FURIN induces vascular endothelial cell death and efferocytosis through enzymatic cleavage of thrombospondin-1.

The vascular endothelium regulates molecular and cellular exchanges between the blood and tissues. Endothelial cell dysfunction and death, triggered by cardiovascular risk factors, can result in endothelial leakage, leading to atherosclerosis. Evidence indicates that the proprotein convertase FURIN can modulate endothelial cell behaviour and promote atherosclerosis. In this study, we investigated the underlying mechanisms: small interfering RNA (siRNA)-induced knockdown of FURIN reduced vascular endothelial cell (VEC) apoptosis and efferocytosis by monocyte-derived macrophages, whereas lentivirus-mediated overexpression of FURIN had the opposite effect. A co-immunoprecipitation assay and western blot analyses indicated that FURIN interacted with thrombospondin-1 (THBS1). Furthermore quantitative RT-PCR assays and western blot analyses showed that FURIN knockdown resulted in a decrease in THBS1 mRNA and protein levels, whereas THBS1 knockdown attenuated FURIN expression, and these reciprocal regulatory effects were augmented in the presence of LY2109761, an inhibitor of transforming growth factor-β receptors. THBS1 knockdown largely abolished the influence of FURIN on VEC apoptosis and efferocytosis. Further assays indicated that FURIN knockdown enhanced the integrity and reduced the permeability of a monolayer of cultured VECs, which was counteracted by overexpression of THBS1. In a mouse model of atherosclerosis treatment with a FURIN inhibitor decreased VEC apoptosis in atherosclerotic lesions. Overall these results indicate that by cleaving THBS1 and suppressing THBS1 expression FURIN promotes VEC apoptosis and efferocytosis, leading to increased endothelial permeability. These findings provide a new insight into endothelial dysfunction, with atherogenic relevance and potential therapeutic implications. KEY POINTS: Endothelial dysfunction and cell death may lead to endothelial leakage, triggering atherosclerosis. The proprotein convertase FURIN regulates endothelial cell behaviour and promotes atherosclerosis, but its specific mechanisms remain unclear. This study identifies thrombospondin-1 (THBS1) as a novel substrate of FURIN in vascular endothelial cells. FURIN binds to and cleaves THBS1, thereby promoting endothelial apoptosis and efferocytosis, increasing endothelial permeability and impairing vascular homeostasis. These findings provide new insights into endothelial dysfunction with atherogenic and therapeutic relevance.