ESR 4: Determine the role of Hippo pathway in the genetic susceptibility to develop renal lesions
Supervisor: Fabiola Terzi
PhD Student: Biagina Ruscica
Epidemiological and experimental studies indicate that the progression of chronic kidney disease after an initial injury is genetically determined. However, the genetic networks that account for the predisposition to progress are still unknown. Our recent results obtained in two strains of mice that differentially react to nephron reduction suggest that the Hippo pathway might play a role. In fact, two of the effectors of the pathway, YAP and TAZ, seem to have a divergent role. Moreover, their role seems to change according to the nephron compartment. The aim of the project is thus to define the role of YAP and TAZ focusing on the tubular homeostasis during CKD progression.
The Hippo pathway is an evolutionarily conserved serine/threonine kinase cascade that exerts crucial effects in tissue homeostasis and on organ size during the development. The physiological output of this kinase cascade is two transcriptional coactivators, Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ, also known as WWTR1). When YAP and TAZ are active, they translocate into the nucleus to interact with several transcription factors promoting the expression of a group of genes involved in cell proliferation, survival and differentiation. These two proteins may act as mechanosensors, able to read a broad range of mechanical cues and translate them in cell-specific transcriptional programmes. Nevertheless, YAP and TAZ function appears to be cell-and context-dependent and in the kidney, YAP and TAZ are constitutively expressed in podocytes and distal tubules. From the preliminary results obtained from our mice model, we thought that YAP and TAZ might have redundant roles in tubules. Unexpectedly, the mouse model KO for both Yap and Taz developed severe tubular lesions and renal failure. However, paradoxically, the expression levels of YAP, TAZ and their target genes were massively increased after the deletion and YAP mainly activated in tubular cells.
Objectives and methodology
The main goal of this project will be to identify novel modifier genes of CKD progression by applying an experimental model of CKD, the unilateral ureteral obstruction (UUO), to different strains of mice. Recent GWAS have mapped several CKD susceptibility loci. However, the genes and the genetic networks that account for the increased susceptibility to CKD progression remain mostly unidentified. Indeed, the genetic complexity of human populations and the difficulty of standardizing analyses of environmental factors in complex diseases have hampered the identification of these modifiers. We decided to take advantage of our experimental models of CKD to uncover candidate modifiers. Remarkably, our recent data showed that the predisposition to develop renal lesions after UUO varies widely among 16 strains of mice. In particular, some strains were resistant to renal deterioration. The specific objectives of ESR4 project will be to 1) better phenotype the kidney of the 16 strains of mice and characterize the cellular events that protect kidneys from lesion development after UUO using quantitative PCR, immunohistochemistry and intravital microscopy, 2) identify the candidate genes that predispose to either renal deterioration or renal protection after UUO by using haplotype association mapping, 3) validate the candidate modifiers using the CRISPR/Cas9 technology.
- Identify the targeted genetic networks responsible of the renal lesions in tubular cells expressing or not YAP and TAZ. Discover specific targets of YAP and TAZ would help us to define pathways that could be relevant to human diseases.
- Determine the molecular mechanisms by which YAP/TAZ shape tubular cells would help to understand the pathophysiology of tubular epithelia maintenance.
- Elucidate the role of mechanical stresses in tubular YAP/TAZ activation should help to better understand the importance of mechanical forces in renal pathophysiology.