Introduction: Myalgic encephalomyelitis, or chronic fatigue syndrome (ME/CFS) is a devastating and poorly understood illness that is estimated to effect 0.1-2.8% of the population. Attempts to uncover the causative factors behind ME/CFS have been inconclusive, however a recent investigation has provided encouraging results, identifying a mitochondrial Complex V defect which may act as a precipitating factor in the disease. The Complex V defect is accompanied by other changes including elevated Target of Rapamycin Complex I (TORC1) signalling and elevated expression of mitochondrial proteins. This project therefore aims to determine if the mitochondrial Complex V defect is the causal factor of the other defects observed in ME/CFS cells.
Methodology: We manipulated Complex V function in the eukaryotic model Dictyostelium discoideum by genetically altering expression of ATP12, an essential assembly factor involved in Complex V biogenesis. We created 3 distinct groups of transformants, with antisense inhibition and wildtype overexpression groups featuring reduced and elevated expression of ATP12, respectively, and a W142R point mutant expression group that is associated with Complex V deficiency in humans. Mitochondrial function and respiration were investigated directly by assaying various parameters of mitochondrial activity, as well as the use of seahorse respirometry.
Findings: Our results indicate that impaired ATP12 function results in a downregulation in ATP consuming processes, demonstrated by elevated ATP steady state levels and reduced growth rates. Conversely, overexpression of ATP12 enhances mitochondrial activity, with increased growth rates and ROS production.
Conclusions: Functional impairments to Complex V result in various changes that denote a downregulation in ATP consuming processes, as well as compensatory increases in mitochondrial complex activity that may act to stabilise intracellular ATP levels. These findings suggest that altered Complex V function in ME/CFS is a contributing, but not causal factor in ME/CFS.