Aperçu du projet

Subcellular compartmentalization between the nucleus and cytoplasm is primarily governed by two systems; 1) active nucleocytoplasmic transport (NCT) regulated by Ran-GTPase and involving nuclear transport receptors such as Importin β-1, and 2) macromolecular nuclear pore complexes (NPCs), comprised of >30 nucleoporin (Nups) embedded in the nuclear envelope. FG-Nups, the largest family of Nups, line the NPC central channel and create a permeability barrier between the nucleus and cytoplasm. It has been proposed that abnormalities of either system could underlie nuclear depletion and cytoplasmic aggregation of TDP-43; the characteristic pathology of 97% of ALS cases, including sporadic ALS (sALS).

The most commonly known genetic cause of ALS are hexanucleotide repeat expansions in the C9orf72 gene, which induce gain-of-function (GOF) and loss-of-function (LOF) mechanisms. It has been speculated that both

GOF and LOF effects may be required for neurodegeneration. GOF mechanisms have been shown to affect NCT and NPCs, and I have also demonstrated that C9orf72 LOF disrupts NCT and causes mislocalization of Ran-GTPase, Importin β-1 and FG-Nups.

I hypothesize that C9orf72, via its interaction with Ran-GTPase and Importin β-1, has a crucial role in FG-Nup and NPC homeostasis. In this project, I will demonstrate that loss of C9orf72 affects FG-Nup localization, which has two downstream effects: 1) altered abundance and permeability of NPCs, leading to loss of subcellular compartmentalization, and 2) abnormal localization of FG-Nups, which will contribute to TDP-43 mislocalization.

I will confirm these phenotypes in cell lines and primary mouse neurons, before establishing them in a human neuronal model, which retains its age-related signatures. These studies will characterize a novel pathological cascade that contributes to TDP-43 mislocalization in ALS, expanding our knowledge of these pathomechanisms, further establishing the roles of dysfunctional NCT and NPCs in ALS pathogenesis and opening new avenues for therapeutic development.

Chef d'équipe

Philip McGoldrick , University of Toronto