Aberrant Retrograde Trafficking Of VMAT2 Induced By Parkinson's Diseases Related Mutant Genes

Numerous genetic and biochemical evidences have linked the pathogenesis of Parkinson's disease(PD)to aberrant retrograde membrane trafficking mediated by several recently identified familial PD genes such as LRRK2,Vps35 and Rab29.However,the cargo protein(s)affected by these pathologic trafficking events that is also expressed specifically in dopaminergic neurons and participates in the progressive PD pathogenesis remain unidentified.Vesicular monoamine transporter 2(VMAT2),a membrane protein specifically expressed in monoaminergic neurons and localized to secretory vesicles for monoamine transmitter packaging,was originally identified for its role in protection against neurotoxin MPP+and later for its association with PD pathogenesis.Our own unpublished work on the membrane trafficking of VMAT2 has indicated a role of retrograde trafficking in vesicular localization and function of the transporter.Thus,we hypothesize that VMAT2 may serve as a cargo protein for PD genes which induce an aberrant retrograde trafficking of the transport protein as well as presumably reduce its neuroprotective function.Here we demonstrate biochemically and cellularly that VMAT2 is localized in TGN and undergoes retrograde trafficking in non-neuronal cells.We have shown that PD genes Vps35 and LRRK2 can parallelly regulate the retrograde trafficking of VMAT2,but LRRK2 mediates the retrograde trafficking and vesicular localization of VMAT2 through phosphorylating Rab8,and Rab29 acts as the downstream effector at the TGN for both pathways.Importantly,the PD mutants such as Vps35D620N,LRRK2G2019S and siRNA Rab29 impair the retrograde trafficking,decrease protein stability and disturb vesicular localization,and finally impede the neurotransmitter package of VMAT2.Our data strongly supports that VMAT2 serves as the membrane cargo protein for PD genes and the aberrant retrograde trafficking of VMAT2 and impaired vesicular function may contribute to these PD gene induced selective and progressive pathogenesis in PD.Our work may provide new insight in understanding PD pathogenesis and a novel drug target for therapeutic application of PD clinic.