Rebound effects of NCX3 pharmacological inhibition: A novel strategy to accelerate myelin formation in oligodendrocytes

The Na+/Ca2+ exchanger NCX3 is an important regulator of sodium and calcium homeostasis in oligodendrocyte lineage. To date, no information is available on the effects resulting from prolonged exposure to NCX3 blockers and subsequent drug washout in oligodendroglia. Here, we investigated, by means of biochemical, morphological and functional analyses, the pharmacological effects of the NCX3 inhibitor, the 5–amino-N-butyl-2–(4–ethoxyphenoxy)-benzamide hydrochloride (BED), on NCXs expression and activity, as well as intracellular [Na+]i and [Ca2+]i levels, during treatment and following drug washout both in human MO3.13 oligodendrocytes and rat primary oligodendrocyte precursor cells (OPCs). BED exposure antagonized NCX activity, induced OPCs proliferation and [Na+]i accumulation. By contrast, 2 days of BED washout after 4 days of treatment significantly upregulated low molecular weight NCX3 proteins, reversed NCX activity, and increased intracellular [Ca2+]i. This BED-free effect was accompanied by an upregulation of NCX3 expression in oligodendrocyte processes and accelerated expression of myelin markers in rat primary oligodendrocytes. Collectively, our findings show that the pharmacological inhibition of the NCX3 exchanger with BED blocker maybe followed by a rebound increase in NCX3 expression and reversal activity that accelerate myelin sheet formation in oligodendrocytes. In addition, they indicate that a particular attention should be paid to the use of NCX inhibitors for possible rebound effects, and suggest that further studies will be necessary to investigate whether selective pharmacological modulation of NCX3 exchanger may be exploited to benefit demyelination and remyelination in demyelinating diseases.