We have previously identified and functionally characterized pCharme, a muscle-specific, evolutionary conserved lncRNA acting in the nucleus as an epigenetic regulator. In mouse, pCharme ablation severely impairs myogenic differentiation at early onset, triggering muscle hyperplasia and cardiac remodeling. Mechanistically, pCharme supervises, through direct interaction, the chromatin localization of MATR3, a multifunctional DNA/RNA-binding protein whose mutations were identified in patients affected by myopathies or motor neuron diseases. In particular, mutations that specifically compromise the MATR3 binding to RNA result in the formation of non-physiological, MATR3-containing condensates, which are also hallmarks of neurodegeneration. In line with this, mice expressing a cytoplasmic version of pCharme show mislocalised MATR3 distribution and a significant impairement of neuromotor abilities. This phenotype suggests unpredicted roles for pCharme in maintaining both muscles and neurons and evokes an intriguing "dying-back" phenomenon by which the impairment of muscles would produce retrograde signals contributing to motor neuropathies.
On these premises, we sought to investigate the involvement of the human pCharme into neuromuscular circuitries and neurodegeneration. To this aim, we plan to apply an experimental design where the synergy between CRISPR-Cas9 gene editing and induced pluripotent stem cells technology will allow the study of muscle-nerve connections through the generation of pCharme-KO neuromuscular organoids (NMOs), in which the spinal cord and the skeletal muscle counterparts develop in parallel and functionally interact. Our study is expected to provide an innovative platform to study the human neuromuscular networks and trace the developmental contribution of new classes of genes to neurodegenerative disorders, particularly those in which the formation of a functional neuromuscular junction (NMJ) is early impaired.
