ROR2/PCP a New Pathway Controlling Endothelial Cell Polarity Under Flow Conditions.

BACKGROUND: Endothelial cells (ECs) are sensitive to physical forces created by blood flow, especially to laminar shear stress. Among the cell responses to laminar flow, EC polarization against the flow direction emerges as a key event, particularly during the development and remodeling of the vascular network. EC adopt an elongated planar cell shape with an asymmetrical distribution of intracellular organelles along the axis of blood flow. This study aimed to investigate the involvement of planar cell polarity via the receptor ROR2 (receptor tyrosine kinase-like orphan receptor 2) in endothelial responses to laminar shear stress. METHODS: We generated a genetic mouse model with EC-specific deletion of Ror2, in combination with in vitro approaches involving loss- and gain-of-function experiments. RESULTS: During the first 2 weeks of life, the endothelium of the mouse aorta undergoes a rapid remodeling associated with a loss of EC polarization against the flow direction. Notably, we found a correlation between ROR2 expression and endothelial polarization levels. Our findings demonstrate that deletion of Ror2 in murine ECs impaired their polarization during the postnatal development of the aorta. In vitro experiments further validated the essential role of ROR2 in both EC collective polarization and directed migration under laminar flow conditions. Exposure to laminar shear stress triggered the relocalization of ROR2 to cell-cell junctions where it formed a complex with VE-Cadherin and ß-catenin, thereby regulating adherens junctions remodeling at the rear and front poles of ECs. Finally, we showed that adherens junctions remodeling and cell polarity induced by ROR2 were dependent on the activation of the small GTPase Cdc42. CONCLUSIONS: This study identified ROR2/planar cell polarity pathway as a new mechanism controlling and coordinating collective polarity patterns of EC during shear stress response.

A novel and efficient approach to high-throughput production of HLA-E/peptide monomer for T-cell epitope screening.

Over the past two decades, there has been a great interest in the study of HLA-E-restricted αß T cells during bacterial and viral infections, including recently SARS-CoV-2 infection. Phenotyping of these specific HLA-E-restricted T cells requires new tools such as tetramers for rapid cell staining or sorting, as well as for the identification of new peptides capable to bind to the HLA-E pocket. To this aim, we have developed an optimal photosensitive peptide to generate stable HLA-E/pUV complexes allowing high-throughput production of new HLA-E/peptide complexes by peptide exchange. We characterized the UV exchange by ELISA and improved the peptide exchange readout using size exclusion chromatography. This novel approach for complex quantification is indeed very important to perform tetramerization of MHC/peptide complexes with the high quality required for detection of specific T cells. Our approach allows the rapid screening of peptides capable of binding to the non-classical human HLA-E allele, paving the way for the development of new therapeutic approaches based on the detection of HLA-E-restricted T cells.