One observation I have made of human fibroblasts in culture is that as
they are reaching a high passage number they grow less well or rapidly,
and provide a less nutrious host for a parasite I infect them with. The
point is that they gradually, over approximately half a dozen
replications, they become exhausted. If the shortening of the telomeres
truns off selected genes, then it must be a leaky switch or one which
inteferes with additional genes with each additional replication near the
end of the cell's live. Not an easy theory to prove.
Another observation which should be considered for mortal cells in
culture, and that is that fibroblasts kept in a non-replicating state
with low serum levels age even without replicating. The number of
doublings they are capable of deminishes even though they technically
have not used up the lost potential. There is clearly more to the story.
Unfortunately, I can not claim credit for these observations.
Edward C. Krug Ph.D. E-mail= kruged at essex.hsc.colorado.edu
303-270-7234 (vox), 303-270-8681 (fax) Univ. of Colorado Med. School
