Microglial Activation in the Superior Colliculus After Retinal Ischemia/Reperfusion Injury in Mice

Undergraduate #53
Discipline: Biological Sciences
Subcategory: Cell and Molecular Biology

Joselyn Miller - Alabama State University
Co-Author(s): Sean Silverman, University of North Texas Health Science Center, Fort Worth, TX

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Ischemic injuries within the retina lead to damage of the visual axis, consisting of the retinal ganglion cells (RGCs), optic nerve (ON), and visual centers of the brain. Pathologically, there are similarities to glaucoma, a leading cause of irreversible blindness worldwide. The axons of RGCs, the primary neurons degenerated in glaucoma, primarily terminate at the superficial superior colliculus (SC). Microglia are activated when faced with trauma such as during retinal ischemia/reperfusion (I/R) injury and phagocytize debris or near-death cells. Previous studies have shown that altered microglial function leads to disease, as observed in several neurodegenerative conditions. Purpose: To evaluate microglial activation and response in the visual centers of the brain (SC) in a mouse model to retinal I/R injury. Anesthetized C57BL/6J mice received unilateral intraocular pressure-induced retinal ischemia for 60 minutes followed by restoration of normal blood flow. Mice were sacrificed at 7, 14, 21, and 28 days post I/R. Whole brains were harvested, fixed in 4% PFA for 6 hours, then cryoprotected in 20% sucrose overnight. The SC was excised and frozen in OCT for cryosectioning. Immunofluorescence (IF) for microglia and SC neurons was performed using markers Iba1 (Wako) and NeuN (Millipore), respectively. Microglial density analysis was performed using ImageJ (NIH). The microglial density increased 2X in the contralateral SC hemisphere at 7 days post injury (p<0.05), whereas at 28 days there was increased uniform microglial density between the ipsilateral and contralateral hemispheres. Co-localization of Iba1 and NeuN suggested microglial activation and phagocytosis in the SC. Our results indicate that retinal I/R injury leads to pathogenic changes in the SC microglial population. Furthermore, Iba1 co-localization with SC neurons suggests retinal I/R leads to degeneration of the visual axis, stimulating the microglial population into an active phagocytic state. Future studies will seek to better understand the molecular mechanisms that lead to microglial activation and contribute to pathologic damage to neurons of the visual axis.

Funder Acknowledgement(s): Funded by the Department of Health and Human Services, National Institute of Health, National Heart, Lung and Blood Institute, SMART grant 2R25HL007786-21 to Dr. Thomas Yorio and a grant from the Department of Defense (VISION 10-2-003) to Drs. Abbot Clark and Thomas Yorio.

Faculty Advisor: Abbot Clark,