Possible role of autoantibodies against nephrin in an experimental model of chronic graft-versus-host disease

Detailed Pathophysiology of Minimal Change Disease: Insights into Podocyte Dysfunction, Immune Dysregulation, and Genetic Susceptibility

Minimal Change Disease (MCD) is a predominant cause of idiopathic nephrotic syndrome in the pediatric population, yet presents significant clinical challenges due to its frequent relapses and steroid resistance. Despite its relatively benign histological appearance, MCD is characterized by severe proteinuria, hypoalbuminemia, and edema, which may affect patient outcomes. Current treatment strategies primarily rely on corticosteroids, which are effective in inducing remission but are associated with high relapse rates, steroid resistance, and numerous long-term side effects, underscoring the need for more targeted and effective therapeutic approaches. This narrative review synthesizes current knowledge on the pathophysiological mechanisms underlying MCD, focusing on the following three critical areas: podocyte dysfunction, immune dysregulation, and genetic susceptibility. Podocyte dysfunction, particularly involving alterations in nephrin, plays a central role in the breakdown of the glomerular filtration barrier, leading to the characteristic proteinuria observed in MCD. Immune dysregulation, including the presence of autoantibodies against nephrin and other podocyte components, exacerbates podocyte injury and contributes to disease progression, suggesting an autoimmune component to the disease. Genetic factors, particularly mutations in the NPHS1 and NPHS2 genes, have been identified as significant contributors to disease susceptibility, influencing the variability in treatment response and overall disease severity. Understanding these mechanisms is crucial for developing targeted therapies that address the underlying causes of MCD rather than merely managing its symptoms. This review highlights the need for further research into these pathophysiological processes to pave the way for more personalized and effective treatment strategies, ultimately improving patient outcomes and reducing reliance on corticosteroids.

Liquid biopsy for non-invasive monitoring of patients with kidney transplants

The current tools for diagnosing and monitoring native kidney diseases as well as allograft rejection in transplant patients are suboptimal. Creatinine and proteinuria are non-specific and poorly sensitive markers of injury. Tissue biopsies are invasive and carry potential complications. In this article, we overview the different techniques of liquid biopsy and discuss their potential to improve patients' kidney health. Several diagnostic, predictive, and prognostic biomarkers have been identified with the ability to detect and monitor the activity of native kidney diseases as well as early and chronic allograft rejection, such as donor-derived cell-free DNA, exosomes, messenger RNA/microsomal RNA, proteomics, and so on. While the results are encouraging, additional research is still needed as no biomarker appears to be perfect for a routine application in clinical practice. Despite promising advancements in biomarkers, the most important issue is the lack of standardized pre-analytical criteria. Large validation studies and uniformed standard operating procedures are required to move the findings from bench to bedside. Establishing consortia such as the Liquid Biopsy Consortium for Kidney Diseases can help expedite the research process, allow large studies to establish standardized procedures, and improve the management and outcomes of kidney diseases and of kidney transplant recipients.

Kidney complications of hematopoietic stem cell transplantation

Hematopoietic stem cell transplantation (HSCT) exposes a patient's kidneys to a unique combination of challenges, including high-dose radiation, anemia, chemotherapeutic agents, graft-versus-host disease, opportunistic infections, attenuated and altered immunologic responses, fluid and electrolyte imbalances, and extensive courses of antimicrobial agents. Since the inception of HSCT in the 1950s, there has been increasing interest in defining, determining, and managing the kidney complications that accompany this procedure. In this article, we review the common causes of acute kidney injury and chronic kidney disease that occur with HSCT, including HSCT-associated thrombotic microangiopathy, a distinct cause of chronic kidney disease with a multifactorial cause previously known as bone marrow transplant nephropathy or radiation nephropathy. Additionally, we review other kidney complications, including calcineurin inhibitor nephrotoxicity and chronic graft-versus-host disease-associated glomerulonephritis, that develop post-HSCT. Critically, due to its grave prognosis, it is important to identify HSCT-associated thrombotic microangiopathy early, as well as distinguish it from the other causes of chronic kidney disease.

Effects of oligodeoxynucleotide with CCT repeats on chronic graft versus host disease induced experimental lupus nephritis in mice

A synthesized single-stranded oligodeoxynucleotide (ODN), designed as SAT05f with the sequence of human microsatellite DNA, has been studied for its capacity of alleviating the lupus nephritis in the chronic graft versus host disease (cGVHD) induced lupus-prone mice. In cGVHD model mice, both of continuous and discontinuous treatment with SAT05f was effective on reducing anti-ssDNA antibody production, decreasing renal IgG deposition and delaying the onset of lupus nephritis. In addition, SAT05f could down-regulate TLR9 mRNA expression in splenocytes of cGVHD model mice. These results indicated that SAT05f could be developed as a new therapeutic agent for the treatment of lupus nephritis by inhibiting TLR9 signaling pathways.

A novel method for isolating podocytes using magnetic activated cell sorting

BACKGROUND

A large body of accumulated data has now revealed that podocytes play a major role in the development of proteinuria. However, the mechanisms of podocyte injury, leading to foot process effacement and proteinuria, are still unclear partly due to the current lack of an appropriate strategy for preparing podocytes. In this study, we have developed a novel method of rapid isolation of podocytes from mice using magnetic activated cell sorting with an anti-nephrin antibody.

METHODS

After endothelial cell depletion using anti-CD31 antibody, nephrin-positive cells were prepared from mouse kidneys using magnetic activated cell sorting with polyclonal rabbit anti-nephrin antibody. Purity of the positively sorted cells was determined by confocal microscopy and fluorescence-activated cell sorting (FACS) analysis. Expression profiles of podocyte-specific molecules in the sorted fractions were characterized by qualitative PCR and immunoblot analysis.

RESULTS

Nephrin-positive cells, isolated from mouse kidneys within 6 h, showed dual positivity for synaptopodin and rabbit IgG on confocal microscopy. FACS analysis revealed that the purity of the positively sorted fractions was ∼75%. The nephrin-positive cells sorted by this approach showed a significantly higher expression of podocyte-specific molecules compared with nephrin-negative fractions.

CONCLUSIONS

These data strongly suggest that our novel method for isolating podocytes has great utility for various downstream applications such as genomic analysis, proteomics and transcriptomics to elucidate molecular profiling of podocyte biology in vivo compared with conventional methods as our approach requires only several hours to complete and no tissue culture.

Renal pathology in hematopoietic cell transplantation recipients

Hematopoietic cell transplantation-associated renal injury may be related to a combination of factors including chemotherapy, radiation, infection, immunosuppressive agents, ischemia, and graft-versus-host disease. Renal biopsy specimens from hematopoietic cell transplant recipients at two institutions (Stanford University Medical Center and Oregon Health & Science University) were reviewed in correlation with clinical data. Fifteen cases were identified (post hematopoietic cell transplant time 0.7-14.5 years), including six with autologous hematopoietic cell transplant. Indications for renal biopsy included proteinuria (n=13; nephrotic range in 8), increased serum creatinine (n=10), or both (n=6). Many patients had multiple pathologic findings on renal biopsy. Membranous glomerulonephritis was the most common diagnosis (n=7), including two patients with autologous hematopoietic cell transplant and five with evidence of chronic graft-versus-host disease elsewhere. Four membranous glomerulonephritis patients achieved sustained remission with rituximab therapy. Other glomerular pathology included focal segmental glomerulosclerosis (n=1) and minimal change disease (n=1). Evidence of thrombotic microangiopathy was common (in isolation or combined with other pathology), as was acute tubular necrosis and tubulointerstitial nephritis. Of 14 patients with follow-up (2-64 months, mean 19 months), 6 had chronic renal insufficiency (serum creatinine >1.5 mg/dl), 2 had end stage renal disease, and 6 had essentially normal renal function. Our retrospective study shows that renal dysfunction in hematopoietic cell transplant recipients is often multifactorial, and biopsy may reveal treatable causes. Membranous glomerulonephritis is seen in autologous and allogeneic hematopoietic cell transplant recipients, and may respond to anti-B-cell therapy, which has implications regarding pathogenesis and relationship to graft-versus-host disease.

Target antigens and nephritogenic antibodies in membranous nephropathy: of rats and men

Membranous nephropathy, a disease characterized by an accumulation of immune deposits on the outer aspect of the glomerular basement membrane, is the most common cause of idiopathic nephrotic syndrome in white adults. In the rat model of Heymann nephritis, the target antigen of antibodies is megalin, a multiligand receptor expressed at the podocyte cell surface. This review summarizes key findings provided by this experimental model and by our discovery of neutral endopeptidase being the alloantigen involved in neonatal cases of membranous nephropathy. We discuss the role of alloimmunization as a new mechanism of renal disease and the approach that we use to identify new podocyte antigens. We also summarize current knowledge on the mechanism of proteinuria, with special emphasis on the role of complement. In conclusion, substantial progresses have been made in understanding molecular mechanisms of membranous nephropathy, which should lead to novel therapeutic approaches.

Podocyte antigens and glomerular disease

BACKGROUND

Membranous nephropathy (MN), a major cause of nephrotic syndrome in the adult, is an immune-mediated disease characterized by the accumulation of subepithelial immune deposits leading to complement activation and podocyte injury. However, the target antigens of circulating antibodies are unknown. Current treatments for patients with MN are entirely empirical, and concept-driven therapies are dramatically lacking.

METHODS

Specificity of circulating antibodies and composition of glomerular deposits were analyzed in Heymann nephritis (HN), a faithful rat model of MN, and in a subset of patients with antenatal MN.

RESULTS

20 years after the identification of megalin as the podocyte target antigen of nephritogenic antibodies in HN, we identified the human counterpart of megalin, the enzymatic podocyte antigen neutral endopeptidase (NEP). Antibodies to megalin or NEP induce formation of subepithelial immune deposits and of C5b-9, the membrane attack complex of complement.

CONCLUSION

It is likely that antigens involved in idiopathic MN are expressed at the podocyte membrane. Their identification together with that of immunodominant epitopes may lead to specific antigen/ epitope-based immunotherapy aimed at inducing specific tolerance.

Mechanisms of Disease: alloimmunization in renal diseases

Graft rejection has long been considered the paradigm of renal diseases induced by alloimmunization, particularly alloimmunization directed against HLA antigens. Accumulating evidence indicates that non-HLA immunity also has an important role in clinical transplantation. Targets of alloimmunization include antigens of tubular basement membrane, tubular epithelial cells and endothelial cells. They can be polymorphic allovariants (as shown in the rat) or 'hidden' antigens exposed when the graft is damaged. Alloimmunization can also occur when a person genetically deficient in a renal protein (e.g. the alpha5 (IV) collagen chain in X-linked Alport's syndrome or nephrin in Finnish-type nephrotic syndrome) is transplanted to treat end-stage renal failure. The non-mutated protein in the donor kidney is recognized as a foreign antigen, and the resulting alloimmune response can damage the graft. We have demonstrated that alloimmunity can also affect the native kidney. We have characterized a novel fetomaternal disease in which a genetic defect in the MME gene encoding neutral endopeptidase (NEP) in the mother leads to the development of membranous nephropathy in her fetus (maternal anti-NEP antibodies bind to NEP on fetal podocytes). Our findings raise the possibility that mutations or genetic polyporphisms in MME or other genes expressed by the podocyte are involved in alloimmune-mediated development of membranous nephropathy after kidney or bone marrow transplantation.