Abstract
Purpose :
Whether retinal ganglion cell (RGC) sub-types are preferentially susceptible to glaucomatous damage remains controversial. Early work by others found that large cells of the magnocellular pathway are particularly vulnerable in a non-human primate model of glaucoma. Similar observations have been made in some, but not all, follow-up studies with primate, human, and rodent tissues. The purpose of these experiments was to apply automated image analysis tools to the quantification of RGC populations in multiple mouse models of glaucoma to test whether nuclear size predicts susceptibility.
Methods :
Retinas from control pre-disease (4 mo) and diseased DBA/2J mice (16 mo, n=9 retinas per age), control C57BL/6J (B6; 2-5 mo, n=13 retinas), and B6.nee mice at multiple disease stages (6-8, 12 wks; n=4 retinas per age) were whole-mounted, stained with H&E, and quantitatively assessed using two semi-automated software modules developed in our lab. Using RetFM-J, count and morphometric data for nuclei in the inner retina were generated. Using RetFM-Class, RGCs were auto-classified and their extracted features quantitated for comparative studies between glaucomatous and pre-diseased retinas.
Results :
In DBA/2J retinas, a 71.2% loss of RGCs between 4- and 16-mo-old mice was detected. Median size of nuclei auto-classified as RGCs decreased with glaucoma (from 51.8 µm2 to 50.6 µm2, p=1.2 E-24, Mann-Whitney) as did the mean size (55.5 ± 17.2, n=99,629 nuclei, to 52.9 ± 12.8 µm2, n=27,732 nuclei). In B6 and B6.nee retinas, RGC density was not statistically different between B6 and B6.nee mice under the age of 8 wks (n=4 retinas of 8 wk B6; n=4 retinas of 6-8 wk B6.nee; p=0.99, Student’s t-test). Though there was a clear trend for reduction in RGC number with age, RGC density was also not statistically different between the 6-8 wk versus 12 wk cohorts of B6.nee mice (p=0.21).
Conclusions :
In aged DBA/2J mice with glaucoma, RGCs with largest nuclei appear to be preferentially lost, with surviving RGCs having decreased mean and median nuclear areas. In nee mice with glaucoma, more work is needed to refine the ages of RGC loss, though it is interesting that profound axon damage is occurring at the same ages tested here. Our ongoing analyses are conducting paired quantitative analyses of retinal flat-mounts and optic nerve cross sections to define the critical ages of death and complete an analysis of nuclear area.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.