Dipeptidase 1 promotes ferroptosis in renal tubular epithelial cells in diabetic nephropathy via inhibition of the GSH/GPX4 axis.

Renal tubular injury is an important pathological change associated with diabetic nephropathy (DN), in which ferroptosis of renal tubular epithelial cells is critical to its pathogenesis. Inhibition of the glutathione/glutathione peroxidase 4 (GSH/GPX4) axis is the most important mechanism in DN tubular epithelial cell ferroptosis, but the underlying reason for this is unclear. Our biogenic analysis showed that a zinc-dependent metalloproteinase, dipeptidase 1 (DPEP1), is associated with DN ferroptosis. Here, we investigated the role and mechanism of DPEP1 in DN tubular epithelial cell ferroptosis. DPEP1 upregulation was observed in the renal tubular epithelial cells of DN patients and model mice, as well as in HK-2 cells stimulated with high glucose. Furthermore, the level of DPEP1 upregulation was associated with the degree of tubular injury in DN patients and HK-2 cell ferroptosis. Mechanistically, knocking down DPEP1 expression could alleviate the inhibition of GSH/GPX4 axis and reduce HK-2 cell ferroptosis levels in a high glucose environment. HK-2 cells with stable DPEP1 overexpression also showed GSH/GPX4 axis inhibition and ferroptosis, but blocking the GSH/GPX4 axis could mitigate these effects. Additionally, treatment with cilastatin, a DPEP1 inhibitor, could ameliorate GSH/GPX4 axis inhibition and relieve ferroptosis and DN progression in DN mice. These results revealed that DPEP1 can promote ferroptosis in DN renal tubular epithelial cells via inhibition of the GSH/GPX4 axis.

Pericyte activation accompanied by peritubular capillaries dysfunction and pericyte-to-myofibroblast transition is associated with renal fibrosis in diabetic nephropathy.

Background: Tubulointerstitial renal fibrosis is an essential feature of diabetic nephropathy (DN). Pericytes play a critical role in microvascular diseases and renal fibrogenesis. However, the role of pericytes in DN remains unclear. Herein, we aimed to explore the properties and possible mechanisms of pericytes in renal fibrosis in DN. Methods: We used multiplex immunofluorescence staining to evaluate the location and expression of activated pericytes and to assess capillary dilation and interstitial fibrosis in the kidneys of db/db mice. Pericytes were co-stained for alpha-smooth muscle actin (α-SMA) to determine which ones differentiate into myofibroblasts in db/db mice. Expression of CD34 and platelet-derived growth factor receptor beta (PDGFR-ß) was assessed in kidney tissue from patients with DN by immunohistochemical staining. Results: We found that cell staining for nerve/glial antigen 2 (NG2)+ and PDGFR-ß+ was greater in the kidneys of db/db mice than in those of db/m mice. There was impaired pericyte coverage of blood vessels and capillary dilation in the renal interstitium. These changes were accompanied by increased collagen I staining and an increase in the number of pericytes with profibrotic phenotypes, as identified by increased NG2+/PDGFR-ß+/α-SMA+ and decreased NG2+/PDGFR-ß+/α-SMA- staining. In DN patients, expression of PDGFR-ß was stronger and there was loss of CD34 compared with the findings in control patients with minor glomerular lesions. Conclusion: In this study, we demonstrated that pericyte activation accompanied by peritubular capillary dysfunction and pericytemyofibroblast transition is associated with renal fibrosis in DN.

Renalase Prevents Renal Fibrosis by Inhibiting Endoplasmic Reticulum Stress and Down-Regulating GSK-3ß/Snail Signaling.

Background: Treating renal fibrosis is crucial to delaying chronic kidney disease. The glycogen synthase kinase-3ß (GSK-3ß)/Snail pathway regulates renal fibrosis and Renalase can ameliorate renal interstitial fibrosis. However, it is not clear whether GSK-3ß/Snail signaling affects Renalase action. Here, we explored the role and mechanism of GSK-3ß/Snail in the anti-fibrosis action of Renalase. Materials and methods: We used mice with complete unilateral ureteral obstruction (UUO) and human proximal renal tubular epithelial (HK-2) cells with transforming growth factor-ß1 (TGF-ß1)-induced fibrosis to explore the role and regulatory mechanism of the GSK-3ß/Snail pathway in the amelioration of renal fibrosis by Renalase. Results: In UUO mice and TGF-ß1-induced fibrotic HK-2 cells, the expression of p-GSK-3ß-Tyr216/p-GSK-3ß-Ser9, GSK-3ß and Snail was significantly increased, and endoplasmic reticulum (ER) stress was activated. After Renalase supplementation, fibrosis was alleviated, ER stress was inhibited and p-GSK-3ß-Tyr216/p-GSK-3ß-Ser9, GSK-3ß and Snail were significantly down-regulated. The amelioration of renal fibrosis by Renalase and its inhibitory effect on GSK-3ß/Snail were reversed by an ER stress agonist. Furthermore, when an adeno-associated virus or plasmid was used to overexpress GSK-3ß, the effect of Renalase on delaying renal fibrosis was counteracted, although ER stress markers did not change. Conclusion: Renalase prevents renal fibrosis by down-regulating GSK-3ß/Snail signaling through inhibition of ER stress. Exogenous Renalase may be an effective method of slowing or stopping chronic kidney disease progression.

A prospective study on tryptophan immunoadsorption in AQP4 antibody-positive neuromyelitis optica spectrum disorders.

INTRODUCTION: Neuromyelitis optica spectrum disorders (NMOSD) is a rare inflammatory demyelinating disease of the central nervous system. NMOSD pathogenesis is mainly mediated by antibodies directed against aquaporin4 (AQP4 antibody). Immunoadsorption (IA) could specifically remove pathogenic antibody to alleviate the disease. Until now, prospective studies concerning the efficacy of IA on NMOSD are scarce. This study aims to prospectively evaluate the efficacy and safety of IA in the treatment of NMOSD. PATIENTS AND METHODS: We included patients with AQP4 antibody-positive NMOSD who were hospitalized from September 2019 to September 2020, with no significant improvement in symptoms after 1 week of high-dose intravenous steroid therapy. Tryptophan IA therapy was initiated with five sessions on alternate days. Expanded Disability Status Scale (EDSS), visual acuity, and laboratory values were measured before and after IA, with a follow-up of 6 months. Spinal magnetic resonance imaging (MRI) characteristics were collected. Related side effects were recorded. RESULTS: Seven patients were enrolled in the present study. After five IA, the patients' EDSS decreased from 5.71 ± 2.04 to 4.64 ± 2.29, P = .006. The visual acuity of the three visually impaired patients was improved. AQP4-IgG decreased significantly from 80.00 (interquartile range [IQR], 21.00-80.00) (U/mL) to 9.72 (IQR, 5.21-55.57) (U/mL) (P = .018). MRI of the spinal cord showed the scope of the myelopathy was narrowed and no significant enhancement was observed on postcontrast T1-weighted image at 90 days after treatment. Only one patient had transient hypotension. CONCLUSIONS: Tryptophan IA therapy effectively and safely improved neurological function and visual acuity, and reduced the AQP4 antibody concentration in patients with NMOSD.

Association of short-term blood pressure variability with cardiovascular mortality among incident hemodialysis patients.

OBJECTIVE: To investigate the association of short-term blood pressure variability (BPV) with cardiovascular mortality in hemodialysis (HD) patients, using a reliable index called average real variability (ARV), and to assess the factors associated with ARV in incident HD population. METHODS: A total of 103 HD patients were recruited, with 44-h ambulatory blood pressure monitoring performed after the midweek HD session. Systolic BPV was assessed by SD, coefficient of variation (CV), and ARV, respectively. Laboratory data were obtained from blood samples before the midweek HD. All patients were followed up for 24 months. RESULTS: According to the median of BPV indices, the comparisons between patients with the low and high values were conducted. Kaplan-Meier analysis showed the survival curves corresponding to median of SD and CV exhibit similar performance for the low and high groups (p = .647, p = .098, respectively). In contrast, patients with higher ARV had a lower survival rate than those with lower ARV (77.8% vs. 98.0%, p = .002). After adjustment for demographics and clinical factors, ARV (HR: 1.143; 95% CI: 1.022-1.279, p = .019) and high-sensitivity C-reactive protein (HR: 1.394; 95% CI: 1.025-1.363, p = .021) were associated with increased risk of cardiovascular mortality in HD patients. Age and interdialytic weight gain (IDWG) were related factors for ARV (ß = 0.065, p = .005; ß = 0.825, p = .003, respectively). CONCLUSIONS: Greater ARV was independently associated with increased risk of cardiovascular mortality in HD patients. Age and IDWG were independent related factors for ARV.

The mechanism of long-term low-dose asymmetric dimethylarginine inducing transforming growth factor-ß expression in endothelial cells.

Asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase (NOS) inhibitor, accumulates in plasma during chronic kidney disease (CKD). High plasma levels of ADMA can increase transforming growth factor-ß (TGF-ß) expression, related to renal fibrosis, but the precise molecular mechanism is not explicit. The present study was designed to determine the mechanism through which long-term low-dose ADMA induces TGF-ß expression in endothelial cells and to investigate the molecular mechanism of its action. Human umbilical vein endothelial cells (HUVECs) were exposed to low-dose ADMA (5 and 10 µmol/l) for 7 passages and TGF-ß expression was determined. Human renal glomerular endothelial cells (HRGECs) were exposed to high-dose ADMA (100 µmol/l) which were used to clarify the molecular mechanism. The results showed that long-term low-dose ADMA (5 and 10 µmol/l) increases TGF-ß production in both mRNA and protein levels in HUVECs in a time-dependent manner. We confirmed that exogenous ADMA (100 µmol/l) significantly enhanced stress fiber formation in HRGECs and upregulated TGF-ß expression. Such effects of ADMA in HRGECs were inhibited by pre-treatment with actin depolymerizing agent, actin stabilizing agent, p38 MAPK inhibitor and NADPH oxidase inhibitor. In addition, we demonstrated that ADMA (100 µmol/l) significantly activated nuclear factor-κB (NF-κB) in HRGECs, which was markedly attenuated by actin depolymerizing agent, actin stabilizing agent, p38 MAPK inhibitor and NADPH oxidase inhibitor. In brief, the present study demonstrated that long-term low-dose ADMA induces TGF-ß expression in endothelial cells at both the gene and protein levels. The actin cytoskeleton may be involved in modulation of ADMA-induced NF-κB activation and the ensuing TGF-ß expression in HRGECs.

Actin cytoskeleton-dependent pathways for ADMA-induced NF-κB activation and TGF-ß high expression in human renal glomerular endothelial cells.

Asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase inhibitor, is considered to be an independent risk factor in the progression of chronic kidney diseases (CKD). It can induce kidney fibrosis by increasing transforming growth factor (TGF)-ß1 expression, but its molecular mechanism is unclear. The aim of the present study was to investigate the role of actin cytoskeleton in ADMA-induced TGF-ß1 high expression in human renal glomerular endothelial cells (HRGECs). The structure of stress fibers was visualized by immunofluorescence, nuclear factor-κB (NF-κB) DNA-binding activity was assessed by an electrophoretic mobility shift assay and TGF-ß1 expression was assessed by western blot analysis. Results showed that ADMA induced the assembly of stress fibers, DNA binding of NF-κB, and increasing expression of TGF-ß1. When the dynamics of actin cytoskeleton was perturbed by the actin-depolymerizing agent cytochalasin D and the actin-stabilizing agent jasplakinolide, or ablation of stress fiber bundles by the nicotineamide adenine dinucleotide phosphate oxidase inhibitor apocynin and p38 mitogen-activated protein kinase inhibitor SB203580, ADMA-induced DNA binding of NF-κB and TGF-ß1 expression were inhibited. These results revealed an actin cytoskeleton-dependent mechanism in ADMA-induced NF-κB activation and TGF-ß1 high expression in HRGECs. The specific targeting of the actin cytoskeleton may be a useful strategy to prevent ADMA-activated kidney fibrosis in CKD.