Abstract
SUMMARYHereditary spastic paraplegia (HSP) leads to progressive gait disturbances with lower limb muscle weakness and spasticity. Mutations in SPAST are a major cause of adult-onset, autosomal-dominant HSP. Spastin, the protein encoded by SPAST, is a microtubule-severing protein that is enriched in the distal axon of corticospinal motor neurons, which degenerate in HSP patients. Animal and cell models have identified functions of spastin and mutated spastin but these models lack the gene dosage, mutation variability and genetic background that characterize patients with the disease. In this study, this genetic variability is encompassed by comparing neural progenitor cells derived from biopsies of the olfactory mucosa from healthy controls with similar cells from HSP patients with SPAST mutations, in order to identify cell functions altered in HSP. Patient-derived cells were similar to control-derived cells in proliferation and multiple metabolic functions but had major dysregulation of gene expression, with 57% of all mRNA transcripts affected, including many associated with microtubule dynamics. Compared to control cells, patient-derived cells had 50% spastin, 50% acetylated α-tubulin and 150% stathmin, a microtubule-destabilizing enzyme. Patient-derived cells were smaller than control cells. They had altered intracellular distributions of peroxisomes and mitochondria and they had slower moving peroxisomes. These results suggest that patient-derived cells might compensate for reduced spastin, but their increased stathmin expression reduced stabilized microtubules and altered organelle trafficking. Sub-nanomolar concentrations of the microtubule-binding drugs, paclitaxel and vinblastine, increased acetylated α-tubulin levels in patient cells to control levels, indicating the utility of this cell model for screening other candidate compounds for drug therapies.
Highlights
Hereditary spastic paraplegia (HSP) is a genetically heterogeneous group of disorders that commonly affect the long fibers of the corticospinal tract and posterior columns in the spinal cord, leading to progressive gait disturbances with muscle weakness and spasticity (Salinas et al, 2008)
The protein encoded by SPAST, is a member of the AAA (ATPases associated with diverse cellular activities) group of proteins, which are involved in cell cycle regulation, protein degradation, organelle biogenesis and vesicle-mediated functions (Roll-Mecak and McNally, 2010)
Compared with cells from healthy controls, cells from patients with HSP had 50% of the amount of spastin, in line with the presence of one normal and one mutated copy of SPAST in patient cells. This was associated with a change in the expression of 57% of the genes in patient cells, including many genes associated with microtubule functions, which were significantly altered in patient cells
Summary
Hereditary spastic paraplegia (HSP) is a genetically heterogeneous group of disorders that commonly affect the long fibers of the corticospinal tract and posterior columns in the spinal cord, leading to progressive gait disturbances with muscle weakness and spasticity (Salinas et al, 2008). The protein encoded by SPAST, is a member of the AAA (ATPases associated with diverse cellular activities) group of proteins, which are involved in cell cycle regulation, protein degradation, organelle biogenesis and vesicle-mediated functions (Roll-Mecak and McNally, 2010). The cellular mechanisms whereby SPAST mutations cause axon degeneration are not understood but spastin mutations cause disrupted axonal transport (McDermott et al, 2003; Molon et al, 2004). Consistent with these findings, Spg mutant mice had gait abnormalities, axonal swellings in cortical axons in vitro and reduced anterograde axonal transport of mitochondria and β-amyloid precursor protein (APP)-containing membrane bound organelles (Kasher et al, 2009). Overexpression of mutated SPAST in HEK293 cells led to increased perinuclear distribution of mitochondria and peroxisomes (McDermott et al, 2003)
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