The existence of such cell lines poses another question: are they really
“immortal” or the cells in them will die after the 50 duplications as Hayflick
has established earlier? In his opinion, “if these cell lines prove to be
“immortal”, then the reasons for the alterations of age in all living things are
outside the cells” (Hayflick, 1989).
In my opinion the biological aging in the multicellular organisms is a
natural process and essentially it cannot be practically avoided. The reason
is the cell differentiation approved in the course of evolution during the
building multicellular organisms from their unicellular ancestors. Nature has
not had an alternative. To create higher multicellular organisms (including
the man) it has formed different cell colonies, tissues and organs with the
necessary heterogeneity of their cell composition and functional diversity,
restricting the number of divisions within certain limits. Cell divisions in the
different types of specialized cells (epithelial, muscle, nervous,
erythrocytes, etc.) vary not only in number, but also regarding the time
necessary for their realization. That is why the 50 duplications of cell
populations, established by Hayflick as a limiting factor, should not be
considered a constant, since they can be less, and possibly more.
Limited cell division is valid only for the differentiated cells of higher
multicellular organisms. By creating cell cultures from them and liberating
the cells from the “mysterious influence” of cell differentiation, it is
reasonable to accept that their behaviour will be similar to that of their
ancient ancestors, i.e. inevitably the cell lines will become “immortal”.
As far as the process of cell differentiation is ultimately reduced to
blocking the DNA-synthesis, many authors suppose that including of
specific proteins will lead to deblocking its synthesis, which is observed in
so-called dedifferentiation. Elucidating this question will contribute to
revealing the reasons for cell differentiation and dedifferentiation. That is
why, at present a serious attention is paid to these two mutually connected
and at the same time opposite processes.
Naturally a question arises: can the very DNA aging? For the present
there is no definite answer to this question. But having in mind that in all
unicellular organisms and in the cell cultures of plant and animal origin
already obtained through a routine procedure the division and development
of cells can continue without limits, infinitely theoretically (in the presence of
the necessary conditions), at least within relative broad limits senescence
and daying off of DNA are not observed. But during the prolonged
cultivation alterations occur in it, which lead to “aging”. In natural state that
is avoided by exchanging genetic material in the lower, or fertilization in the
higher organisms.