Courtney Bricker-Anthony

Molecular Changes and Vision Loss in a Mouse Model of Closed-Globe Blast Trauma

PURPOSE To characterize retinal changes and assess vision after an eye-directed air blast. METHODS Adult C57Bl/6 mice were exposed to a blast directed at one eye. Optical coherence tomography and histology were performed to assess retina and optic nerve integrity. Cell death, oxidative stress, and glial reactivity were examined by immunohistochemistry. Visual changes were measured by ERG recordings and the optokinetic reflex. RESULTS In the outer retina, eye blast caused retinal pigment epithelium vacuoles and rare retinal detachments followed by regional cell death. Labeling for nitrotyrosine and markers of pyroptosis (caspase-1) and necroptosis (receptor-interacting protein kinases-1, -3) increased, primarily in the inner retina, after blast. Caspase-1 labeling was restricted primarily to the starburst amacrine cells. A few degenerating axons were detected at 28 days post blast. Despite a lack of substantial cell death or decreased ERG, there was a deficit in visual acuity after blast. CONCLUSIONS Oxidative stress, neuroinflammation, and cell death became increasingly prevalent, over time post blast suggestive of an ongoing neurodegenerative response. Outer retinal changes either resolved or remained focal. In contrast, inner retinal changes were more robust and spread from focal regions to the entire retina over time post blast. Our model of eye blast trauma causes molecular changes and a decrease in visual acuity within the first month post blast despite a lack of overt eye injury. This subtle response matches the delayed presentation of visual deficits in some blast-exposed Veterans.

Neurodegeneration and Vision Loss after Mild Blunt Trauma in the C57Bl/6 and DBA/2J Mouse.

Damage to the eye from blast exposure can occur as a result of the overpressure air-wave (primary injury), flying debris (secondary injury), blunt force trauma (tertiary injury), and/or chemical/thermal burns (quaternary injury). In this study, we investigated damage in the contralateral eye after a blast directed at the ipsilateral eye in the C57Bl/6J and DBA/2J mouse. Assessments of ocular health (gross pathology, electroretinogram recordings, optokinetic tracking, optical coherence tomography and histology) were performed at 3, 7, 14 and 28 days post-trauma. Olfactory epithelium and optic nerves were also examined. Anterior pathologies were more common in the DBA/2J than in the C57Bl/6 and could be prevented with non-medicated viscous eye drops. Visual acuity decreased over time in both strains, but was more rapid and severe in the DBA/2J. Retinal cell death was present in approximately 10% of the retina at 7 and 28 days post-blast in both strains. Approximately 60% of the cell death occurred in photoreceptors. Increased oxidative stress and microglial reactivity was detected in both strains, beginning at 3 days post-injury. However, there was no sign of injury to the olfactory epithelium or optic nerve in either strain. Although our model directs an overpressure air-wave at the left eye in a restrained and otherwise protected mouse, retinal damage was detected in the contralateral eye. The lack of damage to the olfactory epithelium and optic nerve, as well as the different timing of cell death as compared to the blast-exposed eye, suggests that the injuries were due to physical contact between the contralateral eye and the housing chamber of the blast device and not propagation of the blast wave through the head. Thus we describe a model of mild blunt eye trauma.

Erythropoietin either Prevents or Exacerbates Retinal Damage from Eye Trauma Depending on Treatment Timing.

PURPOSE Erythropoietin (EPO) is a promising neuroprotective agent and is currently in Phase III clinical trials for the treatment of traumatic brain injury. The goal of this study was to determine if EPO is also protective in traumatic eye injury. METHODS The left eyes of anesthetized DBA/2J or Balb/c mice were exposed to a single 26 psi overpressure air-wave while the rest of the body was shielded. DBA/2J mice were given intraperitoneal injections of EPO or buffer and analyses were performed at 3 or 7 days post-blast. Balb/c mice were given intramuscular injections of rAAV.EpoR76E or rAAV.eGFP either pre- or post-blast and analyses were performed at 1 month post-blast. RESULTS EPO had a bimodal effect on cell death, glial reactivity, and oxidative stress. All measures were increased at 3 days post-blast and decreased at 7-days post-blast. Increased retinal ferritin and NADPH oxygenases were detected in retinas from EPO-treated mice. The gene therapy approach protected against axon degeneration, cell death, and oxidative stress when given after blast, but not before. CONCLUSIONS Systemic, exogenous EPO and EPO-R76E protects the retina after trauma even when initiation of treatment is delayed by up to 3 weeks. Systemic treatment with EPO or EPO-R76E beginning before or soon after trauma may exacerbate protective effects of EPO within the retina as a result of increased iron levels from erythropoiesis and, thus, increased oxidative stress within the retina. This is likely overcome with time as a result of an increase in levels of antioxidant enzymes. Either intraocular delivery of EPO or treatment with non-erythropoietic forms of EPO may be more efficacious.

Eye-Directed Overpressure Airwave-Induced Trauma Causes Lasting Damage to the Anterior and Posterior Globe: A Model for Testing Cell-Based Therapies

PURPOSE Characterization of the response of the Balb/c mouse to an eye-directed overpressure airwave, with the hypothesis that this mouse strain and model is useful for testing potential therapeutics for the treatment of traumatic eye injury. METHODS The left eyes of adult Balb/c mice were exposed to an eye-directed overpressure airwave. Intraocular pressure (IOP) was measured and eyes were inspected for gross pathology changes. Optical coherence tomography and histology were used to examine the structural integrity of the retina and optic nerve. Immunohistochemistry, in vivo molecular fluorophores, and a multiplex enzyme-linked immunosorbent assay were utilized to identify changes in cell death, neuroinflammation, and oxidative stress. RESULTS This model induced a transient increase in IOP, corneal injuries, infrequent large retinal detachments, retinal pigment epithelium (RPE) vacuolization, glial reactivity, and retinal cell death. Both the corneal damage and RPE vacuolization persisted with time. Optic nerve degeneration occurred as early as 7 days postinjury and persisted out to 60 days. Retinal cell death, increased levels of reactive oxygen species, and neuroinflammation were detected at 7 days postinjury. CONCLUSIONS The injury profile of the Balb/c mouse is consistent with commonly observed pathologies in blast-exposed patients. The damage is throughout the eye and persistent, making this mouse model useful for testing cell-based therapies.