Intestinal catabolism of dietary fructose promotes obesity and insulin resistance via ileal lacteal remodeling

Abstract

High-fructose corn syrup (HFCS) consumption is a risk factor for obesity and metabolic syndrome, yet the underlying mechanisms are incompletely understood. Catabolism of dietary fructose primarily occurs in the small intestine and liver, with fructose breakdown in the liver being pathological, while small intestinal fructose clearance protects the liver. Here, we unexpectedly found that inhibition of fructose catabolism specifically in the small intestine mitigates fructose-induced obesity and insulin resistance. Mechanistically, blocking intestinal fructose catabolism reduces dietary fat absorption, which is associated with a decrease in the surface area of the ileal lacteals and alterations in gut microbiome. Fecal transplantation experiments revealed that such a microbiome stimulates the intestine-resident macrophages, promoting lacteal growth and boosting dietary fat absorption. Given the preclinical and clinical studies reporting the effect of fructose catabolism suppression on mitigating diet-induced obesity, our data suggest that such effects are partly mediated by intestinal lacteal remodeling.

Keywords: Biological Sciences; Fructose; Ketohexokinase; Lacteals; Microbiota; Obesity; Physiology.

Figure 1.. Suppression of intestinal fructose catabolism mitigates HFCS-induced obesity and improves glucose homeostasis.

(A) 8-week-old WT or Khk-C ^ΔVilli male mice were fed water containing 30% HFCS for 12 weeks. (B) Fructose catabolism gene expression in jejunum (n_WT = 4, n_Khk-C = 5). (C, D) Body weight changes and final body weight of mice on HFCS (n_WT = 9, n_Khk-C = 7). (E, F) Fat mass (E) and the ratio of fat mass to body weight (%) (F) (n_WT = 6, n_Khk-C = 4). (G, H) Lean mass (G) and the ratio of lean mass to body weight (%) (H) (n_WT = 6, n_Khk-C = 4). (I-K) Daily chow consumption (I), water intake (J), and total calorie intake (K) per mouse on HFCS (n = 10). (L, M) Daily water intake (L) and total fructose consumption (M) per mouse on varying concentrations of HFCS (n_WT10~20% = 6, n_{WT30%, Khk-C} = 8). (N) Final body weight of mice on 15% or 30% of HFCS (n_WT15% = 6, n_{WT30%, Khk-C} = 8). (O-Q) Fasting insulin (O), homeostatic model assessment of insulin resistance (HOMA-IR) (P), and oral glucose tolerance test (OGTT) (Q) of mice on 15% or 30% of HFCS (n_WT15% = 6, n_{WT30%, Khk-C} = 4). (R, S) Systemic and portal blood levels of GLP-1 (n_WT = 4, n_Khk-C = 5). (T) Final body weight of mice on normal water (n = 9) (U, V) Daily chow (U) or water (V) consumption per mouse on normal water or HFCS (n = 10). Data are mean±s.d. ns, not significant. *p<0.05, **p<0.01, ***p<0.001 by one-way ANOVA followed by Tukey’s test (N-Q) or Student’s t-test.

Figure 2.. Suppression of intestinal fructose catabolism reduces dietary fat absorption and lacteal shortening under HFCS consumption.

(A, B) During 12-week HFCS feeding, dietary fat absorption assay was performed on weeks 4, 8, 12 of HFCS feeding, using oral soybean oil provision followed by circulating and fecal triglyceride (TG) measurements. (C) Measurements of circulating TG levels (C) and the corresponding area under curve (AUC) (D) after 12 weeks of HFCS drinking (n = 10). (E) Measurements of TG excretion in feces collected 120 minutes post-oil gavage after 12 weeks of HFCS drinking (n = 10). (F) Representative immunofluorescence images of intestinal whole mounts showing LYVE-1-positive lacteals (red) and CD31-positive capillaries (green) in mice on HFCS feeding for 12 weeks. Scale bars, 200 μm. (G, H) Lacteal length (G) and the ratio of lacteal/epithelial length (H) in intestinal tissues of mice on HFCS feeding (n = 6). (I) Representative H&E images of intestinal tissues of mice on HFCS feeding. Scale bars, 200 μm. (J, K) Epithelial (J) and capillary length (K) of intestinal tissues in mice on HFCS feeding (n = 6). Data are mean±s.d. ***p<0.001, ****p<0.0001 by Student’s t-test.

Figure 3.. Suppression of intestinal fructose catabolism alters gut microbiome diversity and reduces villus macrophages under HFCS consumption.

(A) Schematic overview of fecal 16S rRNA sequencing across multiple days of HFCS intake. (B) Representative bacterial family compositions from a WT and Khk-C ^ΔVilli mouse at each timepoint. (C) Alpha diversity (Shannon index) across all samples for WT and Khk-C ^ΔVilli mice post-day 14 of HFCS intake (n_WT = 18, n_Khk-C = 28). (D) Differential abundance results from MaAsLin3 showing the five taxa with the strongest associations between WT and Khk-C ^ΔVilli mice post-day 14 of HFCS intake n_WT = 18, n_Khk-C = 28). X-axis represents the model fit coefficient (β) from MaAsLin3, indicating the direction and magnitude of association with the Khk-C ^ΔVilli genotype (positive = enriched in Khk-C ^ΔVilli, negative = enriched in WT). Only Allobaculum spp. was significant with a false discovery rate <0.05. (E) Relative abundance of Allobaculum in WT and Khk-C ^ΔVilli mice post-day 14 of HFCS intake (n_WT = 18, n_Khk-C = 28). (F) Representative immunofluorescence images of intestinal cryosections showing F4/80-positive macrophages (green), E-cadherin-positive epithelial cells (blue), and nuclei (DAPI, turquoise). Scale bars, 50 μm. (G) Relative abundance of macrophages in mice on HFCS for 12 weeks (n = 3). Data are mean±s.d. *p<0.05, **p<0.01 by Student’s t-test.

Figure 4.. Fecal microbiota transplant phenocopies intestine-specific Khk-C depletion mice under HFCS consumption.

(A) Schematic of fecal transplant (twice/week) from donors (WT or Khk-C ^ΔVilli mice on HFCS for 12 weeks; n = 6) to recipients (WT after antibiotics) with HFCS drinking for 8 weeks. (B) Body weight gain of the recipient mice after 8 weeks of fecal transplant and HFCS drinking (n_WT(Donor) = 6, n_Khk-C(Donor) = 5). (C, D) Measurements of circulating TG levels (C) and the AUC (D) in the recipient mice following soybean oil gavage (n_WT(Donor) = 6, n_Khk-C(Donor) = 5). (E) Representative immunofluorescence images of intestinal cryosections showing F4/80-positive macrophages (green), E-cadherin-positive epithelial cells (blue), and nuclei (DAPI, turquoise) in the recipient mice after 8 weeks of fecal transplant and HFCS drinking. Scale bars, 50 μm. (F) Relative abundance of macrophages in the recipient mice (n = 3). (G) Representative immunofluorescence images of cryosections showing LYVE-1-positive lacteals (red), E-cadherin-positive epithelial cells (blue), and nuclei (DAPI, light blue) in the recipient mice after 8 weeks of fecal transplant and HFCS drinking. Scale bars, 50 μm. (H, I) Lacteal length (H) and the ratio of lacteal/epithelial length (I) in intestinal tissues of the recipient mice after 8 weeks of fecal transplant and HFCS drinking (n = 3). Data are mean±s.d. *p<0.05, **p<0.01, ***p<0.001 by Student’s t-test.