Human Cytomegalovirus Inhibits Neuronal Differentiation and Induces Apoptosis in Human Neural Precursor Cells

Abstract

Human cytomegalovirus (HCMV) is the most common cause of congenital infections in developed countries, with an incidence varying between 0.5 and 2.2% and consequences varying from asymptomatic infection to lethal conditions for the fetus. Infants that are asymptomatic at birth may still develop neurological sequelae, such as hearing loss and mental retardation, at a later age. Infection of neural stem and precursor cells by HCMV and consequent disruption of the proliferation, differentiation, and/or migration of these cells may be the primary mechanism underlying the development of brain abnormalities. In the present investigation, we demonstrate that human neural precursor cells (NPCs) are permissive for HCMV infection, by both the laboratory strain Towne and the clinical isolate TB40, resulting in 55% and 72% inhibition of induced differentiation of human NPCs into neurons, respectively, when infection occurred at the onset of differentiation. This repression of neuronal differentiation required active viral replication and involved the expression of late HCMV gene products. This capacity of HCMV to prevent neuronal differentiation declined within 24 h after initiation of differentiation. Furthermore, the rate of cell proliferation in infected cultures was attenuated. Surprisingly, HCMV-infected cells exhibited an elevated frequency of apoptosis at 7 days following the onset of differentiation, at which time approximately 50% of the cells were apoptotic at a multiplicity of infection of 10. These findings indicate that HCMV has the capacity to reduce the ability of human NPCs to differentiate into neurons, which may offer one explanation for the abnormalities in brain development associated with congenital HCMV infection.

Effects of cytomegalovirus infection in human neural precursor cells depend on their differentiation state

“…Nevertheless, the relevance of HCMV-induced differentiation in the context of CNS development and finding why it is reversed when viral concentration increases are a matter for further investigation. In contrast with our findings in SK-N-MC cells, previous reports showed a decrease in NPC differentiation to neurons and glia after HCMV infection (Odeberg et al 2006(Odeberg et al , 2007. Indeed, the experimental methods used in these studies were different, and since we did not induce differentiation, it occurred spontaneously.…”

“…The level of detection of viral particles in the cell lines used here was consistent with the results obtained using a different source of NPC (Luo et al 2008). However, it is dissimilar to those of others who have reported that NPCs are fully permissive to the infection, but few viral particles are released (Odeberg et al 2006). We observed that viral production in SK-N-MC was similar to the one in fibroblasts but not detectable in hNS-1.…”

“…On the other hand, when we infected SK-N-MC with the MOI of 0.01, cellular prolongations were observed suggesting cellular differentiation to a neuron-like morphology, an unexpected finding since we did not add any other stimulus that may account for these changes, and this normally does not occur in an spontaneous way (Higgins et al 2009). This induction of differentiation is in agreement with the recent observation of abnormal, spontaneous, and premature differentiation of NPC induced by HCMV (Odeberg et al 2006;Luo et al 2010). The virus concentrations that we used were much lower than those in previous studies, what may explain the delayed effect observed.…”

“…In addition, cytopathic effect (CPE) in these cells at the multiplicity of infection (MOI) of three plaque formation units (PFU) per cell consisted in formation of syncytia, which can be the result of viral cell to cell dissemination (Luo et al 2008). Infection of these cells may increase the apoptosis frequency and inhibit neuronal and glia differentiation; however, this effect remains controversial since it has also been reported that CMV infection may cause a spontaneous, premature, and abnormal NPC differentiation (Odeberg et al 2006(Odeberg et al , 2007Luo et al 2010).…”

Cytomegalovirus infection induces a stem cell phenotype in human primary glioblastoma cells: prognostic significance and biological impact

“…These findings are in line with our previous results showing that HCMV infection of fetal neural progenitor inhibits their differentiation. 26 Other studies have suggested that halted differentiation of neuroprogenitor cells is an early step in gliomagenesis. 27 Since HCMV proteins and nucleotide sequences seem to be present in most GBMs 16,[28][29][30] and that HCMV-IE expression is a prognostic marker for poor patient survival irrespective of the GBM subtype, 18 our present model of HCMV infection of primary GBM cells appears to recapitulate early events during glioma development.…”