Axon regeneration remains a major roadblock in functional recovery after nervous system injury. Recent studies suggest that regeneration capacity of injured axons is neuronal subtype-specific, but its molecular and cellular determinants remain unknown. Nerve damage triggers complex injury responses in neurons and the surrounding glial cells and macrophages, but how these diverse cell types signal to each other to coordinately regulate axon regeneration is largely unknown. Our long-term goal is to uncover the repertoire of pro- and anti-regeneration factors for designing combinatorial therapy to promote axon regeneration. To fulfill this goal, we have established a sensory neuron axotomy model in Drosophila, which resembles mammalian regeneration models at the phenotypical and molecular levels. In particular, Drosophila sensory neurons display neuronal subtype-specific regeneration. Our model allows the molecular, morphological and physiological characterization of injured neurons, and the surrounding glia and macrophages, at the single-cell resolution. Recent studies have suggested that increase of neuronal activity promotes axon regeneration after injury, but it is unclear whether and how nerve injury alters the activity of neurons, glial cells and macrophages, and how the collective activities in these diverse cell types contribute to axon regeneration. Our objective in current proposal is to determine how glia and macrophages interact with neurons to regulate neuronal subtype-specific firing and regeneration. Specifically, we will test the hypothesis that 1) axotomy-induced neuronal burst firing mediates neuronal subtype-specific regeneration; 2) glia and macrophages signal to injured neurons to regulate neuronal firing and regeneration. In this proposal, we plan to fully leverage the sophisticated Drosophila genetics with state-of-art techniques, including highly reproducible single-neuron axotomy, optogenetics, in vivo time-lapse GCaMP imaging to simultaneously monitor Ca2+ activities in neurons and glia/macrophages, single-neuron transcriptional analysis, to address our hypothesis.
Damage to the adult central nervous system (CNS) often leads to persistent deficits due to the inability of mature neurons to regenerate after injury. More than a million Americans are paralyzed due to spinal cord injuries (SCI), with ~12,000 new cases reported each year in the US alone. Spontaneous recovery is limited, and there is still no treatment for functional recovery after the spinal cord injury. Whereas axons are able to regenerate in the peripheral nervous system (PNS), the growth rate is limited to ~1 mm/day. The incompetence of regeneration often results in atrophy or degeneration of target tissues before re-innervation takes place, especially after proximal axon injury or in senior patients. Under pathological situations such as multiple sclerosis (MS), the second most common neurological disorder leading to disability in young adults, failure of damaged axons to regenerate contributes to non-reversible neurologic dysfunction. The ability of a neuron to regenerate after trauma is governed by the interaction between the extrinsic environment and the intrinsic growth capacity. Extracellular factors from oligodendrocyte, astrocyte, macrophage and fibroblast have been shown to impede neuronal growth, but eliminating these molecules only allows limited axon regrowth, reflecting intrinsic incapability of axon regrowth. Targeting both extrinsic and intrinsic factors represents the future of treatment in promoting of axon regeneration. However, very little is known about how diverse cell types including neurons, glia and macrophages interact with each other to regulate regeneration. In current proposal, we propose to address these important questions in the genetic model organism Drosophila, which shares significant conservation with mammals on regeneration mechanisms.
| Yan, Connie; Wang, Fei; Peng, Yun et al. (2018) Microtubule Acetylation Is Required for Mechanosensation in Drosophila. Cell Rep 25:1051-1065.e6 |
