modeling childhood onset myotonic dystrophy n.
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Modeling Childhood-onset Myotonic Dystrophy

Modeling Childhood-onset Myotonic Dystrophy

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Modeling Childhood-onset Myotonic Dystrophy

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  1. Modeling Childhood-onset Myotonic Dystrophy Jordan Gladman Ph.D. PRPR 9/24/2012

  2. Myotonic Dystrophy Type 1 • Autosomal dominant • 1 in 8000 - most common adult muscular dystrophy • Variable age of onset and phenotype • Congenital • Childhood • Adult Common features: • Progressive skeletal muscle loss • Cardiac defects • Smooth muscle dysfunction • Other multisystem effects including cataracts, insulin resistance, mental retardation

  3. Congenital Myotonic Dystrophy • Children often born from mothers with DM1 • Respiratory and swallowing difficulties • moderate to severe intellectual disabilities • cardiomyopathy • Often need extensive neonatal care • Survivors may strengthen somewhat, but ultimately develop a progressive myopathy similar to the more common forms of the disease • Myotonia absent in neonates

  4. Childhood-Onset Myotonic Dystrophy • Milder than congenital myotonic dystrophy but still more severe than Adult DM1 • No parent of origin effect • Unlike congenital myotonic dystrophy individuals with childhood-onset myotonic dystrophy do not have in utero abnormalities, delayed early motor development, and if present only have mild hypotonia or respiratory problems • Childhood-onset DM1 patients usually have myotonia and frequently have mental handicaps such as a decrease in mean IQ and a range of psychosocial difficulties • As patients age they tend to then also develop features seen in adult onset DM1.

  5. Adult Onset Myotonic Dystrophy • Characteristic appearance: • Myotonia • Muscle weakness and wasting • Low IQ/dementia • Cardiac abnormalities • Hypersomnia/fatigue • Multiple endocrinopathies • Gastrointestinal complaints • Cataracts

  6. Disease severity and Repeating numbers (CTG)n DMPK • Disease severity correlated with (CUG)n repeat size. • Age of Onset, Average age of death, disease symptoms

  7. Caused by a CTG expansion in the 3’-UTR of DMPK (CUG)5-37 AUG Stop DMPK RNA AAAA ORF 5’-UTR 3’-UTR mRNA exported and transcribed (CUG)100+ DMPK protein ORF Coiled coil Trans- mem. AAAA LRR Kinase 3’-UTR mRNA Retained in Nucleus

  8. Mouse Models of DM1 • The perfect mouse model, especially to study therapeutics, does not exist • Multiple labs working on addressing this issue • Most efforts are aimed at adult DM1 Goal: Develop a childhood onset mouse model of DM1 that allows therapeutic testing and can be used to better understand DM1

  9. Transgenic Mouse Design rtTA TRANSGENE (Tet-On System) CMV promoter rtTA Dox Dox GFP-DMPK 3’UTR TRANSGENE DMPK 5’UTR 7X TRE 5’UTR GFP DMPK 3’UTR DMPK 1st INTRON Induction of Dox leads to a robust disease phenotype similar to the phenotype seen in patients

  10. Design Birth P P&T P Start induction of the toxic RNA before birth, as early as conception and monitor disease phenotype - Start with the DM5 mice as we have them well characterized - Mate a DM5 +/- who is induced for 1 months with a DM5 -/- - Keep dox present during mating, pregnancy and rearing CHDM1 P&T Adult DM1 weeks 2 4 6 8 16 infancy childhood adolescent adulthood

  11. Generating a Childhood onset DM1 Birth P P A B P&T CHDM1 P&T Adult DM1 weeks 2 4 6 8 16 infancy childhood adolescent adulthood C D

  12. Skeletal muscle pathology present but not as severe as the adult DM1 Control DM1 CHDM1 Adult DM1

  13. Parent of Origin Both sick DM1 sexes produce pups that are equally sick - Like childhood DM1 in humans there does not seem to be a parent of origin effect

  14. Molecular Analysis of CHDM1 mice A WT CHDM1 Cugbp1 Gapdh Mbnl1 -RT +RT Input -RT +RT NTC Beads B IgG EGFP-DM5 UTR CHDM1 Adult DM1 EGFP-DM5 UTR C WT CHDM1

  15. MBNL1 overexpression, a model for therapeutic testing, corrects myotonia MBNL1-EGFP Leg EGFP Leg A C MBNL1-EGFP Mbnl1 B Gapdh CHDM1 CHDM1 D EGFP Mbnl1 EGFP Mbnl1

  16. A Reminder Birth P P A B P&T CHDM1 P&T Adult DM1 weeks 2 4 6 8 16 infancy childhood adolescent adulthood C D

  17. Early presence of pathological levels of toxic RNA leads to a more severe DM1 phenotype, this is independent of repeat length Remember CHDM1 muscle had a milder pathology than adult muscle

  18. Conclusions Future Directions • Expressing the toxic RNA during development leads to a CHDM1 mouse model • This model is more severe than its adult counterpart • It can be used to test therapeutics • Age of onset, independent of repeat length, has an effect on disease phenotype • Complete this work by evaluation more mice • Move into the DM200 mouse mode • Examine neurological phenotype in these mice

  19. Acknowledgements • Dr. Mani S. Mahadevan • Mahua Mandal • Dr. Ramesh Yadava • Dr. Yun Kim • Qing Yu (Jane) • Dr. Erin P. Foff • Dr. Shagufta Rehman Questions?