Tau inclusions in retinal ganglion cells of human P301S tau transgenic mice: effects on axonal viability.

Tau inclusions play a key role in the pathogenesis of tauopathies. Altered tau levels have been detected in retina and optic nerve of patients with glaucoma, suggesting the possibility of shared pathogenic mechanisms with tauopathies. Here we report that hyperphosphorylated transgenic tau accumulates in the nerve fibre layer and, from 2 months of age, aggregates into filamentous inclusions in retinal ganglion cells of human P301S tau transgenic mice. Axonopathy and accumulation of hyperphosphorylated tau in the nerve fibre layer preceded inclusion formation. Hyperphosphorylated tau and tau inclusions were also detected in cultured retinal explants from 5-month-old transgenic mice. Axonal outgrowth was similar in transgenic and wild-type retinal explants under basal conditions. However, when exposed to growth-promoting stimuli, axon elongation was enhanced in explants from wild-type but not transgenic mice, indicating that the presence of abnormal tau can impair stimulated axonal outgrowth. These findings suggest that the retina is a good model system for investigating tau-driven neurodegeneration and for assessing potential pharmacological modifiers for tauopathies.