Colonization of gnotobiotic mice with DCA-producing bacteria revealed that bile acid modulation increases bile acid-sensitive enterocyte density while reducing stem cells, goblet cells, and transit amplifying cells, with associated changes in PDK4 and MUC2 expression that are recapitulated in human hyperplastic polyps, adenomas, and carcinomas.
Key Findings
Results
Colonization of gnotobiotic mice with a defined bacterial community including the 7α-dehydroxylating species Extibacter muris resulted in DCA production in the colon.
Gnotobiotic mice were used to enable precise control over microbial colonization
Extibacter muris was the specific species responsible for 7α-dehydroxylation, the key step in converting primary to secondary bile acids
This colonization model allowed in vivo study of DCA effects on the intestinal epithelium in a controlled setting
Results
Single-cell RNA sequencing of colonic epithelial cells showed increased cell density of bile acid-sensitive enterocytes in mice exposed to DCA.
ScRNA-Seq was performed on colonic epithelial cells from gnotobiotic mice
The increase was specifically in bile acid-sensitive enterocyte populations
This finding suggests DCA selectively promotes expansion of a specific epithelial cell type
Results
DCA exposure in gnotobiotic mice was associated with fewer stem cells, goblet cells, and transit amplifying cells in the colonic epithelium.
Reductions were observed across three distinct colonic epithelial cell populations: stem cells, goblet cells, and transit amplifying cells
The reduction in goblet cells is consistent with decreased Muc2 expression also observed in the same model
These changes suggest DCA broadly disrupts normal epithelial homeostasis and renewal
Results
DCA exposure was associated with increased expression of pyruvate dehydrogenase kinase (Pdk4) and decreased expression of mucin (Muc2) in murine colonic epithelial cells.
Pdk4 upregulation was identified through scRNA-Seq analysis
Muc2 downregulation is consistent with the observed reduction in goblet cell density
These transcriptional changes were identified as key molecular markers of DCA-induced epithelial responses
Results
PDK expression was increased in human hyperplastic polyps and adenomas compared to normal mucosa.
Immunostaining was performed on human biopsies from an observational patient cohort with hyperproliferative polyps or cancer
PDK upregulation was observed in both hyperplastic polyps and adenomas
This finding parallels the murine scRNA-Seq results, suggesting translational relevance of the animal model findings
Results
MUC2 expression was reduced in human adenomas and carcinomas compared to normal colonic mucosa.
Immunostaining of human biopsies from an observational patient cohort was used to assess MUC2 expression
Reduction was observed in both adenomas and carcinomas but the pattern differed from PDK, which was elevated in hyperplastic polyps and adenomas
This mirrors the Muc2 downregulation observed in DCA-exposed gnotobiotic mice
Results
Treatment of ileostomy patients with chologenic diarrhea using bile acid sequestrants was associated with enhanced epithelial proliferation in colorectal biopsies.
This finding came from an interventional study component involving ileostomy patients treated with bile acid-scavenging drugs
Bile acid sequestrants reduce luminal bile acid levels by binding them in the intestinal lumen
Enhanced proliferation associated with reduced bile acid exposure appears paradoxical given the DCA-proliferation axis described elsewhere, suggesting context-dependent effects
Background
Elevated secondary bile acids, particularly DCA produced by the gut microbiome, influence epithelial cell proliferation and accelerate colorectal cancer development under high-fat dietary conditions.
This relationship between DCA, diet, and CRC risk forms the background rationale for the study
Long-term high fat intake is cited as an adverse dietary condition promoting this axis
The study was motivated by the fact that effects of secondary bile acids on the intestinal epithelium had not previously been studied in detail in vivo
What This Means
This research suggests that secondary bile acids — specifically deoxycholic acid (DCA), which is produced when certain gut bacteria chemically modify bile acids — cause measurable changes in the cells lining the colon. Using specially raised mice that had no bacteria of their own, researchers introduced a defined set of bacteria including one species capable of producing DCA. They then used advanced single-cell genetic analysis to see how different types of colon lining cells responded. They found that DCA exposure increased a type of cell sensitive to bile acids while reducing stem cells (which renew the lining), goblet cells (which produce protective mucus), and transit amplifying cells (which help maintain normal cell turnover). At the molecular level, a gene called PDK4 was turned up, while a mucus-producing gene called MUC2 was turned down.
To check whether these findings were relevant to humans, the researchers examined colon tissue biopsies from patients with pre-cancerous growths (polyps and adenomas) and colon cancer. They found that PDK was elevated in polyps and adenomas, and MUC2 was reduced in adenomas and cancers, mirroring what was seen in the mice. Additionally, when patients with a condition causing excess bile acids in the colon were treated with drugs that soak up bile acids, their colon lining showed increased cell growth, suggesting that bile acid levels directly influence how colon cells behave.
This research suggests that gut bacteria capable of producing DCA, particularly under high-fat dietary conditions, may contribute to the early stages of colorectal cancer development by disrupting the normal balance of colon lining cell types and altering key genes involved in metabolism and mucus production. The parallel findings in mice and humans point to potential relevance for understanding how diet, gut microbes, and bile acids together influence colon cancer risk, and possibly for exploring bile acid-targeting treatments.