| 研究実績の概要 |
The aim of our study was to evaluate the mitochondrial DNA (mtDNA) deletion profile in radiation-induced and sporadic PTCs and in exposed to ionizing radiation (IR) human primary thyrocytes using NGS as a potential individual molecular marker of radiation exposure.
Using primary cultures of human thyrocytes exposed to IR (from 0.5 to 5 Gy), we found a significant dose-dependent increase of mtDNA deletions, while mtDNA content and common deletion (CD) content did not change. Hence, IR can generate large-scale mtDNA deletions in thyrocytes after exposure.
To determine whether deletion-harboring fusion mtDNA species are expressed, and to compare the spectrum of mtDNA deletions with that in primary thyrocytes, we performed RNA-seq. For RNA-seq we used tumor and normal counterparts of radiation-induced and sporadic papillary thyroid carcinomas from exposed or non-exposed childhood patients, respectively.
In Tumor PTC samples we found more than 400 expressed mtDNA fusions sized from 1.9 to 15.1 kb, but only less than 20 of these fusions had high probability of expression as judged by the number of reads. The most frequent breakpoints in highly expressed mtDNA fusions were localized in CYTB, ND6, ND5, ND4, COX3, ATP6 and COX2 mtDNA genes. In Normal thyroid tissue counterparts we did not find such deletions.
The results of our study demonstrate that radiation-induced mtDNA deletions may persist for a long time after exposure, but only those whose size exceeds 1.9 kb are expressed.
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