Description
Evaluation of morphological changes in retinal microglia as a tool for rapid detection of retinotoxic compounds
Wong, Elissa1, Brehl, Roslyn1, Callwood-Jackson, Gabrielle2, Xu, Lin5, Hammer, Daniel1, Qian, Haohua3, Hanig, Joseph4, Cohen, Ethan1*
1Office of Science and Engineering Labs, CDRH/FDA; 2Eleanor Roosevelt High School, 3National Eye Institute/NIH, 4Office of Testing and Research, CDER/FDA, 5Division of Applied Regulatory Science, CDER/FDA
*Corresponding Author
Microglia are the resident immune cells of the retina and brain, and are highly sensitive to a variety of insults, including infection, injury, and environmental toxicants. To aid the development of drugs and medical devices, we explored whether acute changes in the dynamic behavior and morphology of retinal microglia could be used as screening tool for detecting retinotoxic drugs or metal ions. To dynamically image retinal microglia before, during and after compound exposure, we used a novel ex vivo eye cup preparation in which acutely isolated retinas from CX3CR1 EGFP transgenic mice were maintained with carbogenated Ames Ringer at 35°C during time lapse confocal microscopy. We observed that retinal microglia are distributed in two layers in the inner and outer retina and examined the response of both populations of these retinal microglia to known retinotoxic compounds including ATP, kainic acid, cobalt chloride, and imatinib (an anticancer drug previously shown to be retinotoxic). We found distinct differences in the response of the two layers of microglia to bath application of ATP (100µM). Inner microglia underwent a dramatic growth in the number of filopodia-like structures extending from both processes and cell bodies, while outer microglia did not show this growth. Kainic acid (100µM) induced process retraction of the inner microglia in addition to tissue swelling. Preliminary results suggest that cobalt (1mM) led to inner microglial process thickening, without affecting the morphology of outer microglia. We also observed that imatinib (30µM) caused severe microglial process retraction and decreases in process arbor area. We conclude that retinal microglia exhibit a diverse set of dynamic morphological responses to retinotoxic agents and therefore may be of clinical utility as a tool for rapid retinotoxicity screening.
Funding (FDA Office of the Chief Scientist, Oak Ridge Institute of Science and Education)