APOBEC1-mediated editing and attenuation of herpes simplex virus 1 DNA indicate that neurons have an antiviral role during herpes simplex encephalitis.

APOBEC1 (A1) is a cytidine deaminase involved in the regulation of lipids in the small intestine. Herpes simplex virus 1 (HSV-1) is a ubiquitous pathogen that is capable of infecting neurons in the brain, causing encephalitis. Here, we show that A1 is induced during encephalitis in neurons of rats infected with HSV-1. In cells stably expressing A1, HSV-1 infection resulted in significantly reduced virus replication compared to that in control cells. Infectivity could be restored to levels comparable to those observed for control cells if A1 expression was silenced by specific A1 short hairpin RNAs (shRNA). Moreover, cytidine deaminase activity appeared to be essential for this inhibition and led to an impaired accumulation of viral mRNA transcripts and DNA copy numbers. The sequencing of viral gene UL54 DNA, extracted from infected A1-expressing cells, revealed G-to-A and C-to-T transitions, indicating that A1 associates with HSV-1 DNA. Taken together, our results demonstrate a model in which A1 induction during encephalitis in neurons may aid in thwarting HSV-1 infection.

Human immunodeficiency virus type 1 Vpr inhibits axonal outgrowth through induction of mitochondrial dysfunction.

Human immunodeficiency virus type 1 (HIV-1)-infected macrophages damage mature neurons in the brain, although their effect on neuronal development has not been clarified. In this study, we show that HIV-1-infected macrophages produce factors that impair the development of neuronal precursor cells and that soluble viral protein R (Vpr) is one of the factors that has the ability to suppress axonal growth. Cell biological analysis revealed that extracellularly administered recombinant Vpr (rVpr) clearly accumulated in mitochondria where a Vpr-binding protein adenine nucleotide translocator localizes and also decreased the mitochondrial membrane potential, which led to ATP synthesis. The depletion of ATP synthesis reduced the transportation of mitochondria within neurites. This mitochondrial dysfunction inhibited axonal growth even when the frequency of apoptosis was not significant. We also found that point mutations of arginine (R) residues to alanine (A) residues at positions 73, 77, and 80 rendered rVpr incapable of causing mitochondrial membrane depolarization and axonal growth inhibition. Moreover, the Vpr-induced inhibition was suppressed after treatment with a ubiquinone analogue (ubiquinone-10). Our results suggest that soluble Vpr is a major viral factor that causes a disturbance in neuronal development through the induction of mitochondrial dysfunction. Since ubiquinone-10 protects the neuronal plasticity in vitro, it may be a therapeutic agent that can offer defense against HIV-1-associated neurological disease.

Primary target cells of herpes simplex virus type 1 in the hippocampus.

Herpes simplex virus type 1 (HSV-1) causes fatal and sporadic encephalitis in human. The encephalitis-survivors frequently suffer from symptoms of memory deficits. It remains unclear how HSV-1 induces tissue damages in memory formation-associated brain tissues such as the hippocampus. In this study, we examined HSV-1 infection in the hippocampus using a rat HSV-1 infection model. We found profound pathological changes in the hippocampus and large numbers of HSV-1 antigen-positive cells in the dentate gyrus (DG) subfield of HSV-1-infected rats. To understand the precise mechanism of HSV-1-induced tissue damages in the hippocampus, we employed rat organotypic hippocampal slice cultures (OHC) as an in vitro HSV-1 infection model. In OHC, HSV-1 infection predominated in neuronal cells and the infected neuronal cells were severely damaged. Longitudinal analysis indicated that granule cells in DG subfield were extremely vulnerable to HSV-1 infection among neuronal cells in the hippocampus. Since DG granule cells play a crucial role in memory formation, disruption of these cells may be a primary step leading to memory deficits.

Selective infection of CD4+ effector memory T lymphocytes leads to preferential depletion of memory T lymphocytes in R5 HIV-1-infected humanized NOD/SCID/IL-2Rgammanull mice.

To investigate the events leading to the depletion of CD4(+) T lymphocytes during long-term infection of human immunodeficiency virus type 1 (HIV-1), we infected human CD34(+) cells-transplanted NOD/SCID/IL-2Rgamma(null) mice with CXCR4-tropic and CCR5-tropic HIV-1. CXCR4-tropic HIV-1-infected mice were quickly depleted of CD4(+) thymocytes and both CD45RA(+) naïve and CD45RA(-) memory CD4(+) T lymphocytes, while CCR5-tropic HIV-1-infected mice were preferentially depleted of CD45RA(-) memory CD4(+) T lymphocytes. Staining of HIV-1 p24 antigen revealed that CCR5-tropic HIV-1 preferentially infected effector memory T lymphocytes (T(EM)) rather than central memory T lymphocytes. In addition, the majority of p24(+) cells in CCR5-tropic HIV-1-infected mice were activated and in cycling phase. Taken together, our findings indicate that productive infection mainly takes place in the activated T(EM) in cycling phase and further suggest that the predominant infection in T(EM) would lead to the depletion of memory CD4(+) T lymphocytes in CCR5-tropic HIV-1-infected mice.

Human immunodeficiency virus type-1 vulnerates nascent neuronal cells.

Macrophages or microglial cells are the major target cells for HIV-1 infection in the brain. The infected cells release neurotoxic factors that may cause severe neuronal cell damage, especially in the basal ganglia and hippocampus. In this study, we used rat OHC to examine the region-specific neuronal cell damage caused by HIV-1-infected macrophages. When OHC was cocultured with HIV-1-infected MDM, we found that neuronal cells at the GCL of the DG were preferentially killed via apoptosis, and that projection of MF from GCL to PCL of the CA3 region was severely disturbed. We marked precursor cells around the DG region by using an EGFP-expressing retrovirus vector and found that these cells lost the ability to differentiate into neurons when exposed to HIV-1-infected MDM. In the DG, new neurons are normally incorporated into GCL or PCL, while in the presence of HIV-1-infected MDM, mature neurons failed to be incorporated into those layers. These data indicate that the neurotoxic factor(s) released from HIV-1-infected macrophages impede(s) neuronal cell repair in brain tissue. This suggests that DG is the region of the hippocampus most vulnerable to neuronal damage caused by HIV-1 infection, and that its selective vulnerability is most likely due to the highly active neurogenesis that takes place in this region.