Rab3A interacts with spastin to regulate neurite outgrowth in hippocampal neurons.

Investigating novel mechanisms of neurite outgrowth via cytoskeleton is critical for developing therapeutic strategies against neural disorders. Rab3A is a vesicle-related protein distributed throughout the nervous system, but the detailed mechanism related to cytoskeleton remains largely unknown. Our previous reports show that spastin serves microtubule to regulate neurite outgrowth. Here, we asked whether Rab3A could function via modulating spastin during neuronal development. The results revealed that Rab3A colocalized with spastin in cultured hippocampal neurons. Immunoprecipitation assays showed that Rab3A physically interacted with spastin in rat brain lysates. Rab3A overexpression significantly induced spastin degradation; this effect was reversed by leupeptin- or MG-132- administration, suggesting the lysosomal and ubiquitin-mediated degradation system. Immunofluorescence staining further confirmed that Rab3A and spastin immune-colocalized with the lysosome marker lysotracker. In COS7 cells, Rab3A overexpression significantly downregulated spastin expression and abolished the spastin-mediated microtubule severing. Furthermore, overexpression inhibited while genetic knockdown of Rab3A promoted neurite outgrowth. However, this inhibitory effect on neurite outgrowth in hippocampal neurons could be reversed via co-transfection of spastin, indicating that Rab3A functions via its interaction protein spastin. In general, our data identify an interaction between Rab3A and spastin, and this interaction affects the protein stability of spastin and eliminates its microtubule severing function, thereby modulating neurite outgrowth.

SUMOylation of spastin promotes the internalization of GluA1 and regulates dendritic spine morphology by targeting microtubule dynamics.

Dendritic spines are specialized structures involved in neuronal processes on which excitatory synaptic contact occurs. The microtubule cytoskeleton is vital for maintaining spine morphology and mature synapses. Spastin is related to microtubule-severing proteases and is involved in synaptic bouton formation. However, it is not yet known if spastin can be modified by Small Ubiquitin-like Modifier (SUMO) or how this modification regulates dendritic spines. Spastin was shown to be SUMOylated at K427, and its deSUMOylation promoted microtubule stability. In addition, SUMOylation of spastin was shown to affect signalling pathways associated with long term synaptic depression. SUMOylated spastin promoted the development of dendrites and dendritic spines. Moreover, SUMOylated spastin regulated endocytosis and affected the transport of the AMPA receptor, GluA1. Our findings suggest that SUMOylation of spastin promotes GluA1 internalization and regulates dendritic spine morphology through targeting of microtubule dynamics.