Age-Associated Changes in Astrocytes Cilia of Mouse Retina and Optic Nerve

Abstract

Purpose : Defects in primary cilia and ciliary signaling are associated with an array of neurodegenerative diseases. Advanced age is a primary risk factor for many neurodegenerative diseases, including age-related macular degeneration and glaucoma. Primary cilia are sensory organelles that transmit and regulate various cellular communication pathways, including Sonic hedgehog and Wnt signal pathways. Astrocytes and neurons are recognized to form primary cilia in the central nervous system (CNS). While many studies have examined cilia in photoreceptors and CNS neurons, there are few studies based on the role of primary cilia in astrocytes in the anterior visual pathway. This study assessed ciliary frequency (ration of ciliated cells) changes in aged astrocytes within the mouse retina and optic nerve.

Methods : Three- and 20-month-old C57/BL6 mice were used in the study. The globes and optic nerve, including the optic chiasm, were collected and immunostained for cilia markers. Retina whole-mounts were immunostained with astrocytes marker (GFAP antibody) and ciliary markers (Arl13b and gamma-tubulin antibody). Confocal images were captured and analyzed per retina (2 central, 2 middle, 2 peripheral) at high magnifications. The anterior optic nerve and optic chiasm in longitudinal frozen sections were obtained and immunostained with an astrocytic nuclear marker (Sox9 antibody), myelin basic protein (MBP) and ciliary marker (Arl13b antibody). Anterior-to-posterior optic nerve sections were quantified, including the optic nerve head, optic lamina, myelinated region, pre-chiasm, chiasm, and post-chiasm. Statistical analysis was performed using One-way ANOVA and the Student’s t-test.

Results : In mouse retina, most astrocyte ciliation is observed in 3-month-old mice among all regions. Aged retinal astrocytes showed a significant reduction in ciliation in each region (P<0.05, Student t-test). In the optic nerve, chiasm, and post-chiasm regions displayed higher ciliation rates in Sox9-positive astrocytes compared to anterior optic nerve in 3-month-old mice. Interestingly, ciliation in chiasm region significantly decreased compared to the anterior optic nerve in 20-month-old mice (P<0.05, One-way ANOVA).

Conclusions : This novel age-associated alteration was discovered in astrocyte cilium found in the mouse retina and optic nerve. These findings suggest possible involvement of primary cilia in age-associated retinal diseases.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.