Animals and Experimental Design

C57BL/6J mice (The animal Laboratory, Peking University People's Hospital, Beijing, China) were used as an in vivo model for our investigation All animals were kept in 12 hours dark and light cycles and were fed with standard chow and water. All animal protocols were approved by the Institutional Review Board of Peking University People's Hospital and conformed to the Use of Animals in Ophthalmic and Vision Research statement of the Association for Research in Vision and Ophthalmology.

Two types of mice were used in this study: normal and OIR mice. The normal mice were divided into two groups: nontreated normal mice (n = 16) and apelin-treated normal mice (n = 16), which were treated by using an intraperitoneal injection with 20 nmol/kg of apelin. The mice were sacrificed at postnatal day 7 (P7) and P10, respectively. For the OIR mice, they were divided into two separate groups: nontreated OIR mice (n = 15) and treated OIR mice (n = 15), which were treated by using intravitreally injected with 2 µL of 1 mg/mL F13A. Meanwhile, normal mice (n = 15) were used as the control group. The mice were sacrificed at P17.