High-Fat Diet Hijacks a Liver Enzyme to Shut Down Colonic Autophagy and Worsen Colitis

Scientists have traced a surprising path from dietary fat to inflamed colons, and the route runs straight through the liver. A new study published in 3 Biotech from researchers at Peking Union Medical College Hospital and Capital Medical University identifies a hepatic enzyme called Cyp7b1 as a key molecular bridge between a high-fat diet and worsening colitis, offering a mechanistic explanation for a clinical pattern doctors have noticed for years: patients with nonalcoholic fatty liver disease carry a markedly higher risk of developing inflammatory bowel disease.

Cyp7b1 Upregulation Links Fatty Diet to Colonic Damage

The core finding is precise. Mice fed a high-fat diet and then exposed to dextran sulfate sodium (DSS), a standard chemical trigger for colitis, showed significantly worse intestinal inflammation than control animals. That worsening tracked with a specific hepatic change: the upregulation of Cyp7b1, an enzyme involved in bile acid synthesis in the liver. The high-fat diet also reduced levels of two key intestinal barrier proteins, Claudin1 and E-cadherin, and raised counts of Escherichia coli in the gut. Taken together, those shifts point to a structurally compromised intestinal lining that is simultaneously under greater microbial pressure.

What makes the Cyp7b1 finding particularly useful is the correlation data. The researchers combined publicly available datasets with in-house RNA sequencing and found a statistically significant relationship between hepatic Cyp7b1 expression and colonic autophagy markers. That correlation is what allowed them to propose a directional mechanism rather than just an association.

Chenodeoxycholic Acid Blocks Autophagy and Breaks Down the Gut Barrier

Autophagy, the cellular housekeeping process by which damaged organelles and pathogens are digested and recycled, is critical for maintaining the health of the intestinal epithelium. In the high-fat diet mice, three canonical autophagy markers, LC3-II, Beclin1, and ATG5, were suppressed, while P62, a protein that accumulates when autophagic flux is impaired, was elevated. The pattern is a textbook signature of stalled autophagy.

To test whether Cyp7b1 was actually driving this suppression, the team treated colon cells directly with chenodeoxycholic acid (CDCA), a bile acid derivative produced by Cyp7b1. The results replicated the in vivo picture: CDCA decreased Claudin1 and Occludin (both tight-junction proteins essential to barrier integrity), and it also reduced LC3-II, Beclin1, and ATG5 while raising P62. That means a single downstream metabolite of an upregulated liver enzyme is sufficient to impair both the physical seal of the gut epithelium and its capacity to clear cellular debris. A review in Nutrients has described how excessive fat consumption disrupts gut barrier function and promotes low-grade systemic inflammation, but the specific liver-to-colon bile acid route identified here gives that general picture a concrete molecular target.

How Dextran Sulfate Sodium Mouse Models Tested the Hypothesis

The experimental backbone was a DSS-induced colitis model in mice maintained on a high-fat diet. DSS damages the colonic epithelium and triggers inflammation that closely resembles human ulcerative colitis, making it one of the most widely used tools in IBD research; prior work on animal models of ulcerative colitis has validated DSS as a reliable platform for testing mechanistic hypotheses. Layering a high-fat diet on top of DSS exposure allowed the team to isolate the dietary contribution to colitis severity and then look upstream into the liver for explanatory signals.

Public domain data and in-house RNA sequencing were combined to identify gene expression correlations between hepatic and colonic tissue, a methodological move that strengthens the case because the correlation emerged across independent datasets rather than being an artifact of a single experimental run. Cell culture experiments with CDCA then confirmed the mechanistic step at the cellular level.

Limitations and Open Questions About the Liver-Gut Axis

The study's main constraints are scope and species. All in vivo data come from mice, and while DSS colitis is a well-validated model, it does not capture the full genetic and immunological complexity of human IBD. The authors also do not address whether reducing Cyp7b1 activity or blocking CDCA signaling in vivo would actually attenuate colitis, which would be the key proof-of-concept for any therapeutic application. It remains unclear how much of the observed autophagy suppression is due to CDCA specifically versus other metabolic shifts that accompany a high-fat diet, including changes to the gut microbiome itself. Earlier work has shown that high-fat diets interact with gut bacteria to drive intestinal inflammation even before obesity fully develops, suggesting that the Cyp7b1-CDCA axis operates alongside, not instead of, microbial disruption.

The elevation of E. coli in the high-fat diet mice is noted in the findings but not mechanistically explored in depth, leaving open the question of whether CDCA-driven barrier breakdown is upstream or downstream of the microbial shift.

Targeted Therapies for NAFLD-IBD Overlap May Follow

The clinical relevance is real. A meaningful subset of IBD patients also carry a diagnosis of nonalcoholic fatty liver disease, and managing one condition without accounting for the other may leave the underlying liver-gut axis dysfunction unaddressed. If the Cyp7b1-CDCA pathway holds up in human tissue studies, it could become a target for interventions designed specifically for patients at the intersection of metabolic liver disease and intestinal inflammation, a population that currently has no tailored pharmacological strategy.

The next logical steps are human validation: measuring Cyp7b1 expression and CDCA levels in NAFLD patients who develop IBD, and testing whether pharmacological inhibition of the enzyme alters colitis severity in more complex animal models. Those experiments would move the finding from mechanistic insight to actionable biology.