You might be interested in learning about telomeres, telomerase, and telomerase gene therapy.
For example, Boccardi & Herbig (2012): describe a mouse study in which they used telomerase gene therapy to improve the healthspan and lifespan of mice by up to 24%.
As far as I know, we have no successful human trials of similar therapies that have targeted and succeeded at "decreasing the age" of humans.
- However, this source does claim that a woman attempted to do so. I cannot substantiate these claims in any way, so I'm skeptical at best...
Telomere: non-coding nucleotide sequences on the tips of chromosomal DNA strands.
Due to the inability for DNA polymerase to replace RNA primers on the end of linear strands of eukaryotic DNA during DNA replication, ~50-100 base pairs are removed from the daughter strand from each replication event.
The "junk" (i.e., non-coding) telomere sequences (which could repeat 1000s of times) provide buffers against losing more valuable DNA when this happens. Eventually though, the telomeres run out, and replication events could lead to loss of coding regions of DNA...
According to Boccardi & Herbig (2012):
As we age, telomeres in most of our tissues progressively become shorter and therefore likely contribute to the failure of our organs and tissues observed in old age. Supporting this are data demonstrating that healthy lifespan is positively correlated with longer telomeres in humans, and patients suffering from age‐related diseases and premature aging syndromes display shorter telomeres compared to healthy individuals (Zhu et al, 2011).
The enzyme, telomerase can replace these telomeres, but telomerase is really only active in stem cells and white blood cells, so most adult cells lack this regeneration ability.
This is where telomerase gene therapy comes into play.
In the simplest sense, this approach attempts to artificially add telomerase to adult cells to essentially add back telomeres and potentially slow or even reverse the aging process.*
*Note: As far as I know, we don't actually know whether short telomeres are simply an effect of aging or if they are actually the cause of aging (and ultimately death), so this gene therapy is running on an relatively unsupported hypothesis.
For example: Boccardi & Herbig (2012) "Telomerase gene therapy: a novel approach to combat aging".
- They found that adding telomerase to 1 year old mice increased their lifespan by 24%.
Credit: Boccardi & Herbig (2012):
As Boccardi & Herbig (2012) note, however, applied human studies are still a thing of the future.
While these studies provide a proof‐of‐principle that telomerase gene therapy is a feasible and generally safe approach to improve healthspan and treat disorders associated with short telomeres, a clinical application in humans is likely still some time away.
- However, this source does claim that a woman (Elizabeth Parrish, CEO of Bioviva USA Inc. -- notice the website :p) attempted to do so -- I cannot substantiate these claims in any way, so I'm skeptical at best...
Citations and additional suggested reading:
Boccardi, V. and Herbig, U., 2012. Telomerase gene therapy: a novel approach to combat aging. EMBO molecular medicine, 4(8), pp.685-687. read here
Campisi, J., Kim, S.H., Lim, C.S. and Rubio, M., 2001. Cellular senescence, cancer and aging: the telomere connection. Experimental gerontology, 36(10), pp.1619-1637. read here
Zhu, H., Belcher, M. and Van Der Harst, P., 2011. Healthy aging and disease: role for telomere biology?. Clinical Science, 120(10), pp.427-440.