Glucocorticoids mediate stress-induced priming of microglial pro-inflammatory responses

Acute and chronic stress sensitizes or “primes” the neuroinflammatory response to a subsequent pro-inflammatory challenge. While prior evidence shows that glucocorticoids (GCs) play a pivotal role in stress-induced potentiation of neuroinflammatory responses, it remains unclear whether stress-induced GCs sensitize the response of key CNS immune substrates (i.e. microglia) to pro-inflammatory stimuli. An ex vivo approach was used to address this question. Here, stress-induced GC signaling was manipulated in vivo and hippocampal microglia challenged with the pro-inflammatory stimulus LPS ex vivo. Male Sprague–Dawley rats were either pretreated in vivo with the GC receptor antagonist RU486 or adrenalectomized (ADX). Animals were then exposed to an acute stressor (inescapable tailshock; IS) and 24 h later hippocampal microglia were isolated and challenged with LPS to probe for stress-induced sensitization of pro-inflammatory responses. Prior exposure to IS resulted in a potentiated pro-inflammatory cytokine response (e.g. IL-1β gene expression) to LPS in isolated microglia. Treatment in vivo with RU486 and ADX inhibited or completely blocked this IS-induced sensitization of the microglial pro-inflammatory response. The present results suggest that stress-induced GCs function to sensitize the microglial pro-inflammatory response (IL-1β, IL-6, NFκBIα) to immunologic challenges.

Highlight
► Pharmacological and surgical suppression of stress-induced glucocorticoids abrogated the stress-induced sensitization of the microglial pro-inflammatory response ex vivo.