PCSK9 plays a novel immunological role in oxidized LDL-induced dendritic cell maturation and activation of T cells from human blood and atherosclerotic plaque.

BACKGROUND: Activated T cells and dendritic cells (DCs) occur in atherosclerotic plaques. Proprotein convertase subtilisin kexin 9 (PCSK9) targets the LDL-receptor (LDLR) and results in increased LDL levels. We here investigate immune effects of PCSK9 on OxLDL induced DC maturation and T-cell activation.

METHODS: T cells were isolated from carotid specimens of patients undergoing carotid endarterectomy or from peripheral blood of healthy individuals. Human peripheral blood monocytes were differentiated into DCs. Naïve T cells were cocultured with pretreated DCs. The effects of PCSK9 and its inhibition by silencing were studied.

RESULTS: OxLDL induced PCSK9 in DCs and promoted DC maturation with increased expressions of CD80, CD83, CD86 and HLA-DR and the scavenger receptors LOX-1 and CD36. T cells exposed to OxLDL-treated DCs proliferated and produced IFN-γ and IL-17, thus with polarization to Th1 and/or Th17 subsets. Silencing of PCSK9 reversed the OxLDL effects on DCs and T cells. DC maturation was repressed, and the production of TNF-α, IL-1β and IL-6 was limited, while TGF-β and IL-10 secretion and T regulatory cells were induced. OxLDL induced miRNA let-7c, miR-27a, miR-27b, miR-185. Silencing PCSK9 repressed miR-27a and to a lesser extent let-7c. PCSK9 silencing enhanced SOCS1 expression induced by OxLDL. Experiments on T cells from carotid atherosclerotic plaques or healthy individuals showed similar results.

CONCLUSIONS: We demonstrate immunological effects of PCSK9 in relation to activation and maturation of DCs and plaque T cells by OxLDL, a central player in atherosclerosis. This may directly influence atherosclerosis and cardiovascular disease, independent of LDL lowering.