Last time, we discussed what aging is and how DNA alterations that occur during cellular replication plays into aging. To catch everyone up, each cell contains a copy of DNA and so each time new cells are created by a round of replication, the DNA from the original cell must be copied . During this replication process, mistakes can be made, and if our DNA repair mechanisms are not on top of their game, these mistakes go unfixed and aging can be accelerated . Now, let's talk about a few more mechanisms of aging.
On that same note of DNA replication, there is also a correlation between something called "telomere length" and aging. Since DNA is linear, the proteins that copy DNA must replicate from one end to the other. Unfortunately, these proteins are not able to replicate up until the very end of DNA, leaving off a small portion of the DNA each time they perform a round of replication. Luckily, our cells have evolved to accommodate for this deficiency by adding on "telomeres", which are portions at the ends of DNA that do not contain important genetic information (shown in orange) and can therefore be lost without great consequence.
As each replication happens, a part of each telomere is lost and once the replication process starts to cut off important genetic information, the cell dies. Interestingly, it has been shown that mice with either shortened or lengthened telomeres have a decreased or increased lifespan, respectively . If scientists can find a way to delay telomere attrition, it is possible to delay cellular aging.
Largely due to telomere shortening, there is a limit to how many times a cell can divide. This is primarily in order to prevent the DNA damage that is accumulated through replication and over time from being passed on to new cells. This replication limit is called "cellular senescence" and is very beneficial when cells are able to maintain their regenerative capacity and eliminate senescent, or old, cells. Due to either the body's loss of regenerative abilities or a decrease in the ability of the immune system to clear old cells, it has been observed that senescent cells accumulate in tissues as we age . When these senescent cells are left to linger in tissues, they release inflammatory proteins that aggravate surrounding tissue and lead to an increased rate of aging. It has been shown that eliminating senescent cells provides a way to delay or reverse aging and there have been many recent efforts to discover and develop compounds to eliminate or decrease senescent cells .
Interestingly, one of the most extensively proven ways to significantly increase life span is to undergo extreme caloric restriction. By limiting food intake, the body induces a mechanism or pathway that promotes longevity. This could be due to a defensive response, in which the body decreases its overall rate of cell growth and metabolism to accommodate for less nutrient availability, which subsequently retards cellular damage . Don't go extreme dieting just yet, however, as you would need to reduce your calorie intake by around 25 to 50 percent, which may cause inadvertent effects, such as muscle atrophy and bone density loss . The excitement around this discovery lies in the potential for scientists to mimic the specific pathway induced by caloric restriction through pharmacological manipulation .
On a similar note, it has also been found that endurance training and alternate-day fasting can enhance health span by avoiding "mitochondrial degeneration" . Just as stem cells have been making their way around health trends, mitochondria are also becoming of focus in such topics. This is because mitochondria play an important role in every single cell, as they generate cellular energy, called ATP. All active processes within the body, including muscle function, breathing, and metabolism require ATP and not surprisingly, as we age, our mitochondria become less efficient. By preventing mitochondrial degeneration, we can conceivable allow our bodies the availability of more energy, slowing down aging on a cellular level.
Everyone will experience aging, but not necessarily in the same way. We all know those lucky few who stay vibrant and healthy even as the years pass. So, what's their secret? It could be genetics, environmental factors, or their lifestyle, but either way they are probably affecting one of these mentioned mechanisms to decrease the rate of their cellular aging. Stay tuned for more on all things aging and how science is evolving to help people enjoy life while they age.
1. How cells and tissues grow [Internet]. Cancer Research UK. 2014 [cited 2018 Aug 20]. Available from: https://www.cancerresearchuk.org/about-cancer/what-is-cancer/how-cancer-starts/how-cells-and-tissues-grow
2. López-Otín C, Blasco MA, Partridge L, Serrano M, Kroemer G. The Hallmarks of Aging. Cell [Internet]. 2013 Jun 6 [cited 2018 Aug 20];153(6):1194'217. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3836174/
3. Conniff R. The Hunger Gains: Extreme Calorie-Restriction Diet Shows Anti-Aging Results [Internet]. Scientific American. [cited 2018 Aug 20]. Available from: https://www.scientificamerican.com/article/the-hunger-gains-extreme-calorie-restriction-diet-shows-anti-aging-results/
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