Developmental maturation of intestinal and renal thiamin uptake: studies in wild-type and transgenic mice carrying human THTR-1 and 2 promoters.

Thiamin (B1) is an essential micronutrient for normal growth and development. Mammals obtain thiamin through intestinal absorption, while in the kidney thiamin is reabsorbed to prevent its loss in the urine, both processes are specialized, carrier-mediated and involve thiamin transporters-1 and 2 (THTR-1 and THTR-2, respectively; products of the SLC19A2 and SLC19A3 genes). Although thiamin appears to play an important role in neonatal growth, little is currently known about the possible regulation of intestinal and renal thiamin uptake during developmental maturation. We addressed these issues by examining intestinal and renal thiamin uptake and expression of THTR-1 and THTR-2 during early stages of life. We utilized wild-type mice (mice express orthologues of both thiamin transporters) and transgenic mice expressing human SLC19A2 or SLC19A3 promoter-reporter transgenes as a model system and examined carrier-mediated thiamin uptake, mTHTR-1 and 2 protein and mRNA levels and luciferase activity in suckling (13 days), weanling (25-27 days), and adult (60-65 days) mice. Carrier-mediated thiamin uptake by jejunal and renal brush border membrane vesicles (BBMV) both decreased with maturation (suckling>weanling>adult) and were associated with a reduction in mTHTR-1 and mTHTR-2 protein, mRNA levels, and the activity of human SLC19A2 and SLC19A3 promoter-reporter constructs in the intestines and kidneys of transgenic mice. These results are the first to demonstrate that intestinal and renal thiamin uptake are developmentally regulated during early stages of life, mediated through mTHTR-1 and mTHTR-2, and suggest the possible involvement of transcriptional regulatory mechanism(s) in this regulation. Copyright (c) 2005 Wiley-Liss, Inc.