HSV-1 triggers paracrine fibroblast growth factor response from cortical brain cells via immediate-early protein ICP0

Abstract

BackgroundHerpes simplex virus-1 (HSV-1) infections of the central nervous system (CNS) can result in HSV-1 encephalitis (HSE) which is characterized by severe brain damage and long-term disabilities. Different cell types including neurons and astrocytes become infected in the course of an HSE which leads to an activation of glial cells. Activated glial cells change their neurotrophic factor profile and modulate inflammation and repair. The superfamily of fibroblast growth factors (FGFs) is one of the largest family of neurotrophic factors comprising 22 ligands. FGFs induce pro-survival signaling in neurons and an anti-inflammatory answer in glial cells thereby providing a coordinated tissue response which favors repair over inflammation. Here, we hypothesize that FGF expression is altered in HSV-1-infected CNS cells.MethodWe employed primary murine cortical cultures comprising a mixed cell population of astrocytes, neurons, microglia, and oligodendrocytes. Astrocyte reactivity was morphometrically monitored by an automated image analysis algorithm as well as by analyses of A1/A2 marker expression. Altered FGF expression was detected by quantitative real-time PCR and its paracrine FGF activity. In addition, HSV-1 mutants were employed to characterize viral factors important for FGF responses of infected host cells.ResultsAstrocytes in HSV-1-infected cortical cultures were transiently activated and became hypertrophic and expressed both A1- and A2-markers. Consistently, a number of FGFs were transiently upregulated inducing paracrine neurotrophic signaling in neighboring cells. Most prominently, FGF-4, FGF-8, FGF-9, and FGF-15 became upregulated in a switch-on like mechanism. This effect was specific for CNS cells and for a fully functional HSV-1. Moreover, the viral protein ICP0 critically mediated the FGF switch-on mechanism.ConclusionsHSV-1 uses the viral protein ICP0 for the induction of FGF-expression in CNS cells. Thus, we propose that HSV-1 triggers FGF activity in the CNS for a modulation of tissue response upon infection.

The Proteome and Secretome of Cortical Brain Cells Infected With Herpes Simplex Virus

“…To address the possible involvement of different CNS cell types as well as their interaction, we developed a protocol to investigate the proteome and the secretome of mixed primary cultures from the brain cortices of neonatal C57BL/6J mice ( Figure 1A ). As previously established and characterized ( 29 ), we dissected the cortices, and cultured the cells for six days to obtain an ex vivo system which contains the major CNS-cell types ( Figures 1B–J ). The cells were inoculated with HSV-1 for 20 h prior to processing the samples for cell proteome analyses.…”

“…HSV-1 infects neurons, astrocytes, and oligodendrocytes in HSE-patients, mice, and human and murine primary cortical cultures (26)(27)(28)(29)33). Moreover, HSV-1 infection modulates the physiology of other cell types such as oligodendrocytes and microglia, the resident "macrophages" of the brain (27).…”

“…However, so far there are no data on the dynamic proteome in primary cortical cultures that contain neurons and glial cells. This is of particular interest since HSV-1 does not only establish latent infections in neurons, but infects neurons and glial cells during acute CNS infections during an HSE (26)(27)(28)(29).…”

“…Here we analyzed changes in the proteome of primary cells from the murine brain cortex upon infection with HSV-1. As different CNS-cell types may influence the host response by paracrine mechanisms, we used mixed cortical cultures that contain the major cell-types of the brain such as neurons, astrocytes, oligodendrocytes, and microglia ( 29 ). Twenty eight host proteins were differentially regulated upon HSV-1 infection including components of the inflammasome such as the NIMA-related kinase 7 (NEK7), and ArfGap1, a regulator of membrane trafficking and endocytosis which may be important for viral internalization and replication.…”

HCFC1R1 Deficiency Blocks Herpes Simplex Virus-1 Infection by Inhibiting Nuclear Translocation of HCFC1 and VP16

“…The HSV-1 gB gene copy number was clearly reduced as shown by qPCR, suggesting that the HCFC1R1 deficiency affects HSV-1 propagation (Figure 6A). To further ask if loss of HCFC1R1 was correlated with the life cycle of HSV-1, we analyzed the mRNA expression of several viral genes including ICP0 (representing immediate early gene), TK (early gene), and GD (late gene) in the control and BGC-823 HCFC1R1−/− cells by qRT-PCR in 24, 48, and 72 hours after infection (25–27). qRT-PCR data showed that missing HCFC1R1 significantly inhibited the mRNA transcription in BGC-823 HCFC1R1−/− cells at the various time points (Figure 6B, C, D).…”