Mechanisms of Neurological Manifestations in Myotonic Dystrophy Type 1

About This Grant

Project Summary Myotonic Dystrophy Type 1 (DM1) is a progressive neuromuscular disorder affecting 1 in 8,500 individuals. Although primarily characterized by skeletal muscle dysfunction, over 80% of DM1 patients exhibit neurological manifestations, including cognitive impairment, autistic features, ADHD, depression, anxiety, sleep disturbances and excessive daytime sleepiness. DM1 is caused by a CTG repeat expansion in the 3' untranslated region of the DMPK gene. The mutant RNA transcripts containing expanded CUG repeats form nuclear RNA foci and sequester the Muscleblind-Like (MBNL) family of RNA-binding proteins, leading to their functional depletion and the dysregulation of RNA processing. Studies in skeletal muscle have revealed that characteristic DM1 symptoms, including myotonia and muscle weakness, result from mis-splicing of MBNL target genes such as the chloride channel ClC-1 and calcium channel Cav1.1. While knockout of the MBNL paralogs, MBNL1 and MBNL2, reproduces DM1-like neurological phenotypes in mice, the molecular mechanisms underlying DM1 brain pathology remain unclear, particularly whether these symptoms also stem from the dysregulation of alternative splicing or other MBNL-dependent processes such as RNA localization and stability. To investigate the neurological manifestations of DM1, I generated a novel DM1 brain mouse model, CUG960, which expresses 960 interrupted CUG repeats throughout the central nervous system (CNS). This model recapitulates key DM1 features, including nuclear RNA foci, MBNL sequestration, reduced brain weight, and behavioral abnormalities. The CUG960 mouse model is doxycycline-repressible, enabling temporal control of CUG repeat expression for rescue studies. Despite robust physiological and behavioral deficits, CUG960 mice show only modest splicing changes, suggesting additional mechanisms may contribute to the CNS pathology. The goals of this proposal are threefold. First, I will perform behavioral assays and sleep studies on the CUG960 mouse model to determine the short and long-term effects of CUG repeat RNA expression in the CNS and identify brain regions most vulnerable to CUG repeat toxicity. Second, using the CUG960 mouse model, I will identify changes in alternative splicing, gene expression, and RNA localization and determine the relative contributions of nuclear and cytoplasmic MBNL loss-of-function through rescue experiments. Third, I will use the doxycycline-repressible feature of the CUG960 mice to suppress CUG repeat expression at different timepoints to determine if the neurological DM1 symptoms are reversible and define the critical therapeutic time window. Completion of this proposal will establish the direct effects of CUG repeat RNA expression in the CNS, elucidate the molecular mechanisms driving the neurological manifestations in DM1, and determine whether and when these phenotypes can be reversed. These findings will provide crucial insights into the mechanisms underlying DM1 brain disease and inform the development of therapeutic approaches.