Introduction
Dysbiosis of the gut microbiota is involved in the etiopathogenesis of primary biliary cholangitis (PBC). Escherichia coli infection plays a key role in the breakdown of self-immune tolerance, leading to the production of anti-mitochondrial antibodies (AMA). However, the role of intestinal E. coli in PBC remains unclear. Urinary tract infection (UTI) mainly caused by E. coli is a significant risk factor for the onset of PBC. Therefore, we hypothesized that there was a specific strain of uropathogenic E. coli present in the intestine of PBC participating in the pathogenesis of PBC.
Aims & Methods
The aim of the study was to investigate the role of intestinal E. coli in the pathogenesis of PBC. We isolated E. coli strains from the feces of sex- and age- matched PBC patients (n=31) and healthy controls (n=30). We screened the potential E. coli strain depending on the fimbrial gene distribution patterns. Both C57BL/6J and dnTGFβRII mice were gavaged with the screened E. coli strain, E. coli-K12 (K12) and PBS respectively. Liver biopsies from PBC patients and control populations were collected to confirm the distribution of the screened E. coli.
Results
1. We isolated 93 and 90 strains of E. coli from the feces of PBC and healthy controls, respectively. By analyzing the distribution patterns of the fimbrial genes, we identified a strain of E. coli called Ex colonizing in the intestines of PBC specifically, which also caused UTI in patients.
2. We detected a high titre of AMA in the serum of C57BL/6J mice colonized by Ex rather than K12, a control E. coli strain. Furthermore, Ex-infected mice presented severe intestinal barrier destruction compared with K12-infected mice. Ex translocated to the mesenteric lymph nodes (MLN) and liver in Ex-infected mice by fluorescence in situ hybridization, while K12 or PBS-gavaged mice did not. Flow cytometry analysis revealed a significant increase in the proportion of CD11C+MHCII+CD103+ inflammatory dendritic cells (DCs) in the MLN of Ex-infected mice.
3. We gavaged Ex to 4-week-old dnTGFβRII mice that had not yet developed cholangitis. It revealed that Ex-gavage induced earlier production of AMA and significantly enhanced cholangitis compared to K12 and PBS-gavage. Flow cytometry analysis revealed that besides a significant increase in inflammatory DCs in MLN, the proportion of CD8+T cells and CD20+ B cells increased in Ex-infected dnTGFβRII mice.
4. Using 16S rRNA gene sequencing of liver biopsies, the abundance of bacteria and E. coli in PBC livers was significantly increased. Interestingly, we detected E. coli around the bile ducts in PBC liver biopsies by means of specific probes, while the autoimmune hepatitis and non-alcoholic fatty liver disease livers were not.
Conclusion
Our results suggest that an uropathogenic Escherichia coli strain may be the critical causative pathogen for PBC by disrupting the intestinal barrier and translocating to the liver.
References
[1] Tang R, Wei Y, Li Y, et al. Gut microbial profile is altered in primary biliary cholangitis and partially restored after UDCA therapy. Gut. 2018. 67(3): 534-541.
[2] Lleo A, Leung P, Hirschfield GM, Gershwin EM. The Pathogenesis of Primary Biliary Cholangitis: A Comprehensive Review. Semin Liver Dis. 2020. 40(1): 34-48.
[3] Yang Y, Choi J, Chen Y, et al. E. coli and the etiology of human PBC: Antimitochondrial antibodies and spreading determinants. Hepatology. 2022. 75(2): 266-279.