Hypoxic repression of lactate dehydrogenase-b gene expression in the avascular chick retina

Purpose. To study a gene whose expression is repressed by hypoxia in the retina. Methods. Previous work demonstrated that aerobic and anaerobic LDH protein expression changes as a function of oxygen availability in the developing avascular chick retina (Buono and Sheffield 1991. Exp. Eye Res. 53:187-198;199-204). To extend these studies a fragment of the chick LDH-B (aerobic) gene was isolated by RT/PCR and used as a probe for Southern and Northern analyses and genomic library screening. Results. Data from Northern analyses indicates that LDH-B mRNA levels mimic changes observed in LDH-B protein levels during normal chick retinal development. Furthermore LDH-B mRNA levels drop several fold in primary retinal cell cultures exposed to hypoxia for 24 hours and increase to control amounts within 6 hours after oxygen reperfusion in those cultures. Chicken genomic LDH-B clones have been isolated and are currently being analyzed for putative promoter regions controlling hypoxic repression in the retina. Conclusion. Retinal hypoxia has been implicated in the retinopathies associated with neo-vascularization by activation of vascular endothelial growth factor (VEGF) and other genes. While many studies focused on hypoxia induced gene expression have been published, very little is known about gene repression in retina under hypoxic conditions. Our data indicates that the chick retina experiences hypoxia during development and subsequent chronic hypoxia during the lifetime or the animal, however, the chick retina remains avascular. We are examining the repression of LDH-B as a model for retinal gene inactivation during hypoxia and the expression of chick VEGF to understand why this species retina remains avascular under hypoxic conditions.