Cholesterol, LXR activation, and myelin uptake in the macrophage response to diverse signals

Abstract

Abstract Introduction Monocyte-derived macrophages contribute to neurotoxic inflammation during hemorrhagic stroke. Cholesterol is an immunosuppressive molecule present at high levels in the brain, primarily as a component of myelin. Uptake of myelin and activation of the transcription factor LXR downstream of myelin and cholesterol uptake limits the macrophage response to LPS. However, the roles of these molecules in macrophage responses to the endogenous signals present during sterile inflammation are poorly understood. The present study seeks to determine what role myelin, cholesterol, and LXR activation play in modifying macrophage responses to diverse signals. Methods and Results Murine bone marrow-derived macrophages were treated with myelin, cholesterol, or the LXR agonist T0901317 18h before stimulation with S100A9, IFN-g, TNF-a, IL-4, IL-10, TGF-b, p(I:C), Pam3CSK4, or LPS. Production of TNF-a, IL-6, CCL2, and IL-10 were measured by multiplex ELISA. Transcriptome-wide effects were measured by RNA sequencing. Cholesterol limited inflammatory cytokine production in response to LPS but not to other stimuli. The LXR agonist T0901317 did not suppress cytokine production. Principal component analysis revealed that cholesterol had strong effects on the transcriptomic responses to LPS but not to the other stimulations. Myelin affected the transcriptomic response to all inflammatory stimulations. Conclusions Cholesterol limits the macrophage response to LPS, partially through activation of LXR, but does not broadly limit macrophage activation. Uptake of myelin has broader effects than cholesterol, suggesting that non-cholesterol components of myelin modulate the macrophage response. Supported by grants from NIH (R01 NS097728, T32 HL007950) and AHA (Postdoctoral Fellowship 830877)