GDF11 and its receptor ALK4 independently modulate human myoblast migration and fusion

Muscle regeneration is governed by a complex interplay between immune cells and satellite cells (muscle progenitors), orchestrated by signaling molecules of the TGF-β superfamily. Among these, the role of GDF11 activity in skeletal muscle remains contentious, with conflicting evidence suggesting both stimulatory and inhibitory effects. This functional divergence may emerge from the combinatorial activities of its shared type I receptors and context-dependent activation of downstream SMADs. To dissect the role of GDF11 in skeletal myogenesis, we employed a combination of biochemical stimulation and CRISPR-based genetic approaches in chicken or human myoblasts. Analysis of cell proliferation, differentiation, adhesion, and migration revealed that GDF11 does not affect myoblast proliferation or adhesion, but strongly inhibits myotube differentiation and myoblast migration. Furthermore, loss of ACVR1B (ALK4) strongly delays myoblast differentiation, and impairs cell adhesion and migration on laminin-111 (LM111), a known ligand of the integrin VLA-6. Notably, flow cytometry phenotyping demonstrated that ACVR1B -deficient myoblasts exhibit reduced surface levels of the integrin α6 subunit (CD49f) compared to wild-type cells. Together, our findings suggest a GDF11-independent ALK4/VLA6/LM111 axis governing skeletal myoblast adhesion and fusion. Knowledge of these receptor interactions is critical for understanding GDF11’s paradoxical role in muscle cell biology and may inform novel therapeutic strategies to counteract skeletal muscle degeneration and age-related decline.