Laminin β2 Gene Missense Mutation Produces Endoplasmic Reticulum Stress in Podocytes

Abstract

Mutations in the laminin b2 gene (LAMB2) cause Pierson syndrome, a severe congenital nephrotic syndrome with ocular and neurologic defects. LAMB2 is a component of the laminin-521 (a5b2g1) trimer, an important constituent of the glomerular basement membrane (GBM). The C321R-LAMB2 missense mutation leads to congenital nephrotic syndrome but only mild extrarenal symptoms; the mechanisms underlying the development of proteinuria with this mutation are unclear. We generated three transgenic mouse lines, in which rat C321R-LAMB2 replaced mouse LAMB2 in the GBM. During the first postnatal month, expression of C321R-LAMB2 attenuated the severe proteinuria exhibited by Lamb2 2/2 mice in a dose-dependent fashion; proteinuria eventually increased, however, leading to renal failure. The C321R mutation caused defective secretion of laminin-521 from podocytes to the GBM accompanied by podocyte endoplasmic reticulum (ER) stress, likely resulting from protein misfolding. Moreover, ER stress preceded the onset of significant proteinuria and was manifested by induction of the ER-initiated apoptotic signal C/EBP homologous protein (CHOP), ER distention, and podocyte injury. Treatment of cells expressing C321R-LAMB2 with the chemical chaperone taurodeoxycholic acid (TUDCA), which can facilitate protein folding and trafficking, greatly increased the secretion of the mutant LAMB2. Taken together, these results suggest that the mild variant of Pierson syndrome caused by the C321R-LAMB2 mutation may be a prototypical ER storage disease, which may benefit from treatment approaches that target the handling of misfolded proteins.

Essential Role of X-Box Binding Protein-1 during Endoplasmic Reticulum Stress in Podocytes

“…4 Recent evidence has suggested a robust increase in podocyte BiP due to ER stress caused by Pierson syndrome (laminin mutations), Alport syndrome, thin membrane basement disease (collagen IV mutations), Heymann nephritis, puromcyin-induced nephrosis, and mesangioproliferative GN. [5][6][7][8] Therefore, in the current study, we first verified that treatment of cultured podocytes with tunicamycin, an agent that inhibits N-glycosylation of proteins in the ER, results in an increase in ER stress and activation of the UPR. This effect was further validated in vivo by glomeruli isolated from mice injected with rabbit-anti-mouse glomerular basement membrane nephrotoxic sera (NTS).…”

Elevated urinary CRELD2 is associated with endoplasmic reticulum stress–mediated kidney disease

“…, WT, and mutant transgenic mice have all been described previously (5,28). C57BL/6J mice were obtained from The Jackson Laboratory.…”

“…We next investigated whether CRELD2 could serve as a urinary biomarker to detect podocyte ER stress by utilizing a podocyte ER stress-induced NS model that we have developed (5). We have previously shown that Lamb2 -/-mice expressing C321R-LAMB2 in podocytes via the podocyte-specific mouse nephrin promoter (Lamb2 -/-;Tg-C321R mice, hereafter referred to as Tg-C321R mice) resemble features of human NS patients carrying the C321R-LAMB2 mutation (5).…”

“…We have previously shown that Lamb2 -/-mice expressing C321R-LAMB2 in podocytes via the podocyte-specific mouse nephrin promoter (Lamb2 -/-;Tg-C321R mice, hereafter referred to as Tg-C321R mice) resemble features of human NS patients carrying the C321R-LAMB2 mutation (5). We have also shown that, in expression-matched Lamb2 -/-;Tg-WT mice (hereafter referred to as Tg-WT mice), the expression of WT LAMB2 cDNA in podocytes is sufficient to restore the integrity of the glomerular filtration barrier (GFB) in Lamb2 -/-mice (28).…”

“…Tg-C321R mice begin to develop trace proteinuria by 4 weeks of age before any histological changes, then exhibit mild glomerulosclerosis, diffuse foot process effacement, GBM thickening, and overt proteinuria at approximately 6-8 weeks; they finally die after 10-12 weeks (5). At P24-P28, when Tg-C321R mutants exhibit trace proteinuria without notable renal histological alterations, podocyte ER stress induced by the C321R misfolded protein is evident as demonstrated by the upregulation of BiP and CHOP in Tg-C321R podocytes compared with WT and Tg-WT podocytes (5,21). In the current study, we expanded upon these findings by determining whether CRELD2 was also induced and secreted by ER-stressed podocytes at the early stage of proteinuria.…”