ATP bioenergetics and fatigue in young adults with and without major depression.

Fatigue is a pervasive and difficult-to-treat symptom of major depressive disorder (MDD) that contributes to disability. Understanding this problem in its earlier stages will be critical for averting long-term negative outcomes. To investigate the molecular roots of fatigue in early-stage depression, the current work measured bioenergetic mechanisms, with a focus on adenosine triphosphate (ATP), in brain and blood cells in young adults with MDD versus healthy controls (HC). To measure ATP concentration and ATP production rate in the visual cortex, we utilized (31)P magnetic resonance spectroscopy imaging with magnetization transfer ((31)P MRSI-MT) at 7 Tesla, with and without gamma-ATP resonance saturation. ATP level was also measured in peripheral blood mononuclear cells (PBMCs) at rest and after serial addition of mitochondrial inhibitors. Out of 25 participants (mean age 21.8 years), usable data were available for 18 participants for imaging (9 per group); 24 for PBMCs (13 HC; 11 MDD). The MDD group demonstrated higher ATP production rate in the visual cortex than HC, which correlated positively with Fatigue Severity Scale (FSS) scores. ATP concentrations in PBMCs were higher in MDD than HC, and also correlated with FSS scores. After mitochondrial uncoupling, PBMCs in the MDD group had a lower capacity for ATP production than HC. For the first time, we demonstrate an ATP biosignature of fatigue in young adults with MDD that is visible in both brain and peripheral blood. The findings suggest a compensatory mechanism that occurs early in the disease stage.