Recycling - a term that you will certainly come across again and again in everyday life. Whether it is in relation to waste or the sustainable production of various products: recycling makes sense because it saves both resources and energy. Our bodies also use these advantages for themselves. In addition to saving energy and resources, recycling is an effective tool for the body to prevent damage and to eliminate damage that has already occurred. The latter can sometimes be a difficult undertaking. In order to avoid damage in the long term, most components are regularly replaced, regardless of any damage. Large molecules are broken down into their individual parts and reassembled over their entire life - recycling, in other words.
Cell death, removal and replacement
One of the most obvious renewal processes in our body is the regular production of new layers of skin. The upper layer of skin slowly flakes off and is replaced from below by new and continuously dividing cells. However, all of this happens under our radar.
Did you know that house dust consists of up to 80% skin flakes? These shed skin flakes cannot of course be recycled, at least not by our body to form new cell components. Nevertheless, it is cell renewal that is intended to prevent damage. The skin barrier is an important part of our defense system against harmful environmental influences and pathogens, as we already explained in the first part of the series Hallmarks of Health have learned.
But it's not just our skin that renews itself regularly; almost all of the body's cells do this. As soon as cells die, they send various signals to start recycling. First, there are the signals that help the dying cells to be found by phagocytes. These indicate the direction in which the phagocytes must move through the bloodstream and tissue to find the dying cells. They then recognize the dying cells through markers that are presented on the cell surface. These markers activate phagocytosis - the absorption of dead cell components into the phagocytes.
These processes are normal functions of the immune system and otherwise serve to eliminate foreign bodies. To prevent the body from assuming an infection and starting a strong immune reaction, the dying cells also release anti-inflammatory substances. These inhibit an excessive immune reaction. A strong immune reaction is important when it comes to removing pathogens, but in the case of self-induced cell recycling this is not necessary and only wastes energy and causes tissue damage.
Recycling needs balance
The natural mechanism of defective cells is that they want to be found and recycled by phagocytes. It is different with cancer: tumor cells often send out exactly the opposite signals. They inhibit the signals that activate the phagocytosis process and amplify signals that inhibit phagocytosis (CD47). This ensures their survival.
Have you ever heard of homeostasis This is a very important principle in different areas of the body. The term describes the maintenance of a physiological balance. Recycling is about the balance between broken down cells, newly created components and the pool of resources that are used for reconstruction. If this ratio is in balance, the body can work as efficiently as possible without endangering health.
As you may already know, cellular processes run at different speeds depending on the tissue in your body. Cell turnover also occurs at different speeds depending on the tissue. While cells that are constantly working produce more energy and cells that are frequently used need to be renewed more often, there are also tissues in which less activity takes place and the risk of damage is therefore lower. This adaptation also occurs in the renewal of the cells themselves. Most components of the blood, for example, have a very rapid turnover, while cells of the nervous system and heart muscle cells can be recycled relatively slowly or not at all. This also explains why neurodegenerative diseases such as Alzheimer's or Parkinson's cannot be cured in their advanced stages, but can only be slowed down. This is because complete regeneration of already non-functional tissue is only possible to a limited extent with these cells.
Autophagy – Cell-internal digestive system
When you eat food, it goes through various processes and enzymes broken down into its individual components so that your body can then reuse these parts. Every single cell has a similar digestive system - the autophagolysosome. If your body does not have enough energy reserves or misfolded proteins are detected, the autophagosome absorbs proteins from the cytoplasm. The bubble-like phagosomes then fuse with the so-called lysosomes and form the autophasolysosome. Lysosomes are filled with a type of digestive juice that has an acidic pH value and contains digestive enzymes. Experiments have shown that this mechanism is vital for cells. Does it work? Autophagy If this does not happen, there is an accumulation of defective proteins and organelles in the cytoplasm – the cell dies.
You have probably heard of keto diets, intermittent fasting or Calorie restriction These very popular diets stimulate the Autophagy and According to studies on model organisms, they have a positive effect on health and life expectancy.
Did you know?
There are many different ways to fast. For example, the pseudo-fasting of Valter longo in which the molecular pathways of fasting are imitated using specific ingredients. All of these types of fasting are intended to get the metabolism back on track.
Other recycling mechanisms for proteins
In addition to the autophagy mechanism, there is also the ubiquitin proteasome in the intracellular space. If a protein is "ubiquitinated", it is given the "to be disposed of" stamp, so to speak. Subsequently, all proteins with this stamp are degraded by the proteasome.
The autophagy mechanism works very effectively, however, it is limited to the cell interiorSome diseases are characterized by the accumulation of defective proteins outside of cells - for example, tau and beta-amyloids in Alzheimer's dementia. The transport of these proteins out of the cell is carried out by parts of the autophagosome. It is therefore necessary for our health that the recycling mechanisms can do their job in such a way that damaged parts can be replaced. It is therefore important to keep autophagy, the most important recycling system, healthy. One possibility discussed in research is the molecule Spermidin period.
Sources
Literature:
López-Otín, Carlos, and Guido Kroemer. “Hallmarks of health.”Cell184.1 (2021): 33-63.https://pubmed.ncbi.nlm.nih.gov/33340459/
Images:
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