Modern Human Plasticity Notes

Modern Human Plasticity

Epigenetic Modifications

  • Chemical tags present in DNA.
  • Sensitive to environmental factors:
    • Toxins and pollutants.
    • Diet.
    • Social stress.
  • Can switch genes "on" or "off."
  • Can enhance or suppress gene expression.

Histone Modifications

  • Histones are proteins that help make up chromosomes.
  • Serve as "spools" that the DNA winds itself around.
  • Influences DNA replication, transcription, and repair.

DNA Methylation

  • DNA methylation – addition of a methyl group to the DNA strand.
  • Usually suppresses gene expression.
  • Can sometimes enhance gene expression.

Dutch "Hunger Winter" Family Studies

  • Long term study of people born during and after the 1944 – 1945 Dutch famine.
  • IGF2 gene: insulin-like growth factor protein.
    • Essential for fetal growth/development.
    • Plays a role in cardiovascular disease and some cancers.
  • Compared people exposed to famine prenatally with their siblings who were not exposed.
  • Less methylation in the IGF2 gene for exposed siblings.

Systemic Racism

  • Human races are social categories.
  • Ideas about race permeate every aspect of society and have real biological consequences:
    • Medical biases.
    • Access to resources.
    • Social stress.

Epigenetic Aging and Stress

  • Locations where methyl groups are added to DNA vary with age.
  • Can be used to predict “cellular age”.
  • Less methylation as cells age.
  • Accelerated epigenetic ageing in response to stress:
    • Mice.
    • Veterans with PTSD (N = 339).
    • African American males (N = 392).

Stress and the HPA Axis

  • NR3C1 gene: helps to regulate the “fight-or-flight” response.
  • Depression during pregnancy associated with increased methylation of NR3C1 gene in infants.
  • DNA methylation can impede transcription of NR3C1.
  • Improper regulation of cortisol.
  • Compromised immune function.

The Good News!

  • Many epigenetic changes may be reversible.
  • Socioeconomic improvements over the lifespan.
  • Less discrepancies between epigenetic and chronological age.
  • Regulation of enzymes that play a role in DNA methylation.
  • Reversal of stress-induced changes in mice.
  • Already employed in human treatments for cancer.