Browsing by Author "Kiehlbauch, Charles"
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Item ATF4 leads to glaucoma by promoting protein synthesis and ER client protein load(Springer Nature, 2020-11-05) Kasetti, Ramesh B.; Patel, Pinkal D.; Maddineni, Prabhavathi; Patil, Shruti; Kiehlbauch, Charles; Millar, J. Cameron; Searby, Charles C.; Raghunathan, Vijaykrishna; Sheffield, Val C.; Zode, Gulab S.The underlying pathological mechanisms of glaucomatous trabecular meshwork (TM) damage and elevation of intraocular pressure (IOP) are poorly understood. Here, we report that the chronic endoplasmic reticulum (ER) stress-induced ATF4-CHOP-GADD34 pathway is activated in TM of human and mouse glaucoma. Expression of ATF4 in TM promotes aberrant protein synthesis and ER client protein load, leading to TM dysfunction and cell death. These events lead to IOP elevation and glaucomatous neurodegeneration. ATF4 interacts with CHOP and this interaction is essential for IOP elevation. Notably, genetic depletion or pharmacological inhibition of ATF4-CHOP-GADD34 pathway prevents TM cell death and rescues mouse models of glaucoma by reducing protein synthesis and ER client protein load in TM cells. Importantly, glaucomatous TM cells exhibit significantly increased protein synthesis along with induction of ATF4-CHOP-GADD34 pathway. These studies indicate a pathological role of ATF4-CHOP-GADD34 pathway in glaucoma and provide a possible treatment for glaucoma by targeting this pathway.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 CNS axonal degeneration and transport deficits at the optic nerve head precede structural and functional loss of retinal ganglion cells in a mouse model of glaucoma(BioMed Central Ltd., 2020-08-27) Maddineni, Prabhavathi; Kasetti, Ramesh B.; Patel, Pinkal D.; Millar, J. Cameron; Kiehlbauch, Charles; Clark, Abbot F.; Zode, Gulab S.BACKGROUND: Glaucoma is a leading neurodegenerative disease affecting over 70 million individuals worldwide. Early pathological events of axonal degeneration and retinopathy in response to elevated intraocular pressure (IOP) are limited and not well-defined due to the lack of appropriate animal models that faithfully replicate all the phenotypes of primary open angle glaucoma (POAG), the most common form of glaucoma. Glucocorticoid (GC)-induced ocular hypertension (OHT) and its associated iatrogenic open-angle glaucoma share many features with POAG. Here, we characterized a novel mouse model of GC-induced OHT for glaucomatous neurodegeneration and further explored early pathological events of axonal degeneration in response to elevated IOP. METHODS: C57BL/6 J mice were periocularly injected with either vehicle or the potent GC, dexamethasone 21-acetate (Dex) once a week for 10 weeks. Glaucoma phenotypes including IOP, outflow facility, structural and functional loss of retinal ganglion cells (RGCs), optic nerve (ON) degeneration, gliosis, and anterograde axonal transport deficits were examined at various stages of OHT. RESULTS: Prolonged treatment with Dex leads to glaucoma in mice similar to POAG patients including IOP elevation due to reduced outflow facility and dysfunction of trabecular meshwork, progressive ON degeneration and structural and functional loss of RGCs. Lowering of IOP rescued Dex-induced ON degeneration and RGC loss, suggesting that glaucomatous neurodegeneration is IOP dependent. Also, Dex-induced neurodegeneration was associated with activation of astrocytes, axonal transport deficits, ON demyelination, mitochondrial accumulation and immune cell infiltration in the optic nerve head (ONH) region. Our studies further show that ON degeneration precedes structural and functional loss of RGCs in Dex-treated mice. Axonal damage and transport deficits initiate at the ONH and progress toward the distal end of ON and target regions in the brain (i.e. superior colliculus). Most of anterograde transport was preserved during initial stages of axonal degeneration (30% loss) and complete transport deficits were only observed at the ONH during later stages of severe axonal degeneration (50% loss). CONCLUSIONS: These findings indicate that ON degeneration and transport deficits at the ONH precede RGC structural and functional loss and provide a new potential therapeutic window for rescuing neuronal loss and restoring health of damaged axons in glaucoma.Item Effect of Monocarboxylate Transporter 2 Loss on Retinal Ganglion Cell Survival and Function(2023) Murinda, Kudakwashe; Morgan, Autumn; Inman, Denise; Kiehlbauch, CharlesPurpose: 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 (MCT2s) that transport pyruvate, lactate, and ketone bodies, are 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. This study was undertaken to test whether MCT2s are necessary for RGC survival and function. Methods: To test this hypothesis, we used tamoxifen injection 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. Intraocular pressure (IOP) was measured using the TonoLab rebound tonometer. Pattern electroretinogram (PERG) was used to analyze RGC function. We used unbiased stereology (Stereo Investigator, Micro Brightfield) to count the number of retinal ganglion cells in wholemount retina, and ATP levels in retina were also measured. Results: IOP was higher in the ocular hypertension (OHT) groups. MCT2 knockout alone did not impact IOP, nor did it alter baseline PERG amplitude or latency. After OHT, PERG amplitude was significantly lower in the MCT2-knockout mice (p=0.0013). MCT2 knockout alone did not change RGC density. After OHT, RGC density decreased, though in this preliminary analysis, RGC density among the groups was not significantly different. ATP production in the OHT+ Tamoxifen group was significantly higher (1.81 +/- 0.89 ug/ul) than in the naïve control group (0.68 +/- 0.42 ug/ul). Conclusions: MCT2 knockout from RGCs did not change IOP or PERG, suggesting that MCT2 is not necessary for RGC survival. Ocular hypertension decreased PERG amplitude and RGC density, though the magnitude of the decrease may not have been increased by MCT2 knockout. These preliminary data suggest that RGCs are capable of meeting their immediate metabolic needs through means beyond MCT2.Item Lentiviral mediated delivery of CRISPR/Cas9 reduces intraocular pressure in a mouse model of myocilin glaucoma(Springer Nature Limited, 2024-03-24) Patil, Shruti V.; Kaipa, Balasankara R.; Ranshing, Sujata; Sundaresan, Yogapriya; Millar, J. Cameron; Nagarajan, Bhavani; Kiehlbauch, Charles; Zhang, Qihong; Jain, Ankur; Searby, Charles C.; Scheetz, Todd E.; Clark, Abbot F.; Sheffield, Val C.; Zode, Gulab S.Mutations in myocilin (MYOC) are the leading known genetic cause of primary open-angle glaucoma, responsible for about 4% of all cases. Mutations in MYOC cause a gain-of-function phenotype in which mutant myocilin accumulates in the endoplasmic reticulum (ER) leading to ER stress and trabecular meshwork (TM) cell death. Therefore, knocking out myocilin at the genome level is an ideal strategy to permanently cure the disease. We have previously utilized CRISPR/Cas9 genome editing successfully to target MYOC using adenovirus 5 (Ad5). However, Ad5 is not a suitable vector for clinical use. Here, we sought to determine the efficacy of adeno-associated viruses (AAVs) and lentiviruses (LVs) to target the TM. First, we examined the TM tropism of single-stranded (ss) and self-complimentary (sc) AAV serotypes as well as LV expressing GFP via intravitreal (IVT) and intracameral (IC) injections. We observed that LV_GFP expression was more specific to the TM injected via the IVT route. IC injections of Trp-mutant scAAV2 showed a prominent expression of GFP in the TM. However, robust GFP expression was also observed in the ciliary body and retina. We next constructed lentiviral particles expressing Cas9 and guide RNA (gRNA) targeting MYOC (crMYOC) and transduction of TM cells stably expressing mutant myocilin with LV_crMYOC significantly reduced myocilin accumulation and its associated chronic ER stress. A single IVT injection of LV_crMYOC in Tg-MYOC(Y437H) mice decreased myocilin accumulation in TM and reduced elevated IOP significantly. Together, our data indicates, LV_crMYOC targets MYOC gene editing in TM and rescues a mouse model of myocilin-associated glaucoma.