Activation of NRF2 Pathways in Glaucoma
Naguib, Sarah Aymen
Glaucoma results from progressive degeneration and eventual death of retinal ganglion cells (RGCs) and is the leading cause of irreversible blindness worldwide. Neuroprotective agents are needed to protect RGCs because the only current treatments available aim to reduce intraocular pressure (IOP), but these are ineffective in many patients. While the exact etiology of glaucoma is unknown, previous studies have implicated oxidative stress as a factor for neurodegeneration. NRF2 is a regulator of cells’ antioxidant response via its activation of the antioxidant response element and downstream upregulation of antioxidant genes. In the well-characterized microbead occlusion model (MOM) of glaucoma, we showed that NRF2 is phosphorylated and activated by PI3K/Akt weeks prior to glaucomatous neurodegeneration and the retina produces an endogenous antioxidant response to ocular hypertension. NRF2 knockout (KO) mice lack this endogenous antioxidant response and have an accelerated and exacerbated phenotype following microbead injection. To elucidate the cell-type specific role of NRF2 in glaucoma, we generated RGC or astrocyte-specific knockdown mice and induced ocular hypertension. We found that decreased NRF2 in either knockdown group blunted the endogenous antioxidant response, but overexpression of NRF2 in RGCs of either NRF2 KO mice or wildtype mice conferred neuroprotection. We also explored an indirect activator of NRF2, erythropoietin (EPO). We used a mutated form of EPO (EPO-R76E) packaged into PLGA nanoparticles to protect RGCs while not increasing hematocrit and allow for sustained release. We intravitreally injected PLGA.EPO-R76E one day post-IOP elevation. We found that PLGA.EPO-R76E is sufficient to protect wildtype mice from glaucomatous neurodegeneration and retinal oxidative stress. We showed that unlike the retina’s endogenous antioxidant response, in which NRF2 is phosphorylated at 2 weeks post-IOP elevation, PLGA.EPO-R76E upregulates different antioxidants and NRF2 is phosphorylated at 1 week. Additionally, in mice injected PLGA.EPO-R76E, we found that NRF2 phosphorylation was decreased when MAPK was inhibited, showing differential activation of NRF2.