Transcomplementation between different types of respiration-deficient mitochondria with different pathogenic mutant mitochondrial DNAs.

Two cell lines were used for determination of whether interaction occurred between different types of respiration-deficient mitochondria. One was a respiration-deficient rho- cell line having mutant mitochondrial DNA (mtDNA) with a 5,196-base pair deletion including five tRNA genes (tRNAGly, Arg, Ser(AGY), Leu(CUN), His), DeltamtDNA5196, causing Kearns-Sayre syndrome. The other was a respiration-deficient syn- cell line having mutant mtDNA with an A to G substitution at 4,269 in the tRNAIle gene, mtDNA4269, causing fatal cardiomyopathy. The occurrence of mitochondrial interaction was examined by determining whether cybrids constructed by fusion of enucleated rho- cells with syn- cells became respiration competent by exchanging their tRNAs. No cybrids were isolated in selection medium, where only respiration-competent cells could survive, suggesting that no interaction occurred, or that it occurred so slowly that sufficient recovery of mitochondrial respiratory function was not attained by the time of selection. The latter possibility was confirmed by the observations that heteroplasmic cybrids with both mutant mtDNA4269 and DeltamtDNA5196 isolated without selection showed restored mitochondrial respiration activity. This demonstration of transcomplementation between different respiration-deficient mitochondria will help in understanding the relationship between somatic mutant mtDNAs and the roles of such mutations in aging processes.