Neurons Can Outlast Their Host In At Least One Species, But Is That At All Relevant?

A paper on the life span of neurons in relation to their host organism was published earlier in the year and has been doing the rounds in recent days:

Neurons in mammals do not undergo replicative aging, and, in absence of pathologic conditions, their lifespan is limited only by the maximum lifespan of the organism. Whether neuronal lifespan is determined by the strain-specific lifetime or can be extended beyond this limit is unknown. Here, we transplanted embryonic mouse cerebellar precursors into the developing brain of the longer-living Wistar rats. The donor cells integrated into the rat cerebellum developing into mature neurons while retaining mouse-specific morphometric traits.

In their new environment, the grafted mouse neurons did not die at or before the maximum lifespan of their strain of origin but survived as long as 36 mo, doubling the average lifespan of the donor mice. Thus, the lifespan of neurons is not limited by the maximum lifespan of the donor organism, but continues when transplanted in a longer-living host.

This is indeed the barnstorming age of biotechnology. As you might already know, we humans possess many nervous system cells that we were born with and which will last our entire lifetime. This is in contrast to much of the rest of our body where cells are replaced over various timescales, from years for some tissues to days for others. It is even that case that some individual macromolecules within brain cells last unchanged throughout life - not just the cell remaining on station for a lifetime, but some of its fundamental building blocks as well.

The fact that many neurons are never replaced is the source of a range of frailties and age-related conditions that result from increasing damage or buildup of unwanted metabolic byproducts in these long-lived cells. Nonetheless, it seems very reasonable to expect that our neurons are capable of outlasting the present limits of human life span, given the fact that it isn't neurodegeneration that kills supercentenarians - their brain cells are, by and large, still marching along even in the final years. No, death by aging is a systems failure, not a timed simultaneous failure of all the components that make up that system.

Is work on rodent neurons quoted above particularly relevant, or does it change anything? I is interesting, but I think that the answer is "no." We already know that developing the means to repair existing neurons in the brain is necessary. Boosting the rate at which new neurons are created will almost certainly be helpful, but a good portion of the brain stores the data that is the mind - those neurons and their encoded data have to be preserved and maintained, not replaced wholesale. So here it seems to me that knowing that neurons have a longer shelf-life doesn't change anything in the game plan.

Further, there's no guarantee that the longer neuron shelf-life in rodents has any great relevance to human cells. The analogous human study might be to pull long-lived neurons from a supercentenarian and culture them in a 3-D engineered environment that replicates their home tissue as closely as possible. Then you wait - for a fair number of decades. By the time that experiment comes to any interesting result, the whole issue will be moot. Either we will be dead, or SENS-like rejuvenation biotechnologies will be developed, and in either case researchers will already know so much more about cellular biology that they will be long past the point of answering all the questions that the study might help to resolve.

Comments

"Boosting the rate at which new neurons are created will almost certainly be helpful, but a good portion of the brain stores the data that is the mind - those neurons and their encoded data have to be preserved and maintained, not replaced wholesale."

Are you sure about that? Perhaps if full replacement of old neurons with new neurons is done gradually there may still be a continuity of self and memory. In instances of brain injury or amnesia lots of changes sometimes happen in the brain yet we still consider someone to be the same person.

IMO this is the most important life-extension issue, because replacing old neurons with new ones seems significantly more achievable than preserving all the little complex interconnected machinery working inside each individual brain cell. (machinery we don't fully understand) Changing things at the subcellular level has always been the part of SENS that seemed most challenging to me. Is it possible? If not I hope we can sidestep the issue.

Posted by: thehuman at March 3rd, 2013 7:53 PM

This is quite interesting since it may suggest that the high metabolic rate of neurons is not damaging. Also, since the transplanted neurons apparently survive for the entire Wistar life span, perhaps they survive even longer if serially transplanted.

Some science fictionesque possibilities are neural-brain protheses, consciousness migration/sharing, or brain-to-brain interfaces, e.g.,
- Rat Brains Linked to Create "Biological Computer"
http://www.scientificamerican.com/video.cfm?id=rat-brains-linked-to-create-biologi2013-02-28

Posted by: Lou Pagnucco at March 4th, 2013 12:37 PM

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