Abstract TP239: Cholesterol And LXR Signaling In The Macrophage Response To Intracerebral Hemorrhage-relevant Stimulation

Introduction: In the acute phase of intracerebral hemorrhage (ICH), blood-derived macrophages contribute to an inflammatory response that increases neuronal death and worsens patient outcome. A better understanding of the endogenous signals that control this response would aid in development of therapeutics to suppress it. Uptake of free cholesterol limits the macrophage response to microbial ligands, in part through activation of the transcription factor LXR. During ICH, blood-derived macrophages in the hematoma are not exposed to microbes but are exposed to the endogenous inflammatory molecule S100A9 as well as cholesterol in the form of myelin and cell debris. Methods and Results: Murine bone marrow-derived macrophages were treated with cholesterol before stimulation with S100A9 or LPS, which are both TLR4 ligands. The inflammatory response was measured by production of the cytokines/chemokines TNF, IL-6, CCL2, and IL-10 by multiplex ELISA and/or qPCR at 3 and 6 hours after stimulation. Activation of LXR was measured by expression of the LXR target genes Abca1 and Abcg1 by qPCR. Cholesterol limited inflammatory cytokine production in response to LPS but not to S100A9. Treatment with the LXR agonist T0901317 activated Abca1 and Abcg1 more strongly than cholesterol but was not as effective at suppressing cytokine production. Treatment with the LXR antagonist GSK2033 suppressed cholesterol-mediated expression of Abca1 and Abcg1 but did not block all suppressive effects of cholesterol on cytokine production. Conclusions: Cholesterol limits the macrophage response to LPS. This is partially through activation of LXR, but LXR-independent mechanisms are involved as well. Cholesterol does not limit the initial inflammatory response to the ICH-relevant molecule S100A9, which may help explain the robust acute inflammatory response that develops during acute ICH in the presence of abundant cholesterol.