Immunology

Biography

Biography: Orina Belton

Abstract

Conjugated linoleic acid (CLA) has the unique property of inducing regression of pre-established murine atherosclerosis despite a continuing high cholesterol challenge. Our previous findings and those of others cumulatively point to the monocyte/macrophage as the cellular target through which CLA mediates its effect. Understanding the mechanism(s) involved may help identify pathways that limit human disease. In this study, we aimed to define and validate potential mechanisms through which CLA alters monocyte function and confers an atheroprotective phenotype. Transcriptomic analysis of aortic tissue during CLA-induced regression of atherosclerosis identified an enrichment of the IL-10 signalling pathway coincident with increased circulating IL-10 serum levels. Interestingly, we found significantly increased IL-10 production in bone marrow derived macrophages from CLA fed mice. Importantly, CLA supplementation regulated immune cell infiltration of the aorta with increased numbers of Ly6C lo monocytes evident. In addition, we identified increased numbers of Ly6Clo monocytes in the spleen of CLA fed mice and furthermore showed that bone-marrow progenitor cells differentiate to an M2 phenotype during regression of atherosclerosis. As chronic recruitment of monocytes and their subsequent migration through the activated endothelium contributes to atherosclerotic plaque development we next investigated the effect of CLA on monocyte adhesion in vitro and in vivo. We showed that CLA inhibits human peripheral blood monocyte cell (HPBMC) adhesion to activated endothelial cells via loss of CD18 expression, the β2 chain of LFA-1 and Mac-1 integrins. In addition, using a static adhesion assay, we identified that CLA prevents monocytes from binding to ICAM-1 and subsequently reduces the capacity of these cells to polarise. CXCL12-CXCR4 interactions induce a conformational change in β2 integrins, facilitating leukocyte adhesion. We found that CLA inhibits CXCR4 expression, resulting in a failure of monocytes to directionally migrate towards CXCL12. Finally, using intravital microscopy we showed that during CLA induced regression of pre-established atherosclerosis in apoE-/- mice there is reduced leukocyte adhesion and decreased CD18 expression on Gr1+/CD115+ pro-inflammatory monocytes. In summary, the data presented describe a novel immunoregulatory role for CLA in atherosclerosis regression specifically in the alteration of the circulating phenotype of monocytes and in the regulation of monocyte adhesion, polarisation and migration. Overview of Current Research Programmes: The current focus of my research group is the identification ofmechanisms governing the regression of atherosclerosis. My laboratory has established a novel model of atherosclerosis regression in vivo, achieved by administration of conjugated linoleic acid (CLA) in theapoE knockout mouse model of atherosclerosis.We have previously shown that dietary CLAinduces resolution of pre-established lesions in vivo. Importantly we have identified that the monocyte/macrophage is the cellular target through which CLA mediates this effect. Our recent research efforts have focused on the identification of distinct genes/pathways regulated by CLA that may yield further information as to how atherosclerosis can be reversed. To do this we employ an approach that involves confirmation of a phenotypic change in vivo by en face analysis and intravital microscopy. Using a transcriptomic and proteomic approach we then construct networks associated with the altered phenotype, followed by identification of central or “hub” genes which regulate the network. Using cellular models and functional assays we validate a functional role for these hub genes in vitro examining the effect of gene deletion or over expression on, monocyte-endothelial interactions, integrin regulation, adhesion, migration and foam cell formation. We then extend this study into human patients to seek evidence for regulation of the target genes in atherosclerotic disease progression. Through this approach we have identified novel pathways. Some have complimentarity with pathways associated with atherosclerosis susceptibility for example we have recently characterized and ascribed a functional role forSorLA in monocyte migration and have confirmed its regulation in human disease (McCarthy et al 2010). Furthermore, we identified the nuclear receptor co-activator PGC-1as a nexus gene in a network regulated by CLA. In collaboration with Christopher Glass and colleagues at UCSD, we have recently identified that macrophage specific deletion of PGC-1α increases atherosclerosis in vivo. Importantly, we showed that PGC1α is expressed in the plaques of patients where its expression is inversely related to disease progression, raising the possibility that this is a regulatory pathway in human atherosclerosis. Our other research goals arise from our findings that that CLA functions as an anti-inflammatory lipid mediator in vivo, by modifying its Ly6Clo infiltration of the aorta and M2 macrophage polarisation. We have shown that bone-marrow progenitor cells from CLA fed mice differentiate to an M2 phenotype suggesting that the cells derived from these sources may be pre-programmed towards an anti-inflammatory profile before entering established plaques. Thus, CLA may modulate the phenotype of macrophages in vascular lesions that in turn impacts on the progression of atherosclerosis (McCarthy et al., 2013).