Anatomy and Neuroscience - Theses
Permanent URI for this collection
Search Results
1 - 1 of 1
-
ItemChanges in Retinal Ganglion Cells during Disease and Aging( 2020)Healthy retinal ganglion cell (RGC) function is vital for vision, and diseases that cause RGC degeneration can be debilitating. RGC degeneration features prominently during age-related diseases such as glaucoma and diabetic retinopathy. This thesis investigates how RGCs change in models of these diseases and if similar changes can be observed in normal aging. Exploring and comparing functional, structural, and molecular changes that develop in rodent RGCs during pathological states and normal aging can expand our understanding of how they degenerate during disease. Glaucoma is characterised by gradual RGC degeneration and is usually accompanied by increased intraocular pressure (IOP). We first examined the effect of an acute, non-ischemic IOP insult on RGC activity in wildtype mice. In wildtype mice, OFF-RGCs alone showed reduced spontaneous and light-elicited activity after IOP elevation. Next, we explored the role of the P2X7-receptor (P2X7-R) following IOP elevation, as it has been suggested to contribute to RGC death in glaucoma. After IOP elevation in P2X7-R knockout mice, both ON- and OFF-RGCs exhibited reduced light-elicited activity. Staining for P2X7-R in Thy1-YFP-H mice showed greater expression on ON-RGC dendrites than in other RGC cell subtypes. This study demonstrated the dysfunction of OFF-RGCs after acute, non-ischemic IOP elevation was not prevented by P2X7-R ablation. P2X7-R knockout seemed to worsen the effects of IOP elevation as it also caused ON-RGC dysfunction. In early stages of diabetic retinopathy, there is increasing evidence for RGC degeneration, prior to perturbation of other retinal neurons. Examining individual RGC function, we found that after 4 weeks of STZ-induced diabetes OFF-RGCs showed an increase in spiking activity at a single light intensity (220 photoisomerisations/sec/rod) compared to control. No changes in RGC density, synaptic protein puncta counts or Muller glia gliosis were identified. Microglia, however, showed a reduction in volume. These changes early in diabetes, though subtle, suggest dysfunction of the retinal circuitry alongside the development of inflammation. Aging can exacerbate RGC degeneration and contribute to the development of diseases such as glaucoma and diabetes. To probe the effects of age on RGCs in greater detail we used a combination of functional, structural, and molecular techniques. By examining the transcriptomes of isolated RGCs from young and aged mice using RNA-sequencing, we found upregulated genes in the pathways for oxidative stress, protein degradation and synaptic function. The upregulation of these genes may be a defensive strategy against age-related stresses during normal, healthy aging. This appears to be supported by our finding that RGCs were not as susceptible to structural or functional loss with age in comparison to photoreceptors and other cell classes. Overall, we found RGCs were dysfunctional prior to death by using early-stage disease models. The results of this thesis provide evidence that age- and disease-related stressors may invoke divergent responses in RGCs, despite aging being a risk factor for retinopathies. Stressors like increased IOP and hyperglycaemia worsen RGC function in a subtle manner; yet aging itself does not seem to pose a threat to RGC survival or function as RGCs seem more robust when compared to other retinal neurons. Future explorations could consider whether an additive effect of aging and disease may cause RGC defence mechanisms to become compromised