A deletion in the N-terminal polymerizing domain of laminin β2 is a new mouse model of chronic nephrotic syndrome

Abstract

The importance of the glomerular basement membrane (GBM) in glomerular filtration is underscored by the manifestations of Alport and Pierson syndromes, caused by defects in type IV collagen a3a4a5 and the laminin b2 chain, respectively. Lamb2 null mice, which model the most severe form of Pierson syndrome, exhibit proteinuria prior to podocyte foot process effacement and are therefore useful for studying GBM permselectivity. We hypothesize that some LAMB2 missense mutations that cause mild forms of Pierson syndrome induce GBM destabilization with delayed effects on podocytes. While generating a CRISPR/Cas9-mediated analogue of a human LAMB2 missense mutation in mice, we identified a 44-amino acid deletion (LAMB2-Del44) within the laminin N-terminal domain, a domain mediating laminin polymerization. Laminin heterotrimers containing LAMB2-Del44 exhibited a 90% reduction in polymerization in vitro that was partially rescued by type IV collagen and nidogen. Del44 mice showed albuminuria at 1.8-6.0 g/g creatinine (ACR) at one to two months, plateauing at an average 200 g/g ACR at 3.7 months, when GBM thickening and hallmarks of nephrotic syndrome were first observed. Despite the massive albuminuria, some Del44 mice survived for up to 15 months. Blood urea nitrogen was modestly elevated at seven-nine months. Eight to nine-month-old Del44 mice exhibited glomerulosclerosis and interstitial fibrosis. Similar to Lamb2 À/À mice, proteinuria preceded foot process effacement. Foot processes were widened but not effaced at one-two months despite the high ACRs. At three months some individual foot processes were still observed amid widespread effacement. Thus, our chronic model of nephrotic syndrome may prove useful to study filtration mechanisms, long-term proteinuria with preserved kidney function, and to test therapeutics.

A mutation affecting laminin alpha 5 polymerisation gives rise to a syndromic developmental disorder

“…The relative importance of polymerisation to LAMA5 function during fetal development is poorly understood. However, mutations in LAMB2 LN domains cause Pierson syndrome, indicating that abrogated polymerisation is important for maintaining the in vivo integrity and functionality of the glomerular BM (McKee et al, 2018;Funk et al, 2018Funk et al, , 2020. Moreover, recent crystallographic studies have identified a protein interface within the LN domain in the region of a PLENGE sequence motif which appears to be important for this oligomerisation (Hussain et al, 2011).…”

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

“…E884G is capable of interacting with other laminin chains to some degree, as was observed in the LAMB2-Del44 mice [16], allowing trimer formation. Conversely, we observed that that…”

“…Mutations in the LAMB2 gene, encoding the laminin β2 chain, cause disorders with a wide clinical spectrum. Truncating mutations lead to Pierson syndrome, characterised by microcoria, congenital NS, muscular hypotonia and neurodevelopmental defects [12][13][14], whilst missense variants cause a much milder variant of Pierson syndrome or isolated congenital NS [15,16].…”

A Biomimetic In Vitro Model of the Kidney Filtration Barrier Using Tissue‐Derived Glomerular Basement Membrane

“…[ 41 ] Loss or mutation to structural components of the GBM leads to proteinuria and renal disease. [ 42–44 ] GBM/podocyte interactions are also critical to maintaining a stringent size‐selective glomerular filtration barrier, and loss of proteins that mediate podocyte–GBM adhesion leads to proteinuria in animal models. [ 22,23,45 ] This suggests that both the GBM and the podocyte/GBM interface are critical for proper function of the glomerular filtration barrier.…”