DYRK1A role in microtubule-based axonal transport regulates the retrograde dynamics of APP vesicles in human neurons

Abstract

In Alzheimer ́s Disease (AD) the abnormal intracellular distribution of the amyloid precursor protein (APP) affects its processing and, consequently, the generation of Aβ. Axonal transport plays key roles in the neuronal distribution of APP. The dual-specificity- tyrosine phosphorylation-regulated-kinase-1A (DYRK1A) has been associated with AD onset since its overexpression was found in Down syndrome and sporadic AD patients. Experimental evidence confirmed that APP and tau phosphorylations are mediated by DYRK1A. Moreover, DYRK1A can regulate the cytoskeletal architecture by phosphorylation of both tubulin subunits and microtubule-associated proteins. Therefore, we tested whether DYRK1A has a role in APP axonal transport regulation. We developed highly-polarized human-derived neurons in 2D cultures. At day 14 after terminal plating we inhibited DYRK1A for 48hs with harmine (7.5 μM). DYRK1A overexpression was induced to perform live-cell imaging of APP-loaded vesicles in axons and analyzed transport dynamics. A custom-made MATLAB routine was developed to track and analyze single particle dynamics. Short-term harmine treatment reduced axonal APP vesicles density, due to a reduction in retrograde particles. Contrarily, DYRK1A overexpression enhanced axonal APP density, due to an increase in the retrograde and stationary component. Moreover, both harmine-mediated DYRK1A inhibition and DYRK1A overexpression revealed opposite phenotypes on single particle dynamics, affecting primarily dynein processivity. These results revealed an increased retrieval of distal APP vesicles in axons when DYRK1A is overexpressed and reinforce the suggestion that DYRK1A enhance APP endocytosis. Taken together our results suggest that DYRK1A has a relevant role in the regulation of axonal transport and sub-cellular positioning of APP vesicles. Therefore, our work shed light on the role of DYRK1A in axonal transport regulation, and the putative use of harmine to restore axonal transport impairments.