Kalish-Schur, G. | Search bioRxiv

bioRxiv2026

Fibroadipogenic Progenitor Cells Contribute to Tongue Skeletal Muscle Hypertrophy in Beckwith-Wiedemann Syndrome

Beckwith-Wiedemann syndrome (BWS) is a pediatric imprinting disorder characterized by tissue overgrowth, most commonly macroglossia, which can result in airway and feeding complications. Although dysregulated growth is a defining feature of BWS, the cellular interactions that drive organ-specific overgrowth remain poorly understood. We previously demonstrated that BWS macroglossia arises through distinct cell-intrinsic and cell-extrinsic mechanisms depending on molecular subtype. Here, we identify fibroadipogenic progenitor cells (FAPs) as modulators of myogenic differentiation and fusion in the human BWS tongue. BWS-derived FAPs were not increased in abundance in situ and did not exhibit hyperproliferation in vitro. Instead, FAPs from one BWS subtype promoted enhanced differentiation and fusion of normal human myoblasts. Secretome profiling revealed enrichment of CATHEPSIN L and TRANSFERRIN in conditioned media from these FAP populations, and functional perturbation of these factors supported their role in regulating myogenesis. These findings define a non-cell-autonomous mechanism of muscle overgrowth and implicate mesenchymal-myogenic signaling as a context-dependent driver of tissue expansion in an imprinting disorder.

cell biology↗

bioRxiv2026

Myogenic dysregulation underlies tongue overgrowth in Beckwith-Wiedemann syndrome

Macroglossia is a clinically significant feature of Beckwith-Wiedemann syndrome (BWS), but the cellular basis of tongue overgrowth remains poorly defined. Here, using pediatric tongue specimens from molecularly defined BWS subtypes and age-matched nonBWS controls, we show that BWS macroglossia is characterized by skeletal muscle fiber hypertrophy rather than increased fiber number. This phenotype is not explained by expansion or increased proliferation of satellite cells in situ, and prospectively isolated tongue satellite cells do not exhibit enhanced proliferation under growth conditions in vitro. Instead, BWS progenitors adopt distinct differentiation-associated regulatory states. IC2 loss of methylation cells sustain proliferative activity during differentiation and form enlarged myotubes, consistent with a cell-autonomous hypertrophic program. In contrast, pUPD11 cells display activation of NOTCH signaling and progenitor-associated programs, together with attenuated progression toward terminal myogenic differentiation. These findings identify skeletal muscle hypertrophy as a core tissue-level feature of BWS macroglossia and reveal that epigenetically defined BWS subtypes engage divergent myogenic programs that converge on a shared hypertrophic tissue phenotype. Together, these data define subtype-specific myogenic states in a rare human disease tissue and provide a framework for understanding how distinct epigenetic changes can produce a common overgrowth phenotype. HighlightsO_LIBWS macroglossia is associated with skeletal muscle fiber hypertrophy, not fiber hyperplasia C_LIO_LITongue satellite cell abundance and proliferation are not increased in situ in BWS C_LIO_LIIC2 loss of methylation cells sustain proliferation during differentiation and form enlarged myotubes C_LIO_LIpUPD11 cells show enhanced NOTCH signaling and a constrained myogenic state C_LI In briefTichy et al. show that Beckwith-Wiedemann syndrome macroglossia is driven by skeletal muscle hypertrophy and that distinct BWS molecular subtypes engage different myogenic regulatory programs. IC2 loss of methylation cells sustain proliferation during differentiation, whereas pUPD11 cells exhibit NOTCH-associated restraint of myogenic progression.

cell biology↗