Abstract MP141: Role of Cryptochrome in Angiogenesis

Abstract

Background: Although clock genes generate oscillations in about 10 % of all gene expressions as a 24-hour cycle in the cellular level cooperating with the central clock, little is known about the role of clock genes in angiogenesis. Objective: The aim of this study was to determine if a peripheral clock would modulate angiogenesis in a hind limb ischemia (HLI) model. Methods and Results: First, we surgically induced the HLI model in C57BL/6J (wild type; WT) mice (N=6 for each time point) and checked mRNA expressions of clock genes in a local ischemic tissue by PCR array in the setting of blood perfusion recovery. In vitro study, we next investigated those gene expressions in human umbilical vein endothelial cells (HUVECs) with or without stimulation by growth factors. Those data demonstrated that the peripheral clock genes were modulated in ECs and tissues in the presence of growth factors and tissue ischemia. Then, we examined whether inhibition of clock gene expressions had any effects on angiogenesis. For this study, we focused on Cryptochrome (Cry), which is well known as one of the core-loop forming clock genes producing circadian rhythm in mammals. Our loss-of-function study revealed that the abilities of proliferation, migration and tube formation were significantly inhibited by Cry1 and Cry2 double knockdown in HUVECs. Interestingly, although the knockdown of Cry1 and Cry2 changed the mRNA expression of Period2, it did not affect those of BMAL1 and Clock in HUVECs. Finally, we tested if Cry1 and Cry2 double hetero knockout mice of HLI models displayed worse blood perfusion recoveries with deterioration of angiogenesis. As results, compared with control WT mice, Cry1 and Cry2 double knockout mice showed the low capillary density detected by CD31-immunohistochemistry and low tissue blood perfusion demonstrated by laser Doppler perfusion imaging (LDPI) in a HLI. Conclusion: Our data indicated that Cryptochrome as a peripheral clock plays an important role in angiogenesis of the reparative tissue ischemia model.