Podocyte Structure Research Articles

Upregulation of podocyte-secreted angiopoietin-like-4 in diabetic nephropathy.

Podocyte injury plays a key role in the development of diabetic nephropathy (DN). Understanding the changes in podocyte structure and function in diabetes mellitus may lead to novel diagnostic tools and treatment strategies for DN. Albuminuria, histological alterations, and podocyte injury were detected at different time points in streptozotocin (STZ)-induced diabetic rats. Increased urinary albumin-to-creatinine ratios (ACR) and podocyte injury were significantly observed 4weeks post-STZ injection. We determined the glomerular expression and distribution of angiopoietin-like 4 (Angptl4) by immunofluorescence and real-time PCR. Glomerular Angptl4 expression was mostly colocalized with synaptopodin, a podocyte marker, with substantial additional overlap with the glomerular basement membrane (GBM). This finding indicated that Angptl4 might be primarily secreted by podocytes and moved toward the GBM. Moreover, we observed by Western blot analysis and ELISA that the urinary Angptl4 level was gradually upregulated in both STZ-induced rats and diabetic patients with microalbuminuria and macroalbuminuria. We further found that the increased glomerular Angptl4 expression was closely related to the urinary ACR level and podocyte injury. In addition, the urinary Angptl4 expression was closely associated with albuminuria in the rats and patients with DN. This study is the first to show that podocyte-secreted Angptl4 is upregulated in DN and can be detected in urine. Angptl4 might function as a podocyte injury marker and could be a potential and novel diagnostic and therapeutic biomarker for DN.

Cyclooxygenase-2, prostaglandin E2, and prostanoid receptor EP2 in fluid flow shear stress-mediated injury in the solitary kidney.

Hyperfiltration subjects podocytes to increased tensile stress and fluid flow shear stress (FFSS). We showed a 1.5- to 2.0-fold increase in FFSS in uninephrectomized animals and altered podocyte actin cytoskeleton and increased synthesis of prostaglandin E2 (PGE2) following in vitro application of FFSS. We hypothesized that increased FFSS mediates cellular changes through specific receptors of PGE2. Presently, we studied the effect of FFSS on cultured podocytes and decapsulated isolated glomeruli in vitro, and on solitary kidney in uninephrectomized sv129 mice. In cultured podocytes, FFSS resulted in increased gene and protein expression of cyclooxygenase (COX)-2 but not COX-1, prostanoid receptor EP2 but not EP4, and increased synthesis and secretion of PGE2, which were effectively blocked by indomethacin. Next, we developed a special flow chamber for applying FFSS to isolated glomeruli to determine its effect on an intact glomerular filtration barrier by measuring change in albumin permeability (Palb) in vitro. FFSS caused an increase in Palb that was blocked by indomethacin (P < 0.001). Finally, we show that unilateral nephrectomy in sv129 mice resulted in glomerular hypertrophy (P = 0.006), increased glomerular expression of COX-2 (P < 0.001) and EP2 (P = 0.039), and increased urinary albumin excretion (P = 0.001). Activation of the COX-2-PGE2-EP2 axis appears to be a specific response to FFSS in podocytes and provides a mechanistic basis for alteration in podocyte structure and the glomerular filtration barrier, leading to albuminuria in hyperfiltration-mediated kidney injury. The COX-2-PGE2-EP2 axis is a potential target for developing specific interventions to ameliorate the effects of hyperfiltration-mediated kidney injury in the progression of chronic kidney disease.

Proteomics analysis of the non-muscle myosin heavy chain IIa-enriched actin-myosin complex reveals multiple functions within the podocyte.

MYH9 encodes non-muscle myosin heavy chain IIA (NMMHCIIA), the predominant force-generating ATPase in non-muscle cells. Several lines of evidence implicate a role for MYH9 in podocytopathies. However, NMMHCIIA‘s function in podocytes remains unknown. To better understand this function, we performed immuno-precipitation followed by mass-spectrometry proteomics to identify proteins interacting with the NMMHCIIA-enriched actin-myosin complexes. Computational analyses revealed that these proteins belong to functional networks including regulators of cytoskeletal organization, metabolism and networks regulated by the HIV-1 gene nef. We further characterized the subcellular localization of NMMHCIIA within podocytes in vivo, and found it to be present within the podocyte major foot processes. Finally, we tested the effect of loss of MYH9 expression in podocytes in vitro, and found that it was necessary for cytoskeletal organization. Our results provide the first survey of NMMHCIIA-enriched actin-myosin-interacting proteins within the podocyte, demonstrating the important role of NMMHCIIA in organizing the elaborate cytoskeleton structure of podocytes. Our characterization of NMMHCIIA’s functions goes beyond the podocyte, providing important insights into its general molecular role.

Pathogenic autoantibodies from patients with lupus nephritis cause reduced tyrosine phosphorylation of podocyte proteins, including tubulin

IntroductionThe tertiary structure of normal podocytes prevents protein from leaking into urine. Patients with lupus nephritis (LN) develop proteinuria, and kidney biopsies from these patients display a number of podocyte...

The comparative effects of perindopril and catechin on mesangial matrix and podocytes in the streptozotocin induced diabetic rats

BackgroundHyperglycemia and advanced glucose end substance (AGE) are responsible for excessive reactive oxygen species (ROS) production, which causes oxidative stress in diabetes mellitus. Oxidative stress and high blood pressure may cause injury and glomerulosclerosis in the kidney. End-stage kidney failure induced by glomerulosclerosis leads to microalbuminuria (Ma) in diabetic nephropathy. We investigated the effects of an angiotensin converting enzyme inhibitor (ACEI), perindopril, and an antioxidant, catechin, on podocytes and the glomerular mesangial matrix in experimental diabetic nephropathy using ultrastructural visualization and immunohistochemical staining. MethodsWe compared 5 groups of male adult Wistar albino rats: a control group, an untreated diabetic group, and diabetic groups treated with perindopril, catechin, or catechin+perindopril. ResultsBlood glucose values in all diabetic groups were significantly higher than in the control group (p<0.001). The body weight in all diabetic groups was significantly lower than in the control group (p<0.001, p<0.05). The kidney weight in the catechin+perindopril-treated diabetic group was significantly lower than in the untreated diabetic group (p<0.001). In all treated diabetic groups, Ma levels decreased significantly (p<0.001). Mesangial matrix and podocyte damage increased in the untreated diabetic group, but the group treated with catechin+perindopril showed less damage. TGF-beta 1 immunostaining was significantly lower in the catechin-treated and perindopril-treated groups than in the untreated diabetic group (p<0.001). Catechin was more effective than ACEI in preventing podocyte structure. Podocytes appeared to be the first cells affected in diabetes mellitus. When exposed to hyperglycemia, podocytes caused the mesangial matrix to expand. ConclusionsCatechin and perindopril were more effective in preventing renal corpuscle damage when administered together.

Podocytopathy in primary renal failure and de-novo membranous nephropathy post transplantation

BackgroundThe podocyte is a key component of the glomerular filtration barrier, and mutations in podocyte genes account for familiar and sporadic glomerular disease. After renal transplantation, some patients develop autoimmune glomerular disease with antibodies specific to nascent podocyte antigens, a process that can limit graft survival. We aimed to determine the molecular diagnosis in a family with primary renal failure and de-novo membranous nephropathy post transplantation. MethodsWe studied two siblings with primary glomerular disease and post-transplant membranous nephropathy using autozygosity mapping, whole exome sequencing, and post-transplant antibody screening. Native and transplant kidney biopsy samples were assessed in immunohistochemical and electron microscopy studies. The functional effects of the affected gene were studied in zebrafish and human podocytes. FindingsWe identified a novel 129 kb genomic deletion adjacent to exon 1 of IQCJ on chromosome 3 which was homozygous in siblings and heterozygous in their parents. After transplantation, both siblings were seropositive for anti-IQCJ antibodies. Native kidney biopsy tissue identified abnormal podocyte structure and cytoplasmic IQCJ. Transient knockdown of the IQCJ gene in zebrafish caused oedema, consistent with a glomerular phenotype. Human podocytes expressed IQCJ in vesicles resembling autophagosomes. InterpretationWe describe a new podocytopathy based on a genomic deletion on chromosome 3 close to IQCJ, which leads to primary renal failure. After renal transplantation, possession of the homozygous IQCJ deletion causes de-novo membranous nephropathy in the allograft within 12 months with rapid graft loss within 2 years. The dysregulation of this gene might have a role in primary glomerular disease or as a target for de-novo membranous nephropathy after transplantation. FundingWellcome Trust.

Podocyte-specific deletion of NDST1, a key enzyme in the sulfation of heparan sulfate glycosaminoglycans, leads to abnormalities in podocyte organization in vivo

Heparan sulfate proteoglycans have been shown to modulate podocyte adhesion to- and pedicel organization on- the glomerular basement membrane. Recent studies showed that foot process effacement developed in a mutant mouse model whose podocytes were unable to assemble heparan sulfate glycosaminoglycan chains. This study, a further refinement, explored the role of heparan N-sulfation on podocyte behavior. A novel mutant mouse (Ndst1-/-) was developed, having podocyte-specific deletion of NDST1, the enzyme responsible for N-sulfation of heparan sulfate chains. Podocytes having this mutation had foot process effacement and abnormal adhesion to Bowman's capsule. Although glomerular hypertrophy did develop in the kidneys of mutant animals, mesangial expansion was not seen. The lack of heparan N-sulfation did not affect the expression of agrin or perlecan proteoglycan core proteins. Loss of N-sulfation did not result in significant proteinuria, but the increase in the albumin/creatinine ratio was coincident with the development of the enlarged lysosomes in the proximal tubules. Thus, although the renal phenotype of the Ndst1-/- mouse is mild, the data show that heparan chain N-sulfation plays a key role in podocyte organization.

Divergent functions of the Rho GTPases Rac1 and Cdc42 in podocyte injury

Podocytes are highly specialized epithelial cells with complex actin cytoskeletal architecture crucial for maintenance of the glomerular filtration barrier. The mammalian Rho GTPases Rac1 and Cdc42 are molecular switches that control many cellular processes, but are best known for their roles in the regulation of actin cytoskeleton dynamics. Here we employed podocyte-specific Cre-lox technology and found that mice with deletion of Rac1 display normal podocyte morphology without glomerular dysfunction well into adulthood. Using the protamine sulfate model of acute podocyte injury, podocyte-specific deletion of Rac1 prevented foot process effacement. In a long-term model of chronic hypertensive glomerular damage, however, loss of Rac1 led to an exacerbation of albuminuria and glomerulosclerosis. In contrast, mice with podocyte-specific deletion of Cdc42 had severe proteinuria, podocyte foot process effacement, and glomerulosclerosis beginning as early as 10 days of age. In addition, slit diaphragm proteins nephrin and podocin were redistributed and cofilin was de-phosphorylated. Cdc42 is necessary for the maintenance of podocyte structure and function, but Rac1 is entirely dispensable in physiologic steady state. However, Rac1 has either beneficial or deleterious effects depending on the context of podocyte impairment. Thus, our study highlights the divergent roles of Rac1 and Cdc42 function in podocyte maintenance and injury.

Functions of the podocyte proteins nephrin and Neph3 and the transcriptional regulation of their genes

Nephrin and Neph-family proteins [Neph1-3 (nephrin-like 1-3)] belong to the immunoglobulin superfamily of cell-adhesion receptors and are expressed in the glomerular podocytes. Both nephrin and Neph-family members function in cell adhesion and signalling, and thus regulate the structure and function of podocytes and maintain normal glomerular ultrafiltration. The expression of nephrin and Neph3 is altered in human proteinuric diseases emphasizing the importance of studying the transcriptional regulation of the nephrin and Neph3 genes NPHS1 (nephrosis 1, congenital, Finnish type) and KIRREL2 (kin of IRRE-like 2) respectively. The nephrin and Neph3 genes form a bidirectional gene pair, and they share transcriptional regulatory mechanisms. In the present review, we summarize the current knowledge of the functions of nephrin and Neph-family proteins and transcription factors and agents that control nephrin and Neph3 gene expression.

Podocyte Effacement Closely Links to suPAR Levels at Time of Posttransplantation Focal Segmental Glomerulosclerosis Occurrence and Improves With Therapy

Focal segmental glomerulosclerosis (FSGS) recurs after kidney transplantation in more than 30% of cases and can lead to allograft loss. Serum soluble urokinase-type plasminogen activator receptor (suPAR) is implicated in the pathogenesis of native and recurrent FSGS. We conducted a retrospective study of 25 adults with posttransplantation FSGS. We investigated the relationship between suPAR levels and podocyte changes and the impact of therapy on podocyte structure. We assessed response to therapy by improvement in proteinuria, allograft function, and resolution of histologic changes. A median (interquartile range) of 15 (10-23) plasmapheresis sessions was administered; 13 of the subjects also received rituximab. Median pretreatment suPAR levels were higher among those with severe (≥75%) versus those with mild (≤25%) podocyte foot process effacement (13,030 vs. 4806 pg/mL; P=0.02). Overall, mean±SD of proteinuria improved from 5.1±3.8 to 2.1±2.8 mg/dL (P=0.003), mean podocyte effacement decreased from 57%±33% to 22%±22% (P=0.0001), estimated glomerular filtration rates increased from median (interquartile range) of 32.9 (20.6-44.2) to 39.3 (28.8-63.4; P<0.0001), and suPAR levels decreased from a median of 6.781 to 4.129 pg/mL (P=0.02) with therapy. Podocyte effacement is the first pathologic manifestation of FSGS after transplantation. The degree of podocyte effacement correlates with suPAR levels at time of diagnosis. Response to therapy results in significant reduction of suPAR levels and complete or significant improvement of podocyte effacement.

LMX1B is Essential for the Maintenance of Differentiated Podocytes in Adult Kidneys

Mutations of the LMX1B gene cause nail-patella syndrome, a rare autosomal-dominant disorder affecting the development of the limbs, eyes, brain, and kidneys. The characterization of conventional Lmx1b knockout mice has shown that LMX1B regulates the development of podocyte foot processes and slit diaphragms, but studies using podocyte-specific Lmx1b knockout mice have yielded conflicting results regarding the importance of LMX1B for maintaining podocyte structures. In order to address this question, we generated inducible podocyte-specific Lmx1b knockout mice. One week of Lmx1b inactivation in adult mice resulted in proteinuria with only minimal foot process effacement. Notably, expression levels of slit diaphragm and basement membrane proteins remained stable at this time point, and basement membrane charge properties also did not change, suggesting that alternative mechanisms mediate the development of proteinuria in these mice. Cell biological and biophysical experiments with primary podocytes isolated after 1 week of Lmx1b inactivation indicated dysregulation of actin cytoskeleton organization, and time-resolved DNA microarray analysis identified the genes encoding actin cytoskeleton-associated proteins, including Abra and Arl4c, as putative LMX1B targets. Chromatin immunoprecipitation experiments in conditionally immortalized human podocytes and gel shift assays showed that LMX1B recognizes AT-rich binding sites (FLAT elements) in the promoter regions of ABRA and ARL4C, and knockdown experiments in zebrafish support a model in which LMX1B and ABRA act in a common pathway during pronephros development. Our report establishes the importance of LMX1B in fully differentiated podocytes and argues that LMX1B is essential for the maintenance of an appropriately structured actin cytoskeleton in podocytes.

SIRPα signaling regulates podocyte structure and function

Signal-regulatory protein-α (SIRPα) is a transmembrane protein that contains tyrosine phosphorylation sites in its cytoplasmic region; two tyrosine phosphatases, SHP-1 and SHP-2, bind to these sites in a phosphorylation-dependent manner and transduce multiple intracellular signals. Recently, SIRPα was identified as one of the major tyrosine-phosphorylated proteins in the glomeruli and found to be expressed in podocytes. In the present study, we examined the role of SIRPα expression in podocytes using knockin mice (C57BL/6 background) expressing mutant SIRPα that lacks a cytoplasmic region (SIRPα-mutant mice). Light microscopic examination revealed no apparent morphological abnormalities in the kidneys of the SIRPα-mutant mice. On the other hand, electron microscopic examination revealed abnormal podocytes with irregular major processes and wider and flattened foot processes in the SIRPα-mutant mice compared with their wild-type counterparts. Significantly impaired renal functions and slight albuminuria were demonstrated in the SIRPα-mutant mice. In addition, adriamycin injection induced massive albuminuria together with focal glomerulosclerosis in the SIRPα-mutant mice, while their wild-type counterparts were resistant to adriamycin-induced nephropathy. These data demonstrate that SIRPα is involved in the regulation of podocyte structure and function as a filtration barrier under both physiological and pathological conditions.

Angiotensin II Contributes to Diabetic Renal Dysfunction in Rodents and Humans via Notch1/Snail Pathway

In nondiabetic rat models of renal disease, angiotensin II (Ang II) perpetuates podocyte injury and promotes progression to end-stage kidney disease. Herein, we wanted to explore the role of Ang II in diabetic nephropathy by a translational approach spanning from in vitro to in vivo rat and human studies, and to dissect the intracellular pathways involved. In isolated perfused rat kidneys and in cultured human podocytes, Ang II down-regulated nephrin expression via Notch1 activation and nuclear translocation of Snail. Hairy enhancer of split-1 was a Notch1-downstream gene effector that activated Snail in cultured podocytes. In vitro changes of the Snail/nephrin axis were similar to those in renal biopsy specimens of Zucker diabetic fatty rats and patients with advanced diabetic nephropathy, and were normalized by pharmacological inhibition of the renin-angiotensin system. Collectively, the present studies provide evidence that Ang II plays a relevant role in perpetuating glomerular injury in experimental and human diabetic nephropathy via persistent activation of Notch1 and Snail signaling in podocytes, eventually resulting in down-regulation of nephrin expression, the integrity of which is crucial for the glomerular filtration barrier.

Glomerular Filtration Barrier Assembly: An insight

A glomerulus is the network of capillaries that resides in the Bowman's capsule that functions as a filtration unit of kidney. The glomerular function ensures that essential plasma proteins are retained in blood and the filtrate is passed on as urine. The glomerular filtration assembly is composed of three main cellular barriers that are critical for the ultrafiltration process, the fenestrated endothelium, glomerular basement membrane and highly specialized podocytes. The podocytes along with their specialized junctions "slit diaphragm" form the basic backbone of this filtration assembly. The presence of high amounts of protein in urine a condition commonly referred as proteinuria indicates a defective glomerular filtration barrier. Various glomerular disorders including Nephrotic syndrome are characterized by significant alteration in the structure of podocytes that is associated with prolonged increase in the glomerular permeability leading to heavy proteinuria. Recent identification of proteins that are specifically localized at the slit diaphragm whose mutations and knockouts are known to result in loss of renal function has significantly advanced our understanding of the molecular makeup of this filtration assembly. The present review is an effort to summarize the recent developments in this field and highlight our understanding of the glomerular filtration barrier assembly.

Celecoxib modifies glomerular basement membrane, mesangium and podocytes in OVE26 mice, but ibuprofen is more detrimental

The role of COXs/PGs (cyclo-oxygenases/prostaglandins) in diabetic kidneys remains unclear. NSAIDs (non-steroidal anti-inflammatory drugs) that inhibit COXs/PGs are known for their renal toxicity, and COX-2 inhibitors worsen cardiovascular outcomes in susceptible individuals. Given the renal controversies concerning COX-2 inhibitors, we compared the effect of chronic NSAIDs (non-selective, ibuprofen; COX-2-selective, celecoxib) on diabetic kidneys in OVE26 mice from 8 weeks of age. Systolic BPs (blood pressures) were increased by NSAIDs in diabetic mice at 20 weeks, but were unchanged at 32 weeks. Although NSAIDs further increased diabetic kidney/body weight ratios, they did not affect albuminuria. Mesangial matrix was increased 2-fold by celecoxib but not ibuprofen. Electron microscopy revealed that NSAIDs reduced GBM (glomerular basement membrane) thickness and slit pore diameters. Although diabetics had increased glomerular diameters and reduced foot process densities, these were unaltered by NSAIDs. Celecoxib does not exacerbate the diabetic state, but PG inhibition may contribute to disease progression by modifying the GBM, mesangial area and podocyte structure in OVE26 mice. Despite these findings, celecoxib remains safer than a similar dose of ibuprofen. The present study substantiates the need to more closely consider selective COX-2 inhibitors such as celecoxib as alternatives to non-selective NSAIDs for therapeutic management in a setting of chronic kidney disease.

MVps34 Deletion in Podocytes Causes Glomerulosclerosis by Disrupting Intracellular Vesicle Trafficking

Recent studies have suggested that autophagy is a key mechanism in maintaining the integrity of podocytes. The mammalian homologue of yeast vacuolar protein sorting defective 34 (mVps34) has been implicated in the regulation of autophagy, but its role in podocytes is unknown. We generated a line of podocyte-specific mVps34-knockout (mVps34(pdKO)) mice, which were born at Mendelian ratios. These mice appeared grossly normal at 2 weeks of age but exhibited growth retardation and were significantly smaller than control mice by 6 weeks of age, with no difference in ratios of kidney to body weight. mVps34(pdKO) mice developed significant proteinuria by 3 weeks of age, developed severe kidney lesions by 5-6 weeks of age, and died before 9 weeks of age. There was striking podocyte vacuolization and proteinaceous casts, with marked glomerulosclerosis and interstitial fibrosis by 6 weeks of age. Electron microscopy revealed numerous enlarged vacuoles and increased autophagosomes in the podocytes, with complete foot process effacement and irregular and thickened glomerular basement membranes. Immunoblotting of isolated glomerular lysates revealed markedly elevated markers specific for lysosomes (LAMP1 and LAMP2) and autophagosomes (LC3-II/I). Immunofluorescence staining confirmed that the enlarged vacuoles originated from lysosomes. In conclusion, these results demonstrate an indispensable role for mVps34 in the trafficking of intracellular vesicles to protect the normal cellular metabolism, structure, and function of podocytes.

Differential expressions of miRNAs in kidney in puromycin aminonucleoside nephropathy model and intervened effects of Leizhi capsule

To observe the differential expression characteristics of microRNAs (miRNAs) in renal tissues in puromycin aminonucleoside (PAN) nephritic model, and its relationship with key structural molecules of slid diaphragm (SD) nephrin and podocin and expression of skeleton protein synaptopodin; and to explore the in vivo mechanisms of Leizhi capsule (LZC) for ameliorating the expressions of nephrin, podocin and synaptopodin and reducing proteins by regulating the modal rat renal tissues miRNAs. Fifty male Wistar rats were randomly divided into five groups: the control group (A), the model group (B), the LZC-treated group (C), the multi-glycoside of Tripterygium wilfordii (GTW)-treated group (D) and the valsartan-treated group (E). Apart from group A, all of rats in the remaining groups are injected with PAN (100 mg x kg(-1)) through jugular veins to establish the PAN nephropathy model. On the 2nd day after PAN nephropathy model was established, group C was orally administered with LZC (5 mL x kg(-1) x d(-1)) in group C, group DGTW (10 mL x kg(-1) x d(-1)), and E group valsartan (7.5 mL x kg(-1) x d(-1)), while groups A and B were intervened with physiological saline, for 10 days. Body weight and 24 h urinary protein ration (Upro) in all rats were measured at day 0, 3, and 9. All rats were sacrificed at day 11 after the establishment of the model, and their blood and renal tissues were collected to observe such blood biochemical indicators including albumin (Alb), serum creatinine (Scr), blood urea nitrogen (BUN) and glomerular ultrastructure (podocyte foot process form) and expressions of dicer enzyme, nephrin, podocin and synaptopodin in renal tissues. Meanwhile, the differential expressional characteristics of miRNAs in renal cortex were analyzed by biochip assay. Additionally, the differential expressional volumes of rno-miR-23a, rno-miR-300-3p, rno-miR-24 and rno-miR-30c were measured by real-time PCR. Proteinuria, renal dysfunction, hypoproteinemia and podocyte foot process fusion were investigated in model rats induced by PAN. In renal tissues of PAN nephropathy model rats, dicer enzyme affected the expressions of nephrin, podocin and synaptopodin in podocytes, up-regulated the expressions of rno-miR-23a and rno-miR-300-3p, and down-regulated the expressions of rno-miR-24 and rno-miR-30c. The miRNAs with differential expressions included rno-miR-24, rno-miR-30c, rno-miR-23a and rno-miR-300-3p. LZC could improve the general state, proteinuria, serum BUN and podocyte foot process fusion of PAN nephropathy model rats, reduced the expressions of dicer enzyme, increased the expressions of nephrin, podocin and synaptopodin in podocytes, weakened the up-regulated rno-miR-23a and rno-miR-300-3p, and strengthened the down-regulated rno-miR-24 and rno-miR-30c in renal tissues. PAN in vivo impacts the expressions of miRNAs in renal tissues, intervenes the expressions of nephrin, podocin and synaptopodin in podocytes, damages podocyte structures and functions and generates proteinuria by means of differential expression of dicer enayme/miRNAs. LZC can reduce proteinuria in PAN nephropathy model rats. Its mechanism may intervene dicer enayme/miRNAs differential expression, regulate nephrin, podocin and synaptopodin in podocytes and improve podocyte structures and functions.

Roles of adaptor proteins in podocyte biology

Podocytes covering the glomerular basement membrane over the glomerular capillary consist of three morphologically and functionally different segments, the cell body, major processes and extending finger-like foot processes (FPs). The FPs of neighboring podocytes are connected by a continuous adherent junction structure named the slit diaphragm (SD). The extracellular SD is linked to the intracellular, a highly dynamic, cytoskeleton through adaptor proteins. These adaptor proteins, such as CD2-associated protein, zonula occludens 1, β-catenin, Nck and p130Cas, located at the intracellular SD insertion area near lipid rafts, have important structural and functional roles. Adaptor proteins in podocytes play important roles as a structural component of the podocyte structure, linking the SD to the cytoskeletal structure and as a signaling platform sending signals from the SD to the actin cytoskeleton. This review discusses the roles of adaptor proteins in the podocyte cytoskeletal structure and signaling from the SD to the actin cytoskeleton.

Fluid flow shear stress upregulates prostanoid receptor EP2 but not EP4 in murine podocytes

Podocytes in the glomerular filtration barrier regulate the passage of plasma proteins into urine. Capillary pressure and ultrafiltration impact the structure and function of podocytes. The mechanism of podocyte injury by fluid flow shear stress (FFSS) from hyperfiltration in chronic kidney disease (CKD) is not completely understood. Recently, we demonstrated increased synthesis of prostaglandin E2 in podocytes exposed to FFSS. Here, we determine the effect of FFSS on prostanoid receptors EP1–EP4 in cultured podocytes and in Os/+ mouse kidney, a model of hyperfiltration. Results of RT-PCR, qRT-PCR, immunoblotting and immunofluorescence studies indicate that cultured podocytes express EP1, EP2 and EP4 but not EP3. FFSS resulted in upregulated expression of only EP2 in podocytes. Kidney immunostaining showed significantly increased expression of EP2 in Os/+ mice compared with littermate controls. These novel results suggest that EP2 may be responsible for mediating podocyte injury from hyperfiltration-induced augmented FFSS in CKD.

Light Microscopic Visualization of Podocyte Ultrastructure Demonstrates Oscillating Glomerular Contractions

Podocytes, the visceral epithelial cells of the kidney glomerulus, elaborate primary and interdigitating secondary extensions to enwrap the glomerular capillaries. A hallmark of podocyte injury is the loss of unique ultrastructure and simplification of the cell shape, called foot process effacement, which is a classic feature of proteinuric kidney disease. Although several key pathways have been identified that control cytoskeletal regulation, actin dynamics, and polarity signaling, studies into the dynamic regulation of the podocyte structure have been hampered by the fact that ultrastructural analyses require electron microscopic imaging of fixed tissue. We developed a new technique that allows for visualization of podocyte foot processes using confocal laser scanning microscopy. The combination of inducible and mosaic expression of membrane-tagged fluorescent proteins in a small subset of podocytes enabled us to acquire light microscopic images of podocyte foot processes in unprecedented detail, even in living podocytes of freshly isolated glomeruli. Moreover, this technique visualized oscillatory glomerular contractions and confirmed the morphometric evaluations obtained in static electron microscopic images of podocyte processes. These data suggest that the new technique will provide an extremely powerful tool for studying the dynamics of podocyte ultrastructure.