Identification and characterization of a pathological TDP-43 variant in amyotrophic lateral sclerosis and frontotemporal lobar degeneration

TAR DNA-binding protein 43 (TDP-43) proteinopathy is a key pathological feature of a majority of amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) cases. One key feature of pathological TDP-43 is the presence of lower molecular weight (MW) C-terminal species of 25 and 35 kDa, the origins of which were unclear. In investigating the mechanism(s) which generate such species, we identified an abnormal TDP-43 splice variant, TDP-43 r.[106_196del], that was upregulated in ALS. TDP-43 r.[106_196del] contains a 91 base pair splicing deletion in exon 2, leading to translation from a downstream methionine and the production of a N-terminally truncated protein of 35 kDa. This protein isoform, herein referred to as TDP-35, resembles the pathological 35 kDa C-terminal species seen in disease. Expression of TDP-35 in cultured cells and primary motor neurons showed that TDP-35 has reduced solubility, cytoplasmic distribution, increased tendency to form aggregates, and the capacity to induce motor neuron death. Generation of a neo-epitope TDP-35 antibody immunolabeled the pathological 35 kDa TDP-43 species in ALS and FTLD tissues as well as pathological inclusions in ALS spinal cords, providing evidence that the 35 kDa TDP-43 species in ALS and FTLD can be generated by aberrant alternative splicing leading to the use of a downstream start codon, Met85. Expressing TDP-35 in transgenic mice led to the development of regionally selective neuropathology that included downregulation of endogenous mouse TDP-43, age-dependent neurodegeneration, and associated neuroinflammation. Furthermore, TDP-35 transgenic mice developed age-dependent non-spatial memory deficits and were impaired in emotional processing, but retained an intact spatial memory, all of which closely resemble the selective cognitive deficits observed in clinical frontotemporal dementia (FTD). To elucidate the underlying disease mechanism, our interactome study that identified TDP-35-interacting proteins pinpointed the mitochondria-associated ER membrane (MAM) as an affected cellular pathway in TDP-35-mediated pathogenicity. More specifically, TDP-35, but not endogenous TDP-43, redistributes to the MAM and this was associated with an increased mitochondrial-ER association and abnormal morphologies of the ER and mitochondria. In summary, the work encompassed by this thesis has uncovered a novel and exciting cellular mechanism underlying TDP-43-mediated pathogenesis in ALS and FTLD.

Department dc:contributor.department

Laboratory Medicine and Pathobiology

Year dc:date.issued

2015

Author dc:creator

• Chiang, Helen Yu-Shan

Advisor dc:contributor.advisor

• Robertson, Janice

• Amyotrophic lateral sclerosis
• Frontotemporal dementia
• Frontotemporal lobar degeneration
• Mitochondria-associated ER membrane
• Neurodegeneration
• Transgenic mouse model

Handle dc:identifier.uri

http://hdl.handle.net/1807/94567

OAI identifier oai:identifier

oai:utoronto.scholaris.ca:1807/94567