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

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).

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.

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.

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.