Title:Astrocyte-Microglia Cooperation in the Expression of a Pro-Inflammatory Phenotype
Volume: 12
Issue: 5
Author(s): Massimo Barbierato, Laura Facci, Carla Argentini, Carla Marinelli, Stephen D. Skaper and Pietro Giusti
Affiliation:
Keywords:
Glia, cortex, spinal cord, gene expression, nitric oxide, cytokines.
Abstract: Glial cells not only serve supportive and nutritive roles for neurons, but also respond to protracted stress and
insults by up-regulating inflammatory processes. The complexity of studying glial activation in vivo has led to the
widespread adoption of in vitro approaches, for example the use of the bacterial toxin lipopolysaccharide (LPS, a ligand
for toll-like receptor 4 (TLR4)) as an experimental model of glial activation. Astrocyte cultures frequently contain minor
numbers of microglia, which can complicate interpretation of responses. In the present study, enriched (≤5% microglia)
astrocytes cultured from neonatal rat cortex and spinal cord were treated with the lysosomotropic agent L-leucyl-L-leucine
methyl ester to eliminate residual microglia, as confirmed by loss of microglia-specific marker genes. L-Leucyl-L-leucine
methyl ester treatment led to a loss of LPS responsiveness, in terms of nitric oxide and cytokine gene up-regulation and
mediator (pro-inflammatory cytokines, nitric oxide) output into the culture medium. Surprisingly, when
astrocyte/microglia co-cultures were then reconstituted by adding defined numbers of purified microglia to microgliadepleted
astrocytes, the LPS-induced up-regulation of pro-inflammatory gene and mediator output far exceeded that
observed from cultures containing the same numbers of microglia only. Similar behaviors were found when examining
interleukin-1β release caused by activation of the purinergic P2X7 receptor. Given that astrocytes greatly outnumber
microglia in the central nervous system, these data suggest that a similar interaction between microglia and astrocytes in
vivo may be an important element in the evolution of an inflammatory pathology.
