1 inhibitor (30 mg/kg, i.p.), daily between Postnatal Days 10 and 14. Etomoxir aggravated O 2 /rec-induced apoptosis and simplified alveolarization and vascularization in mouse lungs. Similarly, arrested alveolarization and reduced vessel numbers were further augmented in EC-specific Cpt1a-knockout mice compared with wild-type littermates in response to O 2 /rec. Treatment with L-carnitine (300 mg/kg) attenuated O 2 /rec-induced lung injury, including simplified alveolarization and decreased vessel numbers. Altogether, enhancing FAO protects against hyperoxia-induced EC apoptosis and lung injury in neonates.

Hyperoxic Exposure Caused Lung Lipid Compositional Changes in Neonatal Mice

“…In agreement with our findings, neonatal hyperoxia for four weeks augments sphingomyelin species (SM16:0, SM18:0, SM24:0, and SM24:1), long chain ceramides (Cer16:0 and Cer18:0), and very long chain ceramides (Cer24:0 and Cer24:1) in bronchoalveolar lavage fluid from mice [ 28 ], and ceramide is increased in tracheal aspirates of preterm infants [ 9 ]. This may result in increased apoptosis with neonatal exposure to hyperoxia [ 2 , 29 ], despite there being no lung inflammatory responses observed in our 3-day hyperoxia-exposed mice (data not shown). Increased ceramide may be due to either increased hydrolysis of sphingomyelin or de novo synthesis in response to hyperoxic exposure [ 2 ].…”

“…This may result in increased apoptosis with neonatal exposure to hyperoxia [ 2 , 29 ], despite there being no lung inflammatory responses observed in our 3-day hyperoxia-exposed mice (data not shown). Increased ceramide may be due to either increased hydrolysis of sphingomyelin or de novo synthesis in response to hyperoxic exposure [ 2 ].…”

“…Mouse lungs at birth are structurally similar to human neonates born at 30 to 34 weeks of gestation, when the lung is in the saccular phase of development. Thus, hyperoxic exposure in newborn rodents can be used to mimic lung injury in premature infants with BPD, and this model is frequently utilized to investigate pathogenesis and to identify potential therapeutic targets for hyperoxic lung injury in BPD [ 2 , 3 , 4 ].…”

l‐Carnitine protects against 1,4‐benzoquinone‐induced apoptosis and DNA damage by suppressing oxidative stress and promoting fatty acid oxidation in K562 cells

“…Yao et al found that LC supplementation in endothelial cells accelerated FAO and attenuated apoptosis caused by hyperoxia. By using a CPT1 inhibitor (etomoxir, 100 μmol/L), they obtained the opposite result 39 . In addition, Gu et al suggested that full‐length CPT‐1a binds to endogenous bcl‐2, and this binding was critical in regulating apoptosis resistance of lung macrophages 26 .…”

Doxycycline preserves chondrocyte viability and function in human and calf articular cartilage ex vivo

“…After optimization, we seeded cells in Seahorse XF24 microplates (Seahorse Bioscience, Billerica, MA) overnight prior to the measurement of OCR. After optimization, we seeded human chondrocytes (60,000 cells/ well) in a Seahorse XF24 microplate (Seahorse Bioscience, Billerica, MA) overnight prior to the measurement of OCR as described earlier (Yao et al, 2019). The culture media were changed into the assay medium, which was the XF base medium supplemented with 1 mmol/L pyruvate, 2 mmol/L of glutamine, and 10 mmol/L glucose.…”