Region-specific Wnt signaling responses promote gastric polyp formation in patients with familial adenomatous polyposis
Kevin P. McGowan, Elizabeth Delgado, Theresa M. Keeley, Elise S. Hibdon, D. Kim Turgeon, Elena M. Stoffel, Linda C. Samuelson
Kevin P. McGowan, Elizabeth Delgado, Theresa M. Keeley, Elise S. Hibdon, D. Kim Turgeon, Elena M. Stoffel, Linda C. Samuelson
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Research Article Gastroenterology

Region-specific Wnt signaling responses promote gastric polyp formation in patients with familial adenomatous polyposis

Abstract

Germline adenomatous polyposis coli (APC) mutation in patients with familial adenomatous polyposis (FAP) promotes gastrointestinal polyposis, including the formation of frequent gastric fundic gland polyps (FGPs). In this study, we investigated how dysregulated Wnt signaling promotes FGPs and why they localize to the corpus region of the stomach. We developed a biobank of FGP and surrounding nonpolyp corpus biopsies and organoids from patients with FAP for comparative studies. Polyp biopsies and polyp-derived organoids exhibited enhanced Wnt target gene expression. Polyp-derived organoids with intrinsically upregulated Wnt signaling showed poor tolerance to further induction, suggesting that high Wnt restricts growth. Targeted genomic sequencing revealed that most gastric polyps did not arise via APC loss of heterozygosity. Studies in genetic mouse models demonstrated that heterozygous Apc loss increased epithelial cell proliferation in the corpus but not the antrum, while homozygous Apc loss was not maintained in the corpus yet induced hyperproliferation in the antrum. Our findings suggest that heterozygous APC mutation in patients with FAP may be sufficient to drive polyp formation in the corpus region while subsequent loss of heterozygosity to further enhance Wnt signaling is not tolerated. This finding contextualizes the abundant yet benign nature of gastric polyps in FAP patient corpus compared with the rare, yet adenomatous polyps in the antrum.

Authors

Kevin P. McGowan, Elizabeth Delgado, Theresa M. Keeley, Elise S. Hibdon, D. Kim Turgeon, Elena M. Stoffel, Linda C. Samuelson

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Figure 2

Enhanced Wnt signaling in a subset of FAP gastric polyp-derived organoids.

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Enhanced Wnt signaling in a subset of FAP gastric polyp-derived organoid...
(A) Wnt target gene expression was measured in patient-matched polyp (P)/nonpolyp (NP) organoid pairs following 6 days of growth in WR media or following 4 days of growth in WR and 2 days of growth in WR-free media. (B) LGR5 mRNA abundance in FAP organoids grown in WR or WR-free media. Data shown as mean ± SD mRNA abundance relative to the reference gene ACTB (n = 3 individual wells; *P < 0.05, **P < 0.005, ***P < 0.001 by 1-way ANOVA with Tukey’s multiple-comparison test). (C) Heatmap of relative Wnt target gene expression in polyp organoids. Data are shown as mean fold-change relative to the expression of each target gene in matched nonpolyp organoids grown in WR media for 6 days. (D) Heatmap of LGR5 mRNA expression in polyp organoids, shown as mean fold-change relative to patient-matched nonpolyp organoids and ordered from highest to lowest expression. High Wnt and low Wnt denote the classification of polyp-derived lines with increased or similar/decreased LGR5 gene expression. (E) Images of polyp organoids grown for 2 passages (12 days) in WR-free media, demonstrating Wnt-independent growth (scale bars = 100 μm). (F) Growth of organoids cultured for 12 days in 100% or 60% WR media was measured through ATP-dependent luminescence. (G) Images of H87 organoids at day 12 following growth in 100% or 60% WR (scale bars = 200 μm). (H) Relative growth of nonpolyp and polyp organoids clustered by Wnt target gene expression characteristics (high Wnt and low Wnt) in 60% compared with 100% WR media. Each point represents an individual organoid line, shown as the average of triplicate wells. Data shown as mean ± SD of the organoids in that group (n = 4–9 individual organoid lines; *P < 0.05, **P < 0.005 by 1-way ANOVA with Tukey’s multiple-comparison test).