Fig. (1).

A Model for the Role of Astrocytic Cell Cycle Regulation as the Basis of the Inverse Correlation Between the Incidence of Cancer and Neurodegenerative Disease in Aging Brain. An astrogenic balance maintains the neuroenvironment, as healthy astrocytes (B) can re-enter the cell cycle to replenish cell populations in a regulated controlled manner. In aging, senescent astrocytes (A) are no longer able to reenter the cell cycle to replenish the astrocytic cell population, resulting in astrocytic atrophy and subsequent neurodegeneration. Likewise, the dysregulation of the cell cycle earlier in aging can result in malignant astrocytes (C) and tumorigenesis. (A higher resolution / colour version of this figure is available in the electronic copy of the article).