Lack of major mitochondrial bioenergetic changes in cultured skin fibroblasts from aged individuals.

Human skin fibroblasts from young and old donors were cultured in vitro and compared in their mitochondrial morphology and function. A decreased numerical density of mitochondria in the fibroblasts from old individuals was balanced by the increased size of individual mitochondria. The mitochondrial membrane potential, estimated in the intact cells by the difference between the total accumulation ratio of the lipophilic cation tetraphenylphosphonium and the accumulation ratio in presence of uncoupler, was unchanged, as were some mitochondrial enzymatic activities tested in the homogenates. The results point out that the decreased proliferating capacity observed in the fibroblasts from the old subjects was accompanied by a likely decrease of mitochondrial duplication; the decreased energy utilization for cell division balances a possible energetic decline in such way that the steady-state energy status is unchanged.