IUBio

Must an AGING PROCESS be universal?

W.G.VAN.DOORN at ATO.AGRO.NL W.G.VAN.DOORN at ATO.AGRO.NL
Wed Apr 19 06:17:17 EST 1995


In a discussion about the term immortal Oliver Bogler annotated my message and
     wrote:
> 
> > In a discussion about the definition of immortality Oliver Bogler wrote:     
> > > But to me that is no different from saying that the stem cell that divides
> > > at age 120 is immortal because by definition it is derived from a cell
> > > that was onboard at birth. You only get cells from other cells  - they are
> > > not ever made de novo. So the experiment would be to see whether there are
> > > any dividing stem cells at age 120 - and that is all. 
>     
> > I have serious difficulty with this definition. We do not know how long an 
> > individual stem cell lives. The parent cell may divide and then fully 
> > differentiate, i.e. until death. The daughter cell does the same, etc. Each 
> > individual cell may live for a few days only. Yet you call the cell immortal.
> 
> What is an individual cell? Cell A divides to give cells B and C. Where is
> cell A now? Is it dead, just because you can not point to it? If each cell
> lives only a few days the whole organism will die soon.
>         
> > In this definition a cell is immortal when its descendants keep multiplying. 
> > As someone else has said, this would imply, logically, that the only immortal 
> > cell was the first one. 
> 
> This argument would lead to a useless definition of the term immortal -
> see below.
>      
> > Bacteria, which will go on multiplying when regularly placed on a new 
> > substrate, would in this line of thinking also be called immortal, although 
> > we know for a fact that each cell only lives for a day or two.
> >      
> > Also human beings would then be immortal, since they have ever been
>   multiplying (with some success). This shows that the definition defies 
    common sense.
> 
> Again you reveal your confusion in terms of what 'immortality' means in
> the context of cellular senescence.
>  
> >      
> > I could agree with calling a cell culture immortal, but there is some
> hybris in
> >  the word. Isn't it a bit exaggerated? How could we prove it? Things that
> > cannot be proven or disproven are outside the realm of science. The term,
> > therefore, is unscientific.
> 
> Immortal in the normal sense means to live forever, and I agree with you
> this is an unscientific term. However there is a scientific definition of
> the immortal - which I thought we were all using. In the scientific term a
> cell is termed immortal if it generates a lineage of descendants that do
> not undergo senescence at the time when sister cell clones do. We tend to
> be a little sloppy, if you will, in that we call cells immortal - of
> course as individual cells they never are, because they need to keep
> dividing to be termed immortal. As soon as they divide they are gone. What
> is immortal is in fact the clone which they give rise to. 
> 
> One needs to think differently about organisms and cells. Organisms give
> rise to descendants without losing their identity. Therefore it is easy to
> see that they are all individually mortal, while their species may live
> much longer, or even be immortal (meaning the species lives many orders of
> magnitude longer than any inividual). Not so for cells. If all cells have
> a limited life at the time that they are generated then they wouldn't last
> long. If you think of an example: let us consider the first ever cell:
> lets call it A. It divides to make B and C.If B and C are now programmed
> with a finite life span, and their descendants inherit that limit then
> soon all the cells will be dead. (This is exactly what happens when you
> observe fibroblasts senesce - cells derived from the same cell stop
> dividing and senesce at the same time.) Since bacteria, for example have
> lived for millions of years, you could say that they are immortal - all
> the bacteria alive today are related - they all eventually come from the
> first bacterial cell division - they are immortal.
> 
> Oliver
> 
 
I am very glad that we do agree on one thing: the term immortal, in whatever 
context we want to use it (either referring to cells or individuals, or to
cell lines) is unscientific. Cell biologist should try to avoid unscienti-
fic terms.

You call bacteria immortal, yet we know that they live for a few days only. It
is beyond me how we could use one term for two different levels. Level one is 
that of the individual (cell or multicellular organism), the other the level
of the cell line. Most biologists would use the term for the latter purpose
only. 
         
You tell people that disscuss with you rather rapidly that they are confused.
The only thing I am trying to do is to get clear definitions. So let us stay 
polite.     
   
   
As far as I can see it there is a form of circular argument in the terminology
of people working with cell cultures. They established the very interesting 
fact that cells undergo a limited number of divisions, then stop dividing 
unless treated with carcinogenic agents. As cells from older individuals
showed a lower number of divisions the hypothesis was put forward that a 
limited number of cell divisions is a main cause of ageing and death. I think
this is a very plausible thought, but as far as I know there is still quite a 
debate whether this is true. A cell line then is called senescent when
it does not show division any more, and immortalized when it goes on dividing.
Here probably is the fallacy of circular reasoning. Normally, biologist would 
call a cell senescent when it is in a stage of differentiation leading to 
programmed death, this is usually long after its last division.

To call a cell line senescent when it does not divide any more, while the cells
are staying alive looks as if the above hypothesis is taken for a fact. Also
the term immortal can then be understood: a halt to cell division is regarded
as death (related to the individual the cell line was taken from), and when the 
cease-division is overcome it is regarded as life (even 'immortal' life).
     
Would it not be better to use neutral terms for the stages in cell cultures 
like a) dividing, b) quiescent, c) nondividing, and d) carcinogenic, or any
other set of terms that just describes the facts.
     
     
     Wouter van Doorn
     ATO-DLO, Wageningen, Holland 
         
  
     
     
      
        
     
     > 
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> Date: Mon, 10 Apr 1995 15:40:27 -0700
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> From: obogler at ucsd.edu (Oliver Bogler)
> Subject: Re: Must an AGING PROCESS be universal?
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