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Levi Todd, Isabella Palazzo, Natalie Squires, Andrew J Fischer; BMP/SMAD-signaling is necessary for the formation of proliferating Müller glia-derived progenitors. Invest. Ophthalmol. Vis. Sci. 2016;57(12):1132.
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© ARVO (1962-2015); The Authors (2016-present)
Müller glia are the predominant glial cell type in the retina and normally perform homeostatic functions. However, in response to acute retinal injury or treatment with growth factors, Müller glia can become proliferating neurogenic progenitors with the ability to replace lost neurons. Therefore, understanding the mechanisms that orchestrate the ability of Müller glia to transition into Müller glia-derived progenitor cells (MGPCs) is imperative to harnessing the regenerative capacity of the retina. This study investigates whether BMP/SMAD-signaling influences the formation of neurogenic MGPCs in the in vivo chick retina.
All experiments utilized hatched chicks (7-21 days old). Compounds were delivered via intraocular injections where one eye served as the "experimental" eye and the contralateral eye served as the "control". Compounds included recombinant BMP4 to activate BMP/SMAD-signaling, the small molecule inhibitor DMH1 to selectively block the BMP receptor, and recombinant FGF2 to activate MAPK-signaling and stimulate proliferating Müller glia. Retinas were damaged by a single injection of N-Methyl-D-aspartate (NMDA). Intraocular injections of BrdU/EdU were applied during experimental paradigms to label proliferating cells. Following injection paradigms, retinas were harvested and processed for indirect immunofluorescence and digital photomicroscopy. Significance of difference (*p<0.05; n≥5) was determined by using a paired, two-tailed t-test.
We found that pSMAD1/5/8, a readout of active BMP/SMAD-signaling, accumulates selectively in Müller glia in response to injections with BMP4, NMDA or FGF2. We found that DMH1 specifically inhibits the up-regulation of pSMAD induced by BMP4. We also found that inhibition of BMPR1 suppressed the formation of proliferating MGPCs in NMDA and FGF2-treated retinas. Evidence is provided using immunohistochemistry that inhibition of BMP/SMAD-signaling may impact the formation of MGPCs by disrupting Müller glia's ability to up-regulate cFos, pS6 (a readout of mTor-signaling), and the retinal stem cell factor Pax6.
Our data suggests that active BMP/SMAD-signaling is necessary for the formation of MGPCs. This work provides novel data that the BMP/SMAD-signaling is an important component of the network of cell-signaling pathways that regulate the formation or MGPCs and retinal regeneration.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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