Genetic basis of adult-onset nephrotic syndrome and focal segmental glomerulosclerosis

Development of a Diagnostic Model for Focal Segmental Glomerulosclerosis: Integrating Machine Learning on Activated Pathways and Clinical Validation

Background

Focal segmental glomerulosclerosis (FSGS) represents a major global health challenge, with its incidence rising in parallel with advances in diagnostic techniques and the growing prevalence of chronic diseases. This study seeks to enhance the diagnostic accuracy of FSGS by integrating machine learning approaches to identify activated pathways, complemented by robust clinical validation.

Methods

We analyzed data from 163 FSGS patients and 42 living donors across multiple GEO cohorts via the ComBat algorithm to address batch effects and ensure the comparability of gene expression profiles. Gene set enrichment analysis (GSEA) identified key signaling pathways involved in FSGS pathogenesis. We then developed a highly accurate diagnostic model by integrating nine machine learning algorithms into 101 combinations, achieving near-perfect AUC values across training, validation, and external cohorts. The model identified six genes as potential biomarkers for FSGS. Additionally, immune cell infiltration patterns, particularly those involving natural killer (NK) cells, were explored, revealing the complex interplay between genetics and the immune response in FSGS patients. Immunohistochemical analysis validated the expression of the key markers CD99 and OAZ2 and confirmed the association between NK cells and FSGS.

Results

The glmBoost+Ridge model exhibited exceptional diagnostic accuracy, achieving an AUC of 0.998 using just six genes: BANF1, TUSC2, SMAD3, TGFB1, CD99, and OAZ2. The prediction score was calculated as follows: score = (0.3997×BANF1) + (0.5543×TUSC2) + (0.5279×SMAD3) + (0.4118×TGFB1) + (0.8665×CD99) + (0.5996×OAZ2). Immunohistochemical analysis confirmed significantly elevated expression levels of CD99 and OAZ2 in the glomeruli and tubulointerstitial tissues of FSGS patients compared with those of controls.

Conclusion

This study demonstrates a highly accurate machine learning model for FSGS diagnosis. Immunohistochemical validation confirmed elevated expression of CD99 and OAZ2, offering valuable insights into FSGS pathogenesis and potential biomarkers for clinical application.

Natural History and Clinicopathological Associations of TRPC6-Associated Podocytopathy

KEY POINTS

We conducted a clinical, genetic, and pathological analysis on 64 cases from 39 families with TRPC6-associated podocytopathy (TRPC6-AP). Analysis of 37,542 individuals excluded a major contribution of loss-of-function variants to TRPC6-AP, legitimating current drug discovery approaches. This study identifies key features of disease that can help intervention studies design and suggests similarities between TRPC6-AP and primary FSGS.

BACKGROUND

Understanding the genetic basis of human diseases has become integral to drug development and precision medicine. Recent advancements have enabled the identification of molecular pathways driving diseases, leading to targeted treatment strategies. The increasing investment in rare diseases by the biotech industry underscores the importance of genetic evidence in drug discovery and approval processes. Here we studied a monogenic Mendelian kidney disease, TRPC6-associated podocytopathy (TRPC6-AP), to present its natural history, genetic spectrum, and clinicopathological associations in a large cohort of patients with causal variants in TRPC6 to help define the specific features of disease and further facilitate drug development and clinical trials design.

METHODS

The study involved 64 individuals from 39 families with TRPC6 causal missense variants. Clinical data, including age of onset, laboratory results, response to treatment, kidney biopsy findings, and genetic information, were collected from multiple centers nationally and internationally. Exome or targeted sequencing was performed, and variant classification was based on strict criteria. Structural and functional analyses of TRPC6 variants were conducted to understand their effect on protein function. In-depth reanalysis of light and electron microscopy specimens for nine available kidney biopsies was conducted to identify pathological features and correlates of TRPC6-AP.

RESULTS

Large-scale sequencing data did not support causality for TRPC6 protein-truncating variants. We identified 21 unique TRPC6 missense variants, clustering in three distinct regions of the protein, and with different effects on TRPC6 3D protein structure. Kidney biopsy analysis revealed FSGS patterns of injury in most cases, along with distinctive podocyte features including diffuse foot process effacement and swollen cell bodies. Most patients presented in adolescence or early adulthood but with ample variation (average 22, SD ±14 years), with frequent progression to kidney failure but with variability in time between presentation and kidney failure.

CONCLUSIONS

This study provides insights into the genetic spectrum, clinicopathological associations, and natural history of TRPC6-AP.

CLINICAL TRIAL REGISTRY NAME AND REGISTRATION NUMBER:

A Study to Test BI 764198 in People With a Type of Kidney Disease Called Focal Segmental Glomerulosclerosis, NCT05213624.

Precision medicine for focal segmental glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) is one of the common causes of nephrotic syndrome in adults and children worldwide. FSGS consists of a group of kidney diseases classified based on specific histopathological features. The current classification of FSGS makes it difficult to distinguish individual differences in pathogenesis, disease progression, and response to treatment. In recent years, the spread of next-generation sequencing, updates in biological techniques, and improvements of treatment have changed our understanding of FSGS. In this review, we will discuss the use of genetic testing in patients with FSGS, explore its clinical significance from a genetic identification perspective, and introduce several new biomarkers, that may help in the early diagnosis of FSGS and guide the development of specific or targeted therapies, so as to understand the biological characteristics in FSGS. This will certainly help develop more effective and safer treatments and advance precision medicine.

Association of ACTN4 Gene Mutation with Primary Nephrotic Syndrome in Children in Guangxi Autonomous Region, China

Objective: To investigate the association between ACTN4 gene mutation and primary nephrotic syndrome (PNS) in children in Guangxi Autonomous Region, China. Methods: The high-throughput sequencing technology was used to sequence ACTN4 gene in 155 children with PNS in Guangxi Autonomous Region in China, with 98 healthy children serving as controls. Twenty-three exon-specific capture probes targeting ACTN4 were designed and used to hybridize with the genomic DNA library. The targeted genomic region DNA fragments were enriched and sequenced. The protein levels of ACTN4 in both case and control groups were quantified using ELISA method. Results: Bioinformatics analysis revealed five unique ACTN4 mutations exclusively in patients with PNS, including c.1516G>A (p.G506S) on one exon in 2 patients, c.1442 + 10G>A at the splice site in 1 patient, c.1649A>G (p.D550G) on exon in 1 patient, c.2191-4G>A at the cleavage site in 2 patients, and c.2315C>T (p.A772V) on one exon in 1 patient. The c.1649A>G (p.D550G) and c.2315C>T (p.A772V) were identified from the same patient. Notably, c.1649A>G (p.D550G) represents a novel mutation in ACTN4. In addition, three other ACTN4 polymorphisms occurred in both case and control groups, including c.162 + 6C>T (1 patient in case group and 2 patients in control group), c.572 + 11G>A (1 patient in case group and 2 patients in control group), and c.2191-5C>T (4 patients in the case group and 3 patients in control group). The serum ACTN4 concentration in the case group was markedly higher, averaging 544.7 ng/mL (range: 264.6-952.6 ng/mL), compared with 241.20 ng/mL (range: 110.75-542.35 ng/mL) in the control group. Conclusion: Five ACTN4 polymorphisms were identified among children with PNS in Guangxi Autonomous Region, China, including the novel mutation c.1649A>G. The lower serum levels of α-actinin-4 in the case group suggest that this protein might play a protective role in PNS.

The most common founder pathogenic variant c.868G > A (p.Val290Met) in the NPHS2 gene in a representative adult Czech cohort with focal segmental glomerulosclerosis is associated with a milder disease and its underdiagnosis in childhood

Background

Genetic focal segmental glomerulosclerosis (FSGS) is caused by pathogenic variants in a broad spectrum of genes that have a variable representation based on subjects' ethnicity and/or age. The most frequently mutated autosomal recessive gene in FSGS is NPHS2. In this study, we analyzed the spectrum of NPHS2 variants and their associated phenotype in Czech adult FSGS patients.

Methods

A representative cohort of 234 adult patients with FSGS, derived from 225 families originating from all regions of Czechia, was analyzed by massively parallel sequencing. In this study, we focused on the comprehensive analysis of the NPHS2 gene. The histological classification of FSGS followed the Columbia classification.

Results

We detected seven (3%) cases bearing homozygous or compound heterozygous pathogenic NPHS2 variants. A single pathogenic variant c.868G > A (p.Val290Met) was found in the majority of NPHS2-positive cases (86%; 6 out of 7) in histologically confirmed instances of FSGS. Its allele frequency among unrelated NPHS2-associated FSGS patients was 50% (6/12), and Haplotype analysis predicted its origin to be a result of a founder effect. There is an identical V290M-related haplotype on all V290M alleles spanning a 0,7 Mb region flanking NPHS2 in Central European FSGS populations. The phenotype of the p.Val290Met NPHS2-associated FSGS demonstrated a later onset and a much milder course of the disease compared to other NPHS2 pathogenic variants associated with FSGS. The mean age of the FSGS diagnosis based on kidney biopsy evaluation was 31.2 ± 7.46 years. In 50% of all cases, the initial disease manifestation of proteinuria occurred only in adulthood, with 83% of these cases not presenting with edemas. One-third (33%) of the studied subjects progressed to ESRD (2 out of 6) at the mean age of 35.0 ± 2.82 years.

Conclusions

We identified the most prevalent pathogenic variant, p.Val290Met, in the NPHS2 gene among Czech adult FSGS patients, which has arisen due to a founder effect in Central Europe. The documented milder course of the disease associated with this variant leads to the underdiagnosis in childhood. We established the histopathological features of the NPHS2-associated adult FSGS cases based on the Columbia classification. This might improve patient stratification and optimize their treatment.

Ferroptosis is involved in focal segmental glomerulosclerosis in rats

To explore whether ferroptosis is involved in focal segmental glomerulosclerosis (FSGS) and its mechanism. The FSGS rat model was constructed by single nephrectomy combined with fractional tail vein injection of doxorubicin. 24-hour urine protein, serum biochemistry, HE, PAS and Masson pathological staining were measured to assess renal injury. Glomerular and morphological changes of ferroptosis were observed by transmission electron microscopy. Iron content in renal tissue was assessed by Prussian blue staining and iron detection. GSH/GSSG kit was used to detect the content and proportion of reduced/oxidized glutathione. Lipid peroxidation related proteins including MDA expression was assessed by colorimetry. The iron metabolism biomarkers such as hepcidin, ferroportin and TFR, ferroptosis biomarkers such as GPX4, ACSL4, and ferritinophagy biomarkers such as LC3II/LC3I, NCOA4, and FTH1 were detected by Western blot. Significant urinary protein, hyperlipidemia, azotemia, increased serum creatinine and hypoproteinemia were observed in FSGS rats. Histology and electron microscopy showed segmental sclerosis of glomeruli, compensatory enlargement of some glomeruli, occlusion of capillary lumen, balloon adhesion, increased mesangial matrix, atrophy of some tubules, and renal interstitial fibrosis in renal tissue of FSGS rats. The morphology of glomerular foot processes disappeared; the foot processes were extensively fused and some foot processes detached. Mitochondria became smaller, membrane density increased, and mitochondrial cristae decreased or disappeared. In addition, iron deposition was observed in renal tissue of FSGS rats. Compared with the control group, the levels of GSH, GSH/GSSG, GPX4, and ferroportin were reduced and the expression of GSSG, MDA, ACSL4, hepcidin, and TFR was increased in the renal tissue of FSGS rats; meanwhile, the expression of LC3II/LC3I and NCOA4 was increased and the expression of FTH1 was decreased. Ferroptosis is involved in the pathological progression of FSGS, which is probably associated with activation of ferritinophagy. This represents a potential therapeutic target for FSGS.

Modeling of ACTN4-Based Podocytopathy Using Drosophila Nephrocytes

Introduction

Genetic disorders are among the most prevalent causes leading to progressive glomerular disease and, ultimately, end-stage renal disease (ESRD) in children and adolescents. Identification of underlying genetic causes is indispensable for targeted treatment strategies and counseling of affected patients and their families.

Methods

Here, we report on a boy who presented at 4 years of age with proteinuria and biopsy-proven focal segmental glomerulosclerosis (FSGS) that was temporarily responsive to treatment with ciclosporin A. Molecular genetic testing identified a novel mutation in alpha-actinin-4 (p.M240T). We describe a feasible and efficient experimental approach to test its pathogenicity by combining in silico, in vitro, and in vivo analyses.

Results

The de novo p.M240T mutation led to decreased alpha-actinin-4 stability as well as protein mislocalization and actin cytoskeleton rearrangements. Transgenic expression of wild-type human alpha-actinin-4 in Drosophila melanogaster nephrocytes was able to ameliorate phenotypes associated with the knockdown of endogenous actinin. In contrast, p.M240T, as well as other established disease variants p.W59R and p.K255E, failed to rescue these phenotypes, underlining the pathogenicity of the novel alpha-actinin-4 variant.

Conclusion

Our data highlight that the newly identified alpha-actinin-4 mutation indeed encodes for a disease-causing variant of the protein and promote the Drosophila model as a simple and convenient tool to study monogenic kidney disease in vivo.

Genetic Spectrum of Nephrotic Syndrome: Impact of Podocytopathy in Adult Life

A substantial number of patients with focal segmental glomerulosclerosis (FSGS) have a pathogenic genetic mutation in a podocyte protein as the cause of their disease. The mutations can affect a wide range of cell functions including the actin cytoskeleton, cell adhesion and motility, mitochondrial function, and nuclear pore proteins. The likelihood of a genetic cause declines with age, from approximately 30% in children and adolescents to 10% in adulthood, and the specific proteins involved and the pattern of inheritance differ in the 2 age groups. The presence of a genetic cause for FSGS can have important clinical ramifications including the need for a diagnostic kidney biopsy, medical management, and the risk of recurrent disease after kidney transplantation. This review summarizes the spectrum of genetic causes of nephrotic syndrome, primarily FSGS, in adults with a focus on diagnosis, presentation, and management.

Podocentric view of glomerular proteinuria: Focused on cytoskeletal changes and toward promising targeted therapies and challenges

Among renal cells, podocytes (glomerular epithelial cells) are the most critical to prevent plasma proteins from excessive loss by forming their sophisticated foot processes (FP) and slit diaphragms (SD). A general finding in the glomeruli of patients with nephrotic syndrome is the foot processes "effacement" resulted from dysregulated actin cytoskeleton reorganization. Ultrastructural analysis in patients with nephrotic syndrome has demonstrated that such changes tend to be dynamic and can sometimes be reversible. In a more molecular sense, injured podocytes can no longer maintain their tight regulation and "retract" their FP, but not "efface" them. Past studies have revealed multiple exquisite mechanisms and arrays of proteins participating in the regulation of cytoskeletal rearrangement, and these mechanisms serve as potential targets to treat. A major challenge to develop specific therapies is the targeted mechanism has to be crucial and specific enough for podocyte-oriented kidney diseases, and it would be even better to manifest in most of the glomerulonephritis. Studies have shown many approaches targeting different mechanisms, but none of them has been proved to be effective in clinical medicine. Up to the present, Abatacept (Orencia) is the first (and the only) clinical targeted therapy demonstrating limited success. It inhibits the co-stimulatory response of B7-1 (CD80) induced in various types of glomerulonephritis. Future clinical studies have to be expanded to substantiate this highly specific targeted therapy because the Abatacept effect is not generally accepted even within the nephrology community. Nevertheless, there are ongoing searches for specific treatment targeting podocytes through various approaches.

Protective Role of the M-Sec-Tunneling Nanotube System in Podocytes

BACKGROUND

Podocyte dysfunction and loss are major determinants in the development of proteinuria. FSGS is one of the most common causes of proteinuria, but the mechanisms leading to podocyte injury or conferring protection against FSGS remain poorly understood. The cytosolic protein M-Sec has been involved in the formation of tunneling nanotubes (TNTs), membrane channels that transiently connect cells and allow intercellular organelle transfer. Whether podocytes express M-Sec is unknown and the potential relevance of the M-Sec-TNT system in FSGS has not been explored.

METHODS

We studied the role of the M-Sec-TNT system in cultured podocytes exposed to Adriamycin and in BALB/c M-Sec knockout mice. We also assessed M-Sec expression in both kidney biopsies from patients with FSGS and in experimental FSGS (Adriamycin-induced nephropathy).

RESULTS

Podocytes can form TNTs in a M-Sec-dependent manner. Consistent with the notion that the M-Sec-TNT system is cytoprotective, podocytes overexpressed M-Sec in both human and experimental FSGS. Moreover, M-Sec deletion resulted in podocyte injury, with mitochondrial abnormalities and development of progressive FSGS. In vitro, M-Sec deletion abolished TNT-mediated mitochondria transfer between podocytes and altered mitochondrial bioenergetics. Re-expression of M-Sec reestablishes TNT formation and mitochondria exchange, rescued mitochondrial function, and partially reverted podocyte injury.

CONCLUSIONS

These findings indicate that the M-Sec-TNT system plays an important protective role in the glomeruli by rescuing podocytes via mitochondrial horizontal transfer. M-Sec may represent a promising therapeutic target in FSGS, and evidence that podocytes can be rescued via TNT-mediated horizontal transfer may open new avenues of research.

Cytoskeleton Rearrangements Modulate TRPC6 Channel Activity in Podocytes

The actin cytoskeleton of podocytes plays a central role in the functioning of the filtration barrier in the kidney. Calcium entry into podocytes via TRPC6 (Transient Receptor Potential Canonical 6) channels leads to actin cytoskeleton rearrangement, thereby affecting the filtration barrier. We hypothesized that there is feedback from the cytoskeleton that modulates the activity of TRPC6 channels. Experiments using scanning ion-conductance microscopy demonstrated a change in migration properties in podocyte cell cultures treated with cytochalasin D, a pharmacological agent that disrupts the actin cytoskeleton. Cell-attached patch-clamp experiments revealed that cytochalasin D increases the activity of TRPC6 channels in CHO (Chinese Hamster Ovary) cells overexpressing the channel and in podocytes from freshly isolated glomeruli. Furthermore, it was previously reported that mutation in ACTN4, which encodes α-actinin-4, causes focal segmental glomerulosclerosis and solidifies the actin network in podocytes. Therefore, we tested whether α-actinin-4 regulates the activity of TRPC6 channels. We found that co-expression of mutant α-actinin-4 K255E with TRPC6 in CHO cells decreases TRPC6 channel activity. Therefore, our data demonstrate a direct interaction between the structure of the actin cytoskeleton and TRPC6 activity.

Case Report: A Novel Heterozygous Mutation of CD2AP in a Chinese Family With Proteinuria Leads to Focal Segmental Glomerulosclerosis

Idiopathic focal segmental glomerulosclerosis (FSGS) is a relatively frequent kidney disorder that manifest clinically as proteinuria and progressive loss of renal function. Genetic factors play a dominant role in the occurrence of FSGS. CD2-associated protein (CD2AP) is an adapter molecule and is essential for the slit-diaphragm assembly and function. Mutations in the CD2AP gene can contribute to FSGS development. Here, we describe a Chinese family of four generations with unexplained proteinuria. The proband, a 12-year-old boy, was diagnosed as FSGS. Whole-exome sequencing (WES) revealed an unknown frameshift insertion mutation (p.K579Efs^*7) of CD2AP gene that leads to a truncation of CD2AP protein. Bioinformatics strategies predicted that the novel mutation was pathogenic. The mutation was absent in either healthy family members or our 200 healthy controls. In summary, we used WES to explore the genetic lesion of FSGS patients and identified a novel mutation in CD2AP gene. This work broadens the mutation spectrum of CD2AP gene and provides data for genetic counseling to additional FSGS patients.

A novel heterozygous variant of the COL4A4 gene in a Chinese family with hematuria and proteinuria leads to focal segmental glomerulosclerosis and chronic kidney disease

Background

Focal segmental glomerulosclerosis (FSGS), as the frequent primary glomerular diseases in adults, accounts for symptomless proteinuria or nephrotic syndrome with or without renal insufficiency. As the crucial lesion of chronic kidney disease (CKD), accumulating evidence from recent studies show that mutations in Collagen‐related genes may be responsible for FSGS. The aim of this study was to identify the genetic lesion of a Chinese family with FSGS and CKD.

Methods

In this study, we recruited a Han‐Chinese family with unexplained high serum creatinine, hematuria, and proteinuria. Further renal biopsy and renal pathology indicated the diagnosis of FSGS in the proband. Whole‐exome sequencing and Sanger sequencing were employed to explore the pathogenic mutation of this family.

Results

A novel heterozygous mutation (NM_000092 c.2030G>A, p.G677D) of the collagen type IV alpha‐4 gene (COL4A4) was detected. Co‐segregation analysis revealed that the novel mutation was carried by all the five affected individuals and absent in other healthy members as well as in our 200 local control cohorts. Bioinformatics predication indicated that this novel mutation was pathogenic and may disrupt the structure and function of type IV collagen. Simultaneously, this variant is located in an evolutionarily conserved site of COL4A4 protein.

Conclusion

Here, we identified a novel mutation of COL4A4 in a family with FSGS and CKD. Our study expanded the variants spectrum of the COL4A4 gene and contributed to the genetic counseling and prenatal genetic diagnosis of the family. In addition, we also recommended the new classification of collagen IV nephropathies, which may be a benefit to the diagnosis, target drug treatment, and management of patients with COL4A3/COL4A4 mutations.

ECM Characterization Reveals a Massive Activation of Acute Phase Response during FSGS

The glomerular basement membrane (GBM) and extra-cellular matrix (ECM) are essential to maintain a functional interaction between the glomerular podocytes and the fenestrated endothelial cells in the formation of the slit diaphragm for the filtration of blood. Dysregulation of ECM homeostasis can cause Focal segmental glomerulosclerosis (FSGS). Despite this central role, alterations in ECM composition during FSGS have not been analyzed in detail yet. Here, we characterized the ECM proteome changes in miR-193a-overexpressing mice, which suffer from FSGS due to suppression of Wilms' tumor 1 (WT1). By mass spectrometry we identified a massive activation of the acute phase response, especially the complement and fibrinogen pathways. Several protease inhibitors (ITIH1, SERPINA1, SERPINA3) were also strongly increased. Complementary analysis of RNA expression data from both miR-193a mice and human FSGS patients identified additional candidate genes also mainly involved in the acute phase response. In total, we identified more than 60 dysregulated, ECM-associated genes with potential relevance for FSGS progression. Our comprehensive analysis of a murine FSGS model and translational comparison with human data offers novel targets for FSGS therapy.

Identification of a Novel ACTN4 Gene Mutation Which Is Resistant to Primary Nephrotic Syndrome Therapy

ACTN4, a gene which codes for the protein α-actinin-4, is critical for the maintenance of the renal filtration barrier. It is well known that ACTN4 mutations can lead to kidney dysfunction, such as familial focal segmental glomerulosclerosis (FSGS), a common cause of primary nephrotic syndrome (PNS). To elucidate whether other mutations of ACTN4 exist in PNS patients, we sequenced the ACTN4 gene in biopsies collected from 155 young PNS patients (≤16 years old). The patients were classified into five groups: FSGS, minimal change nephropathy, IgA nephropathy, membranous nephropathy, and those without renal puncture. Ninety-eight healthy people served as controls. Samples were subjected to Illumina's next generation sequencing protocols using FastTarget target gene capture method. We identified 5 ACTN4 mutations which occurred only in PNS patients: c.1516G > A (p.G506S) on exon 13 identified in two PNS patients, one with minimal change nephropathy and another without renal puncture; c.1442 + 10G > A at the splice site in a minimal change nephropathy patient; c.2191-4G > A at the cleavage site, identified from two FSGS patients; and c.1649A > G (p.D550G) on exon 14 together with c.2191-4G > A at the cleavage sites, identified from two FSGS patients. Among these, c.1649A > G (p.D550G) is a novel ACTN4 mutation. Patients bearing the last two mutations exhibited resistance to clinical therapies.

Cases in Precision Medicine: APOL1 and Genetic Testing in the Evaluation of Chronic Kidney Disease and Potential Transplant

This article discusses potential indications for genetic testing in an African American patient with chronic kidney disease who is being evaluated for a kidney transplant. Two known risk variants in the APOL1 (apolipoprotein L1) gene predispose to kidney disease and are found almost exclusively in persons of African ancestry. APOL1 risk variants are considered, including whether clinicians should incorporate genetic testing in the screening process for living kidney donors. In addition to APOL1 testing, the role of diagnostic exome sequencing in evaluating potential transplant recipients and donors with a positive family history of kidney disease is discussed.

Mechanisms of Scarring in Focal Segmental Glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) presents with scar in parts of some glomeruli and often progresses to global and diffuse glomerulosclerosis. Podocyte injury is the initial target in primary FSGS, induced by a circulating factor. Several gene variants, for example, APOL1, are associated with increased susceptibility to FSGS. Primary FSGS may be due to genetic mutation in key podocyte genes. Increased work stress after loss of nephrons, epigenetic mechanisms, and various profibrotic pathways can contribute to progressive sclerosis, regardless of the initial injury. The progression of FSGS lesions also involves crosstalk between podocytes and other kidney cells, such as parietal epithelial cells, glomerular endothelial cells, and even tubular epithelial cells. New insights related to these mechanisms could potentially lead to new therapeutic strategies to prevent progression of FSGS.

Network analysis of membranous glomerulonephritis based on metabolomics data

Membranous glomerulonephritis (MGN) is one of the most frequent causes of nephrotic syndrome in adults. It is characterized by the thickening of the glomerular basement membrane in the renal tissue. The current diagnosis of MGN is based on renal biopsy and the detection of antibodies to the few podocyte antigens. Due to the limitations of the current diagnostic methods, including invasiveness and the lack of sensitivity of the current biomarkers, there is a requirement to identify more applicable biomarkers. The present study aimed to identify diagnostic metabolites that are involved in the development of the disease using topological features in the component‑reaction‑enzyme‑gene (CREG) network for MGN. Significant differential metabolites in MGN compared with healthy controls were identified using proton nuclear magnetic resonance and gas chromatography‑mass spectrometry techniques, and multivariate analysis. The CREG network for MGN was constructed, and metabolites with a high centrality and a striking fold‑change in patients, compared with healthy controls, were introduced as putative diagnostic biomarkers. In addition, a protein‑protein interaction (PPI) network, which was based on proteins associated with MGN, was built and analyzed using PPI analysis methods, including molecular complex detection and ClueGene Ontology. A total of 26 metabolites were identified as hub nodes in the CREG network, 13 of which had salient centrality and fold‑changes: Dopamine, carnosine, fumarate, nicotinamide D‑ribonucleotide, adenosine monophosphate, pyridoxal, deoxyguanosine triphosphate, L‑citrulline, nicotinamide, phenylalanine, deoxyuridine, tryptamine and succinate. A total of 13 subnetworks were identified using PPI analysis. In total, two of the clusters contained seed proteins (phenylalanine‑4‑hydroxlylase and cystathionine γ‑lyase) that were associated with MGN based on the CREG network. The following biological processes associated with MGN were identified using gene ontology analysis: 'Pyrimidine‑containing compound biosynthetic process', 'purine ribonucleoside metabolic process', 'nucleoside catabolic process', 'ribonucleoside metabolic process' and 'aromatic amino acid family metabolic process'. The results of the present study may be helpful in the diagnostic and therapeutic procedures of MGN. However, validation is required in the future.