Mitochondria are critical for the function and maintenance of myelinated axons notably through
Adenosine triphosphate (
ATP) production. A direct by-product of this
ATP production is
reactive oxygen species (ROS), which are highly deleterious for neurons. While
ATP shortage and ROS levels increase are involved in several
neurodegenerative diseases, it is still unclear whether the real-time dynamics of both
ATP and ROS production in axonal mitochondria are altered by axonal or demyelinating neuropathies. To answer this question, we imaged and quantified mitochondrial
ATP and
hydrogen peroxide (H2O2) in resting or stimulated peripheral nerve myelinated axons in vivo, using genetically-encoded
fluorescent probes, two-photon time-lapse and CARS imaging. We found that
ATP and H2O2 productions are intrinsically higher in nodes of Ranvier even in resting conditions. Axonal firing increased both
ATP and H2O2 productions but with different dynamics: ROS production peaked shortly and transiently after the stimulation while
ATP production increased gradually for a longer period of time. In neuropathic MFN2R94Q mice, mimicking Charcot-Marie-Tooth 2A disease, defective mitochondria failed to upregulate
ATP production following axonal activity. However, elevated H2O2 production was largely sustained. Finally, inducing
demyelination with
lysophosphatidylcholine resulted in a reduced level of
ATP while H2O2 level soared. Taken together, our results suggest that
ATP and ROS productions are decoupled under neuropathic conditions, which may compromise axonal function and integrity.