The phosphatase calcineurin regulates pathological TDP-43 phosphorylation

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

Genetic analysis of rhythmic behavior in C. elegans

Thesis (Ph. D.)--University of Washington, 2005.How do genetic networks control the behavior of an organism? To approach this problem, I chose the model organism C. elegans, a simple metazoan that displays several easily observed behavioral programs such as locomotion, egg-laying, and defecation. C. elegans defecation is a rhythmic behavior regulated by the intestine, and consists of three muscle contractions occurring at regular intervals. My results suggest that chemosensation and external mechanosensation play no role in regulating the defecation cycle. However, conditions affecting the metabolism of the animal (e.g. starvation, poor food quality, defects in genes important for basic cellular functions) lead to alterations in the cycle period. In addition, I present evidence suggesting that the amount of food consumed is sensed by internal mechanosensors.Several mutants had been previously isolated for their effects on the defecation rhythm, but in most cases their molecular identity was unknown. One of these mutants is dec-2(sa89), which causes a long defecation period. My work reveals that dec-2 encodes a novel secreted protein expressed exclusively in the hypodermis, in contrast to other Dec genes, all of which function in the intestine.dec-2(sa89) is allelic to osm-7(n1515), and both mutations cause resistance to osmotic stress. I show that adaptation to osmotic stress alters the defecation behavior of wild-type C. elegans to the same extent observed in osm-7/dec-2 mutants. C. elegans adapts to osmotic stress by increasing glycerol production, and I find that osm-7/dec-2 mutants have high basal levels of glycerol in the absence of osmotic stress. I have also identified several other genes with mutant phenotypes similar to that of osm-7/dec-2 . These include osm-11, a gene I identified based on homology to osm-7/dec-2, and three collagen genes required for the formation of a substructure in the cuticle.These results lead me to propose a model in which osm-7 and osm-11 are secreted from the hypodermis, interact with the cuticle, and function as negative regulators of the response to osmotic stress. This hypothesis reveals interesting parallels with osmotic stress response in yeast, and future work on these mutants should provide insight into general mechanisms of stress resistance

DOPA Decarboxylase Modulates Tau Toxicity

BACKGROUND: The microtubule-associated protein tau accumulates into toxic aggregates in multiple neurodegenerative diseases. We found previously that loss of D2-family dopamine receptors ameliorated tauopathy in multiple models including a Caenorhabditis elegans model of tauopathy. METHODS: To better understand how loss of D2-family dopamine receptors can ameliorate tau toxicity, we screened a collection of C. elegans mutations in dopamine-related genes (n = 45) for changes in tau transgene–induced behavioral defects. These included many genes responsible for dopamine synthesis, metabolism, and signaling downstream of the D2 receptors. RESULTS: We identified one dopamine synthesis gene, DOPA decarboxylase (DDC), as a suppressor of tau toxicity in tau transgenic worms. Loss of the C. elegans DDC gene, bas-1, ameliorated the behavioral deficits of tau transgenic worms, reduced phosphorylated and detergent-insoluble tau accumulation, and reduced tau-mediated neuron loss. Loss of function in other genes in the dopamine and serotonin synthesis pathways did not alter tau-induced toxicity; however, their function is required for the suppression of tau toxicity by bas-1. Additional loss of D2-family dopamine receptors did not synergize with bas-1 suppression of tauopathy phenotypes. CONCLUSIONS: Loss of the DDC bas-1 reduced tau-induced toxicity in a C. elegans model of tauopathy, while loss of no other dopamine or serotonin synthesis genes tested had this effect. Because loss of activity upstream of DDC could reduce suppression of tau by DDC, this suggests the possibility that loss of DDC suppresses tau via the combined accumulation of dopamine precursor levodopa and serotonin precursor 5-hydroxytryptophan.This work was supported by Department of Veterans Affairs Merit Review Grant No. 1147891 (to BCK), Bright Focus Foundation Grant No. A2014438S (BCK), and National Institutes of Health National Institute of General Medical Sciences Medical Genetics Postdoctoral Training Program Grant No. T32-GM-007454 (to RLK)

DOPA Decarboxylase Modulates Tau Toxicity

BACKGROUND: The microtubule-associated protein tau accumulates into toxic aggregates in multiple neurodegenerative diseases. We found previously that loss of D2-family dopamine receptors ameliorated tauopathy in multiple models including a Caenorhabditis elegans model of tauopathy. METHODS: To better understand how loss of D2-family dopamine receptors can ameliorate tau toxicity, we screened a collection of C. elegans mutations in dopamine-related genes (n = 45) for changes in tau transgene–induced behavioral defects. These included many genes responsible for dopamine synthesis, metabolism, and signaling downstream of the D2 receptors. RESULTS: We identified one dopamine synthesis gene, DOPA decarboxylase (DDC), as a suppressor of tau toxicity in tau transgenic worms. Loss of the C. elegans DDC gene, bas-1, ameliorated the behavioral deficits of tau transgenic worms, reduced phosphorylated and detergent-insoluble tau accumulation, and reduced tau-mediated neuron loss. Loss of function in other genes in the dopamine and serotonin synthesis pathways did not alter tau-induced toxicity; however, their function is required for the suppression of tau toxicity by bas-1. Additional loss of D2-family dopamine receptors did not synergize with bas-1 suppression of tauopathy phenotypes. CONCLUSIONS: Loss of the DDC bas-1 reduced tau-induced toxicity in a C. elegans model of tauopathy, while loss of no other dopamine or serotonin synthesis genes tested had this effect. Because loss of activity upstream of DDC could reduce suppression of tau by DDC, this suggests the possibility that loss of DDC suppresses tau via the combined accumulation of dopamine precursor levodopa and serotonin precursor 5-hydroxytryptophan.This work was supported by Department of Veterans Affairs Merit Review Grant No. 1147891 (to BCK), Bright Focus Foundation Grant No. A2014438S (BCK), and National Institutes of Health National Institute of General Medical Sciences Medical Genetics Postdoctoral Training Program Grant No. T32-GM-007454 (to RLK)