FNDC5 and polycystic ovary syndrome: Similar to the phenotype of human PCOS, the ovary index (calculated by ovary weight/body weight of the same individual mouse) and uterus index (calculated by uterus weight/body weight of the same individual mouse) in PCOS mice increased significantly compared with control mice, while r-irisin treatment reduced the ovary index in PCOS mice, though the uterus index was not changed obviously (Figures 2B,C).