A Biomimetic Amelogenin–Fibronectin Fusion Protein with Dual Cell-Adhesive and Osteoinductive Functions for Alveolar Bone Defect Repair

Periodontitis-induced destruction of periodontal tissues and tooth loss remain major clinical challenges. Although periodontal regenerative therapies aim to reconstruct damaged structures, particularly the repair of alveolar bone defects, current biomaterials have limited capacity to simultaneously promote cell adhesion and osteogenic differentiation. Amelogenin (Am) plays a key role in mineralized tissue development through its highly conserved N-terminal and C-terminal regions, but studies have shown that Am has certain limitations in promoting cell adhesion. In contrast, the arginine-glycine-aspartic acid (RGD) domain of fibronectin (FN) effectively mediates cell–matrix adhesion. Based on these properties, we developed a novel recombinant fusion protein (rtAmR) by combining the conserved regions of Am with the RGD domain of FN. In vitro, rtAmR significantly promoted the adhesion and spreading of human stem cells from the apical papilla (hSCAPs) compared with the control group. Quantitative analysis showed that the number of adherent cells and the cell spreading area in the rtAmR group were 1.9-fold and 2.1-fold higher than those in the rhAm group, respectively. In osteogenic differentiation assays, rtAmR exhibited activity comparable to that of rhAm and even outperformed rhAm in terms of alkaline phosphatase (ALP) activity, collagen type I (COL I) expression, and calcium nodule formation. In a Sprague–Dawley (SD) rat alveolar bone defect model, rtAmR treatment significantly promoted bone regeneration, achieving superior bone volume/total volume (BV/TV) values compared to the rhAm and rhFN groups. Immunohistochemistry revealed that rtAmR did not obviously increase neutrophils, mast cells, or M2 macrophages versus control, confirming its biosafety and suggesting M2-independent osteogenesis. These findings suggest that rtAmR is a promising bifunctional bioactive protein for periodontal bone regeneration.