Extracellular HMGB1 Induced Glomerular Endothelial Cell Injury via TLR4/MyD88 Signaling Pathway in Lupus Nephritis

Previously, our study showed that HMGB1 was significantly elevated in the blood and located in the glomerular endothelium in LN patients. But whether extracellular HMGB1 is involved in the injury of glomerular endothelial cells (GECs) in LN still needs further investigation. Firstly, we detected the levels of SDC-1, VCAM-1, and proteinuria in LN patients and MRL/lpr mice and analyzed their correlations. Then, HMGB1 and TLR4/MyD88 were inhibited to observe the shedding of glycocalyx and injury of GECs in vivo and in vitro. Our results showed that HRGEC injury and SDC-1 shedding played an important role in the increase of permeability and proteinuria formation in LN. Additionally, inhibition of extracellular HMGB1 and/or downstream TLR4/MyD88/NF-κB/p65 signaling pathway also alleviated GEC monolayer permeability, reduced the shedding of the glomerular endothelial glycocalyx, improved the intercellular tight junction and cytoskeletal arrangement, and downregulated the NO level and VCAM-1 expression. These results suggested that extracellular HMGB1 might involve in GEC injury by activating the TLR4/MyD88 signaling pathway in LN, which provided novel insights and potential therapeutic target for the treatment of lupus nephritis.

Glomerular Endothelial Cell-Derived microRNA-192 Regulates Nephronectin Expression in Idiopathic Membranous Glomerulonephritis

BackgroundAutoantibodies binding to podocyte antigens cause idiopathic membranous glomerulonephritis (iMGN). However, it remains elusive how autoantibodies reach the subepithelial space because the glomerular filtration barrier (GFB) is size selective and almost impermeable for antibodies.MethodsKidney biopsies from patients with iMGN, cell culture, zebrafish, and mouse models were used to investigate the role of nephronectin (NPNT) regulating microRNAs (miRs) for the GFB.ResultsGlomerular endothelial cell (GEC)-derived miR-192-5p and podocyte-derived miR-378a-3p are upregulated in urine and glomeruli of patients with iMGN, whereas glomerular NPNT is reduced. Overexpression of miR-192-5p and morpholino-mediated npnt knockdown induced edema, proteinuria, and podocyte effacement similar to podocyte-derived miR-378a-3p in zebrafish. Structural changes of the glomerular basement membrane (GBM) with increased lucidity, splitting, and lamellation, especially of the lamina rara interna, similar to ultrastructural findings seen in advanced stages of iMGN, were found. IgG-size nanoparticles accumulated in lucidity areas of the lamina rara interna and lamina densa of the GBM in npnt-knockdown zebrafish models. Loss of slit diaphragm proteins and severe structural impairment of the GBM were further confirmed in podocyte-specific Npnt knockout mice. GECs downregulate podocyte NPNT by transfer of miR-192-5p–containing exosomes in a paracrine manner.ConclusionsPodocyte NPNT is important for proper glomerular filter function and GBM structure and is regulated by GEC-derived miR-192-5p and podocyte-derived miR-378a-3p. We hypothesize that loss of NPNT in the GBM is an important part of the initial pathophysiology of iMGN and enables autoantigenicity of podocyte antigens and subepithelial immune complex deposition in iMGN.

XCL1 Aggravates Diabetic Nephropathy-Mediated Renal Glomerular Endothelial Cell Apoptosis and Inflammatory Response via Regulating p53/Nuclear Factor-Kappa B Pathway

<b><i>Background:</i></b> Glomerular endothelial cell damage plays an important role in the occurrence and development of diabetic nephropathy (DN). <b><i>Objectives:</i></b> This study aimed to clarify the role of XCL1 in DN-mediated glomerular endothelial cell apoptosis and whether the function was related to the activation of the p53/nuclear factor-kappa B (NF-κB) signaling pathway. <b><i>Methods:</i></b> Candidate biomarkers were identified by least absolute shrinkage and selection operator (LASSO) regression model analysis. The area under the receiver operating characteristic curve value was calculated and used to evaluate the discriminating ability. Cell viability, apoptosis, and interleukin-1β and tumor necrosis factor-α expression at messenger RNA and protein levels were detected by using the Cell Counting Kit-8, flow cytometry, ELISA, real-time polymerase chain reaction, and Western blotting assays. In vivo studies were conducted in the DN mice. <b><i>Results:</i></b> The LASSO regression model displayed good discriminating performance, with a C-index of 0.803 and good calibration, and high XCL1 expression was identified as the predicting factor for DN in diabetes mellitus patients. XCL1 expression was upregulated in glomeruli of db/db mice, which was closely related to the expression of its receptor (XCR1). XCL1 overexpression played an important role in the apoptosis and inflammatory response of high glucose (HG)-treated human renal glomerular endothelial cells. Meanwhile, the expression of p53 and the levels of inflammatory cytokines were upregulated upon XCL1 overexpression. p53 silencing with its inhibitor blocked the apoptotic response and inflammatory response in XCL1-overexpressed cells exposed to HG. Besides, the XCL1 overexpression-induced downregulation of NF-κB was reversed by pifithrin-α pretreatment. <b><i>Conclusions:</i></b> Our findings in this work provided the mechanistic insights into the effects of XCL1 on the modulation of DN development, illustrating that XCL1 might serve as an essential prognostic indicator and therapeutic target for DN progression.

FC 029PODOCYTE AND GLOMERULAR ENDOTHELIAL CELL DERIVED MICRORNAS REGULATE PODOCYTE NEPHRONECTIN IN MEMBRANOUS GLOMERULONEPHRITIS

Background and Aims Autoantibodies binding to podocyte antigens cause idiopathic membranous glomerulonephritis (iMGN). However, it remains elusive how autoantibodies reach the subepithelial space because the glomerular filtration barrier is normally size selective and impermeable for antibodies. Method Kidney biopsies from patients with MGN, cell culture, zebrafish and mice models were used to investigate the role of nephronectin (NPNT) regulating microRNAs (miRs) for the glomerular filtration barrier. Results We found that endothelial cell-derived miR-192-5p and podocyte-derived miR-378a-3p are upregulated in patients with anti-phospholipase A2 receptor antibody positive (PLA2R-ab+) iMGN and regulate glomerular NPNT expression (Fig. 1). Overexpression of miR-378a-3p and miR-192-5p as well as morpholino mediated npnt knockdown in zebrafish induced edema, proteinuria, loss of podocyte markers and podocyte effacement. The most prominent phenotype however were structural changes of the glomerular basement membrane (GBM) with increased lucidity, slicing and lamellation especially of the lamina rara interna (Fig. 2, Fig. 3). The phenotype was comparable to ultrastructural findings seen in iMGN. IgG sized nanoparticles accumulated in lucidity areas of the lamina rara interna and lamina densa of the GBM in npnt knockdown zebrafish models. Loss of slit diaphragm proteins and severe structural impairment of the GBM were further confirmed in podocyte specific Npnt knockout mice (Fig. 4). Conclusion Podocyte NPNT is important for proper glomerular filter function and GBM structure and is regulated by podocyte and glomerular endothelial cell derived miRs. We hypothesize that loss of NPNT in the GBM is part of the pathophysiology of iMGN and enables subepithelial immune complex deposition in iMGN.