Involvement of microglia in early axoglial alterations of the proximal optic nerve induced by experimental glaucoma

GONZÁLEZ FLEITAS MF; SANDE PH; PASQUINI L; DORFMAN D; ROSENSTEIN RE; BOSCO A; BORDONE MP

Seattle

Congreso; Annual Meeting ARVO; 2016

ARVO

Purpose : The progressive degeneration of optic nerve (ON) axons and retinal ganglion cells (RGCs) in glaucoma is accompanied by glial cell alterations. We have developed an experimental model of glaucoma through weekly intracameral injections of chondroitin sulfate (CS). The aim of this work was to study the involvement of microglial reactivity on the early axoglial alterations of the ON in a rat glaucoma model induced by CS. Methods : Adult male Wistar rats received weekly intracameral injections of vehicle or CS up to week 15. RGC number was analyzed by Brn3a-immunoreactivity. Anterograde transport was examined after an intravitreal injection of β-subunit cholera toxin (CTB). Iba1 and ED1 (microglial markers), glial fibrillary acidic protein (GFAP, astrocytes), myelination status (luxol fast blue, LFB), and axons (phosphorylated neurofilament heavy chain (pNFH)) were analyzed in the ON. The involvement of microglial reactivity in ON alterations was examined by a daily treatment with minocycline (30 mg/kg, i.p.) for 2 weeks, starting at 4 weeks of intracameral injections of vehicle or CS.Results : A significant decrease in Brn3a(+) cell number was observed in eyes injected with CS for 10 and 15 (but not 6) weeks. A clear reduction in CTB staining was evident in the superior colliculus (SC) and the lateral geniculate nucleus (LGN) contralateral to CS-injected eyes for 6 and 15 weeks. In the ON from eyes that were hypertensive for 6 weeks, a disruption of CTB transport occurred at the ON proximal myelinated portion. A significant decrease in pNFH-immunoreactivity, an increase in Iba1(+), ED1(+), and GFAP(+) area, and signs of demyelination were observed at 6 and 15 weeks of ocular hypertension. Minocycline did not affect IOP in vehicle- or CS-injected eyes, but it prevented the increase in Iba-1(+), ED-1(+), and GFAP(+) area, and the decrease in pNFH-immunoreactivity and LFB staining induced by 6 weeks of ocular hypertension. Moreover, minocycline preserved CTB anterograde transport from the retina to the SC and LGN.Conclusions : These results support the targeting of microglial reactivity to prevent the early axoglial alterations in the proximal ON.