Abstract
The neurodegenerative disease amyotrophic lateral sclerosis (ALS) affects the spinal cord, brain stem, and cerebral cortex. In this pathology, both neurons and glial cells are affected. However, few studies have analyzed retinal microglia in ALS models. In this study, we quantified the signs of microglial activation and the number of retinal ganglion cells (RGCs) in an SOD1G93A transgenic mouse model at 120 days (advanced stage of the disease) in retinal whole-mounts. For SOD1G93A animals (compared to the wild-type), we found, in microglial cells, (i) a significant increase in the area occupied by each microglial cell in the total area of the retina; (ii) a significant increase in the arbor area in the outer plexiform layer (OPL) inferior sector; (iii) the presence of cells with retracted processes; (iv) areas of cell groupings in some sectors; (v) no significant increase in the number of microglial cells; (vi) the expression of IFN-γ and IL-1β; and (vii) the non-expression of IL-10 and arginase-I. For the RGCs, we found a decrease in their number. In conclusion, in the SOD1G93A model (at 120 days), retinal microglial activation occurred, taking a pro-inflammatory phenotype M1, which affected the OPL and inner retinal layers and could be related to RGC loss.
Highlights
Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease that causes the loss of both lower and upper motor neurons [1,2,3,4,5]
Number of retinas used in the experiment, wild-type animals (WT): n = 6; and SOD1G93A: n = 6
In the outer plexiform layer (OPL) and the inner layer complex (ILC), no significant changes were found in the SOD1G93A group in comparison to the WT group, except in the inferior sector in the OPL, in which the arbor area was larger in the SOD1G93A group (F) than in the wild type group (E), but the difference was only significant in the inferior sector of the OPL
Summary
Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease that causes the loss of both lower and upper motor neurons [1,2,3,4,5]. Microglial activation occurs in ALS, as seen in the mutant mice for SOD1, and on spinal cord samples from ALS patients, which can influence motor neuron damage [16,17,18]. It has been demonstrated in primary motor neuron and glia cultures that exogenous mSOD1(G93A) does not cause directly detectable motor neuron death. In the SOD1G93A group, the microglial tertiary processes were more difficult to distinguish, as they were observed as thickening of the secondary process itself In these animals, the overall appearance of the cell was more robust and larger (Figure 1B,D).
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