The authors gratefully acknowledge the financial support from the National Natural Sciences Foundation of China (81770460, 81570408), the Postdoctoral Research Fellowship of Saskatchewan Health Research Foundation (SHRF, 4144), the Hunan Provincial Natural Science Foundation of China (14JJ2091), the Scientific Research Fund of Hunan Provincial Education Department (12C0339, 10C1178), the start-up funds for PhDs in University of South China (2014XQD37), Zhengxiang scholar program (Prof. Xiangyang Tang) of the University of South China, and the Construct Program of the Key Discipline in Hunan Province.