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The study of lipoproteins, natural nanoparticles comprised of lipids and apolipoproteins that transport fats throughout the body, is of key importance to better understand, treat, and prevent cardiovascular disease. In the current study, we have developed a lipoprotein-based nanoparticle that consists of a quantum dot (QD) core and Cy5.5 labeled lipidic coating. The methodology allows judicious tuning of the QD/Cy5.5 ratio, which enabled us to optimize Förster resonance energy transfer (FRET) between the QD core and the Cy5.5-labeled coating. This phenomenon allowed us to study lipoprotein−lipoprotein interactions, lipid exchange dynamics, and the influence of apolipoproteins on these processes. Moreover, we were able to study HDL-cell interactions and exploit FRET to visualize HDL association with live macrophage cells. [ABSTRACT FROM AUTHOR]

Aims In a recent report, we established at the genome-wide level those genes that are specifically upregulated in the endothelium of atherosclerotic plaques in human arteries. As the transcriptome data revealed that mRNA for the tetraspanin family member CD81 is significantly and specifically upregulated in the endothelium overlying early atheroma, we set out to validate these results on the protein level, and investigate the functional consequences of CD81 upregulation. Methods and results Immunohistochemical analysis in an independent set of donor arteries verified in the endothelium of early human atherosclerotic lesions the enhanced expression of CD81, which appears oxidative stress-dependent. Using lentiviral overexpression and silencing in human umbilical endothelial cells, we established in an in vitro flow adhesion assay that elevated endothelial CD81 is associated with increased monocyte adhesion to non-activated CD81-transduced endothelial cells, approaching the levels normally only attained after tumour necrosis factor α stimulation. The CD81 effect was dependent on both intracellular adhesion molecule 1 (ICAM-1) and vascular cell adhesion molecule 1 (VCAM-1), as it was abolished in the presence of a mixture of anti-ICAM-1 and anti-VCAM-1 antibodies. Flow cytometry revealed that increased CD81 levels did not increase total ICAM-1 and VCAM-1 surface expression. Instead, it concentrated the available adhesion molecules into membrane clusters, as indicated by confocal and electron microscopy. CD81 also colocalized with ICAM-1 and VCAM-1 in the adhesion rings around bound monocytes. Conclusion Endothelial CD81 upregulated in early human atheroma has the potential to play a crucial role in the initial stages of atherosclerotic plaque formation by increasing monocyte adhesion prior to the full-blown inflammatory response. [ABSTRACT FROM AUTHOR]