PIK3CD and fibrosis: In the oral cavity, PDGF-BB binding to PDGFR-β triggers PI3K catalytic activity in oral mucosal fibroblasts, initiating a PDK1-mediated AKT phosphorylation cascade that promotes fibroblast-to-myofibroblast transition, collagen synthesis, and cell migration in oral submucosal fibrosis (Wang Q. et al., 2021).