Abstract 18596: Conjugated Linoleic Acid Targets β2 Integrin Expression to Suppress Monocyte Adhesion

Abstract

Recruitment of monocytes to the damaged endothelium characterizes the early stages of atherosclerosis. Conjugated linoleic acids (CLA) are a group of naturally occurring fatty acids which inhibit the progression and induce regression of pre-established atherosclerosis. We have previously shown that CLA inhibits human peripheral blood monocyte (HPBMC) migration. Here we demonstrate that CLA suppresses adhesion of monocytes to endothelial cells, via inhibition of β2 integrins. We further show that CLA suppresses the CXCR4 signalling pathway thus inhibiting crawling of monocytes towards CXCL12 chemokine. HPBMCs were treated with 10uM of CLA isomers (c9,t11-CLA and t10,c12-CLA), a CLA blend (80:20, c9t,11:t10,c12), control lipids and 5uM of PPARγ agonist (troglitazone) prior to adhesion to HAECs. c9,t11-CLA and CLA blend treatment inhibited monocyte adhesion to HAECs (63±3%, p<0.01 and 68±3%, p<0.01, respectively). Furthermore, c9,t11-CLA and CLA blend inhibited CD18, the β chain of β2 integrin, mRNA (48±14%, p<0.05 and 35±3%, p<0.001) and protein expression (44±13%, p<0.05, and 35±3%, p<0.001) via a PPARγ[[Unable to Display Character: ]]dependent mechanism. Flow cytometry analysis showed that c9,t11-CLA and CLA blend decreased external surface expression of both β chain (10±4%, p<0.05 and 20±5%, p<0.01), and α subunits (CD11a, 13±6%, p<0.05 and 30±5%, p<0.01; CD11b, 8±3%, p<0.05 and 27±7%, p<0.01), suggesting that CLA’s effect on CD18 transcription results in dysfunctional αβ complex formation, altering expression of LFA-1 and Mac-1 integrins. Furthermore, c9,t11-CLA and CLA blend almost completely abolished (by 82% and 89%, p<0.001) adhesion of monocytes to ICAM-1. Immunocytochemistry of adherent cells further confirmed the inhibition of cell spreading. Importantly, CLA suppresses monocyte response to chemoattraction, preventing crawling of cells through a reduction, of CXCR4 expression (c9,t11-CLA, 47±10%, p<0.05; CLA blend, 33±5%, p<0.01). Our findings suggest that CLA inhibits monocyte recruitment by suppressing their sensitivity to chemokines and by inhibiting their ability to firmly attach to ICAM-1.