Inhibition of GCK-IV kinases dissociates cell death and axon regeneration in CNS neurons

Abstract

Axon injury is a hallmark of many neurodegenerative diseases, often resulting in neuronal cell death and functional impairment. Dual leucine zipper kinase (DLK) has emerged as a key mediator of this process. However, while DLK inhibition is robustly protective in a wide range of neurodegenerative disease models, it also inhibits axonal regeneration. Indeed, there are no genetic perturbations that are known to both improve long-term survival and promote regeneration. To identify such a neuroprotective target, we conducted a set of complementary high-throughput screens using a protein kinase inhibitor library in human stem cell-derived retinal ganglion cells (hRGCs). Overlapping compounds that promoted both neuroprotection and neurite outgrowth were bioinformatically deconvoluted to identify specific kinases that regulated neuronal death and axon regeneration. This work identified the role of germinal cell kinase four (GCK-IV) kinases in cell death and additionally revealed their unexpected activity in suppressing axon regeneration. Using an adeno-associated virus (AAV) approach, coupled with genome editing, we validated that GCK-IV kinase knockout improves neuronal survival, comparable to that of DLK knockout, while simultaneously promoting axon regeneration. Finally, we also found that GCK-IV kinase inhibition also prevented the attrition of RGCs in developing retinal organoid cultures without compromising axon outgrowth, addressing a major issue in the field of stem cell-derived retinas. Together, these results demonstrate a role for the GCK-IV kinases in dissociating the cell death and axonal outgrowth in neurons and their druggability provides for therapeutic options for neurodegenerative diseases.

The interplay of autophagy and oxidative stress in the pathogenesis and therapy of retinal degenerative diseases

“…Axons of RGCs degenerate in optic nerve injury and do not regrow; thus, what regulates axon regeneration remains a field of interest to scientists. Many studies have shown the promotion of axon regeneration by molecular therapies [ 194 – 198 ]. However, the length of regenerative axons and synaptic reconnection are still limited [ 199 ].…”

Non-Cell-Autonomous Regulation of Optic Nerve Regeneration by Amacrine Cells

“…Although axon regrowth after injury obviously depends on cell survival, the two processes are distinct, and surviving RGCs do not regenerate axons by default (Chierzi et al, 1999;Goldberg and Barres, 2000;Goldberg et al, 2002a). However, in an exciting recent discovery, Patel et al showed that inhibition of germinal cell kinase IV (GCK-IV) promotes RGC survival without suppressing axon regeneration (Patel et al, 2020).…”

Optic Nerve Engraftment of Neural Stem Cells

“…15 Interestingly, inhibition of the germinal cell kinase Downloaded from iovs.arvojournals.org on 07/26/2021 four kinases that act upstream of DLK can improve neuronal survival without detrimentally affecting RGC axon regeneration, dissociating survival from regeneration. 16 Therefore, because the degree of RGC axon regeneration promoted by optic nerve transplanted NSCs is modest and unlikely to be of functional significance without further augmentation, future studies that seek to form restorative neuronal relays should combine RGC intrinsic approaches that optimize both RGC survival and axon regeneration with optic nerve grafted NSCs. Examples of RGC intrinsic interventions with the potential to synergize with our proposed optic nerve relay strategy include combinatorial approaches that inhibit germinal cell kinase four kinases to enhance RGC survival while promoting RGC axon regeneration through the inhibition of phosphatase and tensin homology or suppressor of cytokine signaling 3 along with growth promoting factors such as CNTF and oncomodulin.…”