Lecture 1 Huntington s Disease

Transcription

1 Lecture 1 Huntington s Disease David Saffen, Ph.D. Principal Investigator Department of Cellular and Genetic Medicine Fudan University, Shanghai, China saffen@fudan.edu.cn

2 Huntington s disease (HD) George Huntington ( ) American physician

3 Characteristics of HD (1) A progressive neurodegenerative disease that causes: 1) movement disorders chorea, motor impersistence, dystonia, rigidity; disturbances in gait and maintenance of posture; fine motor coordination; difficulties with eating and swallowing; slowed saccadic eye movements 2) cognitive difficulties impaired executive functions (e.g., planning & working memory); dementia 3) psychiatric disturbances irritability, apathy, depression, impulse control, obsessive-compulsive disorder, suicidal ideation, mania, psychosis

4 Characteristics of HD (2) Onset of clinical symptoms is usually in middle age (35-44); survival: years after diagnosis; juvenile form also known: Westphal variant Inherited as a dominant gene: 50% of offspring are affected There is no cure; a genetic test is available. Common causes of death include, complications of falls, inanition (exhaustion), dysphagia (starvation), aspiration (choking)

5 Faces of HD Woody Guthrie Arlo Guthrie Nancy Wexler Columbia University John Roder Mount Sinai Hospital

6 Ross CA & Tabriz, Lancet, 2011

7 Degeneration of basal ganglia (striatum = caudate + putamen) in HD HD brain Normal Brain

8 Basal ganglia

9 The basal ganglia and cerebellum regulate movement Cerebral Cortex (motor areas) via thalamus via pons via thalamus Basal Ganglia Cerebellum Motor neurons and interneurons

10 Basal ganglia circuitry Basal ganglia stained for Acetylcholinesterase (coronal section of human brain) ext. =eternal int. = interior p.c. = pars compacta p.r. = pars reticulata

11 Medium spiny projection neurons in the indirect pathway are particularly vulnerable to mhtt; chorea (hyperactivity) may result from hyperactivity of excitatory thalamocortical inputs to the motor cortex due to reduced inhibition of thalamocortical neurons by GPi projection neurons

12 Cortical-basal ganglia loops regulate different types of cortical activities, functioning as automatic transmissions to facilitate the progression from one activity to the next

13 Additional brain areas affected in HD Cerebral cortex. layers 3, 5 and 6 (thinning) Subcortical white matter (loss) CA1 region of hippocampus Thalamus Specific hypothalamic nuclei Amygdala Substantia nigra

14 Histopathological characteristics of HD Decreased cellular staining for nerve fibers, neurofilaments, tubulin and microtubuleassociated protein-2 Cytoplasmic and nuclear inclusions containing mutant huntingtin and polyglutamine Immunofluorescent light micrograph of mhtt aggregates (green) ; mhtt aggregates are also observed in dendrites, dendritic spines and axon terminals.

15 Genetics of HD

16 Prevalence of HD differs among populations worldwide European and European-descent: 5 10 per 100,000 Asian, African and native American populations: 0.5 per 100,000 Founder-effect populations: Lake Maracaibo region of Venezuela Tazmania, Australia; specific areas in Scotland, Wales, Sweden

17 HD disease gene: Huntingtin (HTT) 4p16.3 Encodes a 3144 amino acid protein (HTT) of unknown function. HTT is expressed ubiquitously, but mutant forms containing 40 or more CAG triplets in exon 1 (encoding glutamine) are toxic to neurons, especially medium spiny projection neurons in the striatum (caudate nucleus and putamen). CAG repeat numbers: Normal range: 6-26 Next generation at risk: Incomplete penetrance: Pathogenic: Expansion of repeats occurs more frequently during spermatogenesis compared to oogenesis, so that pathogenic allele are often inherited from fathers. Also, repeats of 40 or more are unstable and tend to increase from generation to generation. This phenomenon explains genetic anticipation : the earlier onset of HD in offspring compared to the parent.

18 Inverse correlations between CAG repeat lengths and age of onset for CAG expansion diseases: Spinocerebellar ataxia (SCA)-1, -2, -3, -6, -7; Spinobulbar muscular atrophy (SBMA) Dentato-rubropallido-luysian atrophy (DRPLA: ATN1 gene) Huntington s disease (HD) Walker FO, 2007

19 Distributions of CAG repeat sizes in normal individuals vary among different populations; the high frequency of long repeats in Western Europeans correlates with the observed higher prevalence of HD in this population Squitieri F et al, 2004

20 Animal models for HD Chemically treated mice and rats quinolinic acid (excitotoxic amino acid) 3-nitropropionic acid (mitochondrial toxin) Genetically engineered mice Double-KO of HTT: embryonic lethal Expression of first exon of mhtt: pathogenic Conditional expression of mhtt: effects reversible Expression of protease-resistant mhtt: protective Expression of aspartate-variants of mhtt: protective Genetically engineered Drosophila and C. elegans

21 Huntingtin protein domain structure and post-translational modifications HEAT repeat unit = 50 aa: Forms two antiparallel alpha-helices hairpins. Units combine to form supercoiled structures with a continuous hydrophobic core. Toxic N-terminal fragments Mediates attachment to membranes Huntingtin localizes primarily to the cytoplasm, but also shuttles into the nucleus; proposed to function as a molecular scaffold. Double KO of HTT is embryonic lethal in mice. Ross CA & Tabriz, Lancet, 2011 Ac = acetylation P = phosphorylation SUMO = small ubiquitin-like modifiers

22 Huntingtin protein binding domains HAP = huntingtin-associated protein = N-terminal membrane-association domain = mediates binding to acidic membrane phospholipids Caviston JP & Holzbaur ELF, 2009

23 Proposed functions of wild-type huntingtin Imarisio S, et al, Biochemical Journal 412, 2008

24 Possible mechanisms to explain genetic dominance of mutant huntingtin Haploinsufficiency Toxic gain-of-function Experimental evidence suggests that the primary pathogenic mechanism is toxic gain-of-function related to CAG expansions Pathogenic effects may begin in early stages of brain development

25 Postulated intracellular pathogenesis of Huntington s disease HAP1 = huntingtin-associated protein 1; ROS = reactive oxygen species PGC1 = peroxisome proliferator-activated receptor, coactivator 1 BDNF = brain-derived neurotrophic factor Ross C and Tabrizi SJ, Lancet, 2011

26 Cellular pathways possibly used as compensatory mechanisms in HD Ross C and Tabrizi SJ, Lancet, 2011

27 Treatment of HD symptoms Movement disorders (chorea): tetrabenazine (a VMAT-inhibitor) haloperidol (antipsychotic; D2 receptor antagonist) clonazepam (anticonvulsant; modulates GABA A receptor) Psychiatric disturbances (psychosis and depression): haloperidol (antipsychotic) fluoxetine, sertraline (SSRIs), nortriptyline (SNRI) VMAT = vesicular monoamine transporter GABA = gamma-aminobutyric acid SSRI = selective serotonin reuptake inhibitor SNRI = serotonin-norepinephrine reuptake inhibitor

28 Research toward new HD therapies Brain Imaging studies Experimental drugs based on cellular studies Genetic screening to identify novel drug targets Transplantation of fetal brain tissue Inhibition of mhtt gene expression

29 MRI in patients with Huntington disease Red = substantial atrophy Yellow = greatest degree of atrophy Estimated years to diagnosis Ross C and Tabrizi SJ, Lancet, 2011

30 Potential targets for HD therapy Wild EJ and Tabrizi SJ, Movement Disorders, 2014

31 Identification of genetic modifier loci for HD age of set and rate of progression Manhattan plot for genetic loci that associate with HD age at onset GeM-HD Consortium, Cell 162, 2015

32 Transplantation of fetal striatal neuroblasts 3d-MRI reconstructions MRI (axial plane) Gallina P et al, Experimental Neurology, FDG-PET (axial plane)

33 Genetic silencing of mhtt gene expression RNAi = RNA inhibition mirna = microrna shrna = short hairpin RNA sirna = short inhibitory Boudreau RL & Davidson BL, 2010

34 Chemically modified oligonucleotides can efficiently block the translation of target proteins using cellular RNAi machinery Yu et al, Cell 150, , 2012

35 Antisense oligonucleotide-mediated Huntingtin Holiday produced sustained improvement of symptoms in mice 2 weeks 8-12 months ASO = antisense oligonucleotide

36 HD in the news: human clinical trial using RNAi approach University College London (Prof. Sarah Tabrizi) and Ionis (ISIS)-Pharmaceuticals (Carlsbad, CA) collaboration

37 References (1) Labbadia J and Morimoto RI, Huntington s disease: underlying mechanisms and emerging concepts, Trends Biochemical Science 38, , 2013 Ross CA and Tabrizi SJ, Hu, Huntington disease: from molecular pathogenesis to clinical treatment, Lancet Neurology 10, 83-98, 2011 Johnson CD and Davidson BL, Huntington s disease: progress toward effective disease-modifying treatments and a cure, Human Molecular Genetics 19, R98-R102, 2010 Carroll, JB et al, Treating the whole body in Huntington s disease, Lancet Neurology 14, , 2015 Wild EJ and Tabrizi SJ, Targets for future clinical trials in Huntington s disease: what s in the pipeline? Movement Disorders 29, 2014 Lee JM et al, Sequence-level analysis of the major European Huntington disease haploptype, American Journal of Human Genetics 97, , 2015

38 References (2) Martin D, et al., Autophagy in Huntington disease and huntingtin in autophagy, Trends in Neuroscience 58, 26-35, 2015 Caviston JP and Holzbaur ELF, Huntingtin as an essential integrator of intracellular vesicular trafficking, Trends in Cell Biology 19, , 2009 GeM-HD Consortium, Identification of genetic factors that modify clinical onset of Huntington s disease, Cell 162, , 2015 Becanovic K et al, A SNP in the HTT promoter alters NF-kB binding and is a bidirectional genetic modifier of Huntington disease, Nature Neuroscience 18, , 2015 Hobbs NZ et al, Onset and Progression of Pathological Atrophy in Huntington disease: a longitudinal MR imaging study, American Journal Neuroradiology 31, , 2010 Gallina P et al, Human striatal neuroblasts develop and build a striatallike structure into the brain of Huntington s disease patients after transplantation, Experimental Neurology 222, 30-41, 2010

39 References (3) Pecho-Vrieseling E et al, Transneuronal propagation of mutant huntingtin contributes to non-cell autonomous pathology in neurons, Nature Neuroscience 17, , 2014 Guo X, et al., Inhibition of mitochondria fragmentation diminishes Huntington s disease associated neurodegeneration, Journal of Clinical Investigation 123, , 2013 Boudreau RL and Davidson BL, RNAi therapeutics for CNS disorders, Brain Research 1338, , 2010 X-H and Yang XW, Huntington Holiday : Progress toward an antisense therapy for Huntington s disease, Neuron 74, , 2012 Aronin N and Moore M, Hunting Down Huntington, The New England Journal of Medicine 367, , 2012 Kordasiewicz HB et al, Sustained therapeutic reversal of Huntington s disease by transient repression of Huntingtin Synthesis, Neuron 74, , 2012

40 Journal Presentations 1. Background Kay C et al. Personalized gene silencing therapeutics for Huntington disease, Clinical Genetics 86, 29-36, Main journal article Alterman JF et al, Hydrophobically modified sirnas silence Huntingtin mrna in primary neurons and mouse brain, Molecular Therapy-Nucleic Acids 4, e266, 2015

41 Internet resources National Institute of Neurological Disorders and Stroke (National Institutes of Health) huntington.htm NIH Hope Through Treatment booklet Huntington Disease Society of America Heredity Disease foundation (Nancy Wexler, President) Huntington s Outreach Project for Education, at Stanford HD Research Crossroads Database

42 Additional slides

43 1. The direct pathway is stimulatory: excitatory inputs from the cortex to putamen are converted into increased excitatory outputs from the thalamus to the cortex Stimulatory pathway

44 2. The indirect pathway (via GPi) is inhibitory: excitatory inputs from the cortex to putamen are converted into reduced excitatory outputs from the thalamus to the cortex Inhibitory pathway GPi = globus pallidus, internal segment

45 3. The indirect (via STN) pathway is inhibitory: excitatory inputs from the cortex to putamen are converted into reduced excitatory outputs from the thalamus to the cortex Inhibitory pathway STN = subthalamic nucleus

46 4. Activation of D1 receptors on MSNs in the putamen by dopamine increases stimulatory inputs from the thalamus to the cortex by activating the direct pathway Stimulatory pathway D1 dopamine receptors Couple to Gs to stimulate The synthesis of camp MSNs = medium spiny neurons

47 5. Activation of D2 receptors on MSNs in the putamen by dopamine increases stimulatory inputs from the thalamus to the cortex by inhibiting the indirect pathway Inhibitory pathway D2 dopamine receptors Couple to Gi/o to inhibit the synthesis of camp

48 6. Medium spiny neurons in the indirect pathway are particularly vulnerable to mhtt; chorea (hyperactivity) may result from hyperactivity of excitatory thalamocortical inputs to the motor cortex due to reduced inhibition of thalamocortical neurons by GPi projection neurons Stimulatory pathway Inhibitory pathway