Neph1 and nephrin interaction in the slit diaphragm is an important determinant of glomerular permeability

Liu, Gang; Kaw, Beenu; Kurfis, Jayson; Rahmanuddin, Syed; Kanwar, Yashpal S.; Chugh, Sumant S.

doi:10.1172/jci200318242

Cited by 170 publications

(38 citation statements)

References 32 publications

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“…The observation that mutation or deletion of nephrin results in both failure of proper foot process morphogenesis and concomitant proteinuria first suggested the hypothesis that nephrin serves as a component of a signaling complex that directly integrates podocyte junctional integrity with cytoskeletal dynamics (3,4,6,14). The observations made herein provide the first direct evidence to our knowledge for a tyrosine phosphorylation-mediated signaling mechanism by which this integrative function is derived.…”

Section: Discussionsupporting

confidence: 51%

“…Several observations suggest that nephrin and the complex of proteins with which it is physically associated serve as a signaling nexus that integrate intercellular junction and cytoskeletal dynamics (12). This complex presumably associates with the foot process's subcortical actin cytoskeleton (13) via intermediary proteins that include ZO-1 (14), CD2ap (15), and CASK (16). While it is unlikely that all of the components of the nephrinassociated protein complex have been defined, it is remarkable that deletion in mice of nephrin-interacting proteins including Neph1, podocin, and CD2ap results in the development of proteinuria and alteration of podocyte cytoskeletal architecture (15,(17)(18)(19).…”

Section: Introductionmentioning

confidence: 99%

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Nephrin ectodomain engagement results in Src kinase activation, nephrin phosphorylation, Nck recruitment, and actin polymerization

Verma¹

2006

Journal of Clinical Investigation

293

411

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A properly established and maintained podocyte intercellular junction, or slit diaphragm, is a necessary component of the selective permeability barrier of the kidney glomerulus. The observation that mutation or deletion of the slit diaphragm transmembrane protein nephrin results in failure of podocyte foot process morphogenesis and concomitant proteinuria first suggested the hypothesis that nephrin serves as a component of a signaling complex that directly integrates podocyte junctional integrity with cytoskeletal dynamics. The observations made herein provide the first direct evidence to our knowledge for a phosphorylation-mediated signaling mechanism by which this integrative function is derived. Our data support the model that during podocyte intercellular junction formation, engagement of the nephrin ectodomain induces transient Fyn catalytic activity that results in nephrin phosphorylation on specific nephrin cytoplasmic domain tyrosine residues. We found that this nephrin phosphorylation event resulted in recruitment of the SH2-SH3 domain-containing adapter protein Nck and assembly of actin filaments in an Nck-dependent fashion. Considered in the context of the role of nephrin family proteins in other organisms and the integral relationship of actin dynamics and junction formation, these observations establish a function for nephrin in regulating actin cytoskeletal dynamics. IntroductionGlomerular visceral epithelial cells play a central role in maintaining the selective filtration barrier of the renal glomerulus. These cells are also termed podocytes to describe the foot-like appearance of numerous interdigitating foot processes that arise from their cell bodies and surround glomerular capillary walls. Glomerular filtrate passes across the specialized intercellular junction -also termed the slit diaphragm -formed at the interface of these interdigitating foot processes.In response to injury, podocytes undergo a dramatic change in morphology termed foot process effacement resulting from alteration in cytoskeletal and intercellular junctional architecture. By electron microscopy, effacement is manifested by retraction and spreading of podocyte processes. Effacement is a fluid and reversible process that directly correlates with the development of proteinuria both in human disease and in experimental models.The cellular and molecular mechanisms that integrate podocyte morphology and filter integrity are incompletely defined. Recent investigations have focused on identifying and characterizing the interrelationships and functions of the molecular components of the foot process intercellular junction because several of these components are necessary for development of normal podocyte structure and filter integrity (reviewed in refs. 1, 2).

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Section: Discussionsupporting

confidence: 51%

Section: Introductionmentioning

confidence: 99%

Nephrin ectodomain engagement results in Src kinase activation, nephrin phosphorylation, Nck recruitment, and actin polymerization

Verma¹

2006

Journal of Clinical Investigation

293

411

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“…However, here we cannot rule out the possibility that the observed SDs are defective. We note that we are not the first to report the existence of proteinuria in the absence of FP effacement; it has also been observed in preeclampsia, in other animal models, and in sporadic human cases (34)(35)(36)(37)(38).…”

Section: Figurementioning

confidence: 66%

Proteinuria precedes podocyte abnormalities inLamb2-/- mice, implicating the glomerular basement membrane as an albumin barrier

Jarad¹

2006

Journal of Clinical Investigation

202

159

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Primary defects in either podocytes or the glomerular basement membrane (GBM) cause proteinuria, a fact that complicates defining the barrier to albumin. Laminin β2 (LAMB2) is a GBM component required for proper functioning of the glomerular filtration barrier. To investigate the GBM's role in glomerular filtration, we characterized GBM and overlying podocyte architecture in relation to development and progression of proteinuria in Lamb2 -/-mice, which model Pierson syndrome, a rare congenital nephrotic syndrome. We found ectopic deposition of several laminins and mislocalization of anionic sites in the GBM, which together suggest that the Lamb2 -/-GBM is severely disorganized, although it is ultrastructurally intact. Importantly, albuminuria was detectable shortly after birth and preceded podocyte foot process effacement and loss of slit diaphragms by at least 7 days. Expression and localization of slit diaphragm and foot process-associated proteins appeared normal at early stages. GBM permeability to the electron-dense tracer ferritin was dramatically elevated in Lamb2 -/-mice, even before widespread foot process effacement. Increased ferritin permeability was not observed in nephrotic CD2-associated protein-null (Cd2ap -/-) mice, which have a primary podocyte defect. Together these data show that the GBM serves as a barrier to protein in vivo and that the glomerular slit diaphragm alone is not sufficient to prevent the passage of albumin into the urinary space.

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“…In immuno-EM, P-cadherin (15) and FAT (18) have been localized in podocytes close to the diaphragm area. However, the P-cadherin expression pattern differs developmentally from that of nephrin (44), and P-cadherin does not immunoprecipitate with nephrin or Neph1 (17). Also, in kidneys of NPHS1 fetuses, which lack slit diaphragm and nephrin, P-cadherin is expressed normally (44).…”

Section: Discussionmentioning

confidence: 99%

“…For proteins of the size of albumin molecules or larger, nephrin is a decisive determinant for glomerular filtration, as seen in 3 genetic mouse models for glomerular protein leakage (13,14). In addition to nephrin, P-cadherin (15), the nephrin homolog Neph1 (16,17), and the large cadherin-like protein FAT (human homologue to the Drosophila tumor suppressor fat) (18) have been localized extracellularly to the slit diaphragm region.…”

Section: Introductionmentioning

confidence: 99%

Nephrin strands contribute to a porous slit diaphragm scaffold as revealed by electron tomography

Wartiovaara¹,

Öfverstedt²,

Khoshnoodi³

et al. 2004

J. Clin. Invest.

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Nephrin is a key functional component of the slit diaphragm, the structurally unresolved molecular filter in renal glomerular capillaries. Abnormal nephrin or its absence results in severe proteinuria and loss of the slit diaphragm. The diaphragm is a thin extracellular membrane spanning the approximately 40-nm-wide filtration slit between podocyte foot processes covering the capillary surface. Using electron tomography, we show that the slit diaphragm comprises a network of winding molecular strands with pores the same size as or smaller than albumin molecules, as demonstrated in humans, rats, and mice. In the network, which is occasionally stratified, immunogold-nephrin antibodies labeled individually detectable globular cross strands, about 35 nm in length, lining the lateral elongated pores. The cross strands, emanating from both sides of the slit, contacted at the slit center but had free distal endings. Shorter strands associated with the cross strands were observed at their base. Immunolabeling of recombinant nephrin molecules on transfected cells and in vitrified solution corroborated the findings in kidney. Nephrin-deficient proteinuric patients with Finnish-type congenital nephrosis and nephrin-knockout mice had only narrow filtration slits that lacked the slit diaphragm network and the 35-nm-long strands but contained shorter molecular structures. The results suggest the direct involvement of nephrin molecules in constituting the macromolecule-retaining slit diaphragm and its pores.

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Neph1 and nephrin interaction in the slit diaphragm is an important determinant of glomerular permeability

Cited by 170 publications

References 32 publications

Nephrin ectodomain engagement results in Src kinase activation, nephrin phosphorylation, Nck recruitment, and actin polymerization

Nephrin ectodomain engagement results in Src kinase activation, nephrin phosphorylation, Nck recruitment, and actin polymerization

Proteinuria precedes podocyte abnormalities inLamb2-/- mice, implicating the glomerular basement membrane as an albumin barrier

Nephrin strands contribute to a porous slit diaphragm scaffold as revealed by electron tomography

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