Serum sulfate level and Slc13a1 mRNA expression remain unaltered in a mouse model of moderate vitamin D deficiency.

Sulfate is essential for healthy foetal growth and neurodevelopment. The SLC13A1 sulfate transporter is primarily expressed in the kidney where it mediates sulfate reabsorption and maintains circulating sulfate levels. To meet foetal demands, maternal sulfate levels increase by twofold in pregnancy via upregulated SLC13A1 expression. Previous studies found hyposulfataemia and reduced renal Slc13a1 mRNA expression in rodent models with either severe vitamin D deficiency or perturbed vitamin D signalling. Here we investigated a mouse model of moderate vitamin D deficiency. However, serum sulfate level and renal Slc13a1 mRNA expression was not decreased by a moderate reduction in circulating vitamin D level. We confirmed that the mouse Slc13a1 5'-flanking region was upregulated by 1,25(OH)2D3 using luciferase assays in a cultured renal OK cell line. These results support the presence of a functional VDRE in the mouse Slc13a1 but suggests that moderate vitamin D deficiency does not impact on sulfate homeostasis. As sulfate biology is highly conserved between rodents and humans, we proposed that human SLC13A1 would be under similar transcriptional regulation by 1,25(OH)2D3. Using an online prediction tool we identified a putative VDRE in the SLC13A1 5'-flanking region but unlike the mouse Slc13a1 sequence, the human sequence did not confer a significant response to 1,25(OH)2D3 in vitro. Overall, this study suggests that moderate vitamin D deficiency may not alter sulfate homeostasis. This needs to be confirmed in humans, particularly during pregnancy when vitamin D and sulfate levels need to be maintained at high levels for healthy maternal and child outcomes.

Molecular analysis of the human placental cysteine dioxygenase type 1 gene.

Sulfate is essential for healthy fetal growth and development. Cysteine dioxygenase type 1 (CDO1) plays an important role in the catabolism of cysteine to sulfate. Cdo1 knockout mice exhibit severe and lethal fetal phenotypes but the involvement of CDO1 gene variants in human development is unknown. We searched the NCBI and Ensembl gene databases and identified four alternatively spliced CDO1 coding mRNA transcripts, as well as 148 validated CDO1 gene variants, including 138 missense, 6 nonsense, 1 frameshift, 1 in-frame deletion, and 2 splice site variants. In silico analyses predicted 68 of the missense variants to be deleterious to CDO1 protein structure and function. We examined the relative abundance of the four CDO1 coding mRNA transcripts in human term placentas using qRT-PCR. CDO1 mRNA variant 2 was the most abundant transcript, with intermediate levels of variant 4 and lower levels of variants 1 and 3. Using in situ hybridization, we localised CDO1 mRNA expression to the syncytiotrophoblast layer of human term placenta. To investigate the regulation of CDO1 gene expression, we analysed the transcriptional activity of the human CDO1 5'-flanking region in the JEG-3 placental cell line using luciferase reporter assays. Transcriptional activities were identified in the regions -5 to -269 and - 269 to -1200 nucleotides upstream of the CDO1 transcription initiation site. Mutational analyses of a single nucleotide polymorphism -289C > G that is common in the general population (allele frequency = 0.37) and a putative transcription factor binding motif (CCAAT enhancer binding protein beta) did not alter transcriptional activity of the CDO1 5'-flanking region. Collectively, this study provides an overview and analysis of human CDO1 for future investigations of this gene in human health.