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Ryan Joseph Donahue, Briana N. Ebbinghaus, Mrinalini Hoon, Robert W Nickells; Exploring the Role of BAX in the Degeneration of Retinal Ganglion Cell Axons and Dendritic Arbors. Invest. Ophthalmol. Vis. Sci. 2019;60(9):651. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Vision requires a functional neuronal circuit from the retina to the brain. The longest and most vulnerable part of this circuit are the retinal ganglion cells (RGCs). To transmit visual inputs to the brain, RGCs require functional dendritic and axonal synaptic connections. Thus, characterizing the pathways that contribute to RGC axonal and dendritic degeneration is critical to developing neuroprotective therapies. The purpose of this project is to test the hypothesis that BAX activation is a mechanism of axonal and dendritic degeneration.
RGCs were labelled with GFP-BAX by viral transduction with AAV2-Pgk-GFP-Bax. GFP-BAX was visualized within axons, dendrites and somas in injured and naïve retinae and optic nerves. Naïve GFP-BAX labelled optic nerves were removed and cultured for 24 hours in the presence or absence of a BH3-mimetic, ABT-737, which stimulates BAX activation. Axon degeneration was quantified by staining for fractin, a marker of caspase dependent actin cleavage. Transcriptional changes of BH3-only genes in the optic nerves of glaucomatous mice and mice after optic nerve crush were assessed using qPCR.
GFP-BAX puncta (indicative of activated BAX) were present in the intra-retinal axons and dendrites of RGCs whose somas also had a punctate localization of GFP-BAX. Similar discrete BAX puncta were observed in axons of the optic nerve. The amount and intensity of fractin staining increased in the presence of ABT-737 and was higher in Bax+/+ mice than in BAX depleted mice. The transcript abundance for the BH3-only gene Noxawas increased in the optic nerves of DBA/2J mice with glaucoma and in mice that had undergone optic nerve crush.
Axons contain all the necessary components to undergo BAX mediated catabolism after the introduction of a BH3-activator. Stimulating BAX activation, increases the rate of degeneration in optic nerve explants. The induction of Noxa in the optic nerve following optic nerve crush and during glaucoma suggests a similar pathway mediates optic nerve degeneration in both models. Ongoing studies are being performed to identify the cell type that expresses Noxa, and to assess dendritic arbor retraction in BAX deficient mice. We anticipate that these results will demonstrate that, in certain contexts, RGCs utilize BAX mediated catabolism to degenerate.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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