Aetokthonotoxin, the Causative Agent of Vacuolar Myelinopathy, Uncouples Oxidative Phosphorylation due to Protonophore Activity

Aetokthonotoxin (AETX) is an emerging environmental toxin produced
by the freshwater cyanobacterium Aetokthonos hydrillicola. Accumulating in the food chain, it causes vacuolar myelinopathy,
a neurological disease affecting a wide range of wildlife characterized
by the development of large intramyelinic vacuoles in the white matter
of the brain. So far, the mode of action of AETX is unknown. After
discovering that AETX is cytostatic and arrests cancer cell lines
in the G1 phase, metabolomic profiling of AETX-treated
cells as well as an assessment of the physicochemical properties of
the compound suggested that AETX is a weakly acidic uncoupler of mitochondrial
respiration. We confirmed this hypothesis by in vitro assays on mammalian cells, finding that AETX has the expected effects
on mitochondrial network morphology, mitochondrial membrane potential,
and oxygen consumption rate, resulting in affected ATP generation.
We confirmed that AETX is capable of transporting protons across lipid
bilayers. In summary, we demonstrate that AETX is a protonophore that
uncouples oxidative phosphorylation in mitochondria, which is the
primary event of AETX intoxication.