Cellular senescence is the aging process of cells: they undergo reduced functionality , for example they no longer replicate, they swell , and when the time comes they are replaced by new cells. In their life cycle , cells divide, multiply and perform precise functions (enterocytes absorb nutrients, neurons transmit nerve impulses, hepatocytes transform molecules to eliminate them, and many others), and at the same time they age. The body has extremely efficient mechanisms for replacing old cells with new ones, in order to maintain the functionality of the systems at their best.
As time passes, this replacement cycle slows down, becomes less efficient, old cells are not replaced and cellular processes are affected. And it is precisely when the signs of this cellular senescence become visible on our skin, on the cardiovascular system, on the joints, on our entire body, that we have entered the aging phase .
But what causes cellular senescence? There are mainly three recognized causes : DNA damage , oxidative stress and decline in autophagy .
Before seeing these three causes in detail, it is appropriate to focus on telomeres . They are often called " anti-aging proteins " or " youth molecules ", but they are always cellular anti-aging and cellular youth. They are like caps that are found at the top and bottom of the DNA chain to protect it, preventing it from falling apart, crumbling and losing the very important information it contains. To better understand their role, here is a quick description of the DNA replication process : telomerase removes the telomere, DNA helicase acts like scissors by cutting the double helix while DNA gyrase opens it, DNA polymerase copies the information, ligase closes the helix and telomerase puts the cap back on at the end. Now, imagine this process repeated thousands and thousands of times over a lifetime. As the cap is removed and replaced, the DNA chain begins to deteriorate , to literally wear out, and the information it contains is no longer as it should be, i.e. perfect.
In light of this, the first of the causes, namely DNA damage, is explained. After being removed and replaced many times, the telomeres shorten , the DNA is no longer protected and there can be both physical damage to the double helix , with loss of nucleotides, and incorrect replication of information .
Reactive oxygen species are strong pro-oxidant agents that can damage DNA (as well as cell membranes and other structures). When these molecules become too many, cells stop the DNA replication process to preserve it. Two factors therefore add up: in the elderly the antioxidant power of the body decreases due to various factors that we will see at another time, and therefore these reactive oxygen species are not neutralised. Furthermore, cells stop replicating DNA and begin to malfunction and slow down all processes. Thus we arrive at the moment of senescence .
Autophagy , or self-digestion , is one of the most important peculiarities of the cell. There are organelles called lysosomes which have the task of eliminating waste, the waste products of the cells, by self-digesting thanks to the presence of enzymes inside them, so that they do not accumulate and the cell can function at its best. This capacity is reduced over time , and this leads to the accumulation of toxins which affect cellular activities. When a cell is no longer able to dispose of these wastes, and they begin to accumulate, the mechanism that leads to senescence is triggered.
Cellular senescence is a fact of life. A cell ages and is replaced with a new one, and this happens at any age, more or less effectively. Can this factor be acted upon? In some ways yes, or at least you can slow it down. A healthy lifestyle , with a varied and nutrient-rich diet , regular physical activity and adequate sleep time are an excellent approach. Furthermore, those factors that are proven to shorten telomeres should be avoided: sunburn and tanning beds (UV rays are extremely harmful), smoking, obesity and excessive stress.
Remember, however, that cellular and body aging are natural. This period of life must be lived with joy, gratitude and respect for everything that these cells and this body have done for us throughout our lives. The way you do this is by adopting healthy habits, avoiding factors that speed up the process of cellular senescence, and keeping an open and positive mind .