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Debjani Gagen, Ross Clark, Paloma Liton, Donna Peters; Integrins Modulate Phagocytosis in Human Trabecular Meshwork (TM) Cells. Invest. Ophthalmol. Vis. Sci. 2013;54(15):377.
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To determine if αvβ3 and αvβ5 integrins play a role in phagocytosis in TM cells.
Phagocytic activity and expression of integrins in immortalized TM-1 cells were analyzed by FACs following a 4h phagocytic challenge with pHrodo-labeled S. aureus bioparticles. To determine the role of αvβ5 integrins, TM-1 cells were transfected with siRNA against the β5 integrin subunit to knockdown αvβ5 integrin expression. Non-targeting siRNA was used as control. To determine if upregulation and/or activation of αvβ3 integrins played a role in phagocytosis in TM cells, TM-1 cells which do not express αvβ3 integrins were transduced with lentiviral vectors expressing wildtype (WT) β3 integrin or constitutively active (CA) β3 integrin. The CA-β3 integrin was created by mutating Thr562 to Asn. In some experiments, HTM cells were treated for 6 days with either Dexamethasone (Dex) to upregulate expression of the β3 integrin, or EtOH as a control.
Forty-eight hours after transfection, αvβ5 expression was reduced by 70% and phagocytic activity decreased by 74% compared to cells transfected with control siRNA. Dex-treated cells showed a 46% increase in activated αvβ3 integrin expression and exhibited a 50% reduction in phagocytic activity compared to EtOH-treated cells. Expression of the CA-β3 integrin also decreased phagocytosis by 33% compared to TM-1 cells expressing the WT-β3 integrin. There was no difference in the phagocytic activity of WT-β3-expressing cells compared to cells transduced with the empty vector. The decrease in phagocytosis was not due to differences in the level of αvβ3 expression, as αvβ3 integrin levels were similar in WT- and CA-β3 integrin-expressing TM-1 cells. In contrast, the activated state of αvβ3 integrins was greater by 91% in CA-β3 integrin-expressing cells compared to WT-β3 integrin-expressing cells. αvβ5 integrin expression was reduced by 60% in both cell lines compared to cells transduced with an empty vector.
Although αvβ5 integrin is needed for phagocytosis, this study suggests that the Dex-induced decrease in phagocytosis may be due to the activation of αvβ3 integrin. The study also offers some molecular insight into how phagocytosis might be decreased in glaucoma.
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