Browsing by Author "Strovas, Timothy J."

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    Pathological phosphorylation of tau and TDP-43 by TTBK1 and TTBK2 drives neurodegeneration
    (BioMed Central, 2018-02-06) Taylor, Laura M.; McMillan, Pamela J.; Liachko, Nicole F.; Strovas, Timothy J.; Ghetti, Bernardino; Bird, Thomas D.; Keene, C. Dirk; Kraemer, Brian C.; Pathology and Laboratory Medicine, School of Medicine
    BACKGROUND: Progressive neuron loss in the frontal and temporal lobes of the cerebral cortex typifies frontotemporal lobar degeneration (FTLD). FTLD sub types are classified on the basis of neuronal aggregated protein deposits, typically containing either aberrantly phosphorylated TDP-43 or tau. Our recent work demonstrated that tau tubulin kinases 1 and 2 (TTBK1/2) robustly phosphorylate TDP-43 and co-localize with phosphorylated TDP-43 in human postmortem neurons from FTLD patients. Both TTBK1 and TTBK2 were initially identified as tau kinases and TTBK1 has been shown to phosphorylate tau epitopes commonly observed in Alzheimer's disease and other tauopathies. METHODS: To further elucidate how TTBK1/2 activity contributes to both TDP-43 and tau phosphorylation in the context of the neurodegeneration seen in FTLD, we examined the consequences of elevated human TTBK1/2 kinase expression in transgenic animal models of disease. RESULTS: We show that C. elegans co-expressing tau/TTBK1 tau/TTBK2, or TDP-43/TTBK1 transgenes in combination exhibit synergistic exacerbation of behavioral abnormalities and increased pathological protein phosphorylation. We also show that C. elegans co-expressing tau/TTBK1 or tau/TTBK2 transgenes in combination exhibit aberrant neuronal architecture and neuron loss. Surprisingly, the TTBK2/TDP-43 transgenic combination showed no exacerbation of TDP-43 proteinopathy related phenotypes. Additionally, we observed elevated TTBK1/2 protein expression in cortical and hippocampal neurons of FTLD-tau and FTLD-TDP cases relative to normal controls. CONCLUSIONS: Our findings suggest a possible etiology for the two most common FTLD subtypes through a kinase activation driven mechanism of neurodegeneration.
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    The phosphatase calcineurin regulates pathological TDP-43 phosphorylation
    (Springer, 2016-10) Liachko, Nicole F.; Saxton, Aleen D.; McMillan, Pamela J.; Strovas, Timothy J.; Currey, Heather N.; Taylor, Laura M.; Wheeler, Jeanna M.; Oblak, Adrian L.; Ghetti, Bernardino; Montine, Thomas J.; Keene, C. Dirk; Raskind, Murray A.; Bird, Thomas D.; Kraemer, Brian C.; Pathology and Laboratory Medicine, School of Medicine
    Detergent insoluble inclusions of TDP-43 protein are hallmarks of the neuropathology in over 90% of amyotrophic lateral sclerosis (ALS) cases and approximately half of frontotemporal dementia (FTLD-TDP) cases. In TDP-43 proteinopathy disorders, lesions containing aggregated TDP-43 protein are extensively post-translationally modified, with phosphorylated TDP-43 (pTDP) being the most consistent and robust marker of pathological TDP-43 deposition. Abnormally phosphorylated TDP-43 has been hypothesized to mediate TDP-43 toxicity in many neurodegenerative disease models. To date several different kinases have been implicated in the genesis of pTDP, but no phosphatases have been shown to reverse pathological TDP-43 phosphorylation. We have identified the phosphatase calcineurin as an enzyme binding to and catalyzing the removal of pathological C-terminal phosphorylation of TDP-43 in vitro. In C. elegans models of TDP-43 proteinopathy, genetic elimination of calcineurin results in accumulation of excess pTDP, exacerbated motor dysfunction, and accelerated neurodegenerative changes. In cultured human cells, treatment with FK506 (tacrolimus), a calcineurin inhibitor, results in accumulation of pTDP species. Lastly, calcineurin co-localizes with pTDP in degenerating areas of the central nervous system in subjects with FTLD-TDP and ALS. Taken together these findings suggest calcineurin acts on pTDP as a phosphatase in neurons. Furthermore, patient treatment with calcineurin inhibitors may have unappreciated adverse neuropathological consequences.
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    The tau tubulin kinases TTBK1/2 promote accumulation of pathological TDP-43
    (PLoS, 2014-12-04) Liachko, Nicole F.; McMillan, Pamela J.; Strovas, Timothy J.; Loomis, Elaine; Greenup, Lynne; Murrell, Jill R.; Ghetti, Bernardino; Raskind, Murray A.; Montine, Thomas J.; Bird, Thomas D.; Leverenz, James B.; Kraemer, Brian C.; Department of Pathology and Laboratory Medicine, IU School of Medicine
    Pathological aggregates of phosphorylated TDP-43 characterize amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD-TDP), two devastating groups of neurodegenerative disease. Kinase hyperactivity may be a consistent feature of ALS and FTLD-TDP, as phosphorylated TDP-43 is not observed in the absence of neurodegeneration. By examining changes in TDP-43 phosphorylation state, we have identified kinases controlling TDP-43 phosphorylation in a C. elegans model of ALS. In this kinome-wide survey, we identified homologs of the tau tubulin kinases 1 and 2 (TTBK1 and TTBK2), which were also identified in a prior screen for kinase modifiers of TDP-43 behavioral phenotypes. Using refined methodology, we demonstrate TTBK1 and TTBK2 directly phosphorylate TDP-43 in vitro and promote TDP-43 phosphorylation in mammalian cultured cells. TTBK1/2 overexpression drives phosphorylation and relocalization of TDP-43 from the nucleus to cytoplasmic inclusions reminiscent of neuropathologic changes in disease states. Furthermore, protein levels of TTBK1 and TTBK2 are increased in frontal cortex of FTLD-TDP patients, and TTBK1 and TTBK2 co-localize with TDP-43 inclusions in ALS spinal cord. These kinases may represent attractive targets for therapeutic intervention for TDP-43 proteinopathies such as ALS and FTLD-TDP.