The Study of Angptl4-Modulated Podocyte Injury in IgA Nephropathy

Angiopoietin-like protein 4 dysregulation in kidney diseases: a promising biomarker and therapeutic target

The global burden of renal diseases is increasingly severe, underscoring the need for in-depth exploration of the molecular mechanisms underlying renal disease progression and the development of potential novel biomarkers or therapeutic targets. Angiopoietin-like protein 4 (ANGPTL4) is a multifunctional cytokine involved in the regulation of key biological processes, such as glucose and lipid metabolism, inflammation, vascular permeability, and angiogenesis, all of which play crucial roles in the pathogenesis of kidney diseases. Over the past 2 decades, ANGPTL4 has been regarded as playing a pivotal role in the progression of various kidney diseases, prompting significant interest from the scientific community regarding its potential clinical utility in renal disorders. This review synthesizes the available literature, provides a concise overview of the molecular biological effects of ANGPTL4, and highlights its relationship with multiple renal diseases and recent research advancements. These findings underscore the important gaps that warrant further investigation to develop novel targets for the prediction or treatment of various renal diseases.

Advancing the clinical assessment of glomerular podocyte pathology in kidney biopsies via super-resolution microscopy and angiopoietin-like 4 staining

Rationale: The tertiary structure of normal podocytes prevents protein from leaking into the urine. However, observing the complexity of podocytes is challenging because of the scale differences in their three-dimensional structure and the close proximity between neighboring cells in space. In this study, we explored podocyte-secreted angiopoietin-like 4 (ANGPTL4) as a potential morphological marker via super-resolution microscopy (SRM). Methods and Results: Specimens from patients with minimal change disease (MCD), focal segmental glomerulosclerosis (FSGS), and membranous nephropathy (MN), along with normal controls, were analyzed via immunofluorescence and immunohistochemistry to determine the expression and localization of ANGPTL4, confirming its extensive presence in podocytes across both healthy and diseased conditions. Immunoelectron microscopy revealed that ANGPTL4 is distributed throughout the podocyte cell body, primary processes, and foot processes. Compared with conventional podocyte markers such as nephrin and synaptopodin, ANGPTL4 excels in depicting the three-dimensional structure of podocytes via SRM imaging. We then refined a protocol using tyramide signal amplification staining and confocal microscopy to uniformly enhance podocyte fluorescence, facilitating the clinical assessment of biopsies. In patients diagnosed with MCD and FSGS, measurements of slit diaphragm density, primary process width, and foot process width were taken after further co-staining with nephrin to identify patterns of podocyte morphological alterations. Distinctive patterns of foot process effacement were identified in MCD and FSGS patients, with FSGS patients showing more pronounced podocyte injury. Conclusions: ANGPTL4 serves as a reliable morphological marker for podocyte analysis, offering enhanced visualization of their three-dimensional structure and facilitating the identification of distinct pathological changes in nephrotic syndrome patients.

The successful use of rituximab in IgA nephropathy patients with podocytopathy: a case series

Background

Immunoglobulin A nephropathy (IgAN) with podocytopathy is a rare pathological type of glomerular disease. The use of rituximab (RTX) in the treatment of glomerular diseases has increased in recent decades, but the efficacy of RTX in the treatment of patients with IgAN and podocytopathy has rarely been reported.

Methods

This was a single-centre retrospective study of IgAN patients with podocytopathy who were treated with RTX as second-line therapy was conducted at our centre from 2019 to 2022. The aim of this study was to investigate the efficacy and safety of RTX in IgAN patients with podocytopathy.

Results

Seven out of eight patients met the criteria for complete remission following RTX therapy. Only one patient experienced adverse events (infectious diarrhoea and pulmonary infection) and experienced relapse 6 months after RTX therapy. The maximum relapse-free time after RTX therapy was 20 months, while the maximum relapse-free time before RTX therapy was only 6 months. The number of relapses before RTX therapy (per year) was one to four; moreover, seven patients did not relapse and maintained remission at the last follow-up despite steroid withdrawal after RTX therapy.

Conclusion

Overall, RTX effectively reduced proteinuria, increased the maximum relapse-free time, reduced the number of relapses per year and helped patients stop steroid use as soon as possible. RTX also helped most patients achieve clinical remission. RTX appears to be an effective and safe alternative for treating IgAN patients with podocytopathy with steroid dependence or frequent relapse.

The ANGPTL4-HIF-1α loop: a critical regulator of renal interstitial fibrosis

BACKGROUND

Renal interstitial fibrosis (RIF) is a progressive, irreversible terminal kidney disease with a poor prognosis and high mortality. Angiopoietin-like 4 (ANGPTL4) is known to be associated with fibrosis in various organs, but its impact on the RIF process remains unclear. This study aimed to elucidate the role and underlying mechanisms of ANGPTL4 in the progression of RIF.

METHODS

In vivo, a chronic kidney disease (CKD) rat model of renal interstitial fibrosis was established via intragastric administration of adenine at different time points (4 and 6 weeks). Blood and urine samples were collected to assess renal function and 24-h urinary protein levels. Kidney tissues were subjected to HE and Masson staining for pathological observation. Immunohistochemistry and real-time quantitative PCR (qRT‒PCR) were performed to evaluate the expression of ANGPTL4 and hypoxia-inducible factor-1α (HIF-1α), followed by Pearson correlation analysis. Subsequently, kidney biopsy tissues from 11 CKD patients (6 with RIF and 5 without RIF) were subjected to immunohistochemical staining to validate the expression of ANGPTL4. In vitro, a fibrosis model of human renal tubular epithelial cells (HK2) was established through hypoxic stimulation. Subsequently, an HIF-1α inhibitor (2-MeOE2) was used, and ANGPTL4 was manipulated using siRNA or plasmid overexpression. Changes in ANGPTL4 and fibrosis markers were analyzed through Western blotting, qRT‒PCR, and immunofluorescence.

RESULTS

ANGPTL4 was significantly upregulated in the CKD rat model and was significantly positively correlated with renal injury markers, the fibrotic area, and HIF-1α. These results were confirmed by clinical samples, which showed a significant increase in the expression level of ANGPTL4 in CKD patients with RIF, which was positively correlated with HIF-1α. Further in vitro studies indicated that the expression of ANGPTL4 is regulated by HIF-1α, which in turn is subject to negative feedback regulation by ANGPTL4. Moreover, modulation of ANGPTL4 expression influences the progression of fibrosis in HK2 cells.

CONCLUSION

Our findings indicate that ANGPTL4 is a key regulatory factor in renal fibrosis, forming a loop with HIF-1α, potentially serving as a novel therapeutic target for RIF.

Neuroblastoma suppressor of tumorigenicity 1 is associated with the severity of interstitial fibrosis and kidney function decline in IgA nephropathy

INTRODUCTION

Recently, circulating neuroblastoma suppressor of tumorigenicity 1 (NBL1) was shown to be strongly associated with kidney disease progression and histological lesions in patients with diabetic kidney disease. This study aimed to examine whether serum NBL1 level was also associated with kidney function and renal histological findings in patients with IgA nephropathy.

METHODS

We evaluated the levels of NBL1 in 109 patients with newly diagnosed biopsy-proven primary IgAN, between 2009 and 2018, at the Nihon University School of Medicine Itabashi Hospital, Tokyo, Japan, using serum obtained immediately before the renal biopsy, and examined the relationship between serum NBL1, renal function and renal histological findings assessed using the Oxford Classification (MEST score). Furthermore, we analyzed the association of serum NBL1 with kidney function decline over time in patients with IgA nephropathy who had follow-up data on the estimated glomerular filtration rate (n = 76).

RESULTS

Serum NBL1 levels in patients with newly diagnosed IgA nephropathy were elevated, as compared to those in healthy individuals (n = 93). Logistic regression analysis demonstrated that the serum NBL1 level was independently and significantly associated with tubular atrophy/interstitial fibrosis. Immunohistochemical staining revealed that NBL1 was highly expressed in the tubulointerstitium. Furthermore, Spearman's rank correlation identified a significant correlation between serum NBL1 level and estimated glomerular filtration rate slope.

CONCLUSIONS

The serum NBL1 level was significantly associated with the severity of renal interstitial fibrosis and kidney disease progression in patients with newly diagnosed IgA nephropathy. Thus, circulating NBL1 may serve as a good biomarker for evaluating renal interstitial fibrosis and the risk of kidney disease progression.

Therapeutic potential of artemisinin and its derivatives in managing kidney diseases

Artemisinin, an antimalarial traditional Chinese herb, is isolated from Artemisia annua. L, and has shown fewer side effects. Several pieces of evidence have demonstrated that artemisinin and its derivatives exhibited therapeutic effects on diseases like malaria, cancer, immune disorders, and inflammatory diseases. Additionally, the antimalarial drugs demonstrated antioxidant and anti-inflammatory activities, regulating the immune system and autophagy and modulating glycolipid metabolism properties, suggesting an alternative for managing kidney disease. This review assessed the pharmacological activities of artemisinin. It summarized the critical outcomes and probable mechanism of artemisinins in treating kidney diseases, including inflammatory, oxidative stress, autophagy, mitochondrial homeostasis, endoplasmic reticulum stress, glycolipid metabolism, insulin resistance, diabetic nephropathy, lupus nephritis, membranous nephropathy, IgA nephropathy, and acute kidney injury, suggesting the therapeutic potential of artemisinin and its derivatives in managing kidney diseases, especially the podocyte-associated kidney diseases.

TNF-α-mediated podocyte injury via the apoptotic death receptor pathway in a mouse model of IgA nephropathy

BACKGROUND

IgA nephropathy (IgAN) is the most common primary glomerular disease worldwide and it is characterized by mesangial IgA deposits. Proteinuria is a common clinical feature of IgAN, which has a critical connection to podocyte injury and has been used as a clinical prognostic factor for IgAN. Evidence has shown that TNF-α released from mesangial cells may lead to podocyte apoptosis.

METHODS

Forty male BALB/c mouse were randomly divided into the control group and IgAN group. A mice model of IgAN was developed by oral administration of bovine serum albumin (BSA) combined with Staphylococcus Enterotoxin B (SEB) tail vein injection. Urinary protein concentrations, renal function, renal morphological, IgA deposition, apoptosis situation, and the mRNA and protein expression of nephrin, podocin, TNF-α, TNFR1, caspase-8 and caspase-3, were detected after 12 weeks.

RESULTS

BSA and SEB can successfully establish an IgAN mouse model, and the main pathological changes are the IgA immune complex deposition in the mesangial area. The gene and protein expression levels of nephrin and podocin were found to be downregulated, and death receptor pathway-related indicators were upregulated, and they were involved in TNF-α-activated podocyte injury and apoptosis in IgAN mice.

CONCLUSION

TNF-α may play an important role in the pathogenesis of podocyte apoptosis in IgAN, and its effects may be mediated through the apoptotic death receptor pathway.