Abstract
Purpose :
Microglia are the innate immune cells of the central nervous system and their acute response to nerve crush injury has been well studied both in the optic nerve and the spinal cord; additionally their response over the course of weeks and months has been well studied in multiple models of glaucoma. However, there have not been studies evaluating the early response of retinal microglia to the apoptosis of retinal ganglion cells, such as occurs in glaucoma. We additionally report on the use of wide-angle confocal laser scanning ophthalmoscopy as a tool to study the response of retinal cells in vivo.
Methods :
Fluorescently labelled microglia are followed in vivo using wide-angle confocal laser scanning ophthalmoscopy to determine when after retinal ganglion cell axonal damage that microglia first exhibit the changes from a resting state to an activated state based on motility, size, and number of cells. To verify this time course and validate the results found in vivo , retina whole mounts from multiple time points after axonal injury are used to quantify both ramification of microglial processes and soma size, both of which are well-established measures of microglial reactivity.
Results :
Wide-angle confocal laser scanning ophthalmoscopy can be used to track the behavior of fluorescently labelled microglial in vivo over time after optic nerve crush injury. By day 4 after injury, there is an increase in the number of microglia in the retina on the side of optic nerve crush injury but not in the control (contralateral) retina. In agreement with this, there is an increase in soma size and a decrease in complexity of arborization of the processes of microglia by day 4 after optic nerve crush injury.
Conclusions :
Retinal microglia assume an activated state within 4 days after crush injury to the axons or retinal ganglion cells, demonstrated by both by wide-angle confocal laser scanning ophthalmoscopy in vivo and in retinal whole mounts. Activation of microglia can be a sensitive marker of damage to retinal ganglion cells, and this activation can be monitored using a non-invasive imaging technique in transgenic mice.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.