Expression of embryonic stem cell markers and osteogenic differentiation potential in cells derived from periodontal granulation tissue

Periodontal granulation tissue - To remove or not to remove, that is the question

Formation of granulation tissue is a fundamental phase in periodontal wound healing with subsequent maturation leading to regeneration or repair. However, persistently inflamed granulation tissue presents in osseous defects as a result of periodontitis and is routinely disrupted and discarded with non-surgical and surgical therapy to facilitate wound healing or improve chances of regeneration. Histological assessment suggests that granulation tissue from periodontitis-affected sites is effectively a chronic inflammatory tissue resulting from impaired wound healing due to persistence of bacterial dysbiotic bioflim. Nevertheless, the immunomodulatory potential and stem cell characteristics in granulation tissue have also raised speculation about the tissue's regenerative potential. This has led to the conception and recent implementation of surgical techniques which preserve granulation tissue with the intention of enhancing innate regenerative potential and improve clinical outcomes. As knowledge of fundamental cellular and molecular functions regulating periodontitis-affected granulation tissue is still scarce, this review aimed to provide a summary of current understanding of granulation tissue in the context of periodontal wound healing. This may provide new insights into clinical practice related to the management of granulation tissue and stimulate further investigation.

Characterization of the soft-tissue wall lining residual periodontal pockets and implications in periodontal wound healing

AIM

To characterize the soft-tissue wall of remaining periodontal pockets for wound healing-related parameters versus healthy gingival crevices in the same individuals.

MATERIALS AND METHODS

Gingival tissues collected from the diseased interface of pockets (GT biopsies) and from healthy gingival crevices (G biopsies) were subjected to RT2-profiler PCR Array for wound healing-related markers and network analysis of differentially expressed genes. Lymphangiogenesis-related gene expression was determined by qRT-PCR. The migration potential of mesenchymal stem cells isolated from GT biopsies (GT-MSCs) and G biopsies (G-MSCs) was evaluated by the scratch- and the transwell migration assays. The total collagen protein content was determined in GT-MSCs and G-MSCs homogenates.

RESULTS

Gene-ontology analysis on significantly upregulated genes expressed in GT biopsies revealed enrichment of several genes involved in processes related to matrix remodeling, collagen deposition, and integrin signaling. No significantly expressed genes were seen in G biopsies. Regarding lymphangiogenesis-related genes, GT biopsies demonstrated greater expression for PROX1 than G biopsies (p = 0.05). Lower migration potential (p < 0.001), yet greater production of collagen protein (p = 0.05), was found for GT-MSCs over G-MSCs.

CONCLUSION

Differential expression patterns of various molecular pathways in biopsies and cell cultures of diseased versus healthy gingival tissues indicate a potential of the former for tissue remodeling and repair.

CLINICAL RELEVANCE

In the course of periodontitis, granulation tissue is formed within a periodontal defect in an attempt to reconstruct the site. Following treatment procedures periodontal granulation tissue remains inflamed but appears to retain healing potential.

Regenerative Potential of Granulation Tissue in Periodontitis: A Systematic Review and Meta-analysis

Methods

Electronic searches were conducted in five databases including CENTRAL, MEDLINE, EMBASE, Web of Science, and Dentistry & Oral Sciences Source using a combination of MeSH terms and keywords up to 21 June 2022. Human studies including patients aged over 18 years with all forms of periodontitis were included. Following the risk of bias assessment, both qualitative and quantitative analyses were performed.

Results

A total of twelve studies were included in qualitative analysis and six of them in quantitative analyses. The evidence suggested that cells derived from periodontitis granulation tissue have osteogenic, adipogenic, chondrogenic, neurogenic, and angiogenic differentiation abilities as well as immunoregulatory properties. In particular, CD44⁺, CD73⁺, CD90⁺, CD105⁺, and CD146⁺ cells were found widely in granulation tissue whilst the only meta-analysis confirmed that CD90⁺ cells were present in lower numbers within the granulation tissue when compared with healthy periodontal tissue (WMD = -23.43%, 95% CI -30.43 to -16.44, p < 0.00001).

Conclusions

This review provided further evidence that granulation tissue from patients with periodontitis can be a potential stem cell source for regenerative therapy.

Porphyromonas gingivalis and dental stem cells crosstalk amplify inflammation and bone loss in the periodontitis niche

Periodontitis is the sixth most prevalent disease, and almost 3.5 billion people are affected globally by dental caries and periodontal diseases. The microbial shift from a symbiotic microbiota to a dysbiotic microbiota in the oral cavity generally initiates periodontal disease. Pathogens in the periodontal microenvironment interact with stem cells to modulate their regenerative potential. Therefore, this review focuses on the interaction between microbes and stem cells in periodontitis conditions. Microbes direct dental stem cells to secrete a variety of pro-inflammatory cytokines and chemokines, which increase the inflammatory burden in the damaged periodontal tissue, which further aggravates periodontitis. Microbial interaction also decreases the osteogenic differentiation potential of dental stem cells by downregulating alkaline phosphatase, runt-related transcription factor 2, type 1 collagen, osteocalcin, osteopontin, and so on. Microbe and stem cell interaction amplifies pro-inflammatory cytokine signaling in the periodontitis niche, decreasing the osteogenic commitment of dental stem cells. A clear understanding of microbial stem cell interactions is crucial in designing regenerative therapies using stem cells in the management of periodontitis.

Structural and recovery mechanisms of 3D dental pulp cell microtissues challenged with Streptococcusmutans in extracellular matrix environment

Cariopathogen Streptococcus mutans exists in infected dental pulp of deciduous teeth and is frequently linked with heart diseases. Organotypic (3D) dental pulp stem cell (DPSC) cultures/microtissues, developed to mimic the physiological conditions in vivo, were utilized to assess the bacterial impact on their (i) 3D structural configuration and (ii) recovery mechanisms. The cultures, developed in extracellular matrix (ECM) bio-scaffold (Matrigel™), interacted with WT and GFP-tagged bacterial biofilms by permitting their infiltration through the ECM. Challenged cell constructs were visualized by F-actin/nuclei staining. Their pluripotency (Sox2) and differentiation (osteocalcin) markers were assessed by immunocytochemistry. Secreted mineral was detected by alizarin red, and 3D structural arrangements were analysed by epi-fluorescence and confocal scanning microscopy. Bacterial biofilm/ECM-embedded DPSC interactions appeared in distinct areas of the microtissues. Bacterial attachment to the cell surface occurred without evidence of invasion. Surface architecture of the challenged versus unchallenged microtissues was apparently unaltered. However, significant increases in thickness (138.42 vs 106.51 µm) and bacterial penetration were detected in challenged structures causing canal-like microstructures with various diameters (12.94 -42.88 µm) and average diameter of 20.66 to 33.42 µm per microtissue. Challenged constructs expressed pluripotency and differentiation markers and secreted the mineral. Presented model shows strong potential for assessing pulp-pathogen interactions in vivo. S. mutans infiltrated and penetrated the microtissues but did not invade the cells or compromise major cell repair mechanisms. These findings would suggest reexamining the role of S. mutans as an endodontic pathogen and investigating DPSC resistance to its pathogenicity.

Comparative Assessment of Oral Mesenchymal Stem Cells Isolated from Healthy and Diseased Tissues

The aim of the present study was to isolate human mesenchymal stem cells (MSCs) from palatal connective and periodontal granulation tissues and to comparatively evaluate their properties. MSCs were isolated using the explant culture method. Adherence to plastic, specific antigen makeup, multipotent differentiation potential, functionality, and ultrastructural characteristics were investigated. The frequency of colony-forming unit fibroblasts for palatal-derived mesenchymal stem cells (pMSCs) was significantly higher than that of granulation tissue-derived mesenchymal stem cells (gtMSCs). A significantly higher population doubling time and lower migration potential were recorded for gtMSCs than for pMSCs. Both cell lines were positive for CD105, CD73, CD90, CD44, and CD49f, and negative for CD34, CD45, and HLA-DR, but the level of expression was different. MSCs from both sources were relatively uniform in their ultrastructure. Generally, both cell lines possessed a large, irregular-shaped euchromatic nucleus, and cytoplasm rich in mitochondria, lysosomes, and endoplasmic reticulum. The periphery of the plasma membrane displayed many small filopodia. MSCs from both cell lines were successfully differentiated into osteogenic, adiopogenic, and chondrogenic lineages. Both healthy and diseased tissues may be considered as valuable sources of MSCs for regenerative medicine owing to the high acceptance and fewer complications during harvesting.

Tracing CD34+ Stromal Fibroblasts in Palatal Mucosa and Periodontal Granulation Tissue as a Possible Cell Reservoir for Periodontal Regeneration

The aim of the present research was to trace CD34+ stromal fibroblastic cells (CD34+ SFCs) in the palatal connective tissue harvested for muco-gingival surgical procedures and in granulation tissues from periodontal pockets using immunohistochemical and transmission electron microscopy. Immunohistochemical analysis targeted the presence of three antigens: CD31, α-smooth muscle actin (α-SMA), and CD34. In the palate, CD31 staining revealed a colored inner ring of the vessels representing the endothelium, α-SMA+ was located in the medial layer of the vasculature, and CD34 was intensely expressed by endothelial cells and artery adventitial cells (considered to be CD34+ SFCs). Granulation tissue showed the same pattern for CD31+ and α-SMA, but a different staining pattern for CD34. Ultrastructural examination of the palatal tissue highlighted perivascular cells with fibroblast-like characteristics and pericytes in close spatial relationship to endothelial cells. The ultrastructural evaluation of granulation tissue sections confirmed the presence of neovasculature and the inflammatory nature of this tissue. The present study traced the presence of CD34+ SFCs and of pericytes in the palatal connective tissue thus highlighting once more its intrinsic regenerative capabilities. The clinical and systemic factors triggering mobilization and influencing the fate of local CD34+SCFs and other progenitors are issues to be further investigated.

Ultrastructural evaluation of mesenchymal stem cells from inflamed periodontium in different in vitro conditions

This research aimed to observe the behavior of mesenchymal stem cells (MSCs) isolated from periodontal granulation tissue (gt) when manipulated ex vivo to induce three-dimensional (3D) spheroid (aggregates) formation as well as when seeded on two bone scaffolds of animal origin. Periodontal gt was chosen as a MSC source because of its availability, considering that it is eliminated as a waste material during conventional surgical therapies. 3D aggregates of cells were generated; they were grown for 3 and 7 days, respectively, and then prepared for transmission electron microscopic analysis. The two biomaterials were seeded for 72 h with gtMSCs and prepared for scanning electronic microscopic observation. The ultrastructural analysis of 3D spheroids remarked some differences between the inner and the outer cell layers, with a certain commitment observed at the inner cells. Both scaffolds showed a relatively smooth surface at low magnification. Macro- and micropores having a scarce distribution were observed on both bone substitutes. gtMSCs grew with relative difficulty on the biomaterials. After 72 h of proliferation, gtMSCs scarcely covered the surface of bovine bone scaffolds, demonstrating fibroblast-like or star-like shapes with elongated filiform extensions. Our results add other data on the possible usefulness of gtMSC and could question the current paradigm regarding the complete removal of chronically inflamed gts from the defects during periodontal surgeries. Until optimal protocols for ex vivo manipulation of MSCs are available for clinical settings, it is advisable to use biocompatible bone substitutes that allow the development of progenitor cells.

Do oral bacteria alter the regenerative potential of stem cells? A concise review

Mesenchymal stem cells (MSCs) are widely recognized as critical players in tissue regeneration. New insights into stem cell biology provide evidence that MSCs may also contribute to host defence and inflammation. In case of tissue injury or inflammatory diseases, e.g. periodontitis, stem cells are mobilized towards the site of damage, thus coming in close proximity to bacteria and bacterial components. Specifically, in the oral cavity, complex ecosystems of commensal bacteria live in a mutually beneficial state with the host. However, the formation of polymicrobial biofilm communities with pathogenic properties may trigger an inadequate host inflammatory-immune response, leading to the disruption of tissue homoeostasis and development of disease. Because of their unique characteristics, MSCs are suggested as crucial regulators of tissue regeneration even under such harsh environmental conditions. The heterogeneous effects of bacteria on MSCs across studies imply the complexity underlying the interactions between stem cells and bacteria. Hence, a better understanding of stem cell behaviour at sites of inflammation appears to be a key strategy in developing new approaches for in situ tissue regeneration. Here, we review the literature on the effects of oral bacteria on cell proliferation, differentiation capacity and immunomodulation of dental-derived MSCs.

Periodontal ligament stem cells: current status, concerns, and future prospects

Periodontal ligament stem cells (PDLSCs), which reside in the perivascular space of the periodontium, possess characteristics of mesenchymal stem cells and are a promising tool for periodontal regeneration. Recently, great progress has been made in PDLSC transplantation. Investigators are attempting to maximize the proliferation and differentiation potential of PDLSCs by modifying culture conditions and applying growth factors. Nevertheless, problems remain. First, incomparability among different studies must be minimized by establishing standard guidelines for culture and identification of PDLSCs. Notably, attention should be paid to the biological safety of PDLSC transplantation. The present review updates the latest findings regarding PDLSCs and discusses standard criteria for culture and identification of PDLSCs. Finally, the review calls for careful consideration of PDLSC transplantation safety.