Neurodegeneration severity can be predicted from early microglia alterations monitoredin vivoin a mouse model of chronic glaucoma

Abstract

Microglia serve key homeostatic roles, and respond to neuronal perturbation and decline with a high spatiotemporal resolution. The course of all chronic CNS pathologies is thus paralleled by local microgliosis and microglia activation, which begin at early stages of the disease. However, the possibility of using live monitoring of microglia during early disease progression to predict the severity of neurodegeneration has not been explored. Because the retina allows live tracking of fluorescent microglia in their intact niche, here we investigated their early changes in relation to later optic nerve neurodegeneration. To achieve this, we used the DBA/2J mouse model of inherited glaucoma, which develops progressive retinal ganglion cell degeneration of variable severity during aging, and represents a useful model to study pathogenic mechanisms of retinal ganglion cell decline that are similar to those in human glaucoma. We imaged CX3CR1+/GFP microglial cells in vivo at ages ranging from 1 to 5 months by confocal scanning laser ophthalmoscopy (cSLO) and quantified cell density and morphological activation. We detected early microgliosis at the optic nerve head (ONH), where axonopathy first manifests, and could track attenuation of this microgliosis induced by minocycline. We also observed heterogeneous and dynamic patterns of early microglia activation in the retina. When the same animals were aged and analyzed for the severity of optic nerve pathology at 10 months of age, we found a strong correlation with the levels of ONH microgliosis at 3 to 4 months. Our findings indicate that live imaging and monitoring the time course and levels of early retinal microgliosis and microglia activation in glaucoma could serve as indicators of future neurodegeneration severity.

Glial coverage in the optic nerve expands in proportion to optic axon loss in chronic mouse glaucoma

“…To identify and measure the relative nerve area corresponding to glial cells and highly degenerative axons, observers masked to nerve identity and axon counts used image segmentation methods recently described (Bosco et al, 2015). First, two observers with expertise in optic nerve histopathology, glaucomatous pathology and image analysis worked together to optimize intensity-threshold parameters to consistently isolate nerve areas occupied by all glial cell types, scar tissue, degenerative axons, blood vessels and meninges, which are explained in detail (Supplemental Methods).…”

“…In a recent study, we detected a highly variable distribution of optic nerve gliosis across DBA/2J mice (Bosco et al, 2015). Here, using this well-established model of chronic glaucoma, we evaluatedwhether the global expansion of glial and scarred nerve territories provides a quantifiable estimate of total axonal loss.…”

“…In human and experimental glaucoma, the progressive damage of optic axons is paralleled by gliosis (Anderson et al, 2005; Bosco et al, 2015; Crish et al, 2010; Dai et al, 2012; Hernandez, 2000; Libby et al, 2005a; Lye-Barthel et al, 2013; Qu and Jakobs, 2013; Sappington et al, 2010; Schlamp et al, 2006; Sofroniew, 2009; Son et al, 2010; Sun and Jakobs, 2012; Sun et al, 2009; Yang et al, 2012). Degenerating optic axons are replaced by reactive glial cells, infiltrating cells and extracellular matrix within atrophic nerve areas, in both human patients and in primate models (Jonas et al, 1995; Quigley et al, 1982; Radius and Pederson, 1984).…”

Evidence Supporting an Association Between Expression of Major Histocompatibility Complex II by Microglia and Optic Nerve Degeneration During Experimental Glaucoma

“…3,6,7 Of arguably greater interest, however, is the recent finding that alterations in microglial function may, in fact, precede RGC injury in glaucoma. 8,9 This result further focuses debate on whether microglial activation is detrimental or beneficial to RGC survival. In support of the hypothesis that reactive microglia are harmful to vulnerable RGCs is the body of evidence demonstrating that suppression of microglial activity is neuroprotective to RGCs in models of experimental glaucoma.…”

Glia-Mediated Retinal Neuroinflammation as a Biomarker in Alzheimer's Disease

“…microglial and macroglial reactivity and increased expression of inflammatory markers) can also be detected in the retina. Recently, Bosco et al [92], using confocal scanning laser ophthalmoscopy to detect green fluorescent protein-labeled retinal microglia in the eye of a glaucoma mouse model, were able to follow the early and progressive activation of microglia [93]. In fact, several authors have described similarities between AD manifestations and glaucoma [94,95,96,97].…”