Age-related changes in anterograde transport, axonal integrity and visuomotor function in DBA/2J and C57BL/6J mice

Abstract

Purpose : Although elevated intraocular pressure (IOP) and age are major risk factors for glaucoma, their effects on glaucoma pathogenesis are incompletely understood. This study evaluated the IOP, visuomotor function, anterograde transport and axonal integrity of the visual system at different ages in the DBA/2J (D2) mouse model of chronic glaucoma, with an aim to probe the onset of glaucomatous changes and their progression. Age-matched C57BL/6J (B6) mice were assessed as a control.

Methods : Four separate groups of D2 and B6 female mice underwent IOP and optokinetic assessments at the age of 5 (D2/B6, n=6/5), 7 (n=6/5), 9 (n=6/5) and 12 (n=13/4) months old (mos) using the TonoLab tonometer and OptoMotry system. Manganese(Mn)-enhanced MRI (MEMRI) of anterograde transport was then performed to a subset of mice (n=2-6 per age per D2/B6 group) in a 9.4-Tesla scanner at 8 hours after binocular intravitreal MnCl₂ injection, and the remaining mice were sacrificed for immunohistochemistry of prechiasmatic optic nerve (ON) integrity.

Results : The IOP of D2 mice increased significantly at 9 mos and progressed further at 12 mos, whereas no apparent IOP difference was found in B6 mice across age (Fig. 1a). Visual acuity of D2 mice continued to worsen from 5 to 9 mos, whereas B6 mice performed better in optokinetics than D2 mice at each age (Fig. 1b). For MEMRI, Mn enhanced to similar extents along D2 and B6 visual pathways at 5 and 7 mos (white arrows in Fig. 1c). Reduced Mn enhancement began in the superior colliculus of D2 mice at 9 mos, and progressed further together with the ON and lateral geniculate nucleus at 12 mos (Fig. 1d); Neurofilament expression gradually decreased in ON of D2 mice from 5 to 12 mos, whereas pan-microglia and Tau expressions gradually increased in ON of D2 mice (Fig. 2). The axonal integrity in B6 mice appeared relatively comparable across age (Fig. 2).

Conclusions : Anterograde Mn transport along the visual pathway in D2 mice began to be disrupted at the onset of IOP increase at 9 mos and progressed further at 12 mos together with further IOP increase, neurofilament loss and elevated pan-microglia and Tau protein levels. Visual acuity in D2 mice appeared to deteriorate earlier than IOP increase and Mn transport disruption and was worse than B6 mice at every age, which suggested additional factors, such as gliosis, are contributing to the visuomotor deficits in D2 mice.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.