A Scary Aging Mechanism
Is viral DNA an aging mechanism?
As a mammal, I found it concerning that so much of my DNA is apparently viral in origin. Repetitive elements can be up to 60% of the mammalian genome and about half of that is “Transposable elements” or “Jumping genes”. [1]
Fortunately, most of these ancient viral sequences have been mutated and are not actively able to still cut and paste their way around your genome. However, there are some that are still able to cause havoc, if not suppressed. These Retrotransposons can cause genome instability, insertional mutagenesis, and transcriptional changes that are deleterious or cancerous in the host.
So evolution has had to control these elements, mostly via epigenetic mechanisms that require some cellular energy. In other words, methyl groups may be added to the DNA to stop them from being expressed, or the histone proteins that DNA is bound to may be altered to shut down expression of transposon sequences, or small “interfering” RNAs can be produced to cause retrotransposon RNA to degrade quickly (this is all standard “epigenetic silencing” so you can read about it elsewhere).
Without this active suppression of our viral DNA, unsuppressed retrotransposon activity can lead to genomic rearrangements, mutations, genomic instability, developmental disorders, and cancer.
Aging
During aging, cells lose their ability to maintain epigenome suppression of viral DNA, leading to issues. It shouldn’t be surprising that failure to suppress ancient viral DNA is a problem, but this problem appears to be an aging mechanism as well. To say that another way, there is growing evident that Retrotransposable elements being activated may be a cause of organism lifespan and health span. [1] There is some evidence for example that transposable elements (TEs) are activated in Alzheimer’s disease (AD). [2]
I currently wonder if endogenous viral DNA is a cancer cause, that impacts people early in life, or a later barrier for the long lived, or perhaps both. Could it be a limit to maximum species lifespan as well?
