Study of epithelial cell HOMEOstasis disruption in polyCYSTic kidney disease. – Homeocyst

To fullfill aim 1, we are generating a mouse model allowing tracabale mosaÎc of Pkd1 inactivation in tubular cells. We have set up a pipeline combining tissue clearing with light-sheet imaging allowing the reconstruction of cortical tubules. This technology will be applied to monitore the evolution of PKD1 deficient cells clusters.

To fullfill aim 2, we have analyzed the impact of cilia ablation on kidney response to tubular obstruction in wild type and Pkd1 mutant animals.

1/ in response to tubular obstruction, cilia promote the expression of distinct pro-inflammatory and fibrotic cytokines, which govern immune cells recruitment and fibrosis

2/ In Polycystic kidney disease, cilia signaling causes early tubule dilation by altering tubular basement structure and composition, resulting in tubule distention and tubular cell stretching. Obstruction further stretch tubular cells and initiate explosive cystogenesis.

1-Primary cilia drive coordinated response to tubular obstruction

2-Primary cilia of Pkd1 deficient tubular cells drive basement membrane remodeling and tubule distention, independantly of cell proliferation.

We are now focusing our attention on the analysis of our newly generated mouse model of traceable Pkd1 mosaïc inactivation & on the role of basement membrane alterations in cystogenesis.

Ongoing.

Autosomal polycystic kidney disease (ADPKD) is responsible for 10% of end-stage renal disease cases. The disease is mainly due to PKD1 (encoding polycystin 1) loss of function mutations, which lead to the formation of proliferating cysts that progressively replace normal renal tissue. While ADPKD patients have germ-line inactivation of a single PKD1 allele, the development of renal cysts requires the loss of the remaining functional PKD1 allele in scattered tubular cells that will undergo clonal expansion to form cysts. Recent evidence from murine ADPKD models suggests that scattered Pkd1-/- cells initially proliferate without forming cysts (“pre-cystic growth”). This apparently quiescent period is followed by the rapid development of cysts (“cystic growth”). These phenomena may be seen as a two steps disruption of epithelial homeostasis. A first step disrupts the control of Pkd1-/- cells pool size allowing polycystin deficient cells to expand within a confluent epithelium where they are surrounded by healthy tubular cells, without altering kidney structure. Subsequently, a second step disrupts the maintenance of tubular architecture leading to cyst formation and kidney failure. To date, pathophysiologic research in the field has mainly focus on the inhibition of cysts growth, which represents a late event in the course of the disease. The therapeutic options identified through this approach have at best only limited efficacy. Therefore, capturing the early events that allows scattered Pkd1-/- tubular cells to expand and form cysts represents a major challenge. The aim of this project is to investigate:
(1) The mechanisms allowing the expansion of Pkd1-/- tubular cells that are scattered in a healthy epithelium during pre-cystic growth in vivo. To this aim, we will combine a state of the art mouse model of genetic mosaicism with deep tissue imaging.
(2) The events triggering the conversion of pre-cystic growth to cystic growth. Here, we will focus our research on the role of inflammatory signals delivered by a specific organelle: the primary cilium.
(3) To investigate the relevance of our findings in human, taking advantage of a large cohort of ADPKD patients.