One of the most important encounters in the history of life took place, long before the earliest animals swam through the water-covered surface of Earth’s ancient past. Our oldest ancestor engulfed a primitive bacterium, a solo, free-floating cell. The two fused to form a mutually beneficial relationship, more than billions of years that lasted. The latter providing a comfortable and safe home, and the former becoming a powerhouse, fueling the processes necessary to maintain life.
To date, this is the best hypothesis for how the mitochondria (organelles) or cellular components came to be. Within the body today, trillions of these bacterial descendants live, churning out ATP, the molecular energy source that sustains our cells. Despite being inextricably integrated into the human body, remnants of their bacterial past are carried by mitochondria, such as their own set of DNA.
These features make mitochondria both a potential source of problems and a critical element of our cells. Mitochondrial DNA harbors mutations. Mitochondria’s many functions are disrupted by age, stress, and other factors, and molecules can be released by the mitochondrial injury similar to that made by bacteria. They can be mistaken by the immune system as foreign invaders, triggering a harmful inflammatory response against own body cell.
There is one organ in the body that is vulnerable to mitochondrial damage is the brain. According to Andrew Moehlman, a postdoctoral researcher who studies neurodegeneration at the US National Institute of NINDS, “The more energetically demanding a cell is, the more mitochondria they have, and the more critical that mitochondria health is — so there’s more potential for things to go wrong.” Each neuron can have up to 2 million mitochondria, according to some estimates.
Now many scientists are focusing on the contributions of mitochondria in brain health. Studies in lab animals and humans suggest these organelles could be the important factors in virtually every type of brain disorder. This includes schizophrenia, depression, autism, Parkinson’s.