The hereditary spastic paraplegia gene, spastin, regulates microtubule stability to modulate synaptic structure and function.
BACKGROUND
Hereditary Spastic Paraplegia (HSP) is a devastating neurological disease causing spastic weakness of the lower extremities and eventual axonal degeneration. Over 20 genes have been linked to HSP in humans; however, mutations in one gene, spastin (SPG4), are the cause of >40% of all cases. Spastin is a member of the ATPases associated with diverse cellular activities (AAA) protein family, and contains a microtubule interacting and organelle transport (MIT) domain. Previous work in cell culture has proposed a role for Spastin in regulating microtubules.


RESULTS
Employing Drosophila transgenic methods for overexpression and RNA interference (RNAi), we have investigated the role of Spastin in vivo. We show that Drosophila Spastin (D-Spastin) is enriched in axons and synaptic connections. At neuromuscular junctions (NMJ), Dspastin RNAi causes morphological undergrowth and reduced synaptic area. Moreover, Dspastin overexpression reduces synaptic strength, whereas Dspastin RNAi elevates synaptic currents. By using antibodies against posttranslationally modified alpha-Tubulin, we find that Dspastin regulates microtubule stability. Functional synaptic defects caused by Dspastin RNAi and overexpression were pharmacologically alleviated by agents that destabilize and stabilize microtubules, respectively.


CONCLUSIONS
Loss of Dspastin in Drosophila causes an aberrantly stabilized microtubule cytoskeleton in neurons and defects in synaptic growth and neurotransmission. These in vivo data strongly support previous reports, providing a probable cause for the neuronal dysfunction in spastin-linked HSP disease. The role of Spastin in regulating neuronal microtubule stability suggests therapeutic targets for HSP treatment and may provide insight into neurological disorders linked to microtubule dysfunction.
Trotta
Nick
N
Department of Biological Sciences, Vanderbilt Kennedy Center for Research on Human Development, Vanderbilt University, Nashville, TN 37235, USA.
Orso
Genny
G
Rossetto
Maria Giovanna
MG
Daga
Andrea
A
Broadie
Kendal
K
D000818:Animals; D030801:Animals, Genetically Modified; D017931:DNA Primers; D004195:Disease Models, Animal; D004330:Drosophila; D004594:Electrophysiology; D005786:Gene Expression Regulation; D006801:Humans; D007150:Immunohistochemistry; D008870:Microtubules / Q000378:metabolism*; D009469:Neuromuscular Junction / Q000378:metabolism; D034622:RNA Interference; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015419:Spastic Paraplegia, Hereditary / Q000235:genetics*; D013569:Synapses / Q000378:metabolism / Q000502:physiology*
D017931:DNA Primers