PDK1 and cholesteatoma: In addition, Zhang et al. showed that the expression of PPARβ/δ was significantly increased in cholesteatoma, and the ligand-activated PPARβ/δ promoted the proliferation of cholesteatoma keratinocytes as a result of the positive regulation of the PDK1/PTEN/AKT/GSK3β/cyclin D1 pathway [186].