A role for PERK in the mechanism underlying fluoride-induced bone turnover

Bioactive extract of Morchella esculenta ameliorates cyclophosphamide-induced mitochondrial dysfunction and cardiotoxicity by modulating KEAP1/NRF2 and pro-inflammatory genes expression

Prevention of anticancer drugs-induced cardiotoxicity remains an imperative area of oncology research as it continues to be a major challenge in cancer chemotherapy. This study was undertaken to investigate the protective effect of methanol extract of Morchella esculenta (ME) against cyclophosphamide (CP)-induced cardiotoxicity. Myocardial damage was assessed by biochemical and histopathological methods. Proinflammatory cytokines gene expression was determined by RT-PCR analysis. To assess the mitochondrial dysfunction, TCA cycle and electron transport chain complexes enzymes activities were determined. Chemical finger print of ME was accomplished by HPTLC. CP (200 mg/kg) treated animals showed elevation in cardiac injury markers which was attenuated by ME (p < 0.05). CP-induced decline of antioxidant status and expression of nuclear factor erythroid 2-related factor 2 were restored by ME. CP-induced expression of NF-ĸB, IL1-β, IL-6, TNF-α, COX-2 and iNOS (p < 0.05) was attenuated by ME (500 mg/kg). Bioactive compounds namely, 5-eicosapentaenoicacid (C20H30O2), 8-hydroxyoctadecadienoic acid (C18H32O3), 4,4-dipo-zetacarotene (C30H44), CynarosideA (C21H32O10) present in the extract might be responsible for cardioprotection. The findings reveal the protective effect of ME against CP-induced cardiomyopathy.

Microstructural Analysis of Cancellous Bone in Fluorosis Rats

Skeletal fluorosis likely alters bone structural properties on the cortical and cancellous tissue levels in view that fluorine ion replaces bone mineral composition. Our previous study showed high bone turnover occurred in cortical bone of skeletal fluorosis. Therefore, this study further analyzed the microstructure of cancellous bone in fluorosis rats. Rats were randomly assigned into three groups: the control, low-dose fluoride group (10 mgF-/kg·day), and high-dose fluoride group (20 mgF-/kg·day). Rats were orally administered with fluoride for 1, 2, and 3 months of periods. The trabecular bone parameters of tibia were detected with micro CT and analyzed with software. The activities of glutathione peroxidase (GPX), superoxide dismutase (SOD), and the content of malondialdehyde (MDA) in serum were measured. Results showed that severity of dental fluorosis rose with the increase of dose and prolongation of fluoride exposure. Meantime, the poorer connectivity and less trabecular bone network were observed in cancellous bone of rats treated with fluoride. Data analysis indicated that fluoride treatment significantly decreased bone volume and connectivity degree, but amplified trabecular space in 1 and 2 months of periods. Intriguingly, trabecular thickness significantly decreased in 1-month high-dose fluoride group, but returned to the control in 3 months of period. Fluoride treatment mainly inhibited the GPX activity and increased the MDA level to activate oxidative stress. This study confirmed that excessive fluoride impaired cancellous bone and caused redox imbalance.

The mechanism of metformin combined with total flavonoids of Rhizoma Drynariae on ovariectomy-induced osteoporotic rats

The present study evaluated the in vitro effect of metformin (Met) and total flavonoids of Rhizoma Drynariae (TFRD) on osteoclasts, osteocytes, and osteoblasts at different stages. We also assessed the effect and mechanism of treatment with Met combined with TFRD on ovariectomy (OVX)-induced osteoporosis in rats. The results showed that Met combined with TFRD significantly promoted the migration of osteoprogenitor cells and stimulated the differentiation and maturation of osteoblast precursor cells. Furthermore, Met combined with TFRD treatment significantly inhibited the osteogenic inhibitor sclerostin (SOST)/dickkopf 1 (DKK1) protein expression and the osteoclast differentiation factor receptor activator of nuclear factor-κB ligand (RANKL)/osteoprotegerin (OPG) ratio in osteocytes. In the in vivo study, Met combined with TFRD effectively reduced bone resorption markers levels, including type-I collagen carboxy-terminal peptide (CTX-1) and tartrate-resistant acid phosphatase (TRAP), and remarkably increased the bone formation marker propeptide of type I procollagen (PINP) level in the serum of rats with osteoporosis. Met combined with TFRD treatment improved bone mineral density (BMD), trabecular microstructure, and mechanical properties of osteoporotic rats. Mechanistically, Met combined with TFRD downregulated SOST and DKK1 levels, and upregulated Wnt10b, β-catenin, runt-related transcription factor 2 (Runx2) et al. Meanwhile, Met combined with TFRD treatment reduced the RANKL/OPG ratio, and reduced the receptor activator of nuclear factor-κB (RANK), nuclear factor of activated T cells c1 (NFATC1), and TRAP levels. In conclusion, Met combined with TFRD ameliorated bone mass in osteoporotic rats through regulating Wnt/β-catenin signaling pathway and OPG/RANKL/RANK axis.

ER Stress, the Unfolded Protein Response and Osteoclastogenesis: A Review

Endoplasmic reticulum (ER) stress and its adaptive mechanism, the unfolded protein response (UPR), are triggered by the accumulation of unfolded and misfolded proteins. During osteoclastogenesis, a large number of active proteins are synthesized. When an imbalance in the protein folding process occurs, it causes osteoclasts to trigger the UPR. This close association has led to the role of the UPR in osteoclastogenesis being increasingly explored. In recent years, several studies have reported the role of ER stress and UPR in osteoclastogenesis and bone resorption. Here, we reviewed the relevant literature and discussed the UPR signaling cascade response, osteoclastogenesis-related signaling pathways, and the role of UPR in osteoclastogenesis and bone resorption in detail. It was found that the UPR signal (PERK, CHOP, and IRE1-XBP1) promoted the expression of the receptor activator of the nuclear factor-kappa B ligand (RANKL) in osteoblasts and indirectly enhanced osteoclastogenesis. IRE1 promoted osteoclastogenesis via promoting NF-κB, MAPK signaling, or the release of pro-inflammatory factors (IL-6, IL-1β, and TNFα). CREBH promoted osteoclast differentiation by promoting NFATc1 expression. The PERK signaling pathway also promoted osteoclastogenesis through NF-κB and MAPK signaling pathways, autophagy, and RANKL secretion from osteoblasts. However, salubrinal (an inhibitor of eIF2α dephosphorylation that upregulated p-eIF2α expression) directly inhibited osteoclastogenesis by suppressing NFATc1 expression and indirectly promoted osteoclastogenesis by promoting RANKL secretion from osteoblasts. Therefore, the specific effects and mechanisms of p-PERK and its downstream signaling on osteoclastogenesis still need further experiments to confirm. In addition, the exact role of ATF6 and BiP in osteoclastogenesis also required further exploration. In conclusion, our detailed and systematic review provides some references for the next step to fully elucidate the relationship between UPR and osteoclastogenesis, intending to provide new insights for the treatment of diseases caused by osteoclast over-differentiation, such as osteoporosis.

Screening of differentially methylated genes in skeletal fluorosis of rats with different types and involvement of aberrant methylation of Cthrc1

Fluoride is a widespread pollutant in the environment. There is a high risk of developing skeletal fluorosis from excessive fluoride exposure. Skeletal fluorosis has different phenotypes (including osteosclerotic, osteoporotic and osteomalacic) under the same fluoride exposure and depends on dietary nutrition. However, the existing mechanistic hypothesis of skeletal fluorosis cannot well explain the condition's different pathological manifestations and their logical relation with nutritional factors. Recent studies have shown that DNA methylation is involved in the occurrence and development of skeletal fluorosis. DNA methylation is dynamic throughout life and may be affected by nutrition and environmental factors. We speculated that fluoride exposure leads to the abnormal methylation of genes related to bone homeostasis under different nutritional statuses, resulting in different skeletal fluorosis phenotypes. The mRNA-Seq and target bisulfite sequencing (TBS) result showed differentially methylated genes in rats with different skeletal fluorosis types. The role of the differentially methylated gene Cthrc1 in the formation of different skeletal fluorosis types was explored in vivo and in vitro. Under normal nutritional conditions, fluoride exposure led to hypomethylation and high expression of Cthrc1 in osteoblasts through TET2 demethylase, which promoted osteoblast differentiation by activating Wnt3a/β-catenin signalling pathway, and participated in the occurrence of osteosclerotic skeletal fluorosis. Meanwhile, the high CTHRC1 protein expression also inhibited osteoclast differentiation. Under poor dietary conditions, fluoride exposure led to hypermethylation and low expression of Cthrc1 in osteoblasts through DNMT1 methyltransferase, and increased the RANKL/OPG ratio, which promoted the osteoclast differentiation and participated in the occurrence of osteoporotic/osteomalacic skeletal fluorosis. Our study expands the understanding of the role of DNA methylation in regulating the formation of different skeletal fluorosis types and provides insights into new prevention and treatment strategies for patients with skeletal 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.

Arsenic-fluoride co-exposure induced endoplasmic reticulum stress resulting in apoptosis in rat heart and H9c2 cells

Exposure to arsenic (As) or fluoride (F) has been shown to cause cardiovascular disease (CVDs). However, evidence about the effects of co-exposure to As and F on myocardium and their mechanisms remain scarce. Our aim was to fill the gap by establishing rat and H9c2 cell exposure models. We determined the effects of As and/or F exposure on the survival rate, apoptosis rate, morphology and ultrastructure of H9c2 cells; in addition, we tested the related genes and proteins of endoplasmic reticulum stress (ERS) and apoptosis in H9c2 cells and rat heart tissues. The results showed that As and/or F exposure induced early apoptosis of H9c2 cells and caused endoplasmic reticulum expansion. Additionally, the mRNA and protein expression levels of GRP78, PERK and CHOP in H9c2 cells were higher in the exposure groups than in the control group, and could be inhibited by 4-PBA. Furthermore, we found that As and/or F exposure increased the expression level of GRP78 in rat heart tissues, but interestingly, the expression level of CHOP protein was increased in the F and As groups, while significantly decreased in the co-exposure group. Overall, our results suggested that ERS-induced apoptosis was involved in the damage of myocardium by As and/or F exposure. In addition, factorial analysis results showed that As and F mainly play antagonistic roles in inducing myocardial injury, initiating ERS and apoptosis after exposure.

Progress of Signaling Pathways, Stress Pathways and Epigenetics in the Pathogenesis of Skeletal Fluorosis

Fluorine is widely dispersed in nature and has multiple physiological functions. Although it is usually regarded as an essential trace element for humans, this view is not held universally. Moreover, chronic fluorosis, mainly characterized by skeletal fluorosis, can be induced by long-term excessive fluoride consumption. High concentrations of fluoride in the environment and drinking water are major causes, and patients with skeletal fluorosis mainly present with symptoms of osteosclerosis, osteochondrosis, osteoporosis, and degenerative changes in joint cartilage. Etiologies for skeletal fluorosis have been established, but the specific pathogenesis is inconclusive. Currently, active osteogenesis and accelerated bone turnover are considered critical processes in the progression of skeletal fluorosis. In recent years, researchers have conducted extensive studies in fields of signaling pathways (Wnt/β-catenin, Notch, PI3K/Akt/mTOR, Hedgehog, parathyroid hormone, and insulin signaling pathways), stress pathways (oxidative stress and endoplasmic reticulum stress pathways), epigenetics (DNA methylation and non-coding RNAs), and their inter-regulation involved in the pathogenesis of skeletal fluorosis. In this review, we summarised and analyzed relevant findings to provide a basis for comprehensive understandings of the pathogenesis of skeletal fluorosis and hopefully propose more effective prevention and therapeutic strategies.

Effects of Different Doses of Calcium on the Mitochondrial Apoptotic Pathway and Rho/ROCK Signaling Pathway in the Bone of Fluorosis Rats

For this study, we investigate more deeply the effect calcium (Ca) develops on the mechanism underlying fluoride-triggered osteocyte apoptosis. We detected the morphology of osteocytes by HE staining, mitochondrial microstructure by using the transmission electron microscope, and the biochemical indexes related to bone metabolism and the expression of apoptosis-related genes. These results showed that NaF brought out the reduced osteocytes and ruptured mitochondrial outer membrane, with a significantly increased StrACP activity by 10.414 IU/L at the 4th week (P < 0.05), markedly upregulating the mRNA expression of Bax, Cyto-C, Apaf-1, caspase-7, ROCK-1, BMP-2, and BGP (P < 0.01), as well as caspase-6 (P < 0.05), while downregulating Bcl-2 by 61.3% (P < 0.01). Through immunohistochemical analysis, we also found that NaF notably increased the protein expression of ROCK-1 (P < 0.05) and Cyto-C, BMP-2, and BGP (P < 0.01), suggesting that NaF triggered the activation of the mitochondrial apoptotic pathway and Rho/ROCK signaling pathway. Nevertheless, 1% Ca supplementation in diet notably enhanced the mRNA expression of Bcl-2 by 39.3% (P < 0.01), thus blocking the increment of the expression of mitochondrial apoptotic pathway-related genes and ROCK-1. Meanwhile, Ca could attenuate the StrACP activity by 10.741 IU/L at the 4th week (P < 0.05) and protect the integrity of the mitochondrial outer membrane. These findings strongly suggest that 1% Ca abated the mitochondrial apoptosis pathway by increasing the anti-apoptotic gene Bcl-2 expression, and effectively inhibited the hyper-activation of ROCK-1, dually protecting the structural integrity of the mitochondrial outer membrane and maintaining normal cellular metabolic function.

Osteopromotive carbon dots promote bone regeneration through the PERK-eIF2α-ATF4 pathway

Bone defects are still an unsolved clinical issue that must be overcome. Carbon dots have shown very promising effects in biological therapy. In the current study, we explored their effects on osteogenesis. Furthermore, we revealed the mechanisms in order to develop novel therapeutic approaches to manage the bone defect. For this study, ascorbic acid carbon dots (CDs) were created by a one-step microwave-assisted method. Results showed that the CDs effectively enhanced matrix mineralization, promoted osteogenic differentiation in vitro, and promoted new bone regeneration in the skull defect model in vivo. Furthermore, our data demonstrated that the ER stress and PERK-eIF2α-ATF4 pathway were activated by the CD-induced increase in intracellular calcium. Taken together, our findings suggest that the PERK pathway plays a critical role in CD-induced osteogenic differentiation, and the CDs created herein have the potential to be used to repair bone defects in clinical practice.

Co-exposure to Arsenic-Fluoride Results in Endoplasmic Reticulum Stress-Induced Apoptosis Through the PERK Signaling Pathway in the Liver of Offspring Rats

Arsenic and fluoride are two of the major groundwater pollutants. To better understand the liver damage induced during development, 24 male rats exposed to fluoride (F), arsenic (As), and their combination (As + F) from the prenatal stage to 90 days after birth were selected for analysis. Histopathological results showed vacuolar degeneration in the As and As + F groups. Compared to those in the control group, aspartate aminotransferase and alanine aminotransferase levels were significantly increased in the combined group. Catalase activity significantly decreased in the treatment groups compared to that in the controls, and the malondialdehyde content in the As and As + F groups was significantly higher than those in the control group. We further evaluated whether this damage is linked to endoplasmic reticulum stress and its related pathways. The mRNA expression levels of PERK, GRP78, EIF2α, ATF4, and CHOP as well as the protein levels of CHOP was significantly increased in the As + F group compared with the control group. These results demonstrate that As, F, and their combination could lead to liver function damage and reduce the antioxidant capacity of the liver to cause oxidative damage to tissues. Moreover, the combination of As and F triggers endoplasmic reticulum stress-induced apoptosis in liver cells by activating the PERK pathway in the unfolded protein response. As and F seem to have different independent effects, whereas their combination resulted in more severe effects overall.

Diagnosis and management of pediatric metabolic bone diseases associated with skeletal fragility

PURPOSE OF REVIEW

The goal of this review is to give an overview of diagnosis and up-to-date management of major pediatric metabolic bone diseases that are associated with bone fragility, including nutritional rickets, hypophosphatemic rickets, osteogenesis imperfecta, Ehlers--Danlos syndrome, Marfan's syndrome, hypophosphatasia, osteopetrosis and skeletal fluorosis.

RECENT FINDINGS

During the past decade, a number of advanced treatment options have been introduced and shown to be an effective treatment in many metabolic bone disorders, such as burosumab for hypophosphatemic rickets and asfotase alfa for hypophosphatasia. On the other hand, other disorders, such as nutritional rickets and skeletal fluorosis continue to be underrecognized in many regions of the world. Genetic disorders of collagen-elastin, such as osteogenesis imperfecta, Ehlers--Danlos syndrome and Marfan's syndrome are also associated with skeletal fragility, which can be misdiagnosed as caused by non-accidental trauma/child abuse.

SUMMARY

It is essential to provide early and accurate diagnosis and treatment for pediatric patients with metabolic bone disorders in order to maintain growth and development as well as prevent fractures and metabolic complications.

The Inverted U-Curve Association of Fluoride and Osteoclast Formation in Mice

The effect of fluoride on osteoclasts is still controversial. In the past, researchers thought that the effects of fluoride on osteoclast and osteoblast formation occurred in a dose-dependent pattern. However, our previous in vitro study showed fluoride elicited a notably different effect on osteoclast formation. To further verify the relationship between fluoride and osteoclast formation in vivo, 60 male C57BL/6 mice were randomly divided into three groups: two treatment groups consuming water supplemented with 50 and 100 mg/L of fluoride, and a third control group with nonsupplemented water. Ion selective electrode method analysis was used to detect bone fluoride content, and the effects of fluoride on bone tissue were assessed with hematoxylin and eosin (HE) staining. Additionally, the expression of BGP and ALP were examined by Western blot analysis, and tartrate-resistant acid phosphatase (TRAP) was assessed with immunohistochemistry. Osteoclasts in bone tissue were identified with a combination method of TRAP staining and cell morphology assessment. Results showed increasing expression of BGP among treatment groups as fluoride exposure increased, and ALP expression in the 100 mg/L treatment group was significantly higher than that for both the 50 mg/L treatment and control groups. The number of osteoclasts in the 50 mg/L group was highest amongst the three groups, followed by the 100 mg/L treatment and then by the control group, with the latter showing significantly fewer osteoclasts than in either treatment group. These results suggest that fluoride enhances bone formation at increasing levels of fluoride exposure. However, the inverted U-curve association was found between fluoride exposure and osteoclast formation, with the higher dose of fluoride having slightly reduced osteoclast formation. The results from this study may provide key insights towards understanding the role of osteoclasts in the progression of skeletal fluorosis.

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.

A mini review of fluoride-induced apoptotic pathways

Fluorine or fluoride can have toxic effects on bone tissue and soft tissue at high concentrations. These negative effects include but not limited to cytotoxicity, immunotoxicity, blood toxicity, and oxidative damage. Apoptosis plays an important role in fluoride-induced toxicity of kidney, liver, spleen, thymus, bursa of Fabricius, cecal tonsil, and cultured cells. Here, apoptosis activated by high level of fluoride has been systematically reviewed, focusing on three pathways: mitochondrion-mediated, endoplasmic reticulum (ER) stress-mediated, and death receptor-mediated pathways. However, very limited reports are focused on the death receptor-mediated apoptosis pathways in the fluoride-induced apoptosis. Therefore, understanding and discovery of more pathways and molecular mechanisms of fluoride-induced apoptosis may contribute to designing measures for preventing fluoride toxicity.

Sodium fluoride (NaF) induces the splenic apoptosis via endoplasmic reticulum (ER) stress pathway in vivo and in vitro

At present, there are no reports on the relationship between fluoride-induced apoptosis and endoplasmic reticulum (ER) stress (ER stress) in the spleen of human and animals in vivo and in vitro. Therefore, the aim of this study was to define sodium fluoride (NaF)-induced apoptosis mediated by ER stress in the spleen of mice in vivo and in vitro. Apoptosis and expression levels of the ER stress-related proteins were detected by flow cytometry and western blot, respectively. The results showed that NaF treatment increased lymphocytes apoptosis, which was consistent with NaF-caused ER Stress. NaF-caused ER stress was characterized by up-regulating protein expression levels of glucose-regulated protein 78 (BiP) and glucose-regulated protein 94 (GRP94), and by activating unfolded protein response (UPR). The signaling pathway of ER stress-associated apoptosis was activated by up-regulating protein expression levels of cleaved cysteine aspartate specific protease-12 (cleaved caspase-12), growth arrest and DNA damage-inducible gene 153 (Gadd153/CHOP) and phosphorylation of JUN N-terminal kinase (p-JNK). Additionally, our in vitro study found that apoptotic rate was decreased with remarkable down-regulation of the cleaved caspase-12, CHOP, p-JNK after ER stress was inhibited by 4-Phenylbutyric acid (4-PBA) treatment. In conclusion, NaF-induced apoptosis may mediated by ER stress in the spleen.

Cell cycle arrest and gene expression profiling of testis in mice exposed to fluoride

Exposure to fluoride results in low reproductive capacity; however, the mechanism underlying the impact of fluoride on male productive system still remains obscure. To assess the potential toxicity in testis of mice administrated with fluoride, global genome microarray and real-time PCR were performed to detect and identify the altered transcriptions. The results revealed that 763 differentially expressed genes were identified, including 330 up-regulated and 433 down-regulated genes, which were involved in spermatogenesis, apoptosis, DNA damage, DNA replication, and cell differentiation. Twelve differential expressed genes were selected to confirm the microarray results using real-time PCR, and the result kept the same tendency with that of microarray. Furthermore, compared with the control group, more apoptotic spermatogenic cells were observed in the fluoride group, and the spermatogonium were markedly increased in S phase and decreased in G2/M phase by fluoride. Our findings suggested global genome microarray provides an insight into the reproductive toxicity induced by fluoride, and several important biological clues for further investigations. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1558-1565, 2017.

Preliminary Analysis of MicroRNAs Expression Profiling in MC3T3-E1 Cells Exposed to Fluoride

Overexposure to fluoride from environmental sources can cause serious public health problems. Disrupted osteoblast function and impaired bone formation were found to be associated with excessive fluoride exposure. A massive analysis of microRNAs (miRNAs) was used to figure out the possible pathways in which fluoride affects osteoblast function. MC3T3-E1 cells were treated with 8 mg/L of fluorine for 7 days. Total RNA of cells was extracted, and their integrity and purity were tested. RNA samples were analyzed by using miRNA array, including miRNA labeling, hybridization, scanning, and expression data analysis to compare the profiling of miRNA expression between control and fluoride-treated group. Transcriptome analysis console and enrichment analysis calculated by miRSystem were used to predict target genes and collect miRNAs pathway maps. Forty-five upregulated and 31 downregulated miRNAs expression were found in the fluoride-treated group, and most of the verified miRNAs were mature. The KEGG pathway enrichment analysis searched out 36 pathways that scored more than 0.1. These pathways mainly included intracellular signaling, cytokines, metabolism, and cytoskeleton-related pathways. Among them, the Wnt, insulin, TGF-beta, hedgehog, VEGF, and notch pathways in osteoblasts were those mainly affected by fluoride treatment. These results have shown a number of higher level systemic pathways activated by overexposure of fluoride in osteoblastic cells and verified that fluoride affected the molecular crosstalk in the osteoblasts.

Fluoride Regulate Osteoblastic Transforming Growth Factor-β1 Signaling by Mediating Recycling of the Type I Receptor ALK5

This study aimed to preliminary investigate the role of activin receptor-like kinase (ALK) 5 as one of TGF-βR1 subtypes in bone turnover and osteoblastic differentiation induced by fluoride. We analyzed bone mineral density and the expression of genes related with transforming growth factor-β1(TGF-β1) signaling and bone turnover in rats treated by different concentrations of fluoride with or without SB431542 in vivo. Moreover, MTT assay, alkaline phosphatase staining, RT-PCR, immunocytochemical analysis and western blot analysis were used to detect the influence on bone marrow stem cells (BMSC) after stimulating by varying concentration of fluoride with or without SB431542 in vitro. The in vivo study showed SB431542 treatment affected bone density and gene expression of rats, which indicated TGF-β1 and ALK5 might take part in fluoride-induced bone turnover and bone formation. The in vitro study showed low concentration of fluoride improved BMSC cells viability, alkaline phosphatase activity, and osteocalcin protein expression which were inhibited by high concentration of fluoride. The gene expression of Runx2 and ALK5 in cells increased after low concentration fluoride treatment which was also inhibited by high concentration of fluoride. Fluoride treatment inhibited gene and protein expression of Samd3 (except 1 mgF-/L). Compared with fluoride treatment alone, cells differentiation was inhibited with SB431542 treatment. Moreover, the expression of Runx2, ALK5 and Smad3 were influenced by SB431542 treatment. In conclusion, this preliminary study indicated that fluoride regulated osteoblastic TGFβ1 signaling in bone turnover and cells differentiation via ALK5.

Effects of fluoride on insulin signaling and bone metabolism in ovariectomized rats

Fluoride is an essential trace element for the maintenance of bone health owing to its capacity to stimulate proliferation and osteoblastic activity that can lead to increased bone formation. However, excessive sodium fluoride (NaF) intake can impair carbohydrate metabolism thereby promoting hyperglycemia, insulin resistance, and changes in insulin signaling. Thus, this study aimed to evaluate the effect of chronic treatment with NaF in bone metabolism, insulin signaling, and plasma concentrations of glucose, insulin, tumor necrosis factor-α (TNF-α), osteocalcin (OCN), and fluoride in ovariectomized rats. Thirty-two ovariectomized Wistar rats were randomly distributed into two groups: Control (OVX-C) and those undergoing treatment with NaF (50mg F/L) in drinking water for 42days (OVX-F). Glucose and insulin levels were assessed, followed by homeostasis model assessment of insulin resistance (HOMA-IR). Akt serine phosphorylation was evaluated by western blotting. Plasma concentrations of TNF-α and OCN were evaluated by ELISA. The left and right tibia was collected for immunohistochemical and histomorphometric analysis, respectively. Chronic treatment with NaF promoted insulin resistance, decreased insulin signal, increased plasma concentration of insulin, fluoride, OCN and TNF-α, decreased trabecular bone area of the tibia, and caused changes in bone metabolism markers in ovariectomized rats. These results suggest the need for caution in the use of NaF for the treatment of osteoporosis, especially in postmenopausal woman.

Three-dimensional co-culture of mesenchymal stromal cells and differentiated osteoblasts on human bio-derived bone scaffolds supports active multi-lineage hematopoiesis in vitro: Functional implication of the biomimetic HSC niche

Recent studies have indicated that the hematopoietic stem/progenitor cell (HSPC) niche, consisting of two major crucial components, namely osteoblasts (OBs) and mesenchymal stromal cells (MSCs), is responsible for the fate of HSPCs. Thus, closely mimicking the HSPC niche ex vivo may be an efficient strategy with which to develop new culture strategies to specifically regulate the balance between HSPC self-renewal and proliferation. The aim of this study was to establish a novel HSPC three-dimensional culture system by co-culturing bone marrow-derived MSCs and OBs differentiated from MSCs without any cytokines as feeder cells and applying bio-derived bone from human femoral metaphyseal portion as the scaffold. Scanning electron microscopy revealed the excellent biocompatibility of bio-derived bone with bone marrow-derived MSCs and OBs differentiated from MSCs. Western blot analysis revealed that many cytokines, which play key roles in HSPC regulation, were comprehensively secreted, while ELISA revealed that extracellular matrix molecules were also highly expressed. Hoechst 33342/propidium iodide fluorescence staining proved that our system could be used to supply a long-term culture of HSPCs. Flow cytometric analysis and qPCR of p21 expression demonstrated that our system significantly promoted the self-renewal and ex vivo expansion of HSPCs. Colony-forming unit (CFU) and long-term culture-initiating cell (LTC-IC) assays confirmed that our system has the ability for both the expansion of CD34+ hematopoietic stem cells (HPCs) and the maintenance of a primitive cell subpopulation of HSCs. The severe-combined immunodeficient mouse repopulating cell assay revealed the promoting effects of our system on the expansion of long-term primitive transplantable HSCs. In conclusion, our system may be a more comprehensive and balanced system which not only promotes the self-renewal and ex vivo expansion of HSPCs, but also maintains primitive HPCs with superior phenotypic and functional attributes.

Analysis of the Role of Insulin Signaling in Bone Turnover Induced by Fluoride

The role of insulin signaling on the mechanism underlying fluoride induced osteopathology was studied. We analyzed the expression of genes related with bone turnover and insulin signaling in rats treated by varying dose of fluoride with or without streptozotocin (STZ) in vivo. Furthermore, insulin receptor (InR) expression in MC3T3-E1 cells (pre-osteoblast cell line) was interfered with small interfering RNA (siRNA), and genes related with osteoblastic and osteoclastic differentiation were investigated in cells exposed to fluoride in vitro for 2 days. The in vivo study indicated the possible role of insulin in bone lesion induced by excessive amount of fluoride. Fluoride activated the InR and Insulin-like growth factor 1 (IGF1) signaling, which were involved in the mechanism underlying fluoride induced bone turnover. The TGFβ1 and Wnt10/β-catenin pathway took part in the mechanism of bone lesion induced by fluoride, and insulin probably modulated the TGFβ1 and β-catenin to exert action on bone turnover during the development of bone lesion. The in vitro study showed the concomitant decrease of OPG, osterix and OCN with inhibition of InR expression in osteoblast, and three genes still was low in cells co-treated with fluoride and InR siRNA, which suggested that fluoride probably stimulated the expression of OPG, osterix and OCN through InR signaling. In conclusion, insulin played the important role in bone lesion induced by excessive amount of fluoride through mediating InR receptor signaling, and IGF1 signaling probably exerted action on bone turnover caused by overdose of fluoride.

Tumor Necrosis Factor-α Attenuates the Osteogenic Differentiation Capacity of Periodontal Ligament Stem Cells by Activating PERK Signaling

BACKGROUND

Human periodontal ligament stem cells (PDLSCs) display efficient osteogenic differentiation capacity but fail to rescue bone breakdown associated with periodontitis. Endoplasmic reticulum (ER) stress and the unfolded protein response have recently been linked to inflammation and osteogenic differentiation. Therefore, the role of the double-stranded RNA-activated protein kinase (PKR)-like ER kinase (PERK) pathway in the impaired osteogenic differentiation ability of PDLSCs treated with tumor necrosis factor (TNF)-α was investigated.

METHODS

PDLSCs were isolated and stimulated with osteogenic media containing 1, 10, or 20 ng/mL TNF-α. Assessment included: 1) expression of runt-related transcription factor 2 and osteocalcin; 2) mRNA expression and activity of alkaline phosphatase; and 3) formation of mineralization nodules. Furthermore, expression of PERK pathway-related factors: 1) glucose-regulated protein (GRP) 78; 2) PERK; 3) activating transcription factor (ATF) 4; and 4) CCAAT-enhancer-binding proteins (C/EBP) homologous protein were also measured. Osteogenic differentiation and inhibition of the PERK pathway were also examined in cells pretreated with an inhibitor of ER stress, 4-phenylbutyric acid (PBA), followed by TNF-α stimulation. Finally, PERK small interfering RNA was used to examine osteogenic differentiation attenuated by TNF-α.

RESULTS

Higher concentrations of TNF-α (10 and 20 ng/mL) impaired osteogenic differentiation of PDLSCs but activated the PERK pathway. Pretreatment of PDLSCs with lower concentrations of 4-PBA prevented the TNF-α-induced upregulation of GRP78, PERK, and ATF4 and recovered differentiation ability. Finally, PERK knockdown also restored osteogenic differentiation.

CONCLUSION

TNF-α attenuates osteogenic differentiation ability of PDLSCs through activation of the PERK pathway.

Streptozotocin Aggravated Osteopathology and Insulin Induced Osteogenesis Through Co-treatment with Fluoride

The role of insulin in the mechanism underlying the excessive fluoride that causes skeletal lesion was studied. The in vitro bone marrow stem cells (BMSC) collected from Kunming mice were exposed to varying concentrations of fluoride with or without insulin. The cell viability and early differentiation of BMSC co-treated with fluoride and insulin were measured by using cell counting kit-8 and Gomori modified calcium-cobalt method, respectively. We further investigated the in vivo effects of varying dose of fluoride on rats co-treated with streptozotocin (STZ). Wistar rats were divided into six groups which included normal control, 10 mg fluoride/kg day group, 20 mg fluoride/kg day group, STZ control, STZ+10 mg fluoride/kg day group, and STZ+20 mg fluoride/kg day group. The rats were administered with sodium fluoride (NaF) by gavage with water at doses 10 and 20 mg fluoride/kg day for 2 months. In a period of one month, half of rats in every group were treated with streptozotocin (STZ) once through intraperitoneal injection at 52 mg/kg body weight. The serum glucose, HbA1c, and insulin were determined. Bone mineral content and insulin release were assessed. The results showed insulin combined with fluoride stimulated BMSC cell viability in vitro. The bone mineral content reduced in rats treated with higher dose of fluoride and decreased immensely in rat co-treated with fluoride and STZ. Similarly, a combination treatment of a high dose of fluoride and STZ decreased insulin sensitivity and activity. To sum up, these data indicated fluoride influenced insulin release, activity, and sensitivity. Furthermore, the insulin state in vivo interfered in the osteogenesis in turn and implied there was a close relation between insulin and bone pathogenesis in the mechanism of fluoride toxicity.

Voriconazole Enhances the Osteogenic Activity of Human Osteoblasts In Vitro through a Fluoride-Independent Mechanism

Periostitis, which is characterized by bony pain and diffuse periosteal ossification, has been increasingly reported with prolonged clinical use of voriconazole. While resolution of clinical symptoms following discontinuation of therapy suggests a causative role for voriconazole, the biological mechanisms contributing to voriconazole-induced periostitis are unknown. To elucidate potential mechanisms, we exposed human osteoblasts in vitro to voriconazole or fluconazole at 15 or 200 μg/ml (reflecting systemic or local administration, respectively), under nonosteogenic or osteogenic conditions, for 1, 3, or 7 days and evaluated the effects on cell proliferation (reflected by total cellular DNA) and osteogenic differentiation (reflected by alkaline phosphatase activity, calcium accumulation, and expression of genes involved in osteogenic differentiation). Release of free fluoride, vascular endothelial growth factor (VEGF), and platelet-derived growth factor (PDGF) was also measured in cell supernatants of osteoblasts exposed to triazoles, with an ion-selective electrode (for free fluoride) and enzyme-linked immunosorbent assays (ELISAs) (for VEGF and PDGF). Voriconazole but not fluconazole significantly enhanced the proliferation and differentiation of osteoblasts. In contrast to clinical observations, no increases in free fluoride levels were detected following exposure to either voriconazole or fluconazole; however, significant increases in the expression of VEGF and PDGF by osteoblasts were observed following exposure to voriconazole. Our results demonstrate that voriconazole can induce osteoblast proliferation and enhance osteogenic activity in vitro. Importantly, and in contrast to the previously proposed mechanism of fluoride-stimulated osteogenesis, our findings suggest that voriconazole-induced periostitis may also occur through fluoride-independent mechanisms that enhance the expression of cytokines that can augment osteoblastic activity.