Targeting monocytic Occludin impairs transendothelial migration and HIV neuroinvasion.

Transmigration of circulating monocytes from the bloodstream to tissues represents an early hallmark of inflammation. This process plays a pivotal role during viral neuroinvasion, encephalitis, and HIV-associated neurocognitive disorders. How monocytes locally unzip endothelial tight junction-associated proteins (TJAPs), without perturbing impermeability, to reach the central nervous system remains poorly understood. Here, we show that human circulating monocytes express the TJAP Occludin (OCLN) to promote transmigration through endothelial cells. We found that human monocytic OCLN (hmOCLN) clusters at monocyte-endothelium interface, while modulation of hmOCLN expression significantly impacts monocyte transmigration. Furthermore, we designed OCLN-derived peptides targeting its extracellular loops (EL) and show that transmigration of treated monocytes is inhibited in vitro and in zebrafish embryos, while preserving vascular integrity. Monocyte transmigration toward the brain is an important process for HIV neuroinvasion and we found that the OCLN-derived peptides significantly inhibit HIV dissemination to cerebral organoids. In conclusion, our study identifies an important role for monocytic OCLN during transmigration and provides a proof-of-concept for the development of mitigation strategies to prevent monocyte infiltration and viral neuroinvasion.

Circulating extracellular vesicles and tumor cells: sticky partners in metastasis.

The intravascular behavior of tumor-derived extracellular vesicles (EVs) and circulating tumor cells (CTCs) lies at the heart of the metastatic cascade. Their capacity to disseminate and stop at specific vascular regions precedes and determines the formation of metastatic foci. We discuss in detail the central role of cellular adhesion molecules (CAMs) that are present on EV/CTC surface, as well as their endothelial ligands, in dictating their arrest site and their capacity to exit the vasculature. We focus on the differences and similarities between CAMs on CTCs and EVs, and speculate about their role in the organotropism of different cancer types. Better understanding of the binding mechanisms might pinpoint potential targets for novel therapies.