MICAL1 Contributes to Myogenic Differentiation by Modulating Actin Remodeling and YAP1 Nuclear Localization in C2C12 Myoblasts.

Molecule Interacting with CasL 1 (MICAL1) is a flavoprotein monooxygenase that promotes filamentous actin (F-actin) depolymerization. Transcriptomic studies have linked MICAL1 downregulation to skeletal muscle atrophy and muscular dystrophy, yet its functional contribution to myogenesis remains unexplored. We found that MICAL1 protein increased progressively during myogenic differentiation of C2C12 cells, reaching a maximum on day 5 in parallel with myosin heavy chain (MyHC). siRNA-mediated MICAL1 silencing produced an ~1.7-fold accumulation of F-actin, while total β-actin protein remained unchanged, indicating a shift in the G-/F-actin equilibrium toward polymerization rather than altered actin expression. The accumulated F-actin reduced YAP1 phosphorylation, promoted its nuclear translocation, and increased the expression of the YAP1 target gene CTGF. MICAL1 depletion also enhanced myoblast proliferation: EdU incorporation and cell viability increased, and PCNA, CCNB1, and CCND1 protein expression was upregulated, while the cell cycle distribution shifted toward the G2/M phase, with a reciprocal loss in G0/G1. Concurrently, MICAL1 knockdown suppressed MyoD, Myogenin, and MyHC throughout differentiation and severely impaired myotube formation, with reductions in the fusion index, myotube area, and length. We conclude that MICAL1 is required for the proliferation-to-differentiation switch in myoblasts and that its activity restrains F-actin-driven YAP1 signaling to permit timely myogenic commitment. MICAL1 may therefore represent a candidate for further investigation in muscle-wasting diseases.