Human Vascular Pericytes and Cytomegalovirus Pathobiology

Pericytes are multipotent cells of the vascular system with cytoplasmic extensions proximal to endothelial cells that occur along the abluminal surface of the endothelium. The interactions between endothelial cells and pericytes are essential for proper microvascular formation, development, stabilization, and maintenance. Pericytes are essential for the regulation of paracellular flow between cells, transendothelial fluid transport, angiogenesis, and vascular immunosurveillance. They also influence the chemical composition of the surrounding microenvironment to protect endothelial cells from potential harm. Dysregulation or loss of pericyte function can result in microvascular instability and pathological consequences. Human pericytes have been shown to be targets for human cytomegalovirus (HCMV) infection and lytic replication that likely contribute to vascular inflammation. This review focuses on human vascular pericytes and their permissiveness for HCMV infection. It also discusses their implication in pathogenesis in the blood⁻brain barrier (BBB), the inner blood⁻retinal barrier (IBRB), the placenta⁻blood barrier, and the renal glomerulus as well as their potential role in subclinical vascular disease.

Zika Virus Infection of the Human Glomerular Cells: Implications for Viral Reservoirs and Renal Pathogenesis

Background

Zika virus (ZIKV) infection in the human renal compartment has not been reported. Several clinical reports have describe high-level persistent viral shedding in the urine of infected patients, but the associated mechanisms have not been explored until now. The current study examined cellular components of the glomerulus of the human kidney for ZIKV infectivity.

Methods

I infected primary human podocytes, renal glomerular endothelial cells (GECs), and mesangial cells with ZIKV. Viral infectivity was analyzed by means of microscopy, immunofluorescence, real-time reverse-transcription polymerase chain reaction (RT-PCR), and quantitative RT-PCR (qRT-PCR), and the proinflammatory cytokines interleukin 1β, interferon β, and RANTES (regulated on activation of normal T cells expressed and secreted) were assessed using qRT-PCR.

Results

I show that glomerular podocytes, renal GECs, and mesangial cells are permissive for ZIKV infection. ZIKV infectivity was confirmed in all 3 cell types by means of immunofluorescence staining, RT-PCR, and qRT-PCR, and qRT-PCR analysis revealed increased transcriptional induction of interleukin 1β, interferon β, and RANTES in ZIKV-infected podocytes at 72 hours, compared with renal GECs and mesangial cells.

Conclusions

The findings of this study support the notion that the glomerulus may serve as an amplification reservoir for ZIKV in the renal compartment. The impact of ZIKV infection in the human renal compartment is unknown and will require further study.

HBV X gene transfection upregulates IL-1beta and IL-6 gene expression and induces rat glomerular mesangial cell proliferation

The X gene of HBV encodes a 17-kD protein, termed HBx, which has been shown to function as a transcriptional trans-activator of a variety of viral and cellular promoter/enhancer elements. The aim of this study was to investigate the effect of HBx on gene expression of interleukin (IL)-1 and IL-6, and proliferation of rat mesangial cells in vitro. The X gene of HBV was amplified by PCR assay, and inserted into the eukaryotic expression vector pCI-neo. The structure of recombinant pCI-neo-X plasmid was proved by restrict endonuclease digestion and sequencing analysis. pCI-neo-X was transfected into cultured rat mesangial cell line in vitro via liposome. HBx expression in transfected mesangial cells was detected by Western blot. The IL-1beta and IL-6 mRNA expression in those cells was assayed by semiquantitative RT-PCR. Mesangial cell proliferation was tested by MTT. The results showed that HBx was obviously expressed in cultured mesangial cell line at 36th and 48th h after transfection. The expression of IL-1beta and IL-6 mRNA was simultaneously increased. The cell proliferation was also obvious at the same time. It was concluded that HBx gene transfection could induce IL-1beta and IL-6 gene expression and mesangial cell proliferation. HBx may play a critical role in mesangial cell proliferation through upregulation of the IL-1beta and IL-6 gene expression.

Genetic analysis of J-virus and Beilong virus using minireplicons

J-virus (JPV), isolated from wild mice in Australia, and Beilong virus (BeiPV), originally isolated from human mesangial cells in China and subsequently detected in rat mesangial cells, represent a new group of paramyxoviruses which have exceptionally large genomes (>19 kb) and contain more than six transcriptional units. In this study, minireplicons were employed to assess the taxonomic status of JPV and BeiPV. Our results demonstrated that, whilst the genome replication machineries of JPV and BeiPV can be interchanged, they were not functional when exchanged with that of Nipah virus. These studies indicate that JPV and BeiPV are closely related to each other and support the classification of these two viruses into a separate genus. In addition, the minireplicons were also used to demonstrate that these large-genome viruses also comply with the 'rule of six' and that over-expression of the C protein has a detrimental effect on minigenome replication.

Endothelin 1 stimulates beta1Pix-dependent activation of Cdc42 through the G(salpha) pathway

Beta1Pix (PAK-interacting exchange factor) is a recently identified guanine nucleotide exchange factor (GEF) for the Rho family small G protein Cdc42/Rac. On stimulation with extracellular signals, GEFs induce the exchange of guanosine diphosphate to guanosine triphosphate, resulting in the activation of the small guanosine 5C-triphosphatases. This activation enables the signal to propagate to downstream effectors. Herein, we show that G(salpha) stimulation by cholera toxin increased Cdc42 activation by endothelin-1 (ET-1), whereas pertussis toxin had no effect. H-89, a protein kinase A (PKA) inhibitor, strongly inhibited Cdc42 activation by ET-1. Moreover, the overexpression of beta1Pix enhanced ET-1-induced Cdc42 activation. The essential role of beta1Pix in ET-1-induced Cdc42 activation was evidenced by the blocking of Cdc42 activation in cells expressing beta1Pix mutant lacking the ability to bind PAK (beta1Pix SH3m[W43K]) or mutant lacking GEF activity (beta1PixdeltaDH). The overexpression of mutant lacking the pleckstrin homology domain beta1PixdeltaPH, which is unable to bind phospholipids, had no effect on Cdc42 activation. These results demonstrate that beta1Pix, along with PKA, plays a crucial role in the regulation of Cdc42 activation by ET-1.

Novel role of toll-like receptor 3 in hepatitis C-associated glomerulonephritis

Hepatitis C virus (HCV) infection is frequently complicated by glomerulonephritis with immune complexes containing viral RNA. We examined the potential influence of Toll-like receptors (TLRs), specifically TLR3 recognition of viral dsRNA exemplified by polyriboinosinic:polyribocytidylic acid [poly(I:C) RNA]. Normal human kidney stained positive for TLR3 on mesangial cells (MCs), vascular smooth muscle cells, and collecting duct epithelium. Cultured MCs have low TLR3 mRNA levels with predominant intracellular protein localization, which was increased by tumor necrosis factor-alpha, interleukin (IL)-1beta, interferon (IFN)-gamma, and the TLR3 ligand poly(I:C) RNA. Poly(I:C) RNA stimulation of MCs increased mRNA and protein synthesis of IL-6, IL-1beta, M-CSF, IL-8/CXCL8, RANTES/CCL5, MCP-1/CCL2, and ICAM-I; it also increased anti-proliferative and proapoptotic effects, the latter of which was decreased by inhibiting caspase-8. In microdissected glomeruli of normal and non-HCV membranoproliferative glomerulonephritis biopsies, TLR3 mRNA expression was low. In contrast TLR3 mRNA expression was significantly increased in hepatitis C-positive glomerulonephritis and was associated with enhanced mRNA for RANTES/CCL5 and MCP-1/CCL2. We hypothesize that immune complexes containing viral RNA activate mesangial TLR3 during HCV infection, thereby contributing to chemokine/cytokine release and effecting proliferation and apoptosis. Thus, TLR3 expression on renal cells, and especially MCs, may establish a link between viral infections and glomerular diseases.

Beilong virus, a novel paramyxovirus with the largest genome of non-segmented negative-stranded RNA viruses

During a subtraction study on gene expression in human kidney mesangial cells (HMCs), cDNA clones with sequence homology to paramyxovirus P, M and F genes were isolated. Subsequent investigation revealed that this particular HMC line was infected with a previously unknown paramyxovirus. Here, we report the isolation and genome characterization of this new virus, now named Beilong virus (BeV). The genome of BeV is 19,212 nucleotides (nt) in length and is the largest among all known members of the order Mononegavirales. The BeV genome contains eight genes in the order 3'-N-P/V/C-M-F-SH-TM-G-L-5'. The SH and TM genes code for a small hydrophobic protein of 76 aa and a transmembrane protein of 254 aa, respectively. The BeV G gene, at 4527 nt, codes for an attachment protein of 734 aa and contains two additional open reading frames (ORFs) in the 3' half of the gene, coding for putative proteins of 299 and 394 aa in length. Although the exact origin of BeV is presently unknown, we provide evidence indicating that BeV was present in a rat mesangial cell line used in the same laboratory prior to the acquisition of the HMC line, suggesting a potential rodent origin for BeV.