Gene Expression Regulatory Pathways and Retinal Ganglion Cell Neuroprotection

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Loss of retinal ganglion cells (RGCs) in glaucoma and traumatic and other optic neuropathies results in permanent partial or complete blindness. Molecular mechanisms that may oppose this RGC death remain an area of active investigation and potential high impact, as bridging RGC survival in chronic optic neuropathies has high potential to preserve or restore vision. Multiple signal transduction pathways have been implicated in RGC neuroprotection, including cAMP and neurotrophic factor-induced mitogen-activated protein kinase (MAPK) signaling pathways. How these pathways synergistically promote RGC survival and elicit their downstream effects remains unknown. Recent data from our labs support a model in which signalosomes organized by the perinuclear scaffold protein muscle A-Kinase Anchoring Protein α (mAKAPα/AKAP6α) mediate cAMP- dependent signaling and potentiate neuroprotective MAPK signaling, resulting in Ets Like-1 protein (Elk-1) transcription factor activation and RGC survival. Identifying this intracellular cAMP signaling compartment specifically relevant to neuroprotection provides a mechanism for spatially distinct cAMP action and should inform the design of strategies providing therapeutics specificity greater than global cAMP elevation with adenylyl cyclase activators or cAMP analogs. In this application, we propose three Specific Aims to test this model and elucidate the mechanism conferring the synergy between cAMP and neurotrophic factor signaling in neuroprotection. Specific Aim 1: Defining Neuroprotective Gene Expression. Using single-cell RNA transcriptome sequencing (scRNA-seq), we will study to what degree similar gene transcription programs are induced by different neuroprotective interventions, including generalized versus compartmentalized cAMP elevation, determine whether individual RGC subtypes are preferentially regulated by cAMP and neurotrophic factor signaling, and identify gene candidates whose altered expression may be critical for neuroprotection in response to therapeutic intervention. Specific Aim 2: Role of Perinuclear Compartmented cAMP Signaling in RGC Neuroprotection. Using new tools to promote or inhibit cAMP and Ca2+ in special intracellular compartments, we will test whether Ca2+-cAMP signaling at RGC mAKAPα signalosomes is uniquely sufficient and/or necessary for RGC neuroprotection after optic nerve crush. Specific Aim 3: Crosstalk Between cAMP- and Neurotrophic Factor-Dependent RGC Neuroprotection. To test whether cAMP and neurotrophic factors promote neuroprotection through co-regulation of ERK1/2-dependent Elk-1 activation, mice with gain- and loss- of-function for Elk-1 in RGCs will be subjected to optic nerve crush and compared for their response to additional treatment with exogenous neurotrophic factors and AAV-mediated mAKAPα signaling compartment enhancement. Together, these Specific Aims will provide molecular insights into the signaling pathways and the altered gene expression that can confer RGC neuroprotection in vivo, while providing proof-of-concept for new strategies to prevent loss of vision in RGC disease.