Mutations in phospholipase C epsilon 1 are not sufficient to cause diffuse mesangial sclerosis

The dominant findings of a recessive man: from Mendel's kid pea to kidney

The research of Mendel, born two centuries ago, still has many direct implications for our everyday clinical work. He introduced the terms "dominant" and "recessive" characters and determined their 3:1 ratio in the offspring of heterozygous "hybrid" plants. This distribution allowed calculation of the number of the phenotype-determining "elements," i.e., the alleles, and has been used ever since to prove the monogenic origin of a disorder. The Mendelian inheritance of monogenic kidney disorders is still of great help in distinguishing them from those with multifactorial origin in clinical practice. Inheritance of most monogenic kidney disorders fits to Mendel's observations: the equal contribution of the two parents and the complete penetrance or the direct correlation between the frequency of the recessive character and the degree of inbreeding. Nevertheless, beyond the truth of these basic concepts, several observations have expanded their genetic characteristics. The extreme genetic heterogeneity, the pleiotropy of the causal genes and the role of modifiers in ciliopathies, the digenic inheritance and parental imprinting in some tubulopathies, and the incomplete penetrance and eventual interallelic interactions in podocytopathies, reflect this expansion. For all these reasons, the transmission pattern in a natural setting may depend not only on the "character" but also on the causal gene and the variant. Mendel's passion for research combined with his modest personality and meticulous approach can still serve as an example in the work required to understand the non-Mendelian universe of genetics.

A broad clinical spectrum of PLCε1-related kidney disease and intrafamilial variability

BACKGROUND

The phenotypic and genotypic spectrum and kidney outcome of PLCε1-related kidney disease are not well known. We attempted to study 25 genetically confirmed cases of PLCε1-related kidney disease from 11 centers to expand the clinical spectrum and to determine the relationship between phenotypic and genotypic features, kidney outcome, and the impact of treatment on outcome.

METHODS

Data regarding demographics, clinical and laboratory characteristics, histopathological and genetic test results, and treatments were evaluated retrospectively.

RESULTS

Of 25 patients, 36% presented with isolated proteinuria, 28% with nephrotic syndrome, and 36% with chronic kidney disease stage 5. Twenty patients underwent kidney biopsy, 13 (65%) showed focal segmental glomerulosclerosis (FSGS), and 7 (35%) showed diffuse mesangial sclerosis (DMS). Of the mutations identified, 80% had non-missense, and 20% had missense; ten were novel. No clear genotype-phenotype correlation was observed; however, significant intrafamilial variations were observed in three families. Patients with isolated proteinuria had significantly better kidney survival than patients with nephrotic syndrome at onset (p = 0.0004). Patients with FSGS had significantly better kidney survival than patients with DMS (p = 0.007). Patients who presented with nephrotic syndrome did not respond to any immunosuppressive therapy; however, 4/9 children who presented with isolated proteinuria showed a decrease in proteinuria with steroids and/or calcineurin inhibitors.

CONCLUSION

PLCε1-related kidney disease may occur in a wide clinical spectrum, and genetic variations are not associated with clinical presentation or disease course. However, clinical presentation and histopathology appear to be important determinants for prognosis. Immunosuppressive medications in addition to angiotensin-converting enzyme inhibitors may be beneficial for selected patients. "A higher resolution version of the Graphical abstract is available as Supplementary information".

Mutational landscape of TRPC6, WT1, LMX1B, APOL1, PTPRO, PMM2, LAMB2 and WT1 genes associated with Steroid resistant nephrotic syndrome

BACKGROUND

Nephrotic syndrome appears as a group of symptoms like proteinuria, edema and hyperlipidemia. Identification of monogenic forms revealed the physiology and pathogenesis of the SRNS.

METHODS AND RESULTS

We performed Illumina panel sequencing of seven genes in 90 Indian patients to determine the role of these genetic mutations in nephrotic syndrome prognosis. Samtool was used for variants calling, and SnpEff and Snpsift did variants annotation. Clinical significance and variant classification were performed by the ClinVar database. In SSNS and SRNS patients, we found 0.78% pathogenic and 3.41% likely pathogenic mutations. Pathogenic mutations were found in LAMB2, LMX1B and WT1 genes, while likely pathogenic mutations were found in (6/13) LAMB2, (2/13) LMX1B, (2/13) TRPC6, (2/13) PTPRO and (1/13) PMM2 genes. Approximately 46% likely pathogenic mutations were contributed to the LAMB2 gene in SSNS and SRNS patients. We also detect 30 VUS (variants of uncertain significance), which were found (17/30) pathogenic and (13/30) likely pathogenic by different prediction tools.

CONCLUSIONS

Multigene panels were used for genetic screening of heterogeneous disorders like nephrotic syndrome in the Indian population. We found pathogenic, likely pathogenic and certain VUS, which were responsible for the pathogenesis of the disease. Therefore, mutational analysis of SSNS and SRNS is necessary to avoid adverse effects of corticosteroids, modify the intensity of immunosuppressing agents, and prevent the disease's progression.

Identification of incompletely penetrant variants and interallelic interactions in autosomal recessive disorders by a population-genetic approach

We aimed to identify incompletely penetrant (IP) variants and interallelic interactions in autosomal recessive disorders by a population-genetic approach. Genotype and clinical data were collected from 9038 patients of European origin with ASL, ATP7B, CAPN3, CFTR, CTNS, DHCR7, GAA, GALNS, GALT, IDUA, MUT, NPHS1, NPHS2, PAH, PKHD1, PMM2, or SLC26A4-related disorders. We calculated the relative allele frequency of each pathogenic variant (n = 1936) to the loss-of-function (LOF) variants of the corresponding gene in the patient ( A C p t V / A C p t L O F ) and the general population ( AC gnomAD V / AC gnomAD LOF ) and estimated the penetrance of each variant by calculating their ratio: ( A C p t V / A C p t L O F ) ( A C g n o m A D V / A C g n o m A D L O F ) (V/LOF ratio). We classified all variants as null or hypomorphic based on the associated clinical phenotype. We found 25 variants, 29% of the frequent 85 variants, to be underrepresented in the patient population (V/LOF ratio <30% with p < 7.22 × 10^-5 ), including 22 novel ones in the ASL, CAPN3, CFTR, GAA, GALNS, PAH, and PKHD1 genes. In contrast to the completely penetrant variants (CP), the majority of the IP variants were hypomorphic (IP: 16/18, 88%; CP: 177/933, 19.0%; p = 5.12 × 10^-10 ). Among them, only the NPHS2 R229Q variant was subject to interallelic interactions. The proposed algorithm identifies frequent IP variants and estimates their penetrance and interallelic interactions in large patient cohorts.

Genetic aspects of congenital nephrotic syndrome: a consensus statement from the ERKNet-ESPN inherited glomerulopathy working group

Congenital nephrotic syndrome (CNS) is a heterogeneous group of disorders presenting with massive proteinuria within the first 3 months of life almost inevitably leading to end-stage kidney disease. The Work Group for the European Reference Network for Kidney Diseases (ERKNet) and the European Society for Pediatric Nephrology (ESPN) has developed consensus statement on genetic aspects of CNS diagnosis and management. The presented expert opinion recommends genetic diagnostics as the key diagnostic test to be ordered already during the initial evaluation of the patient, discusses which phenotyping workup should be performed and presents known genotype-phenotype correlations.

Hypertension induces glomerulosclerosis in phospholipase C-ε1 deficiency

Loss-of-function mutations in phospholipase C-ε1 (PLCE1) have been detected in patients with nephrotic syndrome, but other family members with the same mutation were asymptomatic, suggesting additional stressor are required to cause the full phenotype. Consistent with these observations, we determined that global Plce1-deficient mice have histologically normal glomeruli and no albuminuria at baseline. Angiotensin II (ANG II) is known to induce glomerular damage in genetically susceptible individuals. Therefore, we tested whether ANG II enhances glomerular damage in Plce1-deficient mice. ANG II increased blood pressure equally in Plce1-deficient and wild-type littermates. Additionally, it led to 20-fold increased albuminuria and significantly more sclerotic glomeruli in Plce1-deficient mice compared with wild-type littermates. Furthermore, Plce1-deficient mice demonstrated diffuse mesangial expansion, podocyte loss, and focal podocyte foot process effacement. To determine whether these effects are mediated by hypertension and hyperfiltration, rather than directly through ANG II, we raised blood pressure to a similar level using DOCA + salt + uninephrectomy and norepinephrine. This caused a fivefold increase in albuminuria in Plce1-deficient mice and a significant increase in the number of sclerotic glomeruli. Consistent with previous findings in mice, we detected strong PLCE1 transcript expression in podocytes using single cell sequencing of human kidney tissue. In hemagglutinin-tagged Plce1 transgenic mice, Plce1 was detected in podocytes and also in glomerular arterioles using immunohistochemistry. Our data demonstrate that Plce1 deficiency in mice predisposes to glomerular damage secondary to hypertensive insults.

Clinical genetic testing using a custom-designed steroid-resistant nephrotic syndrome gene panel: analysis and recommendations

BACKGROUND

There are many single-gene causes of steroid-resistant nephrotic syndrome (SRNS) and the list continues to grow rapidly. Prompt comprehensive diagnostic testing is key to realising the clinical benefits of a genetic diagnosis. This report describes a bespoke-designed, targeted next-generation sequencing (NGS) diagnostic gene panel assay to detect variants in 37 genes including the ability to identify copy number variants (CNVs).

METHODS

This study reports results of 302 patients referred for SRNS diagnostic gene panel analysis. Phenotype and clinical impact data were collected using a standard proforma. Candidate variants detected by NGS were confirmed by Sanger sequencing/Multiplex Ligation-dependent Probe Amplification with subsequent family segregation analysis where possible.

RESULTS

Clinical presentation was nephrotic syndrome in 267 patients and suspected Alport syndrome (AS) in 35. NGS panel testing determined a likely genetic cause of disease in 44/220 (20.0%) paediatric and 10/47 (21.3%) adult nephrotic cases, and 17/35 (48.6%) of haematuria/AS patients. Of 71 patients with genetic disease, 32 had novel pathogenic variants without a previous disease association including two with deletions of one or more exons of NPHS1 or NPHS2.

CONCLUSION

Gene panel testing provides a genetic diagnosis in a significant number of patients presenting with SRNS or suspected AS. It should be undertaken at an early stage of the care pathway and include the ability to detect CNVs as an emerging mechanism for genes associated with this condition. Use of clinical genetic testing after diagnosis of SRNS has the potential to stratify patients and assist decision-making regarding management.

Application of next-generation sequencing technology to diagnosis and treatment of focal segmental glomerulosclerosis

A broad range of genetic and non-genetic factors can lead to kidney injury that manifests as focal segmental glomerulosclerosis (FSGS), which can be classified into primary (idiopathic) and secondary forms. Previous genetic approaches to familial or sporadic cases of FSGS or steroid-resistant nephrotic syndrome identified causal mutations in a subset of genes. Recently, next-generation sequencing (NGS) approaches are becoming a part of a standard assessment in medical genetics. Current knowledge of the comprehensive genomic information is changing the way we think about FSGS and draws attention not only to identification of novel causal genes, but also to potential roles for combinations of mutations in multiple genes, mutations with complex inheritance, and susceptibility genes with variable penetrance carrying relatively minor but significant effects. This review provides an update on recent advances in the genetic analysis of FSGS and highlights the potential as well as the new challenges of NGS for diagnosis and mechanism-based treatment of FSGS.

Opportunities and Challenges of Genotyping Patients With Nephrotic Syndrome in the Genomic Era

Both targeted and genome-wide linkage and association studies have identified a number of genes and genetic variants associated with nephrotic syndrome (NS). Genotype-phenotype studies of patients with these variants have identified correlations of clear clinical significance. Combined with improved genomic technologies, this has resulted in increasing, and justifiable, enthusiasm for incorporating our patients' genomic information into our clinical management decisions. Here, we summarize our understanding of NS-associated genetic factors, namely rare causal mutations or common risk alleles in apolipoprotein L1. We discuss the complexities inherent in trying to ascribe risk or causality to these variants, particularly as we seek to extend genetic testing to a broader group of patients, including many with sporadic disease. Overall, the thoughtful application and interpretation of these genetic tests will maximize the benefits to our patients with NS in the form of more precise clinical care.

The etiology of congenital nephrotic syndrome: current status and challenges

BACKGROUND

Congenital nephrotic syndrome (CNS), defined as heavy proteinuria, hypoalbuminemia, hyperlipidemia and edema presenting in the first 0-3 months of life, may be caused by congenital syphilis, toxoplasmosis, or congenital viral infections (such as cytomegalovirus). However, the majority of CNS cases are caused by monogenic defects of structural proteins that form the glomerular filtration barrier in the kidneys. Since 1998, an increasing number of genetic defects have been identified for their involvements in the pathogenesis of CNS, including NPHS1, NPHS2, WT1, PLCE1, and LAMB2.

DATA SOURCES

We searched databases such as PubMed, Elsevier and Wanfang with the following key words: congenital nephrotic syndrome, proteinuria, infants, neonate, congenital infection, mechanism and treatment; and we selected those publications written in English that we judged to be relevant to the topic of this review.

RESULTS

Based on the data present in the literature, we reviewed the following topics: 1) Infection associated CNS including congenital syphilis, congenital toxoplasmosis, and congenital cytomegalovirus infection; 2) genetic CNS including mutation of NPHS1 (Nephrin), NPHS2 (Podocin), WT1, LAMB2 (Laminin-β2), PLCE1 (NPHS3); 3) Other forms of CNS including maternal systemic lupus erythematosus, mercury poisoning, renal vein thrombosis, neonatal alloimmunization against neutral endopeptidase.

CONCLUSION

At present, the main challenge in CNS is to identify the cause of disease for individual patients. To make a definitive diagnosis, with the exclusion of infection-related CNS and maternal-associated disorders, pathology, family history, inheritance mode, and other accompanying congenital malformations are sometimes, but not always, useful indicators for diagnosing genetic CNS. Next-generation sequencing would be a more effective method for diagnosing genetic CNS in some patients, however, there are still some challenges with next-generation sequencing that need to be resolved in the future.

The Genetics of Nephrotic Syndrome

Nephrotic syndrome (NS) is a common pediatric kidney disease and is defined as massive proteinuria, hypoalbuminemia, and edema. Dysfunction of the glomerular filtration barrier, which is made up of endothelial cells, glomerular basement membrane, and visceral epithelial cells known as podocytes, is evident in children with NS. While most children have steroid-responsive nephrotic syndrome (SSNS), approximately 20% have steroid-resistant nephrotic syndrome (SRNS) and are at risk for progressive kidney dysfunction. While the cause of SSNS is still not well understood, there has been an explosion of research into the genetic causes of SRNS in the past 15 years. More than 30 proteins regulating the function of the glomerular filtration barrier have been associated with SRNS including podocyte slit diaphragm proteins, podocyte actin cytoskeletal proteins, mitochondrial proteins, adhesion and glomerular basement membrane proteins, transcription factors, and others. A genetic cause of SRNS can be found in approximately 70% of infants presenting in the first 3 months of life and 50% of infants presenting between 4 and 12 months, with much lower likelihood for older patients. Identification of the underlying genetic etiology of SRNS is important in children because it allows for counseling of other family members who may be at risk, predicts risk of recurrent disease after kidney transplant, and predicts response to immunosuppressive therapy. Correlations between genetic mutation and clinical phenotype as well as genetic risk factors for SSNS and SRNS are reviewed in this article.

Loss-of-function mutations in WDR73 are responsible for microcephaly and steroid-resistant nephrotic syndrome: Galloway-Mowat syndrome

Galloway-Mowat syndrome is a rare autosomal-recessive condition characterized by nephrotic syndrome associated with microcephaly and neurological impairment. Through a combination of autozygosity mapping and whole-exome sequencing, we identified WDR73 as a gene in which mutations cause Galloway-Mowat syndrome in two unrelated families. WDR73 encodes a WD40-repeat-containing protein of unknown function. Here, we show that WDR73 was present in the brain and kidney and was located diffusely in the cytoplasm during interphase but relocalized to spindle poles and astral microtubules during mitosis. Fibroblasts from one affected child and WDR73-depleted podocytes displayed abnormal nuclear morphology, low cell viability, and alterations of the microtubule network. These data suggest that WDR73 plays a crucial role in the maintenance of cell architecture and cell survival. Altogether, WDR73 mutations cause Galloway-Mowat syndrome in a particular subset of individuals presenting with late-onset nephrotic syndrome, postnatal microcephaly, severe intellectual disability, and homogenous brain MRI features. WDR73 is another example of a gene involved in a disease affecting both the kidney glomerulus and the CNS.

A maladaptive role for EP4 receptors in mouse mesangial cells

Roles of the prostaglandin E2 E-prostanoid 4 receptor (EP4) on extracellular matrix (ECM) accumulation induced by TGF-β1 in mouse glomerular mesangial cells (GMCs) remain unknown. Previously, we have identified that TGF-β1 stimulates the expression of FN and Col I in mouse GMCs. Here we asked whether stimulation of EP4 receptors would exacerbate renal fibrosis associated with enhanced glomerular ECM accumulation. We generated EP4^Flox/Flox and EP4^+/− mice, cultured primary WT, EP4^Flox/Flox and EP4^+/− GMCs, AD-EP4 transfected WT GMCs (EP4 overexpression) and AD-Cre transfected EP4^Flox/Flox GMCs (EP4 deleted). We found that TGF-β1-induced cAMP and PGE2 synthesis decreased in EP4 deleted GMCs and increased in EP4 overexpressed GMCs. Elevated EP4 expression in GMCs augmented the coupling of TGF-β1 to FN, Col I expression and COX2/PGE2 signaling, while TGF-β1 induced FN, Col I expression and COX2/PGE2 signaling were down-regulated in EP4 deficiency GMCs. 8 weeks after 5/6 nephrectomy (Nx), WT and EP4^+/− mice exhibited markedly increased accumulation of ECM compared with sham-operated controls. Albuminuria, blood urea nitrogen and creatinine (BUN and Cr) concentrations were significantly increased in WT mice as compared to those of EP4^+/− mice. Urine osmotic pressure was dramatically decreased after 5/6 Nx surgery in WT mice as compared to EP4^+/− mice. The pathological changes in kidney of EP4^+/− mice was markedly alleviated compared with WT mice. Immunohistochemical analysis showed significant reductions of Col I and FN in the kidney of EP4^+/− mice compared with WT mice. Collectively, this investigation established EP4 as a potent mediator of the pro-TGF-β1 activities elicited by COX2/PGE2 in mice GMCs. Our findings suggested that prostaglandin E2, acting via EP4 receptors contributed to accumulation of ECM in GMCs and promoted renal fibrosis.

Association of potentially functional genetic variants of PLCE1 with gallbladder cancer susceptibility in north Indian population

BACKGROUND AND OBJECTIVES

Phospholipase C epsilon 1 (PLCE1) plays crucial roles in carcinogenesis and progression of esophageal and gastric cancers. In the present study, we investigated association of GWAS identified rs2274223 A>G and. rs7922612 T>C polymorphism of PLCE1 with susceptibility to gallbladder cancer (GBC).

METHODS

The study involved genotyping of selected PLCE1 variants in 416 GBC cases and 225 controls. Haplotype analysis was done by SNPStats. In silico analyses were performed using bioinformatic tools.

RESULTS

PLCE1 rs2274223 [AG] and rs7922612 [CC] genotypes were found to be significantly associated with an increased risk of GBC [OR = 1.9, p = 0.002; OR = 2.0, p = 0.04, respectively]. PLCE1 haplotype [Grs2274223-Crs7922612] also showed significant association with GBC [OR = 1.8, p = 0.04]. The association was significant in females and GBC patients with stones and female GBC patients with gallstones [OR = 2.6, p = 0.01; OR = 3.3, p = 0.007], respectively. However, no significant associations with other risk factors such as tobacco usage and age of onset were found. Functional prediction of rs2274223 A>G suggested change in protein coding and splicing regulation.

CONCLUSION

The present study found a significant association of PLCE1 rs2274223 and rs7922612 polymorphisms with susceptibility to GBC probably through gallstone-mediated inflammatory pathway.

Genetic variation in PLCE1 is associated with gastric cancer survival in a Chinese population

BACKGROUND

Two genome-wide association studies on gastric cancer showed a previously unknown gastric cancer susceptible locus in PLCE1 at 10q23. We hypothesized that the single nucleotide polymorphism (SNP) rs2274223 A/G is associated with the survival rate of gastric cancer.

METHODS

We genotyped the above SNP in 940 gastric cancer patients to investigate the association between the polymorphism and gastric cancer survival by the TaqMan method.

RESULTS

We found that patients carrying PLCE1 rs2274223 AA genotype survived for a significantly shorter time than those carrying the AG and GG genotypes (log-rank P = 0.046). This significance was enhanced in the dominant model (AA vs. AG/GG, log-rank P = 0.014). Multivariate Cox regression analyses showed that the AG/GG genotypes were associated with a significantly decreased risk of death from gastric cancer [adjusted hazard ratio (HR) = 0.79, 95% confidence interval (CI) = 0.65-0.95]. Most of stratification analysis did not find an enhanced association between the same genotype and prognosis, except for patients with TNM stage III disease (HR = 0.63, 95% CI = 0.48-0.83).

CONCLUSION

Our findings showed that the PLCE1 SNP rs2274223 was associated with significantly improved gastric cancer survival in a Chinese population. Further functional studies are needed to validate our results.

Pathogenesis and therapy of focal segmental glomerulosclerosis: an update

Focal and segmental glomerulosclerosis (FSGS) is an important cause of steroid-resistant nephrotic syndrome in adults and children. It is responsible for 5-20% of all cases of end-stage kidney disease (ESKD) in the United States. The pathogenesis of FSGS has not been fully elucidated; however, data from molecular studies of familial cases in the last two decades suggest that FSGS is a defect of the podocyte. The therapeutic agents available for treatment of FSGS are not very effective and only a small percentage of affected individuals will achieve complete remission. Recent data from molecular biology and molecular genetics has provided insight into the mechanisms of action of old agents and also identification of other novel therapeutic targets. This review focuses on recent advances in the molecular pathogenesis of FSGS and currently available therapeutic agents as well as potential novel therapies.

Changes in extracellular matrix composition regulate cyclooxygenase-2 expression in human mesangial cells

Glomerular diseases are characterized by a sustained synthesis and accumulation of abnormal extracellular matrix proteins, such as collagen type I. The extracellular matrix transmits information to cells through interactions with membrane components, which directly activate many intracellular signaling events. Moreover, accumulating evidence suggests that eicosanoids derived from cyclooxygenase (COX)-2 participate in a number of pathological processes in immune-mediated renal diseases, and it is known that protein kinase B (AKT) may act through different transcription factors in the regulation of the COX-2 promoter. The present results show that progressive accumulation of collagen I in the extracellular medium induces a significant increase of COX-2 expression in human mesangial cells, resulting in an enhancement in PGE2 production. COX-2 overexpression is due to increased COX-2 mRNA levels. The study of the mechanism implicated in COX-2 upregulation by collagen I showed focal adhesion kinase (FAK) activation. Furthermore, we observed that the activation of the phosphatidylinositol 3-kinase (PI3K)/AKT pathway by collagen I and collagen I-induced COX-2 overexpression was abolished by PI3K and AKT inhibitors. Additionally, we showed that the cAMP response element (CRE) transcription factor is implicated. Finally, we studied COX-2 expression in an animal model, NG-nitro-l-arginine methyl ester hypertensive rats. In renal tissue and vascular walls, COX-2 and collagen type I content were upregulated. In summary, our results provide evidence that collagen type I increases COX-2 expression via the FAK/PI3K/AKT/cAMP response element binding protein signaling pathway.

Hereditary kidney diseases: highlighting the importance of classical Mendelian phenotypes

A Mendelian inheritance underlies a nonnegligible proportion of hereditary kidney diseases, suggesting that the encoded proteins are essential for maintenance of the renal function. The identification of genes involved in congenital anomalies of the kidney and in familial forms of nephrotic syndrome significantly increased our understanding of the renal development and kidney filtration barrier physiology. This review will focus on the classical phenotype and clinical heterogeneity observed in the monogenic forms of these disorders. In addition, the role of susceptibility genes in kidney diseases with a complex inheritance will also be discussed.

Hereditary nephrotic syndrome: a systematic approach for genetic testing and a review of associated podocyte gene mutations

Several genes have been implicated in genetic forms of nephrotic syndrome occurring in children. It is now known that the phenotypes associated with mutations in these genes display significant variability, rendering genetic testing and counselling a more complex task. This review will focus on the recent clinical findings associated with those genes known to be involved in isolated steroid-resistant nephrotic syndrome in children and, thereby, propose an approach for appropriate mutational screening. The recurrence of proteinuria after transplantation in patients with hereditary forms of nephrotic syndrome will also be discussed.

Genetics of nephrotic syndrome: new insights into molecules acting at the glomerular filtration barrier

Nephrotic syndrome is caused by increased permeability of the glomerular filtration barrier for macromolecules. The identification of mutations of various podocyte-expressed proteins as causes of familial nephrotic syndrome has significantly contributed to shedding light into the molecular pathogenesis of nephrotic proteinuria and into the physiology of the glomerular sieve. More recent findings have changed our conception of the glomerular filtration barrier from a relatively static structure to a highly dynamic one. Both the multiprotein slit diaphragm complex around nephrin and the integrin receptor complex that mediates binding of the podocyte to the glomerular basement membrane, may translate outside-inside signaling and lead to podocyte actin cytoskeleton rearrangement. This may enable the podocyte network to adapt to environmental changes and respond to injury. Disturbance in these processes may not only be involved in the pathogenesis of hereditary nephrotic syndrome but also in that of more common acquired proteinuric diseases. Elucidation of the molecular mechanisms involved will possibly open the way to new therapeutic approaches.