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R. Kane, C. Godson, C. O'Brien; The Role of Ventroptin, a BMP–4 Antagonist, in Retinal Angiogenesis . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1754.
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Retinal pericytes are proposed to play a role in the regulation of angiogenesis and neovascularisation by providing vascular stability and controlling endothelial cell proliferation. There is a need to define the molecular mechanisms underlying the development of diabetic retinopathy, with a view to defining novel targets for therapeutic intervention. Using DNA microarray analysis, we have previously shown upregulation of Ventroptin mRNA in retinal pericytes (HRPC) after 48h exposure to hypoxia (1% O2). Ventroptin is a member of a growing family of secretory proteins that antagonise bone morphogenetic proteins (BMPs), including Chordin, Noggin, Cerberus, DAN and Gremlin. BMPs are members of the TGFß superfamily. They are involved in the proliferation and differentiation of many different tissues and organs. In the eye, BMPs have been demonstrated to be negative growth regulators and mediate apoptosis in different tissues.
Human retinal pericytes were cultured in MCDB 131, 5% FBS, 2mM L–glutamine, 100U/ml penicillin and 0.1mg/ml streptomycin. Cells, once confluent, were cultured in hypoxic (1% O2) conditions for 48 hours, with normoxic conditions as control. RT–PCR was carried out for BMP family members and quantitative PCR for Ventroptin. Human in vitro angiogenesis assay; HUVECs and human fibroblasts were obtained (day 1) as cocultures in 24–well plates (AngioKit, TCS CellWorks Ltd., UK). Medium, with treatments or vehicle, was replenished on days 4, 7, and 9. Tubule formation was examined at day 11. Tubules were quantitated and visualised following fixing and staining for CD31 using a combined ELISA and histology kit according to the manufacturer's instructions.
Using semi–quantitative PCR, the predominant BMPs expressed in HRPCs are BMP2, and BMP4. Exposure to hypoxia has no effect on the expression of BMPs in HRPC. Ventroptin is upregulated in HRPC following exposure to hypoxia. Using the AngioKit we have demonstrated that BMP2 stimulates angiogenesis, and BMP4 inhibits angiogenesis.
Both BMP2 and BMP4 are expressed by HRPC, their modulation will determine an overall pro or anti angiogenic effect. Furthermore Ventroptin is known to antagonise the effects of BMP4, and its expression is induced by hypoxia. Therefore, expression of Ventroptin, a novel gene in the context of diabetic retinopathy, in response to hypoxia may modulate the effects of BMP4 on the retinal endothelium.
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