SCF Promotes Dental Pulp Progenitor Migration, Neovascularization, and Collagen Remodeling – Potential Applications as a Homing Factor in Dental Pulp Regeneration

Abstract

Stem cell factor (SCF) is a powerful chemokine that binds to the c-Kit receptor CD117 and has shown promise as a homing agent capable of progenitor cell recruitment. In the present study we have documented high levels of both SCF and its receptor c-Kit in differentiating dental pulp (DP) cells and in the sub-odontoblastic layer of Höhl. In vitro studies using human DP progenitors revealed a significant increase in cell proliferation after100nM SCF application, explained by a 2-fold upregulation in cyclin D3 and FGF2 cell cycle regulators, and a 7-fold increase in CDK4 expression. DP cell migration in the presence of SCF was up-regulated 2.7-fold after a 24 hour culture period, and this effect was accompanied by cytoskeletal rearrangement, a 1.5-fold increase in polymeric F-actin over G-actin, and a 1.8-fold increase in RhoA expression. Explaining the signaling effect of SCF on DP migration, PI3K/Akt and MEK/ERK pathway inhibitors were demonstrated to significantly reduce DP cell migration, while SCF alone doubled the number of migrated cells. ERK and AKT phosphorylation were dramatically upregulated already 3-5 minutes after SCF addition to the culture medium and declined thereafter, classifying SCF as a fast acting chemokine. When applied as an agent to promote tissue regeneration in subcutaneously implanted collagen sponges, SCF resulted in a 7-fold increase in the cell number in the implanted tissue construct, a more than 9-fold increase in capillaries, as well as collagen sponge remodeling and collagen fiber neogenesis. Together, these studies demonstrate the suitability of SCF as a potent aid in the regeneration of dental pulp and other mesenchymal tissues, capable of inducing cell homing, angiogenesis, and tissue remodeling.

Effects of Stem Cell Factor on Cell Homing During Functional Pulp Regeneration in Human Immature Teeth

“…24 As the time frame for proliferation was longer than the time frame for migration, prolonged exposure of a high SCF concentration directly on hMSCs appeared to cause cell distress 20 and not an increased hMSC proliferation. In fact, our finding showed that a responsive dose of SCF promotes cell proliferation similar to the effective dose of recent studies, 21,27 although their observations occurred after a longer time period and in different growth media. Beyond proliferation, high SCF concentrations affected the osteogenic differentiation, since ALP activity was also increased, which is in line with previous studies.…”

“…28 On the molecular level, SCF can stimulate the signaling cascades of PI3K/Akt and MEK/ERK, thereby rapidly increasing ERK and AKT phosphorylation within the cells. 21 Such very early effects can be the reason why at 6 weeks we saw an increase in tissue ingrowth in fibrin gels with SCF compared to fibrin gels alone. For both time points, the amount of regenerated tissue was similar to an earlier study in which tissue regeneration was achieved by stem cell delivery in Normalized expressions of mRNA for DMP1, DSPP, Col1, NGF, and VEGF.…”

“…Beyond proliferation, high SCF concentrations affected the osteogenic differentiation, since ALP activity was also increased, which is in line with previous studies. 20,21 SCF was found to increase the expression of Collagen type I and III, basic fibroblast growth factor, BMP-6, and tissue inhibitor of metalloproteinase 1 and 4 in MSCs. All these proteins are involved in proliferation, chondrogenesis, and extracellular matrix protein regulation.…”

“…21 To address its potential to improve current cell homing strategies in dental pulp tissue engineering, we tested the effect of SCF on the directionality of hMSC migration in vitro and tested its in vivo impact by delivering it with a fibrin gel in a cell homing model. 10 Our results showed that SCF directs migration of mesenchymal stem cells, but has a minor effect on their proliferation and differentiation.…”

“…20 SCF and its receptor were also found in differentiating dental pulp cells and in the subodontoblastic layer of Höhl. 21 In pulp tissue engineering, a previous application of SCF on a collagen sponge either with or without pulp cells showed an increased expression of genes required for collagen remodeling, cell migration, and cell proliferation. 21 However, the application of SCF in a cell homing approach to form a fully functional pulp has not been investigated yet.…”