As shown in Fig. 3b, expression of adhesion proteins on the interface between PIE-implant was significantly lower in the control and local groups compared with the systemic group.

Ln-332 is the major adhesive ligand for integrin α6β4, which interacts with the cytoskeletal elements, and is a component of the hemidesmosomes, epithelial adhesion plaques that tack the plasma membrane of the epithelial cells [21,22,23]. Moreover, Ln is expressed at the interface between the JE and natural tooth [24, 25] and is thought to be critical for the attachment of gingival epithelial cells to substrates [26, 27]. In our previous study, Ln was implicated in the adhesion of the PIE to the dental implant [20, 28]. Therefore, we observed the distribution of Ln during PIE formation around the implant to eliminate the influence of transplanted MSCs on the OE.

Connecting Ln and α6β4 integrin activates intracellular signaling pathways, such as the mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K) signaling pathways, which control cell migration, adhesion, and survival [29,30,31]. Our previous study showed that insulin-like growth factor-1 (IGF-1)-activated PI3K signaling promoted epithelial adhesion via HD activation of PI3K signaling and improved epithelial sealing around the implant [32]. Some studies indicate that MSCs activate intrinsic MSCs or various other cells through paracrine expression of IGF-1, epidermal growth factor (EGF), or platelet-derived growth factor (PDGF). Therefore, we highlight the importance of direct contact between MSCs and epithelial cells in order to change cell characteristics or activate cell differentiation.

GFP/CD-90 double-positive cells were detected and counted in various tissues, including the mucosa around the experimental implants (Fig. 4a, b). Although few double-positive MSCs were observed in the liver and heart 1 day after MSC injection, double-positive MSCs were observed in the lung and peri-implant tissue after both systemic and local injection. Figure 4c shows changes in MSC numbers in the rat blood over time. In the local group, intravascular MSC number peaked at day 5, while in the systemic group, MSC number declined quickly at the early time points 3 days after the administration.