Pleiotropic effects of spastin on neurite growth depending on expression levels

Elena Riano, Monica Martignoni, Giuseppe Mancuso, Daniele Cartelli, Francesca Crippa, Irene Toldo, Gabriele Siciliano, Daniela Di Bella, Franco Taroni, Maria Teresa Bassi, Graziella Cappelletti, Elena I. Rugarli

Research output: Contribution to journalArticlepeer-review

Abstract

Hereditary spastic paraplegia (HSP) is characterized by weakness and spasticity of the lower limbs, owing to degeneration of corticospinal axons. The most common form is due to heterozygous mutations in the SPG4 gene, encoding spastin, a microtubule (MT)-severing protein. Here, we show that neurite growth in immortalized and primary neurons responds in pleiotropic ways to changes in spastin levels. Spastin depletion alters the development of primary hippocampal neurons leading to abnormal neuron morphology, dystrophic neurites, and axonal growth defects. By live imaging with End-Binding Protein 3-Fluorescent Green Protein (EB3-GFP), a MT plus-end tracking protein, we ascertained that the assembly rate of MTs is reduced when spastin is down-regulated. Spastin over-expression at high levels strongly suppresses neurite maintenance, while slight spastin up-regulation using an endogenous promoter enhances neurite branching and elongation. Spastin severing activity is exerted preferentially on stable acetylated and detyrosinated MTs. We further show that SPG4 nonsense or splice site mutations found in hereditary spastic paraplegia patients result in reduced spastin levels, supporting haploinsufficiency as the molecular cause of the disease. Our study reveals that SPG4 is a dosage-sensitive gene, and broadens the understanding of the role of spastin in neurite growth and MT dynamics.

Original languageEnglish
Pages (from-to)1277-1288
Number of pages12
JournalJournal of Neurochemistry
Volume108
Issue number5
DOIs
Publication statusPublished - Mar 2009

Keywords

  • EB3
  • Hereditary spastic paraplegia
  • Microtubule turnover
  • Microtubule- severing
  • Neurite growth

ASJC Scopus subject areas

  • Biochemistry
  • Cellular and Molecular Neuroscience

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