Preferential amplification of a human mitochondrial DNA deletion in vitro and in vivo

Abstract

We generated induced pluripotent stem cells (iPSCs) from patient fibroblasts to yield cell lines containing varying degrees of heteroplasmy for a m.13514 A > G mtDNA point mutation (2 lines) and for a ~6 kb single, large scale mtDNA deletion (3 lines). Long term culture of the iPSCs containing a single, large-scale mtDNA deletion showed consistent increase in mtDNA deletion levels with time. Higher levels of mtDNA heteroplasmy correlated with increased respiratory deficiency. To determine what changes occurred in deletion level during differentiation, teratomas comprising all three embryonic germ layers were generated from low (20%) and intermediate heteroplasmy (55%) mtDNA deletion clones. Regardless of whether iPSCs harbouring low or intermediate mtDNA heteroplasmy were used, the final levels of heteroplasmy in all teratoma germ layers increased to a similar high level (>60%). Thus, during human stem cell division, cells not only tolerate high mtDNA deletion loads but seem to preferentially replicate deleted mtDNA genomes. This has implications for the involvement of mtDNA deletions in both disease and ageing.

Roles of the mitochondrial replisome in mitochondrial DNA deletion formation

“…This 'clonal expansion' of the deletionbearing mtDNA molecules (DmtDNA) in affected individuals can hardly be explained by the sporadic character of the pathogenesis. In fact, a recent comparative study of the expansion of various aberrant mtDNA molecules in dividing induced pluripotent stem cells demonstrated that DmtDNA are preferentially replicated compared to controls or those bearing point mutations (Russell et al, 2018). This finding is in line with other analyses implying that point mutation-bearing mtDNA molecules do not exhibit advantageous replication and clonal expansion (Pallotti et al, 1996;Wilson et al, 2016), and supports the idea of preferential expansion of DmtDNA (Picard et al, 2016).…”

“…In contrast to point mutations, pathogenic mtDNA deletions typically arise de novo and, with rare exceptions (Chinnery et al, 2004), are not inherited by the offspring (Ng and Turnbull, 2016;Kauppila et al, 2017). Phenotypically, primary deletions manifest as the often-fatal Pearson syndrome in infancy, Kearns-Sayre syndrome (KSS) in childhood and adolescence, or late onset progressive external ophthalmoplegia (PEO) (Rocha et al, 2018;Russell et al, 2018). In the clinical scope, the mtDNA mutation load found in sporadic KSS, PEO and Pearson's syndrome is extremely high (>80% in affected tissues) (Moraes et al, 1995).…”

Administration of Enalapril Started Late in Life Attenuates Hypertrophy and Oxidative Stress Burden, Increases Mitochondrial Mass and Modulates Mitochondrial Quality Control Signaling in the Rat Heart

“…Even though this adaptation could seem beneficial, it might be detrimental if the proportion of damaged molecules is not reduced. Indeed, deleted mtDNA can accumulate by virtue of a replicative advantage over wild type molecules [35]. In our experimental model, the administration of enalapril was associated with lower abundance of mtDNA 4834 deletion ( Figure 3B) and reduced severity of oxidative lesions to functional regions of mtDNA (Cytb and D-Loop) (Figure 4).…”

Stochastic survival of the densest and mitochondrial DNA clonal expansion in ageing

“…It was initially proposed that deletions, being smaller, replicate in a shorter time, leading to a replicative advantage [19,29]. This was observed in some specific cases, namely for fast-proliferating cells [30] and cells recovering their mtDNA populations after heavy depletion [31]. However, through numerical simulations it has been shown that the size-induced advantage cannot explain the observed accumulation in non-replicating muscle fibres, especially in short-lived animals [24].…”