Expression of core-binding factor α1 and osteocalcin in fluoride-treated fibroblasts and osteoblasts

Apoptosis and Inflammation Involved with Fluoride-Induced Bone Injuries

BACKGROUND

Excessive fluoride exposure induces skeletal fluorosis, but the specific mechanism responsible is still unclear. Therefore, this study aimed to identify the pathogenesis of fluoride-induced bone injuries.

METHODS

We systematically searched fluoride-induced bone injury-related genes from five databases. Then, these genes were subjected to enrichment analyses. A TF (transcription factor)-mRNA-miRNA network and protein-protein interaction (PPI) network were constructed using Cytoscape, and the Human Protein Atlas (HPA) database was used to screen the expression of key proteins. The candidate pharmacological targets were predicted using the Drug Signature Database.

RESULTS

A total of 85 studies were included in this study, and 112 osteoblast-, 35 osteoclast-, and 41 chondrocyte-related differential expression genes (DEGs) were identified. Functional enrichment analyses showed that the Atf4, Bcl2, Col1a1, Fgf21, Fgfr1 and Il6 genes were significantly enriched in the PI3K-Akt signaling pathway of osteoblasts, Mmp9 and Mmp13 genes were enriched in the IL-17 signaling pathway of osteoclasts, and Bmp2 and Bmp7 genes were enriched in the TGF-beta signaling pathway of chondrocytes. With the use of the TF-mRNA-miRNA network, the Col1a1, Bcl2, Fgfr1, Mmp9, Mmp13, Bmp2, and Bmp7 genes were identified as the key regulatory factors. Selenium methyl cysteine, CGS-27023A, and calcium phosphate were predicted to be the potential drugs for skeletal fluorosis.

CONCLUSIONS

These results suggested that the PI3K-Akt signaling pathway being involved in the apoptosis of osteoblasts, with the IL-17 and the TGF-beta signaling pathways being involved in the inflammation of osteoclasts and chondrocytes in fluoride-induced bone injuries.

Glutamine metabolism in fluorosis: Integrated metabolomics and transcriptomics analysis

OBJECTIVE

To identify the potential metabolic biomarkers of fluorosis and the pathogenesis of fluorosis.

METHODS

Sprague Dawley rats in this study were randomly divided into fluoride exposure and control groups. In the fluoride exposure group, six offspring rats without dental fluorosis were defined as group A, and six offspring rats with dental fluorosis were defined as group C. Eight offspring rats in the control group were defined as group B. The metabolites in plasma were determined using GC-MS, with differential metabolites (DMs) identified using VIP > 1, and P < 0.05. Cluster analysis, KEGG pathway enrichment analysis and Receiver Operating Characteristic (ROC) analysis were subsequently performed. The DMs which were caused by fluoride exposure in the previous study were used to verify our results. The GSE70719 from GEO database were used to support this research at the mRNA level and in vitro experiment were selected to verify above results.

RESULTS

The 13 up-regulated and 4 down-regulated DMs were identified in the group A + C, the 18 up-regulated and 4 down-regulated DMs were identified in group A, and the 12 up-regulated and 2 down-regulated DMs were identified in group C. All groups showed enrichment in Aminoacyl-tRNA synthesis, D-glutamine and D-glutamate metabolism, Nitrogen metabolism, and Purine metabolism pathways. ROC analysis revealed that L-glutamine had excellent diagnostic ability for fluorosis (AUC > 0.85, P < 0.05). Changes in major DMs (L-glutamine, 4-hydroxyproline and L-alanine) were consistent with previous findings. Transcriptomic results showed the significant alteration of GLS gene in the fluoride exposure group. In vitro experiments confirmed decreased GLS and SLC1A5 genes expression.

CONCLUSION

L-glutamine emerges as a potential biomarker for fluorosis. Glutamine metabolism was involved in the pathogenesis of fluorosis.

Alleviative Effects of Exercise on Bone Remodeling in Fluorosis Mice

Fluorine is widely present in nature in the form of fluoride. Prolonged high-dose fluoride exposure can cause skeletal fluorosis, resulting in osteosclerosis, osteoporosis or osteomalacia. It has been proved that exercise is one of the important factors affecting the health of the bone and promoting bone formation. To investigate the effects of exercise on bone remodeling in fluorosis mice, 120 male 3-week-old ICR mice were randomly divided into four groups: control group (C), exercise group (E), fluoride group (F), fluoride plus exercise group (F + E). After 8-week physical exercise and/or fluoride exposure, we evaluated the content of fluorine, the histopathological structure and microstructure of femur, bone metabolism biochemical indexes and oxidative stress related parameters, and the mRNA and protein levels of genes in BMP-2/Smads and OPG/RANKL/RANK signaling pathways. Our results showed that 100 mg/L NaF exposure increased the accumulation of fluoride in bone, altered histology of bone, and enhanced the activities of ALP and TRACP. Meanwhile, excessive fluoride induced oxidative stress in bone tissue by increasing the content of ROS and MDA, and decreasing the activities of antioxidant enzymes. In addition, the results of qRT-PCR suggested that NaF significantly increased the mRNA expression of BMP-2, Smad-5, Col IA1, Col IA2, OPG, RANKL and RANK, as well as the elevated proteins of OPG, RANKL and RANK. However, these fluoride-induced changes were alleviated after moderate exercise. Taken together, these findings indicated that moderate exercise decreased the toxicity of fluoride by reducing the accumulation of fluorine in the body to relieve the bone damage caused by fluorosis.

Anti-apoptotic effect of a static magnetic field in human cells that had been treated with sodium fluoride

Static magnetic field (SMF) is widely used in industry, in consumer devices and diagnostic medical equipment, hence the widespread exposure to SMF in the natural environment and in people occupationally exposed to it. In environment and in some workplaces, there is a risk of exposure also to various chemicals. Environmental factors can affect the cellular processes which can be the cause of the development of various pathological conditions. Therefore, the aim of this study was to assess the effect of SMF on the expression of the apoptosis-related genes in human fibroblast cultures that had been co-treated with fluoride ions. The control and NaF-treated cells were subjected to the influence of SMF with a moderate induction. The flow-cytometric analysis showed that the fluoride ions reduced the number of viable cells and induced early apoptosis. However, exposure to the SMF reduced the number of dead cells that had been treated with fluoride ions. Moreover, specific genes that were involved in apoptosis exhibited a differential expression in the NaF-treated cells and exposure to the SMF yielded a modulation of their transcriptional activity. Our results suggest some beneficial properties of using a moderate-intensity static magnetic field to reduce the adverse effects of fluoride.

The Effects of Fluoride on the Gap-Junctional Intercellular Communication of Rats' Osteoblast

The gap junction protein plays an important role in the bone formation and alteration of these proteins leading to cause bone development. Aim to determine the effects of different concentration of fluoride on gap-junctional intercellular communication (GJIC) related genes and proteins in the rats' osteoblast cells. We treated the osteoblast cells with various concentrations (0, 0.01, 0.1, 0.5, and 1.0 mM) NaF for 24 and 72 h. We used the scrape loading and dye transfer technique to research the intracellular connectivity. Moreover, the mRNA expression levels of connexin 43 (Cx43), connexin45 (Cx45), collagen I, and osteocalcin (OCN) were analyzed by qRT-PCR, the protein expression levels of connexin43 (Cx43) were analyzed by western blotting and immunofluorescence. Our results suggested that the osteoblast proliferations were decreased in the 0.5 and 1 mM NaF groups, after 24 and 72 treatments. The scrape loading and dye transfer experiment showed that the GJIC were increased in the 0.01 mM NaF group and decreased in the 0.5 and 1 mM NaF groups. In addition, the mRNA expressions of Cx43, Cx45, and OCN, and the protein expressions of Cx43 were increased in the 0.01 mM NaF group and decreased in the 0.5 and 1 mM NaF groups. In summary, these results suggest that the low concentration NaF is good for the GJIC, but the high concentration NaF damages the GJIC.

Influence of Calcium Supplementation against Fluoride-Mediated Osteoblast Impairment in Vitro: Involvement of the Canonical Wnt/β-Catenin Signaling Pathway

Fluoride (F) is capable of promoting abnormal proliferation and differentiation in primary cultured mouse osteoblasts (OB cells), although the underlying mechanism responsible remains rare. This study aimed to explore the roles of wingless and INT-1 (Wnt) signaling pathways and screen appropriate doses of calcium (Ca²⁺) to alleviate the sodium fluoride (NaF)-induced OB cell toxicity. For this, we evaluated the effect of dickkopf-related protein 1 (DKK1) and Ca²⁺ on mRNA levels of wingless/integrated 3a (Wnt3a), low-density lipoprotein receptor-related protein 5 (LRP5), dishevelled 1 (Dv1), glycogen synthase kinase 3β (GSK3β), β-catenin, lymphoid enhancer binding factor 1 (LEF1), and cellular myelocytomatosis oncogene (cMYC), as well as Ccnd1 (Cyclin D1) in OB cells challenged with 10^-6 mol/L NaF for 24 h. The demonstrated data showed that F significantly increased the OB cell proliferation rate. Ectogenic 0.5 mg/L DKK1 significantly inhibited the proliferation of OB cells induced by F. The mRNA expression levels of Wnt3a, LRP5, Dv1, LEF1, β-catenin, cMYC, and Ccnd1 were significantly increased in the F group, while significantly decreased in the 10^-6 mol/L NaF + 0.5 mg/L DKK1 (FY) group. The mRNA expression levels of Wnt3a, LRP5, β-catenin, and cMYC were significantly decreased in the 10^-6 mol/L NaF + 2 mmol/L CaCl₂ (F+CaII) group. The protein expression levels of Wnt3a, Cyclin D1, cMYC, and β-catenin were significantly increased in the F group, whereas they were decreased in the F+CaII group. However, the mRNA and protein expression levels of GSK3β were significantly decreased in the F group while significantly increased in the F+CaII group. In summary, F activated the canonical Wnt/β-catenin pathway and changed the related gene expression and β-catenin protein location in OB cells, promoting cell proliferation. Ca²⁺ supplementation (2 mmol/L) reversed the expression levels of genes and proteins related to the canonical Wnt/β-catenin pathway.

A Rat Experimental Study of the Relationship Between Fluoride Exposure and Sensitive Biomarkers

Chronic excessive fluoride exposure impairs human health and damages not only the skeletal system and the teeth but also the soft tissues such as the brain, liver, kidneys, pancreas and spinal cord. However, there is limited research regarding the exposure levels and sensitive biomarkers. This study was aimed to establish the relationship between fluoride exposure and sensitive biomarkers. Ninety-six rats were randomly divided into six groups, with each group exposed to 0, 2, 4, 8, 16 and 32 mg NaF/(kg.bw), respectively. Correlation analysis of the exposure levels, the tissue distributions and the effects was done, and the possible mathematical relationship between the exposure and sensitive biomarkers is discussed. Our findings revealed that the level of serum fluoride can serve as one of the sensitive indicators to reflect the ex-exposure levels (in the present article, ex-exposure means the fluoride exposure pathway from the outside, which differs from the burden of the organism). Furthermore, an equation determining the external exposure dose of serum fluoride was obtained by fitting the coefficient 0.901. Simultaneously, enzyme levels were closely compared with the burden of the tissue, which showed that the activities of alkaline phosphatase significantly correlated with serum fluoride levels (R ² = -0.259, p < 0.05), as well as with the fluoride levels of the lung (R ² = 0.463, ρ < 0.01), the thymus (R ² = 0.429, ρ < 0.05) and the ovary/testicle (R ² = 0.685, ρ < 0.01). Results suggested that excessive fluoride exposure might affect reproduction by altering the activities of alkaline phosphatase. In addition, some indicators related to immunity and calcium absorption exhibited sensitivity to tissue burden, among which activating transcriptional factor 4 (ATF4), an important indicator involved in bone metabolism, was found sensitive to the ex-exposure level. These findings highlight the gap between health effects in epidemiology research and the total intake amount of fluoride from the environment. This study presents a novel insight into the method of establishing the relationship between fluoride exposure and sensitive biomarkers.

TRIB3 inhibits proliferation and promotes osteogenesis in hBMSCs by regulating the ERK1/2 signaling pathway

Osteogenic differentiation in human bone marrow-derived mesenchymal stem cells (hBMSCs) is regulated by various factors, including bone morphogenetic proteins (BMPs), Notch, growth hormones and mitogen-activated protein kinases (MAPKs). Tribbles homolog 3 (TRIB3), a pseudokinase, plays an important role in cancer cells and adipocytes. However, TRIB3 function in osteogenic differentiation is unknown, although it is involved in regulating signaling pathways associated with osteogenic differentiation. Here, we found that TRIB3 was highly expressed during osteogenic differentiation in hBMSCs. Inhibition of focal adhesion kinase (FAK) or phosphatidylinositol 3-kinase (PI3K) resulted in a significant decrease in TRIB3 expression, and expression of TRIB3 was restored by increasing insulin-like growth factor-1 (IGF-1) via activating phosphatidylinositol 3-kinase/protein kinase B (PI3K/AKT) signaling. TRIB3 knock-down enhanced proliferation and decreased osteogenic differentiation at the middle stage of differentiation, and these effects were reversed by inhibiting the activation of extracellular signal-regulated kinase (ERK)-1/2. In conclusion, TRIB3 plays an important role in proliferation and osteogenic differentiation by regulating ERK1/2 activity at the middle stage of differentiation, and expression of TRIB3 is regulated by FAK in a PI3K/AKT-dependent manner.

Effects of fluoride on proliferation and mineralization in periodontal ligament cells in vitro

Fluoride, which is often added to toothpaste or mouthwash in order to protect teeth from decay, may be a novel therapeutic approach for acceleration of periodontal regeneration. Therefore, we investigated the effects of fluoride on proliferation and mineralization in human periodontal ligament cells in vitro. The periodontal ligament cells were stimulated with various concentrations of NaF added into osteogenic inductive medium. Immunohistochemistry of cell identification, cell proliferation, alkaline phosphatase (ALP) activity assay, Alizarin red S staining and quantitative real-time-polymerase chain reaction (RT-PCR) were performed. Moderate concentrations of NaF (50-500 μmol/L) had pro-proliferation effects, while 500 μmol/L had the best effects. ALP activity and calcium content were significantly enhanced by 10 μmol/L NaF with osteogenic inductive medium. Quantitative RT-PCR data varied in genes as a result of different NaF concentrations and treatment periods. We conclude that moderate concentrations of NaF can stimulate proliferation and mineralization in periodontal ligament cells. These in vitro findings may provide a novel therapeutic approach for acceleration of periodontal regeneration by addition of suitable concentrations of NaF into the medication for periodontitis treatment, i.e., into periodontal packs and tissue patches.

Mechanisms of Intracellular Calcium Homeostasis in MC3T3-E1 Cells and Bone Tissues of Sprague-Dawley Rats Exposed to Fluoride

Calcium homeostasis of osteoblasts (OBs) has an important role in the physiology and pathology of bone tissue. In order to study the mechanisms of intracellular calcium homeostasis, MC3T3-E1 cells and Sprague-Dawley rats were treated with different concentrations of fluoride. Then, we examined intracellular-free calcium ion ([Ca(2+)]i) in MC3T3-E1 cells as well as mRNA and protein levels of Cav1.2, the main subunit of L-type voltage-dependent calcium channels (VDCCs), Na(+)/Ca(2+) exchange carriers (NCS), and plasma membrane Ca(2+)-ATPase (PMCA), inositol 1,4,5-trisphosphate receptor (IP3R) channels, sarco/endoplasmic reticulum calcium ATPase 2b (SERCA2b)/ATP2A2 in vitro, and rat bone tissues in vivo. Our results showed that [Ca(2+)]i of fluoride-treated OBs increased in a concentration-dependent manner with an increase in the concentration of fluoride. We also found that the low dose of fluoride led to high expression levels of Cav1.2, NCS-1, and PMCA and low expression levels of IP3R and SERCA2b/ATP2A2, while the high dose of fluoride induced an increase in SERCA2b/ATP2A2 levels and decrease in Cav1.2, PMCA, NCS-1, and IP3R levels. These results demonstrate that calcium channels and calcium pumps of plasma and endoplasmic reticulum (ER) membranes keep intracellular calcium homeostasis by regulating Cav1.2, NCS-1, PMCA, IP3R, and SERCA2b/ATP2A2 expression.

Effect of Sodium Fluoride on the Proliferation and Gene Differential Expression in Human RPMI8226 Cells

Although fluoride is known to reduce the incidence of caries, chronic excessive fluoride exposure can impair human health, even resulting in fluorosis. Now the underlying mechanisms of fluoride-induced toxicity are not fully understood. So, we conducted this study with the purpose of investigating the effect of sodium fluoride (NaF) in human RPMI8226 cells. In this experiment, human RPMI8226 cells were cultured with varied doses of fluoride (10, 20, 40, 80, 160, 320 μM). After 48 h exposure, the change of cell viability was examined by CCK-8 assay, and also the messenger RNA (mRNA) expression of relevant genes was assessed by QRT-PCR. Compared to the control group, fluoride exposure increased the human RPMI8226 cells viability at relatively lower levels (10-160 μM); however, when the concentration reached to 320 μM, the cell proliferation was significantly inhibited (p < 0.05). In addition, the genes mRNA expression, including ANKRD1, CRSP6, KLF2, SBNO2, ZNF649, FANCM, PDGFA, RNF152, CDK10, and CETN2 changed in a concentration-dependent manner and increased with fluoride exposure concentration. The results suggest that overexposure to fluoride (160-320 μM) can induce cytotoxicity and regulate relevant genes expression. Our findings provide novel insights into the mechanisms of action of fluoride-induced toxicity.

The importance of the prenyl group in the activities of osthole in enhancing bone formation and inhibiting bone resorption in vitro

Osteoporosis treatment always aimed at keeping the balance of bone formation and bone resorption. Recently, prenyl group in natural products has been proposed as an active group to enhance the osteogenesis process. Osthole has both the prenyl group and bone-protective activities, but the relationship is still unknown. In this study we found that osthole exerted a potent ability to promote proliferation and osteogenic function of rat bone marrow stromal cells and osteoblasts, including improved cell viability, alkaline phosphatase activity, enhanced secretion of collagen-I, bone morphogenetic protein-2, osteocalcin and osteopontin, stimulated mRNA expression of insulin-like growth factor-1, runt-related transcription factor-2, osterix, OPG (osteoprotegerin), RANKL (receptor activator for nuclear factor-κB ligand), and the ratio of OPG/RANKL, as well as increasing the formation of mineralized nodules. However, 7-methoxycoumarin had no obvious effects. Osthole also inhibited osteoclastic bone resorption to a greater extent than 7-methoxycoumarin, as shown by a lower tartrate-resistant acid phosphatase activity and lower number and smaller area of resorption pits. Our findings demonstrate that osthole could be a potential agent to stimulate bone formation and inhibit bone resorption, and the prenyl group plays an important role in these bone-protective effects.