A novel fly model of TDP-43 proteinopathies: N-terminus sequences combined with the Q/N domain induce protein functional loss and locomotion defects

Transactive response DNA binding protein 43 kDa (TDP-43) is the main protein component of the pathological inclusions observed in neurons of patients affected by different neurodegenerative disorders, including Amyotrophic Lateral Sclerosis (ALS) and Fronto-Temporal Lobar Degeneration (FTLD). The number of studies investigating the molecular mechanisms underlying neurodegeneration are constantly growing however, the role played by TDP-43 in disease onset and progression is still unclear. A fundamental shortcoming that hampers progress is the lack of animal models of aggregation without TDP-43 overexpression. In this manuscript, we have extended our cellular model of aggregation to a transgenic Drosophila line. Our fly model is not based on the overexpression of a wild-type TDP-43 transgene. On the contrary, we engineered a construct that includes only the specific TDP-43 amino acid sequences necessary to trigger aggregate formation and trapping of endogenous dTDP-43 into a non-functional insoluble form. Importantly, the resulting recombinant product lacks of functional RNA recognition motifs (RRMs) thus resulting devoid of specific TDP-43-physiological functions (i.e. splicing regulation ability) that might affect the animal phenotype per se. This novel Drosophila model exhibits an evident degenerative phenotype with reduced life-span and early locomotion defects. Additionally, we show that important proteins involved in neuromuscular junction function, such as syntaxin (SYX), decrease their levels as a consequence of TDP-43/TBPH loss of function implying that the degenerative phenotype is a consequence of TDP-43/TBPH sequestration into the aggregates. Our data lend further support to the role of TDP-43 loss-of-function in the pathogenesis of neurodegenerative disorders. The novel transgenic Drosophila model presented in this study will help to gain further insight into the molecular mechanisms underlying neurodegeneration and will provide a valuable system to test potential therapeutic agents to counteract disease.