Abstract 15294: Activation of Mac-1 Integrin Prevents G-CSF Mediated Monocyte Mobilization and Atherosclerosis Severity in Hypercholesterolemic Mice

Abstract

Background: Leukadherins (LA) are a novel family of Mac-1 agonists that increase cell adhesion and prevent leukocyte mobilization and tissue inflammation. This study brings new insights into how leukadherin LA1 protects hypercholesterolemic ApoE-null mice from excessive atherosclerosis development. Hypothesis: Activation of Mac-1 integrin with leukadherin LA1 retains monocytes in medullary and extramedullary centers and therefore, controls high fat diet induced monocytosis and atherosclerosis in ApoE-null mice. Methods and Results: Once daily administration of LA1 (10mg/kg) for 16 weeks significantly reduced atherosclerosis in the entire aorta and the aortic valve of high fat diet fed ApoE-null mice as determined by Sudan IV staining. The LA1 treatment had not effect on body weight or plasma lipid levels though it significantly reduced the number of circulating monocytes (Lin2- CD11c- CD11b+ by FACS). The remaining circulating monocytes in LA1-treated mice displayed low levels of Ly6C, a marker for inflammation. Interestingly, LA1 caused monocyte retention in the bone marrow (BM) and macrophages (F4/80+ by IHC) in the spleen of hypercholesterolemic mice, which account for the low numbers of monocytes seem in the circulation of these mice. On the other hand, the excessive number of BM monocytes didn’t compromise the number of hematopoietic (Lin- Sca+ c-Kit+) or myeloid (Lin- Sca- c-Kit+) progenitor cells. Finally, we assessed the effect of LA1 on systemic inflammatory mediators using multiplex immunoassay. The plasma levels of G-CSF, one of the main monocyte mobilization cytokines capable of promoting atherosclerosis in ApoE-null mice, were found reduced in a half in treated versus control mice. Conclusions: These data demonstrate that Mac-1 activation with LA1 significantly reduces atherosclerosis in hypercholesterolemic ApoE-null by impairing G-CSF mediated monocyte mobilization from medullary and extramedullary centers.