Abstract
Nephrotic syndrome is characterized by severe proteinuria, hypoalbuminaemia, edema and hyperlipidaemia. Genetic studies of nephrotic syndrome have led to the identification of proteins playing a crucial role in slit diaphragm signaling, regulation of actin cytoskeleton dynamics and cell-matrix interactions. The laminin α5 chain is essential for embryonic development and, in association with laminin β2 and laminin γ1, is a major component of the glomerular basement membrane, a critical component of the glomerular filtration barrier. Mutations in LAMA5 were recently identified in children with nephrotic syndrome. Here, we have identified a novel missense mutation (E884G) in the uncharacterized L4a domain of LAMA5 where homozygous mice develop nephrotic syndrome with severe proteinuria with histological and ultrastructural changes in the glomerulus mimicking the progression seen in most patients. The levels of LAMA5 are reduced in vivo and the assembly of the laminin 521 heterotrimer significantly reduced in vitro. Proteomic analysis of the glomerular extracellular fraction revealed changes in the matrix composition. Importantly, the genetic background of the mice had a significant effect on aspects of disease progression from proteinuria to changes in podocyte morphology. Thus, our novel model will provide insights into pathologic mechanisms of nephrotic syndrome and pathways that influence the response to a dysfunctional glomerular basement membrane that may be important in a range of kidney diseases.
Highlights
A novel model of nephrotic syndrome results from a point mutation in Lama[5] and is modified by genetic background
Nephrotic syndrome is characterized by severe proteinuria, hypoalbuminaemia, edema and hyperlipidaemia
LAMA5 where homozygous mice develop nephrotic syndrome with severe proteinuria with histological and ultrastructural changes in the glomerulus mimicking the progression seen in most patients
Summary
Mary Lyon Centre in Harwell, UK, in specific pathogen-free conditions. All animal procedures were performed under the guidance issued by the Medical Research Council in “Responsibility in the Use of Animals for Medical Research” (July 1993) and in accordance with. DNA from the G1 founder of the pedigree was sent for wholegenome sequencing employing the Illumina HiSeq platform (Oxford Genomics Centre, Wellcome Trust Centre for Human Genetics) and analyzed as previously described.[29] The Lama[5] mutation was validated using Sanger sequencing (Source Bioscience). For transmission electron microscopy (TEM) and scanning electron microscopy (SEM), 1-mm[3] cubes of kidney cortex were fixed in 3% glutaraldehyde and 4% formaldehyde in 0.1 M PIPES Q11 buffer, pH 7.2 (minimum, 1 hour). Samples of medium and cell lysate were run on 3%. As part of a phenotype-driven mutagenesis screen,[29] we identified mice with plasma albumin levels 2 SDs below littermate range at 6 months of age (Figure 1a) and increased levels of urea and creatinine (Figure 1b and c).
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