Mulholland, I. Z. | Search bioRxiv

bioRxiv2025

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.

neuroscience↗

bioRxiv2024

Leukocytes have a heparan sulfate glycocalyx that regulates recruitment during inflammation

The glycocalyx is a proteoglycan-rich layer present on the surface of all mammalian cells that is particularly prevalent on endothelial cells lining the vasculature. It has been hypothesized that the glycocalyx mediates leukocyte migration by masking adhesion molecules and reducing leukocyte adhesion to the endothelium. Leukocyte recruitment is a key driver of inflammatory diseases, including the chronic skin disease, psoriasis. Here, we show that leukocytes express heparan sulfate, an important glycocalyx component, on their cell surface which is lost in response to psoriasis-like skin inflammation, whilst endothelial heparan sulfate expression is not affected. Treatment with a heparan sulfate mimetic during psoriasis-like skin inflammation protected heparan sulfate from cleavage by heparanase and resulted in reduced leukocyte accumulation in skin, yet unexpectedly, led to increased clinical signs of inflammation due to reduced Treg numbers. These findings reshape our understanding of immune cell recruitment by revealing the presence and function of a heparan sulfate glycocalyx on immune cells and highlight the complex effects of heparanase inhibitors on the immune response in this context. One Sentence SummaryLeukocytes express a glycocalyx on their surface which is shed in response to psoriasis-like skin inflammation, facilitating their migration into the skin.

immunology↗