Increased vascular senescence and impaired endothelial progenitor cell function mediated by mutation of circadian gene Per2

Background - Alteration of the circadian rhythm and increased vascular senescence are linked to cardiovascular disease. Per2, a circadian gene, is known to regulate endothelium-dependent vasomotion. However, the mechanism by which Per2 affects endothelial function is unknown. We hypothesize that endothelial dysfunction in Per2 mutant (Per2^m/m) mice is mediated in part by increased vascular senescence and impaired endothelial progenitor cell (EPC) function. Methods and Results - Endothelial cells from Per2^m/m mice exhibit increased protein kinase Akt signaling, greater senescence, and impaired vascular network formation and proliferation. Indeed, Per2 ^m/m mice have impaired blood flow recovery and developed autoamputation of the distal limb when subjected to hind-limb ischemia. Furthermore, matrigel implantation into Per2^m/m mice resulted in less neovascularization. Because EPCs contribute to angiogenesis, we studied the role of Per2 in these cells using bone marrow transplantation. Basal EPC levels were similar between wild-type and Per2^m/m mice. However, compared with wild-type bone marrow transplantation mice, EPC mobilization was impaired in Per2^m/m bone marrow transplantation mice in response to ischemia or VEGF stimulation. Bone marrow transplantation or infusion of wild-type EPC restored blood flow recovery and prevented autoamputation in Per2^m/m mice. Conclusion - These findings indicate that mutation of Per2 causes Akt-dependent senescence and impairs ischemia-induced revascularization through the alteration of EPC function.