Data from: Microglia responses to pro-inflammatory stimuli (LPS, IFNγ+TNFα) and reprogramming by resolving cytokines (IL-4, IL-10)

Microglia respond to CNS injuries and diseases with complex reactions,
often called “activation.” A pro-inflammatory phenotype (also called
classical or M1 activation) lies at one extreme of the reactivity
spectrum. There were several motivations for this study. First, bacterial
endotoxin (lipopolysaccharide, LPS) is the most commonly used
pro-inflammatory stimulus for microglia, both in vitro and in vivo;
however, pro-inflammatory cytokines (e.g., IFNγ, TNFα) rather than LPS
will be encountered with sterile CNS damage and disease. We lack direct
comparisons of responses between LPS and such cytokines. Second, while
transcriptional profiling is providing substantial data on microglial
responses to LPS, these studies mainly use mouse cells and models, and
there is increasing evidence that responses of rat microglia can differ.
Third, the cytokine milieu is dynamic after acute CNS damage, and an
important question in microglial biology is: How malleable are their
responses? There are very few studies of effects of resolving cytokines,
particularly for rat microglia, and much of the work has focused on
pro-inflammatory outcomes. Here, we first exposed primary rat microglia to
LPS or to IFNγ+TNFα (I+T) and compared hallmark functional (nitric oxide
production, migration) and molecular responses (almost 100 genes),
including surface receptors that can be considered part of the sensome.
Protein changes for exemplary molecules were also quantified: ARG1,
CD206/MRC1, COX-2, iNOS, and PYK2. Despite some similarities, there were
notable differences in responses to LPS and I+T. For instance, LPS often
evoked higher pro-inflammatory gene expression and also increased several
anti-inflammatory genes. Second, we compared the ability of two
anti-inflammatory, resolving cytokines (IL-4, IL-10), to counteract
responses to LPS and I+T. IL-4 was more effective after I+T than after
LPS, and IL-10 was surprisingly ineffective after either stimulus. These
results should prove useful in modeling microglial reactivity in vitro;
and comparing transcriptional responses to sterile CNS inflammation in
vivo.