Mesenchymal Stem Cells and Periodontal Regeneration

Regulation of gingival fibroblast phenotype by periodontal ligament cells in vitro

Objectives

Stem cell transplantation has shown modest effects on periodontal tissue regeneration, and it is still unclear how regenerative effects utilizing this modality are mediated. A greater understanding of the basic interactions between implanted and host cells is needed to improve future strategies. The aims of this study were to investigate the effects of periodontal ligament (PDL) cells on expression of periodontal markers and alkaline phosphatase (ALP) activity of gingival fibroblasts (GF).

Materials and Methods

Primary human PDL cells were co‐cultured with primary GF cultures either by direct co‐culture with subsequent FACS sorting or indirect co‐culture using transwell cultures and PDL cell conditioned medium. Expression of periodontal markers, asporin, nestin, and periostin, was assessed by qPCR and immunofluorescence staining. Alkaline phosphatase (ALP) expression was assessed by qPCR, histochemical staining, and activity assessed by para‐nitrophenol enzymatic assay. Single cultures of PDL cells and GF were used as controls. The role of Wnt signaling on ALP activity was assessed via Dkk1‐mediated inhibition.

Results

PDL cells significantly upregulated expression of PDL markers in GF with both direct and indirect co‐culture methods when compared to controls (6.05 vs. 0.73 and 59.48 vs. 17.55 fold change of asporin expression). PDL/GF cell co‐cultures significantly increased ALP activity in GF when compared with single GF cultures. Similar results were obtained when using conditioned medium isolated from PDL cell cultures. Dkk1 caused dose‐dependent reduction in ALP activity of GF cultured in PDL cell conditioned medium.

Conclusions

PDL cells stimulate expression of periodontal markers and osteogenic capacity of gingival fibroblasts via paracrine signaling which can be partially inhibited with addition of the Wnt antagonist, Dkk1.Further studies are required to identify specific secreted factors responsible for this activity.

Comparison of the Expression of Periodontal Markers in Dental and Bone Marrow-derived Mesenchymal Stem Cells

Background:

Periodontal ligament stem cells are a source of mesenchymal stem cells, but it is unclear whether their phenotype is distinct from mesenchymal stem cells derived from different tissues, such as those derived from bone marrow.

Objective:

To investigate the expression of the putative PDL markers asporin, periostin, nestin and cementum protein 1, by periodontal ligament stem cells both constitutively and during osteogenic differentiation when compared to bone marrow-derived mesenchymal stem cells, and dental pulp stem cells.

Methods:

The primary human periodontal ligament, bone marrow, and dental pulp stem cells, and osteoblasts from different donors were cultured in vitro. The expression of periodontal marker associated genes during osteogenic induction was tested by qRT-PCR and immunofluorescence staining.

Results:

Asporin expression was detected in periodontal ligament stem cells and increased markedly during the time in culture (upregulated x53 fold at 21 days post-induction). During osteogenic differentiation, asporin expression significantly decreased in periodontal ligament cells whereas periostin significantly decreased in dental pulp cells. Periostin expression was absent in osteoblasts, but expression gradually increased in all other cells with time in culture. Nestin expression was mainly seen in the periodontal ligament and dental pulp cells and was largely absent in osteoblasts and bone marrow cells. Cementum protein-1 was most highly expressed in bone marrow cells and osteoblasts following osteogenic induction.

Conclusions:

The results provide further evidence that periodontal ligament-derived and bone marrow derived mesenchymal stem cells are phenotypically distinct. Periodontal markers are also expressed in dental pulp stem cells.

hMSC-Derived VEGF Release Triggers the Chemoattraction of Alveolar Osteoblasts

Human mesenchymal stem cells (hMSCs) are promising candidates for regenerative periodontal strategies, due to the broad spectrum of supportive effects on cells and tissues at the site of application. Although positive effects are visible, the understanding of their underlying mechanisms still requires further elucidation. Recently, we have shown that hMSCs are capable to prompt osteogenic differentiation of alveolar osteoblasts, thereby presumably contributing to alveolar bone regeneration. Another issue that is critical in this context is the attraction of hard tissue-forming cells to regeneration sites, but it is an open question whether hMSCs can afford this. In the present manuscript, we show by life cell imaging that in interactive cocultures, hMSCs successfully trigger osteoblast chemotaxis. Gene expression analysis for hMSC-innate chemoattractive biomolecules, orchestrating this process, revealed vascular endothelial growth factor (VEGF), PgE synthase, osteoprotegerin (OPG), monocyte colony-stimulating factor, and transforming growth factor β1, which was confirmed for VEGF and OPG on the protein level. Noteworthy, we showed that only corresponding levels of VEGF but not OPG attracted alveolar osteoblasts similar to hMSC coculture, while VEGF inhibitor abolished both the VEGF and the hMSC-triggered chemoattraction. In summary, we have identified secreted OPG and VEGF proteins as potential chemoattractants, of which further characterization yielded VEGF as a causative for hMSC-directed osteoblast chemotaxis. With respect to the better understanding of potential hMSC-based periodontal regeneration strategies, we propose hMSC-derived VEGF release as a mechanism in the recruitment of hard tissue-forming cells to alveolar bone sites in need of regeneration.