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

• Published in: Fluids and barriers of the CNS 2022-05, Vol.19 (1), p.37-37, Article 37
• Main Authors: Alam, Parvez, Holst, Mikkel R, Lauritsen, Line, Nielsen, Janni, Nielsen, Simone S E, Jensen, Poul Henning, Brewer, Jonathan R, Otzen, Daniel E, Nielsen, Morten S
• Format: Article
• Language: English
• Subjects: alpha-Synuclein - genetics; alpha-Synuclein - metabolism; Alzheimer's disease; Blood vessels; Blood-brain barrier; Brain; Brain - metabolism; Clathrin; Clathrin - metabolism; Endosomes; Endothelial cells; Endothelial Cells - metabolism; Endothelium; Endothelium - metabolism; Experiments; Humans; Internalization; Localization; Monomers; Movement disorders; Neurodegenerative diseases; Oligomers; Parkinson Disease - metabolism; Parkinson's disease; Physiology; Polarization trap; Protein transport; Proteins; Rab7; rab7 GTP-Binding Proteins; Retromer; siRNA; Synuclein; Transcytosis; Vesicular Transport Proteins; α-synuclein
• ISSN: 2045-8118; 2045-8118
• DOI: 10.1186/s12987-022-00334-y

Parkinson's disease is mainly caused by aggregation of α-synuclein (α-syn) in the brain. Exchange of α-syn between the brain and peripheral tissues could have important pathophysiological and therapeutic implications, but the trafficking mechanism of α-syn across the blood brain-barrier (BBB) remains unclear. In this study, we therefore investigated uptake and transport mechanisms of α-syn monomers and oligomers across an in vitro BBB model system. Both α-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 α-syn in brain endothelial cells, we investigated co-localization of α-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 α-syn trafficking via Rab7-decorated carriers. Knockdown of Caveolin1, VPS35, and Rab7 using siRNA did not affect monomeric α-syn uptake into endothelial cells. However, it significantly reduced transcytosis of monomeric α-syn in the luminal-abluminal direction, suggesting a polarized regulation of monomeric α-syn vesicular transport. Our findings suggest a direct role for Rab7 in polarized trafficking of monomeric α-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.