RNA toxicity and neuroglial miscommunication in myotonic dystrophy brains – DM_Neuroglia

Myotonic dystrophy type 1 (DM1) is the most common form of inherited muscular dystrophy in adults, with a worldwide incidence of 1 in 8000. DM1 is a multisystemic condition that affects many tissues as well as age groups. Compelling clinical evidence demonstrates the impairment of the central nervous system (CNS), through cognitive/attention deficits, problems with executive function, prevalent hypersomnia, behavioral changes and intellectual disability in the most severe cases. The neurological manifestations of the disease are highly debilitating and distressing for DM1 patients and their relatives. Today there is no cure for this devastating condition.
DM1 is caused by the expansion of a non-coding CTG trinucleotide repeat in the DMPK gene. Expanded CUG RNA repeats have a trans-dominant toxic effect: they interfere with RNA-binding proteins causing changes in alternative splicing, transcription, localization, stability and polyadenylation of other RNAs, as well as in protein translation. Despite progress in the understanding of DM1 mechanisms in skeletal muscle and heart, there is an urgent need to fill the gap in our understanding of brain disease mechanisms. At the cellular level, we do not know the contribution of each cell type and their interactions to DM1 brain dysfunction. Molecularly, we do not know the nature and extent of RNA abnormalities, or the gene networks and pathways deregulated in different cell types. To develop rational end efficient therapies targeting CNS dysfunction, we must first learn more about the fundamental mechanisms of disease.
We generated DM1 transgenic mice expressing the human expanded DMPK transcripts (DMSXL mice). These mice recreate important features of RNA toxicity, notably in the CNS, and exhibit relevant behavioral and electrophysiological phenotypes, providing a powerful tool to decipher DM1 brain pathogenesis. Using these animals we found a more pronounced toxic effect of RNA transcripts in astrocytes than in neurons. This finding has important implications for the understanding of disease neurobiology and for designing novel therapies.
Our project stems from the need to untangle DM1 brain dysfunction. We will use complementary mouse and human pluripotent stem cell-derived models to investigate how toxic RNA interferes with the physiology of individual cell lineages. First, live cell imaging and immunofluorescence will characterize individual glial and neuronal phenotypes, while cell type-specific RNA sequencing and integrative bioinformatics will identify the molecular events, gene networks and pathways specifically deregulated in astrocytes and neurons. The combined analysis of cell phenotypes with RNA profiles will elucidate underlying disease mechanisms. Second, we will use advanced high-resolution microscopy and dual electrophysiological recordings of neuronal and astroglial activity to study the physical and functional interactions between astrocytes and neurons. Neuroglial interactions are critical for proper brain physiology, and can participate in the development of neurological disorders. Thus, the dissection of the factors that mediate defective neuroglial communication, by global proteomics and/or metabolomics, will reveal novel windows for therapeutic intervention. Pharmacological manipulation of neuroglial communication will first be tested in culture for their capacity to correct defective cellular phenotypes. The most promising agents will then be evaluated in DMSXL mice, through electrophysiological assessment of their ability to correct synaptic neurotransmission. Strategic technology transfer management will liaise with industrial partners to translate our results to clinical settings in future projects. Our findings will have wider implications beyond DM1, helping to understand general mechanisms of RNA toxicity in other diseases, for which DM1 is today the prototype.