Eye / Vision
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12503/32545
Browse
Browsing Eye / Vision by Author "Inman, Denise"
Now showing 1 - 3 of 3
- Results Per Page
- Sort Options
Item Assessing Metabolic Changes in the Retina & Optic Nerve During Glaucoma(2024-03-21) Sepke, Katelynn; Morgan, Autumn; Inman, DenisePurpose: Glaucoma is an optic neuropathy characterized by retinal ganglion cell (RGC) death and optic nerve degeneration. Glial cells such as astrocytes form a metabolic unit with neurons to exchange metabolic substrates and neurotransmitters. When exposed to ocular hypertension (OHT), this metabolic unit is disrupted as astrocytes undergo morphological changes in response to increased pressure. ONHAs also reduce their GLUT1 expression, further exacerbating their metabolic function. It is unknown how these changes impact RGC axon structure and function, so we aim to gain insight into the metabolic relationship between glia and neurons during glaucoma. We hypothesize that glaucoma induces metabolic strain in optic nerve head astrocytes (ONHAs), preventing the exchange of metabolites between neurons, ultimately causing a decline in RGC structure and function. Methods: We have taken a two-sided approach to studying these neural-glial interactions. First, we have induced OHT as well as glucose transport inhibition in ONHAs in vivo to examine the effect of pressure-induced stress on metabolism and the visual system. Currently, we are working in vitro to study the metabolic exchange between RGCs and ONHAs co-cultured in microfluidic chambers when the ONHAs are exposed to biaxial strain as well as GLUT1 KO. Results: Preliminary results in vivo have shown that OHT and glucose transport inhibition in ONHAs disrupt anterograde transport. However, RGCs can compensate for glucose transport inhibition in astrocytes by upregulating GLUT3 and MCT2.In vitro we expect to see RGCs respond to alterations in ONHA metabolism, similarly, upregulating their lactate transporters and relying on mitochondrial metabolism to maintain their energetic needs. Conclusion: Using this model will allow us to directly observe the metabolic changes in the neural-glial unit induced by glaucoma, ultimately providing us insight into targets for future glaucoma therapies.Item Can Nicotinamide Treatment Overcome the Effect of Monocarboxylate Transporter 2 Loss on Retinal Ganglion Cell Survival and Function? dm(2024-03-21) Murinda, Kudakwashe; Inman, Denise; Kiehlbauch, Charles; Morgan, AutumnPurpose: There is currently no cure for the vision loss in glaucoma that is characterized by retinal ganglion cell (RGC) loss and irreversible optic neuropathy. Monocarboxylate transporter 2 (MCT2), which transports pyruvate, lactate, and ketone bodies, is exclusively found in neurons such as the RGCs. We have previously shown that MCT2 is lost during glaucoma, in advance of RGC loss, and MCT2 overexpression protects RGC number and function. We sought to determine if MCT2 is necessary for RGC survival by knocking it out, and to establish whether providing oral nicotinamide (NAM) could compensate for the anticipated metabolic disruption to RGCs. Methods: To test these hypotheses, we injected tamoxifen into Thy1-ERT2-cre: MCT2fl/fl mice to conditionally knock out MCT2 from Thy1-positive RGCs. Control mice carried the MCT2 flox’d allele but were Thy1-ERT2-cre-negative. Control and experimental mice were subjected to ocular hypertension using the magnetic microbead model; separate naïve controls from each genotype were also evaluated. To test the effect of nicotinamide intervention, we repeated the same groups but added the administration of oral nicotinamide to each before inducing ocular hypertension. Intraocular pressure (IOP) was measured using the TonoLab rebound tonometer. Pattern electroretinogram (PERG) and Visual Evoked Potential (VEP) were used to analyze the RGC function. We used unbiased stereology (Stereo Investigator, Micro Brightfield) to count the number of retinal ganglion cells in the wholemount retina, and ATP levels in the retina were also measured. Axon counts were done from plastic-embedded optic nerves. Results: IOP was higher in the ocular hypertension (OHT) groups. MCT2 knockout alone did not impact IOP, nor did it exacerbate RGC function loss post-OHT. After OHT, PERG amplitude was significantly lower in the OHT and KO + OHT treatment groups (p<0.005). RGC function was preserved in the KO + NAM and OHT+NAM groups but was significantly decreased in the KO+OHT group. After OHT, MCT2 KO alone did not alter RGC density but OHT and KO + OHT groups had significantly decreased RGC density (p<0.005). There was no significant decline in RGC density in any of the nicotinamide groups. ATP production in the KO + OHT group was significantly higher (1.81 +/- 0.89 µg/µl) than in the naïve control group (0.68 +/- 0.42 µg/µl). Conclusions: MCT2 knockout alone from RGCs did not change IOP, RGC density, or PERG, suggesting that MCT2 is not necessary for RGC function and survival. Ocular hypertension decreased PERG amplitude and RGC density, and the magnitude of the decrease was not significantly worsened by MCT2 knockout. The nicotinamide groups had no significant loss in RGC density, supporting the proposed neuroprotective effect of NAM administration. These data suggest that RGCs can meet their immediate metabolic needs through means beyond MCT2, and nicotinamide can rescue RGCs in the context of glaucoma.Item Unraveling the Molecular Nexus: Obstructive Sleep Apnea and Glaucoma in a Rat Model(2024-03-21) Donkor, Nina; Mabry, Steve; Wilson, E. Nicole; Gardner, Jennifer J.; Bradshaw, Jessica; Cunningham, Rebecca; Inman, DenisePurpose: Obstructive sleep apnea is a chronic sleep disorder characterized by recurring complete or partial upper airway occlusion. Over the past decade, meta-analyses have established a correlation between this disorder and glaucoma, an ocular neurodegenerative disease, and a leading cause of blindness. However, the link between these pathologies remains elusive. Understanding the mechanisms involved could influence treatment options and reduce the rate of vision loss associated with glaucoma. Using a rat model of sleep apnea, chronic intermittent hypoxia (CIH), we tested the hypothesis that mild sleep apnea initiates morphologic and metabolic changes in the retina that resemble glaucoma. Methods: Rats were randomly assigned to normoxic or CIH groups. The CIH group was exposed to periodic hypoxia during their sleep phase, simulating mild sleep apnea, with oxygen reduction from 21% to 10% and reoxygenation in 6-minute cycles over 8 hours/day for 14 days. The normoxic group experienced similar conditions without changes in oxygen concentration. Subsequently, the eyes were enucleated, and the retina was evaluated for oxidative stress, inflammatory markers, metabolic changes, and hypoxic response modulation using immunohistochemistry and capillary electrophoresis. Results: Immunofluorescence revealed increased expression of 8-OHdG, indicating oxidative stress (nucleic acid damage), as well as the cytokine TNF-α in the CIH group retina compared to controls. No statistically significant differences were observed in HIF-1α protein levels. SIRTUIN-1, a regulator of HIF-1α expression, and the levels of pyruvate dehydrogenase kinase-1 and lactate dehydrogenase-A showed no significant differences between normoxic and CIH groups. Conclusion: The increased oxidative stress and inflammation observed suggest that CIH induces a response in the retina with features shared by early-stage glaucoma. However, the anticipated upregulation of HIF-1α and its targets did not occur, suggesting a greater reduction in oxygen concentration or a longer-term CIH interval may be necessary to observe canonical hypoxic response. Keywords: glaucoma, sleep apnea, chronic intermittent hypoxia, inflammation, oxidative stress