User:Selterma/sandbox

Major Depressive Disorder
The full pathology of Major Depressive Disorder (MDD) has yet to be fully elucidated, however research on Brain Derived Neurotrophic Factor (bdnf) has provided evidence of its relation to MDD and its control by epigenetic modification. bdnf is a protein that is part of the neurotrophin class of growth factors that acts to induce neuron regeneration and neuroplasticity for nerves in both the central and peripheral nervous system. It does this by binding to the trkB receptor, which is a protein receptor found in the cell membrane of cells located in the central and peripheral nervous system, however trkB is most predominantly found in the brain. Once bdnf is bound to trkB, a cascade of downstream effectors act to increase cell generation and plasticity.

bdnf acts as a neuroprotective factor on sections of the HPA axis whose degeneration may cause depression. While human studies have demonstrated decreased levels of bdnf in patients who have MDD or have committed suicide, murine studies have painted a clearer picture of the epigenetic mechanisms relating bdnf to MDD. The main exogenic contributing factor to epigenetic remodelling of bdnf in the HPA axis is stress, which is a known mediating factor of depression. Corticosteroid hormone release as a result of stress acts to methylate at a repressive histone mark on histone 3 at promoter regions of the BDNF gene. Therefore, as a subject is exposed to chronic stress, glucocorticoids may act to cause both acute neural atrophy as well as long-term histone methylation and therefore under-expression, leading to depression.