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Stephnie M. Kennedy, Steven O'Reilly, Paul S. Hiscott, Ian Grierson, Anshoo Choudhary; Thrombspondin-2 Expression in Human Trabecular Meshwork Cells and Induction by TGFβ and Dexamethasone: Implications for Primary Open Angle Glaucoma. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4636.
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Aqueous humour outflow resistance in primary open angle glaucoma (POAG) appears to be associated with changes in the trabecular meshwork (TM) and extracellular matrix. These changes are influenced by growth factors, such as transforming growth factor-beta (TGFβ) and matrix metalloproteinases (MMP). Thrombospondins (TSP)-1 and -2 are matricellular proteins, TSP-1 is a potent activator of TGFβ and TSP-2 mediates MMP-2 and 9 activities. TSP-1 is expressed in human TM and is up-regulated in glaucomatous eyes and by TGFβ and dexamethasone (DEX) in vitro. This study aims to determine the expression of TSP-2 in human TM cells and if it is altered following induction with TGFβ2 or DEX, as well as assessing the MMP-2 protein levels.
Expression of TSP-2 protein and mRNA levels was evaluated in normal human (TM5) and glaucomatous (TM3) TM cell lines using immunohistochemistry, Western blotting and qPCR. Cell lines were treated with 2ng/ml human recombinant TGFβ2 or 10-7M DEX for three days and the expression of TSP-2 was characterised by Western blotting and qPCR. MMP-2 expression was also measured by ELISA.
TM3 and TM5 cells expressed TSP-2 under basal conditions at both the protein and mRNA level. Expression of TSP-2 mRNA was up-regulated in TM5 and TM3 cells, following exposure to DEX (1.3 and 1.97 fold, respectively) and TGF-β2 (221 and 187 fold, respectively), compared to control TM5 untreated cells. TM3 cells displayed increased protein levels up to 20% under basal conditions, compared to the control. Secreted MMP-2 was present in both cell lines under basal conditions and was down-regulated by 50% following exposure to DEX and by 90% following exposure to TGFβ2, compared to the control.
These data suggest that the TSP-2 is expressed by TM cells and up-regulated by DEX and TGFβ2. Suppression of MMP-2 in the TM could lead to an increased deposition of extracellular matrix molecules giving rise to impaired outflow resistance. Given that TSP-1 is a potent activator of TGFβ1 in vivo, it is possible that TSP-2 is an activator of latent TGFβ2 leading to bioactive TGFβ2, which in turn may act as a pathological driver in POAG.
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