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Expression of αsmooth muscle actin in lens epithelia from human donors and cataract patients

Rungger-Brändle, Elisabeth
Conti, Alain
Leuenberger, Peter M.
Published in Experimental Eye Research. 2005, vol. 81, no. 5, p. 539-550
Abstract In order to re-evaluate functional implications of αsmooth muscle actin (αSMA) expression in lens epithelial cells (LECs), we assessed its presence in donor lenses without visible opacities (DON), lenses with mature cataract (CAT), and cataractous lenses with posterior subcapsular opacities (PSO) or anterior subcapsular fibrosis (ASF). The levels of αSMA and transforming growth factor-beta2 (TGFβ2) mRNAs were measured by classical and real-time PCR. Expression and structural organisation of αSMA protein and β-catenin were monitored by Western blotting and confocal microscopy. All DON analysed contained measurable amounts of αSMA mRNA. In CAT without and with PSO, mRNA expression was increased and, again more than doubled in ASF. TGFβ2 mRNA expression varied widely between the individual samples but was slightly increased in ASF. No correlation existed between αSMA or TGFβ2 expression and the age of the donors in any of the lens categories. Confocal microscopy revealed that, in DON and CAT, αSMA was preferentially expressed in a simple granular pattern in single or small clusters of LECs within a normally shaped cobblestone epithelium. Locally, the granules were merged into short stretches at the cell margin. In CAT, a few abnormally shaped cells contained polygonal αSMA structures and short stress fibres. In CAT with PSO and ASF, polygons and stress fibre bundles predominated in spindle-shaped cells. Expression patterns of different complexity were often present in the same epithelium. Apical polygons and basal stress fibres were detected within the same cell and may reflect instability of the interface between epithelium and cortical fibres and changes in adhesion to the capsule, respectively. High levels of βcatenin mRNA and protein were present in all lens types. However, with increasing complexity of αSMA organisation, βcatenin staining disappeared from the cell margin and basal infoldings and was shifted towards the cytoplasm and nucleus. The presence of αSMA in DON, the absence of any correlation between mRNA level and age, and the modest increase in complexity of αSMA-containing structures in CAT argue against an inevitable link between αSMA expression and the development of age-related cataract. Low levels of αSMA expression may reflect repair of normal wear and tear. In pathologic situations such as PSO and ASF, persisting stimulation and additional incentives may induce increased αSMA expression and more elaborate patterning, eventually leading to completion of EMT.
Keywords αsmooth muscle actinBeta cateninCataractogenesisConfocal microscopyEpithelial–mesenchymal transitionRepairTGFbeta
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RUNGGER-BRÄNDLE, Elisabeth et al. Expression of αsmooth muscle actin in lens epithelia from human donors and cataract patients. In: Experimental Eye Research, 2005, vol. 81, n° 5, p. 539-550. https://archive-ouverte.unige.ch/unige:84287

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Deposited on : 2016-06-07

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