Weijie Yuan

Vascular calcification in chronic kidney disease is induced by bone morphogenetic protein-2 via a mechanism involving the Wnt/β-catenin pathway.

Background: Vascular calcification (VC), in which vascular smooth muscle cells (VSMCs) undergo a phenotypic transformation into osteoblast-like cells, is one of the emergent risk factors for the accelerated atherosclerosis process characteristic of chronic kidney disease (CKD). Phosphate is an important regulator of VC. Methods: The expression of different smooth muscle cell or osteogenesis markers in response to high concentrations of phosphate or exogenous bone morphogenetic protein 2 (BMP-2) was examined by qRT-PCR and western blotting in rat VSMCs. Osteocalcin secretion was measured by radioimmunoassay. Differentiation and calcification of VSMCs were examined by alkaline phosphatase (ALP) activity assay and Alizarin staining. Short hairpin RNA-mediated silencing of β-catenin was performed to examine the involvement of Wnt/β-catenin signaling in VSMC calcification and osteoblastic differentiation induced by high phosphate or BMP-2. Apoptosis was determined by TUNEL assay and immunofluorescence imaging. Results: BMP-2 serum levels were significantly higher in CKD patients than in controls. High phosphate concentrations and BMP-2 induced VSMC apoptosis and upregulated the expression of β-catenin, Msx2, Runx2 and the phosphate cotransporter Pit1, whereas a BMP-2 neutralization antibody reversed these effects. Knockdown of β-catenin abolished the effect of high phosphate and BMP-2 on VSMC apoptosis and calcification. Conclusions: BMP-2 plays a crucial role in calcium deposition in VSMCs and VC in CKD patients via a mechanism involving the Wnt/β-catenin pathway.

Effects of genistein on secretion of extracellular matrix components and transforming growth factor beta in high-glucose-cultured rat mesangial cells

The ideal treatment for diabetic nephropathy should slow the progress of renal failure, delay the initiation of dialysis, and protect residual renal function in patients receiving dialysis. Renal mesangial cells play an important role in these processes. In the current study, we investigated the effects of genistein on rodent renal mesangial cells cultured in a high-glucose environment. Since overexpression of the extracellular matrix (ECM) components (type IV collagen and fibronectin) and transforming growth factor beta (TGF-β) have been previously implicated in the development of the renal glomerulus damage of diabetic nephropathy, we included these substances in our study. The results showed that high concentration of glucose (450 mg·dl−1) stimulated the synthesis of type IV collagen and fibronectin and the secretion of TGF-β. These responses were attenuated by genistein (≥5 μmol·l−1) in a dose- and time-dependent manner. In conclusion, we demonstrated that genistein could inhibit the secretion of ECM components and the expression of TGF-β at both the protein and mRNA levels. These findings should be followed up by further studies and clinical trials to verify the potential therapeutic effects of genistein on diabetic nephropathy.

Effect of Neutral pH and Low-Glucose Degradation Product-Containing Peritoneal Dialysis Solution on Residual Renal Function in Peritoneal Dialysis Patients: A Meta-Analysis

Background: Glucose degradation products (GDPs) in peritoneal dialysis (PD) solution (PDS) have been shown to inflict damage to the kidney, which is the major organ for advanced glycosylation end product elimination. Hence, this study investigated whether new PDSs with neutral pH and low-GDPs have a beneficial effect on the preservation of residual renal function (RRF) among PD patients. Methods: Randomized controlled trials examining the effect of neutral pH and low-GDP PDSs on RRF in PD patients >18 years old compared with conventional PDSs were selected. The modality of PD treatment was continuous ambulatory PD. The primary outcome variable was mean RRF value. Weekly Kt/V, urine volume, peritoneal ultrafiltration, blood pressure and all-cause mortality of PD patients were measured as secondary outcome variables. Results: We identified 6 randomized controlled trials and found that patients using low-GDP PDSs had a much slower rate of RRF loss compared with patients using conventional PDSs [mean difference (MD) = 0.45, 95% confidence intervals (CI) 0.10-0.80, p = 0.01]. In addition, weekly Kt/V was markedly improved in the low-GDP PDS group (MD = 0.13, 95% CI 0.06-0.21, p = 0.0005), and urine volume was increased (MD = 110.34, 95% CI 8.58-212.10, p = 0.03). No significant differences were observed between the two groups with respect to peritoneal ultrafiltration, blood pressure and risk of all-cause mortality. Conclusion: Our meta-analysis demonstrates a significant benefit of using low-GDP PDSs for RRF preservation in PD patients. Further trials are needed to determine whether this beneficial effect can affect long-term clinical outcomes.

Effects of hepatitis B virus X gene on apoptosis and expression of immune molecules of human proximal tubular epithelial cells

The hepatitis B virus X protein (HBx) is the most important determinant in viral pathogenesis. HBx regulates HBV replication, cellular transcription, signal transduction, proteasome activity and cell cycle progression. In this study, HK-2 cells were transiently transfected with the HBx gene using a eukaryotic vector, pcDNA3.1/myc-HBx. Transfection with the HBx gene increased the number of apoptotic cells. In addition, cultured HK-2 cells became irregular in shape. The expression of α-SMA and E-cadherin, TLR4, MHC-II and CD40 was increased. The transfection resulted in increased IL-1, IL-6, TNF-α and IFN-γ levels in the supernatant and decreased IL-4 in the supernatant. In conclusion, overexpression of the HBx gene in renal tubular epithelial cells induces apoptosis of HK-2 cells and promotes epithelial-mesenchymal transdifferentiation. HBx transfection upregulates the expression of immune molecules in renal tubular epithelial cells and induces an imbalance in cytokine levels.

DC-SIGN expression on podocytes and its role in inflammatory immune response of lupus nephritis

Podocytes, the main target of immune complex, participate actively in the development of glomerular injury as immune cells. Dendritic cell‐specific intercellular adhesion molecule‐3‐grabbing non‐integrin (DC‐SIGN) is an innate immune molecular that has an immune recognition function, and is involved in mediation of cell adhesion and immunoregulation. Here we explored the expression of DC‐SIGN on podocytes and its role in immune and inflammatory responses in lupus nephritis (LN). Expression of DC‐SIGN and immunoglobulin (Ig)G1 was observed in glomeruli of LN patients. DC‐SIGN was co‐expressed with nephrin on podocytes. Accompanied by increased proteinuria of LN mice, DC‐SIGN and IgG1 expressions were observed in the glomeruli from 20 weeks, and the renal function deteriorated up to 24 weeks. Mice with anti‐DC‐SIGN antibody showed reduced proteinuria and remission of renal function. After the podocytes were stimulated by serum of LN mice in vitro, the expression of DC‐SIGN, major histocompatibility complex (MHC) class II and CD80 was up‐regulated, stimulation of T cell proliferation was enhanced and the interferon (IFN)‐γ/interleukin (IL)‐4 ratio increased. However, anti‐DC‐SIGN antibody treatment reversed these events. These results suggested that podocytes in LN can exert DC‐like function through their expression of DC‐SIGN, which may be involved in immune and inflammatory responses of renal tissues. However, blockage of DC‐SIGN can inhibit immune functions of podocytes, which may have preventive and therapeutic effects.

Vitamin D supplements in chronic kidney disease.

Abstract Chronic kidney disease (CKD) is a significant public health problem and Vitamin D deficiency is prevalent in CKD and might be associated with calcium and phosphate metabolism, cardiovascular disease, infections as well as the progress of kidney dysfunction. Emerging evidence implies that Vitamin D supplements may be of benefit to CKD. Based on existing laboratory and clinical evidence, this review intends to discuss the effectiveness of Vitamin D supplements and controversy in clinical practice. The effect of Vitamin D in CKD patients is summarized in detail from CKD–mineral bone disease, the progression of renal function, cardiovascular events and immune system. Considerable disputes exist for the Vitamin D supplements in CKD, and a growing amount of experimental evidence and some clinical evidence are now gathering from in vitro, animal and epidemiological studies.

Hepatitis B virus X protein modulates renal tubular epithelial cell-induced T-cell and macrophage responses

Renal tubular epithelial cells (RTECs) have an active role in renal inflammation, functioning as antigen‐presenting cells as they constitutively express major histocompatibility complex‐II and co‐stimulatory molecules that can activate T cells and macrophages. Previous studies indicate that inflammatory cell infiltration and tubulointerstitial fibrosis are present in renal biopsies from Hepatitis B virus (HBV)‐associated glomerulonephritis (HBV‐GN) patients. We hypothesized that disorder RTECs may be involved in the progression of HBV‐GN. Here, we measured renal function and inflammatory cells infiltration in C57BL/6J‐TgN mice, and data showed that in C57BL/6J‐TgN mice HBV x protein (HBx) mainly deposited in RTECs, and CD4+ T cells and macrophages infiltrated into the interstitium. In vitro HBx upregulated CD40 expression in RTECs. In HK‐2/CD4+ T cells co‐culture system, we found that HBx‐stimulated HK‐2 cells could activate CD4+ T cells, promote their proliferation, and lead to an imbalance of interleukin (IL)‐4 and interferon‐γ. In HK‐2/macrophages co‐culture system, we found that HBx‐stimulated HK‐2 cells also increased macrophage adherent capacity and promoted MCP‐1 and tumor necrosis factor‐α and IL‐1β secretion. These immune dysfunction may contribute to the pathogenesis of HBV‐GN.

Phosphate stimulates myotube atrophy through autophagy activation: evidence of hyperphosphatemia contributing to skeletal muscle wasting in chronic kidney disease

BackgroundAccelerated muscle atrophy is associated with a three-fold increase in mortality in chronic kidney disease (CKD) patients. It is suggested that hyperphosphatemia might contribute to muscle wasting, but the underlying mechanisms remain unclear. Although evidence indicates that autophagy is involved in the maintenance of muscle homeostasis, it is not known if high phosphate levels can result in activation of autophagy, leading to muscle protein loss.MethodsImmortalized rat L6 myotubes were exposed to a high concentration of phosphate, with or without autophagy inhibition. Myotube atrophy was examined by phase contrast microscopy. Autophagic activity was assessed by measuring the expression of microtubule-associated protein 1 light chain 3 (LC3) and p62 using quantitative real-time polymerase chain reaction and western blot.ResultsPhosphate induced cell atrophy in L6 myotubes in a dose- and time-dependent manner, and these responses were not associated with calcification or osteogenesis. Phosphate also dose- and time-dependently increased the LC3-II/LC3-I ratio. Inhibition of autophagy with wortmannin or knockdown of Atg5 significantly suppressed myotube atrophy caused by high phosphate concentration.ConclusionsHigh phosphate concentration induces muscle cell atrophy through the activation of autophagy. Targeting autophagy could be a therapeutic strategy for preventing muscle wasting caused by hyperphosphatemia.

Hepatitis B virus X protein and proinflammatory cytokines synergize to enhance TRAIL-induced apoptosis of renal tubular cells by upregulation of DR4

Persistent infection with hepatitis B virus (HBV) may lead to HBV-associated glomerulonephritis (HBV-GN). Presence of HBV-DNA and -RNA in renal tubular epithelial cells (RTECs) suggests direct virus-induced injury. Increase in proinflammatory cytokines is also observed under these conditions. Apoptosis by tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) plays a significant role in the pathogenesis of HBV-infections. However, the effects of HBV X protein (HBx) on TRAIL-induced apoptosis of RTECs especially under certain inflammatory conditions remain obscure. Here, we show that HBx synergizes with proinflammatory cytokines to significantly increase TRAIL-induced apoptosis of RTECs. HBx markedly up-regulates death receptor-4 (DR4) expression by enhancing the activation of nuclear factor-kappa B (NF-κB) in the presence of proinflammatory cytokines. Dramatic increase in DR4 expression leads to the sensitization of RTECs to TRAIL-induced apoptosis. Furthermore, in patients with HBV-GN, DR4 expression in the kidneys is significantly elevated and is positively correlated with the HBx and proinflammatory cytokines expression. These findings provide a novel insight into the underlying mechanisms of renal tubule lesions induced by HBx in HBV-GN.

High Mobility Group Box 1 Promotes Aortic Calcification in Chronic Kidney Disease via the Wnt/β-Catenin Pathway

Vascular calcification (VC) is common in chronic kidney disease (CKD), where cardiovascular mortality remains the leading cause of death. Here, we examined the role of high-mobility group box1 (HMGB1), a nuclear DNA-binding protein involved in inflammation, in aortic calcification and renal dysfunction induced by high phosphate in a mouse model of CKD induced by 5/6 nephrectomy. HMGB1 and kidney function markers were measured by ELISA in the serum of CKD patients and in CKD mice. Sections of the aortas of mice were analyzed by immunofluorescence and Alizarin red staining, and protein lysates were generated to analyze the expression of related proteins in response to silencing of HMGB1 or β-catenin by western blotting. Our results showed that serum HMGB1 levels were significantly higher in CKD patients than in healthy controls and related to disease stage. High phosphate promoted the translocation of HMGB1 from the nucleus to the cytosol and aortic calcification in CKD mice in vivo, whereas HMGB1 knockdown ameliorated part of renal and vascular function. β-catenin silencing reversed high phosphate-induced calcification and restored renal marker levels. Taken together, our results suggest that HMGB1 is involved in VC associated with CKD via a mechanism involving the β-catenin.