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Laura M. Currie, Raly Job, Luminita Paraoan, Ian Grierson; Do Cross-linked Actin Networks Form In Cells Other Than The Trabecular Meshwork?. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4665.
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Cross-linked actin networks (CLANs) are straight actin fibers of the cytoskeleton rearranged into geodesic structures and have been previously associated with the trabecular meshwork (TM). The incidence of CLANs in the TM has been found to increase with glaucoma and the steroid dexamethasone (DEX) has long been established to induce CLANs in vitro and ex vivo. We have recently shown CLANs are present in lamina cribrosa cells of the optic nerve head (ONH) and therefore the current study was undertaken to see if other cells in the eye form CLANs, spontaneously or induced by DEX.
A range of 15 ocular and non-ocular cell types were cultured to confluence in media containing serum with or without the addition of DEX (10-7M) for up to 14 days. The DEX concentration used is the optimum for CLAN induction in TM cells. The cells were stained with Alexa-fluor 488 Phalloidin (Invitrogen) to visualize F-actin pattern and stained with Propridium Iodide for nuclei counts. Cells were examined using identical parameters by fluorescent microscopy using TM and ONH cells as positive controls.
So far, CLANs have been found only in the ocular cells from the range analyzed and generally appear to be a feature of primary cultures of epithelioid phenotype rather than transformed cell lines. Human retinal pigment epithelium (HRPE) and rabbit lens epithelium (RLE) spontaneously produced CLANs in 50-60% of cells when cultured in the presence of serum but without DEX. HRPE, but not RLE, also responded to steroid induction increasing CLAN incidence to 75%+. In some cell types CLANs were not inducible with DEX and maintained their natural incidence from culture with serum only. Both bovine corneal endothelium and bovine retinal pigment epithelium retained a CLAN incidence of <5% and bovine iris pigment epithelium at 30%. Transformed cell lines, RPEA19, HeLa, Mel202, J23T3, rarely showed CLANs with or without DEX treatment. Non-ocular primary cultures of human coronary artery smooth muscle cells showed no CLAN incidence.
The presence of CLANs in ocular cells other than the TM may have implications in a number of ocular conditions other than glaucoma. The spontaneous occurance of CLANs in primary cells is a novel finding worthy of further exploration.
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