α-Synuclein and Polyunsaturated Fatty Acids Promote Clathrin-Mediated Endocytosis and Synaptic Vesicle Recycling

alpha-Synuclein (alpha S) is an abundant neuronal cytoplasmic protein implicated in Parkinson's disease (PD), but its physiological function remains unknown. Consistent with its having structural motifs shared with class A1 apolipoproteins, alpha S can reversibly associate with membranes and help regulate membrane fatty acid composition. We previously observed that variations in alpha S expression level in dopaminergic cultured cells or brains are associated with changes in polyunsaturated fatty acid (PUFA) levels and altered membrane fluidity. We now report that alpha S acts with PUFAs to enhance the internalization of the membrane-binding dye, FM 1-43. Specifically, alpha S expression coupled with exposure to physiological levels of certain PUFAs enhanced clathrin-mediated endocytosis in neuronal and non-neuronal cultured cells. Moreover, alpha S expression and PUFA-enhanced basal and -evoked synaptic vesicle (SV) endocytosis in primary hippocampal cultures of wild type (wt) and genetically depleted alpha S mouse brains. We suggest that alpha S and PUFAs normally function in endocytic mechanisms and are specifically involved in SV recycling upon neuronal stimulation.