Differentiation of radial glia cells into astrocytes is a possible ageing
National Agrarian University
id. Geroyev oborony, 15, Kiev 03041, Ukraine
e-mail: boyko-l@rambler.ru
Several obscure facts of gerontology are briefly reviewed. An attempt is made to shape new notions of the phenomenon based on the astrocyte hypothesis of ageing in mammals. This hypothesis interprets mammal ageing as a genetic disease with fatal outcome. The disease is caused by single character acquired by the theromorph lineage of the vertebrates in the course of evolution: the transformation of radial glia cells (RGC) into star-shaped astrocytes during the postnatal development, i.e. the disappearance of the fetal radial ways of nerve cell migration from proliferative zones to the sites of their ultimate localization in the brain of adult individuals. This process is the cause for the mammal brain being postmitotic. The disappearance of RGC induces a cascade of system processes termed age-dependent mechanism of self-destruction of mammals (AMSM). The disappearance of RGC inhibits the replacement of the nerve cells that have exhausted their living resources. Nerve cells are rigidly specialized and have restricted lifetime and ability of reparation. After some period, the level of homeostasis in nerve cells starts changing steadily for the worse due to irreversible pathological changes in the cells (especially in the neurosecretory cells). This brings damage to life-sypport systems of the mammal organism thus causing its death. The species-specific maximum life span is thus determined by the rate of metabolism in the organism. AMSM probably displays a general evolutionary principle: outer factors causing death (in non-ageing organisms) are replaced by inner factors.
