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Bone morphogenetic proteins-2 and -4: negative growth regulators in adult retinal pigmented epithelium
J R Mathura1, N Jafari, J T Chang
1Department of Ophthalmology, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
Purpose:
To determine the relative level and localization of bone morphogenetic protein (BMP-4 mRNA in the retina and retinal pigmented epithelium (RPE) under normal and pathologic conditions, to seek clues regarding possible functions.
Methods:
Clones isolated from an RPE cDNA library were sequenced and used as probes for northern blot analysis. Expression in the retina and RPE was investigated in mouse models using reverse transcription-polymerase chain reaction (RT-PCR) and in situ hybridization. The effect of recombinant proteins on RPE proliferation was investigated by thymidine incorporation.
Results:
Bovine clones with high homology to BMP-2 and BMP4 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 BMP4 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), BMP4 (10 ng/ml), and transforming growth factor (TGF)-,1 (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.
Insights
Bone morphogenetic proteins (BMP-2 and BMP-4) are downregulated in the retina and retinal pigmented epithelium (RPE) during injury, suggesting they regulate tissue repair. Modulating BMPs may treat proliferative retinopathies.
Area of Science:
- Ophthalmology
- Molecular Biology
- Cell Biology
Background:
- Bone morphogenetic proteins (BMPs) are crucial signaling molecules involved in development and tissue repair.
- The role of BMPs in the retina and retinal pigmented epithelium (RPE) is not fully understood.
- Dysregulation of growth factors in the RPE can contribute to blinding conditions.
Purpose of the Study:
- To investigate the expression and localization of bone morphogenetic protein-4 (BMP-4) mRNA in the retina and RPE.
- To determine the role of BMP-4 in normal and pathological ocular conditions.
- To explore the potential function of BMPs as regulators of RPE proliferation.
Main Methods:
- Isolation and sequencing of RPE cDNA clones.
- Northern blot analysis to detect BMP-4 mRNA expression.
- Reverse transcription-polymerase chain reaction (RT-PCR) and in situ hybridization in mouse models.
- Assessing RPE cell proliferation using thymidine incorporation assays.
Main Results:
- BMP-2 and BMP-4 mRNA were detected in bovine RPE and mouse retinal neurons.
- Oxygen-induced ischemic retinopathy and inherited photoreceptor degeneration led to decreased BMP-4 mRNA levels.
- BMP-2, BMP-4, and TGF-β1 inhibited RPE cell proliferation in vitro.
- BMP type II receptor mRNA was found in RPE cells and retinal tissue.
Conclusions:
- BMP-2 and BMP-4 may function as negative growth regulators in the retina and RPE.
- Injury-induced downregulation of BMPs might facilitate tissue repair processes.
- Targeting BMP expression could offer a therapeutic strategy for proliferative retinopathies.