tetracycline and Huntington-Disease

The nematode Caenorhabditis elegans represents an important research model. Convenient methods for conditional induction of gene expression in this organism are not available. Here we describe tetracycline-dependent ribozymes as versatile RNA-based genetic switches in C. elegans. Ribozyme insertion into the 3'-UTR converts any gene of interest into a tetracycline-inducible gene allowing temporal and, by using tissue-selective promoters, spatial control of expression in all developmental stages of the worm. Using the ribozyme switches we established inducible C. elegans polyglutamine Huntington's disease models exhibiting ligand-controlled polyQ-huntingtin expression, inclusion body formation, and toxicity. Our approach circumvents the complicated expression of regulatory proteins. Moreover, only little coding space is necessary and natural promoters can be utilized. With these advantages tetracycline-dependent ribozymes significantly expand the genetic toolbox for C. elegans.

Topics: Animals; Caenorhabditis elegans; Caenorhabditis elegans Proteins; Huntingtin Protein; Huntington Disease; Peptides; RNA, Catalytic; Tetracycline

Protein-protein interactions play an important role in regulating the expression of huntingtin protein (htt). Expansion of polyglutamine tracts in htt results in neurodegenerative Huntington disease. Huntingtin interacting protein (HIP14) is an important interacting partner of htt and the altered interactions have been proposed to play an important role in disease progression. In the present study, an attempt has been made to explore the potential of several known Huntington inhibitors to inhibit HIP14. The docking studies have resulted in the identification of a novel binding site for these inhibitors distinct from the previously known ankyrin repeat domain. The results have been validated using geometry based docking transformations against the other binding pocket. The specificity of binding has been determined with high values of both accuracy and precision. Nine potential inhibitors obtained after screening belong to three distinct classes of compounds viz, carbohydrates (deoxy-glucose), alcohols (including phenolic scaffold) and tetracycline. The compounds form stable complex with protein exhibiting optimal intermolecular and Gibbs free energy. The hydrogen bonding and hydrophobic interactions predominantly contribute to the stability of these complexes. The present study identifies metoprolol, minocyclines and 18 F fluorodeoxyglucose as the best inhibitors that bind specifically to the new site. Therefore, these compounds can further be exploited for their potential to serve in the diagnosis and treatment of Huntington disease. The quantitative predictions provide a scope for experimental testing in future.

Topics: Acyltransferases; Adaptor Proteins, Signal Transducing; Binding Sites; Enzyme Inhibitors; Fluorodeoxyglucose F18; Humans; Huntingtin Protein; Huntington Disease; Hydrogen Bonding; Metoprolol; Minocycline; Models, Molecular; Nerve Tissue Proteins; Nuclear Proteins; Peptides; Protein Binding; Protein Structure, Tertiary; Tetracycline; Thermodynamics

Huntington's Disease (HD) is an inherited neurological disorder causing movement impairment, personality changes, dementia, and premature death, for which there is currently no effective therapy. The modified tetracycline antibiotic, minocycline, has been reported to ameliorate the disease phenotype in the R6/2 mouse model of HD. Because the tetracyclines have also been reported to inhibit aggregation in other amyloid disorders, we have investigated their ability to inhibit huntingtin aggregation and further explored their efficacy in preclinical mouse trials. We show that tetracyclines are potent inhibitors of huntingtin aggregation in a hippocampal slice culture model of HD at an effective concentration of 30 microM. However, despite achieving tissue levels approaching this concentration by oral treatment of R6/2 mice with minocycline, we observed no clear difference in their behavioral abnormalities, or in aggregate load postmortem. In the light of these new data, we would advise that caution be exercised in proceeding into human clinical trials of minocycline.

Topics: Animals; Anti-Bacterial Agents; Behavior, Animal; Doxycycline; Female; Genotype; Hippocampus; Huntingtin Protein; Huntington Disease; Hyperglycemia; Immunohistochemistry; Male; Mice; Minocycline; Nerve Tissue Proteins; Nuclear Proteins; Organ Culture Techniques; Peptides; Phenotype; Postural Balance; Tetracycline

The ability to overexpress full-length huntingtin or large fragments represents an important challenge to mimic Huntington's pathology and reproduce all stages of the disease in a time frame compatible with rodent life span. In the present study, tetracycline-regulated lentiviral vectors leading to high expression levels were used to accelerate the pathological process. Rats were simultaneously injected with vectors coding for the transactivator and wild type (WT) or mutated huntingtin (TRE-853-19Q/82Q) in the left and right striatum, respectively, and analyzed in the 'on' and 'off' conditions. Overexpression of TRE-853-19Q protein or residual expression of TRE-853-82Q in 'off' condition did not cause any significant neuronal pathology. Overexpressed TRE-853-82Q protein led to proteolytic release of N-terminal htt fragments, nuclear aggregation, and a striatal dysfunction as revealed by decrease of DARPP-32 staining but absence of NeuN down-regulation. The differential effect on the DARPP-32/NeuN neuronal staining was observed as early as 1 month after injection and maintained at 3 months. In contrast, expression of a shorter htt form (htt171-82Q) did not require processing prior formation of nuclear aggregates and caused decrease of both DARPP-32 and NeuN neuronal markers at one month post-injection suggesting that polyQ pathology may be dependent on protein context. Finally, the reversibility of the pathology was assessed. Huntingtin expression was turn 'on' for 1 month and then shut 'off' for 2 months. Recovery of DARPP-32 immunoreactivity and clearance of huntingtin aggregates were observed in animals treated with doxycycline. These results suggest that a tetracycline-regulated system may be particularly attractive to model Huntington's disease and induce early and reversible striatal neuropathology in vivo.

Topics: Animals; Cell Nucleus; Corpus Striatum; Dopamine and cAMP-Regulated Phosphoprotein 32; Doxycycline; Female; Gene Expression Regulation; Genetic Vectors; Humans; Huntingtin Protein; Huntington Disease; Lentivirus; Mutation; Nerve Tissue Proteins; Nuclear Proteins; Phosphoproteins; Rats; Rats, Wistar; Tetracycline

The ability to regulate gene expression constitutes a prerequisite for the development of gene therapy strategies aimed at the treatment of neurologic disorders. In the present work, we used tetracycline (Tet)-regulated lentiviral vectors to investigate the dose-dependent neuroprotective effect of human ciliary neurotrophic factor (CNTF) in the quinolinic acid (QA) model of Huntington's disease (HD). The Tet system was split in two lentiviruses, the first one containing the CNTF or green fluorescent protein (GFP) cDNAs under the control of the Tet-response element (TRE) and a second vector encoding the transactivator (tTA). Preliminary coinfection study demonstrated that 63.8% +/- 2.0% of infected cells contain at least two viral copies. Adult rats were then injected with CNTF- and GFP-expressing viral vectors followed 3 weeks later by an intrastriatal administration of QA. A significant reduction of apomorphine-induced rotations was observed in the CNTF-on group. In contrast, GFP-treated animals or CNTF-off rats displayed an ipsilateral turning behavior in response to apomorphine. A selective sparing of DARPP-32-, choline acetyltransferase (ChAT)-, and NADPH-d-positive neurons was observed in the striatum of CNTF-on rats compared to GFP animals and CNTF-off group. Enzyme-linked immunosorbent assay (ELISA) performed on striatal samples of rats sacrificed at the same time point indicated that this neuroprotective effect was associated with the production of 15.5 +/- 4.7 ng CNTF per milligram of protein whereas the residual CNTF expression in the off state (0.54 +/- 0.02 ng/mg of protein) was not sufficient to protect against QA toxicity. These results establish the proof of principle of neurotrophic factor dosing for neurodegenerative diseases and demonstrate the feasibility of lentiviral-mediated tetracycline-regulated gene transfer in the brain.

Topics: Animals; Brain; Choline O-Acetyltransferase; Ciliary Neurotrophic Factor; Disease Models, Animal; DNA, Complementary; Dose-Response Relationship, Drug; Enzyme-Linked Immunosorbent Assay; Female; Genetic Vectors; Green Fluorescent Proteins; Humans; Huntington Disease; Lentivirus; Luminescent Proteins; Neurons; Quinolinic Acid; Rats; Rats, Wistar; Recombinant Fusion Proteins; Tetracycline

Neuronal intranuclear inclusions are a histopathological hallmark of Huntington's disease. Nevertheless, the precise mechanism by which they are formed and their relevance to neuronal cell death and/or dysfunction remains unclear. We recently generated a conditional mouse model of Huntington's disease (HD94) in which silencing expression of mutated huntingtin led to the disappearance of intranuclear aggregates and amelioration of the behavioral phenotype. Here, we analyze primary striatal neuronal cultures from HD94 mice to explore the dynamics of aggregate formation and reversal, the possible mechanisms involved, and the correlation between aggregates and neuronal death. In parallel, we examine symptomatic adult HD94 mice in similar studies and explored the relationship between aggregate clearance and behavioral reversal. We report that, in culture, aggregate formation and reversal were rapid processes, such that 2 d of transgene expression led to aggregate formation, and 5 d of transgene suppression led to aggregate disappearance. In mice, full reversal of aggregates and intranuclear mutant huntingtin was more rapid than reported previously and preceded the motor recovery by several weeks. Furthermore, the proteasome inhibitor lactacystin inhibited the aggregate clearance observed in culture, thus indicating that aggregate formation is a balance between the rate of huntingtin synthesis and its degradation by the proteasome. Finally, neither expression of the mutant huntingtin nor aggregates compromised the viability of HD94 cultures. This correlated with the lack of cell death in symptomatic HD94 mice, thus demonstrating that neuronal dysfunction, and not cell loss, triggered by mutant huntingtin underlies symptomatology.

Topics: Acetylcysteine; Animals; Behavior, Animal; Cell Death; Cell Survival; Cells, Cultured; Corpus Striatum; Cysteine Endopeptidases; Disease Models, Animal; Gene Silencing; Genes, Dominant; Huntingtin Protein; Huntington Disease; Locomotion; Macromolecular Substances; Mice; Mice, Neurologic Mutants; Multienzyme Complexes; Nerve Tissue Proteins; Neurons; Nuclear Proteins; Phenotype; Proteasome Endopeptidase Complex; Remission Induction; Tetracycline; Transgenes; Ubiquitin