Abstract 463: Impairment Of Angiogenesis And Endothelial Progenitor Function By Mutation Of Circadian Gene mPER2
Background: Biological circadian rhythm is tightly regulated and is important in cardiovascular function. Two transcriptional activators, CLOCK and BMAL1, form heterodimeric complexes and induce the expression of several circadian genes. Among those genes are Per1, Per2, Cry1 and Cry2, whose protein products control circadian clock in brain and peripheral tissues. However, the role of Per2 and circadian rhythm in regulating vascular function is not known.
Methods and Results: Per2 mutant mice, which have a deletion in the PAS domain, and their wild type littermates were subjected to hindlimb ischemia. Tissue necrosis, capillary density, blood flow recovery and clinical score were assessed every week for one month. All Per2 mutant mice developed auto-amputation after hindlimb ischemia compared to none for WT mice. In order to assess if Per2 in bone marrow-derived endothelial progenitor cell (EPC) contribute to this vascular defect, bone marrow from WT and Per2 mutant mice were transplanted into irradiated WT mice. Mice, which received Per2 mutant bone marrow, demonstrated 34% less blood flow recovery compared to mice receiving WT bone marrow (P<0.01). Injection of WT EPCs into Per2 mutant mice rescued the auto-amputation phenotype after hindlimb ischemia. Furthermore, blood flow recovery was nearly 2 times greater with WT EPC injection compared to Per2 mutant EPC injection. Both endothelial cells and endothelial progenitor cells isolated from Per2 mutant mice showed decreased proliferation and migration, diminished nitric oxide production and impaired tube formation.
Conclusion: These findings indicate that mutation of the clock gene, Per2, severely impairs angiogenesis and worsens the angiogenic response to ischemic injury. In particular, Per2 mutation in bone marrow-derived ECPs plays a critical role in neovascularization. These results suggest that circadian rhythm regulates vascular function, in part, through effects on EPC function.