VEGF isoforms and their expression after a single episode ofhypoxia or repeated fluctuations between hyperoxia and hypoxia:Relevance to clinical ROP

[摘要] Purpose: Fluctuations in oxygen are associated with the developmentof severe retinopathy of prematurity (ROP) in humans. However, thecausal relationships between oxygen variability and severe ROP remainunknown. We investigated whether isoforms of vascular endothelial growthfactor (VEGF) were differentially stimulated by hypoxia and by repeatedfluctuations between hypoxia and hyperoxia, and whether isoforms weredifferentially expressed in association with intravitreousneovascularization. We also determined whether pigmentepithelium-derived factor (PEDF) was dysregulated by oxygen fluctuationsperhaps contributing to a delay in normal retinal vascular development.Methods: We used the 50/10 oxygen-induced retinopathy (50/10 OIR)model that exposes newborn rat pups to repeated cycles of 24 h of 50%oxygen alternating with 24 h of 10% oxygen to cause a condition similarto human ROP. Animals were euthanized at postnatal day 2 (P2; after onecycle of 50/10% oxygen), P7 (after 3.5 cycles of 50/10% oxygen), and P14(after seven cycles of 50/10% oxygen). Room air raised control rat pupswere also exposed to a single episode of 24 h of hypoxia at P7 and P14and assayed immediately afterwards. Retinal VEGF isoforms and PEDF weremeasured by RT-PCR. Total VEGF protein was measured by ELISA.Results: We found that repeated cycles of hyperoxia and hypoxiacaused greater expression of VEGF protein compared to control than did asingle cycle of hyperoxia and hypoxia. VEGF164 mRNA had a greaterfold change over control after repeated oxygen fluctuations than after asingle episode of hypoxia. However, the other isoforms, VEGF188and VEGF120, were expressed to a similar degree regardless ofwhether the stimulus was a single episode of hypoxia or repeatedfluctuations in oxygen. VEGF164 was the predominant isoformexpressed at the time of maximal intravitreous neovascularization.Retinal PEDF expression was elevated in pups in the 50/10 OIR modelcompared to control at P7, immediately after 50% oxygen. PEDF expressionin the experimental group was similar to control at P18, whenintravitreous neovascularization occurred.Conclusions: Repeated fluctuations in oxygen results in a greaterexpression of the pathologic isoform, VEGF164, than does hypoxiaalone. However, the other isoforms were upregulated to an equivalentdegree over control by repeated fluctuations in oxygen or a singleepisode of hypoxia. Total VEGF protein was increased to a greater degreeby repeated fluctuations in oxygen compared to a single cycle of oxygen.PEDF was increased over control early in the 50/10 OIR model and mayplay a role in the observed delay in retinal vascularization. Thesefindings provide insight into the effect of repeated oxygen fluctuationson the development of severe ROP in preterm infants

[学科分类] 生物化学/生物物理