Actin depolymerization promotes axon regeneration by restoring axonal mitochondrial transport in mouse models of optic neuropathy

Adult mammalian central nervous system (CNS) axons do not spontaneously regenerate after injury. We recently identified multiple genes that promote optic nerve regeneration, protect retinal ganglion cell (RGC) somata and axons, and preserve visual function in mouse glaucoma models. Here, we investigated the downstream molecular mechanisms driving the regenerative and neuroprotective effects of the actin depolymerization molecule gelsolin (<i>Gsn</i>, one of the top up-regulated genes in regenerating RGCs) and the actin regulatory molecules (annexin A2, destrin, cofilin, profilin, latrunculin, and cytochalasin). Adeno-associated virus (AAV)-mediated specific expression of these genes in RGCs or topical delivery of small molecules promoted optic nerve regeneration and RGC protection in an optic nerve crush model and an ocular hypertension glaucoma mouse model. These regenerative effects were associated with a decrease in F-actin in axon shafts. Ex vivo mechanistic studies, furthermore, demonstrated that actin depolymerization enhances axonal mitochondrial transport in RGC axons, suggesting a mechanistic nodal point on which these pro-regeneration molecules converge. We showed that the natural compound latrunculin B targets this unified mechanism in both mouse and human RGCs to promote axon outgrowth. In addition, we detected up-regulated F-actin in aqueous humors of patients with severe glaucoma, emphasizing the translational potential of our findings.