Role of Microvesicles in the Spread of Herpes Simplex Virus 1 in Oligodendrocytic Cells

Abstract

Herpes simplex virus 1 (HSV-1) is a neurotropic pathogen that can infect many types of cells and establishes latent infections in the neurons of sensory ganglia. In some cases, the virus spreads into the central nervous system, causing encephalitis or meningitis. Cells infected with several different types of viruses may secrete microvesicles (MVs) containing viral proteins and RNAs. In some instances, extracellular microvesicles harboring infectious virus have been found. Here we describe the features of shedding microvesicles released by the human oligodendroglial HOG cell line infected with HSV-1 and their participation in the viral cycle. Using transmission electron microscopy, we detected for the first time microvesicles containing HSV-1 virions. Interestingly, the Chinese hamster ovary (CHO) cell line, which is resistant to infection by free HSV-1 virions, was susceptible to HSV-1 infection after being exposed to virus-containing microvesicles. Therefore, our results indicate for the first time that MVs released by infected cells contain virions, are endocytosed by naive cells, and lead to a productive infection. Furthermore, infection of CHO cells was not completely neutralized when virus-containing microvesicles were preincubated with neutralizing anti-HSV-1 antibodies. The lack of complete neutralization and the ability of MVs to infect nectin-1/HVEM-negative CHO-K1 cells suggest a novel way for HSV-1 to spread to and enter target cells. Taken together, our results suggest that HSV-1 could spread through microvesicles to expand its tropism and that microvesicles could shield the virus from neutralizing antibodies as a possible mechanism to escape the host immune response.IMPORTANCE Herpes simplex virus 1 (HSV-1) is a neurotropic pathogen that can infect many types of cells and establishes latent infections in neurons. Extracellular vesicles are a heterogeneous group of membrane vesicles secreted by most cell types. Microvesicles, which are extracellular vesicles which derive from the shedding of the plasma membrane, isolated from the supernatant of HSV-1-infected HOG cells were analyzed to find out whether they were involved in the viral cycle. The importance of our investigation lies in the detection, for the first time, of microvesicles containing HSV-1 virions. In addition, virus-containing microvesicles were endocytosed into CHO-K1 cells and were able to actively infect these otherwise nonpermissive cells. Finally, the infection of CHO cells with these virus-containing microvesicles was not completely neutralized by anti-HSV-1 antibodies, suggesting that these extracellular vesicles might shield the virus from neutralizing antibodies as a possible mechanism of immune evasion.

Extracellular Vesicles in Herpes Viral Spread and Immune Evasion

“…More recent findings ( Bello-Morales et al, 2018 ) have suggested the participation of MVs in HSV-1 spread. Our study described the features of MVs released by the human oligodendroglial (HOG) cell line infected with HSV-1 and their participation in the viral cycle, indicating for the first time that MVs released by HSV-1-infected cells contained virions, were endocytosed by naïve cells, and led to a productive infection.…”

NeuroEVs: Characterizing Extracellular Vesicles Generated in the Neural Domain

“…Therefore, these studies confirmed both mRNA uptake and subsequent translation by the recipient cell (Valadi et al, 2007), a seminal finding that has greatly advanced the field. More recently, EVs have also been shown to prevent antibody-mediated neutralization of encapsulated viral particles, thereby allowing for the propagation of viral infection (Bello-Morales et al, 2018). Additionally, during an activated neuroimmune response, both microglia and astrocytes release EVs that contain the cytokine interleukin-1␤ (IL-1␤), which further contributes to immune signaling (Bianco et al, 2005(Bianco et al, , 2009Colombo et al, 2018).…”

Herpes Simplex Virus 1 Spread in Oligodendrocytic Cells Is Highly Dependent on MAL Proteolipid

“…In direct spread, the viral transmission occurs through cell-to-cell contacts via a mechanism that is still poorly understood. Alternatively, viral spread may occur through extracellular vesicles, which we have shown to occur in OL cells (26,35). In this case, HSV-1 egress is mediated by MVBs (36) and exosomes (37,38).…”

“…In previous studies, we noted a partial colocalization of herpes simplex virus 1 (HSV-1) particles with exogenous MAL in vesicles located at the end of cellular processes in OLs (25). We also reported the role of microvesicles in HSV-1 transmission between OLs (26). Given the involvement of MAL in exosome secretion (7), we investigated whether viral particles might be travelling into MAL-positive vesicles during viral spread (25).…”