Developmental increase of aspartoacylase in oligodendrocytes parallels CNS myelination

Canavan disease, an autosomal-recessive neurogenetic disorder, is caused by mutations in aspartoacylase, an enzyme that deacetylates N-acetylaspartate to generate free acetate in the brain. Earlier studies have shown that aspartoacylase is primarily restricted to myelin synthesizing cells (oligodendroglia) in the CNS. These findings have led us to investigate the developmental expression of aspartoacylase gene in the rat brain in an attempt to shed more light on the role of this enzyme in myelination. In situ hybridization using a 35S riboprobe based on murine aspartoacylase cDNA was used in this study. The probe hybridized mostly to the white matter tracts with different densities depending on the age of the animal and region of the brain examined. Little or no hybridization signals were detected in the 1-day-old rats, whereas the signal was clearly detectable in most of the white matter regions of the CNS in the 11-day-old rats. The signal density markedly increased at postnatal day 17, the peak of myelination. Thereafter, the hybridization signals decreased somewhat but still could be observed in the adult animals. Thus, the developmental expression pattern of aspartoacylase gene in the postnatal brain closely parallels myelination in the CNS. In the CNS, the hybridization signal of ASPA appeared to be restricted primarily to oligodendrocytes, the primary myelin synthesizing cell type in the CNS. However, the signal was not detectable in rat sciatic nerve (Schwann cells) of the peripheral nervous system. These findings indicate that the role of N-acetylaspartate in myelin synthesis is restricted to the CNS. Furthermore, they provide additional support for the acetate deficiency hypothesis of Canavan disease and also make a stronger case for acetate supplementation as an immediate and inexpensive therapy for Canavan disease.