POST-TRANSCRIPTIONAL MODULATORS OF LDL-R IN LIPID METABOLISM AND ATHEROSCLEROSIS - ANIMAL AND HUMAN STUDIES

Low density lipoprotein receptor (LDL-R) is a significant asset of cardiovascular system, plays a critical role in regulating the amount of cholesterol in the blood. Mutation in the LDLR gene causes a lethal clinical condition called “Familial hypercholesterolemia”. To date, more than 1000 mutations have been identified and characterised in LDL-R gene affecting its function. Some recent advances in lipid biology also identified certain proteins those affect LDL-R functionality at post-transcriptional levels, these genes include PCSK9, IDOL and recently altered expression on GPER gene also found linked to affect LDLR expression, these modification on LDL-R eventually leads to increase the circulating cholesterol levels in the blood called “hypercholesterolemia”- which is the primary risk factor of atherosclerosis. We first focus our goal to know the role of PCSK9 protein in carotid atherosclerosis progression and glucose homeostasis by using “carotid artery injury” and “nutrition modified” mice model respectively. Our results indicates that the presence of PCSK9 protein in mice induces neo-intimal hyperplasia upon stimulation, might be due to higher de-differentiating phenotypes of underlying vascular smooth muscle cells (VSMCs). Mice carrying PCSK9 allele had high intimal thickening (p<0.05) and intima-media ratio (p<0.024), and enhanced expression of VSMCs synthetic markers like caldesmon (p<0.01), Col1a1 (p<0.05), and with higher proliferation and migration pattern than PCSK9-KO mice. However, Our results from nutrition modified model, where mice were fed with DIO (Diet induced obesity) diet (20 weeks) indicates that mice with PCSK9 deficiency might causes defect in pancreatic beta-cells functionality as these mice had less tolerance to glucose when tested by glucose tolerance test (GTT) assay, while no change in glucose absorbance were observed between the strains when challenged with intraperitoneal insulin. We also aim to understand the genetic variability of post-transcriptional modulators of LDLR and their role on lipid variability, glucose metabolism and peripheral atherosclerosis progression in human subjects. Various Genome-wide association studies (GWAS) have identified and evaluated several genetic variants on post-transcriptional modulators of LDLR (esp PCSK9 and IDOL gene) and their influence on lipid variability, glucose metabolism and peripheral atherosclerosis progression, however, the results of these variants emerged with admixed results when evaluated on different population. Therefore, our focus was to know the role of certain common variants of PCSK9 (rs11591147; p.R46L), IDOL (rs9370867; p.N342S) and GPER (rs11544331; p.P16L) on lipid variability, glucose metabolism and cIMT progression in Italian general population enrolled in the PLIC study (Progression of lesion in intima-media of carotid artery), The impact of PCSK9 R46L on lipid levels was favourable as found linked in reduction in total cholesterol (-4.40%) and LDL (-7.2%) levels but increases glucose levels (+7.2%) in comparison to R46R carriers, while there was no influence of IDOL (p.N342S) and GPER (p.P16L) on lipid and glucose levels were observed. When analysed for the role on cIMT progression, all studied loci (PCSK9, IDOL and GPER respective variants) did not show any significant association with the progression of carotid intima media thickness. Our next aim was to evaluate the plasma PCSK9 levels in Italian subjects and to perform association studies with clinical parameters. We found a wide range of plasma PCSK9 levels in our Italian studied cohort (range 8-1432 ng/ml), with the significant association with various lipoproteins like LDL (p=0.002), TC(<0.001), Tg (<0.001), HDL(<0.001) etc. However, all these association were found modestly stronger in Men cohort despite of carrying less plasma PCSK9 levels than their age-matched women, We also observed that PCSK9 levels also influenced due to the gender and age and certain hypolipidemics drugs like statins also increases plasma PCSK9 levels. However, plasma PCSK9 levels did not show any significant association with cIMT progression and neither with glucose levels. Nevertheless, we observed that Men with Metabolic syndrome (MetS) tend to present high plasma PCSK9 levels than men of control group (p=0.04). At last, we aim to investigate the epistatic role of our studied genes over plasma PCSK9 levels, if any. We found that PCSK9 R46L and GPER P16L (sex-specific) influences plasma PCSK9 levels, while IDOL N342S variants did not present any alteration in plasma PCSK9 levels. Altogether, these results suggest that PCSK9 presence have both beneficial and adverse outcomes, while no significant association of IDOL and GPER variants with studied clinical phenotypes were observed in Italian general population.