Herpes simplex virus induces neural oxidative damage via microglial cell Toll-like receptor-2.
BACKGROUND
Using a murine model of herpes simplex virus (HSV)-1 encephalitis, our laboratory has determined that induction of proinflammatory mediators in response to viral infection is largely mediated through a Toll-like receptor-2 (TLR2)-dependent mechanism. Published studies have shown that, like other inflammatory mediators, reactive oxygen species (ROS) are generated during viral brain infection. It is increasingly clear that ROS are responsible for facilitating secondary tissue damage during central nervous system infection and may contribute to neurotoxicity associated with herpes encephalitis.


METHODS
Purified microglial cell and mixed neural cell cultures were prepared from C57B/6 and TLR2-/- mice. Intracellular ROS production in cultured murine microglia was measured via 2', 7'-Dichlorofluorescin diacetate (DCFH-DA) oxidation. An assay for 8-isoprostane, a marker of lipid peroxidation, was utilized to measure free radical-associated cellular damage. Mixed neural cultures obtained from beta-actin promoter-luciferase transgenic mice were used to detect neurotoxicity induced by HSV-infected microglia.


RESULTS
Stimulation with HSV-1 elevated intracellular ROS in wild-type microglial cell cultures, while TLR2-/- microglia displayed delayed and attenuated ROS production following viral infection. HSV-infected TLR2-/- microglia produced less neuronal oxidative damage to mixed neural cell cultures in comparison to HSV-infected wild-type microglia. Further, HSV-infected TLR2-/- microglia were found to be less cytotoxic to cultured neurons compared to HSV-infected wild-type microglia. These effects were associated with decreased activation of p38 MAPK and p42/p44 ERK in TLR2-/- mice.


CONCLUSIONS
These studies demonstrate the importance of microglial cell TLR2 in inducing oxidative stress and neuronal damage in response to viral infection.
Schachtele
Scott J
SJ
Center for Infectious Diseases and Microbiology Translational Research, Department of Medicine, University of Minnesota, MN, USA.
Hu
Shuxian
S
Little
Morgan R
MR
Lokensgard
James R
JR
D000818:Animals; D002478:Cells, Cultured; D015237:Dinoprost / Q000031:analogs & derivatives / Q000378:metabolism; D004789:Enzyme Activation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D017628:Microglia / Q000166:cytology / Q000378:metabolism* / Q000821:virology*; D009474:Neurons / Q000473:pathology* / Q000821:virology; D018384:Oxidative Stress; D017382:Reactive Oxygen Species / Q000378:metabolism*; D018139:Simplexvirus / Q000378:metabolism / Q000472:pathogenicity*; D051195:Toll-Like Receptor 2 / Q000235:genetics / Q000378:metabolism*; D014662:Vasoconstrictor Agents / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D017382:Reactive Oxygen Species; D051195:Toll-Like Receptor 2; D014662:Vasoconstrictor Agents; C075750:8-epi-prostaglandin F2alpha; D015237:Dinoprost; D048049:Extracellular Signal-Regulated MAP Kinases; D048051:p38 Mitogen-Activated Protein Kinases