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Cristina Kenney, Marilyn Chwa, Shari Atilano; Retina Has Significant Protective Mechanisms to Eliminate Mitochondria DNA Heteroplasmy SNPs Compared to Blood. Invest. Ophthalmol. Vis. Sci. 2019;60(9):416.
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© ARVO (1962-2015); The Authors (2016-present)
The mitochondrial (mt) DNA within different tissues of an individual are assumed to be very similar to each other. However, retinal cells have been shown to accumulate significant mtDNA damage from oxidative stress generated from levels of high metabolism and exposure to UV light. We used a Next Generation Sequencing (NGS) technology to quantitate and compare the oxidative damage signatures in three different tissues from individuals to characterize similarities and differences between the mtDNA of ocular cells versus blood cells.
Globes and blood from 3 AMD subjects were collected from the San Diego Eye Bank. DNA was extracted from blood, neural retina (retina) and choroid (RPE and choroid). The low frequency heteroplasmy SNPs across the entire mitochondrial genome were analyzed using NGS technology that sequences both strands of mtDNA independently. This method is capable of deep sequencing (average sequencing depth of 30,000; range 1,000 to 100,000) and accurately differentiates low frequency mtDNA heteroplasmy SNPs from DNA modification artifacts.
Germline homoplasmy SNPs that defined haplogroups were consistent in the 3 tissues of each subject. AMD#1 was haplogroup I1a1b; AMD#2 was H7b haplogroup and AMD#3 was U2e2a1 haplogroup. However, analysis of the numbers of SNPs with 5% or less heteroplasmy revealed that the blood had higher numbers of heteroplasmy SNPs compared to choroid and retina: [BL-AMD#1 = 33; CHR-AMD#1 = 5; RET-AMD#1 = 6]; [BL-AMD#2 = 130; CHR-AMD#2 = 3; RET-AMD#2 = 5]; [BL-AMD#3 = 76; CHR=AMD#3 = 30; RET-ID#3 = 1]. When subjects were combined, the blood had significantly greater numbers of heteroplasmy SNPs than the retina alone (95% higher, p = 0.05) or retina/choroid combined (89% higher, p = 0.008).
In summary, within an individual, the blood, choroid and retina contained similar homoplasmy SNPs representing the inherited germline mtDNA genome (e.g., haplogroups). However, using NGS methodology, there were significantly more heteroplasmy SNPs in blood compared to retina and choroid, suggesting significant protection in the retina/choroid as compared to blood. The mechanism(s) by which heteroplasmy SNPs are eliminated from retinal cells are yet to be determined.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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