Crumbs2 Is an Essential Slit Diaphragm Protein of the Renal Filtration Barrier

BackgroundCrumbs2 is expressed at embryonic stages as well as in the retina, brain, and glomerular podocytes. Recent studies identifiedCRB2mutations as a novel cause of steroid-resistant nephrotic syndrome (SRNS).MethodsTo study the function of Crb2 at the renal filtration barrier, mice lacking Crb2 exclusively in podocytes were generated. Gene expression and histologic studies as well as transmission and scanning electron microscopy were used to analyze theseCrb2podKOknockout mice and their littermate controls. Furthermore, high-resolution expansion microscopy was used to investigate Crb2 distribution in murine glomeruli. For pull-down experiments, live cell imaging, and transcriptome analyses, cell lines were applied that inducibly express fluorescent protein–tagged CRB2 wild type and mutants.ResultsCrb2podKOmice developed proteinuria directly after birth that preceded a prominent development of disordered and effaced foot processes, upregulation of renal injury and inflammatory markers, and glomerulosclerosis. Pull-down assays revealed an interaction of CRB2 with Nephrin, mediated by their extracellular domains. Expansion microscopy showed that in mice glomeruli, Crb2 and Nephrin are organized in adjacent clusters. SRNS-associated CRB2 protein variants and a mutant that lacks a putative conservedO-glycosylation site were not transported to the cell surface. Instead, mutants accumulated in the ER, showed altered glycosylation pattern, and triggered an ER stress response.ConclusionsCrb2 is an essential component of the podocyte’s slit diaphragm, interacting with Nephrin. Loss of slit diaphragm targeting and increasing ER stress are pivotal factors for onset and progression of CRB2-related SRNS.

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Mutations in KIRREL1, a slit diaphragm component, cause steroid-resistant nephrotic syndrome

Kidney International ◽

10.1016/j.kint.2019.06.016 ◽

2019 ◽

Vol 96 (4) ◽

pp. 883-889 ◽

Cited By ~ 3

Author(s):

Ashish K. Solanki ◽

Eugen Widmeier ◽

Ehtesham Arif ◽

Shailza Sharma ◽

Ankana Daga ◽

...

Keyword(s):

Nephrotic Syndrome ◽

Slit Diaphragm ◽

Steroid Resistant ◽

Steroid Resistant Nephrotic Syndrome

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TBC1D8B Mutations Implicate RAB11-Dependent Vesicular Trafficking in the Pathogenesis of Nephrotic Syndrome

Journal of the American Society of Nephrology ◽

10.1681/asn.2019040414 ◽

2019 ◽

Vol 30 (12) ◽

pp. 2338-2353 ◽

Cited By ~ 3

Author(s):

Lina L. Kampf ◽

Ronen Schneider ◽

Lea Gerstner ◽

Roland Thünauer ◽

Mengmeng Chen ◽

...

Keyword(s):

Nephrotic Syndrome ◽

Slit Diaphragm ◽

Missense Mutations ◽

Loss Of Function ◽

Cellular Functions ◽

Steroid Resistant ◽

Steroid Resistant Nephrotic Syndrome ◽

Whole Exome ◽

Immortalized Cell

BackgroundMutations in about 50 genes have been identified as monogenic causes of nephrotic syndrome, a frequent cause of CKD. These genes delineated the pathogenetic pathways and rendered significant insight into podocyte biology.MethodsWe used whole-exome sequencing to identify novel monogenic causes of steroid-resistant nephrotic syndrome (SRNS). We analyzed the functional significance of an SRNS-associated gene in vitro and in podocyte-like Drosophila nephrocytes.ResultsWe identified hemizygous missense mutations in the gene TBC1D8B in five families with nephrotic syndrome. Coimmunoprecipitation assays indicated interactions between TBC1D8B and active forms of RAB11. Silencing TBC1D8B in HEK293T cells increased basal autophagy and exocytosis, two cellular functions that are independently regulated by RAB11. This suggests that TBC1D8B plays a regulatory role by inhibiting endogenous RAB11. Coimmunoprecipitation assays showed TBC1D8B also interacts with the slit diaphragm protein nephrin, and colocalizes with it in immortalized cell lines. Overexpressed murine Tbc1d8b with patient-derived mutations had lower affinity for endogenous RAB11 and nephrin compared with wild-type Tbc1d8b protein. Knockdown of Tbc1d8b in Drosophila impaired function of the podocyte-like nephrocytes, and caused mistrafficking of Sns, the Drosophila ortholog of nephrin. Expression of Rab11 RNAi in nephrocytes entailed defective delivery of slit diaphragm protein to the membrane, whereas RAB11 overexpression revealed a partial phenotypic overlap to Tbc1d8b loss of function.ConclusionsNovel mutations in TBC1D8B are monogenic causes of SRNS. This gene inhibits RAB11. Our findings suggest that RAB11-dependent vesicular nephrin trafficking plays a role in the pathogenesis of nephrotic syndrome.

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The importance of genetic study in steroid-resistant nephrotic syndrome

Journal of Renal Injury Prevention ◽

10.15171/jrip.2019.51 ◽

2019 ◽

Vol 8 (4) ◽

pp. 271-282 ◽

Cited By ~ 2

Author(s):

Sepideh Zununi Vahed ◽

Hakimeh Moghaddas Sani ◽

Sima Rajabzadeh ◽

Ziba Nariman-Saleh-Fam ◽

Mina Hejazian ◽

...

Keyword(s):

Nephrotic Syndrome ◽

Current Knowledge ◽

Gene Mutations ◽

Therapeutic Benefit ◽

Steroid Resistance ◽

Steroid Resistant ◽

Steroid Resistant Nephrotic Syndrome ◽

Filtration Barrier ◽

Stage Renal Disease ◽

End Stage

Steroid-resistant nephrotic syndrome (SRNS) is a challenging clinical task. It has heterogeneous etiology and extremely variable clinical outcomes and generally progresses to end-stage renal disease (ESRD). Different gene mutations in podocyte’s slit diaphragm, mitochondria, and cytoskeleton proteins, as well as glomerular basement membrane (GBM) have been associated with SRNS. These proteins regulate the function of the glomerular filtration barrier. Advances in genetic approaches and podocytology have led to discover the SRNS-causing genes that lead to a better understanding of the drug resistance. More than 45 genetic mutations have been recognized in the hereditary form of SRNS. This review offers an update on the current knowledge of steroid resistance-causing gene mutations in podocytes. Understanding the specific genes involved in SRNS would guarantee an optimum therapeutic benefit of steroid treatment.

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Case Report: The Monogenic Familial Steroid-Resistant Nephrotic Syndrome Caused by a Novel Missense Mutation of NPHS2 Gene A593C in a Chinese Family

Frontiers in Pediatrics ◽

10.3389/fped.2021.692727 ◽

2021 ◽

Vol 9 ◽

Author(s):

Ling Bai ◽

Jing Zhuang ◽

Changrong Zhang ◽

Chen Lu ◽

Xuefei Tian ◽

...

Keyword(s):

Nephrotic Syndrome ◽

Missense Mutation ◽

De Novo ◽

Treatment Strategies ◽

Calcineurin Inhibitors ◽

Chinese Family ◽

Gene Variants ◽

Steroid Resistant ◽

Steroid Resistant Nephrotic Syndrome ◽

Filtration Barrier

Background: Pathogenic variants in the NPHS2 gene encoding podocin in kidney podocytes are associated with autosomal recessive steroid-resistant nephrotic syndrome (SRNS) by disrupting podocyte function and the integrity of the glomerular filtration barrier. The outcome is generally poor by progressing into end-stage kidney disease (ESKD). With the help of gene diagnostics, we can further understand the role of podocin of podocytes in the development and progression of SRNS. However, the pathological mutation of NPHS2 and clinical relevance remain further elusive.Case Presentation: Two siblings, a 15-year-old girl and her 10-year-old younger brother from a consanguineous Chinese family, presented with nephrotic syndrome. Both of them developed progressive proteinuria starting from the 5-year-old of age. The renal pathological lesions for them revealed focal segmental glomerulosclerosis (FSGS). There was no response to the glucocorticoid, calcineurin inhibitors, and rituximab treatment. The female affected patient received the hemodialysis treatment due to ESKD in June 2020; the male patient was still in follow-up presenting with SRNS. The mutational screening of the two patients and their parents using Trio whole-exome sequencing showed the NPHS2 gene de novo missense mutation in exon 5 (A593C), for which the two siblings were homozygous and their parents confirmed heterozygous asymptomatic carriers. No other SRNS-related gene variants with the SRNS were determined.Conclusion: Pathological gene variants screening in children clinically suspected with SRNS might be helpful in the diagnosis as well as appropriate decisions on treatment strategies and prediction of prognosis.

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NPHS2Mutations: A Closer Look to Latin American Countries

BioMed Research International ◽

10.1155/2017/7518789 ◽

2017 ◽

Vol 2017 ◽

pp. 1-6 ◽

Cited By ~ 1

Author(s):

Mara Sanches Guaragna ◽

Anna Cristina G. B. Lutaif ◽

Andréa T. Maciel-Guerra ◽

Vera M. S. Belangero ◽

Gil Guerra-Júnior ◽

...

Keyword(s):

Nephrotic Syndrome ◽

Clinical Practice ◽

Glomerular Filtration ◽

Latin American ◽

Glomerular Filtration Barrier ◽

Steroid Resistant ◽

Steroid Resistant Nephrotic Syndrome ◽

Filtration Barrier ◽

Steroid Sensitive ◽

Latin American Countries

Nephrotic syndrome is one of the most common kidney pathologies in childhood, being characterized by proteinuria, edema, and hypoalbuminemia. In clinical practice, it is divided into two categories based on the response to steroid therapy: steroid-sensitive and steroid resistant. Inherited impairments of proteins located in the glomerular filtration barrier have been identified as important causes of nephrotic syndrome, with one of these being podocin, coded byNPHS2gene.NPHS2mutations are the most frequent genetic cause of steroid resistant nephrotic syndrome. The aim of this review is to update the list ofNPHS2mutations reported between June 2013 and February 2017, with a closer look to mutations occurring in Latin American countries.

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Rituximab efficacy in pediatric patients with refractory nephrotic syndrome

International Journal of Research in Medical Sciences ◽

10.18203/2320-6012.ijrms20170911 ◽

2017 ◽

Vol 5 (4) ◽

pp. 1312

Author(s):

Badr A. Alaifan ◽

Ahmed A. Jamjoom ◽

Raghad I. Jamal Aldeen ◽

Mohammad F. Hariri ◽

Raghad F. Hakim ◽

...

Keyword(s):

Nephrotic Syndrome ◽

Standard Deviation ◽

University Hospital ◽

Steroid Resistant ◽

Steroid Resistant Nephrotic Syndrome ◽

Steroid Dependency ◽

Filtration Barrier ◽

King Abdulaziz University ◽

Steroid Sensitive ◽

Refractory Nephrotic Syndrome

Background: Nephrotic syndrome (NS) in children is a disease of glomerular filtration barrier failure, manifesting with severe proteinuria leading to hypoalbuminemia, hypercholesterolemia, and generalized edema. it could be primary or secondary. In primary NS, also known as idiopathic NS, the histological findings of Primary NS include minimal change disease which mainly respond to steroids (steroid sensitive NS), focal segmental glomerulosclerosis which are usually steroid resistant or membranous nephropathy. Rituximab has been shown to be effective for patients with complicated FRNS/SDNS and refractory SRNS. While the incidence of nephrotic syndrome (NS) is increasing, the morbidity of difficult-to-treat NS is significant.Methods: This is a retrospective cohort study that took place in King Abdulaziz University Hospital from 2012 to 2016. Patients included: Any patient under 18 years, and diagnosed with steroid resistant and dependent nephrotic syndrome. Patients excluded: Any patient above 18 years, and known to have secondary Nephrotic Syndrome.Results: Present study consists of 24 children with nephrotic syndrome (NS) were recruited in the study. In the population 8 patients (33.33 %) were diagnosed with SDNS, while the other 16 patients (66.67%) were diagnosed SRNS. Also, patients who were treated with Rituximab we found that (the mean) number of relapses per year before rituximab was about 2.67±1.49 (standard deviation 1.49), while patient who relapsed after rituximab was about 1.09±1.38 (standard deviation 1.38).Conclusions: Rituximab is a biological agent that started to be widely used in difficult nephrotic syndrome cases. The effectiveness of rituximab is most observed in steroid depended nephrotic syndrome patients since it decreases the frequency of relapses and steroid dependency. However, it has been shown that it is less effective in steroid resistant nephrotic syndrome cases and was associated with significant numbers of relapses.

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