S cientists have long known that chronic stress increases the levels of certain hormones, but until the results were released from a recent National Institute of Mental Health (NIMH) study, the process was not understood.
Published in the February 2, 2009 issue of the Proceedings of the National Academy of Sciences, the findings reveal the mechanisms by which cells adaptto cope with sudden or extreme stress, and how repeated or prolonged exposure to stress is likely related to many physical and mental illnesses.
Cortisol, a type of hormone called a glucocorticoid, plays a key role in the brain’s ability to adapt and recover from injury. It also plays a part in getting hormone receptors to the right places, where brain chemicals exert their effects.
Recently scientists learned that glucocorticoid receptors (GRs) move into energy-producing structures in cells called mitochondria, in response to glucocorticoids.
Building on the GR findings, Jing Du, M.D., Ph.D., of the NIMH Mood and Anxiety Disorders Program (MAP) and her colleagues found that in brain cells of rats treated with corticosterone (the equivalent to human cortisol), GR latched onto Bcl-2, a protein that affects how substances get in and out of mitochondria. The GR/Bcl-2 complex moves into the mitochondria and regulates mitochondrial functions.
Brief increases of corticosterone improve mitochondrial functions, but high doses or long-term exposure led to decreased levels of GR and Bcl-2 in mitochondria. The results show that, at first, glucocorticoids boost mitochondrial functions and provide cells with more energy for coping with and adapting to acute challenges. This process appears to be critical in allowing a person to act quickly in an emergency.
However, chronic stress may lead to chronically elevated levels of glucocorticoids, which reduces cell functioning, via the interaction between GR/Bcl-2 and mitochondria. The decrease in proper cell function is at the root of some mental illnesses.