ABSTRACT Background High intakes of fructose are associated with metabolic diseases, including hypertriglyceridemia and intestinal tumor growth. Although small intestinal epithelia consist of many different cell types, express lipogenic genes, and convert dietary fructose to fatty acids, there is no information on the identity of the cell type(s) mediating this conversion and on the effects of fructose on lipogenic gene expression. Objectives We hypothesized that fructose regulates the intestinal expression of genes involved in lipid and apolipoprotein synthesis, that regulation depends on the fructose transporter solute carrier family 2 member a5 [Slc2a5 (glucose transporter 5)] and on ketohexokinase (Khk), and that regulation occurs only in enterocytes. Methods We compared lipogenic gene expression among different organs from wild-type adult male C57BL mice consuming a standard vivarium nonpurified diet. We then gavaged twice daily for 2.5 d fructose or glucose solutions (15%, 0.3 mL per mouse) into wild-type, Slc2a5-knockout (KO), and Khk-KO mice with free access to the nonpurified diet and determined expression of representative lipogenic genes. Finally, from mice fed the nonpurified diet, we made organoids highly enriched in enterocyte, goblet, Paneth, or stem cells and then incubated them overnight in 10 mM fructose or glucose. Results Most lipogenic genes were significantly expressed in the intestine relative to the kidney, liver, lung, and skeletal muscle. In vivo expression of Srebf1, Acaca, Fasn, Scd1, Dgat1, Gk, Apoa4, and Apob mRNA and of Scd1 protein increased (P < 0.05) by 3- to 20-fold in wild-type, but not in Slc2a5-KO and Khk-KO, mice gavaged with fructose. In vitro, Slc2a5- and Khk-dependent, fructose-induced increases, which ranged from 1.5- to 4-fold (P < 0.05), in mRNA concentrations of all these genes were observed only in organoids enriched in enterocytes. Conclusions Fructose specifically stimulates expression of mouse small intestinal genes for lipid and apolipoprotein synthesis. Secretory and stem cells seem incapable of transport- and metabolism-dependent lipogenesis, occurring only in absorptive enterocytes.
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Enrichment of hepatic glycogen and plasma glucose from H₂ 18 O informs gluconeogenic and indirect pathway fluxes in naturally feeding mice
Deuterated water (2H2O) is a widely used tracer of carbohydrate biosynthesis in both preclinical and clinical settings, but the significant kinetic isotope effects (KIE) of2H can distort metabolic information and mediate toxicity.18O‐water (H218O) has no significant KIE and is incorporated into specific carbohydrate oxygens via well‐defined mechanisms, but to date it has not been evaluated in any animal model. Mice were given H218O during overnight feeding and18O‐enrichments of liver glycogen, triglyceride glycerol (TG), and blood glucose were quantified by13C NMR and mass spectrometry (MS). Enrichment of oxygens 5 and 6 relative to body water informed indirect pathway contributions from the Krebs cycle and triose phosphate sources. Compared with mice fed normal chow (NC), mice whose NC was supplemented with a fructose/glucose mix (i.e., a high sugar [HS] diet) had significantly higher indirect pathway contributions from triose phosphate sources, consistent with fructose glycogenesis. Blood glucose and liver TG18O‐enrichments were quantified by MS. Blood glucose18O‐enrichment was significantly higher for HS versus NC mice and was consistent with gluconeogenic fructose metabolism. TG18O‐enrichment was extensive for both NC and HS mice, indicating a high turnover of liver triglyceride, independent of diet. Thus H218O informs hepatic carbohydrate biosynthesis in similar detail to2H2O but without KIE‐associated risks.
more » « less- NSF-PAR ID:
- 10376649
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- NMR in Biomedicine
- Volume:
- 36
- Issue:
- 2
- ISSN:
- 0952-3480
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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