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Mitochondrial transfer disrupts mTORC1/Akt signaling modulating biogenesis and respiration

ABSTRACT: Mitochondrial DNA (mtDNA) mutations are a major cause of maternally-inherited disease and have no treatment. Prevention strategies are critically important, but current clinical approaches are far from satisfactory. Legislation has changed in the UK to permit the development of mitochondrial transfer in human embryos, but major concerns have been raised about the mis-match of nuclear and mtDNA from ‘three parents’, with late sequelae being passed through the germ-line to subsequent generations. Matching donor and recipient mtDNA haplogroups is the proposed solution, but the effects of ‘haplogroup matching’ have not been tested experimentally. Here we show major changes in the cellular transcriptome both between and within the major mtDNA haplogroups when mitochondria are transferred between cells on a fixed nuclear genetic background. Larger differences were seen between phylogenetically related sub-haplogroups J1 and J2 which differ by only six nucleotides, than between the major haplogroups and known pathogenic mtDNA mutations. mtDNA transfer altered key cell signaling pathways, most notably the mTOR/Akt and the inflammatory cascade. This affected mitochondrial biogenesis, oxygen consumption, and ATP synthesis, and was blocked by rapamycin. These findings identify a key mediator in retrograde nuclear-mitochondrial signaling which is sensitive to subtle changes in mtDNA sequence. Given the established role of mTOR in cancer, neurodegeneration, and metabolic disease, this provides a mechanism for the association between inherited mtDNA variants and common late onset diseases, and demonstrates unexpected and dramatic effects of mitochondrial transfer not corrected by close haplogroup matching. Overall design: 2 cell lines per haplogroup were included plus the recipient cell (Rho0, 143B, osteosarcoma)

INSTRUMENT(S): Illumina HiSeq 2000 (Homo sapiens)

ORGANISM(S): Homo Sapiens

SUBMITTER: Aurora Gomez-Duran

PROVIDER: GSE74009 | GEO | 2020-02-11

SECONDARY ACCESSION(S): PRJNA298735

REPOSITORIES: GEO

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			Action	DRS
	GSE74009_gencodeV19_gene_count_Rho0_and_haplo.txt.gz	Txt

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Project description:BACKGROUND: The mitochondrial DNA (mtDNA) of the cloned sheep "Dolly" and nine other ovine clones produced by somatic cell nuclear transfer (SCNT) was reported to consist only of recipient oocyte mtDNA without any detectable mtDNA contribution from the nucleus donor cell. In cattle, mouse and pig several or most of the clones showed transmission of nuclear donor mtDNA resulting in mitochondrial heteroplasmy. To clarify the discrepant transmission pattern of donor mtDNA in sheep clones we analysed the mtDNA composition of seven fetuses and five lambs cloned from fetal fibroblasts. RESULTS: The three fetal fibroblast donor cells used for SCNT harboured low mtDNA copy numbers per cell (A: 753 +/- 54, B: 292 +/- 33 and C: 561 +/- 88). The ratio of donor to recipient oocyte mtDNAs was determined using a quantitative amplification refractory mutation system (ARMS) PCR (i.e. ARMS-qPCR). For quantification of SNP variants with frequencies below 0.1% we developed a restriction endonuclease-mediated selective quantitative PCR (REMS-qPCR). We report the first cases (n = 4 fetuses, n = 3 lambs) of recipient oocyte/nuclear donor mtDNA heteroplasmy in SCNT-derived ovine clones demonstrating that there is no species-effect hindering ovine nucleus-donor mtDNA from being transmitted to the somatic clonal offspring. Most of the heteroplasmic clones exhibited low-level heteroplasmy (0.1% to 0.9%, n = 6) indicating neutral transmission of parental mtDNAs. High-level heteroplasmy (6.8% to 46.5%) was observed in one case. This clone possessed a divergent recipient oocyte-derived mtDNA genotype with three rare amino acid changes compared to the donor including one substitution at an evolutionary conserved site. CONCLUSION: Our study using state-of-the-art techniques for mtDNA quantification, like ARMS-qPCR and the novel REMS-qPCR, documents for the first time the transmission of donor mtDNA into somatic sheep clones. MtDNA heteroplasmy was detected in seven of 12 clones tested, whereby all but one case revealed less than 1% mtDNA contribution from the nuclear donor cell suggesting neutral segregation.

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Mitochondrial transfer disrupts mTORC1/Akt signaling modulating biogenesis and respiration

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