The extrafollicular B cell response is a hallmark of childhood idiopathic nephrotic syndrome

The efficacy of the B cell-targeting drug rituximab (RTX) in childhood idiopathic nephrotic syndrome (INS) suggests that B cells may be implicated in disease pathogenesis. However, B cell characterization in children with INS remains limited. Here, using single-cell RNA sequencing, we demonstrate that a B cell transcriptional program poised for effector functions represents the major immune perturbation in blood samples from children with active INS. This transcriptional profile was associated with an extrafollicular B cell response marked by the expansion of atypical B cells (atBCs), marginal zone-like B cells, and antibody-secreting cells (ASCs). Flow cytometry of blood from 13 children with active INS and 24 healthy donors confirmed the presence of an extrafollicular B cell response denoted by the expansion of proliferating RTX-sensitive extrafollicular (CXCR5-) CD21low T-bet+ CD11c+ atBCs and short-lived T-bet+ ASCs in INS. Together, our study provides evidence for an extrafollicular origin for humoral immunity in active INS.

Minnelide combined with anti-ANGPTL3-FLD monoclonal antibody completely protects mice with adriamycin nephropathy by promoting autophagy and inhibiting apoptosis

Minimal change disease (MCD) is the common type of nephrotic syndrome (NS) in children. Currently, there is an urgent need to explore new treatments because of the significant side effects of long-term use of glucocorticoids and immunosuppressive drugs and the failure to reduce proteinuria in some patients. Angiopoietin-like protein 3 (Angptl3) is an essential target of NS, and anti-ANGPTL3-FLD monoclonal antibody (mAb) significantly reduces proteinuria in mice with adriamycin nephropathy (AN). However, some proteinuria is persistent. Minnelide, a water-soluble prodrug of triptolide, has been used for the treatment of glomerular disease. Therefore, the present study aimed to investigate whether minnelide combined with mAb could further protect mice with AN and the underlying mechanisms. 8-week-old C57BL/6 female mice were injected with 25 mg/kg of Adriamycin (ADR) by tail vein to establish the AN model. A dose of 200 μg/kg of minnelide or 20 mg/kg of mAb was administered intraperitoneally for the treatment. In vitro, the podocytes were treated with 0.4 μg/mL of ADR for 24 h to induce podocyte injury, and pretreatment with 10 ng/mL of triptolide for 30 min or 100 ng/mL of mAb for 1 h before ADR exposure was used to treat. The results showed that minnelide combined with mAb almost completely ameliorates proteinuria and restores the ultrastructure of the podocytes in mice with AN. In addition, minnelide combined with mAb restores the distribution of Nephrin, Podocin, and CD2AP and reduces the level of inflammatory factors in mice with AN. Mechanistically, minnelide combined with mAb could further alleviate apoptosis and promote autophagy in mice with AN by inhibiting the mTOR signaling pathway. In vitro, triptolide combined with mAb increases the expression of Nephrin, Podocin, and CD2AP, alleviates apoptosis, and promotes autophagy. Overall, minnelide combined with mAb completely protects the mice with AN by promoting autophagy and inhibiting apoptosis.

Exome sequencing in individuals with congenital anomalies of the kidney and urinary tract (CAKUT): a single-center experience

Individuals with congenital anomalies of the kidney and urinary tract (CAKUT) show a broad spectrum of malformations. CAKUT can occur in an isolated fashion or as part of a syndromic disorder and can lead to end-stage kidney failure. A monogenic cause can be identified in ~12% of affected individuals. This study investigated a single-center CAKUT cohort analyzed by exome sequencing (ES). Emphasis was placed on the question whether diagnostic yield differs between certain CAKUT phenotypes (e.g., bilateral kidney affection, unilateral kidney affection or only urinary tract affection). 86 unrelated individuals with CAKUT were categorized according to their phenotype and analyzed by ES to identify a monogenic cause. Prioritized variants were rated according to the recommendations of the American College of Medical Genetics and Genomics and the Association for Clinical Genomic Science. Diagnostic yields of different phenotypic categories were compared. Clinical data were collected using a standardized questionnaire. In the study cohort, 7/86 individuals had a (likely) pathogenic variant in the genes PAX2, PBX1, EYA1, or SALL1. Additionally, in one individual, a 17q12 deletion syndrome (including HNF1B) was detected. 64 individuals had a kidney affection, which was bilateral in 36. All solved cases (8/86, 9%) had bilateral kidney affection (diagnostic yield in subcohort: 8/36, 22%). Although the diagnostic yield in CAKUT cohorts is low, our single-center experience argues, that, in individuals with bilateral kidney affection, monogenic burden is higher than in those with unilateral kidney or only urinary tract affection.

Multi-population genome-wide association study implicates immune and non-immune factors in pediatric steroid-sensitive nephrotic syndrome

Pediatric steroid-sensitive nephrotic syndrome (pSSNS) is the most common childhood glomerular disease. Previous genome-wide association studies (GWAS) identified a risk locus in the HLA Class II region and three additional independent risk loci. But the genetic architecture of pSSNS, and its genetically driven pathobiology, is largely unknown. Here, we conduct a multi-population GWAS meta-analysis in 38,463 participants (2440 cases). We then conduct conditional analyses and population specific GWAS. We discover twelve significant associations-eight from the multi-population meta-analysis (four novel), two from the multi-population conditional analysis (one novel), and two additional novel loci from the European meta-analysis. Fine-mapping implicates specific amino acid haplotypes in HLA-DQA1 and HLA-DQB1 driving the HLA Class II risk locus. Non-HLA loci colocalize with eQTLs of monocytes and numerous T-cell subsets in independent datasets. Colocalization with kidney eQTLs is lacking but overlap with kidney cell open chromatin suggests an uncharacterized disease mechanism in kidney cells. A polygenic risk score (PRS) associates with earlier disease onset. Altogether, these discoveries expand our knowledge of pSSNS genetic architecture across populations and provide cell-specific insights into its molecular drivers. Evaluating these associations in additional cohorts will refine our understanding of population specificity, heterogeneity, and clinical and molecular associations.

Mycophenolic acid directly protects podocytes by preserving the actin cytoskeleton and increasing cell survival

Mycophenolate Mofetil (MMF) has an established role as a therapeutic agent in childhood nephrotic syndrome. While other immunosuppressants have been shown to positively affect podocytes, direct effects of MMF on podocytes remain largely unknown. The present study examines the effects of MMF's active component Mycophenolic Acid (MPA) on the transcriptome of podocytes and investigates its biological significance. We performed transcriptomics in cultured murine podocytes exposed to MPA to generate hypotheses on podocyte-specific effects of MPA. Accordingly, we further analyzed biological MPA effects on actin cytoskeleton morphology after treatment with bovine serum albumin (BSA) by immunofluorescence staining, as well as on cell survival following exposure to TNF-α and cycloheximide by neutral red assay. MPA treatment significantly (adjusted p < 0.05) affected expression of 351 genes in podocytes. Gene Ontology term enrichment analysis particularly clustered terms related to actin and inflammation-related cell death. Indeed, quantification of the actin cytoskeleton of BSA treated podocytes revealed a significant increase of thickness and number of actin filaments after treatment with MPA. Further, MPA significantly reduced TNFα and cycloheximide induced cell death. MPA has a substantial effect on the transcriptome of podocytes in vitro, particularly including functional clusters related to non-immune cell dependent mechanisms. This may provide a molecular basis for direct beneficial effects of MPA on the structural integrity and survival of podocytes under pro-inflammatory conditions.

Primary cilia suppress Ripk3-mediated necroptosis

Cilia are sensory organelles that project from the surface of almost all cells. Nephronophthisis (NPH) and NPH-related ciliopathies are degenerative genetic diseases caused by mutation of cilia-associated genes. These kidney disorders are characterized by progressive loss of functional tubular epithelial cells which is associated with inflammation, progressive fibrosis, and cyst formation, ultimately leading to end-stage renal disease. However, disease mechanisms remain poorly understood. Here, we show that targeted deletion of cilia in renal epithelial cells enhanced susceptibility to necroptotic cell death under inflammatory conditions. Treatment of non-ciliated cells with tumor necrosis factor (TNF) α and the SMAC mimetic birinapant resulted in Ripk1-dependent cell death, while viability of ciliated cells was almost not affected. Cell death could be enhanced and shifted toward necroptosis by the caspase inhibitor emricasan, which could be blocked by inhibitors of Ripk1 and Ripk3. Moreover, combined treatment of ciliated and non-ciliated cells with TNFα and cycloheximide induced a cell death response that could be partially rescued with emricasan in ciliated cells. In contrast, non-ciliated cells responded with pronounced cell death that was blocked by necroptosis inhibitors. Consistently, combined treatment with interferon-γ and emricasan induced cell death only in non-ciliated cells. Mechanistically, enhanced necroptosis induced by loss of cilia could be explained by induction of Ripk3 and increased abundance of autophagy components, including p62 and LC3 associated with the Ripk1/Ripk3 necrosome. Genetic ablation of cilia in renal tubular epithelial cells in mice resulted in TUNEL positivity and increased expression of Ripk3 in kidney tissue. Moreover, loss of Nphp1, the most frequent cause of NPH, further increased susceptibility to necroptosis in non-ciliated epithelial cells, suggesting that necroptosis might contribute to the pathogenesis of the disease. Together, these data provide a link between cilia-related signaling and cell death responses and shed new light on the disease pathogenesis of NPH-related ciliopathies.

A novel SLC5A2 heterozygous variant in a family with familial renal glucosuria

Familial renal glucosuria (FRG) is characterized by persistent glucosuria despite normal blood glucose levels in the absence of overt tubular dysfunction. SGLT2 is a sodium-glucose cotransporter expressed in the proximal tubule; loss-of-function variants in SLC5A2 are the primary cause of FRG. Heterozygous variants have rarely been reported in Japanese individuals. Here, we identified a novel SLC5A2 heterozygous variant, c.1348G>T: p.Gly450Trp, in a Japanese family comprising two children and their father.

Asymmetric and Symmetric Dimethylarginines as Renal Function Parameters in Paediatric Kidney Diseases: A Literature Review from 2003 to 2022

Asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA), inhibitors of nitric oxide synthase, play important roles in many processes in the body. Most data in the literature concern their importance in adult chronic kidney disease (CKD). According to them, SDMA well reflects the glomerular filtration rate (GFR), and higher ADMA concentrations are associated with hypertension and higher mortality. In addition, both substances are recognised cardiovascular risk factors in CKD. The purpose of this review was to summarise the studies on dimethylarginines in renal diseases in children, about which we have much fewer data. The review focuses specifically on dimethylarginine's relation to routinely used renal function parameters. Finally, we analysed 21 of the 55 articles published between 2003 and 2022 on dimethylarginines in kidney diseases in children (from birth to 18 years of age), obtained by searching PubMed/MEDLINE (search terms: "dimethylarginine" and "kidney").

Multiomics analysis reveals that hepatocyte nuclear factor 1β regulates axon guidance genes in the developing mouse kidney

The transcription factor hepatocyte nuclear factor 1β (HNF-1β) is essential for normal development of the kidney and other epithelial organs. In the developing mouse kidney, HNF-1β is required for the differentiation and patterning of immature nephrons and branching morphogenesis of the ureteric bud (UB). Here, we used ChIP-sequencing (ChIP-seq) and RNA sequencing (RNA-seq) to identify genes that are regulated by HNF-1β in embryonic mouse kidneys. ChIP-seq revealed that HNF-1β binds to 8284 sites in chromatin from E14.5 mouse kidneys. Comparison with previous ATAC-seq and histone modification studies showed that HNF-1β binding peaks colocalized with open chromatin and epigenetic marks of transcriptional activation (H3K27 acetylation, H3K4 trimethylation, H3K4 monomethylation), indicating that the binding sites were functional. To investigate the relationship between HNF-1β binding and HNF-1β-dependent gene regulation, RNA-seq was performed on UB cells purified from wild-type and HNF-1β mutant embryonic kidneys. A total of 1632 genes showed reduced expression in HNF-1β-deficient UB cells, and 485 genes contained nearby HNF-1β binding sites indicating that they were directly activated by HNF-1β. Conversely, HNF-1β directly repressed the expression of 526 genes in the UB. Comparison with snATAC-seq analysis of UB-derived cells showed that both HNF-1β-dependent activation and repression correlated with chromatin accessibility. Pathway analysis revealed that HNF-1β binds near 68 axon guidance genes in the developing kidney. RNA-seq analysis showed that Nrp1, Sema3c, Sema3d, Sema6a, and Slit2 were activated by HNF-1β, whereas Efna1, Epha3, Epha4, Epha7, Ntn4, Plxna2, Sema3a, Sema4b, Slit3, Srgap1, Unc5c and Unc5d were repressed by HNF-1β. RNAscope in situ hybridization showed that Nrp1, Sema3c, Sema3d, Sema6a, and Slit2 were expressed in wild-type UB and were dysregulated in HNF-1β mutant UB. These studies show that HNF-1β directly regulates the expression of multiple axon guidance genes in the developing mouse kidney. Dysregulation of axon guidance genes may underlie kidney defects in HNF-1β mutant mice.

Influenza virus vaccination in pediatric nephrotic syndrome significantly reduces rate of relapse and influenza virus infection as assessed in a nationwide survey

Although vaccination may precipitate relapses of nephrotic syndrome (NS) in children with idiopathic NS, no data are available regarding NS activity regarding influenza (flu) virus infections and NS relapses after receiving inactivated flu vaccines. We conducted a nationwide study of children aged 6 months to 15 years with idiopathic NS to assess the relationship between NS relapse, flu vaccination, and flu infections. We used a multivariate Poisson regression model (MPRM) to calculate the risk ratio (RR) for flu infection and for NS relapse in children with and without flu vaccination. Data of 306 children were assessed. The MPRM in all 306 children showed a significantly lower RR for flu infection (RR: 0.21, 95% confidence interval CI 0.11-0.38) and for NS relapse (RR: 0.22, 95% CI 0.14-0.35) in children receiving flu vaccination compared with unvaccinated children. In an additional MPRM only among 102 children receiving flu vaccination, they had a significantly lower risk for NS relapse during the post-vaccination period (RR: 0.31. 95% CI 017-0.56) compared with the pre-vaccination period. Although our study was observational, based on the favorable results of flu vaccinations regarding flu infections and NS relapse, the vaccine may be recommended for children with NS.

Biallelic loss-of-function variants in KCNJ16 presenting with hypokalemic metabolic acidosis

KCNJ16 encodes K_ir5.1 and acts in combination with K_ir4.1, encoded by KCNJ10, to form an inwardly rectifying K⁺ channel expressed at the basolateral membrane of epithelial cells in the distal nephron. This K_ir4.1/K_ir5.1 channel is critical for controlling basolateral membrane potential and K⁺ recycling, the latter coupled to Na-K-ATPase activity, which determines renal Na⁺ handling. Previous work has shown that Kcnj16^-/- mice and SS^Kcnj16-/- rats demonstrate hypokalemic, hyperchloremic metabolic acidosis. Here, we present the first report of a patient identified to have biallelic loss-of-function variants in KCNJ16 by whole exome sequencing who presented with chronic metabolic acidosis with exacerbations triggered by minor infections.

Management of congenital nephrotic syndrome: consensus recommendations of the ERKNet-ESPN Working Group

Congenital nephrotic syndrome (CNS) is a heterogeneous group of disorders characterized by nephrotic-range proteinuria, hypoalbuminaemia and oedema, which manifest in utero or during the first 3 months of life. The main cause of CNS is genetic defects in podocytes; however, it can also be caused, in rare cases, by congenital infections or maternal allo-immune disease. Management of CNS is very challenging because patients are prone to severe complications, such as haemodynamic compromise, infections, thromboses, impaired growth and kidney failure. In this consensus statement, experts from the European Reference Network for Kidney Diseases (ERKNet) and the European Society for Paediatric Nephrology (ESPN) summarize the current evidence and present recommendations for the management of CNS, including the use of renin-angiotensin system inhibitors, diuretics, anticoagulation and infection prophylaxis. Therapeutic management should be adapted to the clinical severity of the condition with the aim of maintaining intravascular euvolaemia and adequate nutrition, while preventing complications and preserving central and peripheral vessels. We do not recommend performing routine early nephrectomies but suggest that they are considered in patients with severe complications despite optimal conservative treatment, and before transplantation in patients with persisting nephrotic syndrome and/or a WT1-dominant pathogenic variant.