Nonimmunologic targets of immunosuppressive agents in podocytes

Inhibition of intrarenal PRR-RAS pathway by Ganoderma lucidum polysaccharide peptides in proteinuric nephropathy

Excessive proteinuria leads to renal dysfunction and damage. Ganoderma lucidum polysaccharide peptide (GL-PP) and Ganoderma lucidum polysaccharide peptide 2 (GL-PP2) are biologically active compounds extracted from Ganoderma lucidum. GL-PP has a relative molecular weight of 37,121 with 76.39 % polysaccharides and 16.35 % polypeptides, while GL-PP2 has a relative molecular weight of 31,130, composed of 64.14 % polysaccharides and 17.73 % polypeptides. The xylose: mannose: glucose monosaccharide ratios in GL-PP and GL-PP2 were 4.83:1:7.03 and 2.35:1:9.38, respectively. In this study, we investigated the protective effects of GL-PP and GL-PP2 on proteinuria-induced renal dysfunction and damage using rat and cell models. Both compounds reduced kidney injury, proteinuria, and inhibited the (pro)renin receptor (PRR)-renin-angiotensin system (RAS) pathway, inflammatory cell infiltration, oxidative stress, and fibrosis. GL-PP2 showed stronger inhibition of cyclooxygenase-2 and inducible nitric oxide synthase proteins compared to GL-PP. In cell models, both compounds displayed anti-inflammatory properties and improved cellular viability by inhibiting the PRR-RAS pathway. GL-PP2 has higher feasibility and productivity than GL-PP in pharmacology and industrial production. It shows promise in treating proteinuria-induced renal disease with superior anti-inflammatory effects and economic, safe industrial application prospects. Further research is needed to compare efficacy, mechanisms, clinical applications, and commercial feasibility of GL-PP and GL-PP2.

Levamisole Modulation of Podocytes' Actin Cytoskeleton in Nephrotic Syndrome

Podocytes play a central role in glomerular diseases such as (idiopathic) nephrotic syndrome (iNS). Glucocorticoids are the gold standard therapy for iNS. Nevertheless, frequent relapses are common. In children with iNS, steroid-sparing agents are used to avoid prolonged steroid use and reduce steroid toxicity. Levamisole is one of these steroid-sparing drugs and although clinical effectiveness has been demonstrated, the molecular mechanisms of how levamisole exerts its beneficial effects remains poorly studied. Apart from immunomodulatory capacities, nonimmunological effects of levamisole on podocytes have also been suggested. We aimed to elaborate on the effects of levamisole on human podocytes in iNS. RNA sequencing data from a human podocyte cell line treated with levamisole showed that levamisole modulates the expression of various genes involved in actin cytoskeleton stabilization and remodeling. Functional experiments showed that podocytes exposed to puromycin aminonucleoside (PAN), lipopolysaccharides (LPS), and NS patient plasma resulted in significant actin cytoskeleton derangement, reduced cell motility, and impaired cellular adhesion when compared to controls, effects that could be restored by levamisole. Mechanistic studies revealed that levamisole exerts its beneficial effects on podocytes by signaling through the glucocorticoid receptor and by regulating the activity of Rho GTPases. In summary, our data show that levamisole exerts beneficial effects on podocytes by stabilizing the actin cytoskeleton in a glucocorticoid receptor-dependent manner.

Defining diagnostic trajectories in patients with podocytopathies

Podocytopathies are glomerular disorders in which podocyte injury drives proteinuria and progressive kidney disease. They encompass a broad spectrum of aetiologies, resulting in pathological pictures of minimal-changes, focal segmental glomerulosclerosis, diffuse mesangial sclerosis or collapsing glomerulopathy. Despite improvement in classifying podocytopathies as a distinct group of disorders, the histological definition fails to capture the relevant biological heterogeneity underlying each case, manifesting as extensive variability in disease progression and response to therapies. Increasing evidence suggests that podocytopathies can result from a single causative factor or a combination of multiple genetic and/or environmental risk factors with different relative contributions, identifying complex physiopathological mechanisms. Consequently, the diagnosis can still be challenging. In recent years, significant advances in genetic, microscopy and biological techniques revolutionized our understanding of the molecular mechanisms underlying podocytopathies, pushing nephrologists to integrate innovative information with more conventional data obtained from kidney biopsy in the diagnostic workflow. In this review, we will summarize current approaches in the diagnosis of podocytopathies, focusing on strategies aimed at elucidating the aetiology underlying the histological picture. We will provide several examples of an integrative view of traditional concepts and new data in patients with suspected podocytopathies, along with a perspective on how a reclassification could help to improve not only diagnostic pathways and therapeutic strategies, but also the management of disease recurrence after kidney transplantation. In the future, the advantages of precision medicine will probably allow diagnostic trajectories to be increasingly focused, maximizing therapeutic results and long-term prognosis.

Hemizygous nonsense variant in the moesin gene (MSN) leads to a new autoimmune phenotype of Immunodeficiency 50

Here, we present the findings of an investigation involving two male siblings with juvenile total tooth loss, early-onset chronic leg ulcers, and autoimmune thyroiditis, as well as focal segmental glomerulosclerosis with associated pulmonary emphysema in one and diabetes mellitus in the other. The clinical picture and lupus anticoagulant, cryoglobulin, and cold agglutinin positivity suggested the diagnosis of antiphospholipid syndrome. Flow cytometry analysis showed immunophenotypes consistent with immune dysregulation: a low number of naive T cells, elevated CD4+ T cell counts, and decreased CD8+ T-cell counts were detected, and more than half of the T-helper population was activated. Considering the siblings' almost identical clinical phenotype, the genetic alteration was suspected in the background of the immunodeficiency. Whole exome sequencing identified a previously not described hemizygous nonsense variant (c.650G>A, p.W217X) within exon 6 of the moesin (MSN) gene localized on chromosome X, resulting in significantly decreased MSN mRNA expression compared to healthy controls. We present a putative new autoimmune phenotype of Immunodeficiency 50 (MIM300988) characterized by antiphospholipid syndrome, Hashimoto's thyroiditis, leg ulcers, and juvenile tooth loss, associated with W217X mutation of the MSN gene.

Beneficial effects of procyanidin B2 on adriamycin-induced nephrotic syndrome mice: the multi-action mechanism for ameliorating glomerular permselectivity injury

Despite considerable advances in prevention, diagnosis, and therapy, nephrotic syndrome (NS) remains a significant cause of high morbidity and mortality globally. As a result, there is an urgent need to identify novel effective preventative and therapeutic agents for NS. NS is implicated in glomerular permselectivity injury, which can be attributed to oxidative distress, inflammation, lipid nephrotoxicity, podocyte apoptosis, autophagy dysfunction, and slit diaphragm (SLD) dysfunction. In addition to its well-documented antioxidant potency, procyanidin B2 (PB2) may exhibit pleiotropic effects by targeting various canonical signaling events, such as NF-κB, PPARs, PI3K/Akt, mTOR, and the caspase family. As a result, PB2 may be a promising therapeutic target against NS. To test this hypothesis, we established an Adriamycin (ADR)-induced NS mouse model to evaluate the pleiotropic renoprotective effects of PB2 on NS. Here, we demonstrated that PB2 improves podocyte injury via inhibition of NOX4/ROS and Hsp90/NF-κB to exhibit antioxidant and anti-inflammatory potency, respectively. We also show that PB2 indirectly activates the PI3K/Akt axis by regulating SLD protein levels, resulting in normalized podocyte apoptosis and autophagy function. Further, loss of albumin (ALB) induces lipid nephrotoxicity, which we found to be alleviated by PB2 via activation of PPARα/β-mediated lipid homeostasis and the cholesterol efflux axis. Interestingly, our results also suggested that PB2 reduces electrolyte abnormalities and edema. In addition, PB2 may contribute protective effects against trace element dys-homeostasis, which, through alleviating serum ALB loss, leads to a protective effect on glomerular permselectivity injury. Taken together, our results reveal that the identified mechanisms of PB2 on NS are multifactorial and involve inhibition of oxidative distress and inflammatory responses, as well as improvements in podocyte apoptosis and autophagy dysfunction, amelioration of lipid nephrotoxicity, and modulation of electrolyte abnormalities and edema. Thus, we provide a theoretical basis for the clinical application of PB2 against NS.

Protective effects of rituximab on puromycin-induced apoptosis, loss of adhesion and cytoskeletal alterations in human podocytes

Podocytes are highly specialized cells playing a key role in the filtration function of the kidney. A damaged podocyte ultrastructure is associated with a reorganization of the actin cytoskeleton and accompanied with a loss of adhesion to the glomerular basement membrane leading to proteinuria in many forms of glomerular diseases, e.g. nephrotic syndrome. If the first-line therapy with glucocorticoids fails, alternative immunosuppressive agents are used, which are known to have the potential to stabilize the actin cytoskeleton. A new option for preventing relapses in steroid dependent nephrotic syndrome is the monoclonal antibody rituximab, which, in addition to its B-cell depleting effect, is assumed to have direct effects on podocytes. We here provide data on the non-immunological off-target effects of the immunosuppressant rituximab on podocyte structure and dynamics in an in vitro puromycin aminonucleoside model of podocyte injury. A conditionally immortalized human podocyte cell line was used. Differentiated podocytes were treated with puromycin aminonucleoside and rituximab. Our studies focussed on analyzing the structure of the actin cytoskeleton, cellular adhesion and apoptosis using immunofluorescence staining and protein biochemistry methods. Treatment with rituximab resulted in a stabilization of podocyte actin stress fibers in the puromycin aminonucleoside model, leading to an improvement in cell adhesion. A lower apoptosis rate was observed after parallel treatment with puromycin aminonucleoside and rituximab visualized by reduced nuclear fragmentation. Consistent with this data, Western-blot analyses demonstrated that rituximab directly affects the caspase pathways by inhibiting the activation of Caspases-8, -9 and -3, suggesting that rituximab may inhibit apoptosis. In conclusion, our results indicate an important role of the immunosuppressant rituximab in terms of stability and morphogenesis of podocytes, involving apoptosis pathways. This could help to improve therapeutical concepts for patients with proteinuria mediated by diseased podocytes.

How immunosuppressive drugs may directly target podocytes in glomerular diseases

Podocytes are the direct target of immunologic injury in many immune-mediated glomerular diseases, leading to proteinuria and subsequent kidney failure. Immunosuppressive agents such as steroids, calcineurin inhibitors, and rituximab are the commonly used treatment strategies in this context for their immunotherapeutic or anti-inflammatory properties. However, in recent years, studies have demonstrated that immunosuppressive agents can have a direct effect on podocytes, introducing the concept of the non-immunologic mechanism of kidney protection by immunomodulators. In this review, we focus on the mechanisms by which these agents may directly target the podocyte independent of their systemic effects and examine their clinical significance.

A critical role of the podocyte cytoskeleton in the pathogenesis of glomerular proteinuria and autoimmune podocytopathies

Selective glomerular filtration relies on the membrane separating the glomerular arterioles from the Bowman space. As a major component of the glomerular filtration barrier, podocytes form foot processes by the actin cytoskeleton, which dynamically adjusts in response to environmental changes to maintain filtration barrier integrity. The slit diaphragms bridge the filtration slits between neighboring foot processes and act as signaling hubs interacting with the actin cytoskeleton. Focal adhesions relay signals to regulate actin dynamics while allowing podocyte adherence to the basement membrane. Mutations in actin regulatory and signaling proteins may disrupt the actin cytoskeleton, resulting in foot process retraction, effacement, and proteinuria. Large-scale gene expression profiling platforms, transgenic animal models, and other in vivo gene delivery methods now enhance our understanding of the interactions among podocyte focal adhesions, slit diaphragms, and actin dynamics. In addition, our team found that at least 66% of idiopathic nephrotic syndrome (INS) children have podocyte autoantibodies, which was defined as a new disease subgroup-, autoimmune podocytopathies. This review outlines the pathophysiological mechanisms of podocyte cytoskeleton protein interactions in proteinuria and glomerular podocytopathy.

An updated view of the pathogenesis of steroid-sensitive nephrotic syndrome

Idiopathic nephrotic syndrome is the most common childhood glomerular disease. Most forms of this syndrome respond to corticosteroids at standard doses and are, therefore, defined as steroid-sensitive nephrotic syndrome (SSNS). Immunological mechanisms and subsequent podocyte disorders play a pivotal role in SSNS and have been studied for years; however, the precise pathogenesis remains unclear. With recent advances in genetic techniques, an exhaustive hypothesis-free approach called a genome-wide association study (GWAS) has been conducted in various populations. GWASs in pediatric SSNS peaked in the human leukocyte antigen class II region in various populations. Additionally, an association of immune-related CALHM6/FAM26F, PARM1, BTNL2, and TNFSF15 genes, as well as NPHS1, which encodes nephrin expressed in podocytes, has been identified as a locus that achieves genome-wide significance in pediatric SSNS. However, the specific mechanism of SSNS development requires elucidation. This review describes an updated view of SSNS pathogenesis from immunological and genetic aspects, including interactions with infections or allergies, production of circulating factors, and an autoantibody hypothesis.

Drug-Induced Nephrotoxicity Assessment in 3D Cellular Models

The kidneys are often involved in adverse effects and toxicity caused by exposure to foreign compounds, chemicals, and drugs. Early predictions of these influences are essential to facilitate new, safe drugs to enter the market. However, in current drug treatments, drug-induced nephrotoxicity accounts for 1/4 of reported serious adverse reactions, and 1/3 of them are attributable to antibiotics. Drug-induced nephrotoxicity is driven by multiple mechanisms, including altered glomerular hemodynamics, renal tubular cytotoxicity, inflammation, crystal nephropathy, and thrombotic microangiopathy. Although the functional proteins expressed by renal tubules that mediate drug sensitivity are well known, current in vitro 2D cell models do not faithfully replicate the morphology and intact renal tubule function, and therefore, they do not replicate in vivo nephrotoxicity. The kidney is delicate and complex, consisting of a filter unit and a tubular part, which together contain more than 20 different cell types. The tubular epithelium is highly polarized, and maintaining cellular polarity is essential for the optimal function and response to environmental signals. Cell polarity depends on the communication between cells, including paracrine and autocrine signals, as well as biomechanical and chemotaxis processes. These processes affect kidney cell proliferation, migration, and differentiation. For drug disposal research, the microenvironment is essential for predicting toxic reactions. This article reviews the mechanism of drug-induced kidney injury, the types of nephrotoxicity models (in vivo and in vitro models), and the research progress related to drug-induced nephrotoxicity in three-dimensional (3D) cellular culture models.

Therapeutic trials in adult FSGS: lessons learned and the road forward

Focal segmental glomerulosclerosis (FSGS) is not a specific disease entity but a lesion that primarily targets the podocyte. In a broad sense, the causes of the lesion can be divided into those triggered by a presumed circulating permeability factor, those that occur secondary to a process that might originate outside the kidneys, those caused by a genetic mutation in a podocyte or glomerular basement membrane protein, and those that arise through an as yet unidentifiable process, seemingly unrelated to a circulating permeability factor. A careful attempt to correctly stratify patients with FSGS based on their clinical presentation and pathological findings on kidney biopsy is essential for sound treatment decisions in individual patients. However, it is also essential for the rational design of therapeutic trials in FSGS. Greater recognition of the pathophysiology underlying podocyte stress and damage in FSGS will increase the likelihood that the cause of an FSGS lesion is properly identified and enable stratification of patients in future interventional trials. Such efforts will facilitate the identification of effective therapeutic agents.

A Rare Autosomal Dominant Variant in Regulator of Calcineurin Type 1 (RCAN1) Gene Confers Enhanced Calcineurin Activity and May Cause FSGS

BACKGROUND

Podocyte dysfunction is the main pathologic mechanism driving the development of FSGS and other morphologic types of steroid-resistant nephrotic syndrome (SRNS). Despite significant progress, the genetic causes of most cases of SRNS have yet to be identified.

METHODS

Whole-genome sequencing was performed on 320 individuals from 201 families with familial and sporadic NS/FSGS with no pathogenic mutations in any known NS/FSGS genes.

RESULTS

Two variants in the gene encoding regulator of calcineurin type 1 (RCAN1) segregate with disease in two families with autosomal dominant FSGS/SRNS. In vitro, loss of RCAN1 reduced human podocyte viability due to increased calcineurin activity. Cells expressing mutant RCAN1 displayed increased calcineurin activity and NFAT activation that resulted in increased susceptibility to apoptosis compared with wild-type RCAN1. Treatment with GSK-3 inhibitors ameliorated this elevated calcineurin activity, suggesting the mutation alters the balance of RCAN1 regulation by GSK-3β, resulting in dysregulated calcineurin activity and apoptosis.

CONCLUSIONS

These data suggest mutations in RCAN1 can cause autosomal dominant FSGS. Despite the widespread use of calcineurin inhibitors in the treatment of NS, genetic mutations in a direct regulator of calcineurin have not been implicated in the etiology of NS/FSGS before this report. The findings highlight the therapeutic potential of targeting RCAN1 regulatory molecules, such as GSK-3β, in the treatment of FSGS.

CD80 Insights as Therapeutic Target in the Current and Future Treatment Options of Frequent-Relapse Minimal Change Disease

Minimal change disease (MCD) is the most common cause of idiopathic nephrotic syndrome in children, and it is well known for its multifactorial causes which are the manifestation of the disease. Proteinuria is an early consequence of podocyte injury and a typical sign of kidney disease. Steroid-sensitive patients react well with glucocorticoids, but there is a high chance of multiple relapses. CD80, also known as B7-1, is generally expressed on antigen-presenting cells (APCs) in steroid-sensitive MCD patients. Various glomerular disease models associated with proteinuria demonstrated that the detection of CD80 with the increase of urinary CD80 was strongly associated closely with frequent-relapse MCD patients. The role of CD80 in MCD became controversial because one contradicts finding. This review covers the treatment alternatives for MCD with the insight of CD80 as a potential therapeutic target. The promising effectiveness of CD20 (rituximab) antibody and CD80 inhibitor (abatacept) encourages further investigation of CD80 as a therapeutic target in frequent-relapse MCD patients. Therapeutic-based antibody towards CD80 (galiximab) had never been investigated in MCD or any kidney-related disease; hence, the role of CD80 is still undetermined. A new therapeutic approach towards MCD is essential to provide broader effective treatment options besides the general immunosuppressive agents with gruesome adverse effects.

Podocytopathies

Podocytopathies are kidney diseases in which direct or indirect podocyte injury drives proteinuria or nephrotic syndrome. In children and young adults, genetic variants in >50 podocyte-expressed genes, syndromal non-podocyte-specific genes and phenocopies with other underlying genetic abnormalities cause podocytopathies associated with steroid-resistant nephrotic syndrome or severe proteinuria. A variety of genetic variants likely contribute to disease development. Among genes with non-Mendelian inheritance, variants in APOL1 have the largest effect size. In addition to genetic variants, environmental triggers such as immune-related, infection-related, toxic and haemodynamic factors and obesity are also important causes of podocyte injury and frequently combine to cause various degrees of proteinuria in children and adults. Typical manifestations on kidney biopsy are minimal change lesions and focal segmental glomerulosclerosis lesions. Standard treatment for primary podocytopathies manifesting with focal segmental glomerulosclerosis lesions includes glucocorticoids and other immunosuppressive drugs; individuals not responding with a resolution of proteinuria have a poor renal prognosis. Renin-angiotensin system antagonists help to control proteinuria and slow the progression of fibrosis. Symptomatic management may include the use of diuretics, statins, infection prophylaxis and anticoagulation. This Primer discusses a shift in paradigm from patient stratification based on kidney biopsy findings towards personalized management based on clinical, morphological and genetic data as well as pathophysiological understanding.

Levamisole in Children with Idiopathic Nephrotic Syndrome: Clinical Efficacy and Pathophysiological Aspects

Steroid sensitive nephrotic syndrome is one of the most common pediatric glomerular diseases. Unfortunately, it follows a relapsing and remitting course in the majority of cases, with 50% of all cases relapsing once or even more often. Most children with idiopathic nephrotic syndrome respond initially to steroid therapy, nevertheless repeated courses for patients with relapses induce significant steroid toxicity. Patients with frequent relapses or steroid dependency thus require alternative treatment, such as cyclophosphamide, cyclosporine, tacrolimus, mycophenolate mofetil, levamisole, or rituximab. To reduce the relapse rate, several drugs have been used. Among these, levamisole has been considered the least toxic and least expensive therapy. Several randomized controlled trials (RCT) showed that levamisole is effective in reducing the relapse risk in steroid sensitive forms of nephrotic syndrome with a low frequency of side effects. Levamisole is a synthetic imidazothiazole derivative with immune-modulatory properties. In this article, we review recent data from randomized trials and observational studies to assess the efficacy of levamisole in frequently relapsing nephrotic syndrome and steroid-dependent nephrotic syndrome.

Characterization of the myoepithelial cells in the major salivary glands of the fruit bat Artibeus jamaicensis

Bats constitute one of the most numerous mammalian species. Bats have a wide range of dietary habits and include carnivorous, haematophagous, insectivorous, frugivorous and nectivorous species. The salivary glands of these species have been of particular research interest due to their structural variability among chiropterans with different types of diets. Myoepithelial cells (MECs), which support and facilitate the expulsion of saliva from the secretory portions of salivary glands, are very important for their function; however, this cell type has not been extensively studied in the salivary glands of bats. In this study, we characterized the MECs in the major salivary glands of the fruit bat Artibeus jamaicensis. Herein, we describe the morphology of the parotid, submandibular and sublingual glands of A. jamaicensis at the light- and electro-microscopic level and the distribution of MECs in these glands, as defined by their expression of smooth-muscle markers such as α-smooth muscle actin (SMAα) and desmin, and of epithelial cell markers, such as KRT14. We found that the anatomical locations of the major salivary glands in this bat species are similar to those of humans, except that the bat sublingual gland appears to be unique, extending to join the contralateral homologous gland. Morphologically, the parotid gland has the characteristics of a mixed-secretory gland, whereas the submandibular and sublingual glands were identified as mucous-secretory glands. MECs positive for SMAα, KRT14 and desmin were found in all of the structural components of the three glands, except in their excretory ducts. Desmin is expressed at a lower level in the parotid gland than in the other glands. Our results suggest that the major salivary glands of A. jamaicensis, although anatomically and structurally similar to those of humans, play different physiological roles that can be attributed to the dietary habits of this species.

Melanocortin 1 receptor agonist protects podocytes through catalase and RhoA activation

Drugs containing adrenocorticotropic hormone have been used as therapy for patients with nephrotic syndrome. We have previously shown that adrenocorticotropic hormone and a selective agonist for the melanocortin 1 receptor (MC1R) exert beneficial actions in experimental membranous nephropathy with reduced proteinuria, reduced oxidative stress, and improved glomerular morphology and function. Our hypothesis is that MC1R activation in podocytes elicits beneficial effects by promoting stress fibers and maintaining podocyte viability. To test the hypothesis, we cultured podocytes and used highly specific agonists for MC1R. Podocytes were subjected to the nephrotic-inducing agent puromycin aminonucleoside, and downstream effects of MC1R activation on podocyte survival, antioxidant defense, and cytoskeleton dynamics were studied. To increase the response and enhance intracellular signals, podocytes were transduced to overexpress MC1R. We showed that puromycin promotes MC1R expression in podocytes and that activation of MC1R promotes an increase of catalase activity and reduces oxidative stress, which results in the dephosphorylation of p190RhoGAP and formation of stress fibers through RhoA. In addition, MC1R agonists protect against apoptosis. Together, these mechanisms protect the podocyte against puromycin. Our findings strongly support the hypothesis that selective MC1R-activating agonists protect podocytes and may therefore be useful to treat patients with nephrotic syndromes commonly considered as podocytopathies.

Organ-on-a-chip and the kidney

Traditional approaches to pathophysiology are advancing but still have many limitations that arise from real biologic systems and their associated physiological phenomena being too complicated. Microfluidics is a novel technology in the field of engineering, which provides new options that may overcome these hurdles. Microfluidics handles small volumes of fluids and may apply to various applications such as DNA analysis chips, other lab-on-a-chip analyses, micropropulsion, and microthermal technologies. Among them, organ-on-a-chip applications allow the fabrication of minimal functional units of a single organ or multiple organs. Relevant to the field of nephrology, renal tubular cells have been integrated with microfluidic devices for making kidneys-on-a-chip. Although still early in development, kidneys-on-a-chip are showing potential to provide a better understanding of the kidney to replace some traditional animal and human studies, particularly as more cell types are incorporated toward the development of a complete glomeruli-on-a-chip.