Fluoride regulates the expression of extracellular matrix HSPG and related signaling pathways FGFR3 and Ihh/PTHrP feedback loop during endochondral ossification

The molecular mechanisms of glycosaminoglycan biosynthesis regulating chondrogenesis and endochondral ossification

Disorders of chondrocyte differentiation and endochondral osteogenesis are major underlying factors in skeletal developmental disorders, including tibial dysplasia (TD), osteoarthritis (OA), chondrodysplasia (ACH), and multiple epiphyseal dysplasia (MED). Understanding the cellular and molecular pathogenesis of these disorders is crucial for addressing orthopedic diseases resulting from impaired glycosaminoglycan synthesis. Glycosaminoglycan is a broad term that refers to the glycan component of proteoglycan macromolecules. It is an essential component of the cartilage extracellular matrix and plays a vital role in various biological processes, including gene transcription, signal transduction, and chondrocyte differentiation. Recent studies have demonstrated that glycosaminoglycan biosynthesis plays a regulatory role in chondrocyte differentiation and endochondral osteogenesis by modulating various growth factors and signaling molecules. For instance, glycosaminoglycan is involved in mediating pathways such as Wnt, TGF-β, FGF, Ihh-PTHrP, and O-GlcNAc glycosylation, interacting with transcription factors SOX9, BMPs, TGF-β, and Runx2 to regulate chondrocyte differentiation and endochondral osteogenesis. To propose innovative approaches for addressing orthopedic diseases caused by impaired glycosaminoglycan biosynthesis, we conducted a comprehensive review of the molecular mechanisms underlying chondrocyte glycosaminoglycan biosynthesis, which regulates chondrocyte differentiation and endochondral osteogenesis. Our analysis considers the role of genes, glycoproteins, and associated signaling pathways during chondrogenesis and endochondral ossification.

The role of FGF9-mediated TGF-β1/Smad signaling in enamel hypoplasia induced by exposure to fluoride and SO2 in rats

Many geographical areas of the world are polluted by both fluoride and sulfur dioxide (SO2). However, the effects of simultaneous exposure to fluoride and SO2 on teeth are unknown. Fibroblast growth factor-9 (FGF9) and transforming growth factor-β1 (TGF-β1) are key signaling molecules in enamel development. The purpose of the study was to explore the effects of co-exposure to fluoride and sulfur dioxide on enamel and to investigate the role and mechanism of FGF9 and TGF-β1. First, sodium fluoride (NaF) and SO2 derivatives were used to construct rat models and evaluate the enamel development of rats. Then, TGF-β1 (cytokine) treatment, SIS3 (inhibitor) treatment and FGF9 gene knockdown were used to explore the mechanism of enamel damage in vitro. The results showed that enamel column crystals in the exposed group were characterized by enamel hypoplasia, as indicated by alterations such as disarrangement of enamel column crystals, space widening and breakage. Ameloblasts also showed pathological changes such as ribosome loss, mitochondrial swelling, nuclear fragmentation and chromatin aggregation. The protein expression of FGF9 was higher and the protein expression of AMBN, TGF-β1 and p-Smad2/3 protein was lower in the groups treated with fluoride and SO2 individually or in combination compared with the control group. Further studies showed that TGF-β1 significantly upregulated p-Smad2/3 and AMBN protein expression and reduced the inhibitory effects of fluoride and SO2; furthermore, SISI blocked the effect of TGF-β1. In addition, knockdown of FGF9 upregulated TGF-β1 protein expression, further activated Smad2/3 phosphorylation, eliminated the inhibitory effects of fluoride and SO2, and increased the protein expression of AMBN. In brief, the study confirms that co-exposure to fluoride and SO2 can result in enamel hypoplasia in rats and indicates that the underlying mechanism may be closely related to the effect of FGF9 on enamel matrix protein secretion through inhibition of the TGF-β1/Smad signaling pathway.

Fluoride increases the susceptibility of developmental dysplasia of the hip via increasing capsular laxity triggered by cell apoptosis and oxidative stress in vivo and in vitro

The etiology of developmental dysplasia of the hip (DDH) is multifactorial, including breech presentation and hip capsular laxity. In particular, hip laxity is the main contributor to DDH by changing the ratio and distribution of collagens. Also, fluoride (F) affects collagens from various tissue besides bone and tooth. To investigate the association of DDH and excessive F intake, we conducted this research in lab on cell and animal model simultaneously. We established animal model of combination of DDH and F toxicity. The incidence of DDH in each group was calculated, and hip capsules were collected for testing histopathological and ultrastructural changes. The primary fibroblasts were further extracted from hip capsule and treated with F. The expression of collagen type I and III was both examined in vivo and in vitro, and the level of oxidative stress and apoptosis was also tested identically. We revealed that the incidence of DDH increased with F concentration. Furthermore, the oxidative stress and apoptosis levels of hip capsules and fibroblasts both increased after F exposure. Therefore, this study shows that excessive F intake increases susceptibility to DDH by altering hip capsular laxity in vivo and in vitro respectively. We believe that F might be a risk factor for DDH by increasing hip laxity induced by triggering fibroblast oxidative stress and apoptosis.

Role of the hippo signaling pathway in the extracellular matrix degradation of chondrocytes induced by fluoride exposure

To identify the role of the Hippo signaling pathway in the extracellular matrix degradation of chondrocytes induced by fluoride exposure. Environmental response genes (ERGs) of bone injury induced by fluoride exposure were obtained from the Comparative Toxicogenomics Database, and annotated by STRING for KEGG pathway enrichment analysis. The CCK-8 kit was used to measure the proliferation of ATDC5 cells. The malondialdehyde (MDA), total antioxidant capacity (T-AOC), total superoxide dismutase (T-SOD), and glutathione peroxidase (GSH-PX) levels in ATDC5 cells were measured using oxidative stress detection kit. Western blot analysis was used to measure the p-MST1/2, p-LATS1/2, and p-YAP/YAP1 expression levels in the Hippo pathway and the COL2A1, ACAN and MMP13 expression levels in the cartilage matrix. Localizations of YAP1 and COL2A1 proteins in chondrocytes were performed using cell immunofluorescence. Continuous data from the multiple groups were compared using one-way analysis of variance, and then the differences between groups were tested with Dunnett's t-test, with the test level α = 0.05. The 145 ERGs of bone injury induced by fluoride exposure were identified, and KEGG enrichment analysis revealed Hippo signaling pathways significantly related to bone injury. A CCK-8 assay revealed that the viability of the ATDC5 cells was significantly decreased with increased fluorine concentration. The MDA content in 20 mg/L sodium fluoride (NaF) exposure group was significantly higher than that in the control group, the T-SOD, T-AOC and GSH-PX activities in 15 and 20 mg/L NaF exposure groups were significantly lower than those in the control group (P < 0.05). Western blot results showed the protein levels of p-MST1/2, p-LATS1/2 and p-YAP1 in 15 and 20 mg/L NaF exposure groups were significantly lower than those in the control group, while the YAP1 protein level in 20 mg/L NaF group was significantly higher than that in the control group. The COL2A1 and ACAN proteins in 20 mg/L NaF group were significantly decreased, while the MMP13 protein level in 15 and 20 mg/L NaF groups were significantly increased (P < 0.05). It was observed that the expression of YAP1 protein expression level in the cytoplasm decreased with the increased fluoride exposure, whereas that the expression level of YAP1 protein in the nucleus increased. Fluoride inhibited the proliferation of ATDC5 cells, induced oxidative stress, inhibited the activity of the Hippo pathway, and eventually led to cartilage matrix degradation.

Biological role of heparan sulfate in osteogenesis: A review

Heparan sulfate (HS) is extensively expressed in cells, for example, cell membrane and extracellular matrix of most mammalian cells and tissues, playing a key role in the growth and development of life by maintaining homeostasis and implicating in the etiology and diseases. Recent studies have revealed that HS is involved in osteogenesis via coordinating multiple signaling pathways. The potential effect of HS on osteogenesis is a complicated and delicate biological process, which involves the participation of osteocytes, chondrocytes, osteoblasts, osteoclasts and a variety of cytokines. In this review, we summarized the structural and functional characteristics of HS and highlighted the molecular mechanism of HS in bone metabolism to provide novel research perspectives for the further medical research.

Manganese deficiency induces avian tibial dyschondroplasia by inhibiting chondrocyte proliferation and differentiation

Manganese (Mn) is an essential trace element for bone growth, and its deficiency has been shown to increase the incidence of leg abnormalities in fast-growing broilers, such as tibial dyschondroplasia (TD). Proliferation and differentiation of growth plate chondrocyte are critical for tibia development, but their roles in Mn deficiency-induced TD remains to be elucidated. Thirty 1-day-old Arbor Acres chicks were randomly divided into two groups and fed with control diet (60 mg Mn/kg diet) and Mn-deficiency diet (22 mg Mn/kg diet) for 42 days, respectively. Mn deficiency-induced TD model was successfully established and samples from proximal tibia metaphysis and growth plate were collected for assays. Pathological observation showed that Mn deficiency induced morphological abnormality and irregular arrangement of chondrocytes in proliferative and hypertrophic zone of tibial growth plate. Also, Mn deficiency decreased mRNA and protein expression levels of type II collagen and type X collagen in tibial growth plate, indicating the impairment of proliferating and hypertrophic chondrocytes. Moreover, down-regulated gene expression levels of Sox9, Tgf-β, Ihh, Runx2, Mef2c and Bmp-2 were shown in tibial growth plate of Mn-deficiency group, demonstrating that Mn deficiency inhibited the transcription levels of key regulators to disrupt chondrocyte proliferation and differentiation. Collectively, these findings confirmed that Mn deficiency affected the proliferation and differentiation of chondrocytes in tibial growth plate via inhibiting related regulatory factors, leading to TD in broilers.

Long-term exposure to the fluoride blocks the development of chondrocytes in the ducks: The molecular mechanism of fluoride regulating autophagy and apoptosis

Long-term exposure to excessive fluoride causes chronic damage in the body tissues and could lead to skeletal and dental fluorosis. Cartilage damage caused by excessive fluoride intake has gained wide attention, but how fluoride accumulation blocks the development of chondrocytes is still unclear. Here, we report a negative correlation between the length and growth plate width after NaF treatments via apoptosis and autophagy, with shrinkage of cells, nuclear retraction, dissolution of chondrocytes. Whereas, fluoride exposure had no significant effect on the number and distribution of the osteoclasts which were well aligned. More importantly, fluoride exposure induced apoptosis of tibial bone through CytC/Bcl-2/P53 pathways via targeting Caspase3, Caspase9, Bak1, and Bax expressions. Meanwhile, the Beclin1, mTOR, Pakin, Pink, and p62 were elevated in NaF treatment group, which indicated that long-term excessive fluoride triggered the autophagy in the tibial bone and produced the chondrocyte injury. Altogether, fluoride exposure induced the chondrocyte injury by regulating the autophagy and apoptosis in the tibial bone of ducks, which demonstrates that fluoride exposure is a risk factor for cartilage development. These findings revealed the essential role of CytC/Bcl-2/P53 pathways in long-term exposure to fluoride pollution and block the development of chondrocytes in ducks, and CytC/Bcl-2/P53 can be targeted to prevent fluoride induced chondrocyte injury.

Involvement of Bmal1 and circadian clock signaling in chondrogenic differentiation of ATDC5 cells by fluoride

Skeletal fluorosis causes growth plate impairment and growth retardation during bone development. However, the mechanism of how fluoride impairs chondrocyte is unclear. To explore the effect of fluoride on chondrocyte differentiation and the regulation of circadian clock signaling pathway during chondrogenesis, we treated ATDC5 cells with fluoride and carried out a series of experiments. 10^-3 M fluoride inhibited cell viability and significantly decreased the expression of Sox9 and Col2a1 (P < 0.05). Fluoride inhibited proteoglycan synthesis and decreased significantly the expression of Aggrecan, Ihh and Col10a1 (P < 0.05). Meanwhile, fluoride significantly inhibited the expression of Bmal1 and disrupted circadian clock signaling pathway (P < 0.05). Furthermore, fluoride disrupted the time-dependent expression of circadian clock molecules and stage-specific differentiation markers. Overexpression of Bmal1 by lentivirus reversed the adverse effects of fluoride on chondrogenesis. These results suggested that fluoride inhibited chondrocyte viability and delayed chondrocyte differentiation. Fluoride delayed chondrogenesis partly via interfering with Bmal1 and circadian clock signaling pathway. Nevertheless, the specific mechanism of circadian clock in fluoride-induced cartilage damage needs to be further studied.