Mitochondrial vulnerability and increased susceptibility to nutrient-induced cytotoxicity in fibroblasts from leigh syndrome French canadian patients.

Yan Burelle,Charles Morin,Julie Thompson Legault,Gabrielle Boucher,Lise Coderre,Christine Des Rosiers,Chantal Bemeur,Marie-Eve Rivard,Maria Moran

doi:10.1371/journal.pone.0120767

Yan Burelle, Charles Morin + Show 7 more

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https://doi.org/10.1371/journal.pone.0120767

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Abstract

Mutations in LRPPRC are responsible for the French Canadian variant of Leigh Syndrome (LSFC), a severe disorder characterized biochemically by a tissue-specific deficiency of cytochrome c oxidase (COX) and clinically by the occurrence of severe and deadly acidotic crises. Factors that precipitate these crises remain unclear. To better understand the physiopathology and identify potential treatments, we performed a comprehensive analysis of mitochondrial function in LSFC and control fibroblasts. Furthermore, we have used this cell-based model to screen for conditions that promote premature cell death in LSFC cells and test the protective effect of ten interventions targeting well-defined aspects of mitochondrial function. We show that, despite maintaining normal ATP levels, LSFC fibroblasts present several mitochondrial functional abnormalities under normal baseline conditions, which likely impair their capacity to respond to stress. This includes mitochondrial network fragmentation, impaired oxidative phosphorylation capacity, lower membrane potential, increased sensitivity to Ca2+-induced permeability transition, but no changes in reactive oxygen species production. We also show that LSFC fibroblasts display enhanced susceptibility to cell death when exposed to palmitate, an effect that is potentiated by high lactate, while high glucose or acidosis alone or in combination were neutral. Furthermore, we demonstrate that compounds that are known to promote flux through the electron transport chain independent of phosphorylation (methylene blue, dinitrophenol), or modulate fatty acid (L-carnitine) or Krebs cycle metabolism (propionate) are protective, while antioxidants (idebenone, N-acetyl cysteine, resveratrol) exacerbate palmitate plus lactate-induced cell death. Collectively, beyond highlighting multiple alterations in mitochondrial function and increased susceptibility to nutrient-induced cytotoxicity in LSFC fibroblasts, these results raise questions about the nature of the diets, particularly excess fat intake, as well as on the use of antioxidants in patients with LSFC and, possibly, other COX defects.

Highlights

The French Canadian variant of Leigh Syndrome (LSFC) is an autosomal recessive mitochondrial respiratory chain disorder with a carrier frequency of about 1/23 in the Saguenay-Lac-StJean region of Quebec [1,2,3]
Despite reduced c oxidase (COX) activity, ATP content was comparable in control and LSFC fibroblasts, indicating that overall cellular energy status was not impaired under basal conditions (Fig. 1I)
At the level of respiratory performance, our results indicate that in LSFC fibroblasts, reduced expression of LRPPRC and the resulting 55% loss in COX activity was sufficient to reduce maximal ADP-stimulated respiration by 35% when the electron transport chain (ETC) was energized with substrates for complex I, and by 43% when mitochondria respired with substrates for complex II

Summary

Introduction

The French Canadian variant of Leigh Syndrome (LSFC) is an autosomal recessive mitochondrial respiratory chain disorder with a carrier frequency of about 1/23 in the Saguenay-Lac-StJean region of Quebec [1,2,3]. It is caused by mutation of the LRPPRC gene encoding a leucinerich pentatricopeptide repeat protein that regulates the stability of most mitochondrial mRNA’s, all of which encode proteins involved in oxidative phosphorylation (OXPHOS) [4,5]. LSFC is distinguished from classic Leigh syndrome by the occurrence of fulminant acidotic crises, which represent the major cause of morbidity in these patients [2,3]

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