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A. E. Sears, G. Hoppe, J. E. Sears; Triamcinolone Acetonide Induces Synthesis and Secretion of Thrombospondin 1 by Human Müller Cells. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1730. doi: https://doi.org/.
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To determine whether the antiangiogenic potency of triamcinolone acetonide (TA) is mediated by thrombospondin-1 (TSP1). Glucocorticoids can directly inhibit VEGF-induced neovascularization downstream of the VEGF-R2. We hypothesize that these effects are mediated at least in part by a secreted factor from glia.
A human Müller cell line (MIO-M1) was incubated for 24 hrs without serum prior to addition of TA. Cells were then treated with TA doses ranging from 0.1 to 1 mg/mL for various time periods. Conditioned media and cells were collected separately and TSP1 content was analyzed by Western blotting using monoclonal antibody (clone A6.1) followed by chemiluminescent detection. A pulse-chase protocol as well as mifepristone were used to determine the modes of TSP1 downregulation.
TA treatment increased the cellular content of TSP1 and caused significant accumulation of TSP1 in culture media. The magnitude of TSP1 upregulation was time- and dose-dependent. The sustained elevated secretion of TSP1 by Müller cells was evident up to 72 hrs in the continuous presence of TA. Removal of TA resulted in slow dampening of TSP1 production, which remained at higher that control levels even 24 hrs later. Mifepristone at nearly equimolar concentrations normalized TSP1 levels in TA-treated MIO-M1 cells.
Production of TSP1 by retinal glia in response to corticosteroid therapy may represent a potent antiangiogenic mechanism. Sustained, prolonged TSP1 secretion may also explain the beneficial effect of TA on vascular permeability. Stoichiometric inhibition of TSP1 with mifepristone suggests that TSP1 is induced through the cytosolic glucocorticoid receptor that functions as a ligand dependent transcription factor.
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