While many Americans are terrified at the thought of aging, it happens to the best of us.
Aging is a rather broad illness, characterized as the deterioration and impaired function of one's body. Scientists have admitted that if we knew more about aging and its process, then we could better identify which medicines to provide to people to ease their aches, pains, and worries as they get older.
Spanish scientist Dr. Lopez-Otin, Ph.D., from the University of Oviedo, and his colleagues have found nine hallmarks of aging that are the same across organisms. These hallmarks are mostly cellular, as aging begins at the cellular level and then spreads to the tissues, muscles, joints, organs, and bones.
The nine hallmarks include:
1. Altered Intercellular Communication - cells, like neurons in the brain, stop passing signals to each other effectively because they have begun to deteriorate. This hinders the body form functioning normally as these signals are necessary for proper cognitive and motor functions
2. Stem Cell Exhaustion - all adult bodies have stem cells; they are found mainly in the bone marrow and are used to make new blood cells as well as bones, cartilage, and connective tissues. They also allow the body to heal itself after injury, in addition to keeping blood oxygen levels stable. When these stem cells become exhausted, they stop making blood cells and new tissues to replace older or damaged tissues. This can be problematic as we age because bones and tissues also get older and need replacements. This can lead to anemia, osteoporosis, and intestinal malfunctions. Stem cells are not regenerated as easily as other cells are, and so rejuvenating stem cells are difficult but can reverse signs of aging at the cellular level.
3. Cellular Sleep - cellular senescence, or the state at which a cell is essentially asleep, contributes to aging. In this state, cells have stopped growing and dividing. This can be problematic, as cells die and are replaced often while we are young. As we age, cell turnover slows because of other cellular damage, such as mitochondrial dysfunction or genomic instability. In other words, the body doesn't want to make more cells that don't do their jobs. An accumulation of these senescent cells, however, may aggravate other damaged cells or lead to issues with immunity. So while cellular sleep starts out as a beneficial process, preventing damaged cells from propagating, it also speeds the aging process as cell regeneration ceases.
4. Mitochondrial Dysfunction - the mitochondria in cells are where energy is made for the rest of the cell. As we age, the machinery used to make the energy stops working as effectively. A lack of energy can cause cells to die, as they can't perform their other functions without energy and can impact cellular signaling as outlined above. This leads to aging because the lack of energy decreases the lifespan of both the cells and their tissues.
5. Deregulated Nutrient Sensing - as the genetic issues of aging worsen, the body will try to take up fewer nutrients in an effort to repair itself. Studies have shown that dietary restriction can increase lifespan, and it seems the body tries to do this naturally. By not overloading already damaged cells and DNA with nutrients, the body can repair the damage that has been done. However, this only works when nutrients are restricted for a short time; a lack of nutrients can be harmful, as the body can no longer tend to itself the way it did before it began to age.
6. Decrease in Protein Genesis - much of the physical signs of aging are based on the instability of proteins, as well as the cessation of making new proteins. Often, proteins need to be a very particular shape in order to work effectively. When they are made improperly as a result of aging, the body will immediately degrade them. For example, collagen, a protein that works to plump up the skin while we are young, is often made improperly as we age, or even not made at all. A lack of this essential protein is what causes us to look wrinkled or develop saggy skin.
7. Changes to DNA - as a result of cellular processes working less efficiently, our DNA responds by becoming less likely to work. The environment created by cellular issues like mitochondrial dysfunction and cellular sleep causes the DNA to turn itself off. If the DNA is off, it can no longer command that new cells be made or certain cellular functions be carried out. Changes to DNA that turn it off contribute to aging, as nothing new can be generated and the body is stuck with all of its deteriorating cells. However, scientists have indicated that changes to the DNA are reversible and that this may lead to an anti-aging treatment.
8. DNA Damage - as we age, our DNA may randomly degrade as a result of the loss of its protective factors, telomeres. Telomeres bind the ends of the DNA strands in order to keep them safe from mutation and degradation. As we age, the telomeres, instead of the DNA, are worn down, but make the DNA more susceptible to being worn down as well. As DNA is our genetic information, it decides our hair color, eye color, as well as operative functions like providing the information to replenish cellular machinery like mitochondria or stem cells in the body.
9. Genomic Instability - as DNA damage and changes accumulate, the DNA becomes less apt to fix itself. In our youth, issues with DNA are easily fixed, due to the lack of aging factors listed above. However, as damage builds up in the body over time, DNA becomes less apt to give instructions for making new cells or proteins, leading to further aging.
The research team has been clear that wrinkles and sagging skin are not the sole signs of aging; we age everyday even as our cells perform their normal functions. While there may be no products or creams to solve aging at the cellular level, the new challenge is to understand the connections between each hallmark and how best to control them. "We don't aspire to immortality, just to the possibility of making life a little better for us all," said Dr. Lopez-Otin.
Source: Lopex-Otin C, Serrano M, Partridge L, Blasco MA, Kroemer G. The Hallmarks of Aging. Cell. 2013.