The Impact Of Parkin On Dopaminergic Synaptic Function Through Interacting With Synaptojanin-1

Parkin gene mutations have been implicated in autosomal-recessive early-onset parkinsonism and the pathogenesis of Parkinson's disease(PD)is not clear at present.Parkin,also named PARK2,is an E3 ubiquitin ligase and participates in ubiquitin-proteasome system(UPS).A putative mechanism by which mutations of Parkin cause PD would be abnormal accumulation of its substrates due to altered E3 ligase activity for ubiquitin-proteasome dependent protein turnover.Over the past few decades,accumulating evidence has suggested that the loss of parkin could alter normal synaptic function but the precise mechanism remains unclear.In order to understand the specific mechanism of parkin protein affecting synaptic function,we have screened out one synapse associated protein named synaptojanin-1(syj-1)which interacting with parkin by proteomic techniques.In the brain slice of wild mice,immunofluorescence assay also demonstrates that both of them can be Co-located.Further studies have found that parkin directly interacts with syj-1 specifically through its IBR,R2 domains and mediates the degradation of syj-1 through UPS pathway,which means that syj-1 is a novel substrate for the E3 ubiquitin ligase parkin.Also,western blot assay has confirmed that syj-1 protein levels are elevated in parkin KO mice striatum,which means that syj-1 takes part in the pathogenesis of PD.Furthermore,knocking down parkin by small interfering RNA in SH-SY5 Y cells enhanced the number of surface GluR1 receptors,which is consistent with an increase in the number of GluR1 receptors induced by overexpression of syj-1 in SH cells.And overexpression of parkin in SH cells reduced surface GluR1 receptors.These results indicate that the impact of parkin on the dopaminergic synaptic function could be through syj-1.Our study reveals the important mechanism of parkin in the regulation of synaptic function,which may provide a new way to father understand the pathogenesis of PD and the important function of parkin.