Characterization of a Drosophila model of Huntington's disease

Abstract

Huntington's disease (HD) is an autosomal dominant neurological disorder caused by a polyglutamine (polyQ) repeat expansion in the huntingtin (Htt) protein. The disease is characterized by neurodegeneration and formation of neuronal intracellular inclusions primarily in the striatum and cortex, leading to personality changes, motor impairment, and dementia. To date, the molecular mechanisms that underlie the neurodegenerative process remain to be defined. Development of transgenic Drosophila HD models may facilitate dissection of molecular and cellular pathways that lead to disease pathology and suggest potential strategies for treatment. To explore mutant Htt-mediated mechanisms of neuronal dysfunction, we generated transgenic Drosophila that express the first 548 amino acids of the human Htt gene with either a pathogenic polyglutamine tract of 128 repeats (Htt-Q128) or a nonpathogenic tract of 0 repeats (Htt-QO). Characterization of these transgenic lines indicates formation of cytoplasmic and neuritic Htt aggregates in our Drosophila HD model that sequester other non-nuclear polyQ-containing proteins and block axonal transport.

(cont.) To further explore axonal transport defects in Huntington's disease, we generated Drosophila transgenic strains expressing 588 aa or exon 1 N-terminal fragments of human huntingtin encoding pathogenic (HttQ138) or nonpathogenic (HttQ15) proteins tagged with mRFP and/or eGFP. These transgenic lines enable in vivo imaging of Htt aggregation and trafficking in live Drosophila, providing a unique resource for tracking Htt in real time. Our findings indicate that expression of mutant Htt may impair axonal transport through both aggregate-dependent and -independent means. Finally, to assay the therapeutic effect of expression of an intracellular antibody (intrabody) against Htt, we generated double transgenic lines coexpressing pathogenic Htt (mRFP-HttQ138) with the V12.3 intrabody. Intrabody expression caused suppression of aggregation in both neuronal and non-neuronal cell types, but failed to rescue mutant Htt-mediated cellular dysfunction. In summary, our Drosophila HD model provides an ideal in vivo system for examination of mutant Htt-mediated cellular defects, particularly impairment of axonal transport, and may facilitate rapid development and validation of potential treatments for Huntington's disease.