RESUMEN
Sequence polymorphisms in a 58-kilobase (kb) interval on chromosome 9p21 confer a markedly increased risk of coronary artery disease (CAD), the leading cause of death worldwide. The variants have a substantial effect on the epidemiology of CAD and other life-threatening vascular conditions because nearly one-quarter of Caucasians are homozygous for risk alleles. However, the risk interval is devoid of protein-coding genes and the mechanism linking the region to CAD risk has remained enigmatic. Here we show that deletion of the orthologous 70-kb non-coding interval on mouse chromosome 4 affects cardiac expression of neighbouring genes, as well as proliferation properties of vascular cells. Chr4(Delta70kb/Delta70kb) mice are viable, but show increased mortality both during development and as adults. Cardiac expression of two genes near the non-coding interval, Cdkn2a and Cdkn2b, is severely reduced in chr4(Delta70kb/Delta70kb) mice, indicating that distant-acting gene regulatory functions are located in the non-coding CAD risk interval. Allele-specific expression of Cdkn2b transcripts in heterozygous mice showed that the deletion affects expression through a cis-acting mechanism. Primary cultures of chr4(Delta70kb/Delta70kb) aortic smooth muscle cells exhibited excessive proliferation and diminished senescence, a cellular phenotype consistent with accelerated CAD pathogenesis. Taken together, our results provide direct evidence that the CAD risk interval has a pivotal role in regulation of cardiac Cdkn2a/b expression, and suggest that this region affects CAD progression by altering the dynamics of vascular cell proliferation.
Asunto(s)
Deleción Cromosómica , Cromosomas de los Mamíferos/genética , Enfermedad de la Arteria Coronaria/genética , Animales , Aorta/patología , Proliferación Celular , Células Cultivadas , Senescencia Celular/genética , Cromosomas Humanos Par 9/genética , Enfermedad de la Arteria Coronaria/patología , Inhibidor p15 de las Quinasas Dependientes de la Ciclina/deficiencia , Inhibidor p15 de las Quinasas Dependientes de la Ciclina/genética , Inhibidor p16 de la Quinasa Dependiente de Ciclina/deficiencia , Inhibidor p16 de la Quinasa Dependiente de Ciclina/genética , Embrión de Mamíferos/embriología , Regulación de la Expresión Génica/genética , Predisposición Genética a la Enfermedad/genética , Humanos , Ratones , Miocitos del Músculo Liso/patología , Análisis de SupervivenciaRESUMEN
Scavenger receptor SR-BI has been implicated in HDL-dependent atheroprotective mechanisms. We report the generation of an SR-BI conditional knockout mouse model in which SR-BI gene targeting by loxP site insertion produced a hypomorphic allele (hypomSR-BI). Attenuated SR-BI expression in hypomSR-BI mice resulted in 2-fold elevation in plasma total cholesterol (TC) levels. Cre-mediated SR-BI gene inactivation of the hypomorphic SR-BI allele in hepatocytes (hypomSR-BI-KO(liver)) was associated with high plasma TC concentrations, increased plasma free cholesterol/TC (FC/TC) ratio, and a lipoprotein-cholesterol profile typical of SR-BI-/- mice. Plasma TC levels were increased 2-fold in hypomSR-BI and control mice fed an atherogenic diet, whereas hypomSR-BI-KO(liver) and SR-BI-/- mice developed severe hypercholesterolemia due to accumulation of FC-rich, VLDL-sized particles. Atherosclerosis in hypomSR-BI mice was enhanced (2.5-fold) compared with that in controls, but to a much lower degree than in hypomSR-BI-KO(liver) (32-fold) and SR-BI-/- (48-fold) mice. The latter models did not differ in either plasma lipid levels or in the capacity of VLDL-sized lipoproteins to induce macrophage cholesterol loading. However, reduced atherosclerosis in hypomSR-BI-KO(liver) mice was associated with decreased lesional macrophage content as compared with that in SR-BI-/- mice. These data imply that, in addition to its major atheroprotective role in liver, SR-BI may exert an antiatherogenic role in extrahepatic tissues.