Rod-Like Microglia Are Restricted to Eyes with Laser-Induced Ocular Hypertension but Absent from the Microglial Changes in the Contralateral Untreated Eye

Abstract

In the mouse model of unilateral laser-induced ocular hypertension (OHT) the microglia in both the treated and the normotensive untreated contralateral eye have morphological signs of activation and up-regulation of MHC-II expression in comparison with naïve. In the brain, rod-like microglia align to less-injured neurons in an effort to limit damage. We investigate whether: i) microglial activation is secondary to laser injury or to a higher IOP and; ii) the presence of rod-like microglia is related to OHT. Three groups of mice were used: age-matched control (naïve, n=15); and two lasered: limbal (OHT, n=15); and non-draining portion of the sclera (scleral, n=3). In the lasered animals, treated eyes as well as contralateral eyes were analysed. Retinal whole-mounts were immunostained with antibodies against, Iba-1, NF-200, MHC-II, CD86, CD68 and Ym1. In the scleral group (normal ocular pressure) no microglial signs of activation were found. Similarly to naïve eyes, OHT-eyes and their contralateral eyes had ramified microglia in the nerve-fibre layer related to the blood vessel. However, only eyes with OHT had rod-like microglia that aligned end-to-end, coupling to form trains of multiple cells running parallel to axons in the retinal surface. Rod-like microglia were CD68+ and were related to retinal ganglion cells (RGCs) showing signs of degeneration (NF-200+RGCs). Although MHC-II expression was up-regulated in the microglia of the NFL both in OHT-eyes and their contralateral eyes, no expression of CD86 and Ym1 was detected in ramified or in rod-like microglia. After 15 days of unilateral lasering of the limbal and the non-draining portion of the sclera, activated microglia was restricted to OHT-eyes and their contralateral eyes. However, rod-like microglia were restricted to eyes with OHT and degenerated NF-200+RGCs and were absent from their contralateral eyes. Thus, rod-like microglia seem be related to the neurodegeneration associated with HTO.

Different Ipsi- and Contralateral Glial Responses to Anti-VEGF and Triamcinolone Intravitreal Injections in Rats

“…Recent studies have shown that certain stimuli applied to one eye may trigger molecular and cellular responses in the contralateral untouched retina. This was the case after optic nerve axotomy, 37,63 topical instillation of saline drops, 57 ocular hypertension induced by laser photocoagulation to the limbal tissues, 58,[60][61][62] or after anti-VEGF injection. [29][30][31] At present we do not know the mechanism responsible for the response in the contralateral fellow eyes, but one possibility is the limited systemic absorption of the injected substances, and, alternatively, that retinal or eye injury results in systemic inflammatory or paracrine-mediated effects that reach the fellow eye.…”

Retinal neurodegeneration in experimental glaucoma

“…Animals were sacrificed with an ip overdose of 20% sodium pentobarbital (Dolethal Vetoquinol ® ; Especialidades Veterinarias, S.A., Alcobendas, Madrid, Spain). Recent studies indicate that injury to one eye may produce significant molecular changes in the intact contralateral eye (Bodeutsch et al, 1999;de Hoz et al, 2013;Gallego et al, 2012;L€ onngren et al, 2006;Ramírez et al, 2010;Rojas et al, 2014); thus for control experiments, naïve (intact) animals were used.…”

“…In addition, there are several spontaneous models of experimental glaucoma in mice with a targeted type I collagen mutation (Aihara et al, 2003) or the DBA/2J mice which develops a pigmentary glaucoma Danias et al, 2003;Filippopoulos et al, 2006;Panagis et al, 2010;Pérez de Lara et al, 2014;Reichstein et al, 2007). In our laboratory, laser photocoagulation (LP) of the limbar tissues has been the method of choice to induce OHT in adult albino rats Ramírez et al, 2010;Salinas-Navarro et al, 2010;Schnebelen et al, 2009;Valiente-Soriano et al, 2015b) and in albino de Hoz et al, 2013;Dekeyster et al, 2015;Gallego et al, 2012;Rojas et al, 2014;Salinas-Navarro et al, 2009c) or pigmented (Nguyen et al, 2011;Valiente-Soriano et al, 2015a) mice. In the LP-OHT models, typical observations are a sectorial loss of RGCs, an initial damage to RGC axons somewhere near the ON head, and an alteration of the retrograde axoplasmic transport that precedes RGC death (Chidlow et al, 2011;Martin et al, 2006;Soto et al, 2011;Vidal-Sanz et al, 2012) all of which are also found in a classic model of glaucoma, the DBA/2J mouse Crish et al, 2010;Filippopoulos et al, 2006;Jakobs et al, 2005), thus making this model relevant to advance our knowledge on the retinal pathology induced by OHT.…”

Macro- and microglial responses in the fellow eyes contralateral to glaucomatous eyes

“…The LPEL model in the mouse, seems to be a reliable and reproducible method for studying the pathogenesis associated with glaucoma (Cuenca et al, 2010;de Hoz et al, 2013;Gallego et al, 2012;Rojas et al, 2014;Salinas-Navarro et al, 2009b;Valiente-Soriano et al, 2008). In this experimental model, a substantial rise in the IOP was evident 24 h after lasering and then gradually returning to the basal value after the fifth day, so that by 1 week after lasering, the IOP values in the treated animals were comparable for both eyes.…”