Leonard Hayflick
Did you know that until 1961, we thought that all cells were immortal? Did you know that we didn’t know about cellular senescence (death of cells) until then?
Until Leonard Hayflick stumbled upon cellular senescence, a cell state that happens after cells divide 50–70 times (the Hayflick limit).
Leonard Hayflick is a longevity researcher, who I had a few calls with and who I look up to and admire!
His story
Now, I’m going to tell you a little bit about his story. When he was around 10, his uncle gave him a chemistry set. His parents let him create a sort of chemistry lab in his basement, and he spent his time making explosions, rockets, and experimenting.
Fast forward to middle school. He was sitting in his chemistry class, and he constantly asked questions. For additional knowledge, clarification, you name it.
His teacher finally reached his breaking point and confined him to the chemistry storage room. In there, he found chemicals he didn’t have at home and got permission from his teacher to use them.
This is what fueled his interest in chemistry and the entire field of science.
A curious friend and he met with a clerk at a store that supplied scientific materials. They were set on buying metallic sodium from him (to make a rocket).
They required a note from his mother (who trusted him and his abilities), and they were able to make rockets. Unfortunately, that didn’t sit too well with his neighbours…
He then enlisted in the army 2 days before World War II ended.
After this, he went to college at Penn and transitioned from an interest in chemistry to an interest in microbiology.
This was because, in his introductory microbiology class, he found that the bacteria were all different colors! This fascinated him and sparked his interest in microbiology.
Afterwards, he established his own cell culture lab and then did the famous experiment in which he discovered senescent cells.
His discovery of cellular senescence and what happened
He stumbled upon it while performing a simple cancer cell experiment. He wanted to induce normal human somatic cells with cancer cell fluids and see what happened!
He found that the human cells, while in cell culture, divided a finite amount of times. He describes it as less of a “Eureka!” moment and more of a “Hey, that’s funny…” moment for him.
“Hey, that’s funny…” — Leonard Hayflick discovering cellular senescence 1961
When he first found this out, he confirmed his results numerous times. When he had finally convinced himself that he, in fact, was right, he and his partner Paul Moorhead (potentially next in my article series) were concerned about opposing the, at the time, Central Dogma, of molecular biology.
They were reluctant to release the paper because of the backlash they might get, especially by Alexis Carrel, a famous French scientist, who was adamant that all cells are immortal.
However, they overcame their fears, and released it only to be met with, as expected, backlash. Many scientific publishing services did not publish their paper, as they had previously published work by Alexis Carrel, such as The Journal of Experimental Medicine.
When Hayflick’s thesis was brought up, Carrel’s famous immortal chick cell tissue experiment was called into question.
Carrel essentially grew a chick tissue for over a YEAR, proclaiming it immortal. People were shocked, but Hayflick, later, realized a major flaw in his experiment.
Carrel had been feeding the chick tissue with an extract of the chick’s embryo tissue but had been adding living cells to the tissue being grown as a result. This is why it was, so-called, immortal.
Now, let’s get into the paper that disproved and challenged and shook and — (okay, I'll stop now) Alexis Carrell.
The paper + an explanation of cellular senescence
Okay, okay. So this might be a complex title. But you’ll understand in a second.
First, before we tackle the actual paper, let me explain what he actually discovered. You do know how he discovered it, as I talked about it above, but let me explain this term called “cellular senescence”.
Cellular senescence is a cell state reached once cells have divided a finite amount of times. This occurs in normal human somatic cells.
This occurs when our cells divide. When cell division occurs, we copy the DNA from the ends of our chromosomes. Unfortunately, this process isn’t perfect, and a little bit of DNA is cut off at the ends.
We don’t want to lose all this valuable DNA information, so our bodies have these things called telomeres. They’re like the aglets on the ends of our shoelaces (plastic things), and they’re bits of dispensible DNA information on the ends of our shoelaces.
After a while, our cells stop dividing because our telomeres have gotten too short. This happens after around 50–70 divisions, the Hayflick limit.
Other than telomere shortening/attrition, several factors can induce cellular senescence.
- One is oxidative stress. This is essentially a buildup of free radicals, which are molecules missing an electron.
- Another is mitogenic and oncogenic signaling. When oncogenes (cancer genes) signal, this additionally induces senescence!
Now that I’ve explained it, onto a decently brief summary of the paper.
He begins by stating the limitations of cell growth over an extended period of time (and redefining some basic terms).
“In general, if strains of human cells could be kept continuously under conditions of rapid growth for extended periods of time with the retention of the diploid configuration these objections would not apply.”
Aka if we were able to have cells divide forever and keep their diploid chromosomal configuration (shown below), none of his objections would apply.
Some terms:
- In vivo = experimental procedures performed outside a living organism
- In vitro = experimental procedures performed within a living organism
- Cell Strain = a population of cells subcultivated once or twice in vitro, which do go through cellular senescence!!
- Cell line = a cell culture formed from one cell.
- Primary cell = cells obtained from the original tissue that have been cultivated in vitro for the first time.
“It is the subject of this study to describe and characterize the development of 25 strains of human cells derived from fetal tissue which’ retain true diploidy for extended periods of cultivation without alteration. Specific attention will be given to those cell characteristics which serve to distinguish cell lines from cell strains.”
This is a graph of which cells are lost after a little while. This shows that cell strains live shorter and have finite lifespans compared to cell lines.
He then talks about cell strains (as they have an unlimited supply of any strain, other than the fact that they undergo cellular senescence), and the exact experiment he performed, which was the cancer cell experiment (as I mentioned above).
Then he suggests that cell strains should be used for human virus vaccine production.
TL;DR = He discovered that cell strains have a finite potential for cell division which is around 50–70 times. He additionally discovered that cancer cells are immortal.
Now that we know his story, and what he’s done, let me tell you a bit about his beliefs (what I’ve gathered from my conversations with him).
His beliefs
Let me surprise, shock, and enlighten you with a simple statement.
“Aging is a problem in physics, not biology.” — Leonard Hayflick
Now, you’re probably thinking:
“What? No. But cellular aging. He DISCOVERED cellular aging. How could he say it isn’t the cause of aging??”
Hold your horses. He’s not saying that it is NOT a problem in biology.
Here’s a quick video I made explaining this concept, but let me summarize it below.
Aging is a literal war between physics and biology. There’s the physics component — because of the wear and tear of the human body.
Confused? Let me explain. Just say you own a lab and as a result, you own test tubes. You’d have more test tubes that have been there for one year, than, say, 8 years, right?
This is because they break. Wear and tear along the way, scrapes, accidental dropping, you name it.
This applies to humans too. We suffer from diseases along the way, bruises, and the chance we might be run over by a car is dangerously high.
Additionally, our cells suffer from nanoscale thermal damage. Thermal energy characterized by magnetic nanoparticles screwing up the magnetic fields!!!
He even hosts a conference called “Aging is a problem in physics, not biology.”
Another belief of his is that aging is the second law of thermodynamics. The law states that the total entropy (a measure of the amount of energy which is unavailable to do work) of an isolated system can never decrease over time.
How is this connected to aging?
If we leave organisms that are aging alone, they go from youthful and having a low entropy to being old and having a high entropy.
If left alone, aging systems go spontaneously from youthful, low entropy and order to old, high entropy (work potential being lost) and disorder.
The impact he’s made
Okay, so you’ve PROBABLY guessed by now, but he’s made a HUGE impact, which I will rant about for the next few minutes.
From discovering senescent cells to all around being a great person (and a hilarious one), he’s inspired a ton of people (including myself), in the field of longevity.
Without him, we’d have no senescence labs (or we’d have started research VERY late). Without him, we’d still think our cells were immortal and not be able to tailor treatments to our cells and our cellular health.
We’d still think of aging as aging. Not biological versus chronological aging. Not cellular aging. Just those scary wrinkles that appear on your skin all of a sudden at 30.
People like Calvin Harley (telomeres) or Judy Campisi (anti-cancer genes), or Alex Zhavoronkov (AI + longevity) wouldn’t exist, because longevity wouldn’t really be a field.
When we’d joke about living forever, nobody would bring up zombies, because they’d be irrelevant. Let’s face it, he made them relevant.
He’s my literal inspiration and to all you longevity humans (is that grammar correct? whatever.) out there, he discovered senescent cells. That is HUGE.
He changed the course of action of the idea of living forever and helped bring us closer to that milestone.
Key Takeaways
- Leonard Hayflick is a longevity/microbiology researcher who discovered cellular senescence.
- Him discovering senescent cells was an accident, but it was an accident I’m sure he does not regret.
- He discovered that cell strains have a finite potential for cell division which is around 50–70 times.
- Aging is both physics and biology.
- He changed the course of action of the idea of living forever.
Thank you for reading my article! I hope it blew your mind! If you liked it, check out my other articles and I’d love it if you left a clap or a comment! Additionally, I’ll be speaking at Collision next week — If you want to connect while I’m there, drop me a note on my LinkedIn.
