| dc.description.abstract | Mitochondrial disease (MD) is one of the most challenging groups of inborn disorders featuring a
tissue-specific vulnerability, governed by largely unknown mechanisms. The value of
metabolomics in multi-systemic MD research has been increasingly recognised; however,
minimally invasive biofluids are the sample type that is generally favoured and it remains unknown
whether such systemic metabolomes clearly reflect tissue-specific metabolic alterations. Here,
we mine and cross-compare metabolomes from Ndufs4 knockout (KO) mice with global complex I
(CI) deficiency-related Leigh syndrome (LS) — a complex neurometabolic MD defined by
progressive focal lesions in specific brain regions. With this approach, the study aimed to identify
and evaluate the extent of common and unique metabolic alterations associated with LS, on a
brain regional and systemic level. Semi-targeted liquid chromatography-tandem mass
spectrometry and untargeted gas chromatography time-of-flight mass spectrometry were
performed on seven sample types from Ndufs4 KO (n≥19) vs wild type (WT, n≥20) mice; which
include one lesion-resistant and three lesion-prone brain regions; two skeletal muscles of different
fibre type composition; and urine. To gain mechanistic insight into regional neurodegeneration,
metabolic alterations in the four brain regions were investigated alongside regional respiratory
chain enzyme activity. Enzyme assays confirmed significantly decreased (60–80%) CI activity in
all investigated Ndufs4 KO brain regions, with the lesion-resistant region displaying the highest
residual CI activity (38% of WT). A higher residual CI activity and a less perturbed NADH/NAD+
ratio, correlate with less severe metabolic perturbations in Ndufs4 KO brain regions. Moreover,
less perturbed BCAA oxidation and increased glutamate oxidation seem to distinguish lesionresistant
from -prone KO brain regions, thereby identifying key areas of metabolism to target in
future therapeutic intervention studies. The subsequent cross-comparison of all seven
sample-type metabolomes further revealed widespread alterations in alanine, aspartate,
glutamate, and arginine metabolism in Ndufs4 KO mice. An adaptive rewiring of glutamate and
nitrogen metabolism, along with increased oxidation of alternative respiratory chain ubiquinone
cycle fuels, α-hydroxyglutarate, succinate, and glycerol-3-phosphate seem to be a system-wide
response to CI deficiency. Brain region-specific metabolic signatures include the accumulation of
BCAAs, proline, and glycolytic intermediates, whereas skeletal muscles display evidence of
hyper-catabolism. Furthermore, we describe a systemic dysregulation in one-carbon metabolism
and the tricarboxylic acid cycle, which was not clearly reflected in the Ndufs4 KO brain. Altogether,
our results provide novel insight into brain region-specific and systemic metabolic responses to
LS, while confirming the value of urinary metabolomics when evaluating MD-associated
metabolites but cautioning against mechanistic studies relying solely on systemic biofluids. | en_US |
