Apoptosis in the aging process.

Although many hypotheses have been proposed to explain the aging process, the exact mechanisms are not well defined. Recent accumulating evidence indicates that dysregulation of the apoptotic process may be involved in some aging processes; however, it is still debatable how exactly apoptosis is expressed during aging in vivo. In this review, we discuss recent findings related to apoptosis of individual organs during aging and their significance. We demonstrate that aging enhances apoptosis and susceptibility to apoptosis in several types of intact cells. In contrast, in certain genetically damaged, initiated, and preneoplastic cells, aging suppresses these age-associated apoptotic changes. In various cells, apoptosis enhances the elimination of damaged and dysfunctional cells presumably caused by oxidative stress, glycation, and DNA damage. In these cases, the incidence of apoptosis correlates with the level of accumulated injury. It is concluded that apoptosis plays an important role in the aging process and tumorigenesis in vivo probably as an inherent protective mechanism against age-associated tumorigenesis.