Monoamine oxidases in major depressive disorder and alcoholism

Monoamine oxidases play an integral role in brain function. Both monoamine oxidase A (MAO-A) and monoamine oxidase B (MAO-B) regulate neurochemistry by degrading monoamine neurotransmitters (serotonin, dopamine, and norepinephrine). Any alteration in MAO levels can have devastating effects on the brain and behavior by lowering or raising neurotransmitter levels and producing toxic reactive oxygen species. In this review article, MAO is examined in terms of function and genetic organization, with special focus on recent discoveries related to the transcriptional regulation of MAO. In recent studies, transcriptional regulation involves a repressor protein, R1, for MAO-A and an activator protein, KLF11 (a Krüppel-like factor; also referred to as transforming growth factor-beta early inducible gene 2, TIEG2), for both MAO-A and MAO-B, by binding to Sp/KLF sites in the core promoters of MAO and regulating MAO gene expression. Furthermore, KLF11 may influence MAO-B expression and augment glyceraldehyde-3 phosphate dehydrogenase (GAPDH) to upregulate MAO-B transcription upon exposure to ethanol. Finally, we review recent progress in MAO research and highlight the roles that MAOs play in several psychiatric conditions, including chronic stress, major depressive disorder and alcohol dependence. Further research in this area is needed to better understand MAOs, their transcription factors and signaling pathways in psychiatric illnesses in order to develop new strategies for pharmacological advancement.