Tag: biology

What is Cellular Senescence

Where do senescent cells come from, and why does our body create them?

As over time and as you get older, you accumulate DNA damage in your cells.

DNA damage can happen in a number of different ways, such as radiation and environmental factors, but can also happen naturally through normal cell growth and division.

This DNA damage accumulates and causes what’s known as senescent cells. Senescence means that the cells are old and have undergone aging at the cellular level.

But some cells don’t experience senescence and seem to be able to undergo healthy division almost indefinitely.

Let’s examine the differences between cells that experience senescence and those that don’t.

Somatic Cells: telomere shortening and cell division

In human bodies, our cells divide 2 trillion times per day.. that’s 2,000,000,000,000. [4]

As somatic cells divide, the caps at the end of our cells (called telomeres) slowly lose information after each subsequent cell division.

source: Khan Academy YouTube Channel [3]

When telomeres become too short, the cells stops dividing.

Telomere shortening and other types of DNA damage results in these cells becoming senescent – which means they autonomously stop dividing.

Doing so helps prevent DNA damage from continuing to happen, and being carried over into future child cells. [3]

Our somatic cells can divide between 60-70 times before the telomeres get too short (called the Hayflick limit).

Stem cells: telomerase and DNA repair

Although somatic cells undergo this natural progression towards cellular senescence after a certain number of divisions, not all cells in the body go through these stages.

Stem cells are special – they don’t experience cellular senscence.

Stem cells are able to maintain their mitotic capacity (ability to divide) and avoid senescence because they have a special enzyme called telomerase.

Telomerase helps cells “stay young” and avoid the Hayflick limit because it is able to rejuvenate the lost ends of telomeres after dividing. [4]

Humans have stem cells in all different types of tissue and organs throughout our bodies.

Why don’t somatic cells produce telomerase?

In regular cell function, telomerase is specific to stem cells, and somatic cells are not supposed to produce telomerase.

However, because our body creates 100 billion new cells every single day, mutations can happen where a somatic cell will produce telomerase. This is actually a BAD mutation!

And while telomerase might sound like the key to keep our cells young, unfortunately, its more complicated than that.

Telomerase production in somatic cells results in uncontrollable cell division and growth, which causes cancer.

Even at an extremely low rate of mutation, the high number of cells means more opportunities for cancer to form.

Problems caused by senescent cells

Similar to brain neurons and heart muscle cells, senescent cells don’t divide. They shut down and stop copying DNA and dividing.

Somatic cells undergo senescence to stop dividing and to avoid becoming cancerous. And as humans age, we have more senescent cells in our bodies.

Although good for the prevention of cancer, too many senescent cells is a detriment to human health.

Senescent cells secrete proteins and molecules that cause inflammation. (senescence associated secretory phenotype, or SASP).

Remember, inflammation is BAD. Due to the SASP factors from senescent cells increasing inflammation in our bodies, we experience debilitation and disease at increased rates.

So although we want our somatic cells to avoid growing uncontrollably and causing cancer, we also want to avoid the presence of senescent cells if at all possible.

The future of cellular aging

Scientists are looking into ways to remove senescent cells to improve health. Senolytic drugs, for example, are built to kill these cells.

How do you think the future of cellular aging will look?

Tweet @espressoinsight and let us know what ideas you have.

Sources:

  1. The Hallmarks of Aging https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3836174/
  2. SENS Overview of Cell Senescence https://www.sens.org/overview-of-cell-senescence/
  3. Telomeres and cellular senescence https://www.youtube.com/watch?v=R5YiO6rKr-w
  4. Cell division https://askabiologist.asu.edu/cell-division#:~:text=Organisms%20grow%20because%20cells%20are,trillion%20cells%20divide%20every%20day.

Cholodny-Went: Mental Models To Know #1

The Cholodny-Went Model is an theory in biology from the 1920s that describes how light energy on part of a plant will stimulate growth of the entire plant by producing and transporting a hormone (called auxin), to other parts of the plant that don’t get the benefit of direct light exposure. This is how root systems are grown, as well as leaves and branches on the lower areas of the plant.

The Cholodny-Went theory is valuable because it serves as a model for processes in any realm – human life, business, industry, education, etc. that result in indirect improvements in other areas.

The model is a good example of how positive stimulus in even a small area can have a large positive impact on something that might be seemingly unrelated.

How can this be applied to life and business?

Self improvement: Apply the Cholodny-Went model to improve your life by realizing that certain behaviors and actions can have an indirect positive (or negative) effect on other areas of your life.

Hiring: Good employees are hard to come by. But if you can get hiring done right, the rest of your business will excel in multiple areas as a result. A company is simply made up of the people multiplied by the systems in place that allow those people to be productive. It is a simple principle: having more intelligent and skilled employees means that your company will do better.

Steve Jobs has discussed how getting “A-players” together results in future hiring becoming a self-policing phenomena where they only want to hire other A-players to work with. By hiring a few A-players at a company and allowing them to work together, a company will likely not only have more productive employees, but also impact future hiring by enabling

Exercise: Doing squats might seem like solely a leg exercise, but the effect of doing this simple workout may indirectly help stimulate hypertrophy (muscle growth) throughout the human body. Squats are so intense and require so much physical exertion that they help increase testosterone throughout the body. Leg workouts are known to have this effect as well, but squats have the greatest effect [2]. This indirectly helps you build muscle and strength in your upper body, core, and other areas. The simple act of exercise does more than improve your life physically. The act of doing hard things and pushing yourself may improve your mental and stress levels in other areas of your life.

Product development: Elon Musk has a common business mantra that goes “focus on making the product great”. By applying the Cholodny-Went principle here, we can begin to understand why Elon believes so fervently in this statement. By improving the product, this has a down-stream positive impact on other areas of the company:

  • Lower customer support cost: A better product means that the customer support team has an easier job, with fewer bugs and customer issues to solve.
  • Lower marketing budget: A better product also means that news may spread by word of mouth, so the company needs to do less in the way of advertising.
  • Better finances: a great product will be one that customers are excited to buy. If customers love the product, they will buy more of them, so the company will be more profitable.

Learning: The world of knowledge is seemingly infinite. One of my favorite instagram accounts shares a large amount of Charlie Munger Quotes.

Using the Cholodny-Went model in your own life

There are many ways the Cholodny-Went model may be applied to life and business.

As CMQ investing has discussed on his substack page, using various models when thinking about problems can help you make better decisions.

Leave a comment and share a few areas where you can apply the Cholodny-Went model to improve your own life!

Sources:

  1. https://www.cell.com/current-biology/pdf/S0960-9822(02)70780-X.pdf
  2. Hormonal Response to Leg Exercise: https://pubmed.ncbi.nlm.nih.gov/24276305/

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