Interaction of CD80 with Neph1: a potential mechanism of podocyte injury

The role of podocytes in lupus nephritis: Insights and implications

Lupus nephritis (LN) is a severe complication of systemic lupus erythematosus, with high mortality rates despite medical advancements. The complexity of its pathogenesis, including the pivotal role of podocytes - kidney-localized cells - remains a challenge, lacking effective treatments and biomarkers. Recent studies highlight the significant contribution of these cells to LN's development, particularly through their immune-related functions and interaction with other kidney cells. This new understanding opens possibilities for targeted therapies aimed at these cellular mechanisms. This review aims to summarize these recent developments, shedding light on the intricate involvement of podocytes in LN and potential avenues for innovative treatments.

B7-1 mediates podocyte injury and glomerulosclerosis through communication with Hsp90ab1-LRP5-β-catenin pathway

Podocyte injury is a hallmark of glomerular diseases; however, the underlying mechanisms remain unclear. B7-1 is increased in injured podocytes, but its intrinsic role is controversial. The clinical data here revealed the intimate correlation of urinary B7-1 with severity of glomerular injury. Through transcriptomic and biological assays in B7-1 transgenic and adriamycin nephropathy models, we identified B7-1 is a key mediator in podocyte injury and glomerulosclerosis through a series of signal transmission to β-catenin. Using LC-MS/MS, Hsp90ab1, a conserved molecular chaperone, was distinguished to be an anchor for transmitting signals from B7-1 to β-catenin. Molecular docking and subsequent mutant analysis further identified the residue K69 in the N terminal domain of Hsp90ab1 was the key binding site for B7-1 to activate LRP5/β-catenin pathway. The interaction and biological functions of B7-1-Hsp90ab1-LRP5 complex were further demonstrated in vitro and in vivo. We also found B7-1 is a novel downstream target of β-catenin. Our results indicate an intercrossed network of B7-1, which collectively induces podocyte injury and glomerulosclerosis. Our study provides an important clue to improve the therapeutic strategies to target B7-1.

New Insights into the Treatment of Glomerular Diseases: When Mechanisms Become Vivid

Treatment for glomerular diseases has been extrapolated from the experience of other autoimmune disorders while the underlying pathogenic mechanisms were still not well understood. As the classification of glomerular diseases was based on patterns of juries instead of mechanisms, treatments were typically the art of try and error. With the advancement of molecular biology, the role of the immune agent in glomerular diseases is becoming more evident. The four-hit theory based on the discovery of gd-IgA1 gives a more transparent outline of the pathogenesis of IgA nephropathy (IgAN), and dysregulation of Treg plays a crucial role in the pathogenesis of minimal change disease (MCD). An epoch-making breakthrough is the discovery of PLA2R antibodies in the primary membranous nephropathy (pMN). This is the first biomarker applied for precision medicine in kidney disease. Understanding the immune system’s role in glomerular diseases allows the use of various immunosuppressants or other novel treatments, such as complement inhibitors, to treat glomerular diseases more reasonable. In this era of advocating personalized medicine, it is inevitable to develop precision medicine with mechanism-based novel biomarkers and novel therapies in kidney disease.

Molecular Mechanisms of Proteinuria in Minimal Change Disease

Minimal change disease (MCD) is the most common type of idiopathic nephrotic syndrome in childhood and represents about 15% cases in adults. It is characterized by massive proteinuria, edema, hypoalbuminemia, and podocyte foot process effacement on electron microscopy. Clinical and experimental studies have shown an association between MCD and immune dysregulation. Given the lack of inflammatory changes or immunocomplex deposits in the kidney tissue, MCD has been traditionally thought to be mediated by an unknown circulating factor(s), probably released by T cells that directly target podocytes leading to podocyte ultrastructural changes and proteinuria. Not surprisingly, research efforts have focused on the role of T cells and podocytes in the disease process. Nevertheless, the pathogenesis of the disease remains a mystery. More recently, B cells have been postulated as an important player in the disease either by activating T cells or by releasing circulating autoantibodies against podocyte targets. There are also few reports of endothelial injury in MCD, but whether glomerular endothelial cells play a role in the disease remains unexplored. Genome-wide association studies are providing insights into the genetic susceptibility to develop the disease and found a link between MCD and certain human haplotype antigen variants. Altogether, these findings emphasize the complex interplay between the immune system, glomerular cells, and the genome, raising the possibility of distinct underlying triggers and/or mechanisms of proteinuria among patients with MCD. The heterogeneity of the disease and the lack of good animal models of MCD remain major obstacles in the understanding of MCD. In this study, we will review the most relevant candidate mediators and mechanisms of proteinuria involved in MCD and the current models of MCD-like injury.

Biomarkers in pediatric glomerulonephritis and nephrotic syndrome

Glomerular diseases are often chronic or recurring and thus associated with a tremendous physical, psychological, and economic burden. Their etiologies are often unknown, and their pathogeneses are frequently poorly understood. The diagnoses and management of these diseases are therefore based on clinical features, traditional laboratory markers, and, often, kidney pathology. However, the clinical presentation can be highly variable, the kidney pathology may not establish a definitive diagnosis, and the therapeutic responses and resulting clinical outcomes are often unpredictable. To try to address these challenges, significant research efforts have been made over the last decade to identify potential biomarkers that can help clinicians optimize the diagnosis and prognosis at clinical presentation, as well as help predict long-term outcomes. Unfortunately, these efforts have to date only identified a single biomarker for glomerular disease that has been fully validated and developed for widespread clinical use (anti-PLA2R antibodies to diagnose membranous nephropathy). In this manuscript, we review the definitions and development of biomarkers, as well as the current knowledge on both historical and novel candidate biomarkers of glomerular disease, with an emphasis on those associated with idiopathic nephrotic syndrome.

Losartan Protects Podocytes against High Glucose-induced Injury by Inhibiting B7-1 Expression

The role of B7-1 in podocyte injury has received increasing attention. The aim of this study was to investigate whether losartan protects podocytes of patients with diabetic kidney disease (DKD) by regulating B7-1 and the underlying mechanisms. Rats with streptozotocin-induced DKD were treated with losartan for 8 weeks. Biochemical changes in blood and urine were analyzed. Kidneys were isolated for electron microscopy, immunofluorescence, real-time quantitative PCR (RT-PCR), and Western blot analysis. Immortalized mouse podocyte cells were cultured in normal or high glucose medium in the presence or absence of losartan for 48 h, and then the cells were collected for immunofluorescence, PCR, Western blotting and monolayer permeability detection. The phosphatidylinositol 3-kinase (PI3K) 110α subunit and angiotensin II type 1 receptor (AT1R) plasmids were transfected into podocytes, respectively, and then Western blotting was performed to assess the expression of B7-1 protein. The results showed that losartan ameliorated podocyte structure and function in the rat model of DKD, and reduced the expression of B7-1 protein. Overexpression of PI3K 110α subunit in podocytes attenuated the inhibitory effect of losartan on B7-1 expression in high glucose-stimulated podocytes. The expression of B7-1 was significantly increased by overexpression of AT1R and significantly reduced by blocking PI3K 110α subunit. We conclude that losartan protects podocytes against high glucose-induced injury by inhibiting AT1R-mediated B7-1 expression. This effect is dependent on the AT1R-PI3K 110α subunit pathway.

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

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

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.

Glomerular endothelial cells and podocytes can express CD80 in patients with minimal change disease during relapse

BACKGROUND

Urinary CD80 has emerged as potential biomarker in idiopathic nephrotic syndrome (INS). However, its cellular source remains controversial. The aim of the study was to assess whether CD80 is truly expressed by glomerular cells in INS patients during relapse and in the LPS mouse model of podocyte injury.

METHODS

The presence of CD80 in glomeruli was evaluated by combining immunostaining, immunogold labeling, and in situ hybridization techniques.

RESULTS

CD80 was present along the surface of glomerular endothelial cells (GEC) and rarely in podocytes in six of nine minimal change disease (MCD) patients in relapse, two of eleven patients with focal segmental glomerulosclerosis in relapse, and absent in controls. In mice, CD80 was upregulated at mRNA and protein level in GEC and podocytes, in a similar pattern to that seen in MCD patients.

CONCLUSIONS

Glomerular endothelial cells and podocytes can express CD80 in patients with MCD during relapse. A better understanding of the role of CD80 in glomerular cells may provide further insights into the mechanisms of proteinuria in INS.

Urinary CD80 Discriminates Among Glomerular Disease Types and Reflects Disease Activity

Introduction

Heterogeneity of nephrotic diseases and a lack of validated biomarkers limits interventions and reduces the ability to examine outcomes. Urinary CD80 is a potential biomarker for minimal change disease (MCD) steroid-sensitive nephrotic syndrome (NS). We investigated and validated a CD80 enzyme-linked immunosorbent assay (ELISA) in urine in a large cohort with a variety of nephrotic diseases.

Methods

A commercial CD80 ELISA was enhanced and analytically validated for urine. Patients were from Mayo Clinic (307) and Nephrotic Syndrome Study Network Consortium (NEPTUNE; 104) as follows: minimal change disease (MCD, 56), focal segmental glomerulosclerosis (FSGS, 92), lupus nephritis (LN, 25), IgA nephropathy (IgAN, 20), membranous nephropathy (MN, 49), autosomal dominant polycystic kidney disease (ADPKD, 10), diabetic nephropathy (DN; 106), pyuria (19), and controls (34). Analysis was by Kruskal−Wallis test, generalized estimating equation (GEE) models, and receiver operating characteristic (AUC) curve.

Results

Urinary CD80/creatinine values were highest in MCD compared to other glomerular diseases and were increased in DN with proteinuria >2 compared to controls (control = 36 ng/g; MCD = 139 ng/g, P < 0.01; LN = 90 ng/g, P < 0.12; FSGS = 66 ng/g, P = 0.18; DN = 63, P = 0.03; MN = 69 ng/g, P = 0.33; ng/g, P = 0.07; IgA = 19 ng/g, P = 0.09; ADPKD = 42, P = 0.36; and pyuria 31, P = 0.20; GEE, median, P vs. control). In proteinuric patients, CD80 concentration appears to be independent of proteinuria levels, suggesting that it is unrelated to nonspecific passage across the glomeruli. CD80/creatinine values were higher in paired relapse versus remission cases of MCD and FSGS (P < 0.0001, GEE).

Conclusion

Using a validated ELISA, urinary CD80 levels discriminate MCD from other forms of NS (FSGS, DN, IgA, MN) and primary from secondary FSGS.

Mechanisms of Podocyte Detachment, Podocyturia, and Risk of Progression of Glomerulopathies

Background

Glomerulopathies are the main cause of ESRD. Primary or secondary causes of glomerular diseases comprise more than 70% of cases that end up in renal replacement therapies.

Summary

The total glomerular mass that each individual contains is key to maintaining normal kidney function. Diabetes, hypertension, and any primary or secondary glomerulopathy may threaten the normal glomerular function. In fact, any glomerular insult may alter the glomerular filtration barrier, which in turn is composed by the podocyte, the glomerular basement membrane, and the capillary endothelial cell. Deposition of immune complexes, antibodies, or complement components at the subepithelial, intramembranous, or subendothelial space, and mutations in podocyte, slit diaphragm, or glomerular basement membrane proteins or enzymes are the main etiologies of glomerular alterations. Podocytes are glomerular cells that do not divide under normal circumstances. In this respect, maintenance of the absolute podocyte number per glomer-ulus is critical for normal glomerular function. As the insult progresses, podocytes start to detach from the glomerular basement membrane. When the podocyte loss is over 40% in a glomerulus, glomerulosclerosis develops, and obliteration of the glomerulus is the rule. In clinical grounds, this phenomenon is diagnosed mainly by proteinuria and a decline in glomerular filtration rate.

Key messages

In this review article, the impact of podocyturia in glomerular diseases and the main mechanisms of podocyte detachment are discussed. Finally, potential targets of therapeutic approach are suggested.

ApoL1 induces kidney inflammation through RIG-I/NF-κB activation

The genetic variations of the apolipoprotein L1 (APOL1) gene are associated with non-diabetic kidney diseases. However, very little is known about the role of ApoL1 in glomerular damage. Here, we aimed to identify the function and mechanism of ApoL1 in glomerular damage. The mice were randomly divided into two groups: one group was intraperitoneally injected with phosphate buffer saline (PBS), while the other group was intraperitoneally injected with recombinant ApoL1 every other day for 3 months. Hematoxylin and eosin (HE) and periodic acid Schiff (PAS) staining were used to demonstrate the effects of ApoL1 on kidney inflammation and injury. Furthermore, quantitative real-time polymerase chain reaction (qRT-PCR) and enzyme-linked immunosorbent assay (ELISA) analyses revealed that ApoL1-treated mice exhibited enhanced expression of various inflammation markers in the kidney and serum compared to the PBS-treated mice. Immunofluorescence staining revealed that ApoL1 accumulated in kidney podocytes. Treatment with ApoL1 dose-dependently increased the expression of inflammation markers and apoptotic markers. The abnormal gene expression associated with ApoL1-mediated podocyte inflammation was evaluated using microarray analysis. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses revealed that the upregulated genes were enriched in the inflammation-related processes, such as the RIG-I/NF-κB signaling pathway. Consistently, the knockdown of RIG-I significantly mitigated the ApoL1-induced upregulation of inflammatory and apoptotic markers in the human podocytes. Additionally, the ApoL1-induced glomerular damage was attenuated in AAV-shRIG-I mice. Therefore, the effects of ApoL1 on glomerular damage may be, at least partially, through inducing abnormal expression of inflammatory molecules, which may have important implications for treatment of kidney diseases.

The immune podocyte

PURPOSE OF REVIEW

Lupus nephritis (LN) is a serious manifestation of systemic lupus erythematosus and is characterized by proteinuria and renal failure. Proteinuria is a marker of poor prognosis and is attributed to podocyte loss and dysfunction. It is often debated whether these cells are innocent bystanders or active participants in the pathogenesis of glomerulonephritis.

RECENT FINDINGS

Podocytes share many elements of the innate and adaptive immune system. Specifically, they produce and express complement components and receptors which when dysregulated appear to contribute to podocyte damage and LN. In parallel, podocytes express major histocompatibility complex and co-stimulatory molecules which may be involved in local immune events. Podocyte-specific cytotoxic cells and possibly other immune cells contribute to glomerular damage. Autoantibodies present in lupus sera enter podocytes to upregulate calcium/calmodulin kinase which in turn compromises their structure and function.

SUMMARY

More recent studies point to the restoration of podocyte function using cell targeted approaches to prevent and treat LN. These strategies along with podocyte involvement in the pathogenesis of LN will be addressed in this review.

The renal adverse effects of cancer immunotherapy

Over the past decade, the development and clinical use of immunotherapy agents has increased exponentially. As clinical experience builds with these agents so too does our understanding of the associated adverse effects. In particular, the effects of immunotherapy on the kidneys, individual nephrons, and kidney function remain less well described than the adverse effects on barrier organ systems such as the gastrointestinal tract and skin. However, phase IV post-marketing surveillance and clinical case studies together with basic research has begun to reveal mechanisms by which immunotherapy mediates renal adverse effects. This work may lead to improvements in treatment guidelines and therapy. These advances are particularly important as post-cancer survival increases leaving patients to cope with the consequences of not only the cancer, but the short- and long-term adverse effects of treatment. Here we discuss the major renal adverse effects encountered with individual immunotherapeutic agents, putative mechanisms, their current management, and how cancer survivorship programs can help patients who have been treated with immunotherapy.

Podocytopathy in the mesangial proliferative immunoglobulin A nephropathy: new insights into the mechanisms of damage and progression

Immunoglobulin A nephropathy (IgAN) was defined as a mesangiopathic disease, since the primary site of deposition of IgA immune material is the mesangium, and proliferation of mesangial cells and matrix excess deposition are the first histopathologic lesions. However, the relentless silent progression of IgAN is mostly due to the development of persistent proteinuria, and recent studies indicate that a major role is played by previous damage of function and anatomy of podocytes. In IgAN, the podocytopathic changes are the consequence of initial alterations in the mesangial area with accumulation of IgA containing immune material. Podocytes are therefore affected by interactions of messages originally driven from the mesangium. After continuous insult, podocytes detach from the glomerular basement membrane. This podocytopathy favours not only the development of glomerular focal and segmental sclerosis, but also the progressive renal function loss. It is still debated whether these lesions can be prevented or cured by corticosteroid/immunosuppressive treatment. We aimed to review recent data on the mechanisms implicated in the podocytopathy present in IgAN, showing new molecular risk factors for progression of this disease. Moreover, these observations may indicate that the target for new drugs is not only focused on decreasing the activity of mesangial cells and inflammatory reactions in IgAN, but also on improving podocyte function and survival.

Urinary CD80: a biomarker for a favorable response to corticosteroids in minimal change disease

Minimal Change Disease (MCD) is the most common type of nephrotic syndrome in children. The etiology has remained unknown, although it is commonly thought to be due to an unknown circulating factor that triggers podocyte dysfunction. To date, several changes in podocytes have been reported in MCD, of which one is the expression of CD80, also known as B7.1, which is a costimulatory molecule that is normally expressed on antigen -presenting cells. Some studies suggest that subjects with steroid-sensitive MCD may express CD80 in their podocytes during relapse and that this expression is associated with high urinary levels of CD80. Indeed, subjects with MCD in remission, or subjects with other glomerular diseases, such as focal segmental glomerulosclerosis, have substantially lower levels of urinary CD80 excretion. A recent study has now reported that high levels of urinary CD80 may be a sensitive marker for steroid-sensitivity and that their presence is also associated with long-term preservation of renal function. Thus, urinary CD80 is emerging as a potential biomarker for steroid-responsiveness in children presenting with primary nephrotic syndrome.