Les organismes-modèles pour l’étudedes dystrophies musculaires

mRNA Regulation and Development

Martine Simonelig

Development of a Drosophila model of the human oculopharyngeal muscular dystrophy or OPMD

Translational control of maternal mRNAs during early development in Drosophila

Aymeric Chartier, Nicolas Barbezier, Cédric Soler

Isabelle Busseau, Catherine Papin, Christel Rouget, Willy Joly, Bridlin Barckmann,Anne-Cécile Meunier

mRNA Regulation and Development

Martine Simonelig

Les organismes-modèles:

Quelles maladies génétiques humaines?Cancer, retards mentaux, épilepsie, diabète, infection (immunité innée)...

Maladies neurodégénératives / Dystrophies musculaires

rapidité génétique/outils génétiques très développés

génétiquemammifère/plus proche de l’homme

Les organismes-modèles pour l’étude des maladiesgénétiques humaines

levure

drosophile (Drosophila melanogaster)

nématode (Caenorhabditis elegans)

souris

crible à grande échelle (molécules)

Conservation des génomes et des fonctions moléculaires entre l’homme et les organismes modèles

Gènes impliqués dans des maladies génétiques humaines

77% ont un homologue chez la drosophile

65% ont un homologue chez le nématode

By loss of function of the gene homologous to the human gene mutated in the disease

e.g.: - Fragile X syndrome (mutation in FMR1: fragile X mental retardation 1) (Drosophila model) - Spinal muscular atrophy (mutation in SMN: survival motor neuron) (Drosophila model)

- Duchenne Muscular Dystrophy ( mutation in dystrophin) (C. elegans model)

Two ways to produce an animal model of a human genetic disease

recessive genetic disease due to a loss of function mutationrequires that the animal model has the homologous gene affected in the disease

By expressing or overexpressing the human mutant protein in the animal

Neurodegenerative diseases / Oculopharyngeal Muscular Dystrophy

dominant genetic disease due to a gain of function mutationdoes not require the homologous gene in the animal model

Gal4 Fly stock X UAS Fly stock

UAS/Gal4 embryos, larvae or flies

GAL4

Genomic regulation sequence

cDNA-XUAS polyA

Gal4 drivers: ubiquitous, neurons, photoreceptor neurons, muscles ...

cDNA-XUAS

GAL4

polyA

expression

GAL4

Genomic regulation sequence

Inducible expression in Drosophila using the UAS/Gal4 system (Brand & Perrimon 1993)

Drosophila models of human neurodegenerative diseases

Polyglutamine diseases:at least 9 neurodegenerative diseases due to expansion of a polyglutamine tract indifferent proteins: normal up to 35 glutamines / disease when 40 or more glutamines.- Huntington's (huntingtin)- Spinocerebellar ataxia type 3 (SCA3)- Spinocerebellar ataxia type 1 (ataxin 1)

Non-polyglutamine diseases:- Parkinson's (-synuclein)- Alzheimer's / Tauopathy (tau)

Since 1998Models of neurodegenerative diseasesBy expressing in Drosophila the human mutant protein

Pathology: neurodegeneration, late onset, progressive memory loss, cognitive deficits, movement disorders

At the cellular level: the mutant protein forms insoluble aggregates (protein conformation diseases)

Marsh & Thompson, 2004

Expression of polyglutamine expanded protein in the eye:photoreceptor neurons (GMR-Gal4)

polyglutamine diseases:- Neuronal degeneration- Late onset- Progressive- Onset and severity correlate with polyglutamine repeat length- Early death- Cellular level:Nuclear inclusions (NI) containing the polyglutamine-expanded mutant protein, or the polyglutamine alone with a tag- Control: no NI with 20/27 glutamines.

non-polyglutamine diseases:- Parkinson's: adult onset loss of dopaminergic neurons, filamentous inclusions in neurons (with -synuclein), locomotor dysfunction.

- Alzheimer's / Tauopathy: adult onset, progressive neurodegeneration, accumulation of abnormal tau.

Features of the human diseases that are conserved in Drosophila:

Phenotypes reproduced in Drosophila with 127 glutamines out of the context of a protein: The polyglutamine is intrinsically toxic

Identify suppressor genes of these human diseases in Drosophila,by a genetic approach

to understand molecular mechanisms of the diseaseidentify molecular pathways of the disease

to find targets for possible therapies

identify genes involved in the disease process without a priopri of the molecular function

Mutagenesis, collections of mutants loss of function mutants: chemical mutagenesis, P element inserted randomly in the genome

gain of fonction mutants: P-UAS element inserted randomly in the genome

ScreenSuppressors or enhancers of the phenotype induced by expression of the polyglutaminein the eye (by the UAS/Gal4 system)

phenotype enhancersuppressor

UAS-polyQ/+;GMR-Gal4/+

UAS-polyQ/+;GMR-Gal4/+

UAS-polyQ/+;GMR-Gal4/+

UAS

P-UAS element

gene X

expression

Identify suppressor genes of these human diseases in Drosophila,by a genetic approach (genetic screens)

Suppressor genes of neurodegenerative diseases in Drosophila(by genetic screens)

1999/2007: genetic screens or test of candidates

Suppressors of polyglutamine diseases: increased expression of- P35: viral anti-apoptotic apoptosis

- Chaperone proteins/or pathway:HSP70 (human HSPA1L)HSP40/ HDJ1 (chaperone-related J domain)dTRP2 (chaperone-related J domain)HS response factorDnaJ1 64EF (chaperone)

- ubiquitin/proteasome pathway

- proteins involved in autophagy (protein degradation by lysosomes)

- CBP: histone acetyltransferasesequestration of transcription factors/or histone acetyltransferase by the poly-Q expanded protein

Suppressors of Parkinson’s: increased expression of HSP70

Protein foldingProtein degradation

Major pathways:(N. Bonini, 2007)

1) Prevention of aggregation

2) Protein folding: HSP70 pathway

3) Transcription regulation: inhibitors of histone deacetylase

New approaches to find suppressors of these diseasesin the Drosophila model, based on the cellular pathwaysidentified by genetics

New approaches to find suppressors of these diseasesin the Drosophila model, based on the cellular pathwaysidentified by genetics from 2002/2003

Design of suppressor peptides: for Huntington’s disease

prevents polyglutamine aggregationsuppresses the phenotype in vivo in the Drosophila model (L. Thompson, 2002)

Test of chemical or pharmacological compounds as suppressors- Congo red and cystamine: suppressors in vivo for polyglutamine disease (L. Thompson, 2003)

25Q 25Q

17 aahuntingtin

spacer helice (54 to 67 aa)

myc

Screen of suppressor peptides and test in vivo in the Drosophila model:Polyglutamine Binding Peptide (QBP1) for polyglutamine diseasessuppresses neurodegeneration and early death (T. Toda, 2003)

1) Prevention of aggregation

Chemical compounds as suppressors

3) Transcription regulation: inhibitors of histone deacetylase

2) Protein folding: HSP70 pathway

New approaches to find suppressors of these diseasesin the Drosophila model 2002/2003

Pharmacological compounds as suppressorsGeldanamycin: antibiotic, increases the level of HSP70suppressor in vivo of Parkinson’s disease (N. Bonini, 2002)

Butyrate and SAHA: inhibitors of histone deacetylasessuppressors in vivo of Huntington’s disease (L. Thompson 2001, Min 2003)

From Drosophila models to mouse models

Marsh &Thompson, 2004

New approaches to find suppressors: the Drosophila model as an in vivo test.High throughput test of molecules in Drosophila 2005/2006

Companies that test large collections of molecules (EnVivo Pharmaceuticals)-molecules are delivered in the food from the embryonic stage/ change of the food every day - e.g. 20 000 flies per week of a disease model possible test of collections up to 30 000 molecules

Hits (or positive): their effects are analysed at cellular and molecular levels, for validation

Test of the hits in mouse models

2006: at least one molecule in clinical trials in patients, identified thanksto a Drosophila model, in an academic lab (R. Cagan), for a cancer: Multiple Endocrine Neoplasia Type 2. The molecule stops metastasis.

New approaches to find suppressors: the Drosophila model as an in vivo test.Test of intrabodies in Drosophila 2005

IgG

VH

VL

Ag

Variable Light

Variable Heavy

linker

Intrabodies :single chaine antibodies expressed within the cell

- screen for intrabodies specific to Huntingtin (yeast phage display)

-optimisation of the intrabody(test in yeast model)

In Drosophila (Messer 2005):Cloning of intrabody DNA downstream of UAS: expression with Gal4, whithin the cells expressing polyQ-exon1Huntingtin:

UAS

expression

intrabody

Reduction of neurodegeneration and formation of aggregatesIncrease survival to adulthood (23% without intrabody/ 100% with intrabody)

Models for Muscular Dystrophies:in Drosophila or C. elegans

Duchenne muscularDystrophy

Myotonic Dystrophy

Spinal muscular atrophy(SMA)

dystrophin mutant

Drosophila C. elegans

yes

survival motor neuron(SMN) mutant

yes

yes

yes

no

Oculopharyngealmuscular Dystrophy

expression of the human mutant protein

yes yes

expression of non-coding CUG repeats

yes

Duchenne Muscular Dystrophy

Loss of function mutation / recessive disease / X-linked

The most common of muscular dystrophies: 1 boy / 3500

Extremely severe: wheelchair-bound at 12, respiratory failure in early twenties

No treatment

Mutation in the gene encoding Dystrophin (very big gene: 2.9 megabases, 79 exons) (sporadic cases: 1/10 000 sperm or eggs)

Most DMD patients lack the Dystrophin

Dystrophin: 3685 AA protein present in skeletal and cardiac muscles

Duchenne Muscular Dystrophy

Dystrophin bridges extracellular matrix and cytoskeleton inside muscle cells

DGC:dystrophin glycoproteincomplex

Nowak & Davis 2004

Duchenne Muscular DystrophyPotential mechanisms contributing to muscle degeneration in DMD:

- Structural role of dystrophin: degradation of proteins of the Dystrophin-Glycoprotein complex in the absence of dystrophin: decrease in the amounts of the complex: Muscle fibers are more sensitive to mechanical damage: leads to muscle degeneration, chronic inflammation, susceptibility to oxidative stress

- inappropriate location of membrane components leading to alteration of ionic canals

- Role of the Dystrophin-Glycoprotein complex in the intracellular nitric oxide (NO) pathway: loss of association between DGC and the nitric oxide synthase (nNOS) leads to impaired nitric oxide production: role of NO in epigenetic regulations through the regulation of HDAC (histone deacethylase).

Nitric oxide and HDAC have a role in DMD: rescue of nNOS expression ameliorates the dystrophic phenotype in the mouse model of DMD

deacethylase inhibitors are beneficial in the mouse model

Animal models for Duchenne Muscular Dystrophy

No cell model or in vitro model:need for a model useful for high-throughput screens

Mouse model: mutation in the gene encoding dystrophin (stop codon in exon 23): mdx mice mild myopathy

Possible models in Drosophila or C. elegans: Dystrophin and the proteins of the DGC complex are conserved in Drosophila and C. elegans / in smaller number(dystrobrevin, sarcoglycans, syntrophins, dystroglycan, sarcospan)

muscles with a sarcomeric structure and protein composition similar to mammalian striated muscles (but no satellite cells, and no fusion in C. elegans)

C. elegans model of Duchenne muscular dystrophy

mutation in the Ce gene encoding dystrophin: dys-1 (null mutation)phenotype: hyperactive locomotion, muscular hypercontraction, BUT... no muscle degeneration

Double mutant in dys-1 and MyoD (myogenic factor)

dys-1-; CeMyoDts : locomotion defects / adult onset / progressive over time

(L. Ségalat, Lyon)

CeMyoDts dys-1- dys-1-; CeMyoDts

WT dys-1-; CeMyoDts

dyc-1 overexpression

protein homologous to arat protein interacting withneural nitric oxide synthasenNOS

+

uncoordinated suppressor

dys-1-; CeMyoDtsWT

phalloidin staining: visualization of actine fibers

dys-1-; CeMyoDts

+ prednisone(0.5 mg/ml / steroid)

C. elegans model of Duchenne muscular dystrophy:analysis of muscle structure (optic microscopy)

Identification of prednisone from a test screen of 100 molecules (reduces muscle degeneration)

Prednisone is used as a treatment for DMD boys

Identification of this molecule in the C. elegans model in a blind screen indicates that this model can be used for the search of active molecules

active molecule

Suppressors of Duchenne muscular dystrophyin the C. elegans model

Test of existing pharmaceutical compounds in the DMD C. elegans model :Serotonin (neuro-hormone) is a suppressor of muscle degenerationReduction of serotonin levels leads to muscle degeneration in the CeMyoD mutant

A function of serotonin in musclesSerotonin is beneficial to striated muscles (Ségalat 2006)

- Mutation in the chn-1 gene decreases muscle degeneration in the DMD C. elegans model CHN-1 is the homologue of human CHIP: interacts with E3 ubiquitin ligase and E4 enzyme (ubiquitin-conjugating factor) - A proteasome inhibitor has the same effect (MG132)

Implication of the ubiquitin/proteasome pathway in DMD(Baumeister 2007)

Exon skipping therapy in Duchenne muscular dystrophy

Knowledge of the disease in man, at the molecular levelTest in the mouse model, mdx mouse

(Garcia, Danos /Généthon 2004)

U7 snRNAnonspliceosomal snRNAmodified to be incorporated in spliceosomeused to deliver antisense sequenceduring splicing

antisense RNA

ST

OP

in AAV vector: injected in mice, intramuscular or intra-arterial(adeno-associated virus)

Restoration of dystrophin production

Muscle regenerationRestoration of musclecapacity

Stable over timepossibly permanent

dystrophinspectrin-like repeats

Drosophila model of oculopharyngeal muscular dystrophy: OPMD

Aymeric Chartier, Béatrice Benoit & Martine Simonelig.A Drosophila model of oculopharyngeal muscular dystrophy reveals intrinsic toxicity of PABPN1. EMBO J. 2006, 25, 2253-2262.

Chartier Aymeric, Raz Vered, Sterrenburg Ellen, Verrips Theo C., van der Maarel Silvère & Simonelig Martine. Prevention of oculopharyngeal muscular dystrophy by muscular expression of Llama single-chain intrabodies in vivo. Human Molecular Genetics 2009, 18, 1849-1859.

Contact: Martine.Simonelig@igh.cnrs.fr

http://www.igh.cnrs.fr/equip/Martine.Simonelig/