Oxysterols and the NeuroVascular Unit (NVU): A far true love with bright and dark sides.

The brain is isolated from the whole body by the blood-brain barrier (BBB) which is located in brain microvessel endothelial cells (ECs). Through physical and metabolic properties induced by brain pericytes, astrocytes and neurons (these cells and the ECs referred to as the neurovascular unit (NVU)), the BBB hardly restricts exchanges of molecules between the brain and the bloodstream. Among them, cholesterol exchanges between these two compartments are very limited and occur through the transport of LDLs across the BBB. Oxysterols (mainly 24S and 27-hydroxycholesterol) daily cross the BBB and regulate molecule/cholesterol exchanges via Liver X nuclear Receptors (LXRs). In addition, these oxysterols have been linked to pathological processes in neurodegenerative diseases such as Alzheimer's disease. Here we propose an overview of the actual knowledge concerning oxysterols and the NVU cells in physiological and in Alzheimer's disease.