Abstract TP216: Suppression Of Macrophage Activation By Myelin

Abstract

Introduction: In intracerebral hemorrhage, blood-derived macrophages contribute to a neurotoxic inflammatory response. The endogenous signals that are able to suppress this response are poorly understood. Macrophages likely phagocytose myelin in the CNS during intracerebral hemorrhage and uptake of myelin limits macrophage cytokine production in response to LPS. The components of myelin responsible for its suppressive effects are not well understood, although cholesterol is a likely candidate. Additionally, the broader effects of myelin on macrophage phenotype have not been investigated. Methods and Results: Murine bone marrow-derived macrophages were treated with cholesterol before stimulation with S100A9 or LPS. The inflammatory response was measured by production of TNF, IL-6, CCL2, and IL-10 by ELISA. Cholesterol limited inflammatory cytokine production in response to LPS but not to S100A9. The LXR antagonist GSK2033 partially blocked the suppressive effects of cholesterol but activation of LXR with T0901317 was not sufficient to suppress cytokine production. An RNA-Seq screen was performed to examine broader effects of myelin and cholesterol uptake. BMDMs were pretreated with cholesterol, myelin, or the LXR agonist T0901317 before stimulation with S100A9, LPS, TNF, IFNg, IL-4, IL-10, TGFb, Poly(I:C), or Pam3CSK4. Myelin suppressed responses to all of these stimulations, as did T0901317 but to a lesser extent. Cholesterol suppressed the macrophage response to LPS but not the other stimulations. Conclusions: Myelin broadly limits macrophage responses to pro-inflammatory signals. Cholesterol alone limits the response to LPS, partially through activation of LXR, but LXR-independent mechanisms appear to be involved as well. Cholesterol does not limit the response to other stimulations, suggesting that other components of myelin or activation of phagocytic receptors contribute to suppression of the macrophage response.