Mitochondrial DNA damage is associated with reduced mitochondrial bioenergetics in Huntington's disease.
Oxidative stress and mitochondrial dysfunction have been implicated in the pathology of HD; however, the precise mechanisms by which mutant huntingtin modulates levels of oxidative damage in turn resulting in mitochondrial dysfunction are not known. We hypothesize that mutant huntingtin increases oxidative mtDNA damage leading to mitochondrial dysfunction. We measured nuclear and mitochondrial DNA lesions and mitochondrial bioenergetics in the STHdhQ7 and STHdhQ111 in vitro striatal model of HD. Striatal cells expressing mutant huntingtin show higher basal levels of mitochondrial-generated ROS and mtDNA lesions and a lower spare respiratory capacity. Silencing of APE1, the major mammalian apurinic/apyrimidinic (AP) endonuclease that participates in the base excision repair (BER) pathway, caused further reductions of spare respiratory capacity in the mutant huntingtin-expressing cells. Localization experiments show that APE1 increases in the mitochondria of wild-type Q7 cells but not in the mutant huntingtin Q111 cells after treatment with hydrogen peroxide. Moreover, these results are recapitulated in human HD striata and HD skin fibroblasts that show significant mtDNA damage (increased lesion frequency and mtDNA depletion) and significant decreases in spare respiratory capacity, respectively. These data suggest that mtDNA is a major target of mutant huntingtin-associated oxidative stress and may contribute to subsequent mitochondrial dysfunction and that APE1 (and, by extension, BER) is an important target in the maintenance of mitochondrial function in HD.
Buck Institute for Age Research, Novato, CA 94945, USA.
Almas
A
Siddiqui
Sulay
S
Rivera-Sánchez
María del R
Mdel R
Castro
Karina
K
Acevedo-Torres
Anand
A
Rane
Carlos A
CA
Torres-Ramos
David G
DG
Nicholls
Julie K
JK
Andersen
Sylvette
S
Ayala-Torres
D000818:Animals; D001344:Autopsy; D002467:Cell Nucleus / Q000378:metabolism; D004249:DNA Damage; D004272:DNA, Mitochondrial / Q000187:drug effects / Q000378:metabolism*; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase / Q000235:genetics / Q000378:metabolism*; D005347:Fibroblasts / Q000378:metabolism / Q000473:pathology; D015870:Gene Expression; D006801:Humans; D000071058:Huntingtin Protein; D006816:Huntington Disease / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D006861:Hydrogen Peroxide / Q000494:pharmacology; D051379:Mice; D008928:Mitochondria / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D063269:Mitochondrial Turnover; D009154:Mutation; D017072:Neostriatum / Q000378:metabolism* / Q000473:pathology; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D061251:Primary Cell Culture
D004272:DNA, Mitochondrial; C086055:HTT protein, human; D000071058:Huntingtin Protein; D009419:Nerve Tissue Proteins; D006861:Hydrogen Peroxide; C085108:APEX1 protein, human; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase