Membrane tension regulates syndecan-1 expression through actin remodelling.

Background: The endothelial glycocalyx, located at the interface of vascular lumen, is a carbohydrate-rich complex that controls vascular functions such as solute permeation and mechanotransduction. It anchors to the cell membrane through core proteins, e.g. syndecan-1, which couple to the actin cytoskeleton. Membrane tension plays an important role in the reorganisation of membrane-bound proteins, however, little is known on the effect of the membrane tension on the various components of the glycocalyx.

Methods: Hypo-osmotic stress is used to investigate the effect of the membrane tension on syndecan-1 expression.

Results: Following 20 min exposure to hypo-osmotic medium, the expression of syndecan-1 in the endothelial glycocalyx layer is reduced to 84.7 ± 3.6% (255 mOsm) and 64.7 ± 2.1% (167 mOsm). This reduction, however, is transient and partial recovery is observed at the end of 2 h exposure to the hypo-osmotic medium. The transient reduction of syndecan-1 is associated with depolymerisation of the actin cytoskeleton. Further examination of the effect of actin manipulation reveals that actin depolymerisation by cytochalasin D results in sustained syndecan-1 reduction. In contrast, stabilising actin using jasplakinolide abolishes the transient reduction of syndecan-1completely.

Conclusions: We demonstrate, for the first time, that membrane tension plays an important role in the regulation of syndecan-1 expression and this effect is mediated by the reorganisation of the actin cytoskeleton.

General Significance: Findings in this study suggest a new venue of research on the protective role of the glycocalyx in vascular pathophysiology and diseases.