CDKN2B Regulates TGFß Signaling and Smooth Muscle Cell Investment of Hypoxic Neovessels.

RATIONALE: Genetic variation at the chromosome 9p21 cardiovascular risk locus has been associated with peripheral artery disease, but its mechanism remains unknown. OBJECTIVE: To determine whether this association is secondary to an increase in atherosclerosis, or it is the result of a separate angiogenesis-related mechanism. METHODS AND RESULTS: Quantitative evaluation of human vascular samples revealed that carriers of the 9p21 risk allele possess a significantly higher burden of immature intraplaque microvessels than carriers of the ancestral allele, irrespective of lesion size or patient comorbidity. To determine whether aberrant angiogenesis also occurs under nonatherosclerotic conditions, we performed femoral artery ligation surgery in mice lacking the 9p21 candidate gene, Cdkn2b. These animals developed advanced hindlimb ischemia and digital autoamputation, secondary to a defect in the capacity of the Cdkn2b-deficient smooth muscle cell to support the developing neovessel. Microarray studies identified impaired transforming growth factor ß (TGFß) signaling in cultured cyclin-dependent kinase inhibitor 2B (CDKN2B)-deficient cells, as well as TGFß1 upregulation in the vasculature of 9p21 risk allele carriers. Molecular signaling studies indicated that loss of CDKN2B impairs the expression of the inhibitory factor, SMAD-7, which promotes downstream TGFß activation. Ultimately, this manifests in the upregulation of a poorly studied effector molecule, TGFß1-induced-1, which is a TGFß-rheostat known to have antagonistic effects on the endothelial cell and smooth muscle cell. Dual knockdown studies confirmed the reversibility of the proposed mechanism, in vitro. CONCLUSIONS: These results suggest that loss of CDKN2B may not only promote cardiovascular disease through the development of atherosclerosis but may also impair TGFß signaling and hypoxic neovessel maturation.

Cyclin-dependent kinase inhibitor 2B regulates efferocytosis and atherosclerosis.

Genetic variation at the chromosome 9p21 risk locus promotes cardiovascular disease; however, it is unclear how or which proteins encoded at this locus contribute to disease. We have previously demonstrated that loss of one candidate gene at this locus, cyclin-dependent kinase inhibitor 2B (Cdkn2b), in mice promotes vascular SMC apoptosis and aneurysm progression. Here, we investigated the role of Cdnk2b in atherogenesis and found that in a mouse model of atherosclerosis, deletion of Cdnk2b promoted advanced development of atherosclerotic plaques composed of large necrotic cores. Furthermore, human carriers of the 9p21 risk allele had reduced expression of CDKN2B in atherosclerotic plaques, which was associated with impaired expression of calreticulin, a ligand required for activation of engulfment receptors on phagocytic cells. As a result of decreased calreticulin, CDKN2B-deficient apoptotic bodies were resistant to efferocytosis and not efficiently cleared by neighboring macrophages. These uncleared SMCs elicited a series of proatherogenic juxtacrine responses associated with increased foam cell formation and inflammatory cytokine elaboration. The addition of exogenous calreticulin reversed defects associated with loss of Cdkn2b and normalized engulfment of Cdkn2b-deficient cells. Together, these data suggest that loss of CDKN2B promotes atherosclerosis by increasing the size and complexity of the lipid-laden necrotic core through impaired efferocytosis.

The combination of 9p21.3 genotype and biomarker profile improves a peripheral artery disease risk prediction model.

Peripheral artery disease (PAD) is a highly morbid condition affecting more than 8 million Americans. Frequently, PAD patients are unrecognized and therefore do not receive appropriate therapies. Therefore, new methods to identify PAD have been pursued, but have thus far had only modest success. Here we describe a new approach combining genomic and metabolic information to enhance the diagnosis of PAD. We measured the genotype of the chromosome 9p21 cardiovascular-risk polymorphism rs10757269 as well as the biomarkers C-reactive protein, cystatin C, ß2-microglobulin, and plasma glucose in a study population of 393 patients undergoing coronary angiography. The rs10757269 allele was associated with PAD status (ankle-brachial index < 0.9) independent of biomarkers and traditional cardiovascular risk factors (odds ratio = 1.92; 95% confidence interval, 1.29-2.85). Importantly, compared to a previously validated risk factor-based PAD prediction model, the addition of biomarkers and rs10757269 significantly and incrementally improved PAD risk prediction as assessed by the net reclassification index (NRI = 33.5%; p = 0.001) and integrated discrimination improvement (IDI = 0.016; p = 0.017). In conclusion, a model including a panel of biomarkers, which includes both genomic information (which is reflective of heritable risk) and metabolic information (which integrates environmental exposures), predicts the presence or absence of PAD better than established risk models, suggesting clinical utility for the diagnosis of PAD.

Loss of CDKN2B promotes p53-dependent smooth muscle cell apoptosis and aneurysm formation.

OBJECTIVE: Genomewide association studies have implicated allelic variation at 9p21.3 in multiple forms of vascular disease, including atherosclerotic coronary heart disease and abdominal aortic aneurysm. As for other genes at 9p21.3, human expression quantitative trait locus studies have associated expression of the tumor suppressor gene CDKN2B with the risk haplotype, but its potential role in vascular pathobiology remains unclear. METHODS AND RESULTS: Here we used vascular injury models and found that Cdkn2b knockout mice displayed the expected increase in proliferation after injury, but developed reduced neointimal lesions and larger aortic aneurysms. In situ and in vitro studies suggested that these effects were attributable to increased smooth muscle cell apoptosis. Adoptive bone marrow transplant studies confirmed that the observed effects of Cdkn2b were mediated through intrinsic vascular cells and were not dependent on bone marrow-derived inflammatory cells. Mechanistic studies suggested that the observed increase in apoptosis was attributable to a reduction in MDM2 and an increase in p53 signaling, possibly due in part to compensation by other genes at the 9p21.3 locus. Dual inhibition of both Cdkn2b and p53 led to a reversal of the vascular phenotype in each model. CONCLUSIONS: These results suggest that reduced CDKN2B expression and increased smooth muscle cell apoptosis may be one mechanism underlying the 9p21.3 association with aneurysmal disease.