Zhuang Z. Han, Canada
Centre for Prions and Protein Folding Diseases, University of Alberta Department of MedicineAuthor Of 1 Presentation
CONDENSED TAU CONFORMERS DISRUPT NUCLEAR TRANSPORT
Abstract
Aims
Germline mutations in the MAPT cause some forms of frontotemporal lobar degeneration (FTLD-MAPT). Mutant tau can promote alternative misfolding pathways engendering divergent tau conforms and representing clinical heterogeneity. The repertoire of tau conformers can include liquid-liquid phase separation (LLPS) under conditions of cell-free molecular crowding. In this study, pathobiology of tau conformers undergoing LLPS were studied in live reporter cells.
Methods
Seed-competent tau associated with a common behavioral variant of frontotemporal dementia were cloned by endpoint dilution; the cells were assayed for viability and biochemical markers of cell death and were also assessed by video microscopy and photobleaching to determine dynamic aspects of aggregate formation.
Results
Tau conformers present in FTLD-MAPT cases and transduced into reporter cells had a high propensity to condense on the nuclear envelope and disrupt nuclear-cytoplasmic transport. Nuclear envelope fluorescent tau signals and small fluorescent inclusions in a stable clonal line behaved as a demixed liquid state under live cell conditions; indicative of LLPS effects, these droplets exhibited spherical morphology, fusion events and recovery from photobleaching. While pathogenic mutations in some proteins can interfere with physiological functions of membrane-less organelles, a disease-causing MAPT mutation perturbed nuclear-cytoplasmic transport by gain-of-function formation of LLPS on the nuclear envelope, this acting as a molecular cue to trigger regulated cell death.
Conclusions
Our findings indicate that within a spectrum of alternative conformers, tau undergoing LLPS is a notably toxic species; demixed tau droplets recruiting on the nuclear envelope hinder nuclear-cytoplasmic transport.