Mitochondria

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Introduction to mitochondria

Basic biology teaches that cells are the "building blocks of life" but a cell has building blocks too. These cell building blocks include organelles (organelles literally means little organs). In animal cells, mitochondria are among those organelles. Mitochondria are found in every cell that has a nucleus. In the human body, that means mitochondria are present in every cell except red blood cells.

Mitochondria (the plural of mitochondrion) are often referred to as the “powerhouses of the cell” or “the energy factories of the cell.” They create energy for the cell, thus for our bodies. Think of mitochondria as the digestive system of a cell: they take in nutrients, break them down, and keep the cell full of energy.

The energy that mitochondria create is called adenosine triphosphate (ATP). Mitochondria make ATP through a sequence of reactions called the Krebs cycle, also known as the citric acid cycle or TCA cycle (tricarboxylic acid cycle). The final and perhaps most important step of this Krebs Cycle is called the electron transport chain where a majority of the ATP is created. Along with ATP, mitochondria also release byproducts like carbon dioxide, water, and free radicals. In moderation, free radicals can help us fight infection, but in excess they are injurious, they damage cell tissue and cause inflammation. ApoEε4s are already pro-inflammatory, so it’s in our best interest to keep free radical production, thus inflammation, down.

There are many mitochondria in the body, they make up 10% to 20% of the body by weight. Mitochondria are always working, at any given moment in time a person will only have 6 seconds of ATP left in the body. A person can go 3 days without water, but can’t go more than 6 seconds without ATP. That’s why cyanide is effective as a poison, it disrupts the electron transport chain of the mitochondria.

Mitochondria generate energy for the cell. Some cells need more energy than others, so those cells have more mitochondria. A cell can have hundreds to several thousand mitochondria depending on the function of the cell. The brain, heart, and retina have the most mitochondria and are the ones to suffer first when energy demand exceeds supply. Mitochondria lose their efficiency and become progressively dysfunctional with age. Mitochondrial dysfunction is a key factor in a myriad of diseases, including neurodegenerative and metabolic disorders.

The fundamental units of the brain and nervous system, neurons, require massive amounts of energy to function and can die if they don’t have a constant supply of ATP. To put things in perspective, the brain only makes up 3% of a body's weight, but it uses up 25% of the body's energy and it needs energy 24 hours a day. Anything that disrupts or impairs the brain’s ability to fuel itself has implications on cognition. The first priority of the mitochondria is to keep your cells oxygenized and blood pumping, in other words, basic survival, other functions such as cognitive thinking, is a secondary task, so cognition will suffer in order if mitochondria are unable to keep up with all their demands.

Degraded mitochondria is a hallmark of Alzheimer’s. Whether or not the poorly functioning mitochondria is causing Alzheimer’s is still under discussion, but regardless of if degraded mitochondria are causing, or a consequence, of Alzheimer’s, assuredly optimal mitochondria health sets the foundation for overall health and clear thought.

Mitochondria are shaped to maximize their energy production. They are made of two membranes: an outer membrane that cover the organelle, like a skin, and the inner membrane with multiple folds for increased surface area for chemical reactions to occur. Although typically represented as that bean-like shape in the accompanying graphic, mitochondria are very dynamic, they can change shape, interconnect like a power grid, travel within a cell (a neuronal axon can be a meter long, and mitochondria can travel from the cell body to the extreme end of the synapse where the energy is needed and then back), they can divide to increase their numbers, or fuse with other mitochondrion, all to accommodate the needs of the cell.

It is thought that mitochondria descended from independent bacteria, so as organelles, they act a little different but they live symbiotically inside a cell now. Mitochondria have their own DNA and send DNA coded instructions to the nucleus of the cell and vice versa. While a cell has just one nucleus with one genome, there are many mitochondria in a cell each carry multiple genome copies and these copies vary within a cell. Within one person some mitochondria genomes might be healthy, but other defective, and different cells can have different proportions of affected mitochondria within them. In addition to producing ATP, mitochondria play other crucial roles including calcium homeostasis, metabolism, reactive oxygen species generation, apoptosis (determining which cells should die), intercellular communications, and stress responses.

It doesn’t appear that ApoEε4s have weaker mitochondria, but there is at least one study that identified ApoE4 as more sensitive than E3s or E2s to the damaging free radicals that the mitochondria produce. Therefore it is advisable that ApoEε4s employ extra diligence in strategies to maximize the health of one’s mitochondria. How well your mitochondria function and age depend on three basic components:

• The mitochondria you inherited. Inheritance determines an individual's baseline mitochondrial function and durability. Mitochondrial DNA is inherited solely from the mother. This is why risk for Alzheimer’s Disease is higher in people who have a maternal history of it.
• What you’re exposing your mitochondria to that causes dysfunction, i.e. nutritional deficiencies, hormonal deficiencies, toxins, stress, etc.
• What you’re exposing your mitochondria to keep them running efficiently and/or making them stronger.