Neuronal microtubule dynamics as a novel target for the parkinsonism producing neurotoxin MPTP

Dysfunction of microtubule system is emerging as a novel contributing factor in Parkinson’s disease (PD). Although tubulin, the protein which makes up microtubules, has been described to be a component of Lewy bodies long time ago (Galloway et al., 1992), only recent evidence indicates that the interaction with and the subsequent dysfunction of the microtubule cytoskeleton could be common to toxins known to cause PD and to proteins mutated in PD. We reported earlier that MPP+, the toxic metabolite of MPTP, binds specifically to tubulin and affects microtubule dynamics by acting as a destabilising factor in vitro (Cappelletti et al., 2005). Our current work is focused on the study of the dynamic behaviour of the microtubular cytoskeleton in NGF-differentiated PC12 cells exposed to MPP+. Here we investigate: i) post-translational modifications occurring on tubulin and correlating with stability of microtubules, and ii) tubulin dynamics in live cells. By immunofluorescence and confocal microscopy analysis we found that MPP+ heavily affects microtubule organization and induces the loss of highly labile microtubules at the neuronal tips. By FRAP (fluorescence recovery after photobleaching) experiments of YFP-tubulin in live PC12 cells we examined tubulin dynamics and found that MPP+ induces a significant reduction of tubulin movement at the neuronal tip and along the axon. Since dynamics is crucial in microtubule biological functions, we hypothesise that the altered dynamic behaviour of microtubules caused by MPP+ could profoundly affect the functionality of neurones and, consequently, represent a novel pathogenetic pathway triggering neuronal cell death.