Oxidized Low-Density Lipoprotein Receptor in Lymphocytes Prevents Atherosclerosis and Predicts Subclinical Disease.

BACKGROUND: Although the role of Th17 and regulatory T cells in the progression of atherosclerosis has been highlighted in recent years, their molecular mediators remain elusive. We aimed to evaluate the association between the CD69 receptor, a regulator of Th17/regulatory T cell immunity, and atherosclerosis development in animal models and in patients with subclinical disease. METHODS: Low-density lipoprotein receptor-deficient chimeric mice expressing or not expressing CD69 on either myeloid or lymphoid cells were subjected to a high fat diet. In vitro functional assays with human T cells were performed to decipher the mechanism of the observed phenotypes. Expression of CD69 and NR4A nuclear receptors was evaluated by reverse transcription-polymerase chain reaction in 305 male participants of the PESA study (Progression of Early Subclinical Atherosclerosis) with extensive (n=128) or focal (n=55) subclinical atherosclerosis and without disease (n=122). RESULTS: After a high fat diet, mice lacking CD69 on lymphoid cells developed large atheroma plaque along with an increased Th17/regulatory T cell ratio in blood. Oxidized low-density lipoprotein was shown to bind specifically and functionally to CD69 on human T lymphocytes, inhibiting the development of Th17 cells through the activation of NR4A nuclear receptors. Participants of the PESA study with evidence of subclinical atherosclerosis displayed a significant CD69 and NR4A1 mRNA downregulation in peripheral blood leukocytes compared with participants without disease. The expression of CD69 remained associated with the risk of subclinical atherosclerosis in an adjusted multivariable logistic regression model (odds ratio, 0.62; 95% CI, 0.40-0.94; P=0.006) after adjustment for traditional risk factors, the expression of NR4A1, the level of oxidized low-density lipoprotein, and the counts of different leucocyte subsets. CONCLUSIONS: CD69 depletion from the lymphoid compartment promotes a Th17/regulatory T cell imbalance and exacerbates the development of atherosclerosis. CD69 binding to oxidized low-density lipoprotein on T cells induces the expression of anti-inflammatory transcription factors. Data from a cohort of the PESA study with subclinical atherosclerosis indicate that CD69 expression in PBLs inversely correlates with the presence of disease. The expression of CD69 remained an independent predictor of subclinical atherosclerosis after adjustment for traditional risk factors.

ITAM-based interaction of ERM proteins with Syk mediates signaling by the leukocyte adhesion receptor PSGL-1.

P-selectin glycoprotein ligand 1 (PSGL-1) is a leukocyte adhesion molecule involved in cell tether and rolling on activated endothelium. Our work shows that PSGL-1 associates with Syk. This association is mediated by the actin-linking proteins moesin and ezrin, which directly interact with Syk in an ITAM-dependent manner. PSGL-1 engagement induces tyrosine phosphorylation of Syk and SRE-dependent transcriptional activity. Treatment of cells with the Syk inhibitor piceatannol and overexpression of either a Syk dead kinase mutant or an ITAM-mutated moesin abrogated PSGL-1-induced transcriptional activation. These data unveil a new functional role for the ERMs (ezrin/radixin/moesin) as adaptor molecules in the interactions of adhesion receptors and intracellular tyrosine kinases and show that PSGL-1 is a signaling molecule in leukocytes.

A juxta-membrane amino acid sequence of P-selectin glycoprotein ligand-1 is involved in moesin binding and ezrin/radixin/moesin-directed targeting at the trailing edge of migrating lymphocytes.

P-selectin glycoprotein ligand 1 (PSGL-1) is an adhesion receptor localized on the tips of microvilli that is involved in the rolling of neutrophils on activated endothelium. We found that PSGL-1 was concentrated at the uropod of chemokine-stimulated lymphoid cells. Dynamic fluorescence videomicroscopy analyses of migrating lymphocytes demonstrated that PSGL-1 and moesin redistributed towards the cellular uropod at the trailing edge of these cells, where activated ezrin/radixin/moesin (ERM) proteins were located. An eighteen amino acid sequence in the juxta-membrane region of the PSGL-1 cytoplasmic tail was found to be critical for uropod targeting and moesin binding. Substitution of S336, S348, and the basic cluster R337K338 by alanines within this region significantly impaired both moesin binding and PSGL-1 polarization. These results underline the role of moesin in the subcellular redistribution of PSGL-1 in lymphoid cells and make evident the importance of specific serine residues within the cytoplasmic tail of PSGL-1 for this process.