Effect of 9p21.3 Coronary Artery Disease Locus Neighboring Genes on Atherosclerosis in Mice

Abstract

Background The human 9p21.3 chromosome locus has been shown to be an independent risk factor for atherosclerosis in multiple large scale genome-wide association studies, but the underlying mechanism remains unknown. We set out to investigate the potential role of the 9p21.3 locus neighboring genes, including Mtap, the two isoforms of Cdkn2a, p16Ink4a and p19Arf, and Cdkn2b in atherosclerosis using knockout mice models. Methods and Results Gene targeted mice for neighboring genes, including Mtap, Cdkn2a, p19Arf, and Cdkn2b, were each bred to mice carrying the human APO*E3 Leiden transgene which sensitizes the mice for atherosclerotic lesions through elevated plasma cholesterol. We found that the mice heterozygous for Mtap developed larger lesion compared to wild-type mice (49623±21650 vs. 18899±9604 μm2/section (Mean±SD); p=0.01), with similar morphology as wild type mice. The Mtap heterozygous mice demonstrated changes in metabolic and methylation profiles and CD4+ cell counts. The Cdkn2a knockout mice had smaller lesions compared to wild-type and heterozygous mice and there were no significant differences in lesion size in p19Arf and Cdkn2b mutants as compared to wild type. We observed extensive, tissue-specific compensatory regulation of the Cdkn2a and Cdkn2b genes among the various knockout mice, making the effects on atherosclerosis difficult to interpret. Conclusions Mtap plays a protective role against atherosclerosis, whereas Cdkn2a appears to be modestly proatherogenic. However, no relation was found between the 9p21 genotype and the transcription of 9p21 neighboring genes in primary human aortic vascular cells in vitro. There is extensive compensatory regulation in the highly conserved 9p21 orthologous region in mice.

CDKN2B expression in adipose tissue of familial combined hyperlipidemia patients

“…Ϫ / Ϫ mice have comparable body weights to their APOE*3 Leiden littermates ( 67 ) and only mice expressing reduced levels of both CDKN2A and CDKN2B mRNA develop increased body weights ( 66 ). Here, we show that adding a mitogenic/adipogenic cocktail to 3T3-L1 fi broblasts induced comparable drops in CDKN2B and CDKN2A (its neighbor) mRNA levels ( Fig.…”

“…Interpreting the clinical signifi cance of the increased CDKN2B mRNA levels in the subcutaneous fat of FCHL patients ( Table 2 ) is facilitated by the studies reported here and elsewhere (65)(66)(67). Thus, CDKN2B -defi cient mouse embryonic fi broblasts (MEF) cultured under standard 3T3 conditions exhibit a ‫ف‬ 2-fold higher proliferation rate than wild-type MEFs and following serum deprivation, reenter the S phase of the cell cycle more efficiently ( 65,68 ).…”

Cyclin-dependent kinase inhibitor 2B regulates efferocytosis and atherosclerosis

“…Because the 9p21 locus promotes risk independently of all classical risk factors, it is possible that a therapy that promotes efferocytosis could provide incremental benefit beyond antihypertensive, antidiabetic, and lipid- lowering therapies. Additionally, the contribution of other 9p21 locus genes to phagocytic clearance should be queried, given that compensation of apoptosis and atherosclerosis-regulating genes in this locus can occur in response to stress (19,52). Crosstalk with other efferocytosis pathways should also be investigated, particularly to design therapies that will normalize clearance of dying cells without inducing off-target phagocytosis of healthy cells.…”

“…We recently reported that CDKN2B does play a role in vascular SMC physiology and that Cdkn2b knockout mice develop advanced aneurysms related to accelerated SMC apoptosis and medial thinning (16). Because the mechanism(s) by which 9p21 promote coronary disease remain unclear and the subject of debate (17)(18)(19)(20)(21)(22), we hypothesized that CDKN2B's effects on programmed cell death contribute to the development of CAD by stimulating the accumulation of necrotic debris within the evolving plaque. In the experiments discussed below, we continued to pursue the role of this candidate gene in a murine model of atherogenesis, with a focus on its ability to regulate the clearance of apoptotic bodies (ABs) and the proatherosclerotic consequences of failed phagocytosis.…”

Human Genomics in Cardiovascular Medicine

“…18 On the other hand, a recent report on the various knockout mice suggested extensive compensatory regulation in this 9p21 region. 19 …”