<em>In Vivo </em>Dynamics of Retinal Microglial Activation During Neurodegeneration: Confocal Ophthalmoscopic Imaging and Cell Morphometry in Mouse Glaucoma

Microglia, which are CNS-resident neuroimmune cells, transform their morphology and size in response to CNS damage, switching to an activated state with ...

University of Utah

Glaucoma is a neurodegenerative disease that results in the progressive decline and ultimate death of retinal ganglion cells (RGCs). While multiple risk factors are associated with glaucoma, the mechanisms leading to onset and progression of the disease remain unknown. Molecular analysis in various glaucoma models has revealed involvement of non-neuronal cell populations, including astrocytes, Mueller glia and microglia, at early stages of glaucoma. High-dose irradiation was reported to have a significant long-term protective effect in the DBA/2J (D2) mouse model of glaucoma, although the cellular and molecular basis for this effect remains unclear. In particular, the acute effects of irradiation on specific cell populations, including non-neuronal cells, in the D2 retina and nerve have not been assessed. Here we report that irradiation induces transient reduction in proliferating microglia within the optic nerve head and glial lamina within the first week post-irradiation. This was accompanied by reduced microglial activation, with no effect on astrocyte gliosis in those regions. At later stages we confirm that early high-dose irradiation of the mouse head results in improvement of axonal structural integrity and anterograde transport function, without reduction of intraocular pressure. Thus reduced microglial activation induced by irradiation at early stages is associated with reduced optic nerve and retinal neurodegeneration in the D2 mouse model of glaucoma.

Early reduction of microglia activation by irradiation in a model of chronic glaucoma.

Le glaucome est une maladie neurod&eacute;g&eacute;n&eacute;rative qui entra&icirc;ne le d&eacute;clin progressif et de la mort ultime des cellules ganglionnaires r&eacute;tiniennes (CGR). Alors que plusieurs facteurs de risque sont associ&eacute;s avec le glaucome, les m&eacute;canismes qui conduisent &agrave; l&#39;apparition et la progression de la maladie restent inconnues. Analyse mol&eacute;culaire dans divers mod&egrave;les de glaucome a r&eacute;v&eacute;l&eacute; l&#39;implication des populations de cellules non neuronales, y compris les astrocytes, cellules gliales Mueller et la microglie, aux premiers stades du glaucome. Irradiation de haut-dose a &eacute;t&eacute; signal&eacute;e pour avoir un effet protecteur &agrave; long terme significatif dans le mod&egrave;le de souris DBA/2J (D2) de glaucome, bien que les bases cellulaires et mol&eacute;culaires pour cet effet reste incertaine. En particulier, les effets aigus de l&#39;irradiation sur les populations cellule sp&eacute;cifique, y compris les cellules non neuronales, dans la r&eacute;tine de D2 et du syst&egrave;me nerveux n&#39;ont pas &eacute;t&eacute; &eacute;valu&eacute;es. Nous rapportons ici que l&#39;irradiation induit une r&eacute;duction transitoire dans la prolif&eacute;ration des microglies dans la t&ecirc;te du nerf optique et glial limbe dans la premi&egrave;re post-irradiation semaine. Cela s&#39;est accompagn&eacute; d&#39;activation microgliale r&eacute;duite, sans effet sur la gliose astrocytaire dans ces r&eacute;gions. &Agrave; un stade ult&eacute;rieur, nous confirmons que l&#39;irradiation fortes doses au d&eacute;but des r&eacute;sultats t&ecirc;te souris dans l&#39;am&eacute;lioration de l&#39;int&eacute;grit&eacute; structurale axonale et la fonction de transport ant&eacute;rograde, sans r&eacute;duction de la pression intraoculaire. Activation microgliale r&eacute;duite induite par l&#39;irradiation &agrave; des stades pr&eacute;coces est donc associ&eacute;e &agrave; la r&eacute;duction de nerf optique et neurod&eacute;g&eacute;n&eacute;rescence r&eacute;tinienne chez la souris D2 du glaucome.

R&eacute;duction rapide de l&#39;activation des microglies par irradiation dans un mod&egrave;le de glaucome chronique.

Il glaucoma &egrave; una malattia neurodegenerativa che provoca il progressivo declino e morte finale delle cellule gangliari della retina (RGCs). Mentre pi&ugrave; fattori di rischio sono associati a glaucoma, i meccanismi che portano all&#39;insorgenza e la progressione della malattia rimangano sconosciuti. Analisi molecolare in vari modelli di glaucoma ha rivelato il coinvolgimento delle popolazioni delle cellule non-neuronali, tra cui Mueller glia, astrociti e microglia, alle prime fasi di glaucoma. Irradiazione ad alte dosi &egrave; stato segnalato per avere un significativo effetto protettivo a lungo termine nel modello del mouse DBA/2J (D2) di glaucoma, anche se le basi cellulari e molecolari per questo effetto rimane poco chiara. In particolare, non sono stati valutati gli effetti acuti delle radiazioni sulle popolazioni cellulari specifici, tra cui le cellule non-neuronali, in D2 retina e nervo. Qui riportiamo che quello irradiazione induce riduzione transitoria in microglia proliferare all&#39;interno della testa del nervo ottico e gliale lamina entro il primo post-irradiation della settimana. Questo &egrave; stato accompagnato da microglia ridotta attivazione, senza alcun effetto sulla gliosi di astrociti in quelle regioni. Nelle fasi successive confermiamo che primo irradiazione ad alte dosi dei mouse testa risultati in miglioramento assonale integrit&agrave; strutturale e la funzione di trasporto anterograda, senza riduzione della pressione intraoculare. Cos&igrave; microgliali ridotta attivazione indotta dall&#39;irradiazione a stadi precoci &egrave; associato a ridotta nervo ottico e della retina neurodegenerazione nel modello del mouse D2 di glaucoma.

Precoce riduzione dell&#39;attivazione della microglia di irradiazione in un modello di glaucoma cronico.

Microglia serve key homeostatic roles, and respond to neuronal perturbation and decline with high spatiotemporal resolution. The course of all chronic CNS pathologies is thus paralleled by local microgliosis and microglia activation beginning at early stages. However, the possibility of using live monitoring of microglia during early disease progression to predict the severity of neurodegeneration has not been unexplored. Since 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. Thus, we used the DBA/2J mouse model of inherited glaucoma, which develops progressive retinal ganglion cell degeneration of variable severity during aging, and thus represents a useful model to study pathogenic mechanisms of retinal ganglion cell decline similar to 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.

Cesar O. Romero

Department of Neurobiology & Anatomy

University of Utah

In Vivo Dynamics of Retinal Microglial Activation During Neurodegeneration: Confocal Ophthalmoscopic Imaging and Cell Morphometry in Mouse Glaucoma

Cesar O. Romero

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Department of Neurobiology & Anatomy

University of Utah

In Vivo Dynamics of Retinal Microglial Activation During Neurodegeneration: Confocal Ophthalmoscopic Imaging and Cell Morphometry in Mouse Glaucoma

Department of Neurobiology & Anatomy