The impacts of slc19a3 deletion and intestinal SLC19A3 insertion on thiamine distribution and brain metabolism in the mouse

Authors: WEN, ANITA - University Of California, Davis; ZHU, YING - Tufts University; YEE, SOOK WAH - University Of California San Francisco (UCSF); PARK, BRIAN - Tufts University; GIACOMINI, KATHLEEN - University Of California San Francisco (UCSF); Greenberg, Andrew; Newman, John

Submitted to: Metabolites
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/22/2023
Publication Date: 7/26/2023
Citation: Wen, A., Zhu, Y., Yee, S., Park, B., Giacomini, K.M., Greenberg, A.S., Newman, J.W. 2023. The impacts of slc19a3 deletion and intestinal SLC19A3 insertion on thiamine distribution and brain metabolism in the mouse. Metabolites. https://doi.org/10.3390/metabo13080885.
DOI: https://doi.org/10.3390/metabo13080885

Interpretive Summary: The SLC19A3 gene encodes the Thiamine Transporter 2 (THTR2), a widely expressed protein that is colocalized with other specific and nonspecific thiamine transporters. While recognized as critical for thiamine gut absorption and brain uptake, the relative contribution of THTR2 for thiamine uptake in other organs is unclear. Using a novel transgenic (TG) mouse whole-body THTR2 knockout (KO) expressing the human THTR2 in the intestine, we explored the impact of THTR2 on tissue thiamine and its phosphorylated metabolites and brain metabolomic profiles. KO mice required high dietary thiamine to survive and had 2- to 3-fold lower plasma and brain thiamine levels than WT on an equivalent diet. Blood levels of thiamine vitamers were equivalent between TG and WT mice on the same diets, but TGs had 60% lower thiamine and normal thiamine diphosphate in the brain regardless of diet and showed subtle effects in the heart and liver. The loss THTR2 was also associated with reductions in nucleic acid and amino acid derivatives in the brain. In conclusion, THTR2 loss negatively impacted the brain thiamine pool, but not the key enzymatic co-factor thiamine diphosphate. Regardless, THTR2 loss, mutation or inhibition has the potential to alter the brain metabolome.

Technical Abstract: The SLC19A3 gene product, Thiamine Transporter 2 (THTR2), is ubiquitously expressed and colocalized with other specific and nonspecific thiamine transporters. While recognized as critical for thiamine gut absorption and brain uptake, the relative contribution of THTR2 for thiamine uptake in other organs is unclear. We examined the impact of THTR2 on thiamine, thiamine monophosphate and thiamine diphosphate levels in various tissues using a novel transgenic (TG) whole-body Slc19a3 knockout (KO) model expressing the human SLC19A3 in the intestine. Male and female wildtype (WT) and TG mice were fed either a standard 17mg/kg (1X diet) or a high 85mg/kg thiamine HCl diet (5X diet), while KOs were fed only the 5X diet (n=12/grp). Thiamine vitamers in plasma, red blood cells, duodenum, brain, liver, kidney, heart, and adipose tissue were measured. Untargeted metabolomics were performed on brain tissues of groups with equivalent plasma thiamine concentrations (n=12/group). KO mice had plasma and brain thiamine levels ~2-fold and ~3-fold lower than WT on the 5X diet. The TG mice had equivalent circulating vitamers as the WT mice on the same diets but 60% lower thiamine and normal thiamine diphosphate in the brain regardless of diet. The loss of THTR2 had subtle effects on heart and liver thiamine vitamers. The loss of brain THTR2 was associated with reductions in nucleic acid and amino acid derivatives. In conclusion, THTR2 loss negatively impacted the brain thiamine pool, but not thiamine diphosphate. Regardless, THTR2 loss, mutation or inhibition has the potential to alter the brain metabolome.