Direct neurotoxic effects of dsRNA: Implication of virus-induced neurodegeneration

Abstract

Neurodegeneration occurs in the brain infected by RNA-virus such as Japanese Encephalitis virus or Herpes Simplex virus. Degeneration of neurons may cause cognitive impairment and even loss of memory. Therefore, it has been considered that virus infection is a risk factor leading to the development of Alzheimer’s disease (AD). Our laboratory is among the first to demonstrate that the double-stranded RNA-dependent protein kinase (PKR) plays important roles in mediating neuronal apoptosis in the pathogenesis of AD. We hypothesize that formation of double-stranded RNA released by RNA virus induces neurotoxicity. To test this hypothesis, polyinosine-polycytidylic acid (pIpC) was used as the analog of dsRNA in this study. Application of 20 ug/ml pIpC into primary cultured neurons resulted in an increase in 23% cytotoxicity determined by LDH assay. The results were similar if human neuroblastoma SH-SHY5Y was used instead of primary cortical neurons. Fluorescence microscopic analysis of nuclear with DAPI fluorescent probe or TUNEL assay revealed an increase in apoptotic cell bodies in pIpC-treated neurons as compared to that of control cells. Western-blot analysis detected an increase in the phosphorylation of PKR and its substrate, eukaryotic initiation factor 2α (eIF2α). Furthermore, we investigate whether some well-known neuroprotective agents can protect neurons against pIpC toxicity. Studies were done to investigate whether memantine (a non-competitive NMDA receptor antagonist), minocyclin (a tetracycline) and anti-aging Chinese medicine Lycium barbarum exhibits neuroprotective effects against pIpC toxicity. Taken together, dsRNA produced by RNA virus in the brain exhibit direct toxicity towards neurons. Traditionally used neuroprotective agents, memantine, minocyclin or Lycium barbarum may be useful to reduce dsRNA neurotoxicity by infected RNA virus. As viral infection in the brain during life time may be a pre-disposed risk factor leading to neurodegeneration in aging, the results have high implication in AD.