Thesis Defense by Piotr Bartochowski

Presented by Piotr Bartochowski

December 14, 2023

Edited by Àngel ARGILÉS,

And the joint supervision of 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 decline in kidney function accompanied by dysfunction in other organs.  In the intestine, changes in the intestinal barrier and microbiota have been reported, which may contribute to disease progression 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 gut microbiota during CKD.

A literature review examined the relevance of rodent models of chronic kidney disease (CKD) for studying the gut-kidney axis. Rodent models of CKD allow for the study of changes in the gut and in gut microbiota metabolism, but changes in microbiota composition are not replicated. The main factors affecting the gut microbiota are the method of CKD induction, the animal species, and housing conditions. To improve the transferability of results to humans, it is preferable to use omnivorous species in which CKD 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 rat model of chronic kidney disease (CKD), with or without vascular calcification (VC), using histological and molecular methods. VC is a complication of CKD 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 CKD is a reduction in mucus production, which is more pronounced in the presence of VC. The presence of NLRP6, a key player in intestinal immunity, is reduced in the ileum of animals with CKD, with or without CV. NLRP6 gene expression is positively correlated with several intestinal genes related to tight junctions, the 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 CKD 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 CKD. These changes were assessed using metabarcoding, a next-generation sequencing method. In rats with kidney 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 involved amplicon sequence variants with low contributions to the microbiota (including 13 unique to the CKD microbiota, 6 increased, and 5 decreased compared to the control group). Significant differences in β-diversity were observed between the two time points at the start of the experiment (before surgery) and at the time of sacrifice. These results differ from those in the literature and are at least partly related to methodological issues identified retrospectively.

In conclusion, animal models of CKD are suitable for studying disruptions in the gut-kidney axis. For the first time, changes in the intestinal barrier have been reported in an animal model of CKD with cardiovascular disease. The reduced expression of NLRP6 in the ileum suggests an important role in maintaining intestinal barrier homeostasis. CKD-specific gut microbiota dysbiosis was not observed, but the study needs to be repeated with the inclusion of additional controls.