Activity and Regulation of ALS Causing Variants of Kinesin KIF5A

Axon transport deficits are an emerging theme in the pathogenesis of Amyotrophic Lateral Sclerosis (ALS). In ALS, motor neuron function and survival are reduced leading to progressive weakness. Recently, mutations were identified in ALS patients in KIF5A, which is a neuron-specific anterograde microtubule motor protein. KIF5A contains an N-terminal motor domain, a coiled-coil domain, and a C-terminal domain (CTD) responsible for cargo binding and auto-inhibition. The mutations cause mis-spicing of KIF5A transcript and abnormal CTD structure. Normally, most of KIF5A is inactive in a folded conformation with the motor domain inhibited by the CTD. Cargo binding to the CTD releases this auto-inhibition allowing the motor to walk to the + ends of microtubules in the distal axon. KIF5A has been implicated in the motility of mitochondria and RNA granules but the full list of its cargos is not complete. Kinesin-1 family members KIF5A, KIF5B, KIF5C have overlapping expression patterns but their unique cargos and transport roles in neurons have not been fully characterized. KIF5A is expressed broadly in the nervous system though it is not clear what conveys the selective vulnerability of motor neurons to ALS mutations. Thus, the study of KIF5A ALS has potential to advance understanding of KIF5A specific cargos, how KIF5A motor/cargo complexes are assembled or inhibited, and why KIF5A mediated axon transport is critical for motor neuron function and survival. KIF5A normally has a uniform distribution because most of it is inactive and not participating in cargo transport. Once KIF5A delivers cargos it becomes inactive and is recycled by diffusion to the proximal axon/soma where it is reused. Our preliminary data suggests that KIF5A ALS mutant protein is constitutively active and cannot be autoinhibited or recycled. This leads to its depletion from the soma/proximal neurites and accumulation in the distal neurites of Neuro2A (N2A) cells. Wild type (WT) protein is recruited into these accumulations depleting the neuron of KIF5A. The experiments in this proposal will build on these findings to characterize how KIF5A mutations affect axonal transport and cause ALS. The potential awardee has expertise in the care and study of ALS and the mentor/lab has expertise in the study of kinesins making the team ideal to tackle this challenging problem. Aim 1: Elucidate the effects of KIF5A ALS mutation on the assembly and autoinhibition of KIF5A motor/organelle complexes. Aim 2: Characterize the effects of KIF5A ALS mutation on the transport of cargos. Aim 3: Identify the effects of KIF5A ALS mutation on the health and motor function of Drosophila melanogaster.