Heparan sulfate glycosaminoglycans mediate CXCL4 (PF4) transport across the blood-brain barrier and effects on neurogenesis

CXCL4 (PF4) is a chemokine stored in platelets that has pleiotropic effects across biological settings. These effects include driving of inflammation and fibrosis as well as reversal of the effects of ageing. We have recently demonstrated that CXCL4 function is driven, independently of known chemokine receptors, through binding to glycosaminoglycan (GAG) side chains on proteoglycans within the cell surface glycocalyx. In this study, we have used intravital imaging and radioactive tracer studies, in combination with an exogenous inhibitor and a GAG-binding CXCL4 mutant, to demonstrate that CXCL4 can enter the brain parenchyma of mice by binding to proteoglycans within the cell surface of the endothelial glycocalyx of the blood-brain barrier (BBB). Furthermore, we have also demonstrated that CXCL4 directly promotes neurogenesis in vitro, which is mediated by its ability to oligomerise and bind to GAGs. These findings provide a molecular mechanism for CXCL4 uptake and function within the brain. Furthermore, these data have important implications for understanding CXCL4 during health and disease that may enable development of CXCL4-related therapeutics for inflammatory diseases and ageing.