Surface Of Podocytes Research Articles

#246 Understanding the impact of antiangiogenic drug-induced proteinuria on kidney function in cancer patients

Abstract Background and Aims Proteinuria is a common adverse event associated with the use of vascular endothelial growth factor (VEGF) inhibitor drugs, which are widely employed in oncology for treating various tumors. The incidence of proteinuria of all degrees ranges from 10% to 90%, with proteinuria in the nephrotic range occurring in 1-5% of cases. VEGF plays a crucial role in maintaining the integrity of the glomerular capillary wall. Podocytes, constitutively express VEGF, and VEGF receptors are present on both the surface of glomerular capillary endothelial cells and podocytes. Any disruption in the podocyte-endothelial VEGF axis can lead to the loss of endothelial fenestrations in glomerular capillaries, proliferation of glomerular endothelial cells, loss of podocytes, and subsequent proteinuria. The most common pathological findings include focal segmental glomerulosclerosis and minimal change nephropathy, typically associated with tyrosine kinase inhibitors (TKIs), as well as thrombotic microangiopathy (TMA), more frequently observed in pts treated with anti VEGF. Proteinuria is a recognized risk factor for progressive renal damage and end-stage renal disease. However, it's worth noting that the average treatment duration for patients on anti-angiogenic therapy is considerably shorter than the time indicated by clinical studies as necessary to induce renal damage from proteinuria in healthy individuals. However, the long-term impact of drug-induced proteinuria on renal function remains uncertain. The aim of the study is to investigate the association between proteinuria induced by anti-VEGF/VEGFR drugs and its long-term effects on renal function in cancer patients. Method A retrospective study was conducted on 124 patients undergoing anti-VEGF/VEGFR therapy for ≥6 months. 45% of the patients enrolled in the study were on TKI monotherapy, 36% received TKI plus immune checkpoint inhibitors (ICIs), 10% received anti- VEGF treatment, 7% received TKI + chemotherapy (CT), and 2% received anti-VEGF + ICIs. Among patients, 51% were undergoing treatment for kidney cancer, 25% for thyroid cancer, 14% for colon cancer, 7% for liver cancer, and 5% for lung cancer. The study assessed the time course of estimated glomerular filtration rate (eGFR), the influence of baseline eGFR on subsequent variations, the association between proteinuria and renal function, and the identification of risk factors for proteinuria or renal failure. Proteinuria was quantified as proteinuria/24 h. Results Among the 124 patients, 53 developed proteinuria <1 g/24 h, 41 between 1-3 g/24 h, and 30 >3 g/24 h. Specific data are outlined in Table 1. A trend toward a reduction in eGFR of −5 ml/min/1.73 m2 was observed in all patients after 2 years of treatment. The high proteinuria group exhibited a greater percentage change in eGFR compared to the other groups (−1.5% vs −8.5% vs −12.3%) as depicted in Fig. 1A, along with a time-dependent decrease in eGFR. There was no significant difference in the development of eGFR <30 ml/min/1.73 m2 between groups, and no patients permanently discontinued treatment due to nephrotoxicity. No differences in eGFR reduction were noted among the three groups categorized by baseline eGFR (Fig. 1B). Importantly, renal function after the end of therapy was found to be reversible. Conclusion The study did not find a correlation between the degree of proteinuria secondary to anti-VEGF/VEGFR and significant reductions in renal function. Therefore, treatment can be continued irrespective of the degree of proteinuria. Clinical decisions regarding the continuation of therapy with these drugs should weigh the benefits in terms of survival against the potential risks of toxicity, including a modest reduction in renal glomerular filtration rate.

Containing anti-PLA2R IgG antibody induces podocyte injury in idiopathic membranous nephropathy

Background Idiopathic membranous nephropathy is widely recognized as an autoimmune kidney disease that is accompanied by the discovery of several autoantibodies, and the antibody subclass in the circulation of patients with iMN is mainly IgG. However, the direct pathogenic effect of the containing anti-PLA2R IgG antibody on podocytes is not clear. Method A protein G affinity chromatography column was used to purify serum IgG antibodies. Containing anti-PLA2R IgG antibodies from iMN patients and IgG from healthy controls were also obtained. Based on the established in vitro podocyte culture system, purified IgG antibodies from the two groups were used to stimulate podocytes, and the expression of essential podocyte proteins (podocin), the levels of inflammatory cytokines in the cell supernatant, cytoskeletal disorders, and podocyte apoptosis were analyzed. Results Compared with that in the normal IgG group, the expression of podocin and podocin mRNA was reduced (p = 0.016 and p = 0.005, respectively), the fluorescence intensity of podocin on the surface of podocytes was reduced, the cytoskeleton of podocytes was disordered and reorganized, and the ratio of podocyte apoptosis was increased in the iMN group (p = 0.008). Conclusion The containing anti-PLA2R IgG antibody might have a direct damaging effect on podocytes in idiopathic membranous nephropathy.

THSD7A as a Promising Biomarker for Membranous Nephrosis.

Membranous nephropathy (MN) is an autoimmune disease of the kidney glomerulus and one of the leading causes of nephrotic syndrome. The disease exhibits heterogeneous outcomes with approximately 30% of cases progressing to end-stage renal disease. Traditionally, the standard approach of diagnosing MN involves performing a kidney biopsy. Nevertheless, kidney biopsy is an invasive procedure that poses risks for the patient including bleeding and pain, and bears greater costs for the health system. The clinical management of MN has steadily advanced owing to the identification of autoantibodies to the phospholipase A2 receptor (PLA2R) in 2009 and thrombospondin domain-containing 7A (THSD7A) in 2014 on the podocyte surface. At present, serum anti-PLA2R antibody detection and glomerular PLA2R antigen staining have been used for clinical diagnosis and prognosis, but the related detection of THSD7A has not been widely used in clinical practice. Here, we summarized the emerging knowledge regarding the roles THSD7A plays in MN and its clinical implications as diagnostic, prognostic, and therapeutic response as well as Methods for detecting serum THSD7A antibodies.

Role of lysosomes in insulin signaling and glucose uptake in cultured rat podocytes

Podocytes are sensitive to insulin, which governs the functional and structural integrity of podocytes that are essential for proper function of the glomerular filtration barrier. Lysosomes are acidic organelles that are implicated in regulation of the insulin signaling pathway. Cathepsin D (CTPD) and lysosome-associated membrane protein 1 (LAMP1) are major lysosomal proteins that reflect the functional state of lysosomes. However, the effect of insulin on lysosome activity and role of lysosomes in the regulation of insulin-dependent glucose uptake in podocytes are unknown. Our studies showed that the short-term incubation of podocytes with insulin decreased LAMP1 and CTPD mRNA levels. Insulin and bafilomycin A1 reduced both the amounts of LAMP1 and CTPD proteins and activity of CTPD, which were associated with a decrease in the fluorescence intensity of lysosomes that were labeled with LysoTracker. Bafilomycin A1 inhibited insulin-dependent endocytosis of the insulin receptor and increased the amounts of the insulin receptor and glucose transporter 4 on the cell surface of podocytes. Bafilomycin A1 also inhibited insulin-dependent glucose uptake despite an increase in the amount of glucose transporter 4 in the plasma membrane of podocytes. These results suggest that lysosomes are signaling hubs that may be involved in the coupling of insulin signaling with the regulation of glucose uptake in podocytes. The dysregulation of this mechanism can lead to the dysfunction of podocytes and development of insulin resistance.

Membranous nephropathy: the current state of the problem

Membranous nephropathy (MN) is an autoimmune disease of the kidney glomeruli and one of the leading causes of nephrotic syndrome. The disease exhibits heterogenous outcomes with approximately 30 % of cases progressing to end-stage renal disease. The study of MN pathogenesis has steadily advanced owing to the identification of autoantibodies to the phospholipase A2 receptor (PLA2R) in 2009 and thrombospondin domain-containing 7A (THSD7A) on the podocyte surface in 2014. Approximately 50–80 and 3–5 % of primary MN cases are associated with either anti-PLA2R or anti-THSD7A antibodies, respectively. The presence of these autoantibodies is used for MN diagnosis; antibody levels correlate with disease severity and possess significant biomarker values in monitoring disease progression and treatment response.

#6905 PREVALENCE OF ANTIPLA2R ANTIBODIES IN EGYPTIAN PATIENTS WITH NEPHROTIC SYNDROME

Abstract Background and Aims Primary membranous nephropathy (PMN), a common form of the nephrotic syndrome, is an antibody-mediated autoimmune glomerular disease. Autoimmunity is driven by circulating autoantibodies that bind to one or more antigens on the surface of glomerular podocytes. PLA2R antigen is the most common and prevalent one among these antigens. Anti-PLA2R antibodies are measured in serum and detected within biopsies of primary membranous nephropathy patients. Up to the moment, no clear data about the prevalence of AntiPLA2R antibodies associated PMN in Egyptian patients. The aim of this work was to study the prevalence of antiPLA2R antibodies in Egyptian patients with nephrotic syndrome underwent renal biopsy. Method In this cross-sectional study we recruited 70 adult patients presented with nephrotic range proteinuria to Ain-shams university hospital and a private nephrology center in Cairo during a period of 20 months (from March 2020 to October 2021). All patients first presentation for whom laboratory investigations including serum anti-PLA2R antibodies titer by indirect immunofluorescence and kidney biopsy were done. Anti-PLA2R antibodies were measured in serum, checked in biopsies and correlated with biopsy findings. Results Membranous nephropathy (primary and secondary) was found by biopsy finding in 25 of 70 patients (35.7%) presenting with nephrotic range proteinuria. 21 patients (84%) of the cases of membranous nephropathy had been diagnosed with primary membranous nephropathy and 4 (16%) had been diagnosed with secondary membranous nephropathy. Circulating anti-PLA2R antibodies were detected within serum in 9 (42.85%) of primary MN cases while detection of anti-PLA2R antibodies within the glomerular extracts of primary MN cases was much higher; 17 patients (80.95%). There was positive correlation between serum AntiPLA2R Antibodies titer and U PCR (r = 0.839, P = 0.005) (Fig. 1). Conclusion A we may conclude that, most patients with primary membranous nephropathy have anti-PLA2R antibodies. Detection of anti-PLA2R antibodies within the biopsy has higher sensitivity than serum (80.95% versus 42.85%). Specificity of PLA2R to primary membranous nephropathy is 100%. Patients with high anti-PLA2R titer had higher baseline proteinuria than patients with lower anti-PLA2R titer.

Characterizing Intraindividual Podocyte Morphology In Vitro with Different Innovative Microscopic and Spectroscopic Techniques.

Podocytes are critical components of the glomerular filtration barrier, sitting on the outside of the glomerular basement membrane. Primary and secondary foot processes are characteristic for podocytes, but cell processes that develop in culture were not studied much in the past. Moreover, protocols for diverse visualization methods mostly can only be used for one technique, due to differences in fixation, drying and handling. However, we detected by single-cell RNA sequencing (scRNAseq) analysis that cells reveal high variability in genes involved in cell type-specific morphology, even within one cell culture dish, highlighting the need for a compatible protocol that allows measuring the same cell with different methods. Here, we developed a new serial and correlative approach by using a combination of a wide variety of microscopic and spectroscopic techniques in the same cell for a better understanding of podocyte morphology. In detail, the protocol allowed for the sequential analysis of identical cells with light microscopy (LM), Raman spectroscopy, scanning electron microscopy (SEM) and atomic force microscopy (AFM). Skipping the fixation and drying process, the protocol was also compatible with scanning ion-conductance microscopy (SICM), allowing the determination of podocyte surface topography of nanometer-range in living cells. With the help of nanoGPS Oxyo®, tracking concordant regions of interest of untreated podocytes and podocytes stressed with TGF-β were analyzed with LM, SEM, Raman spectroscopy, AFM and SICM, and revealed significant morphological alterations, including retraction of podocyte process, changes in cell surface morphology and loss of cell-cell contacts, as well as variations in lipid and protein content in TGF-β treated cells. The combination of these consecutive techniques on the same cells provides a comprehensive understanding of podocyte morphology. Additionally, the results can also be used to train automated intelligence networks to predict various outcomes related to podocyte injury in the future.

A novel fusion protein consisting of anti-ANGPTL3 antibody and interleukin-22 ameliorates diabetic nephropathy in mice.

The pathogenic mechanisms of diabetic nephropathy (DN) include podocyte injury, inflammatory responses and metabolic disorders. Although the antagonism of Angiopoietin-like protein 3 (ANGPTL3) can alleviate proteinuria symptoms by inhibiting the activation of integrin αvβ3 on the surface of podocytes, it can not impede other pathological processes, such as inflammatory responses and metabolic dysfunction of glucolipid. Interleukin-22 (IL-22) is considered to be a pivotal molecule involved in suppressing inflammatory responses, initiating regenerative repair, and regulating glucolipid metabolism. Genes encoding the mIL22IgG2aFc and two chains of anti-ANGPTL3 antibody and bifunctional protein were synthesized. Then, the DN mice were treated with intraperitoneal injection of normal saline, anti-ANGPTL3 (20 mg/kg), mIL22Fc (12 mg/kg) or anti-ANGPTL3 /IL22 (25.3 mg/kg) and irrigation of positive drug losartan (20mg/kg/d) twice a week for 8 weeks. In this research, a novel bifunctional fusion protein (anti-ANGPTL3/IL22) formed by the fusion of IL-22 with the C-terminus of anti-ANGPTL3 antibody exhibited favorable stability and maintained the biological activity of anti-ANGPTL3 and IL-22, respectively. The fusion protein showed a more pronounced attenuation of proteinuria and improved dysfunction of glucolipid metabolism compared with mIL22Fc or anti-ANGPTL3. Our results also indicated that anti-ANGPTL3/IL22 intervention significantly alleviated renal fibrosis via inhibiting the expression of the inflammatory response-related protein nuclear factor kappa light-chain enhancer of activated B cells (NF-κB) p65 and NOD-like receptor family pyrin domain-containing protein 3 (NLRP3) inflammasome. Moreover, transcriptome analysis revealed the downregulation of signaling pathways associated with injury and dysfunction of the renal parenchymal cell indicating the possible protective mechanisms of anti-ANGPTL3/IL22 in DN. Collectively, anti-ANGPTL3/IL22 bifunctional fusion protein can be a promising novel therapeutic strategy for DN by reducing podocyte injury, ameliorating inflammatory response, and enhancing renal tissue recovery.

Netrin G1 Is a Novel Target Antigen in Primary Membranous Nephropathy.

Primary membranous nephropathy (MN) is caused by circulating autoantibodies binding to antigens on the podocyte surface. PLA2R1 is the main target antigen in 70%-80% of cases, but the pathogenesis is unresolved in 10%-15% of patients. We used native western blotting to identify IgG4 autoantibodies, which bind an antigen endogenously expressed on podocyte membranes, in the serum of the index patient with MN. These IgG4 autoantibodies were used to immunoprecipitate the target antigen, and mass spectrometry was used to identify Netrin G1 (NTNG1). Using native western blot and ELISA, NTNG1 autoantibodies were analyzed in cohorts of 888 patients with MN or other glomerular diseases. NTNG1 was identified as a novel target antigen in MN. It is a membrane protein expressed in healthy podocytes. Immunohistochemistry confirmed granular NTNG1 positivity in subepithelial glomerular immune deposits. In prospective and retrospective MN cohorts, we identified three patients with NTNG1-associated MN who showed IgG4-dominant circulating NTNG1 autoantibodies, enhanced NTNG1 expression in the kidney, and glomerular IgG4 deposits. No NTNG1 autoantibodies were identified in 561 PLA2R1 autoantibodies-positive patients, 27 THSD7A autoantibodies-positive patients, and 77 patients with other glomerular diseases. In two patients with available follow-up of 2 and 4 years, both NTNG1 autoantibodies and proteinuria persisted. NTNG1 expands the repertoire of target antigens in patients with MN. The clinical role of NTNG1 autoantibodies remains to be defined.

Urinary Podocyte Excretion Predicts Urinary Protein Selectivity and Renal Prognosis.

Background Urinary podocyte excretion is related to a reduction in glomerular podocyte numbers, glomerulosclerosis, and urinary protein selectivity. To elucidate the role of urinary podocytes in proteinuria and renal prognosis and to identify the factors that cause podocyte detachment, we examined urinary podocytes in 120 renal biopsy patients. Methods Podocytes were identified in urinary sediments stained with fluorescent-labeled anti-podocalyxin antibodies in ten high power fields. The amounts of protein bands, separated by SDS-polyacrylamide gel electrophoresis, were calculated using an image software program and the correlation with urinary podocytes was analyzed. Podocyte surface pores were observed using a low-vacuum scanning electron microscope. The renal prognosis, including induction of hemodialysis or 30% reduction in eGFR, was investigated. Results Urinary podocyte excretion showed a higher positive correlation with albumin excretion compared to IgG, prealbumin, and transferrin. There were no significant correlations between urinary podocyte count and low molecular weight proteins, including β2-microglobulin and α1-microglobulin. The number of podocyte surface pores was positively correlated with proteinuria, suggesting enhanced albumin transcytosis. The hemodynamic pressure on the glomerular capillary wall, including products of pulse pressure and pulse rate (water hammer pressure), was positively correlated with urinary podocyte excretion. Urinary podocyte excretion and Tamm–Horsfall protein (THP) were independent risk factors for renal prognosis but were not related to response to treatment. Conclusion Urinary podocyte excretion was correlated with urinary albumin excretion, indicating specific albumin transport by podocytes. Podocytes were detached from the glomerular capillaries by water hammer pressure and THP was involved in the renal prognosis.

Membranous nephropathy: new pathogenic mechanisms and their clinical implications.

Membranous nephropathy (MN) is characterized histomorphologically by the presence of immune deposits in the subepithelial space of the glomerular filtration barrier; its clinical hallmarks are nephrotic range proteinuria with oedema. In patients with primary MN, autoimmunity is driven by circulating autoantibodies that bind to one or more antigens on the surface of glomerular podocytes. Compared with other autoimmune kidney diseases, the understanding of the pathogenesis of MN has substantially improved in the past decade, thanks to the discovery of pathogenic circulating autoantibodies against phospholipase A2 receptor 1 (PLA2R1) and thrombospondin type 1 domain-containing protein 7A (THSD7A). The subsequent identification of more proteins associated with MN, some of which are also endogenous podocyte antigens, might further advance the clinical characterization of MN, including its diagnosis, treatment and prognosis. Insights from studies in patients with MN, combined with the development of novel in vivo and in vitro experimental models, have potential to improve the management of patients with MN. Characterizing the interaction between autoimmunity and local glomerular lesions provides an opportunity to develop more specific, pathogenesis-based treatments.

Anti-phospholipase A2 receptor antibodies directly induced podocyte damage in vitro

Background The pathogenesis of primary membranous nephropathy (MN) involves the antibodies against antigens on the cell surface of podocytes, with the majority of M-type phospholipase A2 receptor (PLA2R), and a profound podocyte dysfunction. The effects of anti-PLA2R antibodies directly to the podocytes remain unclear. Methods Anti-PLA2R antibodies from patients with PLA2R-associated MN were affinity-purified using a column coupled with recombinant human PLA2R protein. Their effects on conditionally immortalized human podocytes were assessed by apoptosis assays, cellular calcium detection, wound healing assay, and immunofluorescent staining. Proteomics analysis was performed by LC-MS/MS and on PANTHER database. Results The stimulation by anti-PLA2R antibodies could induce early-stage apoptosis of podocytes (MFI of Annexin V = 104.3 ± 19.2 vs. 36.7 ± 7.6, p = 0.004). The increase of calcium concentration in podocytes (MFI = 3309.3 ± 363.6 vs. 1776.3 ± 212.7, p = 0.015) might attribute to the endoplasmic reticulum calcium efflux. The expression of calcium/calmodulin-dependent protein kinase IV (CaMK4) was also increased (MFI = 134.4 ± 9.8 vs. 105.3 ± 10.1, p = 0.011). Proteomics results suggested that anti-PLA2R antibody treatment led to damage on cellular structure, and produced functional disorders on protein binding, actin filament binding, and microtubule motor activity. The staining of F-actin on foot process was reduced (MFI = 27.3 ± 2.8 vs. 47.5 ± 1.0, p = 0.001) and the motility and adherence capacity of podocytes were reduced (number of migrated cells = 44.7 ± 3.1 vs. 53.3 ± 4.9, p = 0.001) after incubation with anti-PLA2R antibodies. Conclusion These data indicate that anti-PLA2R antibodies may directly induce podocyte damage independent of the complement system, which expands the mechanism of anti-PLA2R antibodies on MN.

Relationship between Elevated Maternal Serum Podocalyxin Concentrations with Blood Pressure Values and Routine Laboratory Parameters in Preeclampsia

Summary Podocalyxin (PCX) is a glycoprotein member of the CD34 transmembrane sialomucin family and covers the surface of podocytes. It is assumed to be a marker of glomerular endothelial injury. In conditions, podocalyxin excretion in the urine is increased as a result of podocyte injury. Recent studies show that PCX is expressed not only in kidneys but also in the endothelial cells of other organs. Preeclampsia (PE) is characterized by new-onset hypertension, generalized endothelial injury, and glomerular alteration. Having this in mind, in the present study, we aimed to: (1) determine circulating PCX levels in sera of women with preeclampsia and normal pregnancy; (2) explore for an association between PCX and blood pressure and (3) investigate a possible relationship between PCX and routine laboratory markers of cardiac and renal injury/dysfunction. Fifty-five women with preeclampsia were examined. The mean age of patients was 24.9±6 years, and the mean age of the control group of 35 women with normal pregnancies was 24.7±5.4 years. The enzyme-linked immunosorbent assay (ELISA) was used to determine concentrations of PCX. Levels of serum PCX in preeclamptic women were statistically significantly higher than those in women with normal pregnancy: 2.66±0.67 vs. 2.40±0.33 ng/ml (p=0.03). Podocalyxin correlated with SBP (r=0.30; p=0.004), DBP (r=0.35; p=0.0007), uric acid (r=0.32; p=0.002), CPK (r=0.22; 0.03) and its isoenzyme CK-MB (r=0.21; p=0.04). Our results showed significantly higher levels of serum PCX in women with preeclampsia than in healthy pregnancy. Elevated podocalyxin levels are associated with an increase in blood pressure in preeclampsia. We found a relationship between PCX and routine laboratory indicators of cardiac (CPK and CK-MB) and renal injury/dysfunction (uric acid). PCX has the potential as a future preeclampsia diagnostic biomarker.

Mechanisms of Primary Membranous Nephropathy.

Membranous nephropathy (MN) is an autoimmune disease of the kidney glomerulus and one of the leading causes of nephrotic syndrome. The disease exhibits heterogenous outcomes with approximately 30% of cases progressing to end-stage renal disease. The clinical management of MN has steadily advanced owing to the identification of autoantibodies to the phospholipase A2 receptor (PLA2R) in 2009 and thrombospondin domain-containing 7A (THSD7A) in 2014 on the podocyte surface. Approximately 50–80% and 3–5% of primary MN (PMN) cases are associated with either anti-PLA2R or anti-THSD7A antibodies, respectively. The presence of these autoantibodies is used for MN diagnosis; antibody levels correlate with disease severity and possess significant biomarker values in monitoring disease progression and treatment response. Importantly, both autoantibodies are causative to MN. Additionally, evidence is emerging that NELL-1 is associated with 5–10% of PMN cases that are PLA2R- and THSD7A-negative, which moves us one step closer to mapping out the full spectrum of PMN antigens. Recent developments suggest exostosin 1 (EXT1), EXT2, NELL-1, and contactin 1 (CNTN1) are associated with MN. Genetic factors and other mechanisms are in place to regulate these factors and may contribute to MN pathogenesis. This review will discuss recent developments over the past 5 years.

Impaired NEPHRIN localization in kidney organoids derived from nephrotic patient iPS cells

Mutations in the NPHS1 gene, which encodes NEPHRIN, cause congenital nephrotic syndrome, resulting from impaired slit diaphragm (SD) formation in glomerular podocytes. We previously reported NEPHRIN and SD abnormalities in the podocytes of kidney organoids generated from patient-derived induced pluripotent stem cells (iPSCs) with an NPHS1 missense mutation (E725D). However, the mechanisms underlying the disease may vary depending on the mutations involved, and thus generation of iPSCs from multiple patients is warranted. Here we established iPSCs from two additional patients with different NPHS1 mutations and examined the podocyte abnormalities in kidney organoids derived from these cells. One patient had truncating mutations, and NEPHRIN was undetectable in the resulting organoids. The other patient had a missense mutation (R460Q), and the mutant NEPHRIN in the organoids failed to accumulate on the podocyte surface to form SD precursors. However, the same mutant protein behaved normally when overexpressed in heterologous cells, suggesting that NEPHRIN localization is cell context-dependent. The localization of another SD-associated protein, PODOCIN, was impaired in both types of mutant organoids in a cell domain-specific manner. Thus, the new iPSC lines and resultant kidney organoids will be useful resources for dissecting the disease mechanisms, as well as for drug development for therapies.

Podocytes present antigen to activate specific T cell immune responses in inflammatory renal disease.

Infiltration of activated T cells into renal tissue plays an essential role in inflammatory nephropathy. However, the mechanism enabling the renal recruitment and activation of T cells remains elusive. Here we report that inflammatory cytokine-promoted antigen presentation by podocytes is a key for recruiting and activating specific T cells. Our results showed that diabetes-associated inflammatory cytokines IFNγ and IL-17 all upregulated expression of MHC-I, MHC-II, CD80 and CD86 on the podocyte surface. Both IFNγ and IL-17 stimulated the uptake and processing of ovalbumin (OVA) by mouse podocytes, resulting in presentation of OVA antigen peptide on the cell surface. OVA antigen presentation by podocytes was also validated using human podocytes. Furthermore, OVA antigen-presenting mouse podocytes were able to activate OT-I mouse T cell proliferation and inflammatory cytokine secretion, which in turn caused podocyte injury and apoptosis. Finally, OT-I mice subjected to direct renal injection of OVA plus IFNγ/IL-17 but not OVA alone exhibited OVA antigen presentation by podocytes and developed nephropathy in 4 weeks. In conclusion, antigen presentation by podocytes under inflammatory conditions plays an important role in activating T cell immune responses and facilitating immune-mediated glomerular disease development. © 2020 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Domain-Specific Antibodies Reveal Differences in the Membrane Topologies of Apolipoprotein L1 in Serum and Podocytes.

Circulating APOL1 lyses trypanosomes, protecting against human sleeping sickness. Two common African gene variants of APOL1, G1 and G2, protect against infection by species of trypanosomes that resist wild-type APOL1. At the same time, the protection predisposes humans to CKD, an elegant example of balanced polymorphism. However, the exact mechanism of APOL1-mediated podocyte damage is not clear, including APOL1's subcellular localization, topology, and whether the damage is related to trypanolysis. APOL1 topology in serum (HDL particles) and in kidney podocytes was mapped with flow cytometry, immunoprecipitation, and trypanolysis assays that tracked 170 APOL1 domain-specific monoclonal antibodies. APOL1 knockout podocytes confirmed antibody specificity. APOL1 localizes to the surface of podocytes, with most of the pore-forming domain (PFD) and C terminus of the Serum Resistance Associated-interacting domain (SRA-ID), but not the membrane-addressing domain (MAD), being exposed. In contrast, differential trypanolytic blocking activity reveals that the MAD is exposed in serum APOL1, with less of the PFD accessible. Low pH did not detectably alter the gross topology of APOL1, as determined by antibody accessibility, in serum or on podocytes. Our antibodies highlighted different conformations of native APOL1 topology in serum (HDL particles) and at the podocyte surface. Our findings support the surface ion channel model for APOL1 risk variant-mediated podocyte injury, as well as providing domain accessibility information for designing APOL1-targeted therapeutics.

SUN-003 MECHANISM OF SELECTIVE ALBUMINURIA IN MINIMAL CHANGE NEPHROTIC SYNDROME

Water and electrolytes are filtered through slit membranes, however in minimal change nephrotic syndrome with foot process effacement it is not well understood whether albumin molecules will be filtered through the slit membrane. We reported that albumin endocytosis by FcRn was enhanced in the podocyte of puromycin aminonucleoside (PAN)-induced minimal change nephrotic syndrome rat, and treatment with anti-FcRn antibody decreased albumin endocytosis and urinary protein (Kidney Int 2011). Minimal change nephrotic syndrome model was induced by puromycin amino nucleoside, and podocytes were observed by electron microscope and low vacuum scanning electron microscope. Electron microscopy demonstrated many vesicles were observed in the podocytes of PAN rat with 3D observation. SDS-polyacrylamide electrophoresis of glomerular proteins isolated from PAN rats showed that several protein bands were increased than those from control rats, and those increased protein bands were identified as dynein -1, myosin 7 and myosin 9 by mass spectrometry. These motor molecules are capable of transporting vesicles containing albumin in the podocytes of PAN nephrotic rat. In renal biopsy, electron microscopic examination of human minimal change disease cases showed numerous vesicles and microtubules in podocytes, and a number of exocytotic holes were found on the surface of podocytes by low vacuum scanning electron microscopy. In conclusion, podocyte vesicle transport could play an important role in the selective albuminuria in the minimal change nephrotic syndrome.

Human soluble phospholipase A2 receptor is an inhibitor of the integrin-mediated cell migratory response to collagen-I.

Murine membrane-bound phospholipase A2 receptor 1 (PLA2R) is shed and released into plasma in a soluble form that retains all of the extracellular domains. Relatively little is known about human PLA2R. This study examined whether human soluble PLA2R has biological functions and whether soluble PLA2R exists in human plasma. Here, we showed that human recombinant soluble PLA2R (rsPLA2R) bound to collagen-I and inhibited interaction of collagen-I with the extracellular domain of integrin β1 on the cell surface of human embryonic kidney 293 (HEK293) cells. As a result, rsPLA2R suppressed integrin β1-mediated migratory responses of HEK293 cells to collagen-I in Boyden chamber experiments. Inhibition of phosphorylation of FAK Tyr397 was also observed. Similar results were obtained with experiments using soluble PLA2R released from HEK293 cells transfected with a construct encoding human soluble PLA2R. rsPLA2R lacking the fibronectin-like type II (FNII) domain had no inhibitory effects on cell responses to collagen-I, suggesting an important role of the FNII domain in the interaction of rsPLA2R with collagen-I. In addition, rsPLA2R suppressed the migratory response to collagen-IV and binding of collagen-IV to the cell surface of human podocytes that endogenously express membrane-bound, full-length PLA2R. Immunoprecipitation and Western blotting showed the existence of immunoreactive PLA2R in human plasma. In conclusion, human recombinant soluble PLA2R inhibits integrin β1-mediated cell responses to collagens. Further studies are warranted to elucidate whether immunoreactive PLA2R in human plasma has the same properties as rsPLA2R.

Role of biomechanical forces in hyperfiltration-mediated glomerular injury in congenital anomalies of the kidney and urinary tract.

Congenital anomalies of the kidney and urinary tract (CAKUT) including solitary kidney constitute the main cause of progressive chronic kidney disease (CKD) in children. Children born with CAKUT develop signs of CKD only during adolescence and do not respond to renin-angiotensin-aldosterone system blockers. Early cellular changes underlying CKD progression to end-stage renal disease by early adulthood are not well understood. The mechanism of maladaptive hyperfiltration that occurs from loss of functional nephrons, including solitary kidney, is not clear. We re-examine the phenomenon of hyperfiltration in the context of biomechanical forces with special reference to glomerular podocytes. Capillary stretch exerts tensile stress on podocytes through the glomerular basement membrane. The flow of ultrafiltrate over the cell surface directly causes fluid flow shear stress (FFSS) on podocytes. FFSS on the podocyte surface increases 1.5- to 2-fold in animal models of solitary kidney and its effect on podocytes is a subject of ongoing research. Podocytes (i) are mechanosensitive to tensile and shear forces, (ii) use prostaglandin E2, angiotensin-II or nitric oxide for mechanoperception and (iii) use specific signaling pathways for mechanotransduction. We discuss (i) the nature of and differences in cellular responses to biomechanical forces, (ii) methods to study biomechanical forces and (iii) effects of biomechanical forces on podocytes and glomeruli. Future studies on FFSS will likely identify novel targets for strategies for early intervention to complement and strengthen the current regimen for treating children with CAKUT.