Coupled Control of Distal Axon Integrity and Somal Responses to Axonal Damage by the Palmitoyl Acyltransferase ZDHHC17

Abstract

After optic nerve crush (ONC), the cell bodies and distal axons of most retinal ganglion cells (RGCs) degenerate. RGC somal and distal axon degeneration were previously thought to be controlled by two distinct pathways, involving activation of the kinase DLK and loss of the axon survival factor NMNAT2, respectively. However, we found that mutual palmitoylation by the palmitoyl acyltransferase ZDHHC17 couples the DLK and NMNAT2 signals, which together form a "trust, but verify system". In healthy optic nerves, ZDHHC17-dependent palmitoylation ensures NMNAT-dependent distal axon integrity, while following ONC, ZDHHC17-dependent palmitoylation is critical for DLK-dependent somal degeneration. We found that ZDHHC17 also controls survival-versus-degeneration decisions in sensory neurons and identified motifs in NMNAT2 and DLK that govern their ZDHHC17-dependent regulation. These findings suggest that the control of somal and distal axon integrity should be considered as a single, holistic process, involving two palmitoylation-dependent pathways acting in concert.