Background and Aims

PCSK9 is the third gene involved in familial hypercholesterolemia, a major cause of atherosclerosis. Its role in regulating plasma cholesterol levels has been widely reported, and anti-PCSK9 drugs have been developed. Nevertheless, direct interactions between PCSK9 and atherosclerotic pathology are not fully elucidated.

We aim at demonstrating that PCSK9 promotes atherosclerosis through vascular smooth muscle cells (VSMC) involved in foam cells formation, atherosclerosis initiation, and progression.

Methods

Healthy and atheromatous human aortas were collected, tissues were fixed, conditioned media were obtained after 24 hours incubation in serum-free culture medium, and primary VSMC were isolated from media of healthy aortas.

Results

We showed that PCSK9, although present in foam cells from fatty streaks, fibroatheromas and absent in healthy tissues, is not synthesized in the arterial wall. PCSK9 levels were significantly higher in conditioned media from atheromatous aortas than from healthy aortas. Thus, PCSK9 penetrates through the arterial wall by outward convection from the circulation. We showed that primary VSMC uptake PCSK9 when added to the media. Moreover, LRP1 gene was highly expressed in the arterial wall of healthy and affected aortas and blocking its function using the receptor-associated protein (RAP) significantly decreased the uptake of PCSK9 by VSMC. Also, PCSK9 and LOX-1 colocalized in VSMC and PCSK9 uptake was reduced by oxidized LDL.

Conclusions

We characterized the presence of PCSK9 in human atherosclerotic tissues and demonstrated that PCSK9 present in the aortic wall is not synthesized locally. Our results suggest that PCSK9 is being internalized and metabolized through scavenger receptors expressed by VSMC.