Bilateral early activation of retinal microglial cells in a mouse model of unilateral laser-induced experimental ocular hypertension

Abstract

The immune system plays an important role in glaucomatous neurodegeneration. Retinal microglial reactivation associated with ganglion cell loss could reportedly contribute to the glaucoma progression. Recently we have described signs of microglia activation both in contralateral and ocular hypertension (OHT) eyes involving all retinal layers 15 days after OHT laser induction in mice. However, no works available have analyzed the microglial activation at earliest time points after OHT induction (24 h) in this experimental model. Thus, we seek to describe and quantify signs of microglia activation and differences depending on the retinal layer, 24 h after unilateral laser-induced OHT. Two groups of adult Swiss mice were used: age-matched control (naïve) and lasered. In the lasered animals, OHT eyes as well as contralateral eyes were analyzed. Retinal whole-mounts were immunostained with antibodies against Iba-1 and MHC-II. We quantified the number of microglial cells in the photoreceptor layer (OS), outer plexiform layer (OPL), and inner plexiform layer (IPL); the number of microglial vertical processes connecting the OPL and OS; the area of the retina occupied by Iba-1+ cells (Iba1-RA) in the nerve fiber layer-ganglion cell layer (NFL-GCL), the total arbor area of microglial cells in the OPL and IPL and; Iba-1+ cell body area in the OPL, IPL and NFL-GCL. In contralateral and OHT eyes the morphological features of Iba-1+ cell activation were: migration, enlargement of the cell body, higher degree of branching and reorientation of the processes, radial disposition of the soma and processes toward adjacent microglial plexuses, and presence of amoeboid cells acting as macrophages. These signs were more pronounced in OHT eyes. Most of Iba-1+ cells did not express MHC-II; rather, only dendritic and rounded cells expressed it. In comparison with naïve eyes, in OHT eyes and contralateral eyes no significant differences were found in the microglial cell number; but there was a significant increase in Iba1-RA. The total arbor area of microglial cells was significantly decreased in: i) OHT eyes with respect contralateral eyes and naïve-eyes in IPL; ii) OHT eyes with respect to naïve eyes in OPL. The number of microglial vertical processes connecting the OPL and OS were significantly increased in contralateral eyes compared with naïve-eyes and OHT eyes. In OPL, IPL and NFL-GCL, the cell body area of Iba-1+ cells was significantly greater in OHT eyes than in naïve and contralateral eyes, and greater in contralateral eyes than in naïve eyes. A non-proliferative microglial reactivation was detected both in contralateral eyes and in OHT eyes in an early time after unilateral laser-induced OHT (24 h). This fast microglial activation, which involves the contralateral eye, could be mediated by the immune system.

Microglial Activation in the Retina of a Triple-Transgenic Alzheimer’s Disease Mouse Model (3xTg-AD)

“…The microglial soma displacement towards the nuclear layers could explain the thickening in some areas of the retinal nuclear layers and the parallel thinning in plexiform layers observed by OCT using a new method for the segmentation of retinal layers in patients with mild AD [11,46]. In addition, it has been postulated that the vertical arrangement of microglial cells, like that of Müller cells, could assist in the distribution of signaling between different microglial plexuses to communicate to the rest of the retina where damage has occurred [6,47]. Therefore, although Aβ deposits were located in a certain sector of the retinal layer and could generate neuronal apoptosis only in that specific area, microglial activation could spread through the retinal layers and could induce neuronal death after its chronic activation.…”

“…After perfusion fixation, a stitch was made on the upper eyelid to maintain eye orientation. In addition, the nasal caruncle and the insertion of the rectus muscle were used as complementary orientation markers [47]. Later, the eyes were post-fixed for two hours in 4% PFA and kept in 0.1 M PBS.…”

Neuroprotective Effects of FGF2 and Minocycline in Two Animal Models of Inherited Retinal Degeneration

“…[14][15][16][17][18][19] After injury or infection, microglial cells became active. [20][21][22][23] Furthermore, activated microglial cells are believed to contribute to the degenerative events observed in photoreceptor degenerations. [24][25][26] Indeed, we recently described that microglial activation starts simultaneously with the beginning of photoreceptor death in the RCS and P23H-1 rat strains.…”

Reversibility of Retinal Ganglion Cell Dysfunction From Chronic IOP Elevation

“…An important consideration with using the contralateral eye as a control is the possibility that this is also impacted by IOP elevation. 44 Supplementary Figure S3 suggests that there is a trend for contralateral control eyes to return smaller amplitudes than those of age-matched naive controls; however, these differences were not significant.…”

“…Alternatively, IOP-induced microglial reactivity in the IPL may mask ganglion cell dendritic changes. 44 It is of interest that ganglion cell dysfunction progressed but structural measures such as RNFL thickness and RGC cell density did not significantly decrease between 8 and 16 weeks of IOP injury. Although there was a further 3% decline in RGC density, (8wk-OHT: 93.2% 6 1.1%, 16wk-OHT: 90.1% 6 1.7%, P ¼ 0.12), this is unlikely to account for the drop of ganglion cell function from 77.2% after 8 weeks of IOP elevation to 58.9% after 16 weeks of injury.…”