Abstract 5673: Engagement of the Sphingosine 1 Phosphate Receptor 1 Induces Macrophage Egression From Atherosclerotic Lesions in Apolipoprotein E Deficient Mice
Background: The regulation of macrophage (MØ) and T-cell content is crucial to atherosclerotic plaque stability. MØ have the potential to rapidly egress from plaques. Sphingosine 1-Phosphate (S1P) - an integral component of high density lipoproteins (HDL) - reduces leukocyte counts at sites of inflammation. We here tested if short-term treatment with the synthetic S1P analogue FTY720 or the selective S1P receptor 1 (S1P1) agonist AUY954 affects MØ and T-cells in plaques of ApoE deficient (ApoE−/−) mice.
Methods: ApoE−/− and wild type (WT) mice were fed a 16wk western diet. For 3D in vivo Fluorescence-Mediated-Tomography (FMT), 5×106 peritoneal eGFP-MØ labeled with near infrared fluorescent dye (DiR) were given IV 2d prior to 2 or 4d FTY720 (1μg/gBW/d), AUY954 (10μg/gBW twice/d), or vehicle (CTR) treatment. Baseline MØ content was assessed by FMT in a region of interest covering aortic-valve and -arch. On d2 and 4 MØ influx and egress from plaques into the blood were quantified. MØ egress into aortic lymphnodes (LN) was quantified by flow cytometry. T-cell (Thy1.2), MØ (CD68) and lipid content (Oil Red O) were assessed in plaques.
Results: FMT revealed net MØ recruitment during 2 days in CTR (487±151%, d2 vs. d0, p<0.05, n=9) but in neither treatment group (FTY720: 67±11.9%, AUY954: 103±26.5%, p=n.s., n=9/5). After 4 days MØ related signal was reduced consistent with MØ egress from plaques in both treatment groups (FTY720: 40±9.5%, AUY954: 38±10.5%, d4 vs. d0, p<0.05, n=5) but not in CTR (14922.9%, p<n.s., n=5). CD68- and Oil-Red O-pos lesion area decreased by 33% and 26% (FTY720 vs. CTR, n=8, p<0.05). FTY720 but not AUY954 promoted MØ relocation into LN (FTY720: 7.21.9, AUY954: 1.270.73, CTR: 2.20.7, eGFP-MØ/105 cells, FTY720 vs. CTR & AUY954, n=5, p<0.05;). 2d treatment with FTY720 reduced plaque T-cell content (10±2.6 vs. 19±4.4 cells/mm2, FTY720 vs. CTR, p<0.05, n=5).
Conclusions: Both FTY720 and AUY954 rapidly reduce macrophage content in atherosclerotic lesions indicating S1P1 involvement in this process. However, only FTY720 induces MØ relocation into regional LN and reduces plaque T-cell content. Reducing MØ and T-cells in the plaque through engagement of various S1P receptors (FTY720) vs. S1P1 represents a valid strategy for plaque stabilization.