Final Report Summary - DIABLO (Mechanisms of Developmental and Injury-related Axon Branch Loss)
(1) We discovered that during development of motor neurons, individual branches of the neuron’s axonal arbor can be selectively dismantled by local loss of the microtubular cytoskeleton that normally stabilizes axons. This is mediate by an enzyme, spastin, which cuts microtubules, but is also mutated in some forms of neurodegenerative diseases. The activity of spastin appears to be locally regulated by posttranslational modifications along the microtubules. Importantly, this process not only regulates axon stability but also an axon’s signalling to neighboring glial cells in order to regulate the onset of myelin formation.
(2) Mechanisms of axon loss appear to be shared between development and disease and across diseases. For instance, microtubule loss also appears to be an early event in the damage to axons in a specific form of neuroinflammation, where autoantibodies locally destroy astrocytes, an important class of glial cells. Similarly, the formation of nanoscale membrane defects appears to be a shared feature between neuroinflammatory axon loss and traumatically induced axon pathology.
Together, these results provide fundamental insights into the biology of axons, the potential to ameliorate axon loss by targeting subcellular pathology and the risks of interfering with normal development or reparative remodeling.