Muscle-specific mutations accumulate with aging in critical human mtDNA control sites for replication

Abstract

The recently discovered aging-dependent large accumulation of point mutations in the human fibroblast mtDNA control region raised the question of their occurrence in postmitotic tissues. In the present work, analysis of biopsied or autopsied human skeletal muscle revealed the absence or only minimal presence of those mutations. By contrast, surprisingly, most of 26 individuals 53 to 92 years old, without a known history of neuromuscular disease, exhibited at mtDNA replication control sites in muscle an accumulation of two new point mutations, i.e., A189G and T408A, which were absent or marginally present in 19 individuals younger than 34 years. These two mutations were not found in fibroblasts from 22 subjects 64 to 101 years of age (T408A), or were present only in three subjects in very low amounts (A189G). Furthermore, in several older individuals exhibiting an accumulation in muscle of one or both of these mutations, they were nearly absent in other tissues, whereas the most frequent fibroblast-specific mutation (T414G) was present in skin, but not in muscle. Among eight additional individuals exhibiting partial denervation of their biopsied muscle, four subjects >80 years old had accumulated the two muscle-specific point mutations, which were, conversely, present at only very low levels in four subjects <40 years old. The striking tissue specificity of the muscle mtDNA mutations detected here and their mapping at critical sites for mtDNA replication strongly point to the involvement of a specific mutagenic machinery and to the functional relevance of these mutations. R ecently, the discovery of an aging-dependent large accumulation of point mutations in the control region for mtDNA replication of human skin fibroblasts has been reported (1). Particularly striking was the demonstration, in a generally high proportion of molecules (up to 50%), of a T to G transversion at position 414 in the original Cambridge sequence (2), within the promoter for the synthesis of the RNA primer of mtDNA heavy (H)-strand synthesis (3) and for light (L)-strand transcription (4). This mutation was present in more than 50% of the individuals above 65 years of age and absent in younger individuals. In the present work, to investigate the occurrence of these aging-dependent mutations in other cell types, in particular, in postmitotic cells, a screening was carried out for the detection in human muscle of aging-related specific point mutations in the DLP4 and DLP6 segments of the main mtDNA control region, which were the segments previously found to carry the fibroblast mtDNA mutations (1). These two mtDNA segments correspond to one of the hypervariable portions of the main control region (5), and were chosen, for the purpose of analysis, as containing each a uniform melting domain (Y.M., unpublished data). They carry critical sequences for mtDNA replication (Fig. 1A). In particular, DLP4 contains the primary origin of H-strand mtDNA synthesis (O H1 ) (3), whereas DLP6 contains the promoter and start site for H-strand replication RNA...

Detection of the A189G mtDNA heteroplasmic mutation in relation to age in modern and ancient bones

“…Similar cases had already been found in other tissues [3,4] and for other somatic mutations [23]. In the present case, the A189G tissue variability (that is, the difference in both appearance age and heteroplasmy rate variability), could be explained by a difference in the metabolism of muscle and bone [24].…”

“…This oxidative stress increase could thus be at the origin of all cellular molecule damage and in particular, could induce the accumulation of lesions on mitochondrial DNA (mtDNA). These lesions were found in numerous tissues with high metabolism, especially in post-mitotic tissues [3,4,5]. They took several forms -mostly insertions, deletions and heteroplasmic point mutations.…”

“…This transition presents high, easily detectable heteroplasmic mutation rates in muscle tissue. Its level been detected at an increasing rate in muscle tissue from older individuals [4,5,7,8,9].…”

Effects of intrinsic aerobic capacity, aging and voluntary running on skeletal muscle sirtuins and heat shock proteins

“…Both in humans and rodents, DNA mutations are also highly prominent in the muscle of aged individuals (Wang et al 2001;Szczesny, Tann & Mitra 2010). Furthermore, the accumulation of dysfunctional mitochondrial proteins during aging is higher, and the levels of the antioxidant enzymes are lower in mouse skeletal muscle compared to other tissues (Szczesny, Tann & Mitra 2010).…”

Mitochondrial DNA mutations as a fundamental mechanism in physiological declines associated with aging

“…The point mutations, A189G and T408A, were identified in skeletal muscle. The fibroblastspecific T414G was absent in muscle and heart in several studies (Calloway et al ., 2000;Wang et al ., 2001;Nekhaeva et al ., 2002) yet another study found T414G in muscle but not in brain (Murdock et al ., 2000). A more recent study has linked reduced COX activity to an increasing burden of multiple mtDNA point mutations, rather than a single specific point mutation, present in the genes coding for COX (Lin et al ., 2002).…”