Role of histone demethylase KDM6B in HBx-mediated podocyte-macrophage transdifferentiation

Abstract

Objective: To explore the expression of lysine (k)-specific demethylase 6B (KDM6B) in the renal tissues of hepatitis B virus-associated glomerulonephritis (HBV-GN) patients and human podocytes transfected with hepatitis B virus X (HBx) gene, and its role in HBx-mediated podocyte-macrophage transdifferentiation (PMT). Methods: Forty-eight patients diagnosed as HBV-GN by renal biopsy from 2013 to 2018 at the Shanghai Jiaotong University Affiliated First People's Hospital were included in this study. Thirty patients with primary glomerulonephritis (PGN) and fifteen patients with renal tumor were chosen as control group. The expression of KDM6B and macrophage marker F4/80 in renal tissues of HBV-GN patients was observed by immunofluorescence and immunohistochemistry. The association between kidney KDM6B levels and clinical features of HBV-GN patients was analyzed. The expression of KDM6B, F4/80, major histocompatibility complex (MHC)-Ⅱ and CD40 in the podocytes was detected by Western blotting. The contents of interferon-γ (IFN-γ) and interleukin-6 (IL-6) in the supernatant were determined by enzyme-linked immunosorbent assay (ELISA). The small interfering RNA of KDM6B (KDM6B siRNA) was used to silence the expression of KDM6B and the protein levels of KDM6B, F4/80 and tri-methylation of lysine 27 of histone H3 (H3K27me3) induced by HBx gene transfection were detected by Western blotting. Results: Renal KDM6B expression was significantly increased in HBV-GN patients compared to normal control (0.022±0.004 vs 0.006±0.002, P=0.006). There was no significant difference in the positive rate of KDM6B among different pathological types of HBV-GN (P=0.139). Moreover, co-expression of KDM6B and F4/80 could be observed in the podocytes of HBV-GN patients. Patients with estimated glomerular filtration (eGFR)<60 ml·min-1·(1.73 m2)-1or proteinuria ≥ 3.5 g/day had a significantly higher renal KDM6B expression compared to control groups (all P<0.05). In addition, the expression of KDM6B, F4/80, MHC-II and CD40 was significantly up-regulated in the podocytes transfected with HBx gene (all P<0.05). The content of IFN-γ and IL-6 in the supernatant was significantly increased (all P<0.05). After gene silencing of KDM6B, the expression of F4/80 induced by HBx in the podocytes was significantly down-regulated, while the level of H3K27me3 was significantly increased (both P<0.05). Conclusions: HBx could induce KDM6B expression in podocytes and initiate PMT, thereby involving in the dysfunction of immune microenviroment in the renal tissues of HBV-GN.