Effect of TNF-α on the proliferation and osteogenesis of human periodontal mesenchymal stem cells

TNF reduces osteogenic cell fate in PDL cells at transcriptional and functional levels without alteration of periodontal proliferative capacity

AIMS

To investigate the effect of tumor necrosis factor (TNF) on the growth of human periodontal ligament (PDL) cells, their osteogenic differentiation and modulation of their matrix secretion in vitro.

METHODS

The influence of 10 ng/ml TNF on proliferation and metabolic activity of PDL cells was analyzed by cell counting (DAPI [4',6-diamidino-2-phenylindole] staining) and the MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) assay. In addition, cells were cultured under control conditions and osteogenic conditions (media containing 10 mM β-glycerophosphate). Quantitative expression analysis of genes encoding the osteogenic markers alkaline phosphatase (ALP), collagen type I alpha 1 chain (COL1A1), osteoprotegerin (OPG), and osteopontin (OPN) was performed after 7 and 14 days of cultivation. Calcium deposits were stained with alizarin red.

RESULTS

Our studies showed that 10 ng/ml TNF did not affect the survival and metabolic activity of PDL cells. Quantitative expression analysis revealed that long-term cultures with TNF impaired osteogenic cell fate at early and late developmental stages. Furthermore, TNF significantly reduced matrix secretion in PDL cells.

CONCLUSION

The present data confirm TNF as a regulatory factor of proinflammatory remodeling that influences the differentiation behavior but not the metabolism and cell proliferation of the periodontium. Therefore, TNF represents an interesting target for the regulation of orthodontic remodeling processes in the periodontium.

Molecular Basis beyond Interrelated Bone Resorption/Regeneration in Periodontal Diseases: A Concise Review

Periodontitis is the sixth most common chronic inflammatory disease, destroying the tissues supporting the teeth. There are three distinct stages in periodontitis: infection, inflammation, and tissue destruction, where each stage has its own characteristics and hence its line of treatment. Illuminating the underlying mechanisms of alveolar bone loss is vital in the treatment of periodontitis to allow for subsequent reconstruction of the periodontium. Bone cells, including osteoclasts, osteoblasts, and bone marrow stromal cells, classically were thought to control bone destruction in periodontitis. Lately, osteocytes were found to assist in inflammation-related bone remodeling besides being able to initiate physiological bone remodeling. Furthermore, mesenchymal stem cells (MSCs) either transplanted or homed exhibit highly immunosuppressive properties, such as preventing monocytes/hematopoietic precursor differentiation and downregulating excessive release of inflammatory cytokines. In the early stages of bone regeneration, an acute inflammatory response is critical for the recruitment of MSCs, controlling their migration, and their differentiation. Later during bone remodeling, the interaction and balance between proinflammatory and anti-inflammatory cytokines could regulate MSC properties, resulting in either bone formation or bone resorption. This narrative review elaborates on the important interactions between inflammatory stimuli during periodontal diseases, bone cells, MSCs, and subsequent bone regeneration or bone resorption. Understanding these concepts will open up new possibilities for promoting bone regeneration and hindering bone loss caused by periodontal diseases.

Indoleamine 2,3-dioxygenase mediates the therapeutic effects of adipose-derived stromal/stem cells in experimental periodontitis by modulating macrophages through the kynurenine-AhR-NRF2 pathway

OBJECTIVES

Mesenchymal stromal/stem cell (MSC)-based therapy has become a promising approach to periodontal tissue repair. Adipose-derived stromal/stem cells (ASCs), compared with other dental or non-dental MSCs, serve as promising candidates for MSC therapy due to non-invasive acquisition and abundant sources. This study aimed to explore the effects of ASC therapy in experimental periodontitis and the underlying mechanism.

METHODS

Micro-CT was performed to evaluate the alveolar bone parameters following local injection of ASCs. Immunohistochemistry and immunofluorescence were employed to detect the expression of IL-1β, osteocalcin (OCN), nuclear factor (erythroid-derived 2)-like 2 (NRF2), and surface markers of macrophage polarization. Afterward, multiple reaction monitoring (MRM)-based targeted tryptophan metabolomic analysis was used to examine the ASC metabolites. Chromatin immunoprecipitation (ChIP)-qPCR assay was performed to investigate the direct binding of aryl hydrocarbon receptor (AhR) and NRF2.

RESULTS

Alveolar bone loss was reduced, and the ratio of iNOS⁺/CD206⁺ macrophages was significantly decreased after ASC injection in the rat models of periodontitis. ASCs promoted NRF2 expression and activation in macrophages, while NRF2 silencing in macrophages blocked the regulation of ASCs on macrophages. Furthermore, the expression of indoleamine 2,3-dioxygenase (IDO) of ASCs in the inflammatory condition was high. The inhibitor of IDO, 1-methyltryptophan (1-MT), impaired the therapeutic effects of ASCs in experimental periodontitis and regulation of macrophage polarization. Mechanistically, kynurenine (Kyn), a metabolite of ASCs catalyzed by IDO, activated AhR and enhanced its binding to the promoter of NRF2, which stimulated M2 macrophage polarization.

CONCLUSIONS

These findings suggested that ASCs can alleviate ligature-induced periodontitis through modulating macrophage polarization by the IDO-dependent Kyn-AhR-NRF2 pathway, uncovering a novel mechanism and providing a scientific basis for ASC-based therapy in experimental periodontitis.

Reactive morphology of dividing microglia following kainic acid administration

The microglial response to a pathological microenvironment is hallmarked by a change in cellular morphology. Following a pathological stimulus, microglia become reactive and simultaneously divide to create daughter cells. Although a wide array of microglial morphologies has been observed, the exact functions of these distinct morphologies are unknown, as are the morphology and reactivity status of dividing microglia. In this study, we used kainic acid to trigger microglial activation and cell division. Following a cortical kainic acid injection, microglial morphology and proliferation were examined at 3 days post-injection using immunohistochemistry for ionized calcium binding adapter molecule 1 (Iba1) to stain for microglia, and KI67 as a marker of cell division. Individual microglial cells were isolated from photomicrographs and skeletal and fractal analyses were used to examine cell size and spatial complexity. We examined the morphology of microglia in both wildtype and microglia-specific tumor necrosis factor (TNF)-α knockout mice. Data were analyzed using generalized linear mixed models or a two-way ANOVA. We found that dividing microglia had a more reactive morphology (larger cell body area, longer cell perimeter, and less ramification) compared to microglia that were not dividing, regardless of microglial release of TNF-α. However, we also observed dividing microglia with a complex, more ramified morphology. Changes in microglial morphology and division were greatest near the kainic acid injection site. This study uses robust and quantitative techniques to better understand microglial cell division, morphology, and population dynamics, which are essential for the development of novel therapeutics that target microglia.

Vitamin D Enhanced the Osteogenic Differentiation of Cell Spheroids Composed of Bone Marrow Stem Cells

Background and Objectives: Vitamin D is a bone modulator widely used in regenerative medicine. This study aimed to analyze the effects of vitamin D on the osteogenic differentiation and mineralization of human mesenchymal stem cells. Materials and Methods: Spheroids were fabricated using human bone marrow-derived stem cells, and were cultured in the presence of vitamin D at concentrations of 0, 0.1, 1, 10, and 100 nM. Stem cell spheroids were fabricated and the morphological evaluation was conducted on days 1, 3, 7 and 14. Determination of qualitative cellular viability was performed with Live/Dead Kit assay on days 1 and 7. Quantitative cellular viability was evaluated with Cell Counting Kit-8 on days 1, 3, 7, and 14. To analyze the osteogenic differentiation of cell spheroids, alkaline phosphatase activity assays were performed with commercially available kit on days 7 and 14. Real-time polymerase chain reaction was used to determine the expression levels of RUNX2, BSP, OCN, and COL1A1 on days 7 and 14. Results: The stem cells produced well-formed spheroids, and addition of vitamin D did not result in any noticeable changes in the shape. The addition of vitamin D did not significantly change the diameter of the spheroids at 0, 0.1, 1, 10, or 100 nM concentrations. Quantitative cell viability results from days 1, 3, 7 and 14 showed no significant difference between groups (p > 0.05). There was significantly higher alkaline phosphatase activity in the 0.1 nM group when compared with the control group on day 14 (p < 0.05). Real-time polymerase chain reaction results demonstrated that the mRNA expression levels of RUNX2, OCN, and COL1A1 were significantly increased when vitamin D was added to the culture. Conclusions: Based on these findings, we concluded that vitamin D could be applied to the increased osteogenicity of stem cell spheroids.