Proliferation and differentiation defects are key events for the onset of LAMA2-congenital muscular dystrophy

Topic:

Pre-Clinical Research

Poster Number: Virtual

Author(s):

Susana G. Martins, MSc, ce3c, faculty of sciences, university of lisbon, Vanessa Ribeiro, ce3c, faculty of sciences, university of lisbon, Cláudia Paulino-Cavaco, BSc, ce3c, faculty of sciences, university of lisbon, Catarina Melo, ce3c, faculty of sciences, university of lisbon, Hugo Luiz, ce3c, faculty of sciences, university of lisbon, Inês Fonseca, ce3c, faculty of sciences, university of lisbon, Bérénice Saget, ce3c, faculty of sciences, university of lisbon, Ana Rita Carlos, PhD, Faculty of Science of University of Lisbon, Sólveig Thorsteinsdóttir, PhD, Faculty of Science of University of Lisbon

LAMA2-congenital muscular dystrophy (LAMA2-CMD) is a disease caused by mutations in LAMA2, which encodes the laminin-α2 chain of laminins 211 and 221, both extracellular matrix (ECM) glycoproteins. LAMA2-CMD is characterized by muscle weakness and hypotonia present at birth and patients have a reduced life expectancy. No treatment or cure are available. Using the dyW mouse model for LAMA2-CMD we previously established that disease onset occurs between embryonic day 17.5 (E17.5) and E18.5, with muscle growth impairment and a reduction in the number of muscle stem cells (MuSCs) and myoblasts. Here we show that the proliferation rate in Lama2-deficient C2C12 myoblasts, our in vitro model for LAMA2-CMD, is decreased, which is in accordance with an increase in the expression of cyclin inhibitor kinases (CDKs) in the dyW mouse model. Moreover, Lama2-deficient C2C12 myoblasts and skeletal muscles from dyW fetuses display increased DNA damage, which may contribute to the proliferation defect. Lama2-deficient C2C12 myoblasts are also unable to differentiate to the same extent as their wildtype counterparts. To understand which of the pathways involved in extracellular-intracellular communication are affected in the absence of Lama2, we analyzed JAK-STAT and focal adhesion kinase (FAK) signaling pathways. In addition to the previously described overactivation of STAT3, we showed that the absence of Lama2 also increases the phosphorylation of FAK. Since YAP (yes-associated protein) is a transcriptional regulator downstream of FAK and STAT3, we addressed whether YAP levels were altered, and we observed a decrease in Lama2-deficient myoblasts in comparison to wildtype. We are currently investigating if increased phosphorylated STAT3 and FAK and decreased YAP levels directly cause the observed proliferation and/or differentiation defects. Overall, these findings contribute to our understanding of the mechanisms underlying the first steps of LAMA2-CMD, essential for the development of therapies that specifically target the primary events of this incurable disease.