Environment Can Leave “Molecular Scars” Via Epigenetic Processes
A 2020 review article by researchers Julia Richetto and Urs Meyer in the journal Biological Psychiatry provides a good overview of the role epigenetic modifications play in schizophrenia and related disorders.
The article provides a powerful understanding of how the environment can induce long-lasting changes in the structure of DNA (not only in schizophrenia, but also in bipolar disorder). This process, known as epigenetics, can have life-long influences on brain chemistry and behavior, and remarkably, some of these epigenetic changes can even be transmitted to the next generation.
While the sequence of DNA that one inherits from one’s parents does not change over the course of one’s life, what can change is how loosely or tightly the DNA is wound around proteins called histones, making it easier or harder to transcribe the genetic material held there. The addition of a methyl group to DNA usually inhibits transcription, while the addition of an acetyl group to histones usually facilitates transcription. These alterations in the shape of the DNA that result from environmental exposures or behavior can be passed on through generations.
Richetto and Meyer describe these chemical changes to DNA as “molecular scars,” which are left when environmental stress occurs during sensitive developmental periods. For example, patients with schizophrenia who experienced stressors in early life have higher levels of the enzyme histone deacetylase than patients who had stress or trauma later in life. Histone deacetylase would remove the acetyl groups on histones, which would inhibit gene transcription.
Other factors that have been implicated in epigenetic modifications in schizophrenia, such as DNA methylation of key developmental pathways, include pre- or post-natal stress, a challenge to a mother’s immune system during pregnancy, pre- and post-natal nutrition, exposure to drugs or toxic substances, and cannabis use in adolescence.
Richetto and Meyer suggest that epigenetics may explain why schizophrenia (and we would add bipolar disorder) can differ so much across individuals, and may help researchers and clinicians determine how best to treat different individuals.
Editor’s Note: This editor has written about how epigenetic changes can mediate sensitization to the recurrence of life stressors, episodes of mood disorder, and bouts of substance abuse, each of which can drive illness exacerbation and progression in bipolar disorder (see the 2016 article by Robert M. Post in the journal Bipolar Disorders, “Epigenetic basis of sensitization to stress, affective episodes, and stimulants: implications for illness progression and prevention”).
The chemical changes to our DNA, histones, and microRNA emphasize how important it is to begin long-term preventative treatment starting after a first episode of mania. This not only helps limit episode recurrence and the accumulation of stressors and bouts of substance use that can cause illness deterioration, but also limit the placement of these “molecular scars” on our DNA. The key to treating bipolar disorder is: prevent episodes, protect the person and the brain.
