Wallerian degeneration is a conserved program of injury-induced axon degeneration, which emulates the disruption of axonal transport that occurs during the early stages of many neurodegenerative diseases. In recent years, SARM1 has been shown to initiate Wallerian degeneration through intrinsic NADase activity. However, the molecular details of this pathway downstream of SARM1 activation are not well understood.
Axundead (Axed) is a potent regulator of Wallerian degeneration in Drosophila, with loss-of-function mutants resulting in suppression of SARM1-dependent axonal degeneration. Axed is a member of the BTB-domain containing protein family, which play roles in a range of cellular functions, including cytoskeletal organization and protein ubiquitination. However, the mechanism through which Axed regulates axonal degeneration remains unclear.
Bioinformatic analyses of the BTB-domain phylogenetic tree indicates Axed is unique to arthropods and has a distinct domain architecture which may underlie the novel functions of Axed. We utilized Alphafold predictions, Small-Angle X-Ray Scattering (SAXS) and Cryo-EM to characterize the structure of Axed and found that Axed dimerizes in a different structural conformation to related BTB-domain proteins. Proteomic analyses suggest Axed interacts with proteins within energy metabolism pathways. To investigate whether Axed is involved in the drastic loss of axonal ATP that occurs during Wallerian degeneration, we aim to measure cellular ATP dynamics in vivo within sensory axons of the Drosophila wing, through a genetically encoded Förster Resonance Energy Transfer (FRET)-based ATP biosensor.
As a downstream converging point for axon death pathways, understanding Axed will provide valuable insights into how this pathway can be targeted for therapeutic intervention in neurodegenerative disease.