Broad spectrum neuroprotection by the HSV-2 gene ICP10PK includes multiple targets and crosstalk between neurons and glial cells

Abstract

Neurodegenerative diseases are characteristically multi-target and multi-cell conditions that are resistant to presently available therapeutics options. It is widely believed that gene therapy strategies could be a promising alternative to current therapies, but a clinical challenge is the identification of the target gene(s) and the cell to cell interactions that regulate pathogenesis. ICP10PK is an anti-apoptotic herpes simplex virus type 2 (HSV-2) gene. Here we describe the ability of ICP10PK to provide neuroprotection against a wide range of toxic stimuli including caspase and calpain-dependent programmed cell death (PCD), oxidative stress and death caused by genetic alterations, such as SOD1. The mechanism of neuroprotection, including modulation of cell-cell interactions is emphasized. Our data indicate that ICP10PK, delivered with the growth compromised HSV-2 vector deltaRR or by transfection, inhibits PCD induced through the activation of the Ras-dependent MEK/ERK and PI3K/Akt survival pathways. Neuroprotection was seen both in vitro and in vivo, including models of acute excitotoxicity (kainic acid and NMDA), an in vitro model of Parkinson's disease (MPP+), and in vitro and in vivo models of Amyotrophic lateral sclerosis (G93A and G85R SOD1). ICP10PK-mediated neuroprotection was associated with MEK/ERK and PI3K/Akt-dependent release of soluble factors that protected uninfected (ICP10PK-) neurons. They include VEGF, which has paracrine protective activity on adjacent (ICP10PK-) neurons and the chemokine fractalkine (FKN) which functions as a bi-directional mediator of crosstalk between neurons and microglia. FKN released by the ICP10PK+ neurons stimulated microglia to release increased levels of the neuroprotective cytokine (IL-10) while inhibiting the release of the inflammatory cytokine TNF-alpha. Factors released by the ICP10PK+ neurons also modulated astrocytes to release nerve growth factor. ICP10PK has the distinct advantage over other neuroprotective strategies that, in addition to protecting the infected neurons, it modulates them to release neuroprotective soluble factors in a balanced proportion such as to create a self-propagating cycle of neuronal inputs and release of chemical mediators that inhibit the progression of acute and chronic neurodegeneration through protection of uninfected neurons.