Laminin (2 (LAMB2) is a component of Laminin-521, the major laminin trimer of the kidney glomerular basement membrane (GBM). Null mutations in LAMB2 cause Pierson syndrome, characterized by congenital nephrotic syndrome with severe ocular and neurological defects. In contrast, most missense LAMB2 mutations, such as R246Q, cause isolated congenital nephrotic syndrome. To investigate the mechanisms whereby missense mutations cause proteinuria, we have generated transgenic mice in which R246Q mutant (2 is expressed in podocytes at different levels and replaces normal (2 in the GBM. Our preliminary data show that these mice exhibit proteinuria that can be attenuated by increased deposition of mutant R246Q-LAMB2 into the GBM. Moreover, in vitro, secretion of mutant LAMB2 proteins is severely inhibited compared to wild-type. Therefore, we hypothesize that pathogenic LAMB2 point mutations cause protein misfolding, ER stress, and secretion defects both in vitro and in vivo. Chemical chaperones, such as taurodeoxycholic acid (TUDCA), are low molecular weight compounds that can stabilize protein conformation and rescue trafficking-defective misfolded proteins. We have shown that TUDCA treatment of cells expressing the mutants significantly increases the secretion of mutant LAMB2 proteins into the medium. We propose, therefore, that chemical chaperones can improve the folding of mutant LAMB2 proteins, reduce ER stress, and improve the secretion of mutant laminin trimers into the GBM, thereby attenuating proteinuria in Lamb2-/-;mutLAMB2 transgenic mice. To test these hypotheses, we will: 1. Examine whether LAMB2 point mutations cause protein misfolding and ER stress both in vitro and in vivo. 2. Determine whether chemical chaperones can improve the secretion of LAMB2 point mutants and reduce ER stress in vitro. 3. Investigate whether chemical chaperones improve secretion of mutant laminin (2 and attenuate proteinuria in Lamb2-/-;mutLAMB2 mice. These studies will help us to understand the molecular mechanisms underlying the pathogenesis of congenital nephrotic syndrome and assay the feasibility for therapeutic use of chemical chaperones in a relevant animal model. Our results may have significant therapeutic implications for the treatment of congenital nephrotic syndrome in patients carrying missense LAMB2 mutations.
Congenital nephrotic syndrome is an important childhood kidney disease which causes proteinuria and progressive renal failure. We are studying whether the administration of pharmacologically active chaperones can ameliorate proteinuria in an animal model. The results may indicate a new treatment scheme for renal proteinuric diseases.
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