Podocytes Of Patients Research Articles

Activation of the inflammasome and pyroptosis cascade in podocytes of patients with minimal change disease.

In contrast to childhood minimal change disease (MCD), adult-onset MCD frequently recurs and requires prolonged immunosuppressive therapy. Accordingly, an investigation of the pathogenesis of adult MCD is required. MCD is usually accompanied by severe dyslipidaemia. Oxidized low-density lipoprotein (ox-LDL) is known to function in a damage-associated molecular pattern (DAMP) through CD36, triggering the NOD-like receptor thermal protein domain-associated protein 3 (NLRP3) inflammasome and programmed cell death called pyroptosis. However, the relationship between MCD pathogenesis and NLRP3 inflammasome/pyroptosis activation via CD36 is not fully understood. We conducted comprehensive histological and clinical evaluations by analysing renal biopsy (RBx) specimens and urine samples obtained from 26 patients with MCD. These samples were compared with control kidneys from 15 transplant donors and urine samples from 15 healthy volunteers. The number of podocytes was lower in the MCD group than in the control group. Urinary ox-LDL levels were higher in the MCD group than in the control group. Immunofluorescence staining revealed that NLRP3 and CD36 were upregulated in MCD podocytes. Urinary interleukin (IL)-18 levels increased in patients with MCD. Steroid therapy performed before RBx appeared to maintain the podocyte number and reduce urinary ox-LDL and IL-18 levels. In MCD, the NLRP3 inflammasome and pyroptosis cascade seem to be activated via upregulation of CD36 in podocytes, associated with increased urinary ox-LDL. Elevated urinary IL-18 levels suggest that pyroptosis may occur in MCD. Further research is required to confirm the significance of the podocyte NLRP3 inflammasome/pyroptosis in MCD.

#187 Vasorin (VASN) commands podocyte quiescence and glomerular homeostasis. A novel FSGS mechanism?

Abstract Background and Aims Podocyte dysfunction and loss of quiescence contribute to focal segmental glomerulosclerosis (FSGS) and crescentic glomerulonephritis (CGN). Here, we characterized the role of Vasorin (VASN) in podocytes. Method We combined laser capture microdissection and deep RNA sequencing of human glomeruli, RNAscope-based in situ hybridization, immunostaining and mouse models with Vasn-driven fluorescent reporter, targeted Vasn gene deletion in podocytes and cultures of human podocytes. Results VASN mRNA is strongly expressed in healthy human and mouse glomeruli with a podocyte-specific pattern. Both global and podocyte-specific, constitutive or inducible gene deletion of Vasn in mice induced a nephrotic syndrome and kidney failure after day 14, with podocyte dedifferentiation and loss and severe FSGS lesions, indicating a fundamental and non-developmental role of VASN in podocyte homeostasis. Furthermore, we measured markedly decreased VASN expression in podocytes of patients with FSGS and ANCA-associated CGN but not with Minimal Change Disease (MCD) and Membranous Nephropathy (MN). We thus wondered whether VASN abundance could be a disease modifier for glomerulopathies. Mice with podocyte-specific partial heterozygous deletion of Vasn showed no evident baseline renal abnormalities. Still, they showed significantly more podocyte loss, albuminuria and kidney failure than wild-type mice when challenged by type 1 diabetes with glomerular hyperfiltration or CGN experimental models. Human podocytes transduced with lentiviral VASN-targeting shRNA (shVASN) displayed increased focal adhesion dynamics, resistance to oscillating mechanical stretches, enhanced migratory capacity and epithelial-mesenchymal transition (EMT) markers. Moreover, shVASN podocytes had a higher proliferative capacity, increased cell-cycle reentry and a relative S-phase slow-down. Likewise, transcriptomics analysis found the up-regulation of genes involved in cell metabolism, adhesion and EMT and the down-regulation of genes involved in the S to G2/M phase transition. In vivo, we confirmed that VASN deficiency increased podocyte proliferation in situ and urinary shedding. Conclusion These findings highlight the novel role of VASN as an essential master protein that maintains podocyte quiescence and homeostasis during health and kidney diseases while offering a potential new therapeutic target. VASN control mechanisms driving podocyte cell-cycle reentry and detachment and FSGS. Precise mechanisms of VASN functions in podocytes need further insights into VASN molecular partners.

#1004 Single-nucleus RNA sequencing identifies upregulated antigen presentation, apoptosis, mTORC1 signaling and EMT in primary FSGS podocytes

Abstract Background and Aims Primary focal segmental glomerulosclerosis (FSGS) is associated with irreversible podocyte damage, but the underlying cause and pathophysiology are incompletely understood. Furthermore, diagnostic markers that allow reliable differentiation between primary and secondary FSGS subtypes are lacking. We applied single-nucleus RNA-sequencing (snRNA-seq) on podocytes of patients with primary or secondary (maladaptive) FSGS, to identify subtype-specific differentially expressed genes and pathways. Method We used droplet-based snRNA-seq (10X Genomics Chromium) on cryopreserved kidney biopsy cores from human patients with newly diagnosed primary FSGS (n = 9, all nephrotic), maladaptive FSGS (n = 9, not nephrotic), proteinuric controls (PLA2R-positive membranous nephropathy (PLA2R+ MN), n = 3), and healthy controls (pre-perfusion biopsies, n = 4). Differential gene expression (DGE) analysis was done with a pseudobulk method provided by the EdgeR R-package to reduce bias and false discoveries. The fGSEA R-package was used for subsequent gene set enrichment analysis. Results We identified a total of 120 751 high-quality nuclei, of which 2 471 were podocytes (Fig. 1A). DGE analysis identified the top 20 differentially expressed genes (DEGs) per diagnosis (Fig. 1B). Remarkably, primary FSGS podocytes showed more transcriptional similarity to PLA2R+ MN podocytes, compared to maladaptive FSGS podocytes. This underscores the heterogeneity of patients with FSGS and shows that heavy proteinuria, regardless of the underlying diagnosis, may be associated with a distinct transcriptional profile in podocytes. Upregulated genes in primary FSGS podocytes included TIMP1, BTG2, ZNF44, EHD4, ZNF250, ECM1, SEMA4G, PHLDB1, and HDAC5. Upregulation of the matrix metalloproteinase inhibitor TIMP1 may possibly contribute to the development of glomerulosclerosis. Upregulation of BTG2 has previously been found to be pathogenic in FSGS by promoting epithelial-mesenchymal transition (EMT)-induced podocyte injury [1]. Next, gene set enrichment analysis on the identified DEGs in primary FSGS podocytes showed upregulation of pathways involved in antigen presentation (driven by upregulation of HLA-A, HLA-B, HLA-C, HLA-E and B2M), mTORC1 signaling, apoptosis and EMT (Fig. 1C). In maladaptive FSGS, upregulated pathways were mainly involved in extracellular matrix interaction. This may correlate with the significantly higher degree of chronic damage on kidney biopsy in the maladaptive FSGS patients (median Mayo Clinic Chronicity Score of 6.0, IQR [4.0-7.0]) vs. primary FSGS (2.0, [1.0-4.0]) and PLA2R+ MN (1, IQR [1.0-1.5]) (Kruskal-Wallis test, P = 0.007). Conclusion Our results corroborate previous studies that implicate apoptosis, mTORC1 signaling, EMT and auto-immunity in primary FSGS. Our future work will focus on cell-cell interactions within the glomerular niche and validation studies of candidate podocyte-specific genes.

FSGS Recurrence Modeling Using Induced Pluripotent Stem Cell (iPSC)-Derived Podocytes in Patients with Idiopathic Nephrotic Syndrome

FSGS Recurrence Modeling Using Induced Pluripotent Stem Cell (iPSC)-Derived Podocytes in Patients with Idiopathic Nephrotic Syndrome

Activation of acetyl-CoA synthetase 2 mediates kidney injury in diabetic nephropathy.

Albuminuria and podocyte injury are the key cellular events in the progression of diabetic nephropathy (DN). Acetyl-CoA synthetase 2 (ACSS2) is a nucleocytosolic enzyme responsible for the regulation of metabolic homeostasis in mammalian cells. This study aimed to investigate the possible roles of ACSS2 in kidney injury in DN. We constructed an ACSS2-deleted mouse model to investigate the role of ACSS2 in podocyte dysfunction and kidney injury in diabetic mouse models. In vitro, podocytes were chosen and transfected with ACSS2 siRNA and ACSS2 inhibitor and treated with high glucose. We found that ACSS2 expression was significantly elevated in the podocytes of patients with DN and diabetic mice. ACSS2 upregulation promoted phenotype transformation and inflammatory cytokine expression while inhibiting podocytes' autophagy. Conversely, ACSS2 inhibition improved autophagy and alleviated podocyte injury. Furthermore, ACSS2 epigenetically activated raptor expression by histone H3K9 acetylation, promoting activation of the mammalian target of rapamycin complex 1 (mTORC1) pathway. Pharmacological inhibition or genetic depletion of ACSS2 in the streptozotocin-induced diabetic mouse model greatly ameliorated kidney injury and podocyte dysfunction. To conclude, ACSS2 activation promoted podocyte injury in DN by raptor/mTORC1-mediated autophagy inhibition.

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.

Growth associated protein 43 deficiency promotes podocyte injury by activating the calmodulin/calcineurin pathway under hyperglycemia

Podocyte injury is a crucial factor in the pathogenesis of diabetic kidney disease (DKD), and finding potential therapeutic interventions that can mitigate podocyte injury holds significant clinical relevance. This study was to elucidate the role of growth associated protein-43(Gap43) in podocyte injury of high glucose (HG). We confirmed the expression of Gap43 in human glomerulus and found that Gap43 expression was downregulated in podocytes of patients with DKD and HG-treated podocytes in vitro. Gap43 knockdown in podocytes promoted podocyte apoptosis, increased migration ability and decreased nephrin expression, while overexpression of Gap43 markedly suppressed HG-induced injury. Moreover, the increased expression and activity of calcineurin (CaN) were also abrogated by overexpression Gap43 in HG. Pretreatment with a typical CaN inhibitor FK506 in Gap43 knockdown podocytes restored the injury. Mechanistically, co-immunoprecipitation experiments suggested that Gap43 could bind to calmodulin (CaM). Pull-down assay further demonstrated that Gap43 and CaM directly interacts with each other via amino acids 30–52 of Gap43 and amino acids 133–197 of CaM. In addition, we also identified Pax5 as potential transcription inhibitor factor mediating Gap43 expression. In conclusion, the study indicated that the Gap43/CaM-CaN pathway may be exploited as a promising therapeutic target for protecting against podocyte injury in high glucose.

Morphometric analysis of the changes in glomerular podocytes in patients suffereing from proteinuria: An ultrastructural observational study

Morphometric analysis of the changes in glomerular podocytes in patients suffereing from proteinuria: An ultrastructural observational study

Blocking ribosomal protein S6 phosphorylation inhibits podocyte hypertrophy and focal segmental glomerulosclerosis

Ribosomal protein S6 (rpS6) phosphorylation mediates the hypertrophic growth of kidney proximal tubule cells. However, the role of rpS6 phosphorylation in podocyte hypertrophy and podocyte loss during the pathogenesis of focal segmental glomerulosclerosis (FSGS) remains undefined. Here, we examined rpS6 phosphorylation levels in kidney biopsy specimens from patients with FSGS and in podocytes from mouse kidneys with Adriamycin-induced FSGS. Using genetic and pharmacologic approaches in the mouse model of FSGS, we investigated the role of rpS6 phosphorylation in podocyte hypertrophy and loss during development and progression of FSGS. Phosphorylated rpS6 was found to be markedly increased in the podocytes of patients with FSGS and Adriamycin-induced FSGS mice. Genetic deletion of the Tuberous sclerosis 1 gene in kidney glomerular podocytes activated mammalian target of rapamycin complex 1 signaling to rpS6 phosphorylation, resulting in podocyte hypertrophy and pathologic features similar to those of patients with FSGS including podocyte loss, leading to segmental glomerulosclerosis. Since protein phosphatase 1 is known to negatively regulate rpS6 phosphorylation, treatment with an inhibitor increased phospho-rpS6 levels, promoted podocyte hypertrophy and exacerbated formation of FSGS lesions. Importantly, blocking rpS6 phosphorylation (either by generating congenic rpS6 knock-in mice expressing non-phosphorylatable rpS6 or by inhibiting ribosomal protein S6 kinase 1-mediated rpS6 phosphorylation with an inhibitor) significantly blunted podocyte hypertrophy, inhibited podocyte loss, and attenuated formation of FSGS lesions. Thus, our study provides genetic and pharmacologic evidence indicating that specifically targeting rpS6 phosphorylation can attenuate the development of FSGS lesions by inhibiting podocyte hypertrophy and associated podocyte depletion.

The role of serum levels of anti-phospholipase A2 receptor antibodies in the diagnosis of primary membranous nephropathy.

Primary membranous nephropathy (PMN) is one of the most common causes of nephrotic syndrome in adults. The disease process is probably initiated by the binding of circulating autoantibodies to target podocyte antigens. In 2009, Beck et al. found that phospholipase A2 receptor (PLA2R1) was expressed on human podocytes in patients with PMN. Recent evidence suggests that PLA2R1 autoantibodies play an important role in the diagnosis of PMN. The aim of the present study was to compare the serum levels of anti-PLA2R1 in patients with PMN, second MN (SMN), other nephropathies (ON), and healthy controls (HC). The study included 52 patients with PMN, 12 patients with SMN, 49 patients with ON, and 50 healthy controls. The serum concentration of anti-PLA2R1 was determined with ELISA kit (Anti-PLA2R ELISA, IgG, EUROIMMUN, Lübeck, Germany) using MR-96A microplate Reader (MINDRAY). Statistical analysis was performed with SPSS v.22.0. There was significant difference in the serum anti-PLA2R1 concentrations between patient groups and HC (p<0.0001). Compared to HC, the median anti-PLA2R1 level in the PMN group was significantly higher (4.8 RU/ml vs. 34.9 RU/ml, p=0.001), in the ON group it was lower (2.1 RU/ml, p=0.002) and did not differ in patients with SMN (2.9 RU/ml, p=0.193). The anti-PLA2R1 serum levels were significantly higher in the PMN group than in the SMN (p=0.015) and ON (p<0.001) groups. Our results showed that anti-PLA2R1 is significantly increased in patients with PMN. We can conclude that the anti-PLA2R1 serum concentration may be used as a beneficial biomarker for distinguishing PMN from other membranous nephropathies.

Receptor activator of NF-κB mediates podocyte injury in diabetic nephropathy

Receptor activator of NF-κB (RANK) expression is increased in podocytes of patients with diabetic nephropathy. However, the relevance of RANK to diabetic nephropathy pathobiology remains unclear. Here, to evaluate the role of podocyte RANK in the development of diabetic nephropathy, we generated a mouse model of podocyte-specific RANK depletion (RANK-/-Cre T), and a model of podocyte-specific RANK overexpression (RANK TG), and induced diabetes in these mice with streptozotocin. We found that podocyte RANK depletion alleviated albuminuria, mesangial matrix expansion, and basement membrane thickening, while RANK overexpression aggravated these indices in streptozotocin-treated mice. Moreover, streptozotocin-triggered oxidative stress was increased in RANK overexpression but decreased in the RANK depleted mice. Particularly, the expression of NADPH oxidase 4, and its obligate partner, P22phox, were enhanced in RANK overexpression, but reduced in RANK depleted mice. In parallel, the transcription factor p65 was increased in the podocyte nuclei of RANK overexpressing mice but decreased in the RANK depleted mice. The relevant findings were largely replicated with high glucose-treated podocytes invitro. Mechanistically, p65 could bind to the promoter regions of NADPH oxidase 4 and P22phox, and increased their respective gene promoter activity in podocytes, dependent on the levels of RANK. Taken together, these findings suggested that high glucose induced RANK in podocytes and caused the increase of NADPH oxidase 4 and P22phox via p65, possibly together with the cytokines TNF- α, MAC-2 and IL-1 β, resulting in podocyte injury. Thus, we found that podocyte RANK was induced in the diabetic milieu and RANK mediated the development of diabetic nephropathy, likely by promoting glomerular oxidative stress and proinflammatory cytokine production.

Aberrantly glycosylated IgG elicits pathogenic signaling in podocytes and signifies lupus nephritis.

Lupus nephritis (LN) is a serious complication occurring in 50% of patients with systemic lupus erythematosus (SLE) for which there is a lack of biomarkers, a lack of specific medications, and a lack of a clear understanding of its pathogenesis. The expression of calcium/calmodulin kinase IV (CaMK4) is increased in podocytes of patients with LN and lupus-prone mice, and its podocyte-targeted inhibition averts the development of nephritis in mice. Nephrin is a key podocyte molecule essential for the maintenance of the glomerular slit diaphragm. Here, we show that the presence of fucose on N-glycans of IgG induces, whereas the presence of galactose ameliorates, podocyte injury through CaMK4 expression. Mechanistically, CaMK4 phosphorylates NF-κB, upregulates the transcriptional repressor SNAIL, and limits the expression of nephrin. In addition, we demonstrate that increased expression of CaMK4 in biopsy specimens and in urine podocytes from people with LN is linked to active kidney disease. Our data shed light on the role of IgG glycosylation in the development of podocyte injury and propose the development of “liquid kidney biopsy” approaches to diagnose LN.

Upregulated LRRC55 promotes BK channel activation and aggravates cell injury in podocytes.

Podocyte injury is a common hallmark in various glomerular diseases. The level of LRRC55 was increased in podocytes of patients with focal segmental glomerulosclerosis (FSGS), diabetic nephropathy (DN), and membranous nephropathy (MN). Upregulated LRRC55 and increased intracellular Ca2+ led to BK channel activation and the loss of intracellular potassium, resulting in apoptosome formation and caspase-3 activation in angiotensin II (Ang II)-treated podocytes. Knockout of Lrrc55 or the BK channel prevented the BK current and ameliorated podocyte injury in Ang II-treated mice. Upstream, NFATc3 regulated the expression of LRRC55. Increased LRRC55 expression in podocytes was also evident in animal models of FSGS, DN, and MN. Treatment with losartan or LRRC55 siRNA suppressed LRRC55 expression, prevented BK channel activation, and attenuated podocyte injury in animal models of FSGS, DN, and MN. In conclusion, upregulated LRRC55 promotes BK channel activation and aggravates cell injury in podocytes in FSGS, DN, and MN. LRRC55 inhibition may represent a new therapeutic approach for podocyte injury.

In situ evaluation of podocytes in patients with focal segmental glomerulosclerosis and minimal change disease.

Podocyte injury in focal segmental glomerulosclerosis (FSGS) and minimal change disease (MCD) results from the imbalance between adaptive responses that maintain homeostasis and cellular dysfunction that can culminate in cell death. Therefore, an in situ analysis was performed to detect morphological changes related to cell death and autophagy in renal biopsies from adult patients with podocytopathies. Forty-nine renal biopsies from patients with FSGS (n = 22) and MCD (n = 27) were selected. In situ expression of Wilms Tumor 1 protein (WT1), light chain microtubule 1-associated protein (LC3) and caspase-3 protein were evaluated by immunohistochemistry. The foot process effacement and morphological alterations related to podocyte cell death and autophagy were analyzed with transmission electronic microscopy. Reduction in the density of WT1-labeled podocytes was observed for FSGS and MCD cases as compared to controls. Foot process width (FPW) in control group was lower than in cases of podocytopathies. In FSGS group, FPW was significantly higher than in MCD group and correlated with proteinuria. A density of LC3-labeled podocytes and the number of autophagosomes in podocytes/ pedicels were higher in the MCD group than in the FSGS group. The number of autophagosomes correlated positively with the estimated glomerular filtration rate in cases of MCD. The density of caspase-3-labeled podocytes in FSGS and MCD was higher than control group, and a higher number of podocytes with an evidence of necrosis was detected in FSGS cases than in MCD and control cases. Podocytes from patients diagnosed with FSGS showed more morphological and functional alterations resulting from a larger number of lesions and reduced cell adaptation.

Histone deacetylase 4 mediates high glucose-induced podocyte apoptosis via upregulation of calcineurin

Hyperglycemia promotes podocyte apoptosis and plays an important role in the pathogenesis of diabetic nephropathy (DN). Calcium/calcineurin (CaN) signaling is critical for podocyte apoptosis. Therefore, it is essential to elucidate the mechanisms underlying the regulation of CaN signaling. Recent studies reported that histone deacetylase 4 (HDAC4) is involved in podocyte apoptosis in DN. The aim of this study was to determine whether HDAC4 mediates the regulation of CaN and to elucidate the function of HDAC4 in high glucose (HG)-induced podocyte apoptosis. First, we identified the expression of HDAC4 was upregulated in podocytes of patients with DN. In vitro, the results also indicate that the mRNA and protein expression levels of HDAC4 were increased in HG-cultured podocytes. Silencing and overexpression of HDAC4 markedly decreased and increased CaN expression, respectively. Meanwhile, HG-induced podocyte apoptosis was abrogated by HDAC4-knockdown with subsequent decreased Bax expression and increased Bcl-2 expression. In contrast, overexpression of HDAC4 increased podocyte apoptosis and Bax expression, as well as decreased Bcl-2 expression. In addition, podocyte apoptosis induced by HDAC4 overexpression was effectively rescued by FK506, a pharmacological inhibitor of CaN, which was accompanied by decreased Bax and increased Bcl-2 expression. As a novel finding, HG-induced podocyte apoptosis is mediated by the HDAC4/CaN signaling pathway, which presents a promising target for therapeutic intervention in DN.

Appearances Can Be Deceiving - Viral-like Inclusions in COVID-19 Negative Renal Biopsies by Electron Microscopy.

Since the discovery of the causative agent for the novel severe acute respiratory syndrome (SARS)–like pneumonia syndrome pandemic that started in China in 2019 (1,2), a coronavirus named SARS coronavirus 2 (SARS-CoV-2), electron microscopy images have populated the medical literature (2) and media outlets alike displaying the characteristic 60–140 nm round particles surrounded by a “corona” of 9–12 nm distinctive spikes (2). Although many of these images were obtained after “ in vitro ” infection of cultured cells with SARS-CoV-2 (2) and are thus likely a true representation of viral particles, we have observed morphologically indistinguishable inclusions within podocytes and tubular epithelial cells both in patients negative for coronavirus disease 2019 (COVID-19) as well as in renal biopsies from the pre–COVID-19 era. Although direct infection of the kidney is theoretically possible, given the presence of angiotensin-converting enzyme 2 (the receptor used by SARS-CoV-2 to gain access to cells) within proximal tubular epithelium (3) and podocytes (4), the virus has not been detected by real-time RT-PCR in urine samples from patients with COVID-19 (5⇓–7). Additionally, for the virus to have access to kidney parenchyma, viremia should occur, and this has only been detected in a minority of patients (6⇓–8). We would, therefore, like to issue a note of caution for inferring viral tissue infection by morphology alone using electron microscopy images from tissues obtained from biopsies or autopsy material in patients with COVID-19. Moreover, caution should be used when interpreting immunohistochemical results, especially within proximal tubules, which are prone to nonspecific staining by a variety of antibodies due to their intense reabsorptive capacity. Additionally, more specific techniques such as immunoelectron microscopy using specific viral antigens (9), or in situ hybridization for viral RNA, are likely necessary to undoubtedly confirm tissue infection in …

N-glycosylated IgG in patients with kidney transplants increases calcium/calmodulin kinase IV in podocytes and causes injury.

Transplant glomerulopathy (TG) is a major cause of late allograft loss. Increased urine podocin/creatinine ratio in TG signifies accelerated podocyte loss. The mechanisms that lead to podocyte injury in TG remain unclear. We report that IgG from kidney transplant recipients with TG, but not from those without TG, cause a reduction in the expression of nephrin, significant podocyte actin cytoskeleton, and motility changes. These changes are preceded by increased expression of calcium/calmodulin kinase IV (CAMK4). Mechanistically, we found that CAMK4 phosphorylates GSK3β (glycogen synthase kinase 3 beta), activates the Wnt pathway and stabilizes the nephrin transcriptional repressor SNAIL. Silencing neonatal Fc Receptor (FcRn) or CAMK4 prevented the podocyte-damaging effects of IgG from patients with TG. Furthermore, we show that removal of N-linked glycosyl residues from these IgG did not interfere with its entry into the podocytes but eliminated its ability to upregulate CAMK4 and cause podocyte injury. The translational value of these findings is signified by the fact that CAMK4 is increased in podocytes of patients with TG but not in those without TG despite other forms of renal dysfunction. Our results offer novel considerations to limit podocyte injury in patients with kidney transplants, which may lead to eventual glomerular destabilization and transplant glomerulopathy.

Role of Senescent Renal Cells in Pathophysiology of Diabetic Kidney Disease.

Diabetic kidney disease (DKD) is the leading cause of kidney failure in the USA, representing ~ 44% of all cases of kidney failure. Advancements in both glucose management and inhibitors of the renin-angiotensin system have significantly improved prognosis for individuals with DKD, yet DKD continues to affect 30-40% of people with type 2 diabetes and is still a major predictor of mortality in this population. Thus, new interventions are required to address this significant health burden. One potential target for intervention is cellular senescence. Senescence permanently arrests cell division in response to genotoxic, oncogenic, or metabolic stresses-coupled to the secretion of inflammatory cytokines, chemokines, growth factors, proteases, and other molecules that can have potent local and systemic effects. This senescence-associated secretory phenotype (SASP) explains how a relatively small number of senescent cells can promote pathology, and a growing number of degenerative conditions have been found to be caused or aggravated by senescent cells. Many SASP factors are also associated with loss of kidney function. Targeted elimination of senescent cells prevents the development of several degenerative pathologies. Since senescent cells appear in the proximal tubules and podocytes of patients with DKD, they are an appealing target for intervention in these disorders. Here, we review the current literature linking senescence to DKD and speculate on the likely routes to intervention in a clinical setting.

IL-17 aggravates renal injury by promoting podocyte injury in children with primary nephrotic syndrome.

Primary nephrotic syndrome (PNS) is the most common chronic kidney disease in childhood, where podocyte injury is a key factor in the occurrence of kidney disease. In the present study, the expression of IL-17 in renal tissues of patients with PNS and its relationship with podocyte injury were examined. Reverse transcription-quantitative PCR (RT-qPCR), western blot analysis and immunochemistry were used to measure the expression of IL-17 in renal biopsies of patients with ONS, including 9 patients with minimal change nephrotic syndrome (MCNS), 15 patients with mesangial proliferative glomerulonephritis (MsPGN) and 9 patients with focal segmental glomerulosclerosis (FSGS), in addition to 15 normal kidney tissues. IL-17 was found to be highly expressed in the renal tissues from patients with PNS, with the highest expression levels found in tissues from patients with FSGS and the lowest in those from MCNS. A negative correlation was observed between the levels of IL-17 mRNA and PCX mRNA in renal tissues, whereas a positive correlation between IL-17 mRNA levels and the number of urinary podocytes in patients with PNS was found. In vitro, IL-17 induced podocyte apoptosis and reduced the expression of markers associated with podocytes, including Wilm's tumor 1, nephrin, synaptopodin and podocalyxin, whilst increasing the levels of Fas, Fas ligand (FasL), active-caspase-8, active-caspase-3 and phosphorylated-p65. However, treatment with helenalin, a NF-κB inhibitor, decreased p65 phosphorylation, attenuated IL-17-induced podocyte apoptosis and suppressed the IL-17-activated Fas/FasL/caspase-8/caspase-3 apoptotic pathway. Taken together, these observations suggest that IL-17 was highly expressed in renal tissues from patients with PNS, where it induced podocyte apoptosis by activating the Fas/FasL/caspase-8/caspase-3 apoptotic pathway in a NF-κB-dependent manner.

Transcription factor MafB in podocytes protects against the development of focal segmental glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) is a common cause of steroid-resistant nephrotic syndrome. Spontaneous remission of FSGS is rare and steroid-resistant FSGS frequently progresses to renal failure. Many inheritable forms of FSGS have been described, caused by mutations in proteins that are important for podocyte function. Here, we show that a basic leucine zipper transcription factor, MafB, protects against FSGS. MAFB expression was found to be decreased in the podocytes of patients with FSGS. Moreover, conditional podocyte-specific MafB-knockout mice developed FSGS with massive proteinuria accompanied by depletion of the slit diaphragm-related proteins (Nphs1 and Magi2), and the podocyte-specific transcription factor Tcf21. These findings indicate that MafB plays a crucial role in the pathogenesis of FSGS. Consistent with this, adriamycin-induced FSGS and attendant proteinuria were ameliorated by MafB overexpression in the podocytes of MafB podocyte-specific transgenic mice. Thus, MafB could be a new therapeutic target for FSGS.