Quantification and localisation of new myelin synthesis using deuterium oxide and high resolution mass spectrometry

Myelin is a lipid-rich membrane wrapping around neuronal axons and is essential for neurological functions in vertebrates. There is unmet need for therapeutics that stimulate myelin synthesis to treat demyelinating disorders such as multiple sclerosis, however current methods for assessing myelination do not distinguish newly-synthesised from pre-existing myelin. This study describes a mass spectrometry based method to measure new myelin synthesis in adult mice. 25% deuterium oxide was administered for two weeks in the drinking water of mice fed normal chow, chow containing the demyelinating toxin cuprizone, or during spontaneous remyelination following cuprizone withdrawal. Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging was used to localize and quantify the newly synthesised, deuterated myelin lipids in sagittal brain sections. While deuteration was minimal for the myelin-enriched hexosylceramides and phoshatidylethanolamine plasmalogens under basal conditions, deuterated isotopologues of these lipids were found at significantly greater abundance during remyelination, and were localised primarily to the corpus callosum. The method decribed herein provides the means to spatially profile dynamic lipid synthesis in complex tissue environments and will be broadly applicable to many biological contexts requiring monitoring of lipid metabolism.