Chemerin-ChemR23 signaling in tooth development

Immune System of Dental Pulp in Inflamed and Normal Tissue

Teeth are vulnerable to structural compromise, primarily attributed to carious lesions, in which microorganisms originating from the oral cavity deteriorate the mineralized structures of enamel and dentin, subsequently infiltrating the underlying soft connective tissue, known as the dental pulp. Nonetheless, dental pulp possesses the necessary capabilities to detect and defend against bacteria and their by-products, using a variety of intricate defense mechanisms. The pulp houses specialized cells known as odontoblasts, which encounter harmful substances produced by oral bacteria. These cells identify pathogens at an early stage and commence the immune system response. As bacteria approach the pulp, various cell types within the pulp, such as different immune cells, stem cells, fibroblasts, as well as neuronal and vascular networks, contribute a range of defense mechanisms. Therefore, the immune system is present in the healthy pulp to restrain the initial spread of pathogens, and then in the inflamed pulp, it prepares the conditions for necrosis or regeneration, so inflammatory response mechanisms play a critical role in maintaining tissue homeostasis. This review aims to consolidate the existing literature on the immune system in dental pulp, encompassing current knowledge on this topic that explains the diverse mechanisms of recognition and defense against pathogens exhibited by dental pulp cells, elucidates the mechanisms of innate and adaptive immunity in inflamed pulp, and highlights the difference between inflamed and normal pulp tissue.

Chemokine‑like receptor 1‑positive cells are present in the odontoblast layer in tooth tissue in rats and humans

Cluster of differentiation (CD)44 is a marker of dental pulp stem cells and is involved in odontoblast differentiation and calcification. Chemokine-like receptor 1 (CMKLR1), also known as chemerin receptor 23 (ChemR23) is also expressed in odontoblasts and dental pulp stem cells and is involved in inflammation suppression and tooth regeneration. Resolvin E1, a bioactive lipid, is a CMKLR1 ligand that mediates the chemerin-CMKLR1 interaction and suppresses pulpal inflammation. The present study clarified the intracellular and tissue localization of CD44 and CMKLR1 by immunohistochemical staining of normal pulp and pulp with pulpitis from 12-week-old male Wistar rat teeth or human teeth. In addition, the localization of CD44 and CMKLR1 in human dental pulp stem cells was observed by immunofluorescence staining. The present study also examined the involvement of resolvin E1 in inhibiting inflammation and calcification by western blotting. CD44- and CMKLR1-positive cells were confirmed in the odontoblast layer in normal dental pulp of rats and humans. CD44 was mainly localized in the cell membrane and CMKLR1 was mainly found in the cytoplasm of human dental pulp stem cells. CMKLR1 was also confirmed in the odontoblast layer in rats and humans with pulpitis but CD44 was not present. Following treatment of dental pulp stem cells with lipoteichoic acid, which imitates Gram-positive bacterial infection, resolvin E1 did not suppress the expression of cyclooxygenase-2 or of the odontoblast differentiation marker, dentin sialophosphoprotein. Furthermore, resolvin E1 induced the differentiation of dental pulp stem cells into odontoblasts even in the presence of the inflammatory stimulus.

Photoluminescent carbon dots (PCDs) from sour apple: a biocompatible nanomaterial for preventing UHMWPE wear-particle induced osteolysis via modulating Chemerin/ChemR23 and SIRT1 signaling pathway and its bioimaging application

Photoluminescent nanomaterials have been widely employed in several biological applications both in vitro and in vivo. For the first time, we report a novel application of sour apple-derived photoluminescent carbon dots (PCDs) for reducing ultra-high molecular weight polyethylene (UHMWPE) wear particle-induced osteolysis using mouse calvarial model. Generally, aseptic prosthetic loosening seems to be a significant postoperative problem for artificial joints replacement, which is mainly contributed by UHMWPE-induced osteolysis. Hence, inhibiting osteoclastic bone-resorption could minimize UHMWPE-induced osteolysis for implant loosening. Prior to osteolysis studies, the prepared sour apple-derived PCDs were employed for bioimaging application. As expected, the prepared PCDs effectively inhibited the UHMWPE particle-induced osteoclastogenesis in vitro. The PCDs treatment effectively inhibited the UHMWPE-induced osteoclast differentiation, F-actin ring pattern, and bone resorption in vitro. Also, the PCDs reduced the UHMWPE-induced ROS stress as well as the expression level of pro-inflammatory cytokines, including TNF-α, IL-1, IL-6, and IL-8. Further, the qPCR and western blot results hypothesized that PCDs inhibited the UHMWPE wear particle-induced osteolysis through suppressing chemerin/ChemR23 signaling and NFATc1 pathway, along with upregulation of SIRT1 expression. Overall, these findings suggest that the synthesized PCDs could be a potential therapeutic material for minimizing UHMWPE particle-induced periprosthetic osteolysis to avoid postoperative complications.

The utilisation of resolvins in medicine and tissue engineering

Recent advances in the field of regenerative medicine and biomaterial science have highlighted the importance of controlling immune cell phenotypes at the biomaterial interface. These studies have clearly indicated that a rapid resolution of the inflammatory process, mediated by a switch in the macrophage population towards a reparative phenotype, is essential for tissue regeneration to occur. While various biomaterial surfaces have been developed in order to impart immunomodulatory properties to the resulting constructs, an alternative strategy involving the use of reparative biological cues, known as resolvins, is emerging in regenerative medicine. This review reports on the mechanisms via which resolvins participate in the resolution of inflammation and describes their current utilisation in pre-clinical and clinical settings, along with their effectiveness when combined with biomaterial constructs in tissue engineering applications. STATEMENT OF SIGNIFICANCE: The resolution of the inflammatory process is necessary for achieving tissue healing and regeneration. Resolvins are lipid mediators and play a key role in the resolution of the inflammatory response and can be used in as biological cues to promote tissue regeneration. This review describes the various biological inflammatory mechanisms and pathways involving resolvins and how their action results in a pro-healing response. The use of these molecules in the clinical setting is then summarised for various applications along with their limitations. Lastly, the review focuses on the emergence resolvins in tissue engineering products including the use of a more stable form which holds greater prospect for regenerative purposes.

Adipokines in dental pulp: physiological, pathological, and potential therapeutic roles

BACKGROUND

Hundreds of adipokines have been identified, and their extensive range of endocrine functions-regulating distant organs such as oral tissues-and local autocrine/paracrine roles have been studied. In dentistry, however, adipokines are poorly known proteins in the dental pulp; few of them have been studied despite their large number. This study reviews recent advances in the investigation of dental-pulp adipokines, with an emphasis on their roles in inflammatory processes and their potential therapeutic applications.

HIGHLIGHTS

The most recently identified adipokines in dental pulp include leptin, adiponectin, resistin, ghrelin, oncostatin, chemerin, and visfatin. They have numerous physiological and pathological functions in the pulp tissue: they are closely related to pulp inflammatory mechanisms and actively participate in cell differentiation, mineralization, angiogenesis, and immune-system modulation.

CONCLUSION

Adipokines have potential clinical applications in regenerative endodontics and as biomarkers or targets for the pharmacological management of inflammatory and degenerative processes in dental pulp. A promising direction for the development of new therapies may be the use of agonists/antagonists to modulate the expression of the most studied adipokines.

Chemerin/ChemR23 signaling mediates the effects of ultra-high molecular weight polyethylene wear particles on the balance between osteoblast and osteoclast differentiation

Background

Ultra-high molecular weight polyethylene (UHMWPE) is one of the favored materials for total joint replacement, but its wear particles cause osteolysis. This study aims to elucidate the signaling that mediates the effects of UHMWPE particles on bone cells.

Methods

RAW264.7 and MC3T3-E1 cells were treated with UHMWPE particles. Chemerin/ChemR23 signaling was manipulated by either overexpressing Rarres2 and Cmklr1 or silencing Cmklr1. The osteoblast and osteoclast differentiation was evaluated by Alizarin red and TRAP staining, respectively. The expression of osteogenic and osteoclastogenic markers was assessed with quantitative real time PCR and western blot.

Results

UHMWPE particles upregulated the expression of Rarres2 and Cmklr1 in both osteoblast and osteoclast precursor cells. UHMWPE particles induced osteoclast differentiation while inhibited osteoblast differentiation, and this effect was abrogated by silencing Cmklr1 but augmented by the overexpression of Rarres2 and Cmklr1. Similarly, the expression of osteogenic marker genes was inhibited while that of osteoclastogenic marker genes was activated by UHMWPE particles, and this effect was abolished by silencing Cmklr1 and enhanced by Rarres2 and Cmklr1 overexpression.

Conclusions

These results demonstrated that chemerin/ChemR23 signaling plays a central role in the effects of UHMWPE particles on the balance of osteogenic and osteoclastogenic differentiation, which changes the course of bone remodeling and eventually results in osteolysis.

Resolvin E1 accelerates pulp repair by regulating inflammation and stimulating dentin regeneration in dental pulp stem cells

Background

Unresolved inflammation and tissue destruction are considered to underlie the failure of dental pulp repair. As key mediators of the injury response, dental pulp stem cells (DPSCs) play a critical role in pulp tissue repair and regeneration. Resolvin E1 (RvE1), a major dietary omega-3 polyunsaturated fatty-acid metabolite, is effective in resolving inflammation and activating wound healing. However, whether RvE1 facilitates injured pulp-tissue repair and regeneration through timely resolution of inflammation and rapid mobilization of DPSCs is unknown. Therefore, we established a pulp injury model and investigated the effects of RvE1 on DPSC-mediated inflammation resolution and injured pulp repair.

Methods

A pulp injury model was established using 8-week-old Sprague-Dawley rats. Animals were sacrificed on days 1, 3, 7, 14, 21, and 28 after pulp capping with a collagen sponge immersed in PBS with RvE1 or PBS. Hematoxylin-eosin and Masson’s trichrome staining, immunohistochemistry, and immunohistofluorescence were used to evaluate the prohealing properties of RvE1. hDPSCs were incubated with lipopolysaccharide (LPS) to induce an inflammatory response, and the expression of inflammatory factors after RvE1 application was measured. Effects of RvE1 on hDPSC proliferation, chemotaxis, and odontogenic differentiation were evaluated by CCK-8 assay, transwell assay, alkaline phosphatase (ALP) staining, alizarin red staining, and quantitative PCR, and possible signaling pathways were explored using western blotting.

Results

In vivo, RvE1 reduced the necrosis rate of damaged pulp and preserved more vital pulps, and promoted injured pulp repair and reparative dentin formation. Further, it enhanced dentin matrix protein 1 and dentin sialoprotein expression and accelerated pulp inflammation resolution by suppressing TNF-α and IL-1β expression. RvE1 enhanced the recruitment of CD146⁺ and CD105⁺ DPSCs to the damaged molar pulp mesenchyme. Isolated primary cells exhibited the mesenchymal stem cell immunophenotype and differentiation. RvE1 promoted hDPSC proliferation and chemotaxis. RvE1 significantly attenuated pro-inflammatory cytokine (TNF-α, IL-1β, and IL-6) release and enhanced ALP activity, nodule mineralization, and especially, expression of the odontogenesis-related genes DMP1, DSPP, and BSP in LPS-stimulated DPSCs. RvE1 regulated AKT, ERK, and rS6 phosphorylation in LPS-stimulated DPSCs.

Conclusions

RvE1 promotes pulp inflammation resolution and dentin regeneration and positively influences the proliferation, chemotaxis, and differentiation of LPS-stimulated hDPSCs. This response is, at least partially, dependent on AKT, ERK, and rS6-associated signaling in the inflammatory microenvironment. RvE1 has promising application potential in regenerative endodontics.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02141-y.

A unique radioprotective effect of resolvin E1 reduces irradiation-induced damage to the inner ear by inhibiting the inflammatory response

Background

In addition to the direct effects of irradiation, the induced inflammatory response may play an important role in the damage to the inner ear caused by radiotherapy for the treatment of head and neck cancers. Resolvin E1 (RvE1) has anti-inflammatory activity, acting by reducing neutrophil infiltration and proinflammatory cytokine expression. Therefore, in this study we sought to confirm whether the inflammation induced by irradiation was involved in damage to the inner ear after radiotherapy and to investigate the protective effect and underlying mechanism of RvE1 using mouse models.

Methods

A dose of RvE1 was delivered by intraperitoneal injection to mice before irradiation. Changes in the auditory brainstem response (ABR), relative balance ability, inner ear morphology and the expression levels of inflammatory factors in the inner ear were analyzed on days 7 and 14 after irradiation and compared among different experimental groups.

Results

Changes of ABR and relative balance ability showed the inner functions of experimental mice presented severe damage after irradiation, but the damage was significantly alleviated after RvE1 pretreatment compared to irradiation alone. Morphological analysis of the inner ear showed severe damage to the cochlea and vestibule after irradiation. In contrast, damage to the cochlea and vestibule was significantly reduced in the RvE1-pretreated group compared to that in the irradiation alone group. Along with these functional and morphological changes, the mRNA expression level of anti-inflammatory factors interleukin-2 was significantly increased, while those of proinflammatory factors interleukin-6 and tumor necrosis factor-α were significantly decreased in the inner ear of mice after RvE1 pretreatment compared to irradiation alone.

Conclusions

We believe that inflammation induced by irradiation is involved in the damage to the inner ear caused by radiotherapy, and that RvE1 reduces the damage caused by irradiation to the inner ear by regulating the induced inflammatory response.

Resolvin E1 Ameliorates Pulpitis by Suppressing Dental Pulp Fibroblast Activation in a Chemerin Receptor 23-dependent Manner

INTRODUCTION

Timely resolution of pulp inflammation is a prerequisite for the healing of inflamed dental pulp. Stromal cells, particularly fibroblasts, play a critical role in the inflammation resolution process. Resolvin E1 (RvE1) is a lipid-derived endogenous proresolution molecule that mediates this resolution process. In the present study, we investigated the effects of RvE1 on dental fibroblasts during the pathogenesis of pulpitis.

METHODS

The pulp tissues in maxillary incisors of male Sprague-Dawley rats (N = 50) were exposed to the oral environment for 0, 9, 24, and 48 hours, after which they were treated with RvE1 or its vehicle. The inflammatory changes after 24 hours were assessed using hematoxylin-eosin staining, immunohistochemistry, enzyme-linked immunosorbent assay, and quantitative polymerase chain reaction. Chemerin receptor 23 (ChemR23) expression in rat pulp tissues and human dental fibroblasts was detected by immunofluorescence, Western blot analysis, and quantitative polymerase chain reaction. Finally, small interfering RNA-based knockdown studies were performed to evaluate the effects of RvE1 inhibition on proinflammatory genes and nuclear factor kappa B signaling of human dental pulp fibroblasts.

RESULTS

Early treatment (within 24 hours after pulp exposure) with RvE1 promoted a decline in the number of inflammatory cells and gene expression of proinflammatory cytokines. Moreover, it reduced ChemR23 expression in the fibroblastlike cells of inflamed pulp tissues. In vitro, ChemR23 was widely expressed in human dental fibroblasts. RvE1 significantly suppressed cytokine production by fibroblasts, with down-regulation of the nuclear translocation of nuclear factor kappa B p65 in these cells. Knockdown of ChemR23 almost abolished the anti-inflammatory effect of RvE1.

CONCLUSIONS

RvE1 can suppress the activation of dental pulp fibroblasts in a ChemR23-dependent manner and inhibit inflammation in the relevant early stages of pulpitis.

The G-protein coupled receptor ChemR23 determines smooth muscle cell phenotypic switching to enhance high phosphate-induced vascular calcification

Aims

Vascular calcification, a marker of increased cardiovascular risk, is an active process orchestrated by smooth muscle cells. Observational studies indicate that omega-3 fatty acids protect against vascular calcification, but the mechanisms are unknown. The G-protein coupled receptor ChemR23 transduces the resolution of inflammation induced by the omega-3-derived lipid mediator resolvin E1. ChemR23 also contributes to osteoblastic differentiation of stem cells and bone formation, but its role in vascular calcification is unknown. The aim of this study was to establish the role of ChemR23 in smooth muscle cell fate and calcification

Methods and results

Gene expression analysis in epigastric arteries derived from patients with chronic kidney disease and vascular calcification revealed that ChemR23 mRNA levels predicted a synthetic smooth muscle cell phenotype. Genetic deletion of ChemR23 in mice prevented smooth muscle cell de-differentiation. ChemR23-deficient smooth muscle cells maintained a non-synthetic phenotype and exhibited resistance to phosphate-induced calcification. Moreover, ChemR23-deficient mice were protected against vitamin D3-induced vascular calcification. Resolvin E1 inhibited smooth muscle cell calcification through ChemR23. Introduction of the Caenorhabditis elegans Fat1 transgene, leading to an endogenous omega-3 fatty acid synthesis and hence increased substrate for resolvin E1 formation, significantly diminished the differences in phosphate-induced calcification between ChemR23+/+ and ChemR23−/− mice.

Conclusion

This study identifies ChemR23 as a previously unrecognized determinant of synthetic and osteoblastic smooth muscle cell phenotype, favouring phosphate-induced vascular calcification. This effect may be of particular importance in the absence of ChemR23 ligands, such as resolvin E1, which acts as a calcification inhibitor under hyperphosphatic conditions.