Stationary cell cultures as a tool for gerontological studies.

Abstract

Studies of cellular and molecular mechanisms of aging are currently often carried o u t on cells senescing not only in vivo but also in vitro (Hayflick’s model), that is, altering with increasing of population doubling level in culture. However, some data suggest that in some cases the results obtained with this model are not in accord with those of in vivo aging studies. Furthermore, such experiments, as a rule, are comparable in labor-consuming character with routine studies in laboratory animals. In fact, Hayflick himself suggests that cells in vivo never realize their proliferative potential and never reach phase 111. In other words, an organism never ages because of a cell’s limitation, called “Hayflick’s limit.” It ages, we believe,’ because of an accumulation of various kinds of damage in cells due to restriction of cell proliferation during the formation (the differentiation process) of populations of specialized resting cells or very slowly dividing cells. The rate of any type of damage accumulation in the cell population (not in a single cell!) has to depend on the ratio of the rates of three processes: (1) cell proliferation, ( 2 ) spontaneous appearance of damage, and (3) damage repair. Thus, during cell proliferation a “dilution” of the damage occurs. Our data2 demonstrating a direct relation between the average proliferative activity of a cell line or strain and the average DNA molecular weight support this hypothesis. With all this in mind we suppose that it is more advisable to study cellular aging mechanisms using the “stationary phase aging” model.‘ The model is based on the assumption that in cells of stationary cultures various changes similar to those in cells of aging organisms have to appear. Last year we and other investigators obtained many experimental results confirming this assumption. “Age” changes at different levels (accumulation of DNA breaks and DNA protein cross-links, DNA demethylation, changes in spontaneous sister chromatid exchange level, plasma membrane changes, nuclear structure modulations, and decreased rate of mitogenstimulated cell cycling and of cell colony-forming ability a.0.) were shown to occur in stationary cell cultures. These experiments can be carried out in nearly any type of cell including normal and transformed human and animal cells, plant cells, bacteria, mycoplasmas, yeasts, and the like. In particular, we now study the phenomenon of stationary phase aging and the possibility of modulating this kind of cell aging by geroprotectors (physical or chemical factors that retard aging) and geropromoters (factors that accelerate aging) in cyanobacteria cultures. ‘Thus, an evolutionary approach to analysis of the data is provided. Moreover, changes in stationary cell cultures become detectable very soon, as a rule in 2-3 weeks after beginning the experiment. All of these data suggest that the stationary phase aging model is a good alternative to the Hayflick model.