iPSC-derived skeletal muscle spheroids for Duchenne Muscular Dystrophy modeling

The progressive skeletal muscle degeneration observed in Duchenne Muscular Dystrophy (DMD) patients requires multiple cycles of satellite cells (SCs) activation to promote tissue regeneration. Dystrophic SCs present intrinsic defects, and the disrupting fibrotic niche hinders appropriate muscle recovery. Traditional 2D culture systems face challenges in modeling the DMD muscle niche and SCs behavior. Our aim was to validate a 3D culture of skeletal muscle spheroids (iSMS) for DMD modeling, as compared to the traditional 2D culture, while investigating the pathophysiological mechanisms of dystrophin deficiency in vitro.

To compare iSMS with traditional 2D myogenic differentiation, we differentiated wild-type (WT), dystrophic (DMD) isogenic induced pluripotent stem cells (iPSCs), as well as iPSCs derived from DMD patients, characterized myogenic markers levels and assessed differences in proliferation and differentiation using RT-qPCR, immunofluorescence, and flow cytometry.

Our data showed that iSMS improved PAX7 expression in vitro, while MYOD1, MYOG, MYF5, and MYH3 expression were significantly reduced. These findings suggest that, at three weeks of myogenic differentiation, iSMS cultures retained satellite-like cells in a less activated, progenitor-like state. Accordingly, we identified higher expression of canonical Notch signaling genes such as JAG1 and NOTCH1 in iSMS compared to 2D. We also characterized the response of 2D and iSMS to terminal differentiation medium, providing a valuable comparison with muscle fibers derived from human adult myoblasts. Additionally, we showed that DMD iSMS-derived progenitors proliferated at reduced levels compared with WT, a characteristic not observed in progenitors derived from 2D cultures. Finally, we performed iSMS and 2D myogenic differentiation of iPSC lines from three patients with DMD.

Our results highlight important advantages of using the iSMS differentiation platform over 2D for DMD in vitro modeling. Exploring these 3D systems may help to gain a deeper understanding of SCs behavior to advance in novel treatments for DMD, which might be applicable to other forms of muscular disorders.