Cyclin-dependent kinase inhibitor p16INK4a and telomerase may co-modulate endothelial progenitor cells senescence

Endothelial cells (ECs) damage is an initial and pivotal step in the formation of atherosclerosis. Endothelial progenitor cells (EPCs), which have been considered as the precursor of ECs, can migrate and home to the site of injured ECs to divide into mature ECs and keep the integrity of the endothelial monolayer. It has been shown that the number and function of EPCs are negatively correlated with various atherosclerotic risk factors. This finding may be explained partly by accelerated senescence of EPCs induced by telomere attrition or shortening owning to oxidative stress and accumulative ROS. However, elevated telomerase activity which extends the telomere cannot lead to cellular immortal in the presence of the cyclin-dependent kinase inhibitor p16INK4a. Researchers have the opinion that senescence is the balance between the regeneration and cancer. High expression of phosphorylated p16INK4a, which is caused by oxidative stress and accumulative ROS, can prevent tumor cells from unlimited division and becoming malignant ones by accelerating premalignant cells premature senescence. It has been demonstrated that the expression of p16INK4a increases remarkably with age due to oxidative stress and accumulative ROS in some stem and progenitor cells, and regulates these cells age-dependent senescence. It is observed that telomeres shortening exists in these cells. Therefore, it can be hypothesized that p16INK4a, together with telomerase, may co-modulate EPCs senescence.