The actin cytoskeleton of kidney podocytes is a direct target of the antiproteinuric effect of cyclosporine A

Impairment of podocyte function by diphtheria toxin--a new reversible proteinuria model in mice

Diphtheria toxin (DTx) receptor (DTR)-mediated conditional cell ablation in transgenic mice is a powerful tool to analyze cell function in vivo. Transgenic mice with cell-specific expression of the human DTR have been developed that allow conditional depletion of these cells in vivo through administration of the toxin. We have performed a careful analysis of mice after DTx injection and found an unexpected side effect. Treatment of wild-type C57BL/6 mice with DTx leads to a marked transient and completely reversible proteinuria, as a consequence of podocyte dysfunction that is morphologically characterized by foot process fusion and detachment from the glomerular basal membrane. In vitro analysis displayed that DTx-treated podocytes show diminished attachment to basal membrane proteins. Five to 9 days after DTx application the mice recover completely. Glomerular proteinuria is a hallmark of glomerular disease due to dysfunction of the filtration barrier. Rodents have been extensively used experimentally to better define the mechanisms of disease induction and progression. However, nongenetic mouse models of proteinuric glomerular damage are limited and display various shortcomings. We suggest DTx-induced transient kidney dysfunction as a new reversible model of experimental podocyte injury, which could be used as an additional approach to complement studies in human.

Podocyte biology and pathogenesis of kidney disease

Proteinuric chronic kidney disease (CKD), once a rare affliction believed to be mainly caused by genetic mutations, has become a global pandemic that severely diminishes the quality of life for millions. Despite the changing face of CKD, treatment options and resources remain woefully antiquated and have failed to arrest or reverse the effects of kidney-related diseases. Histological and genetic data strongly implicate one promising target: the podocyte. Podocytes are terminally differentiated cells of the kidney glomerulus that are essential for the integrity of the kidney filter. Their function is primarily based on their intricate structure, which includes foot processes. Loss of these actin-driven membrane extensions is tightly connected to the presence of protein in the urine, podocyte loss, development of CKD, and ultimately renal failure.

Circulating suPAR in two cohorts of primary FSGS

Overexpression of soluble urokinase receptor (suPAR) causes pathology in animal models similar to primary FSGS, and one recent study demonstrated elevated levels of serum suPAR in patients with the disease. Here, we analyzed circulating suPAR levels in two cohorts of children and adults with biopsy-proven primary FSGS: 70 patients from the North America-based FSGS clinical trial (CT) and 94 patients from PodoNet, the Europe-based consortium studying steroid-resistant nephrotic syndrome. Circulating suPAR levels were elevated in 84.3% and 55.3% of patients with FSGS patients in the CT and PodoNet cohorts, respectively, compared with 6% of controls (P<0.0001); inflammation did not account for this difference. Multiple regression analysis suggested that lower suPAR levels associated with higher estimated GFR, male sex, and treatment with mycophenolate mofetil. In the CT cohort, there was a positive association between the relative reduction of suPAR after 26 weeks of treatment and reduction of proteinuria, with higher odds for complete remission (P=0.04). In the PodoNet cohort, patients with an NPHS2 mutation had higher suPAR levels than those without a mutation. In conclusion, suPAR levels are elevated in geographically and ethnically diverse patients with FSGS and do not reflect a nonspecific proinflammatory milieu. The associations between a change in circulating suPAR with different therapeutic regimens and with remission support the role of suPAR in the pathogenesis of FSGS.

Pretransplantation combined therapy with plasmapheresis and rituximab in a second living-related kidney transplant pediatric recipient with a very high risk for focal segmental glomerulosclerosis recurrence

Prophylactic PP can provide some protection against post-transplantation recurrences of FSGS, but it cannot prevent recurrences in all cases. Therefore, new preventive therapies are needed. We report on a 7.9-yr-old girl treated with pretransplantation prophylactic combined therapy consisting of four sessions of PP and one dose of rituximab before a second living-related KTX. The patient had a very high risk of post-transplantation FSGS recurrence because this had occurred after the first KTX. During the 36 months since the second transplantation, she has had no evidence of proteinuria or significant infectious complications. Although our experience is too preliminary to draw any generalizable conclusions, pretransplantation combined therapy with PP and rituximab might be a possible option for the prevention of FSGS recurrence in very high-risk recipients undergoing living-donor KTXs.

Permeability factors in nephrotic syndrome and focal segmental glomerulosclerosis

Circulating permeability factors have been identified in the plasma of patients with focal segmental glomerulosclerosis (FSGS). Post-transplant recurrence of proteinuria, improvement of proteinuria after treatment with plasmapheresis, and induction of proteinuria in experimental animals by plasma fractions each provide evidence for such plasma factors. Advanced proteomic methods have identified candidate molecules in recurrent FSGS. We have proposed cardiotrophin-like cytokine-1 as an active factor in FSGS. Another potential permeability factor in FSGS is soluble urokinase receptor. In our studies, in vitro plasma permeability activity is blocked by substances that may decrease active molecules or block their effects. We have shown that the simple sugar galactose blocks the effect of FSGS serum in vitro and decreases permeability activity when administered to patients. Since the identities of permeability factors and their mechanisms of action are not well defined, treatment of FSGS is empiric. Corticosteroids are the most common agents for initial treatment. Calcineurin inhibitors, such as cyclosporine A, and tacrolimus and immunosuppressive medications, including mycophenylate, induce remission is some patients with steroid-resistant or -dependent nephrotic syndrome. Therapies that diminish proteinuria and slow progression in FSGS as well as other conditions include renin-angiotensin blockade, blood pressure lowering and plasma lipid control. Use of findings from in vitro studies, coupled with definitive identification of pathogenic molecules, may lead to new treatments to arrest FSGS progression and prevent recurrence after transplantation.

Second-line options for refractory steroid-sensitive and -resistant nephrotic syndrome

Although initially, many children with idiopathic nephrotic syndrome respond to steroid therapy, a repeated course for patients with relapses often causes significant steroid toxicity. Patients with frequent relapses or steroid dependency thus require alternative treatment, and so far, cyclophosphamide or levamisole have been regarded as first-choice options, although the latter is no longer available in many countries. Data are accumulating that mycophenolic acid may be an alternative for these patients. Calcineurin inhibitors (cyclosporine A or tacrolimus) are usually effective and are often used after cytotoxic treatment, but long-term treatment is necessary, raising concerns regarding the accumulation of side effects. Still, some patients show a tendency to relapse even on this maintenance regimen and some even have a refractory course that creates a medical dilemma. For this situation, recent data have demonstrated an effect of monoclonal antibodies directed to B cells - rituximab, a drug that may also prove to be a therapeutic option in less complicated cases. Patients that do not respond to initial steroid treatment need genetic testing and a renal biopsy, since focal segmental glomerulosclerosis may be present. Treatment options include pulse methylprednisolone, often in addition to calcineurin inhibitors (mainly cyclosporine but also, recently, tacrolimus). Cyctotoxic treatment, especially intravenous cyclophosphamide, has been found to be effective in steroid-resistant nephrotic syndrome by some studies but is inferior to calcineurin inhibitors. In addition, mycophenolic acid and rituximab have been used in children with primary focal segmental glomerulosclerosis; however, response seems to be inferior in comparison with patients with steroid-sensitive nephrotic syndrome. Taken together, idiopathic nephrotic syndrome, including steroid-sensitive as well as steroid-resistant patients, is a potentially serious disorder. Although much progress has been made in recent years and a wide arsenal of immunological interventions is available, some patients have a treatment refractory course. Prospective studies or at least standardization of treatment for complicated cases is urgently needed.

Pharmacokinetics of cyclosporin--a microemulsion in children with idiopathic nephrotic syndrome

OBJECTIVE

We present a prospective study of a microemulsion of cyclosporin to treat idiopathic nephrotic syndrome in ten children with normal renal function who presented cyclosporin trough levels between 50 and 150 ng/ml and achieved complete remission with cyclosporin. To compare the pharmacokinetic parameters of cyclosporin in idiopathic nephrotic syndrome during remission and relapse of the nephrotic state.

METHOD

The pharmacokinetic profile of cyclosporin was evaluated with the 12-hour area under the time-concentration curve (auc0-12) using seven time-point samples. This procedure was performed on each patient during remission and relapse with the same cyclosporin dose in mg/kg/day. The 12-hour area under the time-concentration curve was calculated using the trapezoidal rule. All of the pharmacokinetic parameters and the resumed 4-hour area under the time-concentration curve were correlated with the 12-hour area under the time-concentration curve. ClinicalTrials.gov: NCT01616446.

RESULTS

There were no significant differences in any parameters of the pharmacokinetic of cyclosporin during remission and relapse, even when the data were normalized by dose. The best correlation with the 12-hour area under the time-concentration curve was the 4-hour area under the time-concentration curve on remission and relapse of the disease, followed by the 2-hour level after cyclosporin (c2) dosing in both disease states.

CONCLUSIONS

These data indicate that the same parameters used for cyclosporin therapeutic monitoring estimated during the nephrotic state can also be used during remission. Larger controlled studies are needed to confirm these findings.

The calcineurin-NFAT pathway allows for urokinase receptor-mediated beta3 integrin signaling to cause podocyte injury

Circulating and podocyte-bound urokinase receptor (uPAR) is a mediator of podocyte injury, proteinuria, and focal segmental glomerulosclerosis (FSGS) allowing pathological activation of the uPAR-β3 integrin signaling axis. Clinically, calcineurin inhibitors (e.g., cyclosporine A, CsA) are known to suppress T cells, yet are also being used to reduce proteinuria in FSGS, suggesting the possibility of signal cross talk between uPAR and calcineurin. Calcineurin is known to facilitate the nuclear translocation of the nuclear factor of activated T cells (NFAT). Accordingly, in vivo conditional NFATc1 activation in podocytes leads to proteinuria in mice, yet the downstream targets of NFAT remain unclear. Here, we show that inducible podocyte-specific expression of constitutively active NFATc1 increased podocyte uPAR expression by binding to the Plaur gene promoter (encoding uPAR) in chromatin immunoprecipitation assays. Pathological uPAR signals in podocytes are independent of T cells and affect cell motility via activation, but not expression, changes of the β3 integrin and can be blocked by CsA, NFAT-siRNA, or the cell-permeable NFAT inhibitor (11R-VIVIT) using rodent models of glomerular disease (LPS; 5/6 nephrectomized rats). Taken together, these findings identify podocyte uPAR as a downstream target of NFAT and provide further insights into the pathogenesis of FSGS.

B7-1 expression regulates the hypoxia-driven cytoskeleton rearrangement in glomerular podocytes

Chronic hypoxia has been recognized as a common mechanism driving the progression of many glomerular diseases. Glomerular cells, although susceptible to hypoxic injuries, are less studied to unravel the hypoxia-related influences. In the present study, we showed that both lipopolysaccharide (LPS) and hypoxia induced B7-1 and hypoxia-inducible factor (HIF)-1α expression in podocytes. B7-1, an essential player in the regulation of podocyte stress fibers, interacted directly with the NH(2)-terminal oxygenation domain of HIF-1α protein and, therefore, might interfere with the HIF-related oxidative events. The suggestion was supported by the changes in the expression of inducible nitric oxide synthase and nitric oxide. The orderly arranged stress fibers in differentiated podocytes were disrupted by either LPS or hypoxic stimulation, and the disruption could be rescued if they were brought back to normal oxygen tension. Cell motility increased with the stimulation by LPS and hypoxia, most probably mediated by the induction of B7-1 and HIF-1α, respectively. We generated a B7-1 knockdown podocyte cell line using the lentiviral small interfering RNA system. The LPS- and hypoxia-induced stress fiber disruption was largely prevented in the B7-1 knockdown podocytes. The increased cell motility by LPS and hypoxia stimulations was also ameliorated in the B7-knockdown podocytes. In summary, we found that both B7-1 and HIF were upregulated by LPS and hypoxic stimulations in podocytes and they interacted with each other. Hypoxia disrupted the abundant stress fibers and increased cell motility. These hypoxia-induced changes were prevented in B7-knockdown podocytes, and they highlighted the importance of B7-1 expression in the hypoxia-related podocyte injuries.

Treatment of primary FSGS in adults

Over the last 20 years, primary FSGS has emerged as one of the leading causes of idiopathic nephrotic syndrome in adults, particularly among African Americans. In nephrotic patients, progression to ESRD often occurs over the course of 5-10 years, whereas non-nephrotic patients and those entering a remission have an extremely favorable prognosis. As a result, it is in patients who remain persistently nephrotic despite conservative therapy that a more aggressive therapeutic approach is taken. Primary FSGS was once considered an entity nonresponsive to prednisone or immunosuppressive agents, but it has become apparent over the last 20 years that a substantial portion of nephrotic adults with primary FSGS do respond to treatment with a significantly improved prognosis. The recent histologic classification proposed for FSGS has provided additional insights into the prognosis and response to therapy. This article reviews the current knowledge regarding the presentation, prognosis, and therapeutic approach in adults with primary FSGS.

Low- and high-molecular-weight urinary proteins as predictors of response to rituximab in patients with membranous nephropathy: a prospective study

BACKGROUND

Selective urinary biomarkers have been considered superior to total proteinuria in predicting response to treatment and outcome in patients with membranous nephropathy (MN).

METHODS

We prospectively tested whether urinary (U) excretion of retinol-binding protein (RBP), α1-microglobulin (α1M), albumin, immunoglobulin IgG and IgM and/or anti-phospholipase 2 receptor (PLA(2)R) levels could predict response to rituximab (RTX) therapy better than standard measures in MN. We also correlated changes in antibodies to PLA(2)R with these urinary biomarkers.

RESULTS

Twenty patients with MN and proteinuria (P) >5 g/24 h received RTX (375 mg/m(2) × 4) and at 12 months, 1 patient was in complete remission (CR), 9 were in partial remission (PR), 5 had a limited response (LR) and 4 were non-responders (NR). At 24 months, CR occurred in 4, PR in 12, LR in 1, NR in 2 and 1 patient relapsed. By simple linear regression analysis, UIgG at baseline (mg/24 h) was a significant predictor of change in proteinuria at 12 months (Δ urinary protein) (P = 0.04). In addition, fractional excretion (FE) of IgG, urinary alpha 1 microglobulin (Uα1M) (mg/24 h) and URBP (μg/24 h) were also predictors of response (P = 0.05, 0.04, and 0.03, respectively). On the other hand, UIgM, FEIgM, albumin and FE albumin did not predict response (P = 0.10, 0.27, 0.22 and 0.20, respectively). However, when results were analyzed in relation to proteinuria at 24 months, none of the U markers that predicted response at 12 m could predict response at 24 m (P = 0.55, 0.42, 0.29 and 0.20). Decline in anti-PLA(2)R levels was associated with and often preceded urinary biomarker response but positivity at baseline was not a predictor of proteinuria response.

CONCLUSIONS

The results suggest that in patients with MN, quantification of low-, medium- and high-molecular-weight urinary proteins may be associated with rate of response to RTX, but do not correlate with longer term outcomes.

The KDIGO practice guideline on glomerulonephritis: reading between the (guide)lines--application to the individual patient

The KDIGO guideline for glomerulonephritis is designed to assist health-care providers in treating patients with glomerular diseases. A guideline is not a set of rules but is intended to allow the practitioner to make an informed decision based on the available evidence. Due to its general nature and the variability of strength of the available studies, it is often difficult to directly apply a guideline to the care of an individual patient. This commonly relates to the limited generalizability of the evidence, i.e., does not cover every clinical scenario. To underscore this point, we have introduced within the context of the glomerulonephritis guideline cases with specific features to illustrate the constant need for clinical judgment. These vignettes are intended to demonstrate how the best treatment plans should be individualized and take into account patient preference and clinical acumen, as well as the best available evidence.

Pilot 24 month study to compare mycophenolate mofetil and tacrolimus in the treatment of membranous lupus nephritis with nephrotic syndrome

AIM

This pilot study compared mycophenolate mofetil (MMF) and tacrolimus (Tac) in the treatment of severe membranous lupus nephritis (MLN).

METHOD

This was a 24 month prospective, randomized, open-label multi-centre exploratory study on Chinese patients with biopsy-proven pure Class V MLN with nephrotic syndrome. Patients were randomized to treatment with either MMF or Tac, both in combination with prednisolone and the efficacy and tolerability outcomes were examined.

RESULTS

Sixteen patients were included, seven in the MMF and nine in the Tac treatment arm. At 24 months the complete response, partial response and overall response rates were 57.1% vs. 11.1% (P = 0.049), 14.3% vs. 44.4% (P = 0.197) and 71.4% vs. 55.6% (P = 0.515) in the MMF and Tac groups, respectively. The two groups had similar reduction of proteinuria and longitudinal profiles of serum albumin and creatinine levels. Serum creatinine remained stable in both groups, except in two patients who had a transient increase associated with high Tac blood levels. Adverse events in the MMF group included herpes zoster in one patient and reversible leucopenia in another, while in the Tac group four patients had severe infections and one developed new onset diabetes. No relapse occurred during the study period.

CONCLUSION

Both MMF and Tac when combined with corticosteroids are effective treatment options for severe MLN.

Physiopathology of idiopathic nephrotic syndrome: lessons from glucocorticoids and epigenetic perspectives

Idiopathic nephrotic syndrome (INS) has been studied for decades in attempt to understand the physiopathological mechanisms explaining the disease. It is recognized as a multifactorial disease, with immunological components targeting kidney functions. Many hypotheses have been discussed or tested, including the role of a circulating factor, polymorphisms of genes implicated in lymphocyte maturation and differentiation, and DNA epigenetic modifications. In the present review, the data supporting these different (and probably combinatorial) hypotheses have been reviewed in order to identify and discuss the possible pathways implicated in the physiopathology of INS.

Educational paper: the podocytopathies

In the recent past, hereditary podocytopathies have increasingly been recognized to be involved in the development of steroid-resistant nephrotic syndrome (SRNS). Mutations in podocyte genes substantially alter the development and structural architecture of the podocyte including its interdigitating foot processes. These constitute the basis of the slit diaphragm which is an essential part of the glomerular filtration barrier. Depending on the affected protein, the clinical course is variable with respect to onset and severity of the disease as well as treatment options. In general, hereditary podocytopathies are associated with a poorer renal outcome than the non-genetic variants. In addition, they require a different approach with respect to the applied therapeutic strategies as most patients do not respond to immunosuppressive agents. Therefore, genetic testing of podocyte genes should be considered as a routine diagnostic tool for patients with SRNS because the identification of a genetic origin has a direct implication on clinical course, renal outcome, and genetic counseling. In this educational paper, we will give an overview over the podocyte genes identified so far to be involved into the pathophysiology of hereditary podocytopathies.

Monomeric 14-3-3ζ has a chaperone-like activity and is stabilized by phosphorylated HspB6

Members of the 14-3-3 eukaryotic protein family predominantly function as dimers. The dimeric form can be converted into monomers upon phosphorylation of Ser⁵⁸ located at the subunit interface. Monomers are less stable than dimers and have been considered to be either less active or even inactive during binding and regulation of phosphorylated client proteins. However, like dimers, monomers contain the phosphoserine-binding site and therefore can retain some functions of the dimeric 14-3-3. Furthermore, 14-3-3 monomers may possess additional functional roles owing to their exposed intersubunit surfaces. Previously we have found that the monomeric mutant of 14-3-3ζ (14-3-3ζ_m), like the wild type protein, is able to bind phosphorylated small heat shock protein HspB6 (pHspB6), which is involved in the regulation of smooth muscle contraction and cardioprotection. Here we report characterization of the 14-3-3ζ_m/pHspB6 complex by biophysical and biochemical techniques. We find that formation of the complex retards proteolytic degradation and increases thermal stability of the monomeric 14-3-3, indicating that interaction with phosphorylated targets could be a general mechanism of 14-3-3 monomers stabilization. Furthermore, by using myosin subfragment 1 (S1) as a model substrate we find that the monomer has significantly higher chaperone-like activity than either the dimeric 14-3-3ζ protein or even HspB6 itself. These observations indicate that 14-3-3ζ and possibly other 14-3-3 isoforms may have additional functional roles conducted by the monomeric state.

Sustained activation of N-methyl-D-aspartate receptors in podoctyes leads to oxidative stress, mobilization of transient receptor potential canonical 6 channels, nuclear factor of activated T cells activation, and apoptotic cell death

Atypical N-methyl-D-aspartate (NMDA) receptors are expressed in podocytes. Sustained (≥24 h) application of 50 to100 μM NMDA to immortalized mouse podocytes evoked a marked increase in the production of reactive oxygen species(ROS) such as H₂O₂. This effect of NMDA was associated with increased cell-surface expression of p47(phox), a cytosolic regulatory subunit of the NADPH oxidase NOX2. NMDA-evoked generation of ROS drove an increase in steady-state surface expression of transient receptor potential canonical (TRPC) 6 channels, which was blocked by the NMDA antagonist dizocilpine(MK-801) and by a membrane-permeable scavenger of ROS. The effect of NMDA on TRPC6 was observed using cell surface biotinylation assays and also with whole-cell recordings made under conditions designed to facilitate detection of current through TRPC6. NMDA mobilization of TRPC6 channels was blocked by concurrent treatment with the NMDA antagonist MK-801 and by a membrane-permeable scavenger ofROS. Mobilization of TRPC6 was also evoked by L-homocysteic acid. NMDA treatment also increased nuclear localization of endogenous nuclear factor of activated T cells, which could be blocked by MK-801, by scavenging ROS, by the calcineurin inhibitor cyclosporine, and by the TRPC channel inhibitor 1-[2-(4-methoxyphenyl)-2-[3-(4-methoxyphenyl)propoxy]ethyl]imidazole (SKF-96365). NMDA treatment also evoked robust activation of Rho but not Rac,consistent with previous studies of downstream effectors of TRPC6 activation. Exposing cells to NMDA for 24 h reduced total and cell surface expression of the podocyte markers nephrin and podocin, but there was no loss of cells. With longer NMDA exposure (72 h), we observed loss of cells associated with nuclear fragmentation and increased expression of caspase-3, caspase-6, and Bax, suggesting an apoptotic process.

Podocyte-specific knockout of myosin 1e disrupts glomerular filtration

Myosin 1e (myo1e) is an actin-dependent molecular motor that plays an important role in kidney functions. Complete knockout of myo1e in mice and Myo1E mutations in humans are associated with nephrotic syndrome and focal segmental glomerulosclerosis. In this paper, we tested the hypothesis that myo1e is necessary for normal functions of glomerular visceral epithelial cells (podocytes) using podocyte-targeted knockout of myo1e. Myo1e was selectively knocked out in podocytes using Cre-mediated recombination controlled by the podocin promoter. Myo1e loss from podocytes resulted in proteinuria, podocyte foot process effacement, and glomerular basement membrane disorganization. Our findings indicate that myo1e expression in podocytes is necessary for normal glomerular filtration and that podocyte defects are likely to represent the primary pathway leading to glomerular disease associated with Myo1E mutations.

Is the antiproteinuric effect of cyclosporine a independent of its immunosuppressive function in T cells?

The antiproteinuric effect of cyclosporine A(CsA) has been believed to result from its immunosuppressive effect on the transcription factor NFAT in T cells. However, current evidences supporting this hypothesis are missing. A recent study showed that CsA has a direct antiproteinuric effect on podocytes, suggesting a novel non-immunosuppressive mechanism for CsA's antiproteinuric effect. Conditional NFATc1 activation in podoyctes per se is sufficient to induce proteinuria in mice, indicating that NFAT activation in podocytes is a critical pathogenic molecular event leading to podocyte injury and proteinuria. Meanwhile, evidence showed that TRPC6-mediated Ca(2+) influx stimulates NFAT-dependent TRPC6 expression. Altogether, these advances in podocyte research indicate that calcineurin-NFAT signal or calcineurin-synaptopodin axis has a direct proteinuric effect on podocytes which raises the possibility of developing specific antiproteinuric drugs that lack the unwanted effects of calcineurin or NFAT inhibition.

New players in the pathogenesis of focal segmental glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) is the most common primary glomerular disorder causing end-stage renal disease. Since the first description of this clinicopathological entity in the early 1930s, various studies have identified numerous underlying pathogenetic mechanisms. Nevertheless, FSGS is still a complex, only partially understood and in its classification sometimes confusing disease. A unifying pathophysiological concept has not been identified and might not even exist. However, research efforts of past decades identified FSGS as a podocytopathy with several podocyte molecules being key players in the development and the course of FSGS. Podocytes are crucially involved in the formation of the glomerular barrier and any assault on their delicate physiological balance and architecture can result in the development of proteinuria. The following review article will introduce most recent examples identifying novel players in the complex pathogenesis of FSGS.

Early treatment with glucocorticoids or cyclophosphamide retains the slit diaphragm proteins nephrin and podocin in experimental lupus nephritis

Renal podocytes and their slit diaphragms ensure the integrity of renal basement membrane and prevent urinary protein loss. We have previously reported that decreases of the podocyte slit diaphragm proteins nephrin and podocin represent early events in the podocytopathy of lupus nephritis (LN). We asked whether immunosuppressive agents such as glucocorticoids and cyclophosphamide may have direct effects on podocytes. We assessed in New Zealand Black/New Zealand White (NZB/W) F1 LN mice glomerular nephrin and podocin expression and localization by the use of Western blot and immunofluorescence; mRNA levels were measured by real-time polymerase chain reaction (PCR) and renal histology by light and electron microscopy. Early treatment with glucocorticoids and cyclophosphamide halted the histologic alterations associated with LN, preserving podocyte foot processes. Nephrin and podocin protein expression significantly increased in both glucocorticoid and cyclophosphamide groups as early as after three months of therapy. Real-time PCR revealed similar enhancement in nephrin and podocin mRNA levels after three to six months of treatment. This study documents that early treatment in experimental LN with glucocorticoids or cyclophosphamide preserves slit diaphragm proteins in podocytes and halts histological changes of the glomeruli, thus raising the possibility of a direct protective effect of these drugs on podocytes.

Emerging role of autophagy in kidney function, diseases and aging

Autophagy is a highly conserved process that degrades cellular long-lived proteins and organelles. Accumulating evidence indicates that autophagy plays a critical role in kidney maintenance, diseases and aging. Ischemic, toxic, immunological, and oxidative insults can cause an induction of autophagy in renal epithelial cells modifying the course of various kidney diseases. This review summarizes recent insights on the role of autophagy in kidney physiology and diseases alluding to possible novel intervention strategies for treating specific kidney disorders by modifying autophagy.

Calcineurin regulation of cytoskeleton organization: a new paradigm to analyse the effects of calcineurin inhibitors on the kidney

Calcineurin is a serine/threonine phosphatase originally involved in the immune response but is also known for its role as a central mediator in various non-immunological intracellular signals. The nuclear factor of activated T cell (NFAT) proteins are the most widely described substrates of calcineurin, but ongoing work has uncovered other substrates among which are the cytoskeleton organizing proteins (i.e. cofilin, synaptopodin, WAVE-1). Control over cytoskeletal proteins is of outmost interest because the phenotypic properties of cells are dependent on cytoskeleton architecture integrity, while rearrangements of the cytoskeleton are implicated in both physiological and pathological processes. Previous works investigating the role of calcineurin on the cytoskeleton have focused on neurite elongation, myocyte hypertrophic response and recently in kidney cells structure. Nuclear factor of activated T cell activation is expectedly identified in the signalling pathways for calcineurin-induced cytoskeleton organization, however new NFAT-independent pathways have also been uncovered. The aim of this review is to summarize the current knowledge on the effects of calcineurin on cytoskeletal proteins and related intracellular pathways. These newly described properties of calcineurin on cytoskeletal proteins may explain some of the beneficial or deleterious effects observed in kidney cells associated with the use of the calcineurin inhibitors, cyclosporine and tacrolimus.

Contribution of lysosomal cysteine proteases in cardiac and renal diseases

Cardiac and renal diseases (CRDs) are characterized by extensive remodeling of the extracellular matrix (ECM) architecture of the cardiorenal system. Among the many extracellular proteolytic enzymes present in cardiorenal cells and involved in ECM remodeling, members of the matrix metalloproteinase family and serine protease family have received the most attention. However, recent findings from laboratory and clinical studies have indicated that cysteine protease cathepsins also participate in pathogenesis of the heart and kidney. Deficiency and pharmacological inhibition of cathepsins have allowed their in vivo evaluation in the setting of pathological conditions. Furthermore, recent studies evaluating the feasibility of cathepsins as a diagnostic tool have suggested that the serum levels of cathepsins L, S and K and their endogenous inhibitor cystatin C have predictive value as biomarkers in patients with coronary artery disease and heart and renal failure. The goal of this review is to highlight recent discoveries regarding the contributions of cathepsins in CRDs, particularly hypertensive heart failure and proteinuric kidney disease.

Mechanoregulation of cytoskeletal dynamics by TRP channels

The ability of cells to respond to mechanical stimulation is crucial to a variety of biological processes, including cell migration, axonal outgrowth, perception of pain, cardiovascular responses and kidney physiology. The translation of mechanical cues into cellular responses, a process known as mechanotransduction, typically takes place in specialized multiprotein structures such as cilia, cell-cell or cell-matrix adhesions. Within these structures, mechanical forces such as shear stress and membrane stretch activate mechanosensitive proteins, which set off a series of events that lead to altered cell behavior. Members of the transient receptor potential (TRP) family of cation channels are emerging as important players in mechanotransductory pathways. Localized within mechanosensory structures, they are activated by mechanical stimuli and trigger fast as well as sustained cytoskeletal responses. In this review, we will provide an overview of how TRP channels affect cytoskeletal dynamics in various mechano-regulated processes.

Tacrolimus is an alternative therapy option for the treatment of adult steroid-resistant nephrotic syndrome: a prospective, multicenter clinical trial

BACKGROUND

The optimal therapy for adult steroid-resistant nephrotic syndrome (SRNS) remains a therapeutic challenge. We investigated the efficacy and safety of tacrolimus as a promising regimen in Chinese adult patients.

METHODS

A prospective, multicenter trial was conducted in 9 nephrology centers from 2006 to 2008, in patients with SRNS (defined as failure to respond to 1 mg/kg/day of prednisone for 8, and 16 weeks, in focal segmental glomerulosclerosis). Patients were treated with tacrolimus (TAC) plus prednisone for 12 months. TAC dose was titrated to achieve a target trough blood concentration of 5-10 ng/ml for the first 6 months and 4-6 ng/ml for the subsequent 6 months. The primary outcomes included complete or partial remission [complete remission (CR): proteinuria <0.3 g/24 h, with serum albumin ≥ 3.5 g/dl and stable renal function; partial remission (PR): proteinuria between 0.3 and 3.5 g/24 h and a decrease of at least 50 % from the baseline level, with serum albumin ≥ 3.0 g/dl and stable renal function]. Secondary end-points included relapse rate, changes of clinical parameters (proteinuria, serum albumin, and lipid profile) and adverse events.

RESULTS

Twenty-four patients with SRNS were enrolled. After 6 months of therapy, CR was achieved in 58.3 % of patients and PR in 16.7 %, yielding a final response rate of 75.0 %. The decrease in proteinuria was 43.1 ± 17.5 % after the first month of treatment (P < 0.001). Complete or PR was achieved in 6 of 8 patients with minimal change disease, 4 of 6 patients with mesangioproliferative glomerulonephritis (MsPGN), 6 of 7 patients with focal segmental glomerulosclerosis (FSGS), and all 2 patients with IgA nephropathy. Two patients (1 with MsPGN and 1 with FSGS) experienced relapses during the subsequent 6 months of follow-up. Adverse events included infection, hand tremor, diarrhea, acute reversible or persistent nephrotoxicity.

CONCLUSIONS

In conjunction with prednisone, TAC may be an alternative therapeutic regimen for adult SRNS patients. However, adverse events in these patients should be carefully monitored, especially at the beginning of treatment. Randomized controlled trials with longer follow-up are warranted.

Progress in pathogenesis of proteinuria

Aims. Proteinuria not only is a sign of kidney damage, but also is involved in the progression of renal diseases as an independent pathologic factor. Clinically, glomerular proteinuria is most commonly observed, which relates to structural and functional anomalies in the glomerular filtration barrier. The aim of this paper was to describe the pathogenesis of glomerular proteinuria. Data Sources. Articles on glomerular proteinuria retrieved from Pubmed and MEDLINE in the recent 5 years were reviewed. Results. The new understanding of the roles of glomerular endothelial cells and the glomerular basement membrane (GBM) in the pathogenesis of glomerular proteinuria was gained. The close relationships of slit diaphragm (SD) molecules such as nephrin, podocin, CD2-associated protein (CD2AP), a-actinin-4, transient receptor potential cation channel 6 (TRPC6), Densin and membrane-associated guanylate kinase inverted 1 (MAGI-1), α3β1 integrin, WT1, phospholipase C epsilon-1 (PLCE1), Lmx1b, and MYH9, and mitochondrial disorders and circulating factors in the pathogenesis of glomerular proteinuria were also gradually discovered. Conclusion. Renal proteinuria is a manifestation of glomerular filtration barrier dysfunction. Not only glomerular endothelial cells and GBM, but also the glomerular podocytes and their SDs play an important role in the pathogenesis of glomerular proteinuria.

Dysregulated nephrin in diabetic nephropathy of type 2 diabetes: a cross sectional study

BACKGROUND

Podocyte specific proteins are dysregulated in diabetic nephropathy, though the extent of their expression loss is not identical and may be subject to different regulatory factors. Quantifying the degree of loss may help identify the most useful protein to use as an early biomarker of diabetic nephropathy.

METHODOLOGY/PRINCIPAL FINDINGS

Protein expression of synaptopodin, podocin and nephrin were quantified in 15 Type 2 diabetic renal biopsies and 12 control patients. We found statistically significant downregulation of synaptopodin (P<0.0001), podocin (P = 0.0002), and nephrin (P<0.0001) in kidney biopsies of diabetic nephropathy as compared with controls. Urinary nephrin levels (nephrinuria) were then measured in 66 patients with Type 2 diabetes and 10 healthy controls by an enzyme-linked immunosorbent assay (Exocell, Philadelphia, PA). When divided into groups according to normo-, micro-, and macroalbuminuria, nephrinuria was found to be present in 100% of diabetic patients with micro- and macroalbuminuria, as well as 54% of patients with normoalbuminuria. Nephrinuria also correlated significantly with albuminuria (rho = 0.89, p<0.001), systolic blood pressure (rho = 0.32, p = 0.007), and correlated negatively with serum albumin (rho = -0.48, p<0.0001) and eGFR (rho = -0.33, p = 0.005).

CONCLUSIONS/SIGNIFICANCE

These data suggest that key podocyte-specific protein expressions are significantly and differentially downregulated in diabetic nephropathy. The finding that nephrinuria is observed in a majority of these normoalbuminuric patients demonstrates that it may precede microalbuminuria. If further research confirms nephrinuria to be a biomarker of pre-clinical diabetic nephropathy, it would shed light on podocyte metabolism in disease, and raise the possibility of new and earlier therapeutic targets.

Complete remission induced by tacrolimus and low-dose prednisolone in adult minimal change nephrotic syndrome: A pilot study

Background

Few clinical trials have examined the replacement of steroids with other immunosuppressive drugs as a primary treatment modality for minimal change disease (MCD) in adults. We studied the efficacy of tacrolimus to induce complete remission (CR) in adults with MCD.

Methods

We enrolled 14 adults with MCD and nephrotic-range proteinuria. All patients were treated with oral tacrolimus 0.05 mg/kg twice daily and prednisolone 0.5 mg/kg/day. CR was defined as a urine protein to creatinine ratio of<0.2 g protein/g creatinine (g/g cr). The primary outcome was cumulative percentage of CR during 16 weeks.

Results

The mean urine protein to creatinine ratio at enrollment was 10.9 g/g cr (range: 4.2–18.1 g/g cr). The trough tacrolimus level was maintained at 5.99±2.63 ng/mL. CR was achieved by 13/14 (92.8%) patients within 8 weeks. The cumulative CR rate was 7.7% (1/14), 64.2% (9/14), 71.3% (10/14), and 92.9% (13/14) at 1 week, 2 weeks, 4 weeks, and 8 weeks, respectively. The one remaining patient achieved CR at 20 weeks after treatment, who was followed up for a further 4 weeks. The mean time to achieve CR in the 14 patients was 4.64±5.11 (1–20) weeks. Three cases suffered adverse events of abdominal pain, diarrhea, or new-onset diabetes mellitus.

Conclusion

Tacrolimus and low-dose prednisolone therapy induced CR rapidly (71.3% by 4 weeks and 100% by 20 weeks) and effectively in adult patients with MCD.

Saquinavir in steroid-dependent and -resistant nephrotic syndrome: a pilot study

BACKGROUND

Some difficult cases of idiopathic nephrotic syndrome (NS) have been treated with a HIV protease inhibitor provided with proteasome-inhibiting activity. The objective of this study was to limit nuclear factor κB (NF-κB) activation which is up-regulated in these patients, aiming at decreasing proteinuria and prednisone need.

METHODS

Ten cases with long-lasting (up to 15 years) history of NS with steroid dependence (six cases, of which three with secondary steroid resistance) or resistance to steroids (four cases) unsuccessfully treated with multiple immunosuppressive drugs, accepted a treatment with the protease inhibitor saquinavir. p50/p65 NF-κB nuclear localization and immunoproteasome/proteasome messenger RNA (mRNA) were monitored in peripheral blood mononuclear cells (PBMCs). The effects of saquinavir on NF-κB nuclear localization in cultured PBMCs and in immortalized human podocytes were assessed.

RESULTS

After a median follow-up of 14.7 months (6-68.7), 1/4 primary steroid-resistant NS (SRNS) and 5/6 steroid-dependent NS or secondary SRNS became infrequent (5) or frequent (1) relapsers, with 63% prednisone reduction (from 25.3 to 8.4 mg/kg/month, P = 0.015). Saquinavir was effective in association with low doses of calcineurin inhibitors (cyclosporine 2 mg/kg/day or tacrolimus 0.01-0.06 mg/kg/day). No side effects were observed apart from transitory mild diarrhoea. In PBMCs, NF-κB was down-regulated, while MECL-1 immunoproteasome/beta2 proteasome mRNA ratio was reversed to normal values. In culture, saquinavir blunted NF-κB activation in human podocytes and in PBMCs.

CONCLUSIONS

In this pilot study, a HIV antiprotease drug reduced proteinuria and had a steroid-sparing effect in some multidrug-resistant/-dependent NS. This observation warrants further investigation.

Current concepts of the podocyte in nephrotic syndrome

Nephrotic syndrome is a disorder of the glomerular filtration barrier, and central to the filtration mechanism of the glomerular filtration barrier is the podocyte. We are starting to better understand how this cell, with its unique architectural features, fulfils its exact filtration properties. The multiprotein complex between adjacent podocyte foot processes, the slit diaphragm, is essential to the control of the actin cytoskeleton and cell morphology. Many of the proteins within the slit diaphragm, including nephrin, podocin, transient receptor potential-6 channel, and α-actinin-4, have been identified via genetic studies of inherited nephrotic syndromes. Signaling from slit diaphragm proteins to the actin cytoskeleton is mediated via the Rho GTPases. These are thought to be involved in the control of podocyte motility, which has been postulated as a focus of proteinuric pathways. Nephrotic syndrome is currently treated with immunosuppressive therapy, with significant adverse effects. These therapies may work in nephrotic syndrome due to specific effects on the podocytes. This review aims to describe our current understanding of the cellular pathways and molecules within the podocyte relevant to nephrotic syndrome and its treatment. With our current knowledge of the cellular biology of the podocyte, there is much hope for targeted therapies for nephrotic syndromes.

The struggle for energy in podocytes leads to nephrotic syndrome

Podocytes are terminally differentiated post-mitotic cells similar to neurons, and their damage leads to nephrotic syndrome, which is characterized by massive proteinuria associated with generalized edema. A recent functional genetic approach has identified the pathological relevance of several mutated proteins in glomerular podocytes to the mechanism of proteinuria in hereditary nephrotic syndrome. In contrast, the pathophysiology of acquired primary nephrotic syndrome, including minimal change disease, is still largely unknown. We recently demonstrated the possible linkage of an energy-consuming process in glomerular podocytes to the mechanism of proteinuria. Puromycin aminonucleoside nephrosis, a rat model of minimal change disease, revealed the activation of the unfolded protein response (UPR) in glomerular podocytes to be a cause of proteinuria. The pretreatment of puromycin aminonucleoside rat podocytes and cultured podocytes with the mammalian target of rapamycin (mTOR) inhibitor everolimus further revealed that mTOR complex 1 consumed energy, which was followed by UPR activation. In this paper, we will review nutritional transporters to summarize the energy uptake process in podocytes and review the involvement of the UPR in the pathogenesis of glomerular diseases. We will also present additional data that reveal how mTOR complex 1 acts upstream of the UPR. Finally, we will discuss the potential significance of targeting the energy metabolism of podocytes to develop new therapeutic interventions for acquired nephrotic syndrome.

Non-muscle myosins and the podocyte

Proteinuria is often accompanied by a pathological change in the glomerulus that is refereed as effacement of the podocyte foot processes. The highly dynamic podocyte foot processes contain an actin-based contractile apparatus comparable to that of pericytes, which needs to be precisely and temporally controlled to withstand high pressure in the capillaries and to maintain intact glomerular filtration properties. This review outlines the most recent concepts on the function of the podocyte contractile apparatus with a focus on the role of non-muscle myosins as they have been highlighted by studies in monogenic hereditary proteinuric diseases.

Tacrolimus improves the proteinuria remission in patients with refractory IgA nephropathy

BACKGROUND

Tacrolimus has been reported to be effective in refractory nephrotic syndrome, such as focal segmental glomerulosclerosis and membranous nephropathy. Some IgA nephropathy (IgAN) patients with massive proteinuria showed resistance to steroids and/or cytotoxic immunosuppressants based on the supportive therapy with renin- angiotensin system blockade. The efficacy and safety of tacrolimus in such refractory IgAN patients are extremely ambiguous, and the mechanism of tacrolimus improving proteinuria remission needs to be investigated.

METHODS

14 refractory IgAN patients were enrolled. The patients received tacrolimus (0.05-0.1 mg/kg/day) and prednisone (0.5 mg/kg/day) for at least 6 months. Synaptopodin and calcineurin expression were detected in renal tissues of patients who received re-biopsy. A puromycin aminonucleoside (PAN)-induced human podocyte injury model was applied to investigate the possible role of tacrolimus in proteinuria remission.

RESULTS

Of the 14 patients enrolled, 3 were withdrawn because serum creatinine increased over 30% baseline. In 11 patients treated with tacrolimus over 6 months, 9 showed complete or partial remission and 7 achieved remission within 1 month. In renal tissues, the expression of calcineurin increased while synaptopodin decreased and recovered partially after tacrolimus therapy. In an in vitro study, F-actin disrupted in human podocytes after stimulation of PAN, while calcineurin increased and synaptopodin decreased. After co-treatment with tacrolimus the reorganization of F-actin and the expression of calcineurin and synaptopodin recovered.

CONCLUSIONS

Tacrolimus showed a rapid proteinuria remission in refractory IgAN patients. The possible mechanism of tacrolimus to proteinuria remission might be podocyte cytoskeleton stabilization through inhibition of calcineurin expression.

Outcomes of maintenance therapy with tacrolimus versus azathioprine for active lupus nephritis: a multicenter randomized clinical trial

AIM

The optimal maintenance therapy for active diffuse lupus nephritis remains to be established. In this study, we explored the efficacy and safety of tacrolimus for maintaining remission of active lupus nephritis compared to that of azathioprine.

METHODS

Seventy patients with biopsy-proven lupus nephritis who achieved remission were enrolled in nine nephrology centers in China from 2006 to 2008. Patients were randomized either to tacrolimus plus prednisone (n = 34) or azathioprine plus prednisone (n = 36) for six months. Tacrolimus was titrated to achieve a trough blood concentration of 4-6 ng/mL, and the dosage of azathioprine was 2 mg/kg/d. Prednisone was administered at a dose of 10 mg/d to both groups. The primary outcome was incidence of relapse. Response, clinical parameters and adverse effects were secondary endpoints.

RESULTS

After six months of therapy, two of the azathioprine-treated patients developed renal relapse compared to none of the tacrolimus-treated patients (p = 0.49; odds ratio, 1.06; 95% CI (0.98, 1.15)). Leucopenia (defined as < 2000 cells per cubic millimeter) was significantly more frequent in the azathioprine group than the tacrolimus group (47% vs. 9%, p < .001).

CONCLUSION

In conjunction with prednisone, maintenance therapy with tacrolimus and azathioprine has a similar low rate of renal relapse, and the tacrolimus regimen has a more favorable safety profile, with less leucopenia. However, since our study lacked sufficient power, longer follow-up is needed to draw final conclusions.

Genetic causes of focal segmental glomerulosclerosis: implications for clinical practice

Focal segmental glomerulosclerosis (FSGS) is a common cause of steroid-resistant nephrotic syndrome in children and adults. Although FSGS is considered a podocyte disease, the aetiology is diverse. In recent years, many inheritable genetic forms of FSGS have been described, caused by mutations in proteins that are important for podocyte function. In the present commentary, we review these genetic causes of FSGS and describe their prevalence in familial and sporadic FSGS. In routine clinical practice, the decision to perform the costly DNA analysis should be based on the assessment if the results affect the care of the individual patient with respect to the evaluation of extra-renal manifestations, treatment decisions, transplantation and genetic counselling.

The Gne M712T mouse as a model for human glomerulopathy

Pathological glomerular hyposialylation has been implicated in certain unexplained glomerulopathies, including minimal change nephrosis, membranous glomerulonephritis, and IgA nephropathy. We studied our previously established mouse model carrying a homozygous mutation in the key enzyme of sialic acid biosynthesis, N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase. Mutant mice died before postnatal day 3 (P3) from severe glomerulopathy with podocyte effacement and segmental glomerular basement membrane splitting due to hyposialylation. Administration of the sialic acid precursor N-acetylmannosamine (ManNAc) led to improved sialylation and survival of mutant pups beyond P3. We determined the onset of the glomerulopathy in the embryonic stage. A lectin panel, distinguishing normally sialylated from hyposialylated glycans, used WGA, SNA, PNA, Jacalin, HPA, and VVA, indicating glomerular hyposialylation of predominantly O-linked glycoproteins in mutant mice. The glomerular glycoproteins nephrin and podocalyxin were hyposialylated in this unique murine model. ManNAc treatment appeared to ameliorate the hyposialylation status of mutant mice, indicated by a lectin histochemistry pattern similar to that of wild-type mice, with improved sialylation of both nephrin and podocalyxin, as well as reduced albuminuria compared with untreated mutant mice. These findings suggest application of our lectin panel for categorizing human kidney specimens based on glomerular sialylation status. Moreover, the partial restoration of glomerular architecture in ManNAc-treated mice highlights ManNAc as a potential treatment for humans affected with disorders of glomerular hyposialylation.

Small molecule-mediated activation of the integrin CD11b/CD18 reduces inflammatory disease

The integrin CD11b/CD18 (also known as Mac-1), which is a heterodimer of the α(M) (CD11b) and β(2) (CD18) subunits, is critical for leukocyte adhesion and migration and for immune functions. Blocking integrin-mediated leukocyte adhesion, although beneficial in experimental models, has had limited success in treating inflammatory diseases in humans. Here, we used an alternative strategy of inhibiting leukocyte recruitment by activating CD11b/CD18 with small-molecule agonists, which we term leukadherins. These compounds increased the extent of CD11b/CD18-dependent cell adhesion of transfected cells and of primary human and mouse neutrophils, which resulted in decreased chemotaxis and transendothelial migration. Leukadherins also decreased leukocyte recruitment and reduced arterial narrowing after injury in rats. Moreover, compared to a known integrin antagonist, leukadherins better preserved kidney function in a mouse model of experimental nephritis. Leukadherins inhibited leukocyte recruitment by increasing leukocyte adhesion to the inflamed endothelium, which was reversed with a blocking antibody. Thus, we propose that pharmacological activation of CD11b/CD18 offers an alternative therapeutic approach for inflammatory diseases.

Adenovirus-mediated gene transfer of TGF-β1 to the renal glomeruli leads to proteinuria

The mechanism of proteinuria in many common kidney diseases involves glomerular hemodynamic effects and local expression of angiogenic, fibrogenic, and vasoactive factors. Transforming growth factor (TGF)-β has been associated with many diseases involving proteinuria and renal fibrosis. TGF-β has been shown to induce podocyte dedifferentiation in vitro, but its in vivo effects on the glomerular filtration barrier are not well described. In this study, we used an adenovirus vector to transfer active TGF-β1 to the glomeruli of rat kidneys. Transient TGF-β1 overexpression induced significant proteinuria, podocyte foot process effacement, nephrin down-regulation, and nephrinuria. The expression of synaptopodin was also significantly down-regulated by TGF-β1. Increased glomerular expression of Snail, suggestive of an in vivo dedifferentiation process, was associated with a loss of podocyte epithelial markers. The expression of angiopoietin-1 and angiopoietin-2 was significantly increased in TGF-β1-transfected glomeruli, and TGF-β1 increased the expression of the angiopoietin receptor, Tie2, in podocyte cell culture. TGF-β1 down-regulated nephrin and synaptopodin expression in podocytes in cell culture; this effect was reversed by the blockade of both angiopoietin and Tie2 activities. These findings suggest that locally produced TGF-β1 can cause podocyte dedifferentiation marked by a loss of synaptopodin, nephrin, and foot process effacement, partly regulated by angiopoietins. This process represents a novel pathway that may explain proteinuria in a variety of common renal diseases.