Live axonal transport disruption by mutant huntingtin fragments in Drosophila motor neuron axons

C Sinadinos,T Burbidge-King,D Soh,L.M Thompson,J.L Marsh,A Wyttenbach,A.K Mudher

doi:10.1016/j.nbd.2009.02.012

C Sinadinos, T Burbidge-King + Show 5 more

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https://doi.org/10.1016/j.nbd.2009.02.012

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Abstract

Huntington's Disease is a neurodegenerative condition caused by a polyglutamine expansion in the huntingtin (Htt) protein, which aggregates and also causes neuronal dysfunction. Pathogenic N-terminal htt fragments perturb axonal transport in vitro. To determine whether this occurs in vivo and to elucidate how transport is affected, we expressed htt exon 1 with either pathogenic (HttEx1Q93) or non-pathogenic (HttEx1Q20) polyglutamine tracts in Drosophila. We found that HttEx1Q93 expression causes axonal accumulation of GFP-tagged fast axonal transport vesicles in vivo and leads to aggregates within larval motor neuron axons. Time-lapse video microscopy, shows that vesicle velocity is unchanged in HttEx1Q93-axons compared to HttEx1Q20-axons, but vesicle stalling occurs to a greater extent. Whilst HttEx1Q93 expression did not affect locomotor behaviour, external heat stress unveiled a locomotion deficit in HttEx1Q93 larvae. Therefore vesicle transport abnormalities amidst axonal htt aggregation places a cumulative burden upon normal neuronal function under stressful conditions.

Highlights

Neurodegeneration in Huntington's Disease (HD), caused by an N-terminal polyglutamine expansion within the huntingtin (Htt) protein (The Huntington's Disease Collaborative Research Group, 1993), involves progressive death of neurons in the striatum and cortex (Reiner et al, 1988)
As axonal mutant HttEx1 aggregates may contribute to transport disruption (Gunawardena et al, 2003), we studied the axonal distribution of HttEx1 in fixed motor neuron axons within the peripheral nerves of dissected larvae
large aggregates (LAg) are significantly elevated in HttEx1Q93 larvae raised at 23 °C relative to OreR (Fig. 1B, C, p b 0.05, n = 5) and there is a trend towards increased LAg in HttEx1Q93 versus HttEx1Q20 (Fig. 1C, p = 0.13)

Summary

Introduction

Neurodegeneration in Huntington's Disease (HD), caused by an N-terminal polyglutamine (polyQ) expansion within the huntingtin (Htt) protein (The Huntington's Disease Collaborative Research Group, 1993), involves progressive death of neurons in the striatum and cortex (Reiner et al, 1988). As clinical progression can precede extensive neuronal death (Vonsattel et al, 1985), focus has centred on early pathological events that disrupt neuronal function prior to neuronal demise. Axonal dysfunction may represent one such event, as post mortem brain tissue from pre-symptomatic HD sufferers exhibits axonal degeneration of striatal projection neurons (Albin et al, 1992) and cortico-striatal afferents (Sapp et al, 1999). Dystrophic neurites, and swellings of accumulated cargoes indicative of axonal transport disruption, have been localised to aggregated htt inclusion bodies (A.K. Mudher).

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