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First published online 29 June 2004
doi: 10.1242/jcs.01221

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Under stress, the absence of intermediate filaments from Müller cells in the retina has structural and functional consequences

¹ Department of Medical Biochemistry, The Sahlgrenska Academy at Göteborg University, Medicinaregatan 9C, SE-41390 Göteborg, Sweden
² Paul Flechsig Institute for Brain Research, Leipzig University, Jahnallee 59, 04109 Leipzig, Germany
³ Center for Transgene Technology and Gene Therapy, Institute for Biotechnology, KU Leuven, Herestraat 49, Leuven, B-3000, Belgium
⁴ Institute for Pathology, Tübingen University, Liebermeisterstrasse 8, 72076 Tübingen, Germany

^* Author for correspondence (e-mail: milos.pekny{at}medkem.gu.se)

Accepted 15 March 2004

In epithelial and muscle cells, intermediate filaments (IFs) are important for resistance to mechanical stress. The aim of this study was to elucidate whether IFs are also important for providing resistance to mechanical stress in the Müller cells of the retina and whether this has any pathophysiological consequences. We used mice deficient in IF proteins glial fibrillary acidic protein and/or vimentin (GFAP^–/–, Vim^–/– and GFAP^–/– Vim^–/–), and stress on the retina was applied by excision of the eyes immediately post mortem (compared with in situ fixation) or by inducing a neovascular response to oxygen-induced retinopathy (OIR). The structure of unchallenged retinas was normal, but mechanical stress caused local separation of the inner limiting membrane (ILM) and adjacent tissue from the rest of the retina in GFAP^–/– Vim^–/– mice and, to a lesser extent, in Vim^–/– mice. This detachment occurred within the endfeet of Müller cells, structures normally rich in IFs but IF-free in GFAP^–/– Vim^–/– mice. Hypoxia-induced neovascularization was comparable in all groups of mice with respect to the retinal surface area occupied by new vessels. However, the vessels traversed the ILM and penetrated the vitreous body less frequently than in wild-type retinas (31-55% in Vim^–/–, 66-79% in GFAP^–/– Vim^–/–). We conclude that IFs are important for maintaining the mechanical integrity of Müller-cell endfeet and the inner retinal layers under a mechanical challenge. Furthermore, the absence of IFs in Müller cells leads to an abnormal response of the vascular system to ischemia, specifically decreased ability of newly formed blood vessels to traverse the ILM.

Key words: Intermediate filament, Vimentin, GFAP, Müller cell, Oxygen-induced retinopathy, VEGF-A

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