Factors That Activate Senescence

 FACTORS THAT ACTIVATE SENESCENCE

Many different factors activate senescence in cells and have been implicated in the aging process. In normal cells, the length of the telomeres controls whether or not cells senesce. During the replication of chromosomes, DNA polymerase cannot replicate the DNA at the distal tips of the chromosomes. Consequently, each chromosome shortens each time the cell divides ( Fig. 20.1 ). When the telomeres reach a critically short length, the cell enters senescence.




Another factor that activates senescence and may contributeto aging is DNA damage. Normal metabolic activity produces a variety of reactive oxygen metabolites (ROM) that attack various proteins, lipids, and the DNA. This damage accumulates until it reaches a threshold. After that point, the cells may initiate senescence or apoptosis, depending on the severity and extent of the damage ( Fig. 20.2 ). Consequently, highly defective cells do not accumulate in the body.


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