Thesis defense by Piotr Bartochowski

Presented by Piotr Bartochowski

December 14, 2023

Edited by Àngel ARGILÉS,

And co-supervision by Nathalie GAYRARD and Magali CORDAILLAT-SIMMON

Changes in the intestinal barrier and gut microbiota in animal models of chronic kidney disease and vascular calcification

Summary:

Chronic kidney disease (CKD) is characterized by a persistent reduction in kidney function accompanied by dysfunction in other organs.  In the intestine, changes in the barrier and microbiota have been reported, which could contribute to the progression of the disease through chronic intestinal inflammation and the production of uremic toxins. In this context, the objective of this thesis is to identify changes in the intestinal barrier and microbiota during CRF.

In a literature review, the relevance of animal models of CRF for studying the gut-kidney axis was examined. Rodent models of CRF allow for the study of changes in the gut and gut microbiota metabolism, but changes in microbiota composition are not reproduced. The main factors affecting the gut microbiota are the method of inducing CRF, the animal species, and the housing conditions. To improve the transposition of results to humans, it is preferable to use omnivorous species in which CRF has been surgically induced and which are housed separately under controlled conditions.

The second study focused on characterizing the intestinal barrier of the ileum and colon in a model of CRF with or without vascular calcification (VC) in rats, using histological and molecular methods. VC is a complication of CRF characterized by the accumulation of phosphate and calcium crystals in the smooth muscle cells of the arteries, leading to a loss of elasticity and contractility, which promotes cardiovascular disease. The main change observed in animals with CRF is a reduction in mucus production, which is more pronounced in the presence of VC. The presence of NLRP6, an important player in intestinal immunity, is reduced in the ileum of animals with CRF with or without PC. NLRP6 gene expression is positively correlated with several intestinal genes related to tight junctions, immune response, and the antioxidant system, and negatively correlated with renal fibrosis and plasma indoxyl sulfate levels. The concentration of this uremic toxin increases with CRF and is positively associated with CV and negatively associated with mucus production.

The third study aimed to identify changes in the composition of the gut microbiota during CRF. These changes were assessed using metabarcoding, one of the next-generation sequencing methods. In rats with renal failure, the composition of the gut microbiota did not appear to differ from that of the control group (overall composition, α-diversity, and β-diversity). The few significant differences concern amplicon sequence variants with low contributions to the microbiota (including 13 unique to the CKD microbiota, 6 increased and 5 reduced compared to the control group). Significant differences in β-diversity were observed between the two points at the start of the experiment (before surgery) and at the time of sacrifice. These results differ from those reported in the literature and are at least partly related to methodological issues identified retrospectively.

In conclusion, animal models of CKD are suitable for studying disturbances in the gut-kidney axis. For the first time, changes in the intestinal barrier in an animal model of CKD with CV have been reported. The reduction in NLRP6 expression in the ileum suggests an important role in maintaining intestinal barrier homeostasis. No CKD-specific gut microbiota dysbiosis was observed, but the study needs to be repeated with the inclusion of additional controls.