The Mechanism of Sigma 1 Receptor Mediated Neuroprotection in Glaucoma

The long-term goal of our laboratory is to develop successful neuroprotective treatments for glaucoma. Glaucoma is a blinding disease for which neuroprotective treatments are desperately needed. In the visual system, retinal ganglion cells (RGCs) conduct impulses to the visual cortex via RGC axons which form the optic nerve (ON). Loss of RGCs and their axons are the underlying cellular cause of many optic neuropathies including glaucoma. RGC axons are particularly vulnerable to damage at the optic nerve head (ONH) where ONH astrocytes (ONHAs) are the main glial cell. This proposal focuses on sigma-1 receptor (S1R) as a promising therapeutic target in glaucoma. S1R is a ligand operated molecular chaperone that generally elicits pro-survival responses via regulation of protein-protein interactions. Although activation of S1R using the canonical ligand (+)-pentazocine (PTZ) reduces axon loss in a rat microbead model of glaucoma, the cell-specific mechanisms by which S1R provides this neuroprotection are not well-known. Here, we investigate a novel function of S1R as a regulator of the ONHA secretome. Previous studies indicate that S1R interacts with proteins mediating secretion and in vitro experiments suggest that the presence of S1R in ONHAs is required for supporting RGC health in co-culture experiments. Three specific aims are proposed to investigate the central hypothesis that S1R mediates neuroprotection in RGCs by regulating the ONHA secretome. Aim 1 uses novel cell-specific S1R knockout (KO) mice to determine the extent to which S1R in astrocytes versus RGCs is necessary for neuroprotection using the microbead and silicone oil models of glaucoma. Aim 2 tests the hypothesis that S1R regulates the ONHA secretome to enable RGC protection. A combination of molecular and genetic approaches are used to tag, concentrate, and identify secreted proteins in ONHA-conditioned media with/without S1R activation and in presence/absence of ocular hypertension and ER stress. Comparison of the changing secretome under different conditions will identify specific components with the potential to promote RGC survival. Aim 3 addresses the molecular pathways induced in RGCs by the S1R-mediated ONHA secretome. A combination of in vitro and in vivo approaches will be used to investigate how S1R in ONHAs alters RGC mitochondrial localization and metabolism. In addition, we will determine transcriptome and translatome changes that occur in RGCs upon exposure to the ONHA secretome. Successful completion of this proposal will identify new therapeutic targets within the astrocyte secretome. Modulating the astrocyte secretome offers a novel druggable approach to mitigate factors leading to RGC death.