Abstract
Purpose :
Mechanical properties of the peripapillary sclera (PPS) likely influence the vulnerability of optic nerve (ON) axons to glaucomatous damage. Here we investigated eyes and optic nerves of mice with a substantial deficiency in collagen type I, the major structural fibrillar molecule of the sclera.
Methods :
Ubi-Cre3 col1a1wt/fl mice lacking one allele of Col1a1 were investigated. Col1a1 encodes for the pro-alpha1(I) chain that is essential for formation of triple stranded collagen type I. Knockdown of Col1a1 mRNA expression and protein synthesis was analyzed via real-time RT-PCR and western blot respectively. Ocular phenotypes of mutant mice and their control littermates were analyzed by histological staining of sagittal sections, including measurement of central corneal thickness (CCT) and retinal thickness. Axial length of enucleated native eyes was measured with a digital caliper. Myelinated ON axons were visualized and counted in PPD-stained ON cross-sections, whereas RGC somata were quantified on retinal whole mounts with an immunofluorescence staining against RBPMS.
Results :
At three months of age, mutant mice showed a significant 50 % (p = 0.02) reduction in Col1a1 mRNA in scleral RNA that resulted in a 75 % reduction (p = 0.03) of translated COL1A1 at five months of age. Axial length and retinal thickness of Ubi-Cre3 col1a1wt/fl mice were not different from that of control littermates, while the cornea of mutant mice was thinner (98.9 µm ± 12.2 versus 86.3 µm ± 4.4, p = 0.015). Otherwise, there were no obvious light microscopical differences in ocular morphology. At two months of age, myelinated ON axon number was not different between mutant mice and their control littermates (36,918 ± 4310 versus 39,095 ± 5000). This was different in 5-month-old animals that showed a significant (p = 0.008) reduction in ON axons (40,215 ± 4854 versus 33,598 ± 7588). The findings correlated with a reduction of RGC somata (2370 ± 315 per mm2 versus 1139 ± 277, p = 0.04).
Conclusions :
We conclude that reduction in collagen type I causes a chronic and continuous loss of ON axons like that seen in glaucoma. The changes are likely induced by alteration of the mechanical properties of the sclera.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.