? Glaucoma is a neurodegenerative disease in which there is specific loss of retinal ganglion cells (RGCs). Current therapies center around lowering intraocular pressure (IOP) although this can be challenging in some patients. In order to advance towards a neuroprotective strategy that could complement IOP-lowering, we have been identifying potential neuroprotective targets in primary RGCs using high- throughput functional genomic screening. The first iteration of this work, using RNA interference, identified dual leucine zipper kinase (DLK) and leucine zipper kinase (LZK) as key mediators of RGC cell death and validated the biology in rodent models of optic neuropathy, including glaucoma. Since then, we have completed a clustered regularly-interspaced short palindromic repeat (CRISPR)-based screen in order to identify genes whose knockout further potentiates the RGC protection conferred by DLK/LZK inhibition. The top new hit in this screen was glycogen synthase kinase three beta (GSK-3?). Highlighting the utility of our agnostic screening approach, multiple groups have previously found that while GSK-3? is indeed activated in RGCs after axonal injury, GSK- 3? loss alone does not increase RGC survival. We have shown however, in the setting of DLK/LZK pathway inhibition, GSK-3? loss does lead to a further increase in RGC survival. Moreover, we found an unexpected synergy in neurite degeneration with inhibition of DLK/LZK and GSK-3? leading to robust neurite protection. The central hypothesis of this proposal is that DLK/LZK and GSK-3? cooperate, potentially as a result of their ability to dually phosphorylate myocyte enhancer factor 2A (MEF2A), to cause somal and axonal degeneration and that simultaneous inhibition of DLK, LZK and GSK-3? is required for maximal neuroprotection. In order to test this hypothesis in vivo and to create a generalizable method for gene multitargeting in vivo, we have developed a novel adeno-associated virus (AAV)/CRISPR vector. This uses a novel insight about the compact H1 promoter which allows both guide RNA (gRNA) and S. pyogenes Cas9 (SpCas9) to be delivered in a single AAV virus, overcoming a major hurdle in the field of therapeutic gene editing.
Specific aim 1 (SA1) will develop AAV/CRISPR vectors to multitarget DLK/LZK/GSK-3?, validate them in primary RGCs and then use the resulting cells to explore the role of MEF2A as a key convergence point of GSK-3? and DLK/LZK signaling. SA2 will use AAV/CRISPR vectors in vivo to test whether DLK/LZK/GSK-3? inhibition affects normal retinal structure/function and whether multitargeting leads to long-term preservation of electrophysiologically-active RGCs and decreased axon degeneration in the mouse optic nerve crush model. Finally, SA3 will use a more therapeutically-relevant design, in which the AAV/CRISPR virus delivers all of the CRISPR components, to test the hypothesis that kinase multitargeting in RGCs improves visual outcomes in a rat glaucoma model. Together, we anticipate this proposal will lead to a robust RGC neuroprotective strategy for combined axonal and somal preservation and the development of a novel AAV/CRISPR therapeutic.
We previously identified dual leucine zipper kinase (DLK) and leucine zipper kinase (LZK) as promising neuroprotective targets in retinal ganglion cell (RGC) degenerations/optic neuropathies like glaucoma. More recently, we have used a clustered regularly interspaced short palindromic repeat (CRISPR)-based screen in primary RGCs to identify glycogen synthase kinase three beta (GSK-3?) inhibition as an effective strategy to potentiate the axonal and somal protection conferred by DLK/LZK inhibition. In this proposal, we develop and use a novel adeno-associated virus (AAV)/CRISPR vector to test the hypothesis that combined DLK, LZK and GSK-3? inhibition is needed for sustained protection of functional RGCs in rodent models of optic neuropathy, including in a rat model of glaucoma.
