Targeting monocytic Occludin impairs monocyte transmigration and HIV neuroinvasion

Transmigration of circulating monocytes from the bloodstream toward the central nervous system (CNS) represents a hallmark of neuroinflammation and plays an important role during viral encephalitis and HIV-associated neurocognitive disorders (HAND). The molecular mechanisms involved in monocyte transmigration through endothelia has been extensively studied, but how monocytes locally unzip tight junction-associated proteins (TJAPs) of the endothelium composing the neurovascular unit (NVU) to reach the CNS remains poorly understood. Here, we show that human circulating monocytes express the TJAP Occludin (OCLN) to promote transmigration through cerebral microvessel endothelial cells. Silencing monocytic OCLN (mOCLN) impairs monocyte transmigration, while mOCLN overexpression increases transmigration. Using high-resolution live cell imaging, we observed that mOCLN clusters at the monocyte-endothelium interface during the transmigration process, forming a transient ring of mOCLN at the site of diapedesis. Furthermore, we designed OCLN-derived peptides targeting its extracellular loop (EL) 1 or 2 to prevent potential trans-homotypic interactions of mOCLN with endothelial OCLN. We found that transmigration of human monocytes was significantly inhibited upon treatment with the EL2 peptide in vitro and in zebrafish embryos, while preserving vascular integrity. Monocyte transmigration toward the brain is an important process for HIV neuroinvasion and here, we showed that the treatment of transmigrating monocytes with the EL2 peptide prevents the dissemination of HIV 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 HIV neuroinvasion. ### Competing Interest Statement The authors have declared no competing interest.