Drosophila TDP-43 dysfunction in glia and muscle cells cause cytological and behavioural phenotypes that characterize ALS and FTLD

Abstract

Amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) are neurodegenerative disorders that are characterized by cytoplasmic aggregates and nuclear clearance of TAR DNA-binding protein 43 (TDP-43). Studies in Drosophila, zebrafish and mouse demonstrate that the neuronal dysfunction of TDP-43 is causally related to disease formation. However, TDP-43 aggregates are also observed in glia and muscle cells, which are equally affected in ALS and FTLD; yet, it is unclear whether glia- or muscle-specific dysfunction of TDP-43 contributes to pathogenesis. Here, we show that similar to its human homologue, Drosophila TDP-43, Tar DNA-binding protein homologue (TBPH), is expressed in glia and muscle cells. Muscle-specific knockdown of TBPH causes age-related motor abnormalities, whereas muscle-specific gain of function leads to sarcoplasmic aggregates and nuclear TBPH depletion, which is accompanied by behavioural deficits and premature lethality. TBPH dysfunction in glia cells causes age-related motor deficits and premature lethality. In addition, both loss and gain of Drosophila TDP-43 alter mRNA expression levels of the glutamate transporters Excitatory amino acid transporter 1 (EAAT1) and EAAT2. Taken together, our results demonstrate that both loss and gain of TDP-43 function in muscle and glial cells can lead to cytological and behavioural phenotypes in Drosophila that also characterize ALS and FTLD and identify the glutamate transporters EAAT1/2 as potential direct targets of TDP-43 function. These findings suggest that together with neuronal pathology, glial- and muscle-specific TDP-43 dysfunction may directly contribute to the aetiology and progression of TDP-43-related ALS and FTLD.

Drosophila lines with mutant and wild type human TDP-43 replacing the endogenous gene reveals phosphorylation and ubiquitination in mutant lines in the absence of viability or lifespan defects

“…These results showed that most, if not all, neurons expressed hTDP-43, similar to results reported for TBPH expression in the adult CNS [10, 48]. In flies expressing wild type hTDP-43, the majority of the FLAG-TDP-43 signal was located in the nucleus (Fig 4B).…”

Functional complementation in Drosophila to predict the pathogenicity of TARDBP variants: evidence for a loss-of-function mechanism

“…In recent studies, by our own and collaborating laboratories, both loss and gain of TBPH resulted in highly similar phenotypic and transcriptome alterations (Diaper et al, 2013b;Vanden Broeck et al, 2013). A consistent observation throughout these and other reports was that TBPH dysfunction, caused by either increased or decreased levels of TBPH, results in neuronal loss (Diaper et al, 2013a(Diaper et al, , 2013bFeiguin et al, 2009;Lin et al, 2011;Ritson et al, 2010;Vanden Broeck et al, 2013;Wang et al, 2011). In addition, our work suggested that both conditions lead to a specific microtubule-based disruption of ecdysteroid receptor-mediated gene program switching at the pupal to adult transition resulting in apoptosis of bursicon neurons and early adult maturation and wing expansion defects (Vanden Broeck et al, 2013).…”

“…Expression of wild-type human TDP-43 causes retinal degeneration, neuronal death, and axonal loss (Choksi et al, 2014;Estes et al, 2011;Hanson et al, 2010;Li et al, 2010;Miguel et al, 2011;Ritson et al, 2010). A consistent observation is that the severity of wild-type TDP-43 toxicity is strongly dependent on its expression levels (Diaper et al, 2013a(Diaper et al, , 2013bEstes et al, 2011;Feiguin et al, 2009;Gregory et al, 2012;Li et al, 2010Li et al, , 2013bLu et al, 2009;Ritson et al, 2010;Voigt et al, 2010) and RNA-binding properties (Ihara et al, 2013;Voigt et al, 2010). However, when comparing wild-type and ALS-associated TDP-43 mutants results have been inconsistent.…”

Glial cells in amyotrophic lateral sclerosis

“…Differences in transgene expression level and differences in the nature of the mutation and species being studied almost certainly underlie the discrepancies in these studies, and make comparison difficult. In addition, a recent study reported that muscle specific knockdown or overexpression of the Drosophila TDP-43 orthologue TBPH, causes motor abnormalities versus motor deficits with early lethality respectively (Diaper et al, 2013). The authors suggested that changes in the Drosophila orthologues for EAAT1/EAAT2 which are involved in glutamate transport, might underlie the phenotype in both knockdown as well as overexpression models.…”