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Elizabeth Cone-Kimball, Mary Ellen Pease, Julie Schaub, Ericka Oglesby, Ian Pitha, Cathy Nguyen, Harry A Quigley; Mitochondrial movement and density in mouse ocular explant model after experimental glaucoma. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4606.
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© ARVO (1962-2015); The Authors (2016-present)
To study retinal ganglion cell intra-axonal changes with IOP elevation in an explanted mouse globe—optic nerve.
Mice expressing cyan fluorescent protein in mitochondria were exposed to bead-induced IOP elevation for 1 or 3 days. The optic nerve head and nerve were then imaged by laser scanning microscopy in special chambers to measure mitochondrial size, density, % in motion, and speed (both anterograde and retrograde directions). The explant model provides stable intra-axonal structure and functional measures for 3 hours ex vivo.
In data submitted for publication, chronic IOP elevation led to 13% shorter mitochondria length (fission) and 30% greater density immediately behind the globe (p=0.025). IOP increase to 30 mm Hg for 60 minutes reduced % mitochondria in motion by 50%. In the present extended experiments, we found that normal mean mitochondrial length (2.5 + 1.67 µm) was reduced to 2.3 + 1.43 µm after 3 days of prior IOP elevation (n.s.). While short term IOP increase produced greater mitochondrial density, longer IOP increase led to lower density: down 19.2% @ 1 day, down 32.3% @ 3 days (p=0.22, p=0.12, t-test). Mean mitochondria speed was normally 0.19 µm/s anterograde and 0.32 µm/s retrograde (p<0.001, t-test), with 3X more moving anterograde (p=0.05, t-test) and moving longer distances in anterograde between pauses (8.22 µm vs 7.32 µm, p=0.5, t-test). In controls, 6.3% of mitochondria were moving in either direction at a given time, but that decreased to 1.2% after 1 day of IOP elevation (1 of 173).
Changes in mitochondrial structure, density and speed may underlie or represent important events in glaucomatous axonopathy. Ocular—optic nerve explants provide real time measurement of the earliest events in experimental glaucoma as well as quantitative outcomes for neuroprotection therapy development.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
Figure 1. A: Longitudinal image of Optic nerve head showing mitochondria expression in control explant. B: 3 day glaucoma explant showing mitochondrial transport block with clumping (arrow head, bar = 10µm).
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