SFRP2 and cholesteatoma: Because no upregulation of INHBB and INHA was observed in cholesteatoma fibroblasts, we concluded that upregulated INHBA in cholesteatoma-specific fibroblasts forms a homodimer, activin A. SFRP2 and IGF2 (secreted proteins that are upregulated in cholesteatoma fibroblasts except activin A) did not promote osteoclast differentiation; therefore, we used activin A protein for further in vitro experiments (Supplementary Fig. S8b–e).