A08 Synaptic vesicle recycling is disrupted in a mouse model of huntington’s disease

Background An emerging theme in neurodegenerative diseases, including Huntington’s Disease (HD), is that presynaptic dysfunction plays a role in neurodegeneration and disease progression. In HD the huntingtin protein (Htt) produced has an expanded polyglutamine stretch, likely causing altered protein function. Htt is enriched at the presynapse, suggesting it may have a role in presynaptic function. At the presynapse, synaptic vesicles fuse with the plasma membrane in a process called exocytosis to release neurotransmitter into the synaptic cleft. Following exocytosis, synaptic vesicles are retrieved and recycled via endocytosis. If this cycle is disrupted, synaptic frailty and degeneration can occur. Aims The aim of this study was to investigate presynaptic function in a mouse model of HD. Methods Primary neuronal cultures were made from Q140 knock-in mice and wild-type (wt) controls. Presynaptic function was monitored using the genetically encoded reporter, synaptophysin-phluorin, in combination with manipulation of the levels of Htt. This was achieved by silencing expression using hsiRNA or over-expression of Htt. Results We demonstrate that striatal primary neurons from Q140 mice display an activity-dependent slowing of endocytosis. Silencing of mutant Htt in Q140 cultures had no effect on endocytic rate, however, silencing of wt-Htt in control cultures, recapitulated the defect. This suggests a loss of Htt function phenotype. Supporting this, over-expression of wt-Htt in Q140 neurons rescued the endocytic defect. Slowing of endocytosis was also observed in heterozygous cultures, which more accurately represents the genetics of HD patients. Conclusions We have uncovered a loss of wt-Htt, activity-dependent presynaptic defect in a model of HD. This is important because understanding the mechanisms underpinning events which occur early in disease progression may represent new targets for therapeutic intervention.