Hypothesis

Age‑associated increase in colonic mucosal fucosylation creates a lectin‑rich microenvironment that sequesters the MLH1 protein, promoting its epigenetic silencing and thus driving mismatch repair deficiency in histologically normal epithelium.

Rationale

• Recent work shows that age‑related dysregulation of intestinal epithelial fucosylation, driven by microbiome dysbiosis, is heightened in older adults with stage II CRC and can be transmitted via aged fecal microbiota [4].
• Epigenetic hypermethylation of the hMLH1 promoter rises with age, reaching 22.5% in >75‑year‑olds and 36% in >85‑year‑olds, preceding visible lesions [1][2].
• Lectins such as DC‑SIGN and Langerin bind fucose moieties and have been shown to recruit DNA‑methyltransferases to glycoprotein complexes in other epithelial contexts.
• Field cancerization spreads aberrant methylation and genomic instability across histologically normal mucosa, providing a fertile ground for lectin‑MLH1 interactions [3].

Combining these observations, we propose that elevated fucosylated glycans on the apical surface of colonic epithelial cells act as molecular traps for lectins that, upon binding, scaffold DNMT1 and HDAC complexes to the MLH1 promoter, reinforcing methylation and suppressing transcription.

Testable Predictions

1. In colonic crypts from older donors, MLH1 protein will co‑localize with fucosylated epitopes and lectin markers (e.g., DC‑SIGN) more frequently than in young donors.
2. Pharmacological inhibition of fucosyltransferase activity (using 2‑F‑fucose) or blockade of lectin binding (with anti‑DC‑SIGN antibodies) will reduce hMLH1 promoter methylation in aged organoid cultures.
3. Transplanting aged microbiota into germ‑free young mice will increase mucosal fucosylation, elevate lectin‑MLH1 complexes, and raise hMLH1 methylation compared with transplants from young microbiota.
4. Individuals with high colonic fucosylation (measured by lectin staining of biopsy‑derived normal mucosa) will show higher odds of age‑accelerated PhenoAge and prevalent dMMR status, independent of chronological age.

Experimental Approach

• Human tissue: Obtain paired normal‑appearing colonic biopsies from donors stratified by age (<45, 45‑65, >65) and CRC status. Perform immunofluorescence for MLH1, fucose (UEA‑1 lectin), and DC‑SIGN; quantify co‑localization and correlate with hMLH1 promoter methylation by bisulfite pyrosequencing.
• Organoid model: Derive colonic organoids from young and aged donors. Treat with 2‑F‑fucose (10 mM) or anti‑DC‑SIGN (5 µg/mL) for 72 h. Measure MLH1 mRNA (qRT‑PCR), promoter methylation, and microsatellite instability assay.
• Mouse microbiota transplant: Colonize germ‑free mice with feces from aged (≥20 mo) or young (≥2 mo) donors. After 8 weeks, assess colonic fucosylation (lectin blot), lectin‑MLH1 interaction (co‑IP), and hMLH1 methylation.
• Clinical correlation: In a cohort of patients undergoing screening colonoscopy, score normal mucosa fucosylation by lectin immunohistochemistry, compute PhenoAge from blood, and determine MMR status by MSI testing. Use logistic regression to test whether fucosylation predicts dMMR after adjusting for age.

Potential Confounders and Mitigation

• Inflammation can independently affect fucosylation and methylation; we will control for histologic inflammatory scores and cytokine levels.
• Microbiota composition varies; we will shotgun‑sequence feces to include major taxa as covariates.
• Organoid passage may drift epigenetically; we will limit to passages ≤ 5 and validate with fresh biopsies.

Implications

If validated, this mechanism links a microbiome‑driven glycan shift to epigenetic silencing of a key DNA‑repair gene, offering a concrete target for prevention: fucosylation inhibitors or lectin blockers could preserve MLH1 expression in the aging colon, reducing field cancerization and CRC incidence. It also provides a biomarker (mucosal fucosylation) that may distinguish biological from chronological age for personalized risk stratification.