Characterizing ocular pathology in an animal model of Alzheimer’s disease

Previous studies have characterized common pathological hallmarks of Alzheimer’s disease such as amyloid accumulation and plaque consolidation in the brain. The difficulty in accessing the brain in vivo has remained a barrier to the diagnosis or measuring the progression of the disease. Studies have shown that, in addition to amyloid deposition, angiogenesis and increased blood-brain barrier permeability are present in the brain of Alzheimer’s patients and animal models. Our study investigated whether these pathologies could be recapitulated in a more accessible organ associated with the central nervous system: the eyes. Using the Tg2576 model of Alzheimer’s disease, a transgenic mouse model which expresses human amyloid, an increase in amyloid was seen in the eyes of these mice and it was determined that the amyloid coalesced primarily around retinal blood vessels. This link between amyloid and ocular vasculature prompted a pilot study using a proteome profiler and found increased proangiogenic factors in the eyes and brains of the Tg2576 mouse, 20 proteins of which were upregulated in both organs. Performing further analyses of functional pathways on these findings revealed several reoccurring proteins in several pathways across both organs, including chemokines and fibroblast growth factors. Additional evidence of angiogenic processes was determined via the increased expression of CD105, a marker of neoangiogenesis, in whole eye homogenates of Tg2576 mice. When the distribution of the increased vasculature was examined, while the Tg2576 retina did not have increased amounts of CD105⁺CD31⁺ microvessels, the choroid did have more CD31⁺ vessels. Importantly, expression of tight junction proteins zonula occludens-1 (ZO-1) and occludin was decreased in the Tg2576 retinal pigment epithelia and in whole eye homogenates, respectively. Along with evidence of an increased presence of albumin in whole eye homogenates, these results suggest that there is increased permeability in the Tg2576 eyes. Our findings provide new insights into concurrent pathologies exhibited in a commonly used Alzheimer’s mouse model, suggesting that the eyes may be used as a proxy for brain pathology.Science, Faculty ofMicrobiology and Immunology, Department ofGraduat

Are eyes more than just windows to the soul? : Exploring the link between age-related macular degeneration and Alzheimer's disease

Science, Faculty ofMicrobiology and Immunology, Department ofUnreviewedGraduat

Expression of the neuroprotective protein aryl hydrocarbon receptor nuclear translocator 2 correlates with neuronal stress and disability in models of multiple sclerosis

Background: Axonal degeneration and neuronal loss have been described as the major causes of irreversible clinical disability in multiple sclerosis (MS). The aryl-hydrocarbon receptor nuclear translocator 2 (ARNT2) protein has been associated with neuroprotection in models of ischemia and neuronal responses to stressors. Methods: To characterize its potential to influence inflammatory neurodegeneration, we examined ARNT2 expression in the experimental autoimmune encephalomyelitis (EAE) model of MS and characterized mediators that influence ARNT2 expression as well as plausible partners and targets. Results: Arnt2 message and protein levels dropped significantly in EAE spinal cords as disease developed and were lowest at peak disability. ARNT2 expression is prominent in neuronal cell bodies within the gray matter with some staining in glial fibrillary acidic protein (GFAP)+ astrocytes in healthy animals. At peak disease, ARNT2 expression is reduced by 20–50% in gray matter neurons compared to healthy controls. ARNT2 intensity in neurons throughout the EAE spinal cord correlated inversely with the degree of immune cell infiltration (r = − 0.5085, p < 0.01) and axonal damage identified with SMI32 staining (r = − 0.376, p = 0.032). To understand the relationship between ARNT2 expression and neuronal health, we exposed enriched cortical cultures of neurons to hydrogen peroxide (H2O2) to mimic oxidative stress. H2O2 at lower doses rapidly increased ARNT2 protein levels which returned to baseline within 3–4 h. Exposure to higher doses of H2O2) dropped ARNT2 levels below baseline, preceding cytotoxicity measured by morphological changes and lactate dehydrogenase release from cells. Decreases in ARNT2 secondary to staurosporine and H2O2 preceded increases in cleaved caspase 3 and associated apoptosis. We also examined expression of neuronal pas 4 (Npas4), whose heterodimerization with ARNT2 drives expression of the neurotrophic factor brain-derived neurotrophic factor (Bdnf). Like ARNT2, Npas4 levels also decline at the onset of EAE and are linked to decreases in Bdnf. In vitro, H2O2 exposure drives Npas4 expression that is tied to increases in Bdnf. Conclusion: Our data support ARNT2 as a neuronal transcription factor whose sustained expression is linked to neuronal and axonal health, protection that may primarily be driven through its partnering with Npas4 to influence BDNF expression.Medicine, Faculty ofPathology and Laboratory Medicine, Department ofReviewedFacult