Artigo retina

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Retinal Glial (Muller) Cells: Sensing and Responding ¨ to Tissue Stretch
Niclas Lindqvist,1 Qing Liu,1 Joachim Zajadacz,2 Kristian Franze,1,3 and Andreas Reichenbach1
PURPOSE. To test whether Muller glial cells sense, and respond ¨ to, mechanical tension in the retina. METHODS. A device was designed to stretch the retina at right angles to its surface, across retinal layers. Pieces ofretina were mounted between two hollow tubes, and uniaxial force was applied to the tissue using a micrometer-stepping motor. Mul¨ ler cells were selectively stained with the fluorescent, calciumsensitive dye X-Rhod-1 and were monitored in real time during retinal stretch in vitro. Immunohistochemistry was used to study protein levels and activation of intracellular pathways in stretched retinas.RESULTS. Muller cells responded acutely with transient in¨ creases in fluorescence during stretch, indicative of increased intracellular calcium levels. All the Muller cells elongated uni¨ formly, and there was no apparent difference between retinal layers in resistance against mechanical deformation. After stretch, Muller cells showed fast activation of extracellular ¨ signal-regulated kinase (after15 minutes), upregulation of transcription factor c-Fos (after 1 hour), and basic fibroblast growth factor (after 3 hours). No changes in intermediate filament protein expression were observed in Muller cells up to 3 hours ¨ after stretch. CONCLUSIONS. A novel technique was developed for real-time monitoring of Muller cells during retinal stretch, which al¨ lowed the identification of Muller cells asa mechanorespon¨ sive cell type. Mechanical stress triggers molecular responses in Muller cells that could prevent retinal damage. (Invest Oph¨ thalmol Vis Sci. 2010;51:1683–1690) DOI:10.1167/iovs.09-4159 he retina is a thin lamella on the inside of the eye that is responsible for photodetection. According to its ontogenetic origin from the distal part of the ocular vesicle, it is continuous withthe underlying retinal pigment epithelium (RPE) at its peripheral (blind) margin. However, most of the retinal tissue is only loosely adherent to the RPE and is kept in place mainly by intraocular pressure through the vitreous body and by a (relatively) negative pressure in the subretinal space resulting from water efflux through the RPE.1 The retina may be injured by tractional forces in a varietyof conditions. For example, if degenerative axial myopia results from excessive ocular growth, the retina becomes overstretched, which causes tractional retinal detachment or splitting of retinal layers (retinoschisis).2,3 The retina may be injured by tractional forces in proliferative diabetic retinopathy or in X-linked juvenile retinoschisis and even during “normal” aging, when the shrinkingvitreous body may pull on the retina, leading to retinal detachment, retinoschisis, or both.4,5 Furthermore, traumatic events may cause axial stretch of the retina,6 and the diurnal thickness oscillations of the choroid may induce physiological axial stretch,7 though this remains to be studied in detail. Under all physiological (and many pathologic) conditions, the structural integrity of the retinais strikingly well maintained if one considers its fragility.8 This study was conducted to determine whether there are cells in the retina that are sensitive to mechanical stress and that respond to mechanical stress by cellular reactions to promote the maintenance of structural integrity. The retina is built of several cellular layers, constituted by several types of neurons and glial cells.Whereas most retinal cells, including all classes of retinal neurons, are confined to one or a few layers, the Muller glial cells span the entire retinal ¨ thickness.9 Their somata are localized to the inner nuclear layer (INL), and have two emanating radially oriented stem processes, one abutting the inner (vitread) surface by an end foot and the other reaching the outer limiting membrane and then...
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