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Y. Zhang, A. Maminishkis, C. Zhi, R. Li, R. Agarwal, S. S. Miller, C. F. Wildsoet; Apomorphine Regulates TGF-β1 and TGF-β2 Expression in Human Fetal Retinal Pigment Epithelial Cells. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3845.
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While the mechanisms of visually-mediated myopic development induced by either form deprivation or defocusing lenses remain poorly understood, previous work has implicated the neurotransmitter, dopamine, and the cytokine, TGF-β, in eye growth regulation. This study evaluated the possibility that dopaminergic regulation of TGF-β secretion from RPE serves as a mechanism for transferring ocular growth-regulating signals originating in the retina to the choroid and sclera.
Human fetal RPE (hfRPE) were cultured on inserts. Using real-time PCR and Western blots, we examined gene expression for dopamine and TGF-β receptors, TGF-β isoforms, and protein expression for dopamine and TGF-β receptors. Apomorphine (APO), a dopamine receptor agonist, was applied to the apical side of the hfRPE culture for 24 hours (concentration range of 0.2 to 20 µM) and secretion of TGF-β isoforms into the culture media (apical and basal sides) determined by ELISA.
Both dopamine receptors (D1DR, D2DR), and TGF-β receptors (TβR-I, TβR-II, TβR-III), as well as TGF-β1 and TGF-β2 were detected in hfRPE by real-time PCR. The expression of D2DR was 87-fold higher than D1DR although expression levels of both receptors were low compared to the expression levels of the three TGF-β receptors. The expression of TβR-II was 4.6-fold and 1.8-fold higher than TβR-I and TβR-III respectively. Cultured hfRPE expressed high levels of TGF-β1 and TGF-β2, and the expression of TGF-β1 was 5-fold higher than TGF-β2. D2DR, TβR-I, and TβR-II proteins were detected in Western blots. In untreated cells, the secretion of TGF-β1 and TGF-β2 into the media was mainly limited to the apical side (328.7 pg/ml or 98.8% & 1799.0 pg/ml or 97.7%, respectively). The secretion of both TGF-β1 and TGF-β2 was significantly increased in a dose-dependent manner in response to APO, and was now greater on the basal side. Total secretion (levels in apical+basal media) was increased up to 10.67 fold (0.2 µM APO) and 1.94 fold (2 µM APO) for TGF-β1 and TGF-β2 respectively. For the basal side alone, 0.2 µM APO induced 282.9 fold and 181.6 fold increases in the secretion of TGF-β1 and TGF-β2 respectively.
The altered secretion by cultured hfRPE cells of TGF-β1 and TGF-β2 in response to apomorphine implies dopaminergic regulation. These results offer a plausible mechanism by the RPE could serve as a signal relay for eye growth modulatory signals.
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