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Y. Yandiev, Y. Lu, T. Pannicke, K. Franze, E.-Q. Wei, A. Bringmann, J. Käs, P. Wiedemann, A. Reichenbach; Biomechanical Properties of Müller Cells in Health and Disease. Invest. Ophthalmol. Vis. Sci. 2009;50(13):6248.
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The mechanical properties of neuronal and glial cells are poorly investigated. Recently we showed that both neurons and glial cells are very soft ("rubber elastic"), and intriguingly, glial cells are even softer than their neighboring neurons. Thus, they might act as a soft embedding for neurons, protecting them in case of mechanical trauma, and also as a soft substrate required for neurite growth and facilitating neuronal plasticity (Lu et al., 2006, PNAS 103:17759-17764). However, in cases of reactive gliosis and glial scar formation the biomechanical properties of the cells may change. In particular, glial scars are thought to constitute stiff obstacles to axon growth although experimental data are missing. Changes in the cytoskeleton have been proposed to play a role in this context. Müller cells in normal retinae express the intermediate filament, vimentin. In virtually all retinal diseases, Müller cells upregulate the expression of vimentin and start to express another intermediate filament, glial fibrillary acidic protein (GFAP). The aim of the present study was to compare the biomechanical properties of normal and reactive Müller cells.
We used gliotic Müller cells isolated from the postischemic retina of rats. Transient retinal ischemia was induced by elevation of the intraocular pressure above systolic blood pressure for 1 h. Acutely isolated Müller cells of adult rats were used in biophysical measurements with scanning force microscopy.
Seven days after ischemia, increased expression of the intermediate filaments GFAP and vimentin in Müller cells was demonstrated by immunohistochemistry. Young’s modulus was recorded in the endfoot, inner process, and soma regions of the cells. Both the endfoot and the inner process were significantly stiffer in gliotic Müller cells as compared to controls. No significant difference was seen in the soma region.
The data might be explained by the fact that intermediate filaments are mainly located in the endfoot and inner process. Although there is a relation between increased expression of intermediate filaments and increased stiffness of the cells, it should be kept in mind that other cytoskeletal proteins or cell organelles may significantly contribute to the biomechanical properties of the cells.
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