Increased gene dosage of the Ink4/Arf locus does not attenuate atherosclerosis development in hypercholesterolaemic mice

Abstract 

Rationale

Human genome-wide association studies have identified genetic variants in the chromosome 9p21 region that confer increased risk of coronary artery disease and other age-related diseases. These variants are located in a block of high linkage disequilibrium with the neighboring Ink4/Arf tumor-suppressor locus (also named CDKN2A/CDKN2B). Since previous studies suggest an atheroprotective role of the Ink4/Arf locus, here we assessed whether gain-of-function of the encoded genes can be exploited therapeutically to reduce atherosclerosis.

Methods

Generation and characterization of apolipoprotein E-null mice carrying an additional transgenic copy of the entire Ink4/Arf locus (apoE−/−Super-Ink4/Arf) that reproduces the normal expression and regulation of the endogenous locus.

Results

Although liver and aorta of apoE−/−Super-Ink4/Arf mice only showed a trend towards increased Ink4/Arf transcript levels compared to apoE−/− controls, cultured macrophages with increased Ink4/Arf gene dosage exhibited augmented apoptosis induced by irradiation with ultraviolet light, indicating that low level of transgene overexpression can lead to augmented Ink4/Arf function. However, increased Ink4/Arf gene dosage did not affect atherosclerosis development in different vascular regions of both male and female apoE−/− mice fed either normal or high-fat diet. Increased gene dosage of Ink4/Arf similarly had no effect on atheroma cell composition or collagen content, an index of plaque stability.

Conclusion

In contrast with previous studies demonstrating cancer resistance in Super-Ink4/Arf mice carrying an additional transgenic copy of the entire Ink4/Arf locus, our results cast doubt on the potential of Ink4/Arf activation as a strategy for the treatment of atherosclerotic disease.

Keywords: Ink4/Arf, CDKN2A/B, p15^Ink4b, p16^Ink4a, 9p21, Atherosclerosis