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Introduction: The unique architecture of glomerular podocytes is integral to kidney filtration. Interdigitating foot processes extend from the podocyte cell body, wrap around fenestrated capillaries, and form specialized junctional complexes termed slit diaphragms to create a molecular sieve. However, the full complement of proteins which maintain foot process integrity, and how this localized proteome changes with disease, remain to be elucidated.Methods: Proximity-dependent biotin identification (BioID) enables the identification of spatially localized proteomes. To this end, we developed a novel in vivo BioID knock-in mouse model. We utilized the slit diaphragm protein podocin (Nphs2) to create a podocin–BioID fusion. Podocin–BioID localizes to the slit diaphragm, and biotin injection leads to podocyte-specific protein biotinylation. We isolated the biotinylated proteins and performed mass spectrometry to identify proximal interactors.Results and Discussion: Gene ontology analysis of 54 proteins specifically enriched in our podocin–BioID sample revealed ‘cell junctions,’ ‘actin binding,’ and ‘cytoskeleton organization’ as top terms. Known foot process components were identified, and we further uncovered two novel proteins: the tricellular junctional protein Ildr2 and the CDC42 and N-WASP interactor Fnbp1l. We confirmed that Ildr2 and Fnbp1l are expressed by podocytes and partially colocalize with podocin. Finally, we investigated how this proteome changes with age and uncovered a significant increase in Ildr2. This was confirmed by immunofluorescence on human kidney samples and suggests altered junctional composition may preserve podocyte integrity. Together, these assays have led to new insights into podocyte biology and support the efficacy of utilizing BioID in vivo to interrogate spatially localized proteomes in health, aging, and disease.

Podocyte injury plays a key role in pathogenesis of many kidney diseases with increased podocyte foot process width (FPW), an important measure of podocyte injury. Unfortunately, there is no consensus on the best way to estimate FPW and unbiased stereology, the current gold standard, is time consuming and not widely available. To address this, we developed an automated FPW estimation technique using deep learning. A U-Net architecture variant model was trained to semantically segment the podocyte-glomerular basement membrane interface and filtration slits. Additionally, we employed a post-processing computer vision approach to accurately estimate FPW. A custom segmentation utility was also created to manually classify these structures on digital electron microscopy (EM) images and to prepare a training dataset. The model was applied to EM images of kidney biopsies from 56 patients with Fabry disease, 15 with type 2 diabetes, 10 with minimal change disease, and 17 normal individuals. The results were compared with unbiased stereology measurements performed by expert technicians unaware of the clinical information. FPW measured by deep learning and by the expert technicians were highly correlated and not statistically different in any of the studied groups. A Bland-Altman plot confirmed interchangeability of the methods. FPW measurement time per biopsy was substantially reduced by deep learning. Thus, we have developed a novel validated deep learning model for FPW measurement on EM images. The model is accessible through a cloud-based application making calculation of this important biomarker more widely accessible for research and clinical applications., (Copyright © 2023 International Society of Nephrology. Published by Elsevier Inc. All rights reserved.)

Podocytes are an integral part of the glomerular filtration barrier, a structure that prevents filtration of large proteins and macromolecules into the urine. Podocyte function is dependent on actin cytoskeleton regulation within the foot processes, structures that link podocytes to the glomerular basement membrane. Actin cytoskeleton dynamics in podocyte foot processes are complex and regulated by multiple proteins and other factors. There are two key signal integration and structural hubs within foot processes that regulate the actin cytoskeleton: the slit diaphragm and focal adhesions. Both modulate actin filament extension as well as foot process mobility. No matter what the initial cause, the final common pathway of podocyte damage is dysregulation of the actin cytoskeleton leading to foot process retraction and proteinuria. Disruption of the actin cytoskeleton can be due to acquired causes or to genetic mutations in key actin regulatory and signaling proteins. Here, we describe the major structural and signaling components that regulate the actin cytoskeleton in podocytes as well as acquired and genetic causes of actin dysregulation.

Paraneoplastic nephrotic syndrome (PNS) is a complication seen in cancer patients. Ultrastructural examination shows the accumulation of proteins and the presence of foot process (FP) effacement in the glomeruli of PNS patients. Previously, we reported that orthotopic xenografts of Lewis lung carcinoma 1 in C57BL/6 mice caused them to develop lung cancer with albuminuria. This implies that these mice can be used as a model of human disease and suggests that Lewis lung carcinoma 1 cell-secreted proteins (LCSePs) contain nephrotoxic molecules and cause inflammation in renal cells. As podocyte effacement was present in glomeruli in this model, such podocyte injury may be attributable to either soluble LCSeP or LCSeP deposits triggering pathological progression. LCSePs in conditioned media was concentrated for nephrotoxicity testing. Integrin-focal adhesion kinase (FAK) signaling and inflammatory responses were evaluated in podocytes either exposed to soluble LCSePs or seeded onto substrates with immobilized LCSePs. FAK phosphorylation and interleukin-6 expression were higher in podocytes attached to LCSePs substrates than in those exposed to soluble LCSePs. Notably, LCSeP-based haptotaxis gave rise to altered signaling in podocytes. When podocytes were stimulated by immobilized LCSePs, FAK accumulated at focal adhesions, synaptopodin dissociated from F-actin, and disrupting the interactions between synaptopodin and α-actinin was observed. When FAK was inhibited by PF-573228 in immobilized LCSePs, the association between synaptopodin and α-actinin was observed in the podocytes. The association of synaptopodin and α-actinin with F-actin allowed FP stretching, establishing a functional glomerular filtration barrier. Therefore, in this mouse model of lung cancer, FAK signaling prompts podocyte FP effacement and proteinuria, indicative of PNS., (Copyright © 2023 United States & Canadian Academy of Pathology. Published by Elsevier Inc. All rights reserved.)

Background. O-linked β-N-acetylglucosamine modification (O-GlcNAcylation) is a post-translational modification of intracellular proteins, serving as a nutrient sensor. Growing evidence has demonstrated its physiological and pathological importance in various mammalian tissues. This study examined the physiological role of O-GlcNAcylation in podocyte function and development. Methods. O-GlcNAc transferase (Ogt) is a critical enzyme for O-GlcNAcylation and resides on the X chromosome. To abrogate O-GlcNAcylation in podocytes, we generated congenital and tamoxifen (TM)-inducible podocyte-specific Ogt knockout mice (Podo-Ogty/y/- and TM-Podo-Ogty/y/-, respectively) and analyzed their renal phenotypes. Results. Podo-Ogty/y/- mice showed normal podocyte morphology at birth. However, they developed albuminuria at 8 weeks of age, increasing progressively until age 32 weeks. Glomerular sclerosis, proteinuria-related tubulointerstitial lesions and markedly altered podocyte foot processes, with decreased podocin expression, were observed histologically in 32-week-old Podo-Ogty/y/- mice. Next, we induced adult-onset deletion of the Ogt gene in podocytes by TM injection in 8-week-old TM-Podo-Ogty/y/- mice. In contrast to Podo-Ogty/y/- mice, the induced TM-Podo-Ogty/y/- mice did not develop albuminuria or podocyte damage, suggesting a need for O-GlcNAcylation to form mature foot processes after birth. To test this possibility, 3-week-old Podo-Ogty/y/- mice were treated with Bis-T-23, which stimulates actin-dependent dynamin oligomerization, actin polymerization and subsequent foot process elongation in podocytes. Albuminuria and podocyte damage in 16-week-old Podo-Ogty/y/- mice were prevented by Bis-T-23 treatment. Conclusions. O-GlcNAcylation is necessary for maturation of podocyte foot processes, particularly after birth. Our study provided new insights into podocyte biology and OGlcNAcylation. [ABSTRACT FROM AUTHOR]

Protein mimotopes, or blocking peptides, are small therapeutic peptides that prevent protein-protein interactions by selectively mimicking a native binding domain. Inexpensive technology facilitates straightforward design and production of blocking peptides in sufficient quantities to allow preventive and therapeutic trials in both in vitro and in vivo experimental disease models. The kidney is an ideal peptide target, since small molecules undergo rapid filtration and efficient bulk absorption by tubular epithelial cells. Because the half-life of peptides is markedly prolonged in the kidneys compared with the bloodstream, blocking peptides are an attractive tool for treating diverse renal diseases, including ischemia, proteinuric states, such as membranous nephropathy and focal and segmental glomerulosclerosis, and renal cell carcinoma. Therapeutic peptides represent one of the fastest-growing reagent classes for novel drug development in human disease, partly because of their ease of administration, high binding affinity, and minimal off-target effects. This review introduces the concepts of blocking peptide design, production, and administration and highlights the potential use of therapeutic peptides to prevent or treat specific renal diseases. [ABSTRACT FROM AUTHOR]

Introduction: The unique architecture of glomerular podocytes is integral to kidney filtration. Interdigitating foot processes extend from the podocyte cell body, wrap around fenestrated capillaries, and form specialized junctional complexes termed slit diaphragms to create a molecular sieve. However, the full complement of proteins which maintain foot process integrity, and how this localized proteome changes with disease, remain to be elucidated. Methods: Proximity-dependent biotin identification (BioID) enables the identification of spatially localized proteomes. To this end, we developed a novel in vivo BioID knock-in mouse model. We utilized the slit diaphragm protein podocin ( Nphs2 ) to create a podocin-BioID fusion. Podocin-BioID localizes to the slit diaphragm, and biotin injection leads to podocyte-specific protein biotinylation. We isolated the biotinylated proteins and performed mass spectrometry to identify proximal interactors. Results and Discussion: Gene ontology analysis of 54 proteins specifically enriched in our podocin-BioID sample revealed 'cell junctions,' 'actin binding,' and 'cytoskeleton organization' as top terms. Known foot process components were identified, and we further uncovered two novel proteins: the tricellular junctional protein Ildr2 and the CDC42 and N-WASP interactor Fnbp1l. We confirmed that Ildr2 and Fnbp1l are expressed by podocytes and partially colocalize with podocin. Finally, we investigated how this proteome changes with age and uncovered a significant increase in Ildr2. This was confirmed by immunofluorescence on human kidney samples and suggests altered junctional composition may preserve podocyte integrity. Together, these assays have led to new insights into podocyte biology and support the efficacy of utilizing BioID in vivo to interrogate spatially localized proteomes in health, aging, and disease., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Gerlach, Imseis, Cooper, Santos and O’Brien.)

Aim The current study was designed to observe the ultrastructural changes of podocyte foot processes during the remission phase and its relationship with the amount of the proteinuria in patients with minimal change disease ( MCD). Methods Electron micrographs of glomerular capillaries were taken from 33 adult cases with MCD, including 12 cases with nephrotic syndrome, 15 cases in partial remission and six cases in complete remission. The foot processes were classified into three grades by the ratio of the height to basal width: 0.5-1, 1-2 and ≥2. The foot process width ( FPW) and the number of foot processes in different grades per 10 μm of glomerular basement membrane ( GBM) were measured. Normal renal tissues from 12 nephrectomies for renal carcinoma were selected as controls. Results There were statistical differences ( P = 0.001) in the mean FPW among the nephrotic group (1566.4 ± 429.4 nm), partial remission group (1007.8 ± 234.9 nm), complete remission group (949.8 ± 168.2 nm) and normal controls (471.9 ± 51.8 nm). For the height-to-width ratio ≥2, the number of foot process per 10 μm GBM was significantly greater in the normal group than that in the complete remission group (0.84 ± 0.24 vs. 3.84 ± 1.80, P = 0.016). Taking all three groups of patients together, the mean FPW showed correlation with the level of proteinuria (r = 0.506, P = 0.003). Conclusion There may be no causal relationship between proteinuria and foot process effacement. In complete remission phase, both FPW and shape of foot process had not returned to normal while proteinuria disappeared. [ABSTRACT FROM AUTHOR]

Abstract: Mitochondria are crucial organelles that produce and deliver adenosine triphosphate (ATP), by which all cellular processes are driven. Although the mechanisms that control mitochondrial biogenesis, function and dynamics are complex process and vary among different cell types, recent studies provided many new discoveries in this field. Podocyte injury is a crucial step in the development of a large number of glomerular diseases. Glomerular podocytes are unique cells with complex foot processes that cover the outer layer of the glomerular basement membrane, and are the principle cells composing filtration barriers of glomerular capillaries. Little is known on the modalities and the regulation of podocyte's energetics as well as the type of energy substrate primarily used for their activity, recent studies revealed that dysfunction of energy transduction in podocytes may underlie the podocyte injury associated with numerous glomerular diseases. We herein review and discuss the importance of a fine regulation of energy metabolism in podocytes for maintaining their cellular structure and related kidney function. In the future, understanding these mechanisms will open up new areas of treatment for glomerular diseases. [Copyright &y& Elsevier]

The kidney filtration barrier consists of the capillary endothelium, the glomerular basement membrane and the slit diaphragm localized between foot processes of neighbouring podocytes. We report that collagen XVII, a transmembrane molecule known to be required for epithelial adhesion, is expressed in podocytes of normal human and mouse kidneys and in endothelial cells of the glomerular filtration barrier. Immunoelectron microscopy has revealed that collagen XVII is localized in foot processes of podocytes and in the glomerular basement membrane. Its role in kidney has been analysed in knockout mice, which survive to birth but have high neonatal mortality and skin blistering and structural abnormalities in their glomeruli. Morphometric analysis has shown increases in glomerular volume fraction and surface densities of knockout kidneys, indicating an increased glomerular amount in the cortex. Collagen XVII deficiency causes effacement of podocyte foot processes; however, major slit diaphragm disruptions have not been detected. The glomerular basement membrane is split in areas in which glomerular and endothelial basement membranes meet. Differences in the expression of collagen IV, integrins α3 or β1, laminin α5 and nephrin have not been observed in mutant mice compared with controls. We propose that collagen XVII has a function in the attachment of podocyte foot processes to the glomerular basement membrane. It probably contributes to podocyte maturation and might have a role in glomerular filtration. [ABSTRACT FROM AUTHOR]

As an integral member of the filtration barrier in the kidney glomerulus, the podocyte is in a unique geographical position: It is exposed to chemical signals from the urinary space (Bowman's capsule), it receives and transmits chemical and mechanical signals to//from the glomerular basement membrane upon which it elaborates, and it receives chemical and mechanical signals from the vascular space with which it also communicates. As with every cell, the ability of the podocyte to receive signals from the surrounding environment and to translate them to the intracellular milieu is dependent largely on molecules residing on the cell membrane. These molecules are the first-line soldiers in the ongoing battle to sense the environment, to respond to friendly signals, and to defend against injurious foes. In this review, we take a membrane biologist's view of the podocyte, examining the many membrane receptors, channels, and other signaling molecules that have been implicated in podocyte biology. Although we attempt to be comprehensive, our goal is not to capture every membrane-mediated pathway but rather to emphasize that this approach may be fruitful in understanding the podocyte and its unique properties. [ABSTRACT FROM AUTHOR]

In addition to skeletal muscle and the nervous system, α-dystroglycan is found in the podocyte basal membrane, stabilizing these cells on the glomerular basement membrane. Fukutin, named after the gene responsible for Fukuyama-type congenital muscular dystrophy, is a putative glycosyltransferase required for the post-translational modification of α-dystroglycan. Chimeric mice targeted for both alleles of fukutin develop severe muscular dystrophy; however, these mice do not have proteinuria. Despite the lack of a functional renal defect, we evaluated glomerular structure and found minor abnormalities in the chimeric mice by light microscopy. Electron microscopy revealed flattening of podocyte foot processes, the number of which was significantly lower in the chimeric compared to wild-type mice. A monoclonal antibody against the laminin-binding carbohydrate residues of α-dystroglycan did not detect α-dystroglycan glycosylation in the glomeruli by immunoblotting or immunohistochemistry. In contrast, expression of the core α-dystroglycan protein was preserved. There was no statistical difference in dystroglycan mRNA expression or in the amount of nephrin and α3-integrin protein in the chimeric compared to the wild-type mice as judged by immunohistochemistry and real-time RT-PCR. Thus, our results indicate that appropriate glycosylation of α-dystroglycan has an important role in the maintenance of podocyte architecture. [ABSTRACT FROM AUTHOR]

The tyrosine phosphorylation of nephrin is reported to regulate podocyte morphology via the Nck adaptor proteins. The Pak family of kinases are regulators of the actin cytoskeleton and are recruited to the plasma membrane via Nck. Here, we investigated the role of Pak in podocyte morphology. Pakl/2 were expressed in cultured podocytes. In mouse podocytes, Pak2 was predominantly phosphorylated, concentrated at the tips of the cellular processes, and its expression and/or phosphorylation were further increased when differentiated. Overexpression of rat nephrin in podocytes increased Pakl/2 phosphorylation, which was abolished when the Nck binding sites were mutated. Furthermore, dominant-negative Nck constructs blocked the Paki phosphorylation induced by antibody-mediated cross linking of nephrin. Transient transfection of constitutively kinase-active PakI into differentiated mouse podocytes decreased stress fibers, increased cortical F-actin, and extended the cellular processes, whereas kinase-dead mutant, kinase inhibitory construct, and Pak2 knockdown by shRNA had the opposite effect. In a rat model of puromycin aminonucleoside nephro- sis, Pakl/2 phosphorylation was decreased in glomeruli, concomitantly with a decrease of nephrin tyrosine phosphorylation. These results suggest that Pak contributes to remodeling of the actin cytoskeleton in podocytes. Disturbed nephrin-Nck-Pak interaction may contribute to abnormal morphology of podocytes and proteinuria. [ABSTRACT FROM AUTHOR]

Background/Aims: Morphological change of podocytes is closely correlated with the development of proteinuria. Podocalyxin is a major sialoglycoprotein of the podocytes and is thought to be involved in the maintenance of the foot processes structure. Our aim was to examine the mechanism by which podocalyxin contributes to the morphological change of podocytes. Methods: We searched protein(s) which coprecipitate with podocalyxin using rat glomerular lysate. Localization of podocalyxin and the coprecipitated protein, cortactin, was studied in a model of puromycin aminonucleoside (PAN) nephrosis by immunocytochemistry. Tyrosine phosphorylation of cortactin was examined. Association of the podocalyxin/cortactin complex with the actin cytoskeleton was evaluated by extraction with Triton-X and immunoblotting. Results: Cortactin was found to be co-immunoprecipitated with podocalyxin. Immunocytochemical analysis revealed that these 2 proteins colocalized in the apical side of podocytes. In PAN nephrosis, localization of cortactin was altered after the onset of proteinuria, with increased tyrosine phosphorylation. Simultaneously, the dissociation of the podocalyxin/cortactin complex from the actin cytoskeleton was induced. Conclusions: These results indicate that cortactin mediates interaction between podocalyxin and actin filaments in podocytes and that alteration of this interaction may play a role in the process of morphological change of podocytes. Copyright © 2009 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

The pathogenesis of minimal change nephrotic syndrome (MCNS) remains unclear. Respiratory tract viruses could contribute to MCNS, and respiratory syncytial virus (RSV) is the most common one. In this study, we planned to investigate the effects of RSV on the proteinuria and glomerular structure of rats and to explore the role of RSV in the pathogenesis of MCNS. Rats were inoculated with 6 × 102, 104, and 106 PFU (plaque-forming units) RSV and killed on days 4, 8, 14, 28, and 60 postinoculation (RSV4, RSV8, RSV14, RSV28, and RSV60). The proteinuria and serum parameters were measured; renal histology was observed by light microscopy and electron microscopy; immune complex deposits were detected by immunofluorescence microscopy; and RSV RNA and RSV titer were determined by in situ hybridization and plaque assay, respectively. After inoculation, the proteinuria increased, especially in 6 × 106 PFU RSV14,28. The serum albumin of 6 × 106 PFU RSV14,28 and different-titer RSV60 decreased. Slight hypercellularity in minority glomeruli and swelling in partial tubular epithelial cells were observed in RSV4,8, whereas a relief of the above changes and no abnormalities were detected in RSV14 and RSV28,60, respectively, under a light microscope. Extensive foot process effacement was observed in 6 × 106 PFU RSV14,28,60 under an electron microscope. No immune complex deposits were detected in the renal tissues. RSV RNA signal and RSV titer of renal tissues, depending on the dose of inoculum, reached their climax on day 8 postinoculation. Our study reports for the first time that RSV can lead to nephropathy in rats on days 14–60 postinoculation, especially in 6 × 106 PFU RSV-inoculated rats, which may be a new exploration of the pathogenesis of MCNS.Kidney International (2007) 71, 388–396. doi:10.1038/sj.ki.5002030; published online 3 January 2007 [ABSTRACT FROM AUTHOR]

Vascular endothelial growth factor (VEGF) is anti-cytotoxic in podocytes. Moreover, it has been suggested that nephrin, a cell adhesion molecule of the podocyte slit diaphragm, can contribute to antiapoptotic mechanisms in these cells. We therefore investigated whether VEGF signals to reduce apoptosis and the role of nephrin in this survival mechanism. Flow cytometry showed that podocytes with nephrin mutations had a significantly greater proportion of apoptosis. Although VEGF reduced apoptosis in human conditionally immortalized podocytes [wild-type (WT)] by 18.1% of control (P < 0.001), it was unable to do so in nephrin-deficient human conditionally immortalized podocytes. Moreover, Western blotting and immunodetection with an anti-nephrin antibody showed that the phosphorylation of nephrin, compared with serum-starved WTs, was significantly increased (ratio of 3.36 ± 1.2 to control, P < 0.05) by VEGF treatment and significantly reduced by treatment with a neutralizing VEGF monoclonal antibody (mAb) (ratio of 0.2 ± 0.09 to control, P < 0.05). The AKT signaling pathway has been implicated in nephrin-mediated inhibition of apoptosis in transfected cells, but the role of this pathway has not previously been shown in podocytes. Surprisingly, exogenous VEGF decreased AKT/ PKB phosphorylation in normal podocytes but increased it in nephrindeficient podocytes. We suggest therefore that both exogenous and endogenous (podocyte derived) VEGF can stimulate the phosphorylation of nephrin and through this action may prevent podocyte apoptosis. However, the involvement of AKT in this survival response in normal human podocytes is not clear. [ABSTRACT FROM AUTHOR]

Effects of high glucose and TGF-β1 on the expression of collagen IV and vascular endothelial growth factor in mouse podocytes. Background. The podocyte takes center stage in the pathogenesis of glomerular basement membrane (GBM) thickening and proteinuria in diabetic glomerulopathy. In part, GBM thickening may occur when the podocyte synthesizes increased amounts of collagen IV. Proteinuria may develop if the podocyte secretes excessive amounts of vascular endothelial growth factor (VEGF), which may increase the glomerular permeability to macromolecules. The augmented production of collagen IV and VEGF may be caused by metabolic mediators of diabetes such as hyperglycemia and transforming growth factor-β (TGF-β). Methods. The effects of high glucose and exogenous TGF-β1 were examined on a mouse podocyte cell line that retains its differentiated phenotype. The gene expression and protein production of certain alpha chains of collagen IV, the major isoforms of VEGF, and components of the TGF-β system were assayed. An inhibitor of TGF-β signaling was used to determine whether some of the high glucose effects might be mediated by the TGF-β system. Results. Compared with normal glucose (5.5 mmol/L), high glucose (HG, 25 mmol/L) for 14 days stimulated [3 H]-proline incorporation, a measure of collagen production, by 1.8-fold, and exogenous TGF-β1 (2 ng/mL) for 24 hours stimulated proline incorporation by 2.4-fold. Northern analysis showed that exposure to HG for 14 days increased the mRNA level of α1(IV) collagen by 51% and α5(IV) by 90%, whereas treatment with TGF-β1 (2 ng/mL) for 24 hours decreased the mRNA level of α1(IV) by 36% and α5(IV) by 40%. Consistent with these effects on mRNA expression, Western blotting showed that HG increased α1(IV) protein by 44% and α5(IV) by 28%, while TGF-β1 decreased α1(IV) protein by 29% and α5(IV) by 7%. In contrast to their... [ABSTRACT FROM AUTHOR]

Aims/hypothesis. Changes in podocyte number and morphology have been implicated in the pathogenesis of proteinuria and the progression of human and experimental kidney disease. This study sought to examine podocyte foot process and slit pore architecture in experimental diabetic nephropathy and to determine whether such changes were modified with renoprotective intervention by blockade of the renin-angiotensin system. Methods. The number of filtration slits per 100 μm of glomerular basement membrane was assessed by transmission electron microscopy and quantitated histomorphometrically in control animals and in rats with 24 weeks of streptozotocin-induced diabetes. Diabetic rats were either untreated or received the angiotensin converting enzyme inhibitor ramipril, or the angiotensin II type 1 receptor antagonist, valsartan. Results. When compared with control animals, diabetes was associated with a decrease in the number of slit pores per unit length of glomerular basement membrane, indicative of podocyte foot process broadening. Both ramipril and valsartan attenuated these ultrastructural changes to a similar degree. These differences remained after correcting for glomerular volume as a possible confounding variable. Conclusion/interpretation. Preservation of podocyte architecture could contribute to the renoprotective effects of renin-angiotensin system blockade in diabetic nephropathy. [Diabetologia (2001) 44: 878–882] [ABSTRACT FROM AUTHOR]

Despite increasing awareness and therapeutic options chronic kidney disease (CKD) is still and important health problem and glomerular diseases constitute and important percentage of CKD. Proteinuria/albuminuria is not just a marker; but it also plays a direct pathogenic role in renal disease progression of CKD. Glomerular filtration barrier (GFB) which consists of fenestrated endothelial cells, fused basal membrane and interdigitating podocyte foot process and filtration slits between foot process is the major barrier for proteinuria/albuminuria. Many glomerular diseases are characterized by disruption of GFB podocytes, foot process and slit diaphragm. Many proteinuric diseases are non-specifically targeted by therapeutic agents such as steroids and calcineurin inhibitors with systemic side effects. Thus, there is unmet need for more efficient and less toxic therapeutic options to treat glomerular diseases. In recent years, modification of dietary intake, has been gained to treat pathologic processes introducing the concept of 'food as a medicine'. The effect of various nutritional products on podocyte function and structure is also trending, especially in recent years. In the current review, we summarized the effect of nutritional interventions on podocyte function and structure. [Display omitted] [ABSTRACT FROM AUTHOR]

Murine monoclonal antibody (MoAb) 5-1-6 was already reported to bind to epithelial cell foot processes and to cause proteinuria in rats. In vivo kinetics of the injected MoAb 5-1-6, relationship between the quantity of kidney-binding antibody and proteinuria, and changes In the amount of antigenic molecule recognized by this MoAb in the proteinuric state were studied. The amount of total kidney-binding antibody (TKAb) as determined 1 h alter a 2 mg administration was 50.8 ± 10.4 μg/2 kidneys, and TKAb declined to 1.9 ± 0.4 at day 15. The minimum dose of MoAb required to induce proteinuria was 125 μg as the injected dose. This dose corresponded to 12.8 μg of TKAb at 1 h and 0.34 μg of TKA bat day 5. The amount of MoAb 5-1-6 binding to isolated normal glomeruli was also shown to exceed 147.7 μg/76000 glomeruli, indicating proteinuria to be induced provided more than 8.7% (= 12.8/147.7) of the critical epitopes is specifically occupied by MoAb. The total amount of MoAb 5-1-6 bound to glomeruli in vivo and in vitro was assayed with [125]-labelled anti-mouse IgG. The amount of [125] anti-mouse IgG bound to glomeruli was 6.93 ± 0.45 μg/10 000 glomeruli from rat 5 days after this MoAb injection and 26.58 ± 0.66 μg/10 000 control glomeruli. indicating the decrease in the number of MoAb 5-1-6-rccognized antigen molecules in glomeruli isolated from the rat in proteinuric state induced by this MoAb. Thus, the MoAb 5-1-6-recognized molecule itself may principally function to regulate the permeability of the glomerular capillary wall and the decrease of the molecule may lead to proteinuria. [ABSTRACT FROM AUTHOR]

Ultrastructural changes in the podocytes were studied during the development of, and recovery from, acute puromycin aminonucleoside (PAN) nephrosis using high-resolution scanning electron microscopy (hrSEM) and transmission electron microscopy (TEM). In the process of development of PAN nephrosis, four types of early structural changes were observed before total loss of foot processes: formation of cytoplasmic blebs, masking of filtration clefts, flattening of foot processes, and retraction of foot processes. The masking of filtration clefts visualized by hrSEM corresponded to the multiplication of slit diaphragms and adhesion of foot processes in the TEM findings, and preceded retraction of the foot processes. Changes of podocyte configuration were produced. Recovery from this change of podocyte configuration began as islands of podocyte interdigitation, and was proceeded by expansion of the islands. During recovery, the primary processes were re-established either by retraction or perforation of the thin cytoplasm after the formation of foot processes. We conclude that loss of foot processes begins with the masking of filtration clefts. Recovery from the change in podocyte configuration begins with the formation of new foot processes. [ABSTRACT FROM AUTHOR]

Nephrotoxic serum nephritis was produced in rats by intraperitoneal injections of rabbit nephrotoxic serum. Heterologous and autologous phases of nephritis were demonstrated by immunofluorescence and ultrastructural studies. Scanning electron microscopy showed changes in the surface of the podocytes, swelling of the arm-like cytoplasmic processes, and disappearance of the pedicles. The podocyte alterations are discussed. [ABSTRACT FROM AUTHOR]

Podocytes are an integral part of the glomerular filtration barrier, a structure that prevents filtration of large proteins and macromolecules into the urine. Podocyte function is dependent on actin cytoskeleton regulation within the foot processes, structures that link podocytes to the glomerular basement membrane. Actin cytoskeleton dynamics in podocyte foot processes are complex and regulated by multiple proteins and other factors. There are two key signal integration and structural hubs within foot processes that regulate the actin cytoskeleton: the slit diaphragm and focal adhesions. Both modulate actin filament extension as well as foot process mobility. No matter what the initial cause, the final common pathway of podocyte damage is dysregulation of the actin cytoskeleton leading to foot process retraction and proteinuria. Disruption of the actin cytoskeleton can be due to acquired causes or to genetic mutations in key actin regulatory and signaling proteins. Here, we describe the major structural and signaling components that regulate the actin cytoskeleton in podocytes as well as acquired and genetic causes of actin dysregulation. [ABSTRACT FROM AUTHOR]

Background: O-linked β- N -acetylglucosamine modification O-GlcNAcylation) is a post-translational modification of intracellular proteins, serving as a nutrient sensor. Growing evidence has demonstrated its physiological and pathological importance in various mammalian tissues. This study examined the physiological role of O-GlcNAcylation in podocyte function and development., Methods: O-GlcNAc transferase (Ogt) is a critical enzyme for O-GlcNAcylation and resides on the X chromosome. To abrogate O-GlcNAcylation in podocytes, we generated congenital and tamoxifen (TM)-inducible podocyte-specific Ogt knockout mice (Podo-Ogt y/- and TM-Podo-Ogt y/- , respectively) and analyzed their renal phenotypes., Results: Podo-Ogt y/- mice showed normal podocyte morphology at birth. However, they developed albuminuria at 8 weeks of age, increasing progressively until age 32 weeks. Glomerular sclerosis, proteinuria-related tubulointerstitial lesions and markedly altered podocyte foot processes, with decreased podocin expression, were observed histologically in 32-week-old Podo-Ogt y/- mice. Next, we induced adult-onset deletion of the Ogt gene in podocytes by TM injection in 8-week-old TM-Podo-Ogt y/- mice. In contrast to Podo-Ogt y/- mice, the induced TM-Podo-Ogt y/- mice did not develop albuminuria or podocyte damage, suggesting a need for O-GlcNAcylation to form mature foot processes after birth. To test this possibility, 3-week-old Podo-Ogt y/- mice were treated with Bis-T-23, which stimulates actin-dependent dynamin oligomerization, actin polymerization and subsequent foot process elongation in podocytes. Albuminuria and podocyte damage in 16-week-old Podo-Ogt y/- mice were prevented by Bis-T-23 treatment., Conclusions: O-GlcNAcylation is necessary for maturation of podocyte foot processes, particularly after birth. Our study provided new insights into podocyte biology and O-GlcNAcylation., (© The Author 2017. Published by Oxford University Press on behalf of ERA-EDTA. All rights reserved.)