scholarly journals A Review of Podocyte Biology

2018 ◽  
Vol 47 (Suppl. 1) ◽  
pp. 3-13 ◽  
Author(s):  
Puneet Garg
Keyword(s):  
Minimal Change Disease ◽  
Intercellular Junctions ◽  
Minimal Change ◽  
Glomerular Sclerosis ◽  
Renal Glomerulus ◽  
Detailed Structure ◽  
Filtration Barrier ◽  
Potential Applications ◽  
Foot Process ◽  
Glomerular Capillaries

Background: Podocyte biology is a developing science that promises to help improve understanding of the mechanistic nature of multiple diseases associated with proteinuria. Proteinuria in nephrotic syndrome has been linked to mechanistic dysfunctions in the renal glomerulus involving the function of podocyte epithelial cells, including podocyte foot process effacement. Summary: Developments in imaging technology are improving knowledge of the detailed structure of the human renal glomerulus and cortex. Podocyte foot processes attach themselves to the glomerular capillaries at the glomerular basement membrane (GBM) forming intercellular junctions that form slit diaphragm filtration barriers that help maintain normal renal function. Damage in this area has been implicated in glomerular disease. Injured podocytes undergo effacement whereby they lose their structure and spread out, leading to a reduction in filtration barrier function. Effacement is typically associated with the presence of proteinuria in focal segmental glomerulosclerosis, minimal change disease, and diabetes. It is thought to be due to a breakdown in the actin cytoskeleton of the foot processes, complex contractile apparatuses that allow podocytes to dynamically reorganize according to changes in filtration requirements. The process of podocyte depletion correlates with the development of glomerular sclerosis and chronic kidney disease. Focal adhesion complexes that interact with the underlying GBM bind the podocytes within the glomerular structure and prevent their detachment. Key Messages: Knowledge of glomerular podocyte biology is helping to advance our understanding of the science and mechanics of the glomerular filtering process, opening the way to a variety of new potential applications for clinical targeting.

scholarly journals P0338CRUMBS HOMOLOG2-EZRIN SIGNALING INDUCED PODOCYTE INJURY, LEADING TO MINIMAL-CHANGE DISEASE(MCD) AND FOCAL SEGMENTAL GLOMERULOSCLEROSIS(FSGS)

2020 ◽  
Vol 35 (Supplement_3) ◽  
Author(s):  
Ichiro Hada
Keyword(s):  
Electron Microscopy ◽  
Nephrotic Syndrome ◽  
Cell Line ◽  
Focal Segmental Glomerulosclerosis ◽  
Minimal Change Disease ◽  
Immunofluorescence Microscopy ◽  
Minimal Change ◽  
Podocyte Injury ◽  
Heavy Proteinuria ◽  
Foot Process

Abstract Background and Aims The etiology and cellular pathogenesis of podocyte injury leading to minimal-change disease (MCD) and focal segmental glomerulosclerosis (FSGS) remain largely obscure. Genetic mutation of crumbs homolog 2 (CRB2) is a cause of congenital nephrotic syndrome. Type-1 transmembrane proteins including CRB2 transduce outside-in signals that are involved in various cellular events including changes in the cytoskeletal network. The aim of the present study is to determine whether alteration of CRB2-mediated signaling in podocytes causes MCD and FSGS. Method Mice were immunized with a partial recombinant protein including the extracellular part of mouse CRB2. Urinalysis was obtained, and the kidney was subjected to histopathology. Kidney samples were also subjected to immunofluorescence microscopy and glomerular isolation to determine whether activation of the ezrin/radixin/moesin (ERM) family of cross-linkers between plasma membrane proteins and the actin cytoskeleton is involved in the pathogenesis of this nephrotic model. A CRB2-expressing mouse podocyte cell line was generated and incubated with anti-CRB2 antibody, and cell lysates were subjected to immunoblot analysis of ERM phosphorylation. The presence of anti-CRB2 antibody in the serum was determined by Western blot analysis. Results Apparent anti-CRB2 antibody was detected in the serum from 4 weeks onward. Immunized mice developed proteinuria at 4 weeks, which continued at least until 29 weeks. Mice developing extremely heavy proteinuria also developed hematuria from 18 weeks onward. Light microscopy revealed MCD in mice with proteinuria alone and FSGS in mice with heavy proteinuria and hematuria. Immunofluorescence microscopy revealed positive granular IgG staining in podocyte foot processes, but not complement C3. Electron microscopy and immuno-electron microscopy revealed alteration of actin organization associated with prominent foot process effacement. Strong phosphorylation of ezrin was observed in the glomerulus from the proteinuric stage and in the cellular lysates from the CRB2-expressing podocyte cell line incubated with anti-CRB2 antibody. Conclusion The current data revealed that binding of anti-CRB2 antibody to the extracellular domain of CRB2 on the podocyte foot process activated the ezrin-cytoskeleton network, leading to podocyte injury. Our data also indicated that signaling by this one molecular can induce two different phenotypes of glomerular injury: MCD and FSGS. In our model, the signaling was activated by anti-CRB2 antibody, but in patients with nephrotic syndrome the CRB2 ligands remain unknown. Therefore, it will be important to identify the soluble factors interacting with CRB2, which may be novel factors contributing to the pathogenesis of MCD and FSGS.

scholarly journals The cell biology of renal filtration

2015 ◽  
Vol 209 (2) ◽  
pp. 199-210 ◽  
Author(s):  
Rizaldy P. Scott ◽  
Susan E. Quaggin
Keyword(s):  
Cell Biology ◽  
Molecular Size ◽  
Renal Glomerulus ◽  
Glomerular Filtration Barrier ◽  
Glomerular Diseases ◽  
Glomerular Function ◽  
Selective Filter ◽  
Circulating Cells ◽  
Filtration Barrier ◽  
Glomerular Capillaries

The function of the kidney, filtering blood and concentrating metabolic waste into urine, takes place in an intricate and functionally elegant structure called the renal glomerulus. Normal glomerular function retains circulating cells and valuable macromolecular components of plasma in blood, resulting in urine with just trace amounts of proteins. Endothelial cells of glomerular capillaries, the podocytes wrapped around them, and the fused extracellular matrix these cells form altogether comprise the glomerular filtration barrier, a dynamic and highly selective filter that sieves on the basis of molecular size and electrical charge. Current understanding of the structural organization and the cellular and molecular basis of renal filtration draws from studies of human glomerular diseases and animal models of glomerular dysfunction.

scholarly journals Minimal Change Disease and IgA Deposition: Separate Entities or Common Pathophysiology?

2013 ◽  
Vol 2013 ◽  
pp. 1-3
Author(s):  
Brandon S. Oberweis ◽  
Aditya Mattoo ◽  
Ming Wu ◽  
David S. Goldfarb
Keyword(s):  
Iga Nephropathy ◽  
Minimal Change Disease ◽  
Minimal Change ◽  
Dramatic Improvement ◽  
Creatinine Ratio ◽  
Urine Protein ◽  
Common Cause ◽  
History Of ◽  
Foot Process

Introduction. Minimal Change Disease (MCD) is the most common cause of nephrotic syndrome in children, while IgA nephropathy is the most common cause of glomerulonephritis worldwide. MCD is responsive to glucocorticoids, while the role of steroids in IgA nephropathy remains unclear. We describe a case of two distinct clinical and pathological findings, raising the question of whether MCD and IgA nephropathy are separate entities or if there is a common pathophysiology.Case Report. A 19-year old man with no medical history presented to the Emergency Department with a 20-day history of anasarca and frothy urine, BUN 68 mg/dL, Cr 2.3 mg/dL, urinalysis 3+ RBCs, 3+ protein, and urine protein : creatinine ratio 6.4. Renal biopsy revealed hypertrophic podocytes on light microscopy, podocyte foot process effacement on electron microscopy, and immunofluorescent mesangial staining for IgA. The patient was started on prednisone and exhibited dramatic improvement.Discussion. MCD typically has an overwhelming improvement with glucocorticoids, while the resolution of IgA nephropathy is rare. Our patient presented with MCD with the uncharacteristic finding of hematuria. Given the improvement with glucocorticoids, we raise the question of whether there is a shared pathophysiologic component of these two distinct clinical diseases that represents a clinical variant.

Discovery of Autoantibodies Targeting Nephrin in Minimal Change Disease Supports a Novel Autoimmune Etiology

2021 ◽  
pp. ASN.2021060794
Author(s):  
Andrew Watts ◽  
Keith Keller ◽  
Gabriel Lerner ◽  
Ivy Rosales ◽  
A. Collins ◽  
...  
Keyword(s):  
Nephrotic Syndrome ◽  
Animal Studies ◽  
Minimal Change Disease ◽  
Molecular Classification ◽  
Minimal Change ◽  
Filtration Barrier ◽  
Steroid Dependent ◽  
Renal Biopsies ◽  
End Stage ◽  
Autoimmune Etiology

Background Failure of the glomerular filtration barrier, primarily by loss of slit diaphragm architecture, underlies nephrotic syndrome in minimal change disease. The etiology remains unknown. The efficacy of B cell-targeted therapies in some patients, together with the known proteinuric effect of antinephrin antibodies in rodent models, prompted us to hypothesize that nephrin autoantibodies may be present in patients with minimal change disease. Methods We evaluated sera from patients with minimal change disease enrolled in the Nephrotic Syndrome Study Network (NEPTUNE) cohort and from our own institutions for circulating nephrin autoantibodies by indirect ELISA and by immunoprecipitation of full-length nephrin from human glomerular extract or a recombinant purified extracellular domain of human nephrin. We also evaluated renal biopsies from our institutions for podocyte-associated punctate IgG colocalizing with nephrin by immunofluorescence Results In two independent patient cohorts, we identified in a subset of patients with minimal change disease circulating nephrin autoantibodies during active disease that were significantly reduced or absent during treatment response. We correlated the presence of these autoantibodies with podocyte-associated punctate IgG in renal biopsies from our institutions. We also identified a patient with steroid-dependent childhood minimal change disease that progressed to end-stage kidney disease; she developed a massive posttransplant recurrence of proteinuria that was associated with high pretransplant circulating nephrin autoantibodies. Conclusions Our discovery of nephrin autoantibodies in a subset of adults and children with minimal change disease aligns with published animal studies and provides further support for an autoimmune etiology. We propose a new molecular classification of nephrin autoantibody minimal change disease to serve as framework for instigation of precision therapeutics for these patients.

scholarly journals Loss of phosphatidylserine flippase β-subunit Tmem30a in podocytes leads to albuminuria and glomerulosclerosis

2021 ◽  
Author(s):  
Wenjing Liu ◽  
Lei Peng ◽  
Wanli Tian ◽  
Yi Li ◽  
Ping Zhang ◽  
...  
Keyword(s):  
Focal Segmental Glomerulosclerosis ◽  
Membranous Nephropathy ◽  
Minimal Change Disease ◽  
Critical Role ◽  
Minimal Change ◽  
Mouse Retina ◽  
Β Subunit ◽  
Filtration Barrier ◽  
Segmental Glomerulosclerosis

Phosphatidylserine (PS) is asymmetrically concentrated in the cytoplasmic leaflet of eukaryotic cell plasma membranes. This asymmetry is regulated by a group of P4 ATPases (named PS flippases) and its β-subunit TMEM30A. The disruption of PS flippase leads to severe human diseases. Tmem30a is essential in the mouse retina, cerebellum and liver. However, the role of Tmem30a in the kidney, where it is highly expressed, remains unclear. Podocytes in the glomerulus form a branched interdigitating filtration barrier that can prevent the traversing of large cellular elements and macromolecules from the blood into the urinary space. Damage to podocytes can disrupt the filtration barrier and lead to proteinuria and podocytopathy, including focal segmental glomerulosclerosis, minimal change disease, membranous nephropathy, and diabetic nephropathy. We observed reduced TMEM30A expression in patients with minimal change disease and membranous nephropathy, indicating potential roles of TMEM30A in podocytopathy. To investigate the role of Tmem30a in the kidney, we generated a podocyte-specific Tmem30a knockout (KO) mouse model using the NPHS2-Cre line. Tmem30a KO mice displayed albuminuria, podocyte degeneration, mesangial cell proliferation with prominent extracellular matrix accumulation and eventual progression to focal segmental glomerulosclerosis (FSGS). Our data demonstrate a critical role of Tmem30a in maintaining podocyte survival and glomerular filtration barrier integrity. Understanding the dynamic regulation of the PS distribution in the glomerulus provides a unique perspective to pinpoint the mechanism of podocyte damage and potential therapeutic targets.

scholarly journals Mechanisms of Glomerular Albumin Filtration and Tubular Reabsorption

2012 ◽  
Vol 2012 ◽  
pp. 1-9 ◽  
Author(s):  
Akihiro Tojo ◽  
Satoshi Kinugasa
Keyword(s):  
Early Stage ◽  
Collecting Duct ◽  
Distal Tubule ◽  
Minimal Change Nephrotic Syndrome ◽  
Minimal Change ◽  
Membrane Rupture ◽  
Filtration Barrier ◽  
Podocyte Detachment ◽  
Foot Process

Albumin is filtered through the glomerulus with a sieving coefficient of 0.00062, which results in approximately 3.3 g of albumin filtered daily in human kidneys. The proximal convoluted tubule reabsorbs 71%, the loop of Henle and distal tubule 23%, and collecting duct 3% of the glomerular filtered albumin, thus indicating that the kidney plays an important role in protein metabolism. Dysfunction of albumin reabsorption in the proximal tubules, due to reduced megalin expression, may explain the microalbuminuria in early-stage diabetes. Meanwhile, massive nonselective proteinuria is ascribed to various disorders of the glomerular filtration barrier, including podocyte detachment, glomerular basement membrane rupture, and slit diaphragm dysfunction in focal segmental glomerulosclerosis, membranous nephropathy, and other glomerulonephritis. Selective albuminuria associated with foot process effacement and tight junction-like slit alteration is observed in the patients with minimal-change nephrotic syndrome, and the albumin uptake is enhanced in the podocyte cell body, possibly mediated by albumin receptors in the low-dose puromycin model. The role of enhanced podocyte albumin transport needs to be investigated to elucidate the mechanism of the selective albuminuria in minimal-change disease.

scholarly journals Dosage-dependent role of Rac1 in podocyte injury

2016 ◽  
Vol 310 (8) ◽  
pp. F777-F784 ◽  
Author(s):  
Xiaoyang Wan ◽  
Mi-Sun Lee ◽  
Weibin Zhou
Keyword(s):  
Kidney Injury ◽  
Small Gtpase ◽  
Glomerular Sclerosis ◽  
Transgenic Zebrafish ◽  
Dependent Manner ◽  
Podocyte Injury ◽  
Filtration Barrier ◽  
Foot Process Effacement ◽  
Rac1 Activity ◽  
Foot Process

Activation of small GTPase Rac1 in podocytes is associated with rodent models of kidney injury and familial nephrotic syndrome. Induced Rac1 activation in podocytes in transgenic mice results in rapid transient proteinuria and foot process effacement, but not glomerular sclerosis. Thus it remains an open question whether abnormal activation of Rac1 in podocytes is sufficient to cause permanent podocyte damage. Using a number of transgenic zebrafish models, we showed that moderate elevation of Rac1 activity in podocytes did not impair the glomerular filtration barrier but aggravated metronidazole-induced podocyte injury, while inhibition of Rac1 activity ameliorated metronidazole-induced podocyte injury. Furthermore, a further increase in Rac1 activity in podocytes was sufficient to cause proteinuria and foot process effacement, which resulted in edema and lethality in juvenile zebrafish. We also found that activation of Rac1 in podocytes significantly downregulated the expression of nephrin and podocin, suggesting an adverse effect of Rac1 on slit diaphragm protein expression. Taken together, our data have demonstrated a causal link between excessive Rac1 activity and podocyte injury in a dosage-dependent manner, and transgenic zebrafish of variable Rac1 activities in podocytes may serve as useful animal models for the study of Rac1-related podocytopathy.

Minimal change disease

2018 ◽  
Author(s):  
Patrick Niaudet ◽  
Alain Meyrier
Keyword(s):  
Differential Diagnosis ◽  
Nephrotic Syndrome ◽  
Renal Biopsy ◽  
Minimal Change Disease ◽  
Minimal Change ◽  
Direct Effects ◽  
Glomerular Filtration Barrier ◽  
Common Cause ◽  
Filtration Barrier ◽  
Steroid Responsiveness

Minimal change disease is the most common cause of nephrotic syndrome in childhood but is not rare in adults. The factors altering permeability of the glomerular filtration barrier are not known, but podocyte structure is significantly altered in the condition and it seems certain that this cell is the target of whatever factors are responsible for the condition. It is still not clear that it is immunologically mediated and many of the agents used to treat it have direct effects on the podocyte. The differential diagnosis includes any other disease causing nephrotic syndrome, and a renal biopsy narrows this down. In children, steroid unresponsiveness is often used as a diagnostic test, and consideration of genetic or other pathologies reserved for patients who show no or poor steroid responsiveness.

scholarly journals Mechanism Underlying Selective Albuminuria in Minimal Change Nephrotic Syndrome

2019 ◽  
Vol 2019 ◽  
pp. 1-8
Author(s):  
Akihiro Tojo
Keyword(s):  
Nephrotic Syndrome ◽  
A Priori ◽  
Minimal Change Nephrotic Syndrome ◽  
Cytoplasmic Dynein ◽  
Minimal Change ◽  
Filtration Barrier ◽  
Urinary Protein Level ◽  
Foot Process ◽  
Albumin Receptor ◽  
Albumin Endocytosis

As water and solutes are filtered through the slit membrane, it is an a priori concept that a slit membrane is an essential filtration barrier for proteins, including albumin. However, in cases of minimal change nephrotic syndrome, the number of slit membranes is reduced by the foot process effacement and tight junction-like cell adhesion. Furthermore, albumin endocytosis is enhanced in the podocytes under condition of minimal change disease, and albumin is selectively transported by the albumin receptor FcRn. Suppressing the endocytosis of albumin with anti-FcRn antibody decreases the urinary protein level. The expression of motor molecules, such as cytoplasmic dynein 1 and myosin IX, is increased in the podocytes under conditions of minimal change nephrotic syndrome, suggesting the enhanced transport of vesicles containing albumin. Podocyte vesicle transport may play an important role in the pathology of selective albuminuria in cases of nephrotic syndrome.

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