Previously, it was believed that human beings were born with the complete set of neurons that they would need for their entire lifetime and were incapable of forming new neurons later in life. But new evidence has contradicted this theory and we now know that human beings are capable of forming new neurons in later life. In this brief, we shall discuss what kills brain cells, the mechanisms through which this happens and the implications of brain deterioration.
What is neurodegeneration?
Neurons are the basic working unit of the brain; they may also be called brain cells. They transmit information to other neurons, muscles or glands.
During intra uterine life and shortly after birth, the nervous system is created in humans with 50% more neurons. These extra neurons are degraded through a programmed cell death mechanism known as apoptosis. Later in life, neuronal death that is unprogrammed and deleterious can happen; this is referred to as necrotic cell death to differentiate it from apoptosis. It may occur following traumatic brain injury, inflammation, exposure to environmental toxins, infections or genetic mutations.
Neurodegeneration is the progressive degradation of brain cells through necrotic processes. When this happens, the brain loses some key functions such as memory, cognition, judgment and intelligence. Neurodegeneration is a key element in the development of several chronic illnesses that affect the brain such as Alzheimer’s, Parkinson’s, dementia and Huntington disease. As much as these diseases differ in their presentation, the changes that happen at a cellular level are closely interlinked. Understanding the causes of brain deterioration is helpful in ameliorating the above-mentioned diseases.
What causes neurodegeneration?
The real triggers for neurodegeneration are hazy; however, a few factors have shown a positive correlation. Scientists are continuously looking into these factors in the hope that they can find possible cures for neurodegenerative diseases. The key factors include aging, exposure to toxic substances, inflammation, infections, genetic mutations and traumatic injuries. We shall look at a few of these factors.
· Aging
There are quite a few theories that have attempted to explain cognitive decline as a person age. Some theorists have also argued against the notion that brain deterioration is a natural process of aging. Whichever the case is, we are aware that most degenerative diseases have a late onset making it apparent that brain deterioration has something to do with aging.
Aging is associated with mitochondrial mutations and oxidative stress which occur over time. These two factors have been linked to neurodegeneration. Loss of mitochondrial function can also contribute to an accumulation of toxins in the brain. These toxins can kill brain cells.
· Buildup of toxins in the brain
Toxins can accumulate in the brain for several reasons such as injury, inflammation and infections. Chemical toxicity results in necrotic cell death. For example, the buildup of proteins tau and amyloid in Alzheimer’s disease results in neurodegeneration.
· Genetic mutations
Researchers at the University of Michigan have discovered a lipid molecule PI(3,5)P2 that is vital for the survival of nervous system cells. When this molecule undergoes mutation or is absent, brain cells begin to die.
· Autophagic block
Autophagy is a process through which the body gets rid of damaged cells by delivering them to lysosomes for degradation. In autophagy, defective cells are pushed out, so the brain remains “clean.” But when autophagy has been blocked, normal cells are broken down and thrown out leading to neurodegeneration. Science has confirmed that mutations of autophagic cells promote neurodegeneration. Alzheimer’s disease and Parkinson’s disease are both linked to defects in the autophagic pathways.
It is clear that all these factors that cause brain cells to die are interrelated. In some cases, neurons begin to malfunction and lose communication with other neurons and glands. When this happens, the symptoms will be similar to those that appear when brain cells have been destroyed.
Implications of neurodegeneration
Neurodegeneration is the trigger for the development and progression of neurodegenerative diseases. In trying to find a cure for neurodegenerative diseases, scientists have been forced to investigate the process of reversing or inhibiting neurodegeneration.