Loss of hybridizable ribosomal DNA from human post-mitotic tissues during aging: I. Age-dependent loss in human myocardium.

DNA obtained from 29 male humans at autopsy was hybridized in liquid phase with tritium-labelled 18 and 28S ribosomal RNA (rRNA) in order to determine whether a change in the dosage in rDNA, which codes for rRNA, occurs during human aging. The individuals ranged in age from 3 months to 76 years. It was found that the amount of rDNA hybridizable per 260 nm absorption unit by DNA decreases by about 0.5% per year with a regression coefficient of about -0.83. These findings confirm earlier ones from this laboratory and indicate either a loss of these key genes during aging of humans or decreased hybridizability due to some other factor or factors. In any event, this degree of loss or inactivation of genes involving an all protein synthesis would seem to impair function of post-mitotic cells in response to maximal stress to about the same degree that function is lost in various human organ systems during aging, as defined by Shock and others.