Bone morphogenetic proteins-2 and -4: negative growth regulators in adult retinal pigmented epithelium.
OBJECTIVE
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.
Mathura
J R
JR
Department of Ophthalmology, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
Jafari
N
N
Chang
J T
JT
Hackett
S F
SF
Wahlin
K J
KJ
Della
N G
NG
Okamoto
N
N
Zack
D J
DJ
Campochiaro
P A
PA
D000818:Animals; D015152:Blotting, Northern; D055396:Bone Morphogenetic Protein 2; D055415:Bone Morphogenetic Protein 4; D052006:Bone Morphogenetic Protein Receptors, Type II; D019485:Bone Morphogenetic Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000494:pharmacology; D002417:Cattle; D002455:Cell Division; D002478:Cells, Cultured; D017931:DNA Primers / Q000737:chemistry; D004195:Disease Models, Animal; D015536:Down-Regulation; D015870:Gene Expression; D006801:Humans; D017403:In Situ Hybridization; D007231:Infant, Newborn; D051379:Mice; D008810:Mice, Inbred C57BL; D010857:Pigment Epithelium of Eye / Q000187:drug effects / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D012333:RNA, Messenger / Q000096:biosynthesis*; D011994:Recombinant Proteins; D012160:Retina / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism* / Q000473:pathology; D012162:Retinal Degeneration / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D012178:Retinopathy of Prematurity / Q000209:etiology / Q000378:metabolism / Q000473:pathology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016212:Transforming Growth Factor beta / Q000096:biosynthesis / Q000235:genetics*
C525718:BMP2 protein, human; C525809:BMP4 protein, human; C525719:Bmp2 protein, mouse; C525810:Bmp4 protein, mouse; D055396:Bone Morphogenetic Protein 2; D055415:Bone Morphogenetic Protein 4; D019485:Bone Morphogenetic Proteins; D017931:DNA Primers; D012333:RNA, Messenger; D011994:Recombinant Proteins; D016212:Transforming Growth Factor beta; C499469:recombinant human bone morphogenetic protein-2; D017346:Protein Serine-Threonine Kinases; C498218:BMPR2 protein, human; C498219:Bmpr2 protein, mouse; D052006:Bone Morphogenetic Protein Receptors, Type II