Mitochondrial DNA variants can mediate methylation status of inflammation, angiogenesis and signaling genes.

Mitochondrial (mt) DNA can be classified into haplogroups representing different geographic and/or racial origins of populations. The H haplogroup is protective against age-related macular degeneration (AMD), while the J haplogroup is high risk for AMD. In the present study, we performed comparison analyses of human retinal cell cybrids, which possess identical nuclei, but mtDNA from subjects with either the H or J haplogroups, and demonstrate differences in total global methylation, and expression patterns for two genes related to acetylation and five genes related to methylation. Analyses revealed that untreated-H and -J cybrids have different expression levels for nuclear genes (CFH, EFEMP1, VEGFA and NFkB2). However, expression levels for these genes become equivalent after treatment with a methylation inhibitor, 5-aza-2'-deoxycytidine. Moreover, sequencing of the entire mtDNA suggests that differences in epigenetic status found in cybrids are likely due to single nucleotide polymorphisms (SNPs) within the haplogroup profiles rather than rare variants or private SNPs. In conclusion, our findings indicate that mtDNA variants can mediate methylation profiles and transcription for inflammation, angiogenesis and various signaling pathways, which are important in several common diseases.

Mitochondrial DNA variants mediate energy production and expression levels for CFH, C3 and EFEMP1 genes: implications for age-related macular degeneration.

BACKGROUND: Mitochondrial dysfunction is associated with the development and progression of age-related macular degeneration (AMD). Recent studies using populations from the United States and Australia have demonstrated that AMD is associated with mitochondrial (mt) DNA haplogroups (as defined by combinations of mtDNA polymorphisms) that represent Northern European Caucasians. The aim of this study was to use the cytoplasmic hybrid (cybrid) model to investigate the molecular and biological functional consequences that occur when comparing the mtDNA H haplogroup (protective for AMD) versus J haplogroup (high risk for AMD). METHODOLOGY/PRINCIPAL FINDINGS: Cybrids were created by introducing mitochondria from individuals with either H or J haplogroups into a human retinal epithelial cell line (ARPE-19) that was devoid of mitochondrial DNA (Rho0). In cybrid lines, all of the cells carry the same nuclear genes but vary in mtDNA content. The J cybrids had significantly lower levels of ATP and reactive oxygen/nitrogen species production, but increased lactate levels and rates of growth. Q-PCR analyses showed J cybrids had decreased expressions for CFH, C3, and EFEMP1 genes, high risk genes for AMD, and higher expression for MYO7A, a gene associated with retinal degeneration in Usher type IB syndrome. The H and J cybrids also have comparatively altered expression of nuclear genes involved in pathways for cell signaling, inflammation, and metabolism. CONCLUSION/SIGNIFICANCE: Our findings demonstrate that mtDNA haplogroup variants mediate not only energy production and cell growth, but also cell signaling for major molecular pathways. These data support the hypothesis that mtDNA variants play important roles in numerous cellular functions and disease processes, including AMD.