Diet‐Induced Dysbiosis and Genetic Background Synergize With Cystic Fibrosis Transmembrane Conductance Regulator Deficiency to Promote Cholangiopathy in Mice

Abstract

The most typical expression of cystic fibrosis (CF)–related liver disease is a cholangiopathy that can progress to cirrhosis. We aimed to determine the potential impact of environmental and genetic factors on the development of CF‐related cholangiopathy in mice. Cystic fibrosis transmembrane conductance regulator (Cftr)−/− mice and Cftr +/+ littermates in a congenic C57BL/6J background were fed a high medium‐chain triglyceride (MCT) diet. Liver histopathology, fecal microbiota, intestinal inflammation and barrier function, bile acid homeostasis, and liver transcriptome were analyzed in 3‐month‐old males. Subsequently, MCT diet was changed for chow with polyethylene glycol (PEG) and the genetic background for a mixed C57BL/6J;129/Ola background (resulting from three backcrosses), to test their effect on phenotype. C57BL/6J Cftr −/− mice on an MCT diet developed cholangiopathy features that were associated with dysbiosis, primarily Escherichia coli enrichment, and low‐grade intestinal inflammation. Compared with Cftr +/+ littermates, they displayed increased intestinal permeability and a lack of secondary bile acids together with a low expression of ileal bile acid transporters. Dietary‐induced (chow with PEG) changes in gut microbiota composition largely prevented the development of cholangiopathy in Cftr −/− mice. Regardless of Cftr status, mice in a mixed C57BL/6J;129/Ola background developed fatty liver under an MCT diet. The Cftr −/− mice in the mixed background showed no cholangiopathy, which was not explained by a difference in gut microbiota or intestinal permeability, compared with congenic mice. Transcriptomic analysis of the liver revealed differential expression, notably of immune‐related genes, in mice of the congenic versus mixed background. In conclusion, our findings suggest that CFTR deficiency causes abnormal intestinal permeability, which, combined with diet‐induced dysbiosis and immune‐related genetic susceptibility, promotes CF‐related cholangiopathy.

The gut microbial influence on cholestatic liver disease

“…In mice lacking a functional cystic fibrosis gene (CFTR), which alters bile composition, induction of colitis has been shown to cause biliary inflammation that could be attenuated using antibiotics, likely caused by pro‐inflammatory lipopolysaccharide (LPS) . Interestingly, the cholangiopathy observed in these mice can be attenuated by diet . These are intriguing observations, but the circulating levels of LPS in PSC patients was not elevated compared with controls .…”

Modifier genes in cystic fibrosis-related liver disease

“…According to this hypothesis, the loss of CFTR function would contribute to pH dysregulation and thereby would promote cholangiocyte injury 13 . Evidence has also been provided to indicate that the loss of CFTR affected innate immunity and promoted gut dysbiosis, which in turn would induce intestinal inflammation, endotoxinemia and CFLD [20][21][22][23][24] . New functions of CFTR in cholangiocytes were recently described, i.e., the regulation of cell polarity, and of toll-like receptor 4 (TLR4) response via the activation of the tyrosine kinase Src 20 .…”

“…Moreover, the impairment in barrier function is expected to increase the back-diffusion of toxic bile acids, and thereby to further aggravate peribiliary inflammation and fibrogenesis. We alo recently showed in CF mouse models, that the development of CFLD features required the combination of CFTR defect with both genetic and environmental factors such as diet-induced dysbiosis 24,25 .…”

“…We recently demonstrated that CFLD, i.e., cholangiopathy features, was markedly influenced by the genetic background in Cftr knockout mice 24 . By comparing Cftr knockout mice in a congenic C57BL/6J or mixed C57BL/6J;129/Ola background, we found that cholangiopathy occurred only in mice of the congenic background.…”

“…Protein-protein interactions predicted by the analysis of genes overexpressed in the liver of the congenic mice formed a large network, displaying links between inflammation, fibrosis and cell (presumably cholangiocyte) proliferation 24 . This result supported the view that cholangiopathy arising in CF, is the result of an ill-adapted innate immune response to endotoxins coming from the intestine and triggering a pro-inflammatory response 20 .…”