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Jessica E Weinstein, Jeffrey Goldberg, Michael Steketee; Developmental Distribution of Mitochondria in Retinal Ganglion Cell Axons. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4953.
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© ARVO (1962-2015); The Authors (2016-present)
Retinal ganglion cells (RGCs) lose their regenerative capacity through early postnatal development. Mitochondria are key players in RGC survival and potentially in axon regeneration. In order to further understand how mitochondria regulate survival and regeneration, we investigated the differences in mitochondrial size and mass throughout specific developmental stages.
Retinal whole mounts and optic nerves were obtained from transgenic Thy1/cox8A-mtCFP mice at postnatal (P) days 9, 13, 15 and adult. Additional retinal mounts and optic nerves were also obtained from Thy1/cox8A-mtCFP mice undergoing experiments with either eyelid suturing at P11, premature eye opening at P10 or intravitreal injection. For intravitreal injection P10, P11 or P13 mice received a 1-2 uL intravitreal injection of BSS, BayK8644, tetrodotoxin (TTX), Brain-derived-neurotrophic factor (BDNF) or TTX and BDNF. Samples obtained from all conditions were perfused or fixed by immersion for 2-3 hours with 4% PFA at room temperature and then mounted and imaged by confocal microscopy, examining RGC axons in the nerve fiber layer and optic nerve. Images were analyzed using ImageJ. A limited age range was also examined using electron microscopy (EM) and analyzed in Axiovision.
Mitochondria were detected in RGC axons in the nerve fiber layer and optic nerve using both fluorescence and EM. Mitochondrial size (per mitochondria) and mass (per axon area) in the nerve fiber layer and optic nerve increased significantly from P9 until adulthood, with a particularly abrupt increase from P13-P15. This significant increase is suppressed when eyelids are sutured shut or neuronal activity is partially blocked. This suppression effect can be partially overcome with the neurotrophin BDNF.
Mitochondrial size and mass in RGC axons in the retina and optic nerve increase significantly during a short postnatal window coincident with eye opening. Based on our experiments this increase appears to be light- or activity-dependent. Understanding mitochondrial dynamics and distribution may lead to new approaches to enhance RGCs’ survival and regeneration.
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