Smad2/3 Signaling Mediates the Atrophic Response in Vocal Fold Myoblasts In Vitro

Background/Objectives Vocal fold (VF) muscle atrophy, often associated with neuromuscular disorders and aging, can lead to voice‐related disability. Myostatin is well‐known to mediate skeletal muscle atrophy via Smad2/3 signaling, whereas TGF‐β1, a potent inducer of Smad2/3 signaling, is upregulated following VF injury. However, the impact of Smad2/3 signaling on laryngeal muscles remains unclear. This study provides foundational insight regarding Smad2/3‐dependent atrophic responses of VF skeletal muscle cells, to ultimately develop novel therapeutic strategies for VF muscle atrophy. Study Design In vitro. Methods Myoblasts isolated from the rat thyroarytenoid muscle were differentiated into myotubes in myogenic differentiation medium ±500 ng/mL myostatin or 10 ng/mL TGF‐β1, in the presence or absence of an ALK4/5 inhibitor or siRNA targeting Smad2 and Smad3. Myotube formation and activation of Smad2/3 (nuclear localization of Smad2/3) were assessed via immunofluorescence. Transcription related to myotube differentiation and Smad2/3 signaling was quantified by qRT‐PCR. Results Both myostatin and TGF‐β1 suppressed myogenic differentiation, increased Smad2/3 nuclear intensity, downregulated Myh2 , and upregulated downstream targets of Smad2/3 ( Ccn2 and Serpine1 ) and Fbox32 , an atrophy‐related gene. These effects were more pronounced with TGF‐β1 than with myostatin and were reversed by inhibition of ALK4/5. Furthermore, Smad2/3 knockdown via siRNA promoted myogenic differentiation, further supporting the role of Smad2/3 signaling in the atrophic response in VF myoblasts. Conclusions Smad2/3 signaling mediates differentiation of VF myoblasts and TGF‐β1, a potent mediator of fibrosis, elicited a more pronounced atrophic response than myostatin. Smad2/3 may be an attractive therapeutic target for VF muscle atrophy. Level of Evidence NA.