Nephronophthisis (NPHP), one of the most frequent genetic causes of chronic renal failure in the first three decades of life, is a group of autosomal recessive diseases characterized by progressive kidney cystic degeneration and fibrosis. Mutations in the gene GLIS2/NPHP7 are the cause of nephronophthisis type 7 both in humans and mice. GLIS2 is a transcription factor with high sequence homology to GLI1, GLI2 and GLI3, the vertebrate orthologs of Drosophila Ci (cubitus interruptus). Like Drosophila Ci, GLI proteins are key molecules in the vertebrate Hedgehog (Hh) signaling, a pathway highly conserved in the evolution and central in the regulation of proliferation, differentiation and repair during embryonc and postnatal life. We have recently tested and confirmed the hypothesis that Glis2 is a repressor of Hh signaling in the postnatal kidney and demonstrated that malfunctioning of this pathway results in kidney cysts and fibrosis, increased inflammatory infiltration and apoptosis, but the molecular events leading to this kidney phenotype are still unexplained. Preliminary studies performed in my laboratory have unexpectedly revealed that loss of Glis2 results in over expression of Toll like receptor 2 (Tlr2) and other components of the pro-inflammatory TLR/NF-?B pathway in kidney epithelial cells and in the Tlr2-dependent activation of this pathway. We have also found that expression of several miRNAs in kidney epithelial cells is controlled by Glis2, suggesting that microRNAs are effectors of Glis2/Hh signaling in mouse kidneys. We propose to test in vivo the effect of the inhibition of TLR-2/NF-?B signaling on the inflammatory infiltration and fibrosis in Glis2mut/mut mice kidneys by generating Tlr2-/-;Glis2mut/mut and Myd88flox/flox;Glis2mut/mut;KspCre double mutants and establishing Tlr2-/-;Glis2mut/mut bone marrow chimeras. In addition, we propose to systematically identify at genome wide level the canonical and non-canonical Glis2 target genes by chromatin immunoprecipitation-highly parallel sequencing (ChIP-Seq) and high-throughput microRNA sequencing (miRNA-Seq). In light of our most recent results, identifying downstream effectors that are deregulated in Glis2 knockout kidneys has gained even more importance, and is likely to produce further insights in the complex regulatory network that is altered in our model of cystic kidney diseases and fibrosis.
Nephronophthisis (NPHP) is an inherited disease causing cystic and fibrotic degeneration of the kidneys and is one of the most frequent genetic causes of chronic renal failure in the first three decades of life. Neither mechanistic explanations nor effective therapies are currently available for this and other cystic kidney diseases. The purpose of this study is to use the mouse model of NPHP7 to unveil the basic biological processes that result in progressive kidney cystic disease and fibrosis could open the way to future therapies.
