Hepatitis B Virus X Protein Reduces Podocyte Adhesion via Downregulation of α3β1 Integrin

Abstract

Background/Aims: Hepatitis B virus (HBV)-associated glomerulonephritis (HBV-GN) is characterized by a reduced number of podocytes due to apoptosis and shedding from the basement membrane. However, the pathological mechanism of HBV-GN is unclear. We previously showed that hepatitis B virus X protein (HBx) promotes apoptosis in tubular epithelial cells. In this study, we transfected podocytes with HBx and examined the effects on adhesion and apoptosis of these cells. Methods: Podocytes were transfected with pc-DNA3.1 (+)-HBx. One control group was not transfected and another control group was transfected with empty plasmids. Podocyte adhesion was assessed by a fluorescence assay, apoptosis was measured by flow cytometry and fluorescence microscopy, and expression of α3β1 integrin was determined by western blotting and the reverse transcription polymerase chain reaction (RT-PCR). Activity of caspase-8 was measured by a spectrophotometric assay. Results: Relative to controls, podocytes with pc-DNA3.1(+)-HBx had reduced cell adhesion, increased apoptosis, reduced expression of α3β1 integrin, and increased caspase-8 activity. β1 integrin blockage reduced podocyte adhesion, but increased apoptosis and caspase-8 activity. Treatment of transfected podocytes with a caspase-8 inhibitor (Z-IETD-FMK) had no effect on the HBx-mediated integrin downregulation and reduced podocyte adhesion, suggesting that α3β1 integrin downregulaton is sufficient to alter cell adhesion. Conclusions: Our in vitro results indicate that HBx reduced podocyte adhesion and expression of α3β1 integrin, and increased apoptosis. Moreover, HBx-mediated downregulation of α3β1 integrin expression is sufficient to reduce podocyte adhesion. HBx-induced apoptosis of podocytes may contribute to HBV-GN.

Hepatitis�B virus X protein decreases nephrin expression and induces podocyte apoptosis via activating STAT3

“…HBx is considered the most important determinant in viral pathogenesis (22,23); it is a necessary transcription factor for HBV replication, having an trans-activation effect, which can promote viral replication and induce apoptosis directly, and subsequently induce the occurrence of an inflammatory reaction and serve an important role in cell transformation and proliferation (24,25). Due to the widely trans-activation properties of the HBx gene and its effect on glomerular foot cells, mesangial cells and renal tubule epithelial cells (26)(27)(28)(29), it is considered to have an important role in the pathogenesis of HBV-GN (28,29). A previous study by Zhang et al (15) demon-15) demon-) demonstrated that podocyte number was significantly decreased in the glomeruli of children with HBV-GN, while HBx protein was visualized within the glomerulus in 71% children with HBV-GN, where the expression of HBx protein was localized mainly in the cytoplasm of podocytes, with lower expression in the nuclei of the podocytes (19).…”

“…Apoptosis is a major method involved in podocyte decline (35,36), and the present study confirmed that HBx could increase the apoptosis of podocytes. Recently, studies have investigated the mechanisms underlying HBx-induced apoptosis of renal tubular cells (29,37), and He et al (28) suggested that HBx could reduce podocyte adhesion via downregulation of α3β1 integrin.…”

Autophagy Dysregulation in Diabetic Kidney Disease: From Pathophysiology to Pharmacological Interventions

“…Podocytes or glomerular epithelial cells constitute a critical component of the glomerular filtration barrier (GFB). As podocytes have no capacity to regenerate themselves, their loss, when significant, will subsequently result in an alteration of the GBF, leading to proteinuria and renal failure [ 63 , 64 , 65 , 66 ].…”

ATF4-dependent heme-oxygenase-1 attenuates diabetic nephropathy by inducing autophagy and inhibiting apoptosis in podocyte

“…Podocytes or glomerular epithelial cells are terminally specialized cells that play a critical role in forming the glomerular filtration barrier. Structural changes or injuries in podocytes are associated with renal injury resulting in proteinuria and severe renal insufficiency [3][4][5][6], and contributes to DN [7].…”