Epigenetics and cortisol

• Epigenetics is the study of the changes in organisms that are caused

  by chemicals which modify gene expression rather than

  alteration of the genetic code itself.
• The chemical reactions can change the rate at which a gene is expressed, resulting in too much or too little of a particular protein.
• Chemical changes can be inherited in DNA
• Epigenetic modification example: DNA Methylation

  It is when a methyl group (CH3) is added to a cytosine nucleotide on

  the DNA of a gene. This causes the DNA to wrap too tightly around

  histone proteins - so the DNA cannot be ‘accessed’ by DNA

  polymerase for transcription (or therefore translation) of the protein

  to occur.

  In general over-methylation is associated with gene silencing

  (switching off genes) and under-methylation is associated with gene

  activation (switching on genes).
• Mental health issues:

  • Brain functions are now known to affected by epigenetics and changed gene expression.
  • Epigenetic changes are also known to be involved in various mental health issues such as depression, addiction and schizophrenia.
  • Many antidepressants work by changing gene expression. Some of these are thought to reverse the effects of DNA methylation.
• Childhood trauma:

  • Childhood trauma is an environmental factor that leaves an epigenetic mark on the brain.
  • There are links to the hormone cortisol that is released in response to stress. It is known that the average concentration of the hormone cortisol tends to be higher in adults who had traumatic childhoods, even if their mental health was healthy at the time of measuring.
• Cortisol:

  • Cortisol is a hormone that is released from the adrenal glands in response to stress; It has many functions such as increasing blood glucose levels and blood pressure.
  • The more stressed we are the more cortisol we produce.
  • Adults who had traumatic childhoods have higher concentrations of cortisol, which may increase their vulnerability to mental health issues
• Cortisol production is controlled by the hippocampus in the brain
• Cortisol production:

  1. Cortisol production is controlled by the hippocampus in the brain
  2. In response to stress the hippocampus sends impulses to the hypothalamus, which releases two hormones, corticotrophin-releasing hormone and arginine vasopressin.
  3. These 2 hormones stimulate the pituitary gland which responds by releasing the hormone adrenocorticotrophic hormone into the blood.
  4. When the cells of the adrenal glands take up this hormone, they release cortisol
• There is a negative feedback loop because as the cortisol circulates in the bloodstream it binds to glucocorticoid receptors on the hippocampus, which responds be sending nerve impulses to the hypothalamus, inhibiting it from releasing cortisol.

  This stops us from being constantly overstressed.
• Epigenetics can decrease gene expression so there is decreased proteins so decreased glucocorticoid protein receptors. This means the number of cortisol that can attach is not enough to cause the hippocampus to produce inhibitory impulses.
• cortisol = increased blood pressure and increased blood glucose levels
• Adults who suffered from traumatic childhoods are constantly overstressed. They produce too much cortisol all of the time.
• Epigenetics hypothesis:

  • one hypothesis is that terrible early childhood experiences change certain physical aspects of the brain during a key developmental period - this may have an epigenetic component which causes an alteration in gene expression in the brain, which predisposes adults to increased risk of mental illness