Context-Dependent Regulation of Epithelial Cell Behaviour by Palatal Connective Tissue Graft-Derived Fibroblasts via EGF and HB-EGF Signalling.

AIM: To investigate how human palatal fibroblasts (HPFs) from anterior (A) or posterior (P) subepithelial connective tissue grafts (CTGs) regulate oral epithelial cell behaviour, focusing on epidermal growth factor (EGF) and heparin-binding EGF-like growth factor (HB-EGF). MATERIALS AND METHODS: Oral epithelial cells were cocultured with either A-HPFs or P-HPFs under indirect and direct conditions. Proliferation and differentiation were assessed by BrdU, qRT-PCR and immunofluorescence. Growth factor signalling was analysed by ELISA, inhibition/neutralisation experiments, siRNA knockdown and immunoblotting. RESULTS: A-HPFs promoted epithelial proliferation but not differentiation under indirect conditions. In contrast, direct contact triggered epithelial differentiation and AP-1 gene induction. EGF mediated proliferation via the EGF receptor (EGFR), whereas HB-EGF induced differentiation via the ErbB4 receptor. HB-EGF knockdown selectively impaired expression of differentiation-associated and AP-1 genes without affecting proliferation. Distinct intracellular signalling was observed, with Erk1/2 activation predominating in indirect coculture and Akt and Stat5 activation in direct coculture. CONCLUSION: This mechanistic in vitro study supports a model in which A-CTG-derived fibroblasts regulate epithelial responses through a transition from paracrine EGF-EGFR to juxtacrine HB-EGF-ErbB4 signalling during wound healing. These findings provide a biological basis for personalised strategies to optimise graft selection and biomaterial functionalisation in periodontal and peri-implant therapy.