The role of TGFβ receptor 1-smad3 signaling in regulating the osteoclastic mode affected by fluoride

MicroRNAs in fluorosis pathogenesis: impact on dental, skeletal, and soft tissues

Fluoride-induced toxicity (fluorosis) poses a significant health concern globally, affecting millions of individuals. Understanding the molecular mechanisms underlying fluorosis, particularly the role of microRNAs (miRNAs), is crucial for developing effective preventive and therapeutic strategies. This review explores the pivotal role of miRNAs in the pathogenesis of fluorosis, particularly examining its impact on both hard (skeletal and dental) and soft (brain, liver, kidney, heart, and reproductive organs) tissues. Skeletal fluorosis manifests as abnormal bone mineralization and structure, while dental fluorosis affects enamel formation. In vitro and in vivo studies suggest a significant involvement of miRNAs in the progression of these conditions. For skeletal fluorosis, miR-124, miR-155, and miR-200c-3p have been identified as key regulators, while miR-296-5p and miR-214-3p are implicated in dental fluorosis. Moreover, soft tissue fluorosis encompasses a spectrum of adverse effects on various organs, including the brain, liver, kidneys, heart, and reproductive system. In soft tissues, miRNAs, such as miR-124, miR-200c-3p, miR-132, and miR-34b-5p, have been linked to cellular damage and dysfunction. Notably, miRNAs exert their effects through the modulation of critical pathways involved in fluorosis pathology, including Wnt signaling, apoptosis, cell cycle, and autophagy. Understanding the regulatory roles of miRNAs in fluorosis pathogenesis holds promise for identifying biomarkers and therapeutic targets. However, further research is needed to elucidate the molecular mechanisms underlying miRNA-mediated responses to fluoride exposure. Integration of miRNA research into fluorosis studies could facilitate the development of diagnostic tools and therapeutic interventions, thus mitigating the detrimental effects of fluorosis on both hard and soft tissues.

Decrypting the skeletal toxicity of vertebrates caused by environmental pollutants from an evolutionary perspective: From fish to mammals

The rapid development of modern society has led to an increasing severity in the generation of new pollutants and the significant emission of old pollutants, exerting considerable pressure on the ecological environment and posing a serious threat to both biological survival and human health. The skeletal system, as a vital supportive structure and functional unit in organisms, is pivotal in maintaining body shape, safeguarding internal organs, storing minerals, and facilitating blood cell production. Although previous studies have uncovered the toxic effects of pollutants on vertebrate skeletal systems, there is a lack of comprehensive literature reviews in this field. Hence, this paper systematically summarizes the toxic effects and mechanisms of environmental pollutants on the skeletons of vertebrates based on the evolutionary context from fish to mammals. Our findings reveal that current research mainly focuses on fish and mammals, and the identified impact mechanisms mainly involve the regulation of bone signaling pathways, oxidative stress response, endocrine system disorders, and immune system dysfunction. This study aims to provide a comprehensive and systematic understanding of research on skeletal toxicity, while also promoting further research and development in related fields.

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.

TGF-β1/Smad3 Signaling Is Required to Alleviate Fluoride-Induced Enamel Hypomineralization

Excessive fluoride intake during enamel development can affect enamel mineralization, leading to dental fluorosis. However, its potential mechanisms remain largely unexplored. In the present study, we aimed to investigate the impact of fluoride on the expressions of RUNX2 and ALPL during mineralization and the effect of TGF-β1 administration on fluoride treatment. A dental fluorosis model of newborn mice and an ameloblast cell line ALC were both used in the present study. The mice of the NaF group, including the mothers and newborns, were fed with water containing 150 ppm NaF after delivery to induce dental fluorosis. The mandibular incisors and molars showed significant abrasion in the NaF group. Immunostaining, qRT-PCR, and Western blotting analysis indicated that exposure to fluoride markedly down-regulated RUNX2 and ALPL in mouse ameloblasts and ALCs. Besides, fluoride treatment significantly decreased the mineralization level detected by ALP staining. Furthermore, exogenous TGF-β1 up-regulated RUNX2 and ALPL and promoted mineralization, while the addition of SIS3 could block such TGF-β1-induced up-regulation. In TGF-β1 conditional knockout mice, the immunostaining of RUNX2 and ALPL was weaker compared with wild-type mice. Exposure to fluoride inhibited the expressions of TGF-β1 and Smad3. Co-treatment of TGF-β1 and fluoride up-regulated RUNX2 and ALPL compared with the fluoride alone treatment, promoting mineralization. Collectively, our data indicated that TGF-β1/Smad3 signaling pathway was necessary for the regulatory effects of fluoride on RUNX2 and ALPL, and the fluoride-induced suppression of ameloblast mineralization was mitigated by activating TGF-β1/Smad3 signaling pathway.

The Role of Trace Elements and Minerals in Osteoporosis: A Review of Epidemiological and Laboratory Findings

The objective of the present study was to review recent epidemiological and clinical data on the association between selected minerals and trace elements and osteoporosis, as well as to discuss the molecular mechanisms underlying these associations. We have performed a search in the PubMed-Medline and Google Scholar databases using the MeSH terms "osteoporosis", "osteogenesis", "osteoblast", "osteoclast", and "osteocyte" in association with the names of particular trace elements and minerals through 21 March 2023. The data demonstrate that physiological and nutritional levels of trace elements and minerals promote osteogenic differentiation through the up-regulation of BMP-2 and Wnt/β-catenin signaling, as well as other pathways. miRNA and epigenetic effects were also involved in the regulation of the osteogenic effects of trace minerals. The antiresorptive effect of trace elements and minerals was associated with the inhibition of osteoclastogenesis. At the same time, the effect of trace elements and minerals on bone health appeared to be dose-dependent with low doses promoting an osteogenic effect, whereas high doses exerted opposite effects which promoted bone resorption and impaired bone formation. Concomitant with the results of the laboratory studies, several clinical trials and epidemiological studies demonstrated that supplementation with Zn, Mg, F, and Sr may improve bone quality, thus inducing antiosteoporotic effects.

Serum Levels of CXCR4, SDF-1, MCP-1, NF-κB and ERK1/2 in Patients with Skeletal Fluorosis

C-X-C motif chemokine receptor 4 (CXCR4), stromal cell-derived factor-1 (SDF-1), monocyte chemoattractant protein-1 (MCP-1), extracellular signal-regulated kinase 1/2 (ERK1/2) and nuclear factor-κB (NF-κB) affect bone cells and play an important role in bone and joint diseases, but the data on CXCR4, SDF-1, MCP-1, ERK1/2 and NF-κB in the serum of skeletal fluorosis (SF) patients are inconclusive. Thus, according to the "Diagnostic Criteria for Endemic Skeletal Fluorosis" (WS 192-2008), we enrolled patients with SF (n = 60) as the SF group and those without SF as the controls (n = 60). Serum levels of CXCR4, SDF-1, MCP-1, ERK1/2 and NF-κB were detected by enzyme-linked immunosorbent assays (ELISAs). Serum SDF-1, CXCR4, MCP-1 and NF-κB levels were significantly higher in the SF group than in the control group. Within the serum of SF patients, CXCR4 and SDF-1 levels were positively correlated with NF-κB levels. There was no correlation between MCP-1 levels and those of ERK1/2 or NF-κB. SDF-1 and CXCR4 may activate the NF-κB pathway, and MCP-1 affects the occurrence and development of SF by regulating osteocytes through other pathways. The SDF-1/CXCR4 axis and MCP-1 signalling pathway provide a new theoretical basis for the occurrence and development of SF.

Fluoride Exposure Provokes Mitochondria-Mediated Apoptosis and Increases Mitophagy in Osteocytes via Increasing ROS Production

Fluoride is a persistent environmental pollutant, and its excessive intake causes skeletal and dental fluorosis. However, few studies focused on the effects of fluoride on osteocytes, making up over 95% of all bone cells. This study aimed to investigate the effect of fluoride on osteocytes in vitro, as well as explore the underlying mechanisms. CCK-8, LDH assay, fluorescent probes, flow cytometry, and western blotting were performed to examine cell viability, apoptosis, mitochondria changes, reactive oxygen species (ROS) and mitochondrial ROS (mtROS), and protein expressions. Results showed that sodium fluoride (NaF) exposure (4, 8 mmol/L) for 24 h inhibited the cell viability of osteocytes MLO-Y4 and promoted G0/G1 phase arrest and increased cell apoptosis. NaF treatment remarkably caused mitochondria damage, loss of MMP, ATP decrease, Cyto c release, and Bax/Bcl-2 ratio increase and elevated the activity of caspase-9 and caspase-3. Furthermore, NaF significantly upregulated the expressions of LC-3II, PINK1, and Parkin and increased autophagy flux and the accumulation of acidic vacuoles, while the p62 level was downregulated. In addition, NaF exposure triggered the production of intracellular ROS and mtROS and increased malondialdehyde (MDA); but superoxide dismutase (SOD) activity and glutathione (GSH) content were decreased. The scavenger N-acetyl-L-cysteine (NAC) significantly reversed NaF-induced apoptosis and mitophagy, suggesting that ROS is responsible for the mitochondrial-mediated apoptosis and mitophagy induced by NaF exposure. These findings provide in vitro evidence that apoptosis and mitophagy are cellular mechanisms for the toxic effect of fluoride on osteocytes, thereby suggesting the potential role of osteocytes in skeletal and dental fluorosis.

A systematic review on fluoride-induced epigenetic toxicity in mammals

Fluoride, one of the global groundwater contaminants, is ubiquitous in our day-to-day life from various natural and anthropogenic sources. Numerous in vitro, in vivo, and epidemiological studies are conducted to understand the effect of fluoride on biological systems. A low concentration of fluoride is reported to increase oral health, whereas chronic exposure to higher concentrations causes fluoride toxicity (fluorosis). It includes dental fluorosis, skeletal fluorosis, and fluoride toxicity in soft tissues. The mechanism of fluoride toxicity has been reviewed extensively. However, epigenetic regulation in fluoride toxicity has not been reviewed. This systematic review summarizes the current knowledge regarding fluoride-induced epigenetic toxicity in the in vitro, in vivo, and epidemiological studies in mammalian systems. We examined four databases for the association between epigenetics and fluoride exposure. Out of 932 articles (as of 31 March 2022), 39 met our inclusion criteria. Most of the studies focused on different genes, and overall, preliminary evidence for epigenetic regulation of fluoride toxicity was identified. We further highlight the need for epigenome studies rather than candidate genes and provide recommendations for future research. Our results indicate a correlation between fluoride exposure and epigenetic processes. Further studies are warranted to elucidate and confirm the mechanism of epigenetic alterations mediated fluoride toxicity.

Role of TGF-β1 in Fluoride-Treated Osteoblasts at Different Stages

Little attention has been paid to the tolerance of osteoblasts to fluoride in distinct differentiation stages, and the role of TGF-β1 in fluoride-treated osteoblast differentiation of progenitors and precursors was rarely mentioned in previous studies. The present study aimed to clarify how fluoride affected different differentiation stages of osteoblasts, and to elucidate the role of TGF-β1 in this process. We assessed cell migration, proliferation, DNA damage, and apoptosis of early-differentiated osteoblasts derived from bone marrow stem cells (BMSCs) exposed to fluoride with or without TGF-β1. Subsequently, MC3T3-E1 cells cultured with mineral induction medium were treated with fluoride to test fluoride's effect on late-differentiated osteoblasts. The specific fluoride concentrations and treatment times were chosen to evaluate the role of TGF-β1 in fluoride-induced osteoblastic differentiation and function. Results showed early-differentiated osteoblasts treated with a low dose of fluoride grew and moved more rapidly. TGF-β1 promoted cell proliferation and inhibited cell apoptosis in early-differentiated osteoblasts exposed to a low fluoride dose, but enhanced apoptosis at higher fluoride conditions. In the late-differentiated osteoblasts, the fluorine dose range with anabolic effects was narrowed, and the fluoride range with catabolic effects was widened. Treatment with a low fluoride dose stimulated the alkaline phosphatase (ALP) expression. TGF-β1 treatment inhibited Runx2 expression but increased RANKL expression in late-differentiated osteoblasts exposed to fluoride. Meanwhile, TGF-β1 treatments activated Smad3 phosphorylation but blocked Wnt10b expression in osteoblasts. We conclude that TGF-β1 plays an essential role in fluoride-induced differentiation and osteoblast function via activation of Smad3 instead of Wnt10 signaling.

miR-378d is Involved in the Regulation of Apoptosis and Autophagy of and E2 Secretion from Cultured Ovarian Granular Cells Treated by Sodium Fluoride

Taking excessive sodium fluoride may cause female reproductive dysfunction, but underlying molecular mechanism is unclear. The ovarian granulosa cells are the key endocrine cells releasing reproductive hormones. The miRNAs in the granulosa cells play an important function in regulating reproduction. The aim of this study is to explore the role of miRNAs in granulosa cell apoptosis and autophagy, as well as estradiol (E₂) release in response to excessive sodium fluoride. The ovarian granulosa cells (KGN cells) were treated in vitro by different concentrations of sodium fluoride (NaF) for 24 h. The level of estradiol (E₂) in the incubation medium was measured by ELISA kits. The total RNA and protein were collected and purified from KGN cells. The expression of miRNAs was detected by the real-time PCR. The signal molecules involved in cell apoptosis and autophagy were detected by the real-time PCR and Western blotting. Six miRNAs in granulosa cells were significantly up- or downregulated by NaF and selected for real-time PCR analysis. The miR-378d was the most significantly upregulated one dose dependently by NaF. It was positively correlated to the extent of apoptosis but negatively correlated to the level of autophagy in KGN cells in response to NaF. In addition, miR-378d promoted E₂ release in response to 1 and 2 mM NaF but reduced E₂ release in response to 4 and 8 mM NaF treatments. It is concluded that expression of miR-378d in ovarian granulosa cells is negatively correlated to the autophagy and E₂ release and positively correlated to cell apoptosis under the influence of NaF.

Altered miRNA expression profiling in enamel organ of fluoride affected rat embryos

Evidence has shown that miRNAs could play a role in dental fluorosis, but there is no study has investigated the global expression miRNA profiles of fluoride-exposed enamel organ. In this study, we analysed the differentially expressed (DE) miRNAs between fluoride-treated and control enamel organ for the first time and found several candidate miRNAs and signaling pathways worthy of further research. Thirty Wistar rats were randomly distributed into three groups and exposed to drinking water with different fluoride contents for 10 weeks and during the gestation. The three groups were a control group (distilled water), medium fluoride group (75 mg/L NaF), and high fluoride group (150 mg/L NaF). On the embryonic day 19.5, the mandible was dissected for histological analysis, and the enamel organ of the mandibular first molar tooth germ was collected for miRNA sequencing (miRNA-seq) and quantitative real-time PCR analysis (qRT-PCR). Typical dental fluorosis was observed in the incisors of the prepregnant rats. In addition to the disorganized structure of enamel organ cells, 39 DE miRNAs were identified in the fluoride groups compared with the control group, and good agreement between the miRNA-seq data and qRT-PCR data was found. The functional annotation of the target genes of 39 DE miRNAs showed significant enrichment in metabolic process, cell differentiation, calcium signaling pathway, and mitogen-activated protein kinase(MAPK) signaling pathway terms. This study provides a theoretical reference for an extensive understanding of the mechanism of fluorosis and potential valuable miRNAs as therapeutic targets in fluorosis.

Pharmacokinetics of fluoride in human adults: The effect of exercise

The literature is sparse in terms of the effect of exercise on the pharmacokinetics of fluoride (F) in humans. In a 4-treatment repeated measures cross-over study, we investigated F pharmacokinetics following no exercise (control) and three exercise intensity conditions (light, moderate and vigorous) in healthy adults. At a pre-experimental session, 8 participants (18-30y) residing in a non-fluoridated-area, underwent a VO_{2 max} test to guide the three exercise intensities for the experimental sessions. Participants were on a F-free regime one week before and throughout the four experimental weeks. We measured urinary F excretion (UFE), maximum plasma concentration (Cmax), lag time of Cmax (Tmax), and Area Under the Curve (AUC) for plasma F concentration against time, following F ingestion then no, light, moderate and vigorous exercise. Results showed no statistically significant difference in Tmax among all sessions; whereas Cmax for moderate exercise (226.2 ng/ml) was significantly higher than for no (27.0 ng/ml; p < 0.001), light (105.6 ng/ml; p = 0.016) and vigorous (94.2 ng/ml; p = 0.008) exercise. Mean AUC over 0-90 min following F ingestion was also significantly higher in moderate exercise than for no (p < 0.001), light (p = 0.004) and vigorous (p = 0.001) exercise. Mean UFE over 0-14h was 638.8, 718.7, 574.6 and 450.5  μg for no, light, moderate and vigorous exercise, with no statistically significant differences among different sessions. In conclusion, this human experimental study suggests that moderate exercise may increase the fraction of F absorbed systemically which is therefore available to produce a biological effect. Future studies should be conducted with larger samples, different age groups and using different F doses.

Analysis of the MicroRNA Profile by Sequencing in Ovarian Granular Cells from Women Suffering Fluorosis with Reproductive Dysfunction

Excessive intake of fluoride may cause female reproductive dysfunction but pathological mechanism is unclear. The miRNAs in follicular fluid are a class of small non-coding RNAs from granulosa cells. The aim of this study is to examine the differential expressions of miRNAs in ovarian granulosa cells from women suffering from fluorosis and infertility. Five fluorosis women suffering infertility and 5 non-fluorosis (normal ovarian secretory function control) women were included as two groups. These two groups were indexed by serum and urine fluoride (F) levels as high F group and control group. The concentrations of estradiol (E₂), progesterone (P), human chorionic gonadotropin (HCG), follicle-stimulating hormone (FSH), and luteinizing hormone (LH) were measured by ELISA kits. The characteristics of menstruation from each woman were collected. The total RNA was isolated from granulosa cells for sequencing. The validation was completed by RT-qPCR. There was no significant difference between the two groups on age, the levels of E₂, FSH, P, HCG, and LH in serum, and the characteristics of menstruation. A total of 37 miRNAs were upregulated and 40 miRNAs downregulated in follicular fluid from granulosa cells in the high F group compared with that in the control group. The expression of hsa-miR-29b increased in fluorosis patients identified by the miRNA sequence analysis. The distinct expression patterns of miRNAs in women requiring IVF from fluorosis area provide a new direction for molecular mechanism of fluorosis caused reproductive dysfunction.

Effect of fluoride on osteocyte-driven osteoclastic differentiation

Excessive systemic uptake of inorganic fluorides causes disturbances of bone homeostasis. The mechanism of skeletal fluorosis is still uncertain. This study aimed to study the effect of fluoride on osteocyte-driven osteoclastogenesis and probe into the role of PTH in this process. IDG-SW3 cells seeded in collagen-coated constructs were developed into osteocyte-like cells through induction of mineral agents. Then, osteocyte-like cells were exposed to fluoride in the presence or absence of parathyroid hormone (PTH). Cell viability and their capacity to produce receptor activator of nuclear factor kappa-B ligand (RANKL), osteoprotegerin (OPG) and sclerostin (SOST) were detected by MTT and Western blot assays, respectively. Finally, a transwell coculture system using osteocyte-like cells seeded in the low compartment, and osteoclast precursors added in the inserts was developed to observe the osteocyte-driven osteoclasogenesis response to fluoride with or without PTH, and the expression of molecules involved in this mechanism were measure by real time RT-PCR. Results showed that osteocytes withstood a toxic dose of fluoride, and yet PTH administration significantly reduced osteocytes viability. PTH amplified the effect of fluoride on the expression of osteoclastogenesis-related molecules in osteocyte, but did not enlarged the stimulating effect of fluoride on osteoclastogenesis drove by osteocyte coculture. Gene expression levels of TRAP, RANK, JNK and NFAtc1 significantly increased in fluoride affected osteoclast precursor cocultured with osteocyte-like cells. The impact of fluoride on osteocyte-driven osteoclast differentiation was stronger than that of PTH. In conclusion, osteocyte played a pivotal role on the mechanism underlying fluoride-affected osteoclastogenesis in which RANK-JNK-NFATc1 signaling pathway was involved, and PTH had a significant impact in this process.

Different Effects of Fluoride Exposure on the Three Major Bone Cell Types

Fluoride accumulates and is toxic to bones. Clinical bone lesions occur in a phased manner, being less severe early in the natural course of skeletal fluorosis. Previous research rarely focused on osteocyte, osteoclast, and osteoblast at the same time, although these three types of cells are involved in the process of fluorosis. In this study, commitment of bone cells was performed according to their respective characteristics. Osteocyte-like cells were verified by protein expression of sclerostin (SOST) in IDG-SW3 cell culture with mineral medium. Positive tartrate-resistant acid phosphatase (TRACP) staining, characteristic of osteoclasts, is observed in RAW264.7 cells after administration of RANKL. We successfully purified a high percentage (94%) of bone mesenchymal stem cells (BMSCs) co-expressing CD34 and CD44. Parallel studies were performed to observe cell viability and apoptosis rates in osteocyte, osteoclast, and osteoblast like cells by using MTT and Annexin V FITC assays. Our results demonstrated that osteocytes have a strong tolerance to high fluoride concentrations, while osteoclasts are more sensitive to changes of fluoride dose. The range of anabolic action of fluoride concentration on osteoblast was narrow. Notably, fluoride exposure aggravated apoptosis of osteocyte and osteoclast induced by administration of PTH and TGF-β, respectively. In short, three types of bone cells display disparate responses to fluoride exposure and to PTH- and TGF-β-induced apoptosis.

Sodium fluoride regulates the osteo/odontogenic differentiation of stem cells from apical papilla by modulating autophagy

Fluoride (sodium fluoride) is thought to be essential in the development of tooth, and research shows that fluoride can modulate the differentiation of dental stem cells. However, the effects of fluoride on the committed differentiation of stem cells from apical papilla (SCAPs) and the underlying mechanisms remain unclear. Here, SCAPs were isolated from healthy extracted human third molars with immature roots and then were cultured with NaF conditioned media. Cell Counting Kit-8, EdU staining, and flow cytometry were performed to detected the proliferation activity. Alkaline phosphatase (ALP) activity, Alizarin Red staining, Western blot assay, and real-time reverse-transcription polymerase chain reaction were applied to assess the osteo/odontogenic differentiation NaF-treated SCAPs. Western blot assay and transmission electron microscope were used to evaluate the autophagy involved in the differentiation of SCAPs. ALP activity, ALP protein, and messenger RNA (mRNA) expression showed that 0.5 mM was the optimal concentration for the induction of SCAPs by NaF. 0.5 mM NaF-treated SCAPs induced more mineralized nodules as compared with untreated cells. Moreover, the osteo/odontogenic markers (RUNX2, OSX, DSP, and OCN) in mRNA levels were upregulated while the protein levels of these markers increased considerably in 0.5 mM NaF-treated SCAPs. Furthermore, the autophagy-related proteins (LC3, ATG5, and Beclin1) increased in NaF-treated SCAPs, and the osteo/odontogenic makers significantly decreased while silencing ATG5 to block autophagy. In all, sodium fluoride can regulate the osteo/odontogenic differentiation of SCAPs by modulating autophagy.

Fluorine-contained hydroxyapatite suppresses bone resorption through inhibiting osteoclasts differentiation and function in vitro and in vivo

Objectives

Fluorine, an organic trace element, has been shown to unfavourably effect osteoclasts function at a low dose. Use of hydroxyapatite (HA) has been effective in exploring its roles in promoting bone repair. In this study, we used HA modified with fluorine to investigate whether it could influence osteoclastic activity in vitro and ovariectomy‐induced osteoclasts hyperfunction in vivo.

Materials and methods

Fluorohydroxyapatite (FHA) was obtained and characterized by scanning electron microscope (SEM). Osteoclasts proliferation and apoptosis treated with FHA were assessed by MTT and TUNEL assay. SEM, F‐actin, TRAP activity and bone resorption experiment were performed to determine the influence of FHA on osteoclasts differentiation and function. Moreover, HA and FHA were implanted into ovariectomized osteoporotic and sham surgery rats. Histology and Micro‐CT were examined for further verification.

Results

Fluorine released from FHA slowly and sustainably. FHA hampered osteoclasts proliferation, promoted osteoclasts apoptosis, suppressed osteoclasts differentiation and function. Experiments in vivo validated that FHA participation brought about an inhibitory effect on osteoclasts hyperfunction and less bone absorption.

Conclusion

The results indicated that FHA served as an efficient regulator to attenuate osteoclasts formation and function and was proposed as a candidature for bone tissue engineering applications.

The pathogenesis of endemic fluorosis: Research progress in the last 5 years

Fluorine is one of the trace elements necessary for health. It has many physiological functions, and participates in normal metabolism. However, fluorine has paradoxical effects on the body. Many studies have shown that tissues and organs of humans and animals appear to suffer different degrees of damage after long-term direct or indirect exposure to more fluoride than required to meet the physiological demand. Although the aetiology of endemic fluorosis is clear, its specific pathogenesis is inconclusive. In the past 5 years, many researchers have conducted in-depth studies into the pathogenesis of endemic fluorosis. Research in the areas of fluoride-induced stress pathways, signalling pathways and apoptosis has provided further extensive knowledge at the molecular and genetic level. In this article, we summarize the main results.

Transcriptomics provides mechanistic indicators of fluoride toxicology on endochondral ossification in the hind limb of Bufo gargarizans

Endochondral ossification, the process by which most of the bone is formed, is regulated by many specific groups of molecules and extracellular matrix components. Hind limb of Bufo gargarizans is a model to study endochondral ossification during metamorphosis. Chinese toad (Bufo gargarizans) were exposed to different fluoride concentrations (0, 1, 5, 10 and 20 mg L^-1) from G3 to G42. The development of hind limb of B. gargarizans was observed using the double staining methodology. The transcriptome of hind limb of B. gargarizans was conducted using RNA-seq approach, and differentially expressed gene was also validated. In addition, the location of Sox9 and Ihh in the growth cartilage was determined using in situ hybridization. Our results showed that 5 mg L^-1 stimulated bone mineralization, while 10 and 20 mg L^-1 exposure could inhibit the tibio-fibula, tarsus and metacarpals ossification. Besides, 10 mg F/L treatment could down-regulate Ihh, Sox9, D2, D3, TRα, TRβ, Wnt10, FGF3 and BMP6 expression, while up-regulate ObRb and HHAT mRNA expression in the hind limb of B. gargarizans. Transcript level changes of Ihh, Sox9, D2, D3, TRα, TRβ, Wnt10, FGF3 and BMP6 were consistent with the results of RT-qPCR. In situ hybridization revealed that Ihh was expressed in prehypertrophic chondrocytes, while Sox9 was abundantly expressed in proliferous, prehypertrophic and hypertrophic chondrocytes. However, 10 mg F-/L did not cause any affect in the location of the Ihh and Sox9 mRNA. Therefore, high concentration of fluoride could affect the ossification-related genes mRNA expression and then inhibit the endochondral ossification. The present study thus will greatly contribute to our understanding of the effect of environmental contaminant on ossification in amphibian.

Small molecule inhibitor RepSox prevented ovariectomy-induced osteoporosis by suppressing osteoclast differentiation and bone resorption

Osteoporosis (OP) is a serious metabolic disease that, due to the increased number or function of osteoclasts, results in increased bone brittleness and, therefore, fragile fracture. Some recent studies report the importance of the transforming growth factor β (TGFβ) pathway in bone homeostasis. RepSox is a small molecule inhibitor of TGFβRI that has a wide range of potential application in clinical medicine, except OP. The aim of our study is to evaluate the effects of RepSox on the differentiation and bone resorption of osteoclasts in vitro and in vivo in an ovariectomy (OVX)-induced OP model. An initial analysis showed TGFβRI messenger RNA expression in both bone samples and bone cells. In the in vitro study, RepSox inhibited the receptor activator of nuclear factor κB ligand (RANKL)-induced osteoclast differentiation and bone resorption activity. Real-time polymerase chain reaction (PCR) analysis showed that RepSox suppressed osteoclastic marker gene expression in both dose-dependent and time-dependent manners. In addition, RepSox did not affect osteoblast differentiation, migration or osteoblastic-specific gene expression in vitro. Furthermore, western blot analysis indicated the underlying mechanisms of the RepSox suppression of osteoclastogenesis via the Smad3 and c-Jun N-terminal kinase/activator protein-1 (JNK/AP-1) signaling pathways. Finally, our animal experiments revealed that RepSox prevented OVX-induced bone loss in vivo. Together, our data suggest that RepSox regulates osteoclast differentiation, bone resorption, and OVX-induced OP via the suppression of the Smad3 and JNK/AP-1 pathways.