Selective NADH communication from α-ketoglutarate dehydrogenase to mitochondrial transhydrogenase prevents reactive oxygen species formation under reducing conditions in the heart

• Published in: Basic research in cardiology 2020-09, Vol.115 (5), p.53, Article 53
• Main Authors: Wagner, Michael, Bertero, Edoardo, Nickel, Alexander, Kohlhaas, Michael, Gibson, Gary E., Heggermont, Ward, Heymans, Stephane, Maack, Christoph
• Format: Article
• Language: English
• Subjects: Adenosine triphosphate; Animals; Cardiology; Cardiomyocytes; Cell Respiration; Chains; Congestive heart failure; Dehydrogenase; Dehydrogenases; Depletion; Electron transport chain; Emission analysis; Emissions control; Heart failure; Hydrogen peroxide; Isocitrate dehydrogenase; Ketoglutarate Dehydrogenase Complex - metabolism; Ketoglutaric acid; Krebs cycle; Malate; Medicine; Medicine & Public Health; Mice, Inbred C57BL; Mitochondria; Mitochondria, Heart - metabolism; Muscles; Myocytes; Myocytes, Cardiac - metabolism; NAD - metabolism; NADH; NADP Transhydrogenases - metabolism; NADPH; Nicotinamide; Nicotinamide adenine dinucleotide; Nucleotides; Original Contribution; Oxidative stress; Oxoglutarate dehydrogenase (lipoamide); Pyruvic acid; Reactive oxygen species; Reactive Oxygen Species - metabolism; Rotenone; Single-Cell Analysis; Skeletal muscle; Substrate inhibition; Substrates; Superoxide; Tricarboxylic acid cycle
• ISSN: 0300-8428; 1435-1803; 1435-1803
• DOI: 10.1007/s00395-020-0815-1

In heart failure, a functional block of complex I of the respiratory chain provokes superoxide generation, which is transformed to H 2 O 2 by dismutation. The Krebs cycle produces NADH, which delivers electrons to complex I, and NADPH for H 2 O 2 elimination via isocitrate dehydrogenase and nicotinamide nucleotide transhydrogenase (NNT). At high NADH levels, α-ketoglutarate dehydrogenase (α-KGDH) is a major source of superoxide in skeletal muscle mitochondria with low NNT activity. Here, we analyzed how α-KGDH and NNT control H 2 O 2 emission in cardiac mitochondria. In cardiac mitochondria from NNT-competent BL/6N mice, H 2 O 2 emission is equally low with pyruvate/malate (P/M) or α-ketoglutarate (α-KG) as substrates. Complex I inhibition with rotenone increases H 2 O 2 emission from P/M, but not α-KG respiring mitochondria, which is potentiated by depleting H 2 O 2 -eliminating capacity. Conversely, in NNT-deficient BL/6J mitochondria, H 2 O 2 emission is higher with α-KG than with P/M as substrate, and further potentiated by complex I blockade. Prior depletion of H 2 O 2 -eliminating capacity increases H 2 O 2 emission from P/M, but not α-KG respiring mitochondria. In cardiac myocytes, downregulation of α-KGDH activity impaired dynamic mitochondrial redox adaptation during workload transitions, without increasing H 2 O 2 emission. In conclusion, NADH from α-KGDH selectively shuttles to NNT for NADPH formation rather than to complex I of the respiratory chain for ATP production. Therefore, α-KGDH plays a key role for H 2 O 2 elimination, but is not a relevant source of superoxide in heart. In heart failure, α-KGDH/NNT-dependent NADPH formation ameliorates oxidative stress imposed by complex I blockade. Downregulation of α-KGDH may, therefore, predispose to oxidative stress in heart failure.