Stem Cells: A Key Integrative Hallmark of Aging
There are a number of theories that delve into the question — why do we age? Among the most popular theories is the stem cell theory of aging. The Stem Cell Theory of Aging argues that as we age our stem cells lose the ability to replenish and maintain tissues. Contrary to other theories of aging that cite the source of the damage as the reason we age — DNA Damage Theory of aging and the Free Radical Theory of aging, the stem cell theory contends the response to the damage is the reason we age.
Stem cells (SC) are a special class of cells that have variable potency (can transform into a variety of different cells) and can self-renew. Their main function in the body is to repair and maintain tissues as tissues wear out and turnover. Depending on the system the SC resides in, they have different potencies. A Hemopoietic stem cell (HSC) is a stem cell that is in the circulatory system and can differentiate into all the different types of blood cells and immune cells that circulate our bodies. They are called pluripotent. In contrast, epidermal stem cells can only differentiate into one type of cell and they are called unipotent.
Our cells turnover on a regular basis and need to constantly be replaced as we go on everyday life. Every 2–4 your entire outer layer of skin sheds and is replaced by a new layer that is derived from stem cells. Depending on the type of cell its individual lifespan can range vastly.
As we age our stores of stem cells begin to deplete. They begin to lose there efficacy to maintain organs which subsequently leads to their deterioration and eventual failure. Not only do stem cells deplete as we age but due to epigenetic changes or metabolic stressors they can become less effective at their role in maintaining function.
The therapeutic idea that has been in scientist’s minds for the last two decades is in instances where tissues are deteriorating a strategy to combat that is to introduce new stem cells into the system to help restore the organ. This is widely to treat leukemia (blood cancer) pateints. After chemotherapy which destroys cancer, a bone marrow transplant is used to restore a person’s immune cells.
This idea has now extended to ways in which we could extend longevity using stem-cell therapeutics. There are several companies working on this problem that has gained a lot of attention and investment in the past few years. Cellularity is harvesting Natural Killer cells from the placenta used in tissue regeneration, and augment immunity with the long term goal of increasing healthspan and lifespan. There are also companies like Sammued who have garnered $650 million in funding to develop pharmaceuticals targeting the Wnt pathway. The Wnt pathway plays a large role in maintaining stem cell functionality and they currently have a drug in phase III trials for knee osteoarthritis.