What is the cell life cycle?
Three billion years ago, the only life forms on Earth were single-celled cyanobacteria. They are so simple that there are still unchanged versions of these cyanobacteria at the bottom of the oceans, with no need to evolve for hundreds of millions of years.
Fast forward about 1025 seconds, and blue whales now have as many cells as seconds have passed since those first bacteria came into existence. In the beginning, if a cell died, then the whole organism died. Now, adult humans lose around 70,000,000,000 (that’s billion, with a B) cells every day. How do we survive if literally billions of our cells die every day?
Actually, it’s the only way we survive.
Adult humans have around 37,000,000,000,000 (thirty-seven trillion) cells. There are hundreds of billions of chemical reactions that occur every second inside each of our bodies. Things are bound to go wrong every once in awhile. Luckily, evolution planned for just these occasions, and it gave us a tool called apoptosis to help us out of sticky situations. When a cell starts to malfunction, or it has surpassed the average cellular life expectancy of 5-10 days, or a mutation has occurred that may lead to cancer, apoptosis comes in to save the day.
What is apoptosis?
Apoptosis is sometimes referred to as “programmed cell death”. In essence, whenever a cell senses that something is wrong within itself, several proteins are released within the cell that initiate a chemical cascade.
These enzymes and hormones are stored in the mitochondrial membrane, and when they are released, they rapidly dissolve DNA and cell organelles, packing them neatly within fragments of the former cell membrane to be digested by neighboring cells. In this way, whatever caused the cell to die in the first place is contained and no inflammatory response can endanger the surrounding cells.
Apoptosis is still not fully understood, as there are several pathways that lead to the execution phase. Some are immune-cell mediated while others occur fully within the cell. In either case, proteins called caspases are the active mediators of apoptosis. First, procaspases ensure that the cell really needs to die, and then they activate executioner caspases that actually dismantle the parts of the cell and degrade DNA.
How is the endocannabinoid system (ECS) involved?
As with most homeostatic mechanisms, this one is controlled by the endocannabinoid system. The initiation of production of caspases and the actual process of their biosynthesis are both carried out by endocannabinoid signalling. CB1 and 2 receptors function to either increase or decrease the activity of cAMP and MAP kinase, which are two enzymes that are necessary for the secretion of caspases, and therefore the success of apoptosis.
The acute process of apoptosis is relatively well-understood, but the underlying mechanisms that control it and maintain its balance are only beginning to have their surfaces scratched. One phenomenon that is still unexplainable is the near perfect correlation between apoptosis and replication; the number of cells apoptosed and the number of new cells on any given day is usually within only a few thousand individual cells. The mechanism that keeps these two processes so tightly connected to one another is incredibly complex, but so far researchers believe that the endocannabinoid system is heavily implicated in it.