Novel SLC5A6 mutations lead to B lymphocyte maturation defects with metabolic abnormality rescuable by biotin replenishment

We characterized a family diagnosed with immunodeficiency disease presenting with low immunoglobulin levels and skin dyskeratosis. Exome sequencing revealed compound heterozygous missense variants in SLC5A6, the gene encoding a cellular sodium-dependent multivitamin transporter (SMVT) responsible for transporting vitamins, including biotin (vitamin B7). We showed that the biotin deficiency was caused by the SLC5A6 variants resulting in defective B cell differentiation and antibody deficiency. Altered cellular metabolic profiles, including aberrant mitochondrial respiration and reliance on glycolysis, may underlie the failure in plasma cell maturation. Replenishment of biotin improved plasma cell maturation and recovered the antibody producing activity in the patient and in a CRISPR-Cas9 gene-edited mouse model bearing a patient-specific SLC5A6 variant. Our results demonstrate the critical role of metabolic reprogramming in the maturation of plasma cells and nominate SLC5A6 as a causative gene for immunodeficiency that may be treated by biotin replenishment.

Biotin controls intestinal stem cell mitosis and host-microbiome interactions

Diet is a key regulator of metabolism and interacts with the intestinal microbiome. Here, we study the role of the Drosophila intestinal stem cell (ISC)-specific biotin transporter Smvt in midgut homeostasis, infection-induced regeneration, and tumorigenesis. We show that Smvt-transported biotin in ISCs is necessary for ISC mitosis. Smvt deficiency impairs intestinal maintenance, which can be rescued by the human Smvt, encoded by SLC5A6. ISC-specific, Smvt-silenced flies exhibit microbial dysbiosis, whereby the growth of Providencia sneebia, an opportunistic pathogen, is favored. Dysbiosis correlates with increased Nox expression, reactive oxygen species (ROS), and enterocyte apoptosis. Flies acquire biotin from their diet and microbiota. We show that, when dietary biotin is scarce, biotin-producing commensals, e.g., E. coli, can rescue reduced ISC mitosis. Smvt and commensals also control intestinal tumor growth. Our findings suggest that direct modification of the gut microbiome by biotin can serve as an approach for the treatment of dysbiosis-promoted diseases and tumorigenesis control.

Major involvement of Na(+) -dependent multivitamin transporter (SLC5A6/SMVT) in uptake of biotin and pantothenic acid by human brain capillary endothelial cells

The purpose of this study was to clarify the expression of Na(+) -dependent multivitamin transporter (SLC5A6/SMVT) and its contribution to the supply of biotin and pantothenic acid to the human brain via the blood-brain barrier. DNA microarray and immunohistochemical analyses confirmed that SLC5A6 is expressed in microvessels of human brain. The absolute expression levels of SLC5A6 protein in isolated human and monkey brain microvessels were 1.19 and 0.597 fmol/μg protein, respectively, as determined by a quantitative targeted absolute proteomics technique. Using an antibody-free method established by Kubo et al. (2015), we found that SLC5A6 was preferentially localized at the luminal membrane of brain capillary endothelium. Knock-down analysis using SLC5A6 siRNA showed that SLC5A6 accounts for 88.7% and 98.6% of total [(3) H]biotin and [(3) H]pantothenic acid uptakes, respectively, by human cerebral microvascular endothelial cell line hCMEC/D3. SLC5A6-mediated transport in hCMEC/D3 was markedly inhibited not only by biotin and pantothenic acid, but also by prostaglandin E2, lipoic acid, docosahexaenoic acid, indomethacin, ketoprofen, diclofenac, ibuprofen, phenylbutazone, and flurbiprofen. This study is the first to confirm expression of SLC5A6 in human brain microvessels and to provide evidence that SLC5A6 is a major contributor to luminal uptake of biotin and pantothenic acid at the human blood-brain barrier. In humans, it was unclear (not concluded) about what transport system at the blood-brain barrier (BBB) is responsible for the brain uptakes of two vitamins, biotin and pantothenic acid, which are necessary for brain proper function. This study clarified for the first time that the solute carrier 5A6/Na(+) -dependent multivitamin transporter SLC5A6/SMVT is responsible for the supplies of biotin and pantothenic acid into brain across the BBB in humans. DHA, docosahexaenoic acid; NSAID, non-steroidal anti-inflammatory drug; PGE2, prostaglandin E2.