Bone Morphogenetic Proteins-2 and -4: Negative Growth Regulators in Adult Retinal Pigmented Epithelium

RESULTS. Bovine clones with high homology to BMP-2 and BMP-4 were isolated from a subtracted RPE cDNA library. Northern blot analysis using the clones as probes demonstrated abundant and differential expression in adult bovine RPE, but with RT-PCR and in situ hybridization, expression was also demonstrated in mouse retinal neurons. In mice with oxygen-induced ischemic retinopathy there was a striking decrease in BMP-4 mRNA in the retina within 6 hours of the onset of hypoxia that was maintained for at least 5 days. In mice with inherited photoreceptor degeneration, there was a dramatic decrease in BMP-4 mRNA in retina and RPE during and after the degeneration. mRNA for the type II BMP receptor was observed in freshly isolated and cultured RPE cells, isolated retina, and freshly isolated bovine aortic endothelial cells. Thymidine incorporation in early-passage RPE cells showed a 14-fold stimulation above control with 5% serum that was decreased to 322%, 393%, and 313% in the presence of BMP-2 (10 ng/ml), BMP-4 (10 ng/ml), and transforming growth factor (TGF)-b1 (2 ng/ml), respectively. CONCLUSIONS. BMP-2 and BMP-4 may serve as negative growth regulators in the retina and RPE that are downregulated by injury, to allow tissue repair. Modulation of expression of the BMPs may provide a means to control the exaggerated wound repair that occurs in proliferative retinopathies. (Invest Ophthalmol Vis Sci. 2000;41:592‐ 600)