IL-13Rα2 Regulates C2C12 Myoblast Proliferation via the Akt–Cyclin D1–CDK4 Pathway

Interleukin-13 receptor α2 (IL-13Rα2) has traditionally been considered a decoy receptor; however, its cellular functions beyond the immune system remain unclear. We aimed to investigate the role of IL-13Rα2 in C2C12 myoblast proliferation and differentiation. IL-13Rα2 expression was knocked down in C2C12 cells using siRNA. Myogenic differentiation was evaluated by myosin heavy chain (MyHC) immunostaining and by quantifying the expression of myogenic regulatory and fusion-related genes. Myoblast proliferation was assessed using BrdU incorporation and cell number analyses, and signaling events induced by IL-13Rα2 knockdown were analyzed via immunoblotting and immunocytochemical analysis. IL-13Rα2 knockdown did not alter myogenic differentiation or the expression of fusion-associated genes. In contrast, IL-13Rα2 knockdown significantly increased BrdU incorporation and cell number, accompanied by increased Akt phosphorylation and decreased ERK phosphorylation. Cyclin D1 and cyclin-dependent kinase 4 (CDK4) levels were also increased. Akt inhibition abolished the enhanced proliferation and normalized Cyclin D1/CDK4 levels, whereas ERK activation did not further modify the knockdown-associated phenotype. These findings demonstrate that IL-13Rα2 negatively regulates myoblast proliferation by modulating the Akt–Cyclin D1–CDK4 signaling pathway, while being dispensable for myogenic differentiation.