Polarized α-synuclein trafficking and transcytosis across brain endothelial cells via Rab7-decorated carriers

Parkinson's disease is mainly caused by aggregation of alpha-synuclein (alpha-syn) in the brain. Exchange of alpha-syn between the brain and peripheral tissues could have important pathophysiological and therapeutic implications, but the trafficking mechanism of a-syn across the blood brain-barrier (BBB) remains unclear. In this study, we therefore investigated uptake and transport mechanisms of alpha-syn monomers and oligomers across an in vitro BBB model system. Both alpha-syn monomers and oligomers were internalized by primary brain endothelial cells, with increased restriction of oligomeric over monomeric transport. To enlighten the trafficking route of monomeric alpha-syn in brain endothelial cells, we investigated co-localization of alpha-syn and intracellular markers of vesicular transport. Here, we observed the highest colocalization with clathrin, Rab7 and VPS35, suggesting a clathrin-dependent internalization, preferentially followed by a late endosome retromer-connected trafficking pathway. Furthermore, STED microscopy revealed monomeric alpha-syn trafficking via Rab7-decorated carriers. Knockdown of Caveolin1,VPS35, and Rab7 using siRNA did not affect monomeric alpha-syn uptake into endothelial cells. However, it significantly reduced transcytosis of monomeric alpha-syn in the luminal-abluminal direction, suggesting a polarized regulation of monomeric alpha-syn vesicular transport. Our findings suggest a direct role for Rab7 in polarized trafficking of monomeric alpha-syn across BBB endothelium, and the potential of Rab7 directed trafficking to constitute a target pathway for new therapeutic strategies against Parkinson's disease and related synucleinopathies.

Automated summary

In this study, the researchers investigated the uptake and transport mechanisms of alpha-synuclein monomers and oligomers across the blood-brain barrier (BBB). They found that both monomers and oligomers were internalized by brain endothelial cells, with a higher restriction of oligomeric transport. Additionally, they discovered that monomeric alpha-synuclein trafficked via carriers decorated with Rab7. Knockdown of Caveolin1, VPS35, and Rab7 affected the transcytosis of monomeric alpha-synuclein, suggesting a polarized regulation of its vesicular transport. These findings highlight the importance of Rab7 in the trafficking of monomeric alpha-synuclein across the BBB, suggesting it could be a potential target for therapeutic strategies against Parkinson's disease.