Contribution of atypical chemokine receptor 2/ackr2 in bone remodeling

The cellular landscape of the endochondral bone during the transition to extrauterine life

The cellular complexity of the endochondral bone underlies its essential and pleiotropic roles during organismal life. While the adult bone has received significant attention, we still lack a deep understanding of the perinatal bone cellulome. Here, we have profiled the full composition of the murine endochondral bone at the single-cell level during the transition from fetal to newborn life and in comparison with the adult tissue, with particular emphasis on the mesenchymal compartment. The perinatal bone contains different fibroblastic clusters with blastema-like characteristics in organizing and supporting skeletogenesis, angiogenesis and hematopoiesis. Our data also suggest dynamic inter- and intra-compartment interactions, as well as a bone marrow milieu that seems prone to anti-inflammation, which we hypothesize is necessary to ensure the proper program of lymphopoiesis and the establishment of central and peripheral tolerance in early life. Our study provides an integrative roadmap for the future design of genetic and cellular functional assays to validate cellular interactions and lineage relationships within the perinatal bone.

Identification of potential crosstalk genes and mechanisms between periodontitis and diabetic nephropathy through bioinformatic analysis

Periodontitis and diabetic nephropathy are significant public health concerns globally and are closely related with each other. This study aimed to identify potential crosstalk genes, pathways, and mechanisms associated with the interaction between periodontitis and diabetic nephropathy. Expression profiles of periodontitis and diabetic nephropathy were retrieved from the Gene expression omnibus gene expression omnibus database, and differentially expressed genes (DEGs) were screened, followed by identification of co-expressed differential genes. Gene ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were performed using R software. A protein-protein interaction network was constructed via STRING website, and key crosstalk genes were selected using Cytoscape. Subsequent gene ontology and KEGG analyses were conducted for the key genes, and a validation dataset was obtained from the gene expression omnibus database for differential gene validation. The TRRUST website was employed to identify transcription factors (TFs) associated with the key crosstalk genes between periodontitis and diabetic nephropathy, followed by differential analysis of TFs. A total of 17 crosstalk genes were obtained. Among them, SAMSN1, BCL2A1, interleukin-19, IL1B, RGS1, CXCL3, CCR1, CXCR4, CXCL1, and PTGS2 were identified as key crosstalk genes between periodontitis and diabetic nephropathy. Additionally, 16 key TFs were discovered. This bioinformatic analysis revealed potential crosstalk genes between periodontitis and diabetic nephropathy. The identified key genes participate in signaling pathways, including cytokine signaling and chemokine signaling transduction, which might collectively influence these 2 diseases. These genes may serve as potential biomarkers guiding future research in this field.

Impact of FGF1 on human periodontal ligament fibroblast growth, osteogenic differentiation and inflammatory reaction in vitro

PURPOSE

To investigate in vitro the impact of fibroblast growth factor 1 (FGF1) in comparison to ascorbic acid (AscA) on human periodontal ligament fibroblast (HPdLF) growth, their osteogenic differentiation, and modulation of their inflammatory reaction to mechanical stress.

METHODS

The influence of different concentrations of FGF1 (12.5-200 ng/mL) on growth and proliferation of HPdLF cells was analyzed over 20 days by counting cell numbers and the percentage of Ki67-positive cells. Quantitative expression analysis of genes encoding the osteogenic markers alkaline phosphatase (ALPL), Runt-related transcription factor 2 (RUNX2), osteocalcin (OCN), and osteopontin (OSP), as well as the fibroblast markers vimentin (VIM) and fibroblast-specific protein 1 (FSP1), was performed after 2 and 20 days of cultivation. Metabolic activity was determined by MTT assay. For comparison with AscA, 50 ng/mL FGF1 was used for stimulation for 2 and 20 days. Cell number, percentage of Ki67-positive cells, and expression of osteoblast- and fibroblast-specific genes were examined. Alkaline phosphatase activity was visualized by NBT/BCIP and calcium deposits were stained with alizarin red. Cytokine (IL‑6, IL‑8, COX2/PGE2) expression and secretion were analyzed by qPCR and ELISA in 6 h mechanically compressed HPdLF cultured for 2 days with FGF1 or ascorbic acid.

RESULTS

Higher concentrations of FGF1 promoted cell proliferation upon short-term stimulation, whereas prolonged treatment induced the expression of osteogenic markers even with low concentrations. AscA promotes cell growth more markedly than FGF1 in short-term cultures, whereas FGF1 induced osteogenic cell fate more strongly in long-term culture. Both factors induced an increased inflammatory response of HPdLF to mechanical compression.

CONCLUSION

Our data suggest that FGF1 promotes an osteogenic phenotype of HPdLF and limits inflammatory response to mechanical forces compared to AscA.

Probiotic Bifidobacterium animalis subsp. lactis consumption slows down orthodontic tooth movement in mice

INTRODUCTION

Probiotics are live microorganisms that, when consumed in appropriate amount, can provide health benefits. Although many studies have shown positive results with the use of probiotics in bone loss control, as in periodontal disease, the effect of probiotics on a mechanical force-induced alveolar bone resorption is still unknown. Therefore, this study aimed to investigate the impact of the specific probiotic Bifidobacterium animalis subsp. lactis on bone remodeling induced by orthodontic tooth movement.

METHODS

For this study, thirty C57BL6/J male mice were used and divided into two groups: 1- Mice were orally treated with the probiotic; 2- Mice were treated with vehicle. All mice were submitted to the experimental model of orthodontic tooth movement (OTM). Bone parameters and OTM was evaluated by MicroCT. OTM and TRAP positive cells were analyzed by histomorphometric analysis. Osteoclasts markers were evaluated by qPCR and short chain fatty acids were measured in feces.

RESULTS

Micro-CT analysis showed that probiotic treatment did not modify the alveolar bone parameters. However, supplementation with probiotics restrained the tooth movement, as demonstrated by the reduced distance of OTM. Probiotic-treated mice presented down-regulation of Trap expression and reduced osteoclast numbers compared to the control. Accordingly, probiotics supplemented mice exhibited a higher concentration of short-chain fatty acid in their feces.

CONCLUSIONS

The supplementation with Bifidobacterium animalis subsp. lactis impaired tooth movement without altering the alveolar bone microarchitecture. The effect on bone remodeling induced by Bifidobacterium animalis subsp. lactis may be associated with the short-chain fatty acids' production.

Biomechanical and biological responses of periodontium in orthodontic tooth movement: up-date in a new decade

Nowadays, orthodontic treatment has become increasingly popular. However, the biological mechanisms of orthodontic tooth movement (OTM) have not been fully elucidated. We were aiming to summarize the evidences regarding the mechanisms of OTM. Firstly, we introduced the research models as a basis for further discussion of mechanisms. Secondly, we proposed a new hypothesis regarding the primary roles of periodontal ligament cells (PDLCs) and osteocytes involved in OTM mechanisms and summarized the biomechanical and biological responses of the periodontium in OTM through four steps, basically in OTM temporal sequences, as follows: (1) Extracellular mechanobiology of periodontium: biological, mechanical, and material changes of acellular components in periodontium under orthodontic forces were introduced. (2) Cell strain: the sensing, transduction, and regulation of mechanical stimuli in PDLCs and osteocytes. (3) Cell activation and differentiation: the activation and differentiation mechanisms of osteoblast and osteoclast, the force-induced sterile inflammation, and the communication networks consisting of sensors and effectors. (4) Tissue remodeling: the remodeling of bone and periodontal ligament (PDL) in the compression side and tension side responding to mechanical stimuli and root resorption. Lastly, we talked about the clinical implications of the updated OTM mechanisms, regarding optimal orthodontic force (OOF), acceleration of OTM, and prevention of root resorption.

Maxillary suture expansion: A mouse model to explore the molecular effects of mechanically-induced bone remodeling

The aim of this study was to analyze the effect of rapid maxillary expansion (RME) on hard tissues. Opening loops bonded to the first and second maxillary molars on both sides were used to apply distracting forces of 0.28 N, 0.42 N and 0.56 N at the midpalatal suture for 7 and 14 days. Microcomputed tomography (MicroCT), histomorphometry and quantitative polymerase chain reaction (qPCR) analysis were performed to evaluate RME effectiveness, midpalatal suture remodeling, cell counting of osteoblasts, osteoclasts and chondrocytes and the expression of bone remodeling markers, respectively. All forces at the two different time points resulted in similar RME and enhanced of bone remodeling. Accordingly, increased number of osteoblasts and reduced chondrocytes counting and no difference in osteoclasts were seen after all RME protocols. RME yielded increased expression of bone remodeling markers as osteocalcin (Ocn), dentin matrix acidic phosphoprotein-1 (Dmp1), runt-related transcription factor 2 (Runx2), collagen type I Alpha 1 (Col1a1), alkaline phosphatase (ALP), receptor activator of nuclear factor kappa B (RANK), receptor activator of nuclear factor kappa B ligand (Rankl), osteoprotegerin (Opg), cathepsin K (Ctsk), matrix metalloproteinases 9 and 13 (Mmp9 and 13), transforming growth fator beta 1, 2 and 3 (Tgfb 1, Tgfb 2 and Tgfb3), bone morphogenetic protein 2 (Bmp-2), sclerostin (Sost), beta-catenin-like protein 1 (Ctnnbl) and Wnt signaling pathways 3, 3a and 5a (Wnt 3, Wnt 3a and Wnt 5a). These findings characterize the cellular changes and potential molecular pathways involved in RME, proving the reliability of this protocol as a model for mechanical-induced bone remodeling.

ACKR2 contributes to pulmonary dysfunction by shaping CCL5:CCR5-dependent recruitment of lymphocytes during influenza A infection in mice

Inflammation triggered by influenza A virus (IAV) infection is important for viral clearance, induction of adaptive responses, and return to lung homeostasis. However, an exaggerated immune response, characterized by the overproduction of chemokines, can lead to intense lung injury, contributing to mortality. Chemokine scavenger receptors, such as ACKR2, control the levels of CC chemokines influencing the immune responses. Among the chemokine targets of ACKR2, CCL5 is important to recruit and activate lymphocytes. We investigated the role of ACKR2 during IAV infection in mice. Pulmonary ACKR2 expression was increased acutely after IAV infection preceding the virus-induced lung dysfunction. ACKR2-knockout (ACKR2−/−) mice were protected from IAV, presenting decreased viral burden and lung dysfunction. Mechanistically, the absence of ACKR2 resulted in augmented airway CCL5 levels, secreted by mononuclear and plasma cells in the lung parenchyma. The higher chemokine gradient led to an augmented recruitment of T and B lymphocytes, formation of inducible bronchus-associated lymphoid tissue and production of IgA in the airways of ACKR2−/− mice post-IAV. CCL5 neutralization in ACKR2−/− mice prevented lymphocyte recruitment and increased bronchoalveolar lavage fluid protein levels and pulmonary dysfunction. Finally, CCR5−/− mice presented increased disease severity during IAV infection, displaying increased neutrophils, pulmonary injury and dysfunction, and accentuated lethality. Collectively, our data showed that ACKR2 dampens CCL5 levels and the consequent recruitment of CCR5+ T helper 1 (Th1), T regulatory cells (Tregs), and B lymphocytes during IAV infection, decreasing pathogen control and promoting lung dysfunction in wild type mice. Therefore, ACKR2 is detrimental and CCR5 is protective during IAV infection coordinating innate and adaptive immune responses in mice.

Chemokines and Bone

Chemokines are a family of small proteins, subdivided by their conserved cysteine residues and common structural features. Chemokines interact with their cognate G-protein-coupled receptors to elicit downstream signals that result in cell migration, proliferation, and survival. This review presents evidence for how the various CXC and CC subfamily chemokines influence bone hemostasis by acting on osteoclasts, osteoblasts, and progenitor cells. Also discussed are the ways in which chemokines contribute to bone loss as a result of inflammatory diseases such as rheumatoid arthritis, HIV infection, and periodontal infection. Both positive and negative effects of chemokines on bone formation and bone loss are presented. In addition, the role of chemokines in altering the bone microenvironment through effects on angiogenesis and tumor invasion is discussed. Very few therapeutic agents that influence bone formation by targeting chemokines or chemokine receptors are available, although a few are currently being evaluated.

Chemokines in Physiological and Pathological Bone Remodeling

The bone matrix is constantly remodeled by bone-resorbing osteoclasts and bone-forming osteoblasts. These two cell types are fundamentally different in terms of progenitor cells, mode of action and regulation by specific molecules, acting either systemically or locally. Importantly, there is increasing evidence for an impact of cell types or molecules of the adaptive and innate immune system on bone remodeling. Understanding these influences is the major goal of a novel research area termed osteoimmunology, which is of key relevance in the context of inflammation-induced bone loss, skeletal metastases, and diseases of impaired bone remodeling, such as osteoporosis. This review article aims at summarizing the current knowledge on one particular aspect of osteoimmunology, namely the impact of chemokines on skeletal cells in order to regulate bone remodeling under physiological and pathological conditions. Chemokines have key roles in the adaptive immune system by controlling migration, localization, and function of immune cells during inflammation. The vast majority of chemokines are divided into two subgroups based on the pattern of cysteine residues. More specifically, there are 27 known C-C-chemokines, binding to 10 different C-C receptors, and 17 known C-X-C-chemokines binding to seven different C-X-C receptors. Three additional chemokines do not fall into this category, and only one of them, i.e., CX3CL1, has been shown to influence bone remodeling cell types. There is a large amount of published studies demonstrating specific effects of certain chemokines on differentiation and function of osteoclasts and/or osteoblasts. Chemokine signaling by skeletal cells or by other cells of the bone marrow niche regulates bone formation and resorption through autocrine and paracrine mechanisms. In vivo evidence from mouse deficiency models strongly supports the role of certain chemokine signaling pathways in bone remodeling. We will summarize these data in the present review with a special focus on the most established subsets of chemokines. In combination with the other review articles of this issue, the knowledge presented here confirms that there is a physiologically relevant crosstalk between the innate immune system and bone remodeling cell types, whose molecular understanding is of high clinical relevance.

Expression of biological mediators during orthodontic tooth movement: A systematic review

OBJECTIVES

The aim of the present systematic review was to offer a timeline of the events taking place during orthodontic tooth movement(OTM).

MATERIALS AND METHODS

Electronic databases PubMed, Web of Science and EMBASE were searched up to November 2017. All studies describing the expression of signaling proteins in the periodontal ligament(PDL) of teeth subjected to OTM or describing the expression of signaling proteins in human cells of the periodontal structures subjected to static mechanical loading were considered eligible for inclusion for respectively the in-vivo or the in-vitro part. Risk of bias assessment was conducted according to the validated SYRCLE's RoB tool for animal studies and guideline for assessing quality of in-vitro studies for in-vitro studies.

RESULTS

We retrieved 7583 articles in the initial electronic search, from which 79 and 51 were finally analyzed. From the 139 protein investigated, only the inflammatory proteins interleukin(IL)-1β, cyclooxygenase(COX)-2 and prostaglandin(PG)-E2, osteoblast markers osteocalcin and runt-related transcription factor(RUNX)2, receptor activator of nuclear factor kappa-B ligand(RANKL) and osteoprotegerin(OPG) and extracellular signal-regulated kinases(ERK)1/2 are investigated in 10 or more studies.

CONCLUSION

The investigated proteins were presented in a theoretical model of OTM. We can conclude that the cell activation and differentiation and recruitment of osteoclasts is mediated by osteocytes, osteoblasts and PDL cells, but that the osteogenic differentiation is only seen in stem cell present in the PDL. In addition, the recently discovered Ephrin/Ephs seem to play an role parallel with the thoroughly investigated RANKL/OPG system in mediating bone resorption during OTM.

ST2 regulates bone loss in a site-dependent and estrogen-dependent manner

Interleukin-33 (IL-33) and its receptor, ST2, are implicated in bone remodeling. The lack of estrogen after menopause results in an accelerated bone loss. Here we investigated the role of ST2 in the bone loss induced by estrogen deficiency. ST2-deficient mice (ST2^-/- ) and their littermates (wildtype [WT]) were ovariectomized (OVX), while ovary-intact mice were used as controls. Bone sites were analyzed by microcomputed tomography, histomorphometry, and quantitative real-time polymerase chain reaction (qPCR). Deletion of IL-33 or ST2 resulted in a similar bone loss in the femur and maxilla. Ovariectomy in WT mice caused bone loss in the same areas. The lack of ST2 in OVX mice did not alter bone remodeling in the femur but prevented bone loss in the maxilla. Consistently, ovariectomy increased the IL-33 messenger RNA (mRNA) levels in the maxilla but not in the femur. Under mechanical stimulation, ovariectomy and ST2 deletion independently increased bone remodeling induced by orthodontic tooth movement, which was also associated with a greater number of osteoclasts and a reduced number of osteoblasts in the maxillary bone. ST2^-/- OVX mice, however, displayed twice as many osteoblasts as that of WT OVX mice. Ovariectomy and ST2 deletion differently altered the cytokine mRNA levels in the maxilla. Remarkably, interleukin-10 expression was decreased in both WT OVX and ST2^-/- mice, and this reduction was completely restored in ST2^-/- OVX mice. The results demonstrate that estrogen and IL33/ST2 independently protect against bone loss. However, the ovariectomy-induced bone loss is IL-33/ST2-dependent in the maxilla but not in the femur, indicating a bimodal and site-specific role of ST2 in bone remodeling.

High-fat diet disrupts bone remodeling by inducing local and systemic alterations

A high-fat (HF) diet leads to detrimental effects on alveolar bone (AB); however, the mechanisms linking adiposity to bone loss are poorly understood. This study investigated if AB resorption induced by an HF diet is associated with the regulation of inflammatory gene expression and if adipocytes can directly interfere with osteoclastogenesis. We also evaluated the effects of diet restriction (DR) on bone phenotype. C57BL6/J mice were fed normal chow or an HF diet for 12 weeks. Samples of maxillae, femur, blood and white adipose tissue were analyzed. In vitro co-culture of bone marrow-derived osteoclasts and mature adipocytes was carried out. The results revealed an increased number of osteoclasts and fewer osteoblasts in animals fed the HF diet, which led to the disruption of trabecular bone and horizontal AB loss. Similar effects were observed in the femur. The metabolic parameters and the deleterious effects of the HF diet on AB and the femur were reversed after DR. The HF diet modulated the expression of 30 inflammatory genes in AB such as Fam3c, InhBa, Tnfs11, Ackr2, Pxmp2 and Chil3, which are related to the inflammatory response and bone remodeling. In vitro, mature adipocytes produced increased levels of adipokines, and co-culture with osteoclasts resulted in augmented osteoclastogenesis. The results indicate that the mechanisms by which an HF diet affects bone involve induction of osteoclastogenesis and inflammatory gene expression. Adipokines apparently are key molecules in this process. Strategies to control diet-induced bone loss might be beneficial in patients with preexisting bone inflammatory conditions.

The atypical chemokine receptor ACKR2 drives pulmonary fibrosis by tuning influx of CCR2+ and CCR5+ IFNγ-producing γδT cells in mice

Chemokines coordinate lung inflammation and fibrosis by acting on chemokine receptors expressed on leukocytes and other cell types. Atypical chemokine receptors (ACKRs) bind, internalize, and degrade chemokines, tuning homeostasis and immune responses. ACKR2 recognizes and decreases the levels of inflammatory CC chemokines. The role of ACKR2 in fibrogenesis is unknown. The purpose of the study was to investigate the role of ACKR2 in the context of pulmonary fibrosis. The effects of ACKR2 expression and deficiency during inflammation and fibrosis were analyzed using a bleomycin-model of fibrosis, ACKR2-deficient mice, bone marrow chimeras, and antibody-mediated leukocyte depletion. ACKR2 was upregulated acutely in response to bleomycin and normalized over time. ACKR2^-/- mice showed reduced lethality and lung fibrosis. Bone marrow chimeras showed that lethality and fibrosis depended on ACKR2 expression in pulmonary resident (nonhematopoietic) cells but not on leukocytes. ACKR2^-/- mice exhibited decreased expression of tissue-remodeling genes, reduced leukocyte influx, pulmonary injury, and dysfunction. ACKR2^-/- mice had early increased levels of CCL5, CCL12, CCL17, and IFNγ and an increased number of CCR2⁺ and CCR5⁺ IFNγ-producing γδT cells in the airways counterbalanced by low Th17-lymphocyte influx. There was reduced accumulation of IFNγ-producing γδT cells in CCR2^-/- and CCR5^-/- mice. Moreover, depletion of γδT cells worsened the clinical symptoms induced by bleomycin and reversed the phenotype of ACKR2^-/- mice exposed to bleomycin. ACKR2 controls the CC chemokine expression that drives the influx of CCR2⁺ and CCR5⁺ IFNγ-producing γδT cells, tuning the Th17 response that mediated pulmonary fibrosis triggered by bleomycin instillation.