TNF-α regulates the proteolytic degradation of ST6Gal-1 and endothelial cell-cell junctions through upregulating expression of BACE1

Endothelial dysfunction and monocyte adhesion to vascular endothelial cells are two critical steps in atherosclerosis development, and emerging evidence suggests that protein sialylation is involved in these processes. However, the mechanism underlying this phenomenon remains incompletely elucidated. In this study, we demonstrated that treatment with the proinflammatory cytokine TNF-α disrupted vascular endothelial cell-cell tight junctions and promoted monocyte endothelial cell adhesion. Western blotting and Sambucus nigra lectin (SNA) blotting analyses revealed that TNF-α treatment decreased α-2, 6-sialic acid transferase 1 (ST6Gal-I) levels and downregulated VE-Cadherin α-2, 6 sialylation. Further analysis demonstrated that TNF-α treatment upregulated β-site amyloid precursor protein enzyme 1 (BACE1) expression, thus resulting in sequential ST6Gal-I proteolytic degradation. Furthermore, our results revealed that PKC signaling cascades were involved in TNF-α-induced BACE1 upregulation. Together, these results indicated that the proinflammatory cytokine TNF-α impairs endothelial tight junctions and promotes monocyte-endothelial cell adhesion by upregulating BACE1 expression through activating PKC signaling and sequentially cleaving ST6Gal-I. Thus, inhibition of BACE1 expression may be a new approach for treating atherosclerosis.