Potentiation of amyotrophic lateral sclerosis (ALS)-associated TDP-43 aggregation by the proteasome-targeting factor, ubiquilin 1.
ABSTRACT TDP-43 (43-kDa TAR DNA-binding domain protein) is a major constituent of ubiquitin-positive cytoplasmic aggregates present in neurons of patients with fronto-temporal lobular dementia and amyotrophic lateral sclerosis (ALS). The pathologic significance of TDP-43 aggregation is not known; however, dominant mutations in TDP-43 cause a subset of ALS cases, suggesting that misfolding and/or altered trafficking of TDP-43 is relevant to the disease process. Here, we show that the presenilin-binding protein ubiquilin 1 (UBQLN) plays a role in TDP-43 aggregation. TDP-43 interacted with UBQLN both in yeast and in vitro, and the carboxyl-terminal ubiquitin-associated domain of UBQLN was both necessary and sufficient for binding to polyubiquitylated forms of TDP-43. Overexpression of UBQLN recruited TDP-43 to detergent-resistant cytoplasmic aggregates that colocalized with the autophagosomal marker, LC3. UBQLN-dependent aggregation required the UBQLN UBA domain, was mediated by non-overlapping regions of TDP-43, and was abrogated by a mutation in UBQLN previously linked to Alzheimer disease. Four ALS-associated alleles of TDP-43 also coaggregated with UBQLN, and the extent of aggregation correlated with in vitro UBQLN binding affinity. Our findings suggest that UBQLN is a polyubiquitin-TDP-43 cochaperone that mediates the autophagosomal delivery and/or proteasome targeting of TDP-43 aggregates.
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ABSTRACT: TDP-43 is a pathological signature protein of neurodegenerative diseases with TDP-43 proteinopathies including FTLD-TDP and ALS-TDP. These TDP-43 proteinopathies are characterized with cytoplasmic insoluble TDP-43(+) aggregates in the diseased cells, the formation of which requires the seeding of TDP-25 fragment generated by caspase cleavage of TDP-43. We have investigated the metabolism and mis-metabolism of TDP-43 in cultured cells and found that the endogenous and exogenously over-expressed TDP-43 are degraded not only by ubiquitin proteasome system (UPS) and macroautophagy (MA), but also by the chaperone-mediated autophagy (CMA) mediated through interaction between Hsc70 and ubiquitinated TDP-43. Furthermore, proteolytic cleavage of TDP-43 by caspase(s) is a necessary intermediate step for degradation of a majority of the TDP-43 protein, with the TDP-25/TDP-35 fragments being the main substrates. Finally, we have determined the threshold level of the TDP-25 fragment that is necessary for formation of the cytosolic TDP-43(+) aggregates in cells containing the full-length TDP-43 at an elevated level close to that found in patients with TDP-43 proteinopathies. A comprehensive model of the metabolism and mis-metabolism of TDP-43 in relation to these findings is presented.Journal of Cell Science 05/2014; 127(14). DOI:10.1242/jcs.136150 · 5.33 Impact Factor
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ABSTRACT: Amyotrophic Lateral Sclerosis (ALS) is the most common adult-onset neurodegenerative disorder characterized by the death of large motor neurons in the cerebral cortex and spinal cord (Tandan and Bradley, 1985). Dysfunction and death of these cell populations lead to progressive muscle weakness, atrophy, fasciculations, spasticity and ultimately, paralysis and death usually within 3 to 5 years after disease onset (Mulder, 1982). The estimated worldwide incidence for this disease is around 2 per 100,000 in the general population and the life-long risk to develop ALS is approximately 1:2000. The disease occurs in sporadic (90%) and familial forms (10%) (Gros-Louis, et al., 2006). With the exception of few FALS cases in which other neurodegenerative disorders can simultaneously occur, FALS and SALS are clinically indistinguishable. To date, mutations in the Cu/Zn superoxide dismutase 1 (SOD1) gene have remained the major known genetic causes associated with ALS. However, the mechanism whereby mutant SOD1 causes specific degeneration of motor neurons remains unclear. Nonetheless, many neuronal death pathways have been revealed through studies with transgenic mice expressing SOD1 mutants. Other vertebrate, invertebrate and in vitro models of ALS have also been described. Here, we will review various animal and cellular models that have been used to study the toxicity of ALS-linked gene mutations and also to investigate pathological hallmarks of the disease.AMYOTROPHIC LATERAL SCLEROSIS, Edited by Martin H Maurer, 01/2012: chapter In Vivo and In Vitro Models to Study Amyotrophic Lateral Sclerosis: pages 81-124; InTech., ISBN: 978-953-307-806-9
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ABSTRACT: TDP-43 nuclear protein is involved in several major neurodegenerative diseases that include frontotemporal lobar degeneration with ubiquitin (FTLD-U) bodies and amyotrophic lateral sclerosis (ALS). As a consequence, the role played by this protein in both normal and diseased cellular metabolism has come under very close scrutiny. In the neuronal tissues of affected individuals TDP-43 undergoes aberrant localization to the cytoplasm to form insoluble aggregates. Furthermore, it is subject to degradation, ubiquitination, and phosphorylation. Understanding the pathways that lead to these changes will be crucial to define the functional role played by this protein in disease. Several recent biochemical and molecular studies have provided new information regarding the potential physiological consequences of these modifications. Moreover, the discovery of TDP-43 mutations associated with disease in a limited number of cases and the data from existing animal models have strengthened the proposed links between this protein and disease. In this review we will discuss the available data regarding the biochemical and functional changes that transform the wild-type endogenous TDP-43 in its pathological form. Furthermore, we will concentrate on examining the potential pathological mechanisms mediated by TDP-43 in different gain- versus loss-of-function scenarios. In the near future, this knowledge will hopefully increase our knowledge on disease progression and development. Moreover, it will allow the design of innovative therapeutic strategies for these pathologies based on the specific molecular defects causing the disease.Advances in genetics 02/2009; 66:1-34. DOI:10.1016/S0065-2660(09)66001-6 · 5.41 Impact Factor