Understanding the molecular bases of the axonopathy in HSP
Compelling evidences suggest that defective axon trafficking may be a common mechanism to several neurodegenerative diseases including Hereditary Spastic Paraplegias (HSPs). HSPs are clinically and genetically heterogeneous diseases characterized by a degeneration of corticospinal tract axons, which leads to a bilateral, symmetrical, slowly-progressive spasticity and weakness of the lower extremities. Mutations in the SPG4 gene, encoding spastin, account for approximately 40% of the familial and 6-15% of the sporadic cases with autosomal dominant HSP. Spastin is a member of the AAA ATPase protein family which severs microtubules through an ATP-dependent mechanism. This suggests spastin specific role in the regulation of microtubule dynamics and indeed in related membrane traffic. Interestingly recent results revealed that microtubule-targeting drugs at nanomolar concentrations prevent axonal swelling, the prominent axonal abnormality observed, in SPG4-deficient mice and SPG4 affected patients.
Spastin also interacts with different molecular partners. These interactions partially explain the implication of spastin in cellular functions such as cytokinesis, ER shaping and endosomal traffic. We recently carried out a two-hybrid screen to identify potential new molecular partners of spastin. The preliminary results are interesting and they might clarify the known cellular functions of spastin but also unravel yet unknown functions for spastin.
The aims of our research are:
i) to obtain a qualitative and quantitative view on the role of spastin in the regulation of microtubule dynamics and intracellular axonal trafficking, two parameters that notably participate to axon growth and maintenance and are likely linked to axonal swelling;
ii) to decipher the mechanism of axonal swelling rescue by microtubule-targeting drugs;
iii) to characterize the interaction and the role of the new molecular partners of spastin identified by two-hybrid screen.
Cell line culture; primary neuronal culture; iPSCs; live cell video imaging; immunofluorescence; post-acquisition image processing and analysis; molecular biology; biochemistry.
Andrea BURGO, PhD
Clément PLAUD, PhD student
Vandana JOSHI, IE
I-STEM (Genopole), Evry, France
Brain and Spine Institut (ICM), Paris, France