FA2H-dependent fatty acid 2-hydroxylation in postnatal mouse brain

Abstract

2-Hydroxy fatty acids are relatively minor species of membrane lipids found almost exclusively as N-acyl chains of sphingolipids. In mammals, 2-hydroxy sphingolipids are uniquely abundant in myelin galactosylceramide and sulfatide. Despite the well-documented abundance of 2-hydroxy galactolipids in the nervous system, the enzymatic process of the 2-hydroxylation is not fully understood. To fill this gap, we have identified a human fatty acid 2-hydroxylase gene (FA2H) that is highly expressed in brain. In this report, we test the hypothesis that FA2H is the major fatty acid 2-hydroxylase in mouse brain and that free 2-hydroxy fatty acids are formed as precursors of myelin 2-hydroxy galactolipids. The fatty acid compositions of galactolipids in neonatal mouse brain gradually changed during the course of myelination. The relative ratio of 2-hydroxy versus nonhydroxy galactolipids was very low at 2 days of age (z8% of total galactolipids) and increased 6-to 8-fold by 30 days of age. During this period, free 2-hydroxy fatty acid levels in mouse brain increased 5-to 9-fold, and their composition was reflected in the fatty acids in galactolipids, consistent with a precursor-product relationship. The changes in free 2-hydroxy fatty acid levels coincided with fatty acid 2-hydroxylase activity and with the upregulation of FA2H expression. Furthermore, mouse brain fatty acid 2-hydroxylase activity was inhibited by anti-FA2H antibodies. Together, these data provide evidence that FA2H is the major fatty acid 2-hydroxylase in brain and that 2-hydroxylation of free fatty acids is the first step in the synthesis of 2-hydroxy galactolipids.

Absence of 2-Hydroxylated Sphingolipids Is Compatible with Normal Neural Development But Causes Late-Onset Axon and Myelin Sheath Degeneration

“…Furthermore, upregulation of the FA2H gene expression correlates with the increase in HFA during postnatal brain development (Alderson et al, 2006). FA2H Ϫ/Ϫ mice lack HFA-GalC and HFA-sulfatide in the brain and peripheral nerves, confirming the hypothesis that FA2H is responsible for HFA-sphingolipid synthesis in the nervous system.…”

“…In the nervous system, FA2H is specifically expressed in myelinating cells, and the postnatal upregulation of FA2H expression follows a similar time course as described for oligodendrocyte-specific genes involved in the synthesis of the myelin sheath, e.g., CGT and PLP Alderson et al, 2006). Furthermore, upregulation of the FA2H gene expression correlates with the increase in HFA during postnatal brain development (Alderson et al, 2006).…”

“…It should be noted that HFA-sphingolipids are not detectable in neurons (Raghavan and Kanfer, 1972). Alderson et al (2006) found low amounts of FA2H protein in microglia, but the FA2H protein was not detectable in primary cultured astrocytes (Alderson et al, 2006). It therefore seems not very likely that absence of FA2H in other cell types is responsible for the behavioral phenotype of FA2H Ϫ/Ϫ mice.…”

FA2H is responsible for the formation of 2-hydroxy galactolipids in peripheral nervous system myelin

“…We previously demonstrated that FA2H is expressed in oligodendrocytes in the CNS (15). We further demonstrated that FA2H gene expression was upregulated ?400-fold during postnatal myelination in mouse brain in parallel with other myelin-associated genes.…”

“…In the biosynthesis pathway for 2-hydroxy galactolipids, fatty acid 2-hydroxylase (FA2H) is the major enzyme that catalyzes fatty acid 2-hydroxylation in the CNS (15). FA2H activity increases in the CNS during developmental myelination to provide precursors for the synthesis of myelin 2-hydroxy galactolipids.…”