Ion channels and channelopathies in glomeruli.

An essential step in renal function entails the formation of an ultrafiltrate that is delivered to the renal tubules for subsequent processing. This process, known as glomerular filtration, is controlled by intrinsic regulatory systems and by paracrine, neuronal, and endocrine signals that converge onto glomerular cells. In addition, the characteristics of glomerular fluid flow, such as the glomerular filtration rate and the glomerular filtration fraction, play an important role in determining blood flow to the rest of the kidney. Consequently, disease processes that initially affect glomeruli are the most likely to lead to end-stage kidney failure. The cells that comprise the glomerular filter, especially podocytes and mesangial cells, express many different types of ion channels that regulate intrinsic aspects of cell function and cellular responses to the local environment, such as changes in glomerular capillary pressure. Dysregulation of glomerular ion channels, such as changes in TRPC6, can lead to devastating glomerular diseases, and a number of channels, including TRPC6, TRPC5, and various ionotropic receptors, are promising targets for drug development. This review discusses glomerular structure and glomerular disease processes. It also describes the types of plasma membrane ion channels that have been identified in glomerular cells, the physiological and pathophysiological contexts in which they operate, and the pathways by which they are regulated and dysregulated. The contributions of these channels to glomerular disease processes, such as focal segmental glomerulosclerosis (FSGS) and diabetic nephropathy, as well as the development of drugs that target these channels are also discussed.

Autoantibodies Targeting Nephrin in Podocytopathies.

BACKGROUND: Minimal change disease and primary focal segmental glomerulosclerosis in adults, along with idiopathic nephrotic syndrome in children, are immune-mediated podocytopathies that lead to nephrotic syndrome. Autoantibodies targeting nephrin have been found in patients with minimal change disease, but their clinical and pathophysiological roles are unclear. METHODS: We conducted a multicenter study to analyze antinephrin autoantibodies in adults with glomerular diseases, including minimal change disease, focal segmental glomerulosclerosis, membranous nephropathy, IgA nephropathy, antineutrophil cytoplasmic antibody-associated glomerulonephritis, and lupus nephritis, as well as in children with idiopathic nephrotic syndrome and in controls. We also created an experimental mouse model through active immunization with recombinant murine nephrin. RESULTS: The study included 539 patients (357 adults and 182 children) and 117 controls. Among the adults, antinephrin autoantibodies were found in 46 of the 105 patients (44%) with minimal change disease, 7 of 74 (9%) with primary focal segmental glomerulosclerosis, and only in rare cases among the patients with other conditions. Of the 182 children with idiopathic nephrotic syndrome, 94 (52%) had detectable antinephrin autoantibodies. In the subgroup of patients with active minimal change disease or idiopathic nephrotic syndrome who were not receiving immunosuppressive treatment, the prevalence of antinephrin autoantibodies was as high as 69% and 90%, respectively. At study inclusion and during follow-up, antinephrin autoantibody levels were correlated with disease activity. Experimental immunization induced a nephrotic syndrome, a minimal change disease-like phenotype, IgG localization to the podocyte slit diaphragm, nephrin phosphorylation, and severe cytoskeletal changes in mice. CONCLUSIONS: In this study, circulating antinephrin autoantibodies were common in patients with minimal change disease or idiopathic nephrotic syndrome and appeared to be markers of disease activity. Their binding at the slit diaphragm induced podocyte dysfunction and nephrotic syndrome, which highlights their pathophysiological significance. (Funded by Deutsche Forschungsgemeinschaft and others.).

Sparsentan versus Irbesartan in Focal Segmental Glomerulosclerosis.

BACKGROUND: An unmet need exists for focal segmental glomerulosclerosis (FSGS) treatment. In an 8-week, phase 2 trial, sparsentan, a dual endothelin-angiotensin receptor antagonist, reduced proteinuria in patients with FSGS. The efficacy and safety of longer-term treatment with sparsentan for FSGS are unknown. METHODS: In this phase 3 trial, we enrolled patients with FSGS (without known secondary causes) who were 8 to 75 years of age; patients were randomly assigned to receive sparsentan or irbesartan (active control) for 108 weeks. The surrogate efficacy end point assessed at the prespecified interim analysis at 36 weeks was the FSGS partial remission of proteinuria end point (defined as a urinary protein-to-creatinine ratio of ≤1.5 [with protein and creatinine both measured in grams] and a >40% reduction in the ratio from baseline). The primary efficacy end point was the estimated glomerular filtration rate (eGFR) slope at the time of the final analysis. The change in eGFR from baseline to 4 weeks after the end of treatment (week 112) was a secondary end point. Safety was also evaluated. RESULTS: A total of 371 patients underwent randomization: 184 were assigned to receive sparsentan and 187 to receive irbesartan. At 36 weeks, the percentage of patients with partial remission of proteinuria was 42.0% in the sparsentan group and 26.0% in the irbesartan group (P = 0.009), a response that was sustained through 108 weeks. At the time of the final analysis at week 108, there were no significant between-group differences in the eGFR slope; the between-group difference in total slope (day 1 to week 108) was 0.3 ml per minute per 1.73 m2 of body-surface area per year (95% confidence interval [CI], -1.7 to 2.4), and the between-group difference in the slope from week 6 to week 108 (i.e., chronic slope) was 0.9 ml per minute per 1.73 m2 per year (95% CI, -1.3 to 3.0). The mean change in eGFR from baseline to week 112 was -10.4 ml per minute per 1.73 m2 with sparsentan and -12.1 ml per minute per 1.73 m2 with irbesartan (difference, 1.8 ml per minute per 1.73 m2; 95% CI, -1.4 to 4.9). Sparsentan and irbesartan had similar safety profiles, and the frequency of adverse events was similar in the two groups. CONCLUSIONS: Among patients with FSGS, there were no significant between-group differences in eGFR slope at 108 weeks, despite a greater reduction in proteinuria with sparsentan than with irbesartan. (Funded by Travere Therapeutics; DUPLEX ClinicalTrials.gov number, NCT03493685.).

Inaxaplin for Proteinuric Kidney Disease in Persons with Two APOL1 Variants.

BACKGROUND: Persons with toxic gain-of-function variants in the gene encoding apolipoprotein L1 (APOL1) are at greater risk for the development of rapidly progressive, proteinuric nephropathy. Despite the known genetic cause, therapies targeting proteinuric kidney disease in persons with two APOL1 variants (G1 or G2) are lacking. METHODS: We used tetracycline-inducible APOL1 human embryonic kidney (HEK293) cells to assess the ability of a small-molecule compound, inaxaplin, to inhibit APOL1 channel function. An APOL1 G2-homologous transgenic mouse model of proteinuric kidney disease was used to assess inaxaplin treatment for proteinuria. We then conducted a single-group, open-label, phase 2a clinical study in which inaxaplin was administered to participants who had two APOL1 variants, biopsy-proven focal segmental glomerulosclerosis, and proteinuria (urinary protein-to-creatinine ratio of ≥0.7 to <10 [with protein and creatinine both measured in grams] and an estimated glomerular filtration rate of ≥27 ml per minute per 1.73 m2 of body-surface area). Participants received inaxaplin daily for 13 weeks (15 mg for 2 weeks and 45 mg for 11 weeks) along with standard care. The primary outcome was the percent change from the baseline urinary protein-to-creatinine ratio at week 13 in participants who had at least 80% adherence to inaxaplin therapy. Safety was also assessed. RESULTS: In preclinical studies, inaxaplin selectively inhibited APOL1 channel function in vitro and reduced proteinuria in the mouse model. Sixteen participants were enrolled in the phase 2a study. Among the 13 participants who were treated with inaxaplin and met the adherence threshold, the mean change from the baseline urinary protein-to-creatinine ratio at week 13 was -47.6% (95% confidence interval, -60.0 to -31.3). In an analysis that included all the participants regardless of adherence to inaxaplin therapy, reductions similar to those in the primary analysis were observed in all but 1 participant. Adverse events were mild or moderate in severity; none led to study discontinuation. CONCLUSIONS: Targeted inhibition of APOL1 channel function with inaxaplin reduced proteinuria in participants with two APOL1 variants and focal segmental glomerulosclerosis. (Funded by Vertex Pharmaceuticals; VX19-147-101 ClinicalTrials.gov number, NCT04340362.).

Role of TSP-1 and its receptor ITGB3 in the renal tubulointerstitial injury of focal segmental glomerulosclerosis.

Focal segmental glomerulosclerosis (FSGS), a common cause of primary glomerulonephritis, has a poor prognosis and is pathologically featured by tubulointerstitial injury. Thrombospondin-1 (TSP-1) is an extracellular matrix protein that acts in combination with different receptors in the kidney. Here, we analyzed the tubular expression of TSP-1 and its receptor integrin ß3 (ITGB3) in FSGS. Previously the renal interstitial chip analysis of FSGS patients with tubular interstitial injury showed that the expression of TSP-1 and ITGB3 were upregulated. We found that the expression of TSP-1 and ITGB3 increased in the tubular cells of FSGS patients. The plasma level of TSP-1 increased and was correlated to the degree of tubulointerstitial lesions in FSGS patients. TSP-1/ITGB3 signaling induced renal tubular injury in HK-2 cells exposure to bovine serum albumin and the adriamycin (ADR)-induced nephropathy model. THBS1 KO ameliorated tubular injury and renal fibrosis in ADR-treated mice. THBS1 knockdown decreased the expression of KIM-1 and caspase 3 in the HK-2 cells treated with bovine serum albumin, while THBS1 overexpression could induce tubular injury. In vivo, we identified cyclo-RGDfK as an agent to block the binding of TSP-1 to ITGB3. Cyclo-RGDfK treatment could alleviate ADR-induced renal tubular injury and interstitial fibrosis in mice. Moreover, TSP-1 and ITGB3 were colocalized in tubular cells of FSGS patients and ADR-treated mice. Taken together, our data showed that TSP-1/ITGB3 signaling contributed to the development of renal tubulointerstitial injury in FSGS, potentially identifying a new therapeutic target for FSGS.

The role of the FSGS disease gene product and nuclear pore protein NUP205 in regulating nuclear localization and activity of transcriptional regulators YAP and TAZ.

Mutations in genes encoding nuclear pore proteins (NUPs) lead to the development of steroid-resistant nephrotic syndrome and focal segmental glomerulosclerosis (FSGS). However, the precise molecular mechanisms by which NUP dysfunction contributes to podocyte injury preceding FSGS remain unclear. The tightly regulated activity of Yes-associated protein (YAP) and WW-domain-containing transcription regulator 1 (TAZ), the transcriptional effectors of the Hippo pathway, is crucial for podocytes and the maintenance of the glomerular filter. In this study, we investigate the impact of NUPs on the regulation of YAP/TAZ nuclear import and activity in podocytes. In unbiased interactome studies using quantitative label-free mass spectrometry, we identify the FSGS disease gene products NUP107, NUP133, NUP205, and Exportin-5 (XPO5) as components of YAP and TAZ protein complexes in podocytes. Moreover, we demonstrate that NUP205 is essential for YAP/TAZ nuclear import. Consistently, both the nuclear interaction of YAP/TAZ with TEA domain transcription factor 1 and their transcriptional activity were dependent on NUP205 expression. Additionally, we elucidate a regulatory feedback mechanism whereby YAP activity is modulated in response to TAZ-mediated NUP205 expression. In conclusion, this study establishes a connection between the FSGS disease protein NUP205 and the activity of the transcriptional regulators and Hippo effectors YAP and TAZ and it proposes a potential pathological role of YAP/TAZ dysregulation in podocytes of patients with pathogenic NUP205 variants.

INF2 formin variants linked to human inherited kidney disease reprogram the transcriptome, causing mitotic chaos and cell death.

Mutations in the human INF2 gene cause autosomal dominant focal segmental glomerulosclerosis (FSGS)-a condition characterized by podocyte loss, scarring, and subsequent kidney degeneration. To understand INF2-linked pathogenicity, we examined the effect of pathogenic INF2 on renal epithelial cell lines and human primary podocytes. Our study revealed an increased incidence of mitotic cells with surplus microtubule-organizing centers fostering multipolar spindle assembly, leading to nuclear abnormalities, particularly multi-micronucleation. The levels of expression of exogenous pathogenic INF2 were similar to those of endogenous INF2. The aberrant nuclear phenotypes were observed regardless of the expression method used (retrovirus infection or plasmid transfection) or the promoter (LTR or CMV) used, and were absent with exogenous wild type INF2 expression. This indicates that the effect of pathogenic INF2 is not due to overexpression or experimental cell manipulation, but instead to the intrinsic properties of pathogenic INF2. Inactivation of the INF2 catalytic domain prevented aberrant nuclei formation. Pathogenic INF2 triggered the translocation of the transcriptional cofactor MRTF into the nucleus. RNA sequencing revealed a profound alteration in the transcriptome that could be primarily attributed to the sustained activation of the MRTF-SRF transcriptional complex. Cells eventually underwent mitotic catastrophe and death. Reducing MRTF-SRF activation mitigated multi-micronucleation, reducing the extent of cell death. Our results, if validated in animal models, could provide insights into the mechanism driving glomerular degeneration in INF2-linked FSGS and may suggest potential therapeutic strategies for impeding FSGS progression.

Treatment of IgA Nephropathy: A Rapidly Evolving Field.

The pivotal event in the pathophysiology of IgA nephropathy is the binding of circulating IgA-containing immune complexes to mesangial cells, with secondary glomerular and tubulointerstitial inflammation and fibrosis. The paramount difficulty in the management of IgA nephropathy is the heterogeneity in its clinical presentation and prognosis, requiring an individualized treatment approach. Goal-directed supportive care remains the bedrock of therapy for all patients, regardless of risk of progression. Sodium-glucose transporter 2 inhibitors and sparsentan should be integral to contemporary supportive care, particularly in patients with chronic kidney damage. Pending the development of reliable biomarkers, it remains a challenge to identify patients prone to progression due to active disease and most likely to derive a net benefit from immunosuppression. The use of clinical parameters, including the degree of proteinuria, the presence of persistent microscopic hematuria, and the rate of eGFR loss, combined with the mesangial hypercellularity, endocapillary hypercellularity, segmental glomerulosclerosis, tubular atrophy/interstitial fibrosis, crescents score, is currently the best approach. Systemic glucocorticoids are indicated in high-risk patients, but the beneficial effects wane after withdrawal and come at the price of substantial treatment-associated toxicity. Therapies with direct effect on disease pathogenesis are increasingly becoming available. While targeted-release budesonide has garnered the most attention, anti-B-cell strategies and selective complement inhibition will most likely prove their added value. We propose a comprehensive approach that tackles the different targets in the pathophysiology of IgA nephropathy according to their relevance in the individual patient.

Proteomic Analysis of Idiopathic Nephrotic Syndrome Triggered by Primary Podocytopathies in Adults: Regulatory Mechanisms and Diagnostic Implications.

Idiopathic nephrotic syndrome (NS) is a heterogeneous group of glomerular disorders which includes two major phenotypes: minimal change disease (MCD) and focal segmental glomerulosclerosis (FSGS). MCD and FSGS are classic types of primary podocytopathies. We aimed to explore the molecular mechanisms in NS triggered by primary podocytopathies and evaluate diagnostic value of the selected proteomic signatures by analyzing blood proteome profiling. Totally, we recruited 90 participants in two cohorts. The first cohort was analyzed using label-free quantitative (LFQ) proteomics to discover differential expressed proteins and identify enriched biological process in NS which were further studied in relation to clinical markers of kidney injury. The second cohort was analyzed using parallel reaction monitoring-based quantitative proteomics to verify the data of LFQ proteomics and assess the diagnostic performance of the selected proteins using receiver-operating characteristic curve analysis. Several biological processes (such as immune response, cell adhesion, and response to hypoxia) were found to be associated with kidney injury during MCD and FSGS. Moreover, three proteins (CSF1, APOC3, and LDLR) had over 90% sensitivity and specificity in detecting adult NS triggered by primary podocytopathies. The identified biological processes may play a crucial role in MCD and FSGS pathogenesis. The three blood protein markers are promising for diagnosing adult NS triggered by primary podocytopathies.

Dexamethasone promotes renal fibrosis by upregulating ILT4 expression in myeloid-derived suppressor cells.

Studies have shown that adoptive transfer of myeloid-derived suppressor cells (MDSCs) can alleviate various inflammatory diseases, including glomerulonephritis, but the long-term effects of the transferred MDSCs are still unclear. In addition, although glucocorticoids exert immunosuppressive effects on inflammatory diseases by inducing the expansion of MDSCs, the impact of glucocorticoids on the immunosuppressive function of MDSCs and their molecular mechanisms are unclear. In this study, we found that adoptive transfer of MDSCs to doxorubicin-induced focal segmental glomerulosclerosis (FSGS) mice for eight consecutive weeks led to an increase in serum creatinine and proteinuria and aggravation of renal interstitial fibrosis. Similarly, 8 weeks of high-dose dexamethasone administration exacerbated renal interstitial injury and interstitial fibrosis in doxorubicin-induced mice, manifested as an increase in serum creatinine and proteinuria, collagen deposition and α-SMA expression. On this basis, we found that dexamethasone could enhance MDSC expression and secretion of the fibrosis-related cytokines TGF-ß and IL-10. Mechanistically, we revealed that dexamethasone promotes the expression of immunoglobulin-like transcription factor 4 (ILT4), which enhances the T-cell inhibitory function of MDSCs and promotes the activation of STAT6, thereby strengthening the expression and secretion of TGF-ß and IL-10. Knocking down ILT4 alleviated renal fibrosis caused by adoptive transfer of MDSCs. Therefore, our findings demonstrate that the role and mechanism of dexamethasone mediate the expression and secretion of TGF-ß and IL-10 in MDSCs by promoting the expression of ILT4, thereby leading to renal fibrosis.

Investigating FSGS-like injury in zebrafish larvae by nifurpirinol: efficacy and molecular insight.

Identifying effective drugs for focal segmental glomerulosclerosis (FSGS) treatment holds significant importance. Our high-content drug screening on zebrafish larvae relies on nitroreductase/metronidazole (NTR/MTZ)-induced podocyte ablation to generate FSGS-like injury. A crucial factor for successful drug screenings is minimizing variability in injury induction. For this, we introduce nifurpirinol (NFP) as a more reliable prodrug for targeted podocyte depletion. NFP showed a 2.3-fold increase in efficiency at concentrations 1,600-fold lower compared with MTZ-mediated injury induction. Integration into the screening workflow validated its suitability for the high-content drug screening. The presence of crucial FSGS hallmarks, such as podocyte foot process effacement, proteinuria, and activation of parietal epithelial cells, was observed. After the isolation of the glomeruli from the larvae, we identified essential pathways by proteomic analysis. This study shows that NFP serves as a highly effective prodrug to induce the FSGS-like disease in zebrafish larvae and is well-suited for a high-content drug screening to identify new candidates for the treatment of FSGS.NEW & NOTEWORTHY This research investigated the use of nifurpirinol in nanomolar amounts as a prodrug to reliably induce focal segmental glomerulosclerosis (FSGS)-like damage in transgenic zebrafish larvae. Through proteomic analysis of isolated zebrafish glomeruli, we were further able to identify proteins that are significantly regulated after the manifestation of FSGS. These results are expected to expand our knowledge of the pathomechanism of FSGS.

Podocyte injury at young age causes premature senescence and worsens glomerular aging.

As life expectancy continues to rise, age-related diseases are becoming more prevalent. For example, proteinuric glomerular diseases typified by podocyte injury have worse outcomes in the elderly compared with young patients. However, the reasons are not well understood. We hypothesized that injury to nonaged podocytes induces senescence, which in turn augments their aging processes. In primary cultured human podocytes, injury induced by a cytopathic antipodocyte antibody, adriamycin, or puromycin aminonucleoside increased the senescence-related genes CDKN2A (p16INK4a/p14ARF), CDKN2D (p19INK4d), and CDKN1A (p21). Podocyte injury in human kidney organoids was accompanied by increased expression of CDKN2A, CDKN2D, and CDKN1A. In young mice, experimental focal segmental glomerulosclerosis (FSGS) induced by adriamycin and antipodocyte antibody increased the glomerular expression of p16, p21, and senescence-associated ß-galactosidase (SA-ß-gal). To assess the long-term effects of early podocyte injury-induced senescence, we temporally followed young mice with experimental FSGS through adulthood (12 m of age) and middle age (18 m of age). p16 and Sudan black staining were higher at middle age in mice with earlier FSGS compared with age-matched mice that did not get FSGS when young. This was accompanied by lower podocyte density, reduced canonical podocyte protein expression, and increased glomerular scarring. These results are consistent with injury-induced senescence in young podocytes, leading to increased senescence of podocytes by middle age accompanied by lower podocyte lifespan and health span.NEW & NOTEWORTHY Glomerular function is decreased by aging. However, little is known about the molecular mechanisms involved in age-related glomerular changes and which factors could contribute to a worse glomerular aging process. Here, we reported that podocyte injury in young mice and culture podocytes induced senescence, a marker of aging, and accelerates glomerular aging when compared with healthy aging mice.

WIP1 inhibition as a new therapeutic strategy for collapsing glomerulopathy.

Collapsing glomerulopathy (CG) is an aggressive variant of focal and segmental glomerulosclerosis. Understanding the diverse mechanisms that can drive CG promises to uncover new therapeutic strategies. In this issue, Duret et al. identify WIP1 phosphatase as a therapeutic target for CG. Using genetic ablation and pharmacologic inhibition, they show that blockade of WIP1 activity is protective in 2 different mouse models of CG. This study highlights the complex interplay of glomerular signaling pathways in CG and offers hope for targeted therapies.

A multi-institutional study found a possible role of anti-nephrin antibodies in post-transplant focal segmental glomerulosclerosis recurrence.

Possible roles of anti-nephrin antibodies in post-transplant recurrent focal segmental glomerulosclerosis (FSGS) have been reported recently. To confirm these preliminary results, we performed a multi-institutional study of 22 Japanese pediatric kidney transplant recipients with FSGS including eight genetic FSGS and 14 non-genetic (presumed primary) FSGS. Eleven of the 14 non-genetic FSGS patients had post-transplant recurrent FSGS. Median (interquartile range) plasma levels of anti-nephrin antibodies in post-transplant recurrent FSGS measured using ELISA were markedly high at 899 (831, 1292) U/mL (cutoff 231 U/mL) before transplantation or during recurrence. Graft biopsies during recurrence showed punctate IgG deposition co-localized with nephrin that had altered localization with increased nephrin tyrosine phosphorylation and Src homology and collagen homology A expressions. Graft biopsies after remission showed no signals for IgG and a normal expression pattern of nephrin. Anti-nephrin antibody levels decreased to 155 (53, 367) U/mL in five patients with samples available after remission. In patients with genetic FSGS as in those with non-genetic FSGS without recurrence, anti-nephrin antibody levels were comparable to those of 30 control individuals, and graft biopsies had no signals for IgG and a normal expression pattern of nephrin. Thus, our results suggest that circulating anti-nephrin antibodies are a possible candidate for circulating factors involved in the pathogenesis of post-transplant recurrent FSGS and that this may be mediated by nephrin phosphorylation. Larger studies including other ethnicities are required to confirm this finding.

Anti-nephrin antibodies in recurrence of focal segmental glomerulosclerosis: closer to discovering the Holy Grail?

Recurrent forms of primary focal segmental glomerulosclerosis (FSGS) pose an unmet challenge to nephrologists, both in terms of understanding the underlying pathophysiology and in terms of identifying an effective management strategy of this disease, which frequently leads to kidney graft loss. In the past few decades, experimental observations both in patients and in animal models have led to the hypothesis of the existence of circulating factors driving the loss of integrity of the glomerular filtration barrier in FSGS. Although different circulating factor candidates have been postulated, none has been unequivocally shown to be pathogenic. In the current study, Shirai et al. propose a new candidate for this role by identifying circulating anti-nephrin autoantibodies in a cohort of patients with post-transplant recurrence of primary FSGS. Recent evidence by Watts et al. has also identified anti-nephrin autoantibodies in the circulation and in the kidney biopsies of patients with minimal change disease. If confirmed, the identification of these autoantibodies would both contribute to identifying the elusive circulating factor in FSGS and increase our understanding of the spectrum of proteinuric glomerular lesions, spanning from minimal change disease to FSGS. The quest for the Holy Grail is perhaps closer to completion.

Oligonephronia: another piece in the CKDu jigsaw?

Rates of chronic kidney disease of unknown etiology are high in Aguascalientes, Mexico. Kidneys of adolescents are small by ultrasonography, compatible with oligonephronia, whereas proteinuria and higher estimated glomerular filtration rates and blood pressures among those with relatively higher kidney volumes probably flag relatively greater degrees of compensatory hypertrophy. Glomerulomegaly and podocytopathy, and later segmental glomerulosclerosis in biopsies, suggest a cascade driven by nephron deficiency. Better measures of glomerular number and volume should improve understanding, facilitate risk assessment, and guide interventions.

Anti-nephrin autoantibodies: novel predictors of post-transplant recurrence of focal segmental glomerular sclerosis.

Post-transplant recurrence of focal segmental glomerular sclerosis (FSGS) is a major challenge in the field of kidney transplantation. Currently, the most reliable predictor of FSGS recurrence is disease recurrence in a previous allograft. Recent studies suggest a possible causal role of anti-nephrin autoantibodies in the primary disease (primary FSGS and minimal change disease), as well as post-transplant recurrence of FSGS. In this issue of Kidney International, Batal et al. evaluate pretransplant anti-nephrin autoantibodies as a specific predictor of FSGS recurrence and demonstrate colocalization of nephrin and punctate IgG in anti-nephrin-positive patients with disease recurrence.

Post-transplant recurrence of focal segmental glomerular sclerosis: consensus statements.

Focal segmental glomerular sclerosis (FSGS) is 1 of the primary causes of nephrotic syndrome in both pediatric and adult patients, which can lead to end-stage kidney disease. Recurrence of FSGS after kidney transplantation significantly increases allograft loss, leading to morbidity and mortality. Currently, there are no consensus guidelines for identifying those patients who are at risk for recurrence or for the management of recurrent FSGS. Our work group performed a literature search on PubMed/Medline, Embase, and Cochrane, and recommendations were proposed and graded for strength of evidence. Of the 614 initially identified studies, 221 were found suitable to formulate consensus guidelines for recurrent FSGS. These guidelines focus on the definition, epidemiology, risk factors, pathogenesis, and management of recurrent FSGS. We conclude that additional studies are required to strengthen the recommendations proposed in this review.

Podocyte density as a predictor of long-term kidney outcome in obesity-related glomerulopathy.

Glomerulomegaly and focal segmental glomerulosclerosis are histopathological hallmarks of obesity-related glomerulopathy (ORG). Podocyte injury and subsequent depletion are regarded as key processes in the development of these glomerular lesions in patients with ORG, but their impact on long-term kidney outcome is undetermined. Here, we correlated clinicopathological findings and podocyte depletion retrospectively in patients with ORG. Relative (podocyte density) and absolute (podocyte number per glomerulus) measures of podocyte depletion were estimated using model-based stereology in 46 patients with ORG. The combined endpoint of kidney outcomes was defined as a 30% decline in estimated glomerular filtration rate (eGFR) or kidney failure. Patients with lower podocyte density were predominantly male and had larger body surface area, greater proteinuria, fewer non-sclerotic glomeruli, larger glomeruli and higher single-nephron eGFR. During a median follow-up of 4.1 years, 18 (39%) patients reached endpoint. Kidney survival in patients with lower podocyte density was significantly worse than in patients with higher podocyte density. However, there was no difference in kidney survival between patient groups based on podocyte number per glomerulus. Cox hazard analysis showed that podocyte density, but not podocyte number per glomerulus, was associated with the kidney outcomes after adjustment for clinicopathological confounders. Thus, our study demonstrates that a relative depletion of podocytes better predicts long-term kidney outcomes than does absolute depletion of podocytes. Hence, the findings implicate mismatch between glomerular enlargement and podocyte number as a crucial determinant of disease progression in ORG.

Quantitative assessment of glomerular basement membrane collagen IV α chains in paraffin sections from patients with focal segmental glomerulosclerosis and Alport gene variants.

Focal segmental glomerulosclerosis (FSGS) lesions have been linked to variants in COL4A3/A4/A5 genes, which are also mutated in Alport syndrome. Although it could be useful for diagnosis, quantitative evaluation of glomerular basement membrane (GBM) type IV collagen (colIV) networks is not widely used to assess these patients. To do so, we developed immunofluorescence imaging for collagen α5(IV) and α1/2(IV) on kidney paraffin sections with Airyscan confocal microscopy that clearly distinguishes GBM collagen α3α4α5(IV) and α1α1α2(IV) as two distinct layers, allowing quantitative assessment of both colIV networks. The ratios of collagen α5(IV):α1/2(IV) mean fluorescence intensities (α5:α1/2 intensity ratios) and thicknesses (α5:α1/2 thickness ratios) were calculated to represent the levels of collagen α3α4α5(IV) relative to α1α1α2(IV). The α5:α1/2 intensity and thickness ratios were comparable across all 11 control samples, while both ratios were significantly and markedly decreased in all patients with pathogenic or likely pathogenic Alport COL4A variants, supporting validity of this approach. Thus, with further validation of this technique, quantitative measurement of GBM colIV subtype abundance by immunofluorescence, may potentially serve to identify the subgroup of patients with FSGS lesions likely to harbor pathogenic COL4A variants who could benefit from genetic testing.