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.
Purpose To quantify retinal microglia signs of activation after 24 h of unilateral laser‐induced ocular hypertension (OHT) in OHT‐eyes and their contralateral eyes. Methods Albino Swiss mice were divided into two groups, naïve (n = 6) and lasered (n = 6). Retinal whole‐mounts were immunolabeled with anti Iba‐1 to quantify the: i) number of microglial cells in the photoreceptor layer (PRL), outer plexiform layer (OPL) and inner plexiform layer (IPL); ii) the area of the retina occupied by Iba‐1 + in the nerve fiber layer‐ganglion cells layer (NFL‐GCL) and; iii) the arbor area of microglial cells in the OPL and IPL. iv) the number of microglial vertical processes connecting the OPL and PRL. Results In OHT eyes and contralateral eyes had no significant differences in cell number with respect to naïve. OHT eyes presented a significant decrease in microglial arbor area in the OPL in comparison with control (p < 0.01) and in the IPL in comparison with control and contralateral eyes (p < 0.01 and p < 0.05 respectively). However the retinal area occupied by Iba‐1 + cells in the NFL‐GCL was significantly increased: i) in both contralateral and OHT eyes with respect to control (p < 0.01 in both instances); and ii) in OHT eyes with respect to contralateral eyes (p < 0.05). In contralateral untreated eyes, the number of microglial vertical processes connecting the OPL and PRL were significantly increased in comparison with control and OHT eyes (p < 0.01 and p < 0.05 respectively). Conclusions At 24 h, laser‐induced OHT produces a reactive non‐proliferative microgliotic response both in OHT eyes and in contralateral untreated eyes. Whether this response favors neuroprotection or neurodegeneration needs to be clarify.
Purpose To analyze qualitative retinal microglia signs of activation after 24 h of unilateral laser‐induced ocular hypertension (OHT) in OHT‐eyes and their contralateral eyes. Methods Albino Swiss mice were divided into two groups, naïve (n=6) and lasered (n=9). Retinal whole mounts were immunolabeled with antibodies against Iba‐ 1 and MHC‐II. Results Both in OHT eyes and in contralateral eyes Iba‐1+ cells: i)had morphological signs of activation, being these more intense in OHT eyes than in the contralateral eyes. Iba‐1+cells showed hypertrophy, soma displacement both in their own retinal layer and towards the nearest one and in some instances, reoriented microglial processes from being parallel to being perpendicular to the retinal surface. ii) were dystrophic in some instances in the photoreceptor layer (PRL); iii) in the outer plexiform layer sent processes to the PRL and this was mainly found in contralateral eyes; iv) overall, did not up‐regulate the expression of MHCII . Only in OHT eyes MHCII+ rounded cells were observed in the nerve fiber layer‐ganglion cell layer, being more numerous in the peripheral superior zone of the retina and near the optic disc. These cells were surrounded and phagocyted by numerous ameboid Iba‐1+ cells. In addition, beneath the retinal areas where this event was occurring, microglial cells of the inner plexiform layer and outer plexiform layer oriented their processes towards those areas and surrounding them. Conclusions At 24 h after unilateral OHT, microglial features of activation were observed not only in OHT eyes but, interestingly, also in the contralateral untreated eyes. Whether this activation favors neuroprotection or neurodegeneration needs to be clarify.
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