Abstract

BACKGROUND: Ischemic stroke provokes a neuroinflammatory response and simultaneously promotes release of epinephrine and norepinephrine by the sympathetic nervous system. This increased sympathetic outflow can act on beta2-adrenergic receptors expressed by immune cells such as brain-resident microglia and monocyte-derived macrophages (MDMs), but the effect on post-stroke neuroinflammation is unknown. Thus, we investigated how changes in beta2-adrenergic signaling after stroke onset influence the microglia/MDM stroke response, and the specific importance of microglia/MDM beta2-adrenergic receptors to post-stroke neuroinflammation.METHODS: To investigate the effects of beta2-adrenergic receptor manipulation on post-stroke neuroinflammation, we administered the beta2-adrenergic receptor agonist clenbuterol to mice 3h after the onset of photothrombotic stroke. We immunostained to quantify microglia/MDM numbers and proliferation and to assess morphology and activation 3days later. We assessed stroke outcomes by measuring infarct volume and functional motor recovery and analyzed gene expression levels of neuroinflammatory molecules. Finally, we evaluated changes in cytokine expression and microglia/MDM response in brains of mice with selective knockout of the beta2-adrenergic receptor from microglia and monocyte-lineage cells.RESULTS: We report that clenbuterol treatment after stroke onset causes enlarged microglia/MDMs and impairs their proliferation, resulting in reduced numbers of these cells in the peri-infarct cortex by 1.7-fold at 3days after stroke. These changes in microglia/MDMs were associated with increased infarct volume in clenbuterol-treated animals. In mice that had the beta2-adrenergic receptor specifically knocked out of microglia/MDMs, there was no change in morphology or numbers of these cells after stroke. However, knockdown of beta2-adrenergic receptors in microglia and MDMs resulted in increased expression of TNFalpha and IL-10 in peri-infarct tissue, while stimulation of beta2-adrenergic receptors with clenbuterol had the opposite effect, suppressing TNFalpha and IL-10 expression.CONCLUSIONS: We identified beta2-adrenergic receptor signaling as an important regulator of the neuroimmune response after ischemic stroke. Increased beta2-adrenergic signaling after stroke onset generally suppressed the microglia/MDM response, reducing upregulation of both pro- and anti-inflammatory cytokines, and increasing stroke size. In contrast, diminished beta2-adrenergic signaling in microglia/MDMs augmented both pro- and anti-inflammatory cytokine expression after stroke. The beta2-adrenergic receptor may therefore present a therapeutic target for improving the post-stroke neuroinflammatory and repair process.

View details for DOI 10.1186/s12974-019-1506-4

View details for PubMedID 31138227