Adenovirus infection induces microglial activation: involvement of mitogen‐activated protein kinase pathways

Abstract

Non‐replicating adenovirus (Ad) vectors represent effective tools for long‐term gene expression in the CNS, but they also elicit inflammation. The cellular and molecular mechanisms of such a response are not well‐understood. We show here that infection with Ad causes an activation of microglial cells, the key cells involved in inflammatory and immune‐regulatory functions in the brain. Exposure of cultured rat brain microglia to Ad resulted in an induced production of nitric oxide (NO) and the expression of inducible nitric oxide synthase (iNOS) and the pro‐inflammatory cytokine, TNFα. The roles of signal transduction pathways believed to be involved in microglial activation, in particular, mitogen‐activated protein kinases (MAPKs) and nuclear factor κB (NFκB) were explored by determining their activation in response to Ad infection and by testing the effects of specific pharmacological inhibitors. It was found that Ad strongly activates extracellular signal‐regulated kinase (ERK) and to a lesser extent, p38 MAPK but not NFκB. The kinase inhibitor i.e. PD98059, specific for the ERK pathway, potently inhibits and, in combination with the p38 MAPK inhibitor, SB203580, almost completely abolishes Ad‐induced expression of iNOS and TNFα. The results suggest that Ad uses cellular signal transduction machinery, in particular, the ERK pathway to elicit microglial activation and that increased production by these cells of inflammatory mediators may primarily contribute to CNS inflammatory responses commonly seen in models of gene therapy using Ad vectors.Acknowledgements: Supported by NINDS grant # NS41035‐01.