Human iPSC-based skeletal muscle model of LAMA2-related congenital muscular dystrophy

Congenital muscular dystrophies (CMDs) are rare, devastating pediatric conditions with no specific treatment or cure. The most common form, LAMA2-related CMD, or LAMA2-CMD (previously known as merosin-deficiency and MDC type 1 A), is caused by myofiber instability from loss of the laminin α2 subunit, a critical extracellular matrix protein in skeletal muscle. Progressive weakness from diffuse skeletal muscle degeneration and fibrosis leads to death in childhood. Animal models significantly enhanced the understanding of LAMA2-CMD and spearheaded innovative rescue strategies. However, limitations of animal models including difficulty recapitulating human muscular dystrophy phenotypes and a lack of validated studies with relevant human tissues have stalled clinical translation. In vitro models of human skeletal muscle exhibiting measurable characteristics of patient disease can significantly improve our ability to study disease mechanisms and further advance therapeutics. Skeletal muscle progenitor cells (SMPCs), mature myoblasts and 3-dimensional (3D) skeletal muscle tissue were derived from induced pluripotent stem cells of a LAMA2-CMD patient and her unaffected parents as controls. The 3D skeletal muscle constructs were embedded in hydrogel with and without co-seeding with human fibroblasts as supporting cells. Cell fusion, tissue remodeling, contractility and attachment were then analyzed. The 3D skeletal muscle model forms into bundles of multinucleated myotubes, with spontaneous and induced contractions mirroring in vivo muscle tissue. During the skeletal muscle progenitor cell differentiation phase, the LAMA2-CMD neuroectoderm clusters were smaller and less complex than control cases. Despite this, SMPCs were robust and purified at equivalent rates from the patient and control lines. With further differentiation to mature myotubes, LAMA2-CMD cells had reduced cellular fusion compared to control cells. In engineered 3D-skeletal muscle tissues anchored to micropillars, the LAMA2-CMD skeletal muscle demonstrated dystrophic features such as poor attachment, reduced remodeling into compact skeletal muscle bundles, and reduced ability to withstand acetylcholine-induced contractions. The LAMA2-CMD skeletal muscle fibers consistently rupture upon contraction. A patient-derived in vitro model of LAMA2-CMD was established that exhibits a dystrophic phenotype closely resembling the human disease. This platform represents a valuable human tissue model to enhance translational research and therapeutic development efforts for CMDs.