The phosphomimetic Rab10 T73D mutation in mice leads to postnatal lethality and aberrations in neuronal development

The phosphorylation of the evolutionarily conserved Thr73 residue of Rab10 has been implicated in various neurodegenerative diseases. However, its impact on neuronal physiological function remains poorly understood. In this study, we generated a novel mouse model constitutively expressing the phosphomimetic Rab10 T73D to investigate its effects. Our findings revealed that homozygous Rab10 T73D mutant mice were postnatally lethal and exhibited brain developmental defects characterized by cortical thinning and shortened neuronal processes. Further investigation demonstrated that cultured hippocampal neurons with homozygous T73D mutation displayed decreased axon development, with reduced accumulation of Rab10 at the tips of neuronal processes and increased Rab10 localization at lysosomes. Mechanistically, the T73D mutation induces a constitutively GTP-bound state and while substantially weakening interaction with GDI1, GDI2 and JIP1. These molecular alterations collectively lead to altered T73D Rab10-positive vesicle trafficking dynamics, manifesting as decreased anterograde transport and increased movement velocity. Notably, comparative localization studies in RPE cells confirmed fundamental discrepancies between T73D distribution patterns and authentic phosphorylated Rab10 dynamics, validating limitations of this phosphomimetic approach. Collectively, our study elucidates the potential physiological roles of phosphorylated Rab10 in the regulation of neuronal process outgrowth and underscores its significance in the neural system. Additionally, it highlights the limitations of the T73D mutant in fully mimicking Rab10 phosphorylation.