The fatty acid desaturase (FADS) gene family at 11q12-13.1 includes FADS1 and FADS2, both known to mediate biosynthesis of omega-3 and omega-6 long-chain polyunsaturated fatty acids (LCPUFA). FADS3 is a putative desaturase due to its sequence similarity with FADS1 and FADS2, but its function is unknown. We have previously described 7 FADS3 alternative transcripts (AT) and 1 FADS2 AT conserved across multiple species. This study examined the effect of dietary LCPUFA levels on liver FADS gene expression in vivo and in vitro, evaluated by qRT-PCR. Fourteen baboon neonates were randomized to three diet groups for their first 12 weeks of life: C: Control, no LCPUFA; L: 0.33% docosahexaenoic acid (DHA)/ 0.67% arachidonic acid (ARA) (w/w); and L3: 1.00% DHA/ 0.67% ARA (w/w). Liver FADS1 and both FADS2 transcripts were downregulated by at least 50% in the L3 group compared to controls. In contrast, FADS3 AT were upregulated (L3>C), with four transcripts significantly upregulated by 40% or more. However, there was no evidence for a shift in liver fatty acids to coincide with increased FADS3 expression. Significant upregulation of FADS3 AT was also observed in human liver-derived HepG2 cells after DHA or ARA treatment. The PPARγ antagonist GW9662 prevented FADS3 upregulation, while downregulation of FADS1 and FADS2 was unaffected. Thus, FADS3 AT were directly upregulated by LCPUFA by a PPARγ-dependent mechanism unrelated to regulation of other desaturases. This opposing pattern and mechanism of regulation suggests a dissimilar function for FADS3 AT compared to other FADS gene products.

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Fatty acid desaturase 1 and 2 (FADS1 and FADS2) code for the key desaturase enzymes involved in the biosynthesis of long chain polyunsaturated fatty acids in mammals. FADS3 shares close sequence homology to FADS1 and FADS2 but the function of its gene product remains unknown. Alternative transcripts (AT) generated by alternative splicing (AS) are increasingly recognized as an important mechanism enabling a single gene to code for multiple gene products. We report the first AT of a FADS gene, FADS3, generated by AS. Aided by ORF Finder, we identified putative coding regions of eight AT for FADS3 with 1.34 kb (classical splicing), 1.14 (AT1), 0.77 (AT2), 1.25 (AT3), 0.51 (AT4), 0.74 (AT6), and 1.11 (AT7). In addition we identified a 0.51 kb length transcript (AT5) that has a termination codon within intron 8-9. The expression of each AT was analyzed in baboon neonate tissues and in differentiated and undifferentiated human SK-N-SH neuroblastoma cells. FADS3 AT are expressed in 12 neonate baboon tissues and showed reciprocal increases and decreases in expression changes in response to human neuronal cell differentiation. FADS3 AT, conserved in primates and under metabolic control in human cells, are a putative mediator of LCPUFA biosynthesis and/or regulation.

The fatty acid desaturase genes (FADS1 and FADS2) code for enzymes required for synthesis of omega-3 and omega-6 long-chain polyunsaturated fatty acids (LCPUFA) important in the central nervous system, inflammatory response, and cardiovascular health. SNPs in these genes are associated with numerous health outcomes, but it is unclear how genetic variation affects enzyme function. Here, lymphoblasts obtained from Japanese participants in the International HapMap Project were evaluated for association of expression microarray results with SNPs in the FADS gene cluster. Six SNPs in the first intron of the FADS2 gene were associated with FADS1 expression. A 10-SNP haplotype in FADS2 (rs2727270 to rs2851682) present in 24% of the population was associated with lower expression of FADS1. A highly conserved region coinciding with the most significant SNPs contained predicted binding sites for SREBP and PPARγ. Lymphoblasts homozygous for either the major or minor haplotype were treated with agonists for these transcription factors and expression of FADS1 and FADS2 determined. Simvastatin and the LXR agonist GW3965 both upregulated expression of FADS1 and FADS2; no response was found for PPARγ agonist rosiglitazone. The minor haplotype homozygotes had 20–40% higher induction of FADS1 and FADS2 after simvastatin or GW3965 treatment. A 22 bp polymorphic insertion-deletion (INDEL) was found 137 bp downstream from the putative sterol response element, as well as a 3 or 1 bp INDEL 81–83 bp downstream. All carriers of the minor haplotype had deletions while all carriers of the major haplotype had insertions. Individuals carrying the minor haplotype may be vulnerable to alterations in diet that reduce LCPUFA intake, and especially responsive to statin or marine oil therapy.

The nicotinamide adenine dinucleotide hydrolase (NADase) sterile alpha toll/interleukin receptor motif containing-1 (SARM1) acts as a central executioner of programmed axon death and is a possible therapeutic target for neurodegenerative disorders. While orthosteric inhibitors of SARM1 have been described, this multidomain enzyme is also subject to intricate forms of autoregulation, suggesting the potential for allosteric modes of inhibition. Previous studies have identified multiple cysteine residues that support SARM1 activation and catalysis, but which of these cysteines, if any, might be selectively targetable by electrophilic small molecules remains unknown. Here, we describe the chemical proteomic discovery of a series of tryptoline acrylamides that site-specifically and stereoselectively modify cysteine-311 (C311) in the noncatalytic, autoregulatory armadillo repeat (ARM) domain of SARM1. These covalent compounds inhibit the NADase activity of WT-SARM1, but not C311A or C311S SARM1 mutants, show a high degree of proteome-wide selectivity for SARM1_C311 and stereoselectively block vincristine- and vacor-induced neurite degeneration in primary rodent dorsal root ganglion neurons. Our findings describe selective, covalent inhibitors of SARM1 targeting an allosteric cysteine, pointing to a potentially attractive therapeutic strategy for axon degeneration-dependent forms of neurological disease.