In summary, TARDBP variants may result in clinically and neuropathologically heterogeneous phenotypes linked by a common molecular pathology called TDP-43 proteinopathy.
To test whether nuclear depletion of TDP-43 may contribute to the pathogenesis of AD cases with TDP-43 proteinopathy, we examined the impact of depletion of TDP-43 in populations of neurons vulnerable in AD, and on neurodegeneration in an AD-linked context.
Familial frontotemporal lobar degeneration with transactive response (TAR) DNA-binding protein of 43 kDa (TDP-43) proteinopathy (FTLD-TDP) is most commonly caused by progranulin (GRN) gene mutation.
Neuropathological evaluation of both cases revealed frontotemporal lobar degeneration with TDP-43 proteinopathy type B and selective involvement of upper motor neurons with TDP-43 inclusions.
Thus, activation or restoration of refolding mechanisms may alleviate TDP-43 aggregation in tissues that are uniquely susceptible to TDP-43 proteinopathies.TDP-43 aggregation is linked to various diseases including amyotrophic lateral sclerosis.
In C. elegans, the neurotoxicity and the protein aggregation of TDP-43 were regulated by environmental temperature and heat shock transcriptional factor 1, indicating that a deficiency in protein quality control is a risk factor for TDP-43 proteinopathy.
These results suggest that neurons in the developing forebrain are extremely sensitive to TDP-43 overexpression and that timing of TDP-43 overexpression in transgenic mice must be considered when distinguishing normal roles of TDP-43, particularly as they relate to development, from its pathogenic role in FTLD-TDP and other TDP-43 proteinopathies.
C9orf72-mutation carriers exhibited none or limited <sup>18</sup>F-Flortaucipir retention, indicating that <sup>18</sup>F-Flortaucipir binding in TDP-43 proteinopathies is not a general TDP-43 related phenomenon.
In conclusion, our data show that TDP-43 expression in flies recapitulates several biochemical key features of human TDP-43 proteinopathies, including abnormal phosphorylation on a disease-specific site and processing of the protein.
In the majority of nontauopathy disorders the recently identified TAR DNA-binding protein-43 (TDP-43) is found as the major inclusion protein (TDP-43 proteinopathies), and TDP-43 is also present in motor neuron inclusions of amyotrophic lateral sclerosis.
Factors associated with survival were studied in 84 neuropathologically documented cases of the pre-senile dementia frontotemporal dementia lobar degeneration (FTLD) with transactive response (TAR) DNA-binding protein of 43 kDa (TDP-43) proteinopathy (FTLD-TDP).
These data supports the notion that the functional consequence of nuclear depletion of TDP-43 as determined by cryptic exon incorporation likely occurs as an early event of TDP-43 proteinopathy and may have greater contribution to the pathogenesis of AD than currently appreciated.
We have developed a Caenorhabditis elegans model of TDP-43 proteinopathies to study the cellular, molecular, and genetic underpinnings of TDP-43-mediated neurotoxicity.
Here, after a discussion of stages of TDP-43 proteinopathy during disease progression in various major neurodegenerative diseases, we review previous and most recent studies about the potential pathomechanisms with a particular emphasis on ALS, FTLD, and AD, and discuss the possibility of targeting TDP-43 as a common therapeutic approach to treat neurodegenerative diseases.
Finally, we review current mouse models of TDP-43 and discuss their similarities and potential relevance to human TDP-43 proteinopathies including ALS and FTLD-TDP.
To explore the mechanistic details that result in aberrant accumulation of TDP-43 and to discover potential strategies for therapeutic intervention, we employed a yeast TDP-43 proteinopathy model system.
Altogether, our results suggest that RNA binding is key to the neurodegeneration caused by overexpression of TDP-43, and that abnormalities in RNA processing may be crucial to the pathogenesis of TDP-43 proteinopathy.
Our findings highlight that the phosphatase regulator, GADD34, also functions as a kinase scaffold in response to chronic oxidative stress and recruits CK1ϵ and oxidized TDP-43 to facilitate its phosphorylation, as seen in TDP-43 proteinopathies.
Therapeutic approaches that inhibit SG formation may therefore be effective at suppressing TDP-43-mediated toxicity in patients with ALS and related TDP-43 proteinopathies.
These data suggest that loss of TDP-43 can disrupt the central circuitry of the CNS, opening up identification of alternative therapeutic targets for TDP-43 proteinopathies.
Our work also suggests that decreasing the abundance of neurotoxic TDP-43 species, enhancing degradation or clearance of such TDP-43 derivatives and blocking the spread of the disease phenotype may have therapeutic potential for TDP-43 proteinopathies.