What Happens To Our Body When We Age?

We all know what aging looks like, but how does it actually happen?

9 Hallmarks of Aging

Aging is a very complex progressive process that leads an organism (in our case a person) to impared functions and increases its vulnerability to death. Age is in fact at the top of the list of risk factors for conditions such as heart diseases and cancers — currently the leading causes of death worldwide.

The hallmarks of aging — Image credits: NCBI

Genomic instability

Every single cell that makes up our bodies (and we have billions and billions of them) contains a complete instruction set that, alone, could rebuild us from scratch. This instruction set is called the genome and consists of nucleotide sequences of DNA. Among other things, our genome contains the instructions for the creation of proteins, which are essential for the proper functioning of our cells.

Telomere attrition

Have you ever heard about telomeres? Telomeres are disposable parts of DNA that don’t contain any useful genetic information. They sit at the end of chromosomes (DNA molecules that can be found in the nucleus of each of our cells).

  • First of all, our stem cells (cells that don’t have a specialized function) produce an enzyme called telomerase that rebuilds the pieces of telomeres lost in the cell division process. Specialized cells are not able to produce this useful enzyme themselves but we could activate them through telomerase therapy. A company working on this is Telocyte: using telomerase, they are rebuilding the telomeres of brain cells that became dysfunctional because of Alzheimer’s.
  • Secondly, cancer cells can rebuild their telomeres indefinitely. We don’t know exactly how they do it but, if we could understand the mechanism, we may be able to replicate it for our own cells.
Telomeres protect the integrity of our genetic information — Image credits: Metabolic Medicine

Epigenetic alterations

As seen above, all the cells in our body, regardless of their role, contain the same genome. However, these cells have different roles and perform different functions (e.g. brain cells and muscle cells). How is this possible?

Our cells all have the same DNA but specific cells have specific active and inactive sections of this same DNA

Loss of proteostasis

Proteins allow our cells to do everything, from sensing the environment, digesting the food, contracting a muscle, sending electrical signals etc.

  • Slow down the accumulation of damaged proteins.
  • Counteract their negative effects.
  • Destroy or remove these proteins.

Deregulated nutrient sensing

To function, all cells in our body require nutrients that are absorbed from the food we eat. Our cells have specific mechanisms that allow them to sense when nutrients are abundant (and the cells accelerate growth and metabolism) and when they are scarce (and it’s therefore time to slow down).

Mitochondrial dysfunction

Once the nutrients get inside our cells, small organelles called mitochondria convert them into energy that the cells can use to function and survive. This energy is called adenosine triphosphate or ATP and, for this reason, mitochondria are considered the “powerhouses” of the cells. Mitochondria have their own DNA, different from the DNA contained in the nucleus, which helps them create the proteins they need for their specific function.

Mitochondrial structure — Image credits: National Human Resource Genome Institute

Cellular senescence

As we age, our cells age with us. In fact, after about 50 replications, our cells start breaking down and lose their function. In addition to that, several stress-inducing factors can cause cellular senescence: DNA damage, epigenetic alterations, smoke and ultraviolet rays from the sun.

Stem cell exhaustion

Our bodies need new cells continuously. To meet this need, our cells split several times into identical copies. As we have said, these divisions are limited in specialized cells because of telomere attrition. In stem cells, the possibility of replication is almost infinite, thanks to the enzyme telomerase, which replenish the telomeres.

Altered intercellular communication

Now we come to the last hallmark of aging. Organs, tissues and systems that make up the human body are interrelated and their functioning influences and depends on these connections. To communicate and work with each other, cells use a network of chemical signals about which we still know very little.

In our body, we have about 30,000,000,000,000 cells — Image credits: Healthline

Conclusion

The aging process consists of many interconnected processes. While it might seem that this complexity is a negative feature in understanding how aging works, it can also be used to our advantage. Indeed, finding solutions for one of these hallmarks would positively affect the other hallmarks as well.

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