The atypical sphingolipid SPB 18:1(14Z);O2 is a biomarker for DEGS1 related hypomyelinating leukodystrophy

Sphingolipids (SL) represent a structurally diverse class of lipids that are central to cellular physiology and neuronal development and function. Defects in the sphingolipid metabolism are typically associated with nervous system disorders. The C4-dihydroceramide desaturase (DEGS1) catalyzes the conversion of dihydroceramide to ceramide, the final step in the SL de-novo synthesis. Loss of function mutations in DEGS1 cause a hypomyelinating leukodystrophy, which is associated with increased plasma dihydrosphingolipids (dhSL) and with the formation of an atypical SPB 18:1(14Z);O2 metabolite. Here, we characterize two novel DEGS1 variants of unknown significance (VUS), provide a structural model with a predicted substrate binding site, and propose a regulatory link between DEGS1 and fatty acid desaturase 3 (FADS3). Both VUS involve single amino acid substitutions near the C-terminus within conserved regions of the enzyme. Patient 1 (p.R311K variant) shows severe progressive tetraspasticity, intellectual disability, and epilepsy in combination with brain magnetic resonance imaging (MRI) findings, typical for DEGS1-related leukodystrophy. Patient 2 (p.G270E variant) presents with delayed psychomotor development, oculomotor apraxia, and a normal brain MRI. Plasma from the p.R311K carrier showed a significantly elevated dhSL species and the presence of SPB 18:1(14Z);O2, while the plasma SL profile for the p.G270E variant was not altered. This suggests the p.R331K variant is pathogenic, while the p.G270E appears benign. As an increase in dihydroSL species is also seen in other pathological disorders of the SL metabolism, the SPB 18:1(14Z);O2 seems to be a more specific biomarker to discriminate between pathogenic and benign DEGS1 variants.

Polymorphism and expression level of the FADS3 gene and associated with the growth traits in Hu sheep

Growth traits are the economically important traits of sheep, and screening for genes related to growth and development is helpful for the genetic improvement of ovine growth traits. The fatty acid desaturase 3 (FADS3) is one of the important genes affecting the synthesis and accumulation of polyunsaturated fatty acids in animals. In this study, the expression levels of the FADS3 gene and polymorphism of the FADS3 gene associated with growth traits in Hu sheep were detected using quantitative real-time PCR (qRT-PCR), Sanger sequencing, and KAspar assay. The result showed that the expression levels of the FADS3 gene were widely expressed in all tissues, and the expression level of FADS3 in the lung was significantly higher than in other tissues (p < .05). Then, the polymorphism locus g. 2918 A > C was detected in intron 2 of the FADS3 gene, and associated analysis showed that the mutation in the FADS3 gene was associated significantly with growth traits (including body weight, body height, body length, and chest circumference, p < .05). Therefore, individuals with AA genotype showed significantly better growth traits than those with CC genotype, and FADS3 gene could be a candidate gene for improving growth traits in Hu sheep.

Investigation of FADS Gene Cluster Single Nucleotide Polymorphisms in End-Stage Renal Disease Compared With Normal Controls

End-stage renal disease (ESRD) is a public health problem with a high burden. The condition is associated with abnormalities in lipid metabolism. The fatty acid desaturase (FADS) gene cluster includes three genes that are significantly correlated with a number of pathologic conditions related to abnormal lipid levels. In the current study, we genotyped rs174556, rs99780, and rs7115739 single nucleotide polymorphisms within the FADS cluster in a population of ESRD patients and healthy controls. The rs174556 of the FADS1 gene and rs99780 of the FADS2 gene were not associated with the risk of ESRD in any inheritance model. However, the rs7115739 of FADS3 was associated with the risk of ESRD in all models except for the recessive model. The T allele of this SNP was significantly less prevalent among cases compared with controls [odds ratio (OR) (95% CI) = 0.44 (0.25–0.77), P value = 0.004]. GT and TT genotypes has been shown to decrease the risk of ESRD in a codominant model [OR (95% CI) = 0.49 (0.26–0.92) and OR (95% CI) = 0.18 (0.02–1.6), respectively; P value = 0.019]. In the dominant model, GT + TT status was associated with lower risk of ESRD [OR (95% CI) = 0.45 (0.24–0.82), P value = 0.0078]. Assessment of association between this SNP and risk of ESRD in an overdominant model revealed that GT genotype decreases the risk of this condition [OR (95% CI) = 0.5 (0.27–0.94), P value = 0.029]. Taken together, the rs7115739 of FADS3 is suggested as a putative modulator of the risk of ESRD in the Iranian population.

The 51 kDa FADS3 is secreted in the ECM of hepatocytes and blood in rat

The fatty acid desaturase (Fads) cluster is composed of three genes encoding for the Δ5- and Δ6-desaturases and FADS3. The two former proteins are involved in the fatty acid biosynthesis; the latter one shares a high sequence identity but has still no attributed function. In a previous work performed in rat, we described three isoforms of FADS3 expressed in a tissue-dependent manner. In the present study, we demonstrated a specific subcellular targeting depending on the isoform. In cultured hepatocytes, which mainly expressed the 51 kDa protein, FADS3 was unexpectedly present in the cytosolic fraction, but was also secreted in the extracellular matrix on fibronectin-containing fibers. The secretion pathway was investigated and we determined the presence of exosome-like vesicles on the FADS3-stained fibers. In parallel, FADS3 was detected in blood of hepatic vessel, and particularly in serum. In conclusion, this study demonstrated a very specific intra- and extracellular location of FADS3 in comparison with the Δ5- and Δ6-desaturases, suggesting a unique function for this putative desaturase, even if no activity has been yet identified neither in the extracellular matrix of hepatocytes nor in serum.