Oral Presentation 6th Annual Meeting for Australasian Society for Stem Cell Research 2013

Organelle transport is disrupted in Hereditary Spastic Paraplegia patient stem cells (#14)

Gautam Wali 1 , Youngjun Fan 1 , Ratneswary Sutharsan 1 , Carolyn Sue 2 , Alan Mackay-Sim 1
  1. National Centre for Adult Stemcell Research, Eskitis, Griffith University, Brisbane, QLD, Australia
  2. Kolling Institute of Medical Research, Royal North Shore Hospital, University of Sydney, st Leonards, Sydney, NSW, Australia

Hereditary spastic paraplegia (HSP) is a neurodegenerative disorder that leads to progressive gait disturbances with lower limb muscle weakness and spasticity. Mutations in SPAST gene 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. To date there is no drug treatment available for this disorder. We recently described a patient-derived olfactory stem cell model (ONS cells) for SPAST HSP showing significant disease-associated gene expression, including significant dysregulation in microtubule-associated genes. Additionally there was a significant reduction in acetylated alpha-tubulin, indicating a reduction in the stabilised microtubules, observed in Western blots and in quantitative analysis of cell images. Also observed were changes in the intracellular distributions of two organelles, peroxisomes and mitochondria. Intracellular trafficking of organelles uses microtubules and actin networks. Given evidence for the dysregulation of microtubules in HSP patient ONS cells and the altered organelle distributions we hypothesised that the dynamics of intracellular trafficking may be altered in HSP ONS cells. This was assessed by fluorescent labelling of organelles and time-lapse imaging of living cells to quantify time-dependent changes in the organelle trafficking in 10 patient-derived ONS cell lines and 10 ONS cell lines derived from healthy controls. We investigated undifferentiated ONS cells as well as cells that were differentiated into elongated neuron-like cells. The results show that HSP ONS cells have impaired organelle trafficking, with significantly slower speeds of peroxisome movement in patient-derived cells compared to control-derived cells. This difference was much greater in axon-like processes that contained microtubules but not actin. The presence of actin (not found in axons) reduced the disease-associated difference in trafficking, suggesting that patient cells use actin as a compensatory pathway to compensate for the dysfunctional microtubule. This is the first evidence for trafficking deficits in HSP patient-derived cells.