The Background of Mitochondrial DNA Haplogroup J Increases the Sensitivity of Leber's Hereditary Optic Neuropathy Cells to 2,5-Hexanedione Toxicity

Abstract

Leber's hereditary optic neuropathy (LHON) is a maternally inherited blinding disease due to mitochondrial DNA (mtDNA) point mutations in complex I subunit genes, whose incomplete penetrance has been attributed to both genetic and environmental factors. Indeed, the mtDNA background defined as haplogroup J is known to increase the penetrance of the 11778/ND4 and 14484/ND6 mutations. Recently it was also documented that the professional exposure to n-hexane might act as an exogenous trigger for LHON. Therefore, we here investigate the effect of the n-hexane neurotoxic metabolite 2,5-hexanedione (2,5-HD) on cell viability and mitochondrial function of different cell models (cybrids and fibroblasts) carrying the LHON mutations on different mtDNA haplogroups. The viability of control and LHON cybrids and fibroblasts, whose mtDNAs were completely sequenced, was assessed using the MTT assay. Mitochondrial ATP synthesis rate driven by complex I substrates was determined with the luciferine/luciferase method. Incubation with 2,5-HD caused the maximal loss of viability in control and LHON cells. The toxic effect of this compound was similar in control cells irrespective of the mtDNA background. On the contrary, sensitivity to 2,5-HD induced cell death was greatly increased in LHON cells carrying the 11778/ND4 or the 14484/ND6 mutation on haplogroup J, whereas the 11778/ND4 mutation in association with haplogroups U and H significantly improved cell survival. The 11778/ND4 mutation on haplogroup U was also more resistant to inhibition of complex I dependent ATP synthesis by 2,5-HD. In conclusion, this study shows that mtDNA haplogroups modulate the response of LHON cells to 2,5-HD. In particular, haplogroup J makes cells more sensitive to its toxic effect. This is the first evidence that an mtDNA background plays a role by interacting with an environmental factor and that 2,5-HD may be a risk element for visual loss in LHON. This proof of principle has broad implications for other neurodegenerative disorders such as Parkinson's disease.

A Mutation Threshold Distinguishes the Antitumorigenic Effects of the Mitochondrial Gene MTND1, an Oncojanus Function

“…The rate of mitochondrial ATP synthesis driven by CI and complex II (CII) was determined in aliquots of digitonin-permeabilized cells and normalized on citrate synthase activity as previously described (28). Briefly, aliquots of cells (0.1-0.2 mg protein) were incubated with 5 mmol/L malate plus 5 mmol/L pyruvate (CI substrates) or with 10 mmol/L SA (CII substrate) plus 2 mg/mL rotenone.…”

Leber’s Hereditary Optic Neuropathy Precipitated by Tadalafil Use for Erectile Dysfunction

“…For instance, Ghelli et al reported exposure to n-hexane as being a possible exogenous trigger for LHON due to the effect of 2,5-hexandione on cells carrying LHON mutations. 11 Other environmental factors increase susceptibility to optic neuropathy in patients carrying LHON genes.…”

Le complexebc1de la chaîne respiratoire mitochondriale fonctionne selon l’hypothèse du cycle Q de Mitchell

“…Ces mutants dans la levure (et leurs suppresseurs) pourraient s'avérer être des outils précieux pour éclairer le mécanisme fin de bifurcation des électrons et de mouvement des protons. Les haplogroupes de l'ADNmt, la plupart du temps considé-rés comme neutres, peuvent cependant avoir une influence [20,21], montrant par là que le polymorphisme des haplogroupes n'est pas complètement neutre mais peut avoir un retentissement (faible) sur le fonctionnement des complexes respiratoires en association ou non avec des mutations pathologiques. L'étude des changements d'acides aminés intervenant dans les cytochromes b de divers haplogroupes peut s'avérer utile pour comprendre des mécanismes de fonctionnement de ce complexe.…”