Broadening horizons: the multifaceted functions of ferroptosis in kidney diseases.

Ferroptosis is an iron-dependent programmed cell death pattern that is characterized by iron overload, reactive oxygen species (ROS) accumulation and lipid peroxidation. Growing viewpoints support that the imbalance of iron homeostasis and the disturbance of lipid metabolism contribute to tissue or organ injury in various kidney diseases by triggering ferroptosis. At present, the key regulators and complicated network mechanisms associated with ferroptosis have been deeply studied; however, its role in the initiation and progression of kidney diseases has not been fully revealed. Herein, we aim to discuss the features, key regulators and complicated network mechanisms associated with ferroptosis, explore the emerging roles of organelles in ferroptosis, gather its pharmacological progress, and systematically summarize the most recent discoveries about the crosstalk between ferroptosis and kidney diseases, including renal cell carcinoma (RCC), acute kidney injury (AKI), diabetic kidney disease (DKD), autosomal dominant polycystic kidney disease (ADPKD), renal fibrosis, lupus nephritis (LN) and IgA nephropathy. We further conclude the potential therapeutic strategies by targeting ferroptosis for the prevention and treatment of kidney diseases and hope that this work will provide insight for the further study of ferroptosis in the pathogenesis of kidney-related diseases.

[Genetic analysis of a patient with Alport syndrome due to compound heterozygous variants of COL4A4 gene].

OBJECTIVE: To analyze the clinical phenotype and genetic characteristics of a patient with Alport syndrome. METHODS: A patient with Alport syndrome who had visited the First Affiliated Hospital of Zhengzhou University in November 2020 was selected as the study subject. Clinical data of the patient were collected. High-throughput sequencing was carried out to detect potential variant of the COL4A3, COL4A4 and COL4A5 genes, and Sanger sequencing was carried out for verification of candidate variants in the family. RESULTS: The main clinical manifestations of the patient included hematuria, proteinuria, and impaired hearing. Audiometric testing suggested symmetrical cochlear sensory neural hearing loss on both sides. Renal biopsy revealed mild mesangial proliferative glomerulonephritis. Genetic testing revealed that the patient has harbored compound heterozygous variants of the COL4A4 gene, namely c.940G>A (p.Gly314Ser) and c.3773G>A (p.Gly1258Asp), which were respectively inherited from her father and mother. Neither variant has been reported before, and were predicted to be pathogenic based on the guidelines from the American College of Medical Genetics and Genomics. CONCLUSION: The c.940G>A (p.Gly314Ser) and c.3773G>A (p.Gly1258Asp) compound heterozygous variants of the COL4A4 gene probably underlay the Alport syndrome in this patient. Above finding has enriched the mutational spectrum of the COL4A4 gene.

Quercetin Ameliorates Diabetic Kidney Injury by Inhibiting Ferroptosis via Activating Nrf2/HO-1 Signaling Pathway.

Diabetic nephropathy (DN) is thought to be the major cause of end-stage renal disease. Due to its complicated pathogenesis and the low efficacy of DN treatment, a deep understanding of new etiological factors may be useful. Ferroptosis, a nonapoptotic form of cell death, is characterized by the accumulation of iron-dependent lipid peroxides to lethal levels. Ferroptosis-triggered renal tubular injury is reported to participate in the development of DN, and blocking ferroptosis might be an effective strategy to prevent the development of DN. Quercetin (QCT), a natural flavonoid that is present in a variety of fruits and vegetables, has been reported to ameliorate DN. However, its underlying nephroprotective mechanism is unclear. Herein, we explored the antiferroptosic effect of QCT and verified its nephroprotective effect using DN mice and high glucose (HG)-incubated renal tubular epithelial cell models. We found HG-induced abnormal activation of ferroptosis of renal tubular epithelial cells, and QCT treatment inhibited ferroptosis by downregulating the expression of transferrin receptor 1 (TFR-1) and upregulating the expression of glutathione peroxidase 4 (GPX4), ferritin heavy chain 1 (FTH-1), and the cystine/glutamate reverse antiporter solute carrier family 7 member (SLC7A11) in DN mice and HG-incubated HK-2 cells. Subsequently, both in vitro and in vivo results confirmed that QCT activated the NFE2-related factor 2 (Nrf2)/Heme oxygenase-1(HO-1) signaling pathway by increasing the levels of Nrf2 and HO-1. Therefore, this study supports that QCT inhibits the ferroptosis of renal tubular epithelial cells by regulating the Nrf2/HO-1 signaling pathway, providing a novel insight into the protective mechanism of QCT in DN treatment.

Metabolic Understanding of the Genetic Dysregulation in the Tumor Microenvironment of Kidney Renal Clear Cell Carcinoma.

The metabolic dysregulation is a hallmark of cancers including KIRC, specifically caused by alterations in metabolic genes. Currently, a lack of consensus exists between metabolic signatures in the tumor microenvironment. Here, in this study, we observed the significant correlations of differentially expressed metabolic genes (DEmGs) between KIRC and the related normal samples. Briefly, we collected sets of metabolic genes through RNA-seq data of KIRC and normal tissues from TCGA, followed by the identification of KIRC-related DEmGs. Next, patients were classified into three clusters, and using WGCNA, we identified metabolic genes involved in the survival among different clusters. Furthermore, we investigated survival and clinical parameters along with immune infiltration in the clusters. At the same time, we constructed and validated a prediction model based on these DEmGs. These analyses revealed that the patients having high expression of DEmGs showed poor survival, while infiltration of less-immune cells was associated with the metastasis of KIRC. In the end, we identified NUDT1 as a hub gene as it showed significantly high expression in KIRC samples as well as associated with the survival and prognosis of the patients. Further analysis revealed the oncogenic role of NUDT1 in 786-O and ACHN cells. Thus, we conclude that NUDT1 could be a potential diagnostic and prognostic marker for KIRC.

HNRNPA1-mediated exosomal sorting of miR-483-5p out of renal tubular epithelial cells promotes the progression of diabetic nephropathy-induced renal interstitial fibrosis.

Diabetic nephropathy (DN) is a serious complication in type 1 and type 2 diabetes, and renal interstitial fibrosis plays a key role in DN progression. Here, we aimed to probe into the role and potential mechanism of miR-483-5p in DN-induced renal interstitial fibrosis. In this study, we corroborated that miR-483-5p expression was lessened in type 1 and type 2 diabetic mice kidney tissues and high glucose (HG)-stimulated tubular epithelial cells (TECs), and raised in the exosomes derived from renal tissues in type 1 and type 2 diabetic mice. miR-483-5p restrained the expressions of fibrosis-related genes in vitro and renal interstitial fibrosis in vivo. Mechanistically, miR-483-5p bound both TIMP2 and MAPK1, and TIMP2 and MAPK1 were bound up with the regulation of miR-483-5p on renal TECs under HG conditions. Importantly, HNRNPA1-mediated exosomal sorting transported cellular miR-483-5p out of TECs into the urine. Our results expounded that HNRNPA1-mediated exosomal sorting transported cellular miR-483-5p out of TECs into the urine, thus lessening the restraint of cellular miR-483-5p on MAPK1 and TIMP2 mRNAs, and ultimately boosting extracellular matrix deposition and the progression of DN-induced renal interstitial fibrosis.

Silencing of long noncoding RNA PVT1 inhibits podocyte damage and apoptosis in diabetic nephropathy by upregulating FOXA1.

The number of patients with diabetic nephropathy (DN) is still on the rise worldwide, and this requires the development of new therapeutic strategies. Recent reports have highlighted genetic factors in the treatment of DN. Herein, we aimed to study the roles of long noncoding RNA (lncRNA) plasmacytoma variant translocation 1 (PVT1) and histone 3 lysine 27 trimethylation (H3K27me3) in DN. A model of DN was established by inducing diabetes in mice with streptozotocin. Mouse podocyte clone 5 (MPC5) podocytes and primary podocytes were cultured in normal and high glucose media to observe cell morphology and to quantify PVT1 expression. The roles of PVT1 and enhancer of zeste homolog 2 (EZH2) were validated via loss-of-function and gain-of-function in vitro experiments to identify the interactions among PVT1, EZH2, and forkhead box A1 (FOXA1). The podocyte damage and apoptosis due to PVT1 and FOXA1 were verified with in vivo experiments. PVT1 was highly expressed in MPC5 and primary podocytes in DN patients and in cultures grown in high glucose medium. A large number of CpG (C-phosphate-G) island sites were predicted at the FOXA1 promoter region, where PVT1 recruited EZH2 to promote the recruitment of H3K27me3. The silencing of PVT1 or the overexpression of FOXA1 relieved the damage and inhibited the apoptosis of podocytes in DN, as was evidenced by the upregulated expression of synaptopodin and podocin, higher expression of Bcl-2, and lower expression of Bax and cleaved caspase-3. The key findings of this study collectively indicate that the suppression of lncRNA PVT1 exerts inhibitory effects on podocyte damage and apoptosis via FOXA1 in DN, which is of clinical significance.

Vitamin D protects podocytes from autoantibodies induced injury in lupus nephritis by reducing aberrant autophagy.

SUBJECT: The aim of this study was to investigate whether vitamin D plays a protective role in podocyte injury induced by autoantibodies purified from the serum of patients with lupus nephritis (LN) via reducing aberrant autophagy. METHODS: Autophagic activities of renal tissues of patients with LN were evaluated under transmission electronic microscope (TEM). Immunoglobulin G (IgG) from patients with LN was purified to induce human podocyte injury, and the role of vitamin D in injury was observed. Podocytes were observed under TEM, autophagic activity was evaluated by western blot analysis and quantitative real-time polymerase chain reaction, and mRFP-GFP-LC3B adenovirus was infected into human podocytes in vitro. RESULTS: Significantly higher autophagic levels were observed in patients with LN (P <0.05), and apparently greater autophagic levels in podocytes were shown (P <0.05). Among different classifications of LN, class V (n = 5), III + V (n = 5), and IV + V (n = 5) gained higher autophagic levels than class III (n = 5) and IV (n = 5). Induced autophagy, which was evident by increased LC3B-II and Beclin 1 level, caused consumption of p62, more autophagosomes observed under TEM, and more LC3B dots observed under confocal microscope in the IgG group, along with decreased nephrin expression, which suggests podocyte injury. Reduction of autophagy as well as alleviated podocyte injury was observed in the IgG+ vitamin D group. CONCLUSION: This study demonstrates that vitamin D plays a protective role in podocyte injury induced by autoantibodies from patients with LN and appears to be a novel therapy target in LN.

MiR-130a-5p prevents angiotensin II-induced podocyte apoptosis by modulating M-type phospholipase A2 receptor.

Podocyte apoptosis is considered as the important element that promotes the development and progress of membranous nephropathy (MN). Unfortunately, the underlying mechanism of podocytes apoptosis in MN remains elusive. We compared the renal expressions of miR-130a-5p and M-type phospholipase A2 receptor (PLA2R) between MN patients (n = 30) and 30 controls by qRT-PCR and western blot, respectively. The podocyte damage model in vitro was established by angiotensin II (Ang II, 100 nmol/L) exposure for 24 h. Interaction between miR-130a-5p and PLA2R was determined using dual-luciferase reporter gene assay. MN mice were induced by intravenous injection of cBSA. In this study, miR-130a-5p expression was significantly decreased both in the renal biopsy specimens from MN patients and podocyte cell line AB8/13 following stimulation of Ang II. Overexpressed miR-130a-5p in AB8/13 cells significantly attenuated the Ang II induced-apoptosis in vitro. In contrast, down-regulated miR-130a-5p induced podocyte apoptosis. PLA2R was identified as the target of miR-130a-5p in AB8/13 cells. And up-regulated or down-regulated PLA2R could obviously attenuate the effect of miR-130a-5p overexpression or knockdown on the apoptosis of AB8/13 cells. Furthermore, it was also observed that overexpressed miR-130a-5p by miR-130a-5p agomir could obviously alleviate renal injury in MN mice. In conclusion, decreased miR-130a-5p was contributed to the pathological mechanism of MN through increasing PLA2R expression, which induced podocyte apoptosis.

The Expression of Tristetraprolin and Its Relationship with Urinary Proteins in Patients with Diabetic Nephropathy.

OBJECTIVE: Tristetraprolin (TTP), also known as zinc finger protein 36, is an RNA binding protein that has a significant role in regulating the expression of mRNAs containing AU-rich elements. We postulated that TTP might regulate interleukin (IL)-6 and IL-18 expression in diabetes. This study aimed to test the hypothesis that the levels of TTP are correlated with nephropathy in patients with type 2 diabetes. METHODS: Eighty-seven patients (61.3±9.6 years old) who had been diagnosed with type 2 diabetes mellitus and 41 age and sex matched healthy control subjects were enrolled. The diabetes patients were classified into those without proteinuria, with microalbuminuria, and with clinical proteinuria groups according to the ratio of urinary excretion of albumin/creatinine (ACR). RESULTS: Serum and urinary levels of IL-6 and IL-18 were significantly elevated, but those of TTP were significantly decreased in patients with diabetes as compared with control subjects. In addition, serum and urinary levels of IL-6 and IL-18 were significantly higher, but those of TTP were significantly lower in patients with proteinuria than in patients without proteinuria or with microalbuminuria. There was a significant correlation between serum TTP and IL-6/IL-18 (correlation coefficients of -0.572 and -0.685, P < 0.05). CONCLUSION: These results show that diabetes with clinical proteinuria is accompanied by decreased urinary and serum level of TTP and increased levels of IL-6 and IL-18. Decreased TTP expression might occur prior to the increase in IL-6 and IL-18, and decrease of TTP might provide an earlier marker for glomerular dysfunction than IL-6 and IL-18.

Valsartan combined with clopidogrel and/or leflunomide for the treatment of progressive immunoglobulin A nephropathy.

AIM: The current standard treatment for IgA nephropathy relies on steroid and/or immunosuppressive therapy and angiotensin converting enzyme inhibitors (ACEI) or angiotensin receptor blocker (ARB). This study examines the benefits and safety of combining valsartan with clopidogrel and leflunomide as a treatment for progressive IgA nephropathy. METHODS: Patients with primary IgA nephropathy, confirmed by renal biopsy, were recruited for this study. Patients were separated into four groups (n = 42 each) after 2 months of run-in period of valsartan treatment. All patients were treated with valsartan alone (Group 1) or valsartan and either clopidogrel (Group 2) or leflunomide (Group 3) or both clopidogrel and leflunomide (Group 4). Each group was followed up for their next 24 months for 24 h urinary protein excretion, serum creatinine and estimated glomerular filtration rate (eGFR) to assess the effect of the treatment. Adverse effects were recorded concurrently to evaluate the safety of the treatment. RESULTS: Of all 168 patients, 107 were males and 61 were females, with an average age of 33.8 ± 8.79 years. Baseline characteristics were comparable among the four groups (P > 0.05) prior to the experimental treatment. There was a significant (P < 0.05) decrease in 24 h urinary protein excretion after 4 months of experimental treatment. At the end of the 24 months, groups 3 and 4 showed a respective 62.35% and 69.47% reduction in proteinuria. The serum creatinine was significantly higher (P < 0.05) in group 1 and 2 at the end of the follow-up, and their respective eGFR was significantly lower. The incidence of cardiovascular complication was 11.9% and 9.5% for group 1 and 3, respectively. CONCLUSIONS: The treatment with Valsartan combined with Clopidogrel and Leflunomide can reduce the urinary proteins loss and renal function deterioration for IgA nephropathy patients and cause minimal adverse reactions. Our study suggests a new clinical treatment option for IgA nephropathy.