Abstract
Background: To analyze the course of microglial and macroglial activation in injured and contralateral retinas after unilateral optic nerve crush (ONC). Methods: The left optic nerve of adult pigmented C57Bl/6 female mice was intraorbitally crushed and injured, and contralateral retinas were analyzed from 1 to 45 days post-lesion (dpl) in cross-sections and flat mounts. As controls, intact retinas were studied. Iba1+ microglial cells (MCs), activated phagocytic CD68+MCs and M2 CD206+MCs were quantified. Macroglial cell changes were analyzed by GFAP and vimentin signal intensity. Results: After ONC, MC density increased significantly from 5 to 21 dpl in the inner layers of injured retinas, remaining within intact values in the contralateral ones. However, in both retinas there was a significant and long-lasting increase of CD68+MCs. Constitutive CD206+MCs were rare and mostly found in the ciliary body and around the optic-nerve head. While in the injured retinas their number increased in the retina and ciliary body, in the contralateral retinas decreased. Astrocytes and Müller cells transiently hypertrophied in the injured retinas and to a lesser extent in the contralateral ones. Conclusions: Unilateral ONC triggers a bilateral and persistent activation of MCs and an opposed response of M2 MCs between both retinas. Macroglial hypertrophy is transient.
Highlights
The retina is part of the central nervous system (CNS) and is a widely used model to study the response of CNS neurons and glial cells to insults and potential neuroprotective therapies.Glial cells are pivotal in the maintenance of CNS homeostasis and neuronal well-being, so glial deregulation leads to neuronal disfunction and death [1,2,3]
Changes of microglial cells (MCs) density were assessed with Iba1, whereas activation states were assessed with CD68 and CD206
Expression of CD68 (Figure 1C,D) and CD206 (Figure 1E,F)—markers of MC activation—was observed in very few MCs that were positive for both markers and preferentially located around the optic nerve (ON) and the ciliary body (CB, Figure 1D,F)
Summary
The retina is part of the central nervous system (CNS) and is a widely used model to study the response of CNS neurons and glial cells to insults and potential neuroprotective therapies.Glial cells are pivotal in the maintenance of CNS homeostasis and neuronal well-being, so glial deregulation leads to neuronal disfunction and death [1,2,3]. MCs maintain the homeostasis, prune the synapses and patrol the tissue [12] They are found in a resting state, a definition that has been recently revisited, and it is known as a surveying state because MCs do not rest but actively scan their surroundings in search of damage or infection [8,13]. To analyze the course of microglial and macroglial activation in injured and contralateral retinas after unilateral optic nerve crush (ONC). Results: After ONC, MC density increased significantly from 5 to 21 dpl in the inner layers of injured retinas, remaining within intact values in the contralateral ones In both retinas there was a significant and long-lasting increase of CD68+MCs. Constitutive CD206+MCs were rare and mostly found in the ciliary body and around the optic-nerve head.
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