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Yumi Ueki, Sara Reardon, Thomas A. Reh; Activation of the BMP/Smad1/5/8 Signaling Pathway After Retinal Injury in Mouse. Invest. Ophthalmol. Vis. Sci. 2011;52(14):5363.
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© ARVO (1962-2015); The Authors (2016-present)
While it is well documented that fish regenerate retinal neurons from Müller cells in response to injury, this regenerative response in the mammalian retina is limited. The purpose of this study is to identify mechanisms that limit regenerative ability of Müller cells in the mammalian retina.
All experiments involving animals were performed according to the ARVO statement for the Use of Animals in Ophthalmic and Vision Research. In our in vivo study, all drugs and growth factors were delivered by intravitreal injection. We isolated Müller cells from the retinas of Hes5-GFP transgenic mice using FACS. Müller cell-specific RNA was extracted after light or NMDA damage, and we used Affymetrix mouse gene ST arrays to compare differences in gene expression between Müller glia from uninjured retinas and after retinal injury. Expression of selected genes was verified by real-time PCR, immunohistochemistry (IHC) and Western blot. Retinal explant cultures were used to investigate factors that affect the response of Müller cells to injury. The degree of Müller cell proliferation was evaluated by detecting EdU incorporation both in vivo and in vitro.
Many genes reported to be upregulated in injured fish Müller cells, including GFAP and the LIF/STAT3 signaling genes, were also upregulated in the injured mouse Müller cells. There was an interesting difference between the two species: while some BMP signaling components were upregulated in our injured mouse Müller cells, this upregulation was not reported in the fish retina. IHC showed phosphorylation of a BMP signaling mediator, Smad1/5/8, in the mouse Müller cells after light or NMDA damage. Moreover, retinal injury caused an increase in expression of Id1/3 (genes downstream of BMP/Smad activation) in Müller cells. Smad1/5/8 phosphorylation and Id1/3 induction were effectively blocked by intravitreal injection of BMP inhibitors, dorsomorphin (DM) or LDN-193189. In explant cultures, Müller glia can be stimulated to proliferate by EGF treatment, and inhibiting BMP signaling with DM significantly reduced the number of EdU-positive Müller compared to the control.
The BMP/Smad signaling is activated in the mammalian Müller cells in response to retinal injury. This activation may be an important regulator of the mammalian Müller cell response to injury, and may limit their regenerative potential.
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