Pleiotropic effect of MATR3 in pluripotent stem cells

Matrin3 (MATR3) is an RNA binding protein involved in many roles in the nucleus, such as chromatin architecture and gene expression regulation, modulating transcriptional and post-transcriptional processes as RNA splicing and mRNA stabilization. Nevertheless, some functions of MATR3 within the cells are not entirely clear. MATR3 has been associated with Amyotrophic Lateral Sclerosis (ALS), a neurodegenerative disease that damages motor neuron (MN) cells and leads to progressive muscle paralysis and respiratory failure. A better understanding of MATR3 activity within cell physiology could represent an essential breakthrough for studying MATR3-associated pathologies. Using MATR3-silenced human pluripotent stem cell (hiPSC) line model, we collected data on the MATR3 role in the pluripotency and in the neural induction and differentiation. We found that the downregulation of MATR3 alters the expression level of crucial self-renewal factors such as OCT4, NANOG, KLF4, and LIN28A. We observed MATR3 acts at multiple levels of the gene expression, i.e. regulating YTHDF1 expression, and in RNA metabolism, having a role in mRNA stabilization and translation. The reduction of stemness potential caused by MATR3 downregulation creates a defect during the neurodifferentiation process, which does not arrest motor neurons formation but induces selective alterations that may affect motor neurons functionality. Indeed, several morphological and molecular abnormalities were observed during the neuronal differentiation, such as the alterations of the formation of neuroepithelial rosettes that arise in a reduction of neurite lengths and arborization in neuronal cells. On this basis, we investigated neuronal differentiation in the brain organoids grown from iPSCs derived from ALS patients fibroblasts. We show, for the first time, that MATR3 is a critical factor in orchestrating the stemness network through transcriptional, post-transcriptional, and translational regulation, therefore affecting the differentiation of mature neurons.