title: Conditional (intestinal-specific) knockout of the riboflavin transporter-3 (RFVT-3) impairs riboflavin absorption.
abstract: Riboflavin (RF) is indispensable for normal cell metabolism, proliferation, and growth. The RFVT-3 protein (product of the Slc52a3 gene) is expressed in the gut with the expression being restricted to the apical membrane domain of the polarized intestinal epithelial cells. The relative contribution of RFVT-3 to total carrier-mediated RF uptake in the native intestine, however, is not clear. We addressed this issue in the current investigation using a conditional (intestinal-specific) RFVT-3 knockout (cKO) mouse model developed by the Cre/Lox approach. All RFVT-3 cKO mice were found to be RF deficient and showed a significant growth and development retardation; also, nearly two-thirds of them died prematurely between the age of 6 and 12 wk. In vivo (intestinal and colonic loops) and in vitro (native isolated intestinal epithelial cells) uptake studies showed a severe inhibition in carrier-mediated RF uptake in the cKO mice compared with control littermates. We also observed a significant increase in the level of expression of oxidative stress-responsive genes in the intestine of the cKO mice compared with control littermates. Supplementation of the RFVT-3 cKO mice with pharmacological doses of RF led to a complete correction of the growth retardation and to normalization in the level of expression of the oxidative stress-responsive genes in the gut. These results show, for the first time, that the RFVT-3 system is the main transporter involved in carrier-mediated RF uptake in the native mouse small and large intestine, and that its dysfunction impairs normal RF body homeostasis.
authors.affiliation: Departments of Medicine, Physiology and Biophysics, University of California, Irvine, California; Department of Medical Research, Veterans Affairs Medical Center, Long Beach, California; and.
authors.forename: Veedamali S
authors.initials: VS
authors.lastname: Subramanian
authors.affiliation: Department of Medical Research, Veterans Affairs Medical Center, Long Beach, California; and.
authors.forename: Nils
authors.initials: N
authors.lastname: Lambrecht
authors.affiliation: Division of Biomedical Sciences, University of California, Riverside, California.
authors.forename: Christian
authors.initials: C
authors.lastname: Lytle
authors.affiliation: Departments of Medicine, Physiology and Biophysics, University of California, Irvine, California; Department of Medical Research, Veterans Affairs Medical Center, Long Beach, California; and hmsaid@uci.edu.
authors.forename: Hamid M
authors.initials: HM
authors.lastname: Said
mesh_terms: D000818:Animals; D003106:Colon / Q000378:metabolism; D002658:Developmental Disabilities / Q000235:genetics; D004847:Epithelial Cells / Q000378:metabolism; D015870:Gene Expression / Q000235:genetics; D006130:Growth Disorders / Q000235:genetics; D006706:Homeostasis / Q000235:genetics; D007408:Intestinal Absorption / Q000235:genetics*; D007413:Intestinal Mucosa / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D018384:Oxidative Stress / Q000235:genetics; D012256:Riboflavin / Q000378:metabolism*; D014815:Vitamins / Q000378:metabolism*
chemical_list: D026901:Membrane Transport Proteins; C588176:RFVT2 protein, mouse; D014815:Vitamins; D012256:Riboflavin
keywords: intestine