Abstract
Purpose :
Ocular hypertension (OHT) is a serious side effect of glucocorticoid (GC) therapy and if untreated, it can leads to secondary open-angle glaucoma. However, the precise mechanism of GC-induced glaucomatous neurodegeneration is not understood largely due to lack of proper mouse model that exhibits glaucomatous neurodegeneration similar to human glaucoma. Using a novel mouse model of GC-induced OHT, we determined whether prolonged GC-induced OHT leads to glaucomatous neurodegeneration and further explored the pathological mechanisms of axonal degeneration and role of neuroinflammation in glaucoma.
Methods :
C57BL/6J mice were injected with either Dexamethasone Acetate (Dex) or Vehicle (Veh) via periocular-route, once a week for 10-weeks. IOP was measured every week and glaucomatous neurodegeneration was examined at 5 and 10-weeks of treatment using pattern ERG (pERG), whole mount retina staining with RBPMS antibody and PPD staining and transmission electron microscopy (TEM) for optic nerve (ON) degeneration. Reactive astrocytes, axonal cytoskeleton changes and immune cells at ON head (ONH) were assessed by immunostaining. Cholera toxin B (CTB) was used to trace axon anterograde transport deficits.
Results :
Periocular injections of Dex caused significant and prolonged IOP elevation (Δ ≥3.5-5 mmHg) and outflow facility reduction (by ~40%) compared to Veh-injected mice. Dex-induced OHT was associated with increased ECM deposition and cytoskeleton changes in the TM. Interestingly, Dex-induced sustained OHT led to glaucomatous neurodegeneration after 10 weeks of treatment including significant functional and structural loss of RGCs as evident from reduced pERG amplitudes (10µV v/s 25µV) and ~36% loss of RGCs in whole mount retina RBPMS staining. Neuronal labelling with CT-B demonstrated anterograde transport deficits in Dex-treated eyes (Fig 1), with increased reactive astrocytes at ONH. We also observed ~40% loss of optic nerve axons in PPD staining. TEM analysis of ON further demonstrated chronic demyelination of optic nerve axons with mitochondrial accumulation and immune cells infiltration, which was further confirmed by immunostaining (Fig 2).
Conclusions :
These data highlights that GC-induced OHT causes inflammatory demyelination of the optic nerve axons, which results in glaucomatous neurodegeneration.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.