Aging is associated with increased reactive gliosis and accelerated retinal ganglion cell loss after optic nerve injury.

Abstract

Purpose : Aging is a risk factor in the development of glaucoma, an optic neuropathy characterized by progressive degeneration of retinal ganglion cells (RGCs). Astrocytes interact closely with RGCs and have been demonstrated to be maladaptive to injury in aged humans; however, the mechanisms related to aging or to astrocyte reactivity in optic neuropathies are poorly understood. In this study, we utilized an optic nerve crush (ONC) injury model to test the hypothesis that aging increases susceptibility to nerve injury by altering glial responses.

Methods : Young adult (3-months old) and aged (16-months old) C57/Bl6 wild-type mice underwent ONC in the left eye by implementation of self-closing forceps 1mm posterior to the globe for 1 second. Injured and fellow uninjured eyes were collected on post-injury day (PID)-3 and PID-7. Retinal whole mounts were prepared and stained for RGC-specific marker Rbpms and glial-specific markers S100β and GFAP. To further investigate candidate pathways and mechanisms for differentiated injury response in aged animals, whole retina transcriptomics was performed on PID-3.

Results : Cell counts revealed a significant decrease in RGC density at PID-3 among aged (-18.7±0.94%, n=6, p=0.01) but not young mice. By PID-7, young and aged animals demonstrated 64.1% and 51.2% loss of Rbpms cells, without significant difference between age groups. Aged animals demonstrated a significant decrease in S100β cell density (265.7 vs 224.5 cells/mm², n=6, p=0.002) and GFAP reactivity (1.5 x 10⁶ vs 1.1 x 10⁶ integrated density per field, n=6, p=0.0003) compared to young animals at uninjured baseline. Significant increases were seen in S100β cell density on PID-7 in both young and aged animals, but GFAP reactivity was significantly increased on PID-7 in aged animals alone. Whole retina transcriptomics on PID-3 is underway, and may reveal early differential molecular changes that occur in aged animals in response to injury.

Conclusions : Age-related acceleration of neurodegenerative RGC loss after optic nerve injury is associated with increased reactive gliosis. Elucidating RGC and glial cell responses after optic nerve injury in young and aged animals could clarify mechanisms of progressive vision loss in age-related optic neuropathies (e.g., glaucoma) and assist development of novel neuroprotective strategies.

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