Streptozotocin-induced rat diabetes model

All animal experiments were approved by the Animal Use and Care Committee of Zhongshan Ophthalmic Center at the Sun Yat-Sen University. All animals were handled in accordance with the approved guideline. Male Brown-Norway rats (6–8 weeks) were purchased from Vital River (Beijing, China). For diabetes induction, the rats were fasted overnight prior to diabetes induction. The rats were anesthetized and diabetes was induced by a single intraperitoneal injection of streptozotocin (STZ) (50 mg/kg, S0130, Sigma). Age-matched control rats were injected with the vehicle (0.1 mol/L citrate buffered saline, pH 4.5). After injection, the rats were supplied with food and water with 10% sucrose. Blood glucose concentration of the rats was measured using a glucometer (Roche) according to the manufacturer’s instructions. The rats were diagnosed with diabetes when their blood glucose concentration exceeded 16 mmol/L one week after STZ injection. Their bodyweight and blood glucose concentration were subsequently measured at 1, 2, 3 and 4 months after STZ injection. All rats were housed individually and provided with food and water ad libitum in an air-conditioned room under 12-hour light/dark cycle. Ten weeks after STZ injection, intravitreal injection of VEGF-B (PeproTech) or BSA was performed (500 ng/eye) every five days and for three times. Five days after the last injection of VEGF-B/BSA, the rats were euthanized and eyes harvested for analysis. All rats were intraperitoneally anesthetized with chloral hydrate (350 mg/kg).