A novel model of nephrotic syndrome results from a point mutation in Lama5 and is modified by genetic background

Nephrotic syndrome is characterised by severe proteinuria, hypoalbuminaemia, oedema and hyperlipidaemia. Genetic studies of nephrotic syndrome have led to the identification of proteins playing a crucial role in slit diaphragm signalling, 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, it is a major component of the glomerular basement membrane. Mutations in LAMA5 were recently identified in children with nephrotic syndrome. We have identified a novel missense mutation (E884G) in the uncharacterised L4a domain of LAMA5 where homozygous mice develop nephrotic syndrome with severe proteinuria with histological and ultrastructural changes in the glomerulus. 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 had a significant effect on aspects of disease progression from proteinuria to changes in podocyte morphology. This novel model will provide insights into patho-mechanisms of nephrotic syndrome and pathways that influence the response to a dysfunctional glomerular basement membrane