Multi-targeted neuroprotection by the HSV-2 gene ICP10PK includes robust bystander activity through PI3-K/Akt and/or MEK/ERK-dependent neuronal release of vascular endothelial growth factor and fractalkine

摘要

Hippocampal cultures infected with the ΔRR vector for the HSV-2 anti-apoptotic gene ICP10PK survive cell death triggered by a wide variety of insults. Survival includes robust protection of uninfected neurons, but the mechanism of this bystander activity is still unclear. Here we report that ICP10PK+ neurons release soluble factors that protect uninfected neurons from NMDA and MPP+-induced apoptosis. Release depends on ICP10PK-mediated activation of the Ras signaling pathways MEK/ERK and PI3-K/Akt, and it was not seen for cultures infected with the ICP10PK negative vector ΔPK. The released neuroprotective factors include vascular endothelial growth factor (VEGF) and fractalkine, the levels of which were significantly higher in conditioned media from hippocampal cultures infected with ΔRR (NCMΔRR) than ΔPK or phosphate-buffered saline (mock infection). VEGF neutralization inhibited the neuroprotective activity of NCMΔRR, indicating that the VEGF protective function is through neuron-neuron cross-talk. NCMΔRR also stimulated microglia to release increased levels of IL-10 and decreased levels of TNF-α that were protective for uninfected neurons. These release patterns were not seen for microglia given NCMΔRR in which fractalkine was neutralized, indicating that the fractalkine protective function is through bidirectional neuron-microglia communication. Collectively, the data indicate that ΔRR is a multiple target strategy to rescue neurons from excitotoxic injury.