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R. Wong, T. Dentchev, P. Krajacic, A. Trifunovic, N.–G. Larsson, J. Dunaief; MitoDNA Mutator Mice Expressing a Homozygous Knock–In Mutation of PolgA Exhibit Retinal Degeneration: A Model for the Ageing Retina . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2574.
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© ARVO (1962-2015); The Authors (2016-present)
Mutations and deletions of mitochondrial DNA (mtDNA) accumulate in numerous tissues during the natural aging process in humans, monkeys and rodents. Over time, these mutations amass in certain cells causing respiratory chain deficiency in a variety of tissues. Mice with a homozygous knock–in mutation expressing a proof–reading–deficient version of PolgA, the nucleus–encoded catalytic subunit of mtDNA polymerase, exhibit a threefold to fivefold increase in the levels of point mutations and increased amounts of deleted mtDNA. These mtDNA–mutator mice exhibited phenotypes suggestive of premature onset of age–related characteristics including weight loss, reduced subcutaneous fat, alopecia, kyphosis, osteoporosis, anemia, reduced fertility and heart enlargement. The aim of this current study was to describe the retinal pathology of these mice through morphometric analysis, immunohistochemistry and electron microscopy.
Retinas were studied from three wild type mice and four homozygous knock–in mtDNA–mutator mice. Morphometric analysis quantified the total retinal thickness (TRT), inner nuclear layer (INL) thickness, outer nuclear layer (ONL) thickness, INL nuclei number, ONL nuclei number, and the number of ganglion cells (GC) and retinal pigment epithelial (RPE) cells per 250 microns. Immunohistochemistry and TUNEL quantified apoptosis. Electron microscopy was used to analyze the ultrastructural abnormalities.
Mean TRT in microns (208.5 ± 6.2 vs 174.4 ± 7.0; p < 0.05) and number of ONL nuclei per row (10.5 ± 0.4 vs. 8.2 ± 0.5; p < 0.05) were significantly reduced in the mtDNA–mutator mice as compared to wild type mice. Differences in INL thickness, number of INL, and number of GC per 250 microns was not significant. Electron microscopy of the mtDNA–mutator mice revealed mitochondria that were swollen in subsets of photoreceptor and RPE cells. RPE cells with swollen mitochondria had attenuated apical microvilli and overlying membranous debris. TUNEL positive RPE and photoreceptor nuclei were present only in the retinas from mtDNA–mutator mice.
These data demonstrate that there is morphometric and ultrastructual retinal pathology in mtDNA–mutator mice in the region of the photoreceptor and RPE cells. This pathology is similar to some aspects of aging in the RPE/photoreceptor complex and should become a valuable tool for the study of aging in these cells.
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