Genetic analysis of crescentic nephritis in rats

Glomerulonephritis is the term used to describe inflammation of the small filtering units (glomeruli) of the kidney, and is a major cause of kidney failure worldwide. Whilst the precise cause of most types of glomerulonephritis is unknown, most are due to an abnormal immune response in which the immune system attacks and damages the kidney. The risk of developing glomerulonephritis is determined in part by inherited (genetic), factors but few of these have been identified. In order to investigate these genetic factors, and to develop new approaches to treatment, an experimental model of glomerulonephritis has been developed in our laboratory. By cross breeding a rat strain resistant to glomerulonephritis with a strain that is susceptible, two genetic areas have been identified that are highly likely to carry genes that confer susceptibility in the experimental model. Further selected breeding of these strains will allow us to narrow the genetic areas sufficiently to begin a search for genes related to the development of glomerulonephritis. We will examine selected genes for changes (mutations) that might explain this difference. The identification of these genes will improve our understanding of susceptibility to glomerulonephritis in the experimental model and will provide candidate genes to be investigated in human glomerulonephritis. Knowledge of these genes may lead to improved new therapies in patients.

Crescentic glomerulonephritis in humans frequently progresses to end-stage renal failure if untreated. Several rodent models of crescentic glomerulonephritis have been developed. Those in the rat show the closest histological similarity to human disease. The Wistar-Kyoto (WKY) rat is uniquely susceptible to crescentic glomerulonephritis amongst rat strains tested, as demonstrated by susceptibility to nephrotoxic nephritis (NTN) and experimental autoimmune glomerulonephritis (EAG). The purpose of this project is to identify genes that predispose to the development of NTN in the WKY rat. In a genome-wide linkage analysis of F2 offspring of NTN-susceptible WKY and NTN-resistant Lewis rats we have identified two quantitative trait loci (QTL), Ntn1 and Ntn2 on chromosomes 13 and 16 with highly significant Lod scores (Lod 8), linked to crescent formation and proteinuria. Congenic strains, in which each QTL is isolated from background effects elsewhere in the genome, are currently being derived in our laboratory. In this project we will (1) complete the derivation of the congenic strains; (2) characterise the congenic strains for NTN susceptibility in order to confirm that the introgressed segments contain NTN susceptibility gene(s); (3) breed and phenotype a series of congenic sublines each carrying a segment of the differential chromosome from the informative congenic lines as a tool for fine mapping to a resolution of 2cM; (4) use bioinformatic and comparative analysis of the human and mouse genomes to construct comprehensive gene maps of the QTLs and to provide ?in silico? functional annotation and expression profiles to prioritise candidate genes contained within the critical intervals and (5) sequence biologically plausible candidate genes in the WKY and LEW parental strains for mutations. Possible functional mutations will be tested in functional assays as appropriate. In follow-up experiments that are beyond the scope of the 3-year grant, putative causal mutations will need to be tested definitively in complementation assays. Whilst identical genes may not be involved in human crescentic glomerulonephritis, it is anticipated that an understanding of the molecular and cellular pathways underlying susceptibility to NTN in the WKY rat will lead to important insights into the pathogenesis of human crescentic glomerulonephritis and may also allow the design of novel therapies.