AGING-DEPENDENT FUNCTIONAL ALTERATIONS OF MITOCHONDRIAL-DNA (MTDNA) FROM HUMAN FIBROBLASTS TRANSFERRED INTO MTDNA-LESS CELLS

To investigate the role that aging-dependent accumulation of mitochond rial DNA (mtDNA) mutations plays in the senescence processes, mitochon dria from fibroblasts of 21 normal human individuals between 20 weeks (fetal) and 103 years of age were introduced into human mtDNA-less (rh o degrees) 206 cells by cytoplast x rho degrees cell fusion, and 7-31 transformant clones were isolated from each fusion, A slight cell dono r age-dependent decrease in growth rate was detected in the transforma nts. Using an O-2 consumption rate of 1 fmol/min/cell, which was not o bserved in any transformant among 158 derived from individuals 20 week s (fetal) to 37 years of age, as a cutoff to identify respiratory-defi cient clones, 11 such clones were found among 198 transformants derive d from individuals 39-103 years of age. Furthermore, conventional and nonparametric analysis of the respiratory rates of 356 clones revealed a very significant decrease with donor age, In other analyses, a very significant age-dependent decline in the mtDNA content of the clones was observed, without, however, any significant correlation with the d ecrease in O-2 consumption rate in the defective transformants, These observations clearly indicate the occurrence in the fibroblast-derived trans formants of two independent, age-related functional alterations of mtDNA, presumably resulting from structural damage to this genome.