# Energy Metabolism Under Stress: Late‐Stage Leigh Syndrome Reveals Profound Cardiometabolic Perturbations in Ndufs4 KO Mice

## TL;DR

This study shows that a genetic mutation in mice leads to severe heart energy issues by disrupting key metabolic pathways.

## Contribution

The study reveals novel cardiometabolic disruptions caused by whole-body complex I deficiency in a Leigh syndrome mouse model.

## Key findings

- Ndufs4 KO hearts show a 98.9% reduction in complex I activity and a 63.9% decline in complex I-driven respiration.
- Significant reductions in energy substrates like fatty acids, glucose, and TCA cycle intermediates are observed in Ndufs4 KO mice.
- Disruptions in dimethylglycine, glutamic acid, and lysine metabolism are linked to cardiac bioenergetic failure.

## Abstract

The deficiency of mitochondrial complex I (CI), a key regulator of cellular energy homeostasis and metabolic flexibility, is a prevalent driver of cardiovascular pathology in mitochondrial disorders. The Ndufs4 knockout (KO) mouse model of Leigh syndrome (LS), which lacks a critical CI subunit, exhibits severe cardiac abnormalities secondary to encephalomyopathy. However, the metabolic basis of LS‐associated cardiac dysfunction remains poorly understood. This study aims to evaluate how whole‐body CI deficiency affects cardiac bioenergetics and metabolism in late‐stage Ndufs4 KO mice. We assessed respiratory chain enzyme activities and oxygen consumption rates using kinetic spectrophotometric assays and high‐resolution respirometry, respectively, in mitochondria isolated from Ndufs4 KO and wild‐type mouse hearts. Cardiometabolic profiling was performed on a well‐powered cohort, employing untargeted GC‐TOFMS, 1H‐NMR and semi‐targeted LC‐MS/MS. Ndufs4 KO hearts showed a 98.9% reduction in CI activity and a 63.9% decline in CI‐driven respiration, halving CI's contribution to combined CI + II respiration and prompting a shift toward CII‐driven respiration. Cardiometabolic profiles revealed significant reductions in energy‐generating substrates, including long‐chain fatty acids, glucose, lactic acid and 3‐hydroxybutyric acid, along with lower levels of anaplerotic amino acids and TCA cycle intermediates, particularly succinic acid. Additionally, profound disruptions were observed in dimethylglycine, glutamic acid and lysine metabolism. We conclude that whole‐body CI deficiency results in severe cardiac bioenergetic and metabolic dysregulation, characterised by reduced CI‐dependent respiration and extensive substrate reduction across multiple metabolic pathways. These findings underscore the metabolic vulnerability of the CI‐deficient heart and suggest potential therapeutic targets for managing cardiomyopathy in mitochondrial disease.

Cardiac bioenergetic and metabolic perturbations in late‐stage Leigh syndrome. Whole‐body NDUFS4 loss severely impairs cardiac complex I activity and respiration, shifting reliance to complex II and reducing glycolytic, TCA, and amino acid‐derived energy‐generating substrates in the heart. These findings reveal profound cardiometabolic vulnerability underlying cardiac manifestations of Leigh syndrome.