BCNCT

Elevated low-density lipoprotein cholesterol (LDL-C) is the most important causative factor of atherosclerosis and associated cardiovascular (CV) diseases. The LDL receptor (LDLR) is the pathway by which LDL are cleared from the plasma. PCSK9 is a major inhibitor of the LDLR. It is therefore essential to elucidate the molecular mechanisms of PCSK9 inhibition as well as the role of PCSK9 in patients at high CV risk such as those (i) who developed recurrent CV events despite statin treatment, or those who present with familial hypercholesterolemia (FH), or those who require vascular surgery for peripheral artery disease (PAD). Our 1st hypothesis is that the enzyme PCSK5 is a natural inhibitor that cleaves PCSK9, and thereby positively impacts on circulating LDL. Using mouse models, we will demonstrate that PCSK5 catalyzes the inactivation of PCSK9 in vivo. We will also assess if PCSK9 cleavage is relevant in humans by setting up a specific ELISA assay. Our 2nd hypothesis is that interactions between the protein AnxA2 and PCSK9 inhibit PCSK9 function. This will be tested by correlating AnxA2 and PCSK9 levels in human plasma and by over-expressing AnxA2 in mice. We will investigate the molecular mechanisms by which AnxA2 modulates PCSK9 function. Our 3rd hypothesis is that elevated plasma PCSK9 alters the LDLC reduction and CV protection achieved by statins. This will be tested by measuring plasma PCSK9 in patients on low and high doses of atorvastatin. We will establish correlations between PCSK9 levels, changes in circulating lipids and the recurrence of CV events over 5 years, in a large clinical trial. Our 4th hypothesis is that plasma PCSK9 strongly and positively correlate with LDL levels in familial hypercholesterolemia (FH). This will be tested using plasma samples of 400 FH patients. The function of PCSK9 will be assessed in lymphocytes and fibroblasts isolated from these patients. Our 5th hypothesis is that PCSK9 variably modulate atherosclerotic lesion calcification in peripheral arteries. This will be tested using biological samples from patients scheduled for carotid or femoral surgery. We will investigate whether PCSK9 aggravates vascular smooth muscle cells calcification using artificial blood vessels. This proposal will comprehensively investigate the molecular and cellular mechanisms by which PCSK9 function is inhibited in vivo. Greater understanding into the biological modulation of PCSK9 will ultimately facilitate the design of small molecule inhibitors. The results of these studies will also have profound implications in terms of identifying which patients will benefit most from therapies combining a statin and a PCSK9 inhibitor.