Accumulation of mtDNA variations in human single CD34+ cells from maternally related individuals: effects of aging and family genetic background

Abstract

Marked sequence variation in the mtDNA control region has been observed in human single CD34(+) cells, which persist in vivo and are present also in differentiated hematopoietic cells. In this study, we analyzed 5071 single CD34(+) cells from 49 individuals (including 31 maternally related members from four families and 18 unrelated donors) in order to determine the mutation spectrum within the mtDNA control region in single cells, as related to aging and family genetic background. Many highly mutated sites among family members were hypervariable sites in the mtDNA control region. Further, CD34(+) cells from members of the same family also shared several unique mtDNA variants, suggesting pedigree-specific occurrence of these variants. Overall age-related accumulation of mtDNA mutations in CD34(+) cells varied in different families, suggesting a specific accumulation pattern, which might be modulated by family genetic background. Our current findings have implications for the occurrence of mtDNA mutations in hematopoietic stem cells and progenitors.

Figure 1

Pedigrees of the four families analyzed in this study. Members of four families (A, B, C, and D) were recruited for examination of mtDNA control region sequence in single CD34⁺ cells. Individuals who provided blood samples are marked in grey; ages are listed in Table 1.

Figure 2

Number of mtDNA control region haplotypes in a population of CD34⁺ cells. Haplotype frequencies were defined by the number of haplotypes (characterized by nucleotide substitutions)/100 single CD34⁺ cells from unrelated healthy individuals and family members. (A) All 51 samples were derived from 49 healthy donors in the age range of 0–89, in which two donors were sampled twice at different time points (Yao et al., 2007b). Among them, 32 individuals were newly recruited from four families (6 from family A, 16 from Family B, 8 from Family C, and 2 from Family D). The other 17 individuals consisted of previously reported 14 healthy donors (Ogasawara et al., 2005; Yao et al., 2007b; Yao et al., 2007d) and three cord blood donors (this study). The number of haplotypes in each donor was shown relative to the donors’ age: (B) 6 members of Family A, (C) 16 members of Family B, and (D) 4 members (C-1, C-4, C-7 and C-8) of Family C.

Figure 3

Mutational hot spots of the mtDNA control region in single CD34⁺ cells and in reported complete mtDNAs from worldwide populations. Mutational hot spots were scored, according to their occurrences in the respective individual, but with disregarding their frequencies in a cell population from the individual. As the number of donors in each family varied, we arbitrarily regarded a certain site as a mutational hot spot if mutations hit the site at least in 3 donors in 18 unrelated healthy individuals (A), 2 donors in Family A (N=6) (C), and 4 donors in Family B (N=16) (D). The 18 unrelated healthy individuals included one member (C-2) of Family C in addition to 17 unrelated donors (14 reported healthy individuals (Ogasawara et al., 2005; Yao et al., 2007b; Yao et al., 2007d) and three cord blood donors). The mutational hot spots in worldwide mtDNAs are listed (B) when mutations appear at least 30 times in the global tree of 2196 complete mtDNA sequences (Soares et al., 2009).