(OR18-06-23) The Impacts of slc19a3 Deletion and Intestinal SLC19A3 Insertion on Thiamine Distribution and Brain Metabolism in the Mouse

Objectives: Thiamine Transporter 2 (THTR2), coded by gene SLC19A3, is broadly expressed and colocalized with other thiamine transporters. While known for thiamine intestinal absorption and brain uptake, the relative contribution of THTR2 on thiamine uptake into other organs is unclear. We investigated the impact of THTR2 on thiamine vitamer status in various tissues using wildtype (WT), mTHTR2-knockout mice (KO), and a novel transgenic (TG) line with the mTHTR2 knockout background expressing the human THTR2 under the villin1 promoter. We hypothesized that the loss of THTR2 would reduce vitamer levels in tissues that normally express this transporter such as in the brain, heart, kidneys, and duodenum and that greater thiamine exposure would rescue these levels. If vitamers were reduced, we expected metabolism to be affected.

Methods: WT, TG, and KO mice were fed ad libtum either a standard thiamine diet at 17mg/kg thiamine HCl diet (1X diet) or a high thiamine diet at (5X diet) for 5 weeks (n=6/group). The KO mice on the 1X diet were not viable and were excluded from the study. Plasma, red blood cells, duodenum, brain, liver, kidney, heart, and adipose tissue were collected and analyzed for thiamine, thiamine monophosphate (TMP) and thiamine diphosphate (TDP) via liquid-chromatography-tandem mass spectrometry. Linear regression models controlling for plasma thiamine, genotype and sex were built. Untargeted metabolomics were performed on brain tissue, and differentiating metabolites were analyzed via partial least square-discriminant analysis.

Results: On the 5X diet, KO mice survived but had 2-fold lower plasma thiamine than WT mice. While the TG groups had equivalent duodenum and circulating vitamers compared to WT mice, the TG mice had 60% lower thiamine, 35% lower TMP and normal TDP in the brain as were seen in the KO mice. From the regression models, THTR2 also showed minor effects on heart and liver vitamer levels. Though the active cofactor TDP in the brain was not impacted, the loss of THTR2 was associated with changes in amino acid and nucleic acid metabolite levels.

Conclusions: In conclusion, we determined that THTR2 was irreplaceable for the brain thiamine pool. Though TDP levels were not affected by the transporter loss, mutation or inhibition of THTR2 has the potential to alter brain metabolism.

Funding Sources: NIH grants, UC Davis Jastro Shields Award, USDA Project grants