GSK3ss impairs KIF1A transport in a cellular model of Alzheimers disease but does not regulate motor motility at S402
Impairment of axonal transport is an early pathological event that precedes neurotoxicity in Alzheimer’s disease (AD). Soluble amyloid-β oligomers (AβOs), a causative agent of AD, activate intracellular signaling cascades that trigger phosphorylation of many target proteins, including tau, resulting in microtubule destabilization and transport impairment. Here, we investigated how KIF1A, a kinesin-3 family motor protein required for the transport of neurotrophic factors, is impaired in mouse hippocampal neurons treated with AβOs. By live cell imaging, we observed that AβOs inhibit transport of KIF1A-GFP similarly in wildtype and tau knockout neurons, indicating that tau is not required for this effect. Pharmacological inhibition of glycogen synthase kinase 3β (GSK3β), a kinase overactivated in AD, prevented the transport defects. By mass spectrometry on KIF1A immunoprecipitated from transgenic AD mouse brain, we detected phosphorylation at Ser 402, which conforms to a highly conserved GSK3β consensus site, and confirmed that this site is phosphorylated by GSK3β in vitro. Finally, we tested whether a phosphomimic of S402 could modulate KIF1A motility in control and AβO-treated mouse neurons and in a Golgi dispersion assay devoid of endogenous KIF1A. In both systems, transport driven by mutant motors was similar to that of wildtype motors. In conclusion, GSK3β impairs KIF1A transport but does not regulate motor motility at S402. Further studies are required to determine the specific phosphorylation sites on KIF1A that regulate its cargo binding and/or motility in physiological and disease states.
SIGNIFICANCE STATEMENT Axonal transport of proteins and organelles is required for neuronal function and survival and is impaired in Alzheimer’s disease (AD). Pathogenic mechanisms that directly impact motor protein motility prior to neuronal toxicity have not been widely investigated. Here, we show that KIF1A, the primary kinesin motor required for transport of neurotrophic factors, is impaired in mouse neurons treated with amyloid-β oligomers, a causative agent of AD. Inhibition of GSK3β, a kinase overactivated in AD, prevents these defects. We detected phosphorylation of S402, a highly conserved GSK3β consensus site, in KIF1A immunoprecipitated from AD mouse brain. However, a phosphomimic of S402 did not modulate KIF1A motility in cell-based assays. Thus, GSK3β impairs KIF1A transport but likely not through phosphorylation at S402.