Novel inhibitor N-cyclopropyl-4-((4-((4-(trifluoromethyl)phenyl)sulfonyl)piperazin-1-yl)methyl)benzamide attenuates RANKL-mediated osteoclast differentiation in vitro.

Both cyclopropyl amide and piperazine sulfonamide functional groups are known for their various biological properties used for drug development. Herein, we synthesized nine new derivatives with different substituent groups incorporating these moieties and screened them for their anti-osteoclast differentiation activity. After analyzing the structure-activity relationship (SAR), the inhibitory effect against osteoclastogenesis was determined to be dependent on the lipophilicity of the compound. Derivative 5b emerged as the most effective dose-dependent inhibitor after TRAP staining with an IC50 of 0.64 µM against RANKL-induced osteoclast cells. 5b was also able to suppress F-acting ring formation and bone resorption activity of osteoclasts in vitro. Finally, well-acknowledged gene and protein osteoclast-specific marker expression levels were decreased after 5b administration on primary murine osteoclast cells.

Evaluation of Bone Turnover Markers in Patients with Acute and Chronic Leukemia.

This study investigated different bone biomarkers (cross-linked carboxy-terminal telopeptide of type 1 collagen (CTX-1), pyridinoline (PYD), osteocalcin (OC), interleukin-6 receptor (IL-6R), calcium (Ca), and magnesium (Mg)) in terms of their metabolism in 4 different leukemia subtypes (ALL, AML, CLL and CML). The design was case control study with 30 controls and 60 cases of leukemia patients. Authors have reported many results regarding decrease as well as increase of specific bone biomarker under investigation with each leukemia subtype when compared to control. In addition, Authors reported correlations between each biomarker level and leukemia subtypes.

Ginkgetin attenuates bone loss in OVX mice by inhibiting the NF-κB/IκBα signaling pathway.

Background: Osteoporosis is a disease associated with bone resorption, characterized primarily by the excessive activation of osteoclasts. Ginkgetin is a compound purified from natural ginkgo leaves which has various biological properties, including anti-inflammation, antioxidant, and anti-tumor effects. This study investigated the bone-protective effects of ginkgetin in ovariectomized (OVX) mice and explored their potential signaling pathway in inhibiting osteoclastogenesis in a mouse model of osteoporosis. Methods: Biochemical assays were performed to assess the levels of Ca, ALP, and P in the blood. Micro CT scanning was used to evaluate the impact of ginkgetin on bone loss in mice. RT-PCR was employed to detect the expression of osteoclast-related genes (ctsk, c-fos, trap) in their femoral tissue. Hematoxylin and eosin (H&E) staining was utilized to assess the histopathological changes in femoral tissue due to ginkgetin. The TRAP staining was used to evaluate the impact of ginkgetin osteoclast generation in vivo. Western blot analysis was conducted to investigate the effect of ginkgetin on the expression of p-NF-κB p65 and IκBα proteins in mice. Results: Our findings indicate that ginkgetin may increase the serum levels of ALP and P, while decreasing the serum level of Ca in OVX mice. H&E staining and micro CT scanning results suggest that ginkgetin can inhibit bone loss in OVX mice. The TRAP staining results showed ginkgetin suppresses the generation of osteoclasts in OVX mice. RT-PCR results demonstrate that ginkgetin downregulate the expression of osteoclast-related genes (ctsk, c-fos, trap) in the femoral tissue of mice, and this effect is dose-dependent. Western blot analysis results reveal that ginkgetin can inhibit the expression of p-NF-κB p65 and IκBα proteins in mice. Conclusion: Ginkgetin can impact osteoclast formation and activation in OVX mice by inhibiting the NF-κB/IκBα signaling pathway, thereby attenuating bone loss in mice.

Part II: A new perspective for modeling the bone remodeling process: Biology, mechanics, and pathologies.

In this paper, we explore the effects of biological (pathological) and mechanical damage on bone tissue within a benchmark model. Using the Finite Element Methodology, we analyze and numerically test the model's components, capabilities, and performance under physiologically and pathologically relevant conditions. Our findings demonstrate the model's effectiveness in simulating bone remodeling processes and self-repair mechanisms for micro-damage induced by biological internal conditions and mechanical external ones within bone tissue. This article is the second part of a series, where the first part presented the mathematical model and the biological and physical significance of the terms used in a simplified benchmark model. It explored the bone remodeling model's application, implementation, and results under physiological conditions.

Collagen structures of demineralized bone paper direct mineral metabolism.

Bone is a dynamic mineralized tissue that undergoes continuous turnover throughout life. While the general mechanism of bone mineral metabolism is documented, the role of underlying collagen structures in regulating osteoblastic mineral deposition and osteoclastic mineral resorption remains an active research area, partly due to the lack of biomaterial platforms supporting accurate and analytical investigation. The recently introduced osteoid-inspired demineralized bone paper (DBP), prepared by 20-µm thin sectioning of demineralized bovine compact bone, holds promise in addressing this challenge as it preserves the intrinsic bony collagen structure and retains semi-transparency. Here, we report on the impact of collagen structures on modulating osteoblast and osteoclast-driven bone mineral metabolism using vertical and transversal DBPs that exhibit a uniaxially aligned and a concentric ring collagen structure, respectively. Translucent DBP reveals these collagen structures and facilitates longitudinal tracking of mineral deposition and resorption under brightfield microscopy for at least 3 wk. Genetically labeled primary osteogenic cells allow fluorescent monitoring of these cellular processes. Osteoblasts adhere and proliferate following the underlying collagen structures of DBPs. Osteoblastic mineral deposition is significantly higher in vertical DBP than in transversal DBP. Spatiotemporal analysis reveals notably more osteoblast adhesion and faster mineral deposition in vascular regions than in bone regions. Subsequent osteoclastic resorption follows these mineralized collagen structures, directing distinct trench and pit-type resorption patterns. In vertical DBP, trench-type resorption occurs at an 80% frequency, whereas transversal DBP shows 35% trench-type and 65% pit-type resorption. Our studies substantiate the importance of collagen structures in regulating mineral metabolism by osteogenic cells. DBP is expected to serve as an enabling biomaterial platform for studying various aspects of cellular and extracellular bone remodeling biology.

Osteogenic Differentiation of Human Gingival Fibroblasts Inhibits Osteoclast Formation.

Gingival fibroblasts (GFs) can differentiate into osteoblast-like cells and induce osteoclast precursors to differentiate into osteoclasts. As it is unclear whether these two processes influence each other, we investigated how osteogenic differentiation of GFs affects their osteoclast-inducing capacity. To establish step-wise mineralization, GFs were cultured in four groups for 3 weeks, without or with osteogenic medium for the final 1, 2, or all 3 weeks. The mineralization was assessed by ALP activity, calcium concentration, scanning electron microscopy (SEM), Alizarin Red staining, and quantitative PCR (qPCR). To induce osteoclast differentiation, these cultures were then co-cultured for a further 3 weeks with peripheral blood mononuclear cells (PBMCs) containing osteoclast precursors. Osteoclast formation was assessed at different timepoints with qPCR, enzyme-linked immunosorbent assay (ELISA), TRAcP activity, and staining. ALP activity and calcium concentration increased significantly over time. As confirmed with the Alizarin Red staining, SEM images showed that the mineralization process occurred over time. Osteoclast numbers decreased in the GF cultures that had undergone osteogenesis. TNF-α secretion, a costimulatory molecule for osteoclast differentiation, was highest in the control group. GFs can differentiate into osteoblast-like cells and their degree of differentiation reduces their osteoclast-inducing capacity, indicating that, with appropriate stimulation, GFs could be used in regenerative periodontal treatments.

Advances of long non-coding RNAs in osteoclast differentiation and osteoporosis.

INTRODUCTION: Osteoclasts, which are responsible for bone resorption, are specialized multinucleated cells generated from monocyte/macrophage progenitor cells or hematopoietic stem cells (HSCs). Physiological bone remodeling can become pathological, such as osteoporosis, when osteoclastogenesis is out of balance. Thousands of long noncoding RNAs (lncRNAs) influence important molecular and biological processes. Recent research has revealed gene expression regulation function that numerous lncRNAs regulate nuclear domain organization, genome stability. Furthermore, the research of lncRNAs has substantial clinical implications for the treatment of existing and new diseases. AREAS COVERED: In this review, we gather the most recent research on lncRNAs and their potential for basic research and clinical applications in osteoclast and osteoporosis. We also discuss the findings here in order to fully understand the role of lncRNAs in osteoclast differentiation and osteoporosis, as well as to provide a solid basis for future research exploring associated mechanisms and treatments. EXPERT OPINION: LncRNA has been considered as an important role in the regulation of osteoclast differentiation and osteoporosis. It is exciting to investigate pathophysiological processes in osteoporosis and the therapeutic potential of lncRNAs. We hope that this review will offer promising prospects for the development of precision and individualized approaches to treatment.

Emerging Insights into the Endocrine Regulation of Bone Homeostasis by Gut Microbiome.

Gut microbiota plays an important role in the regulation of bone homeostasis and bone health. Recent studies showed that these effects could be mediated through microbial metabolites released by the microbiota like short-chain fatty acids, metabolism of endogenous molecules such as bile acids, or a complex interplay between microbiota, the endocrine system, and the immune system. Importantly, some studies showed a reciprocal relationship between the endocrine system and gut microbiota. For instance, postmenopausal estrogen deficiency could lead to dysbiosis of the gut microbiota, which could in turn affect various immune response and bone remodeling. In addition, evidence showed that shift in the indigenous gut microbiota caused by antibiotics treatment may also impact normal skeletal growth and maturation. In this mini-review, we describe recent findings on the role of microbiome in bone homeostasis, with a particular focus on molecular mechanisms and their interactions with the endocrine and immune system. We will also discuss the recent findings on estrogen deficiency and microbiota dysbiosis, and the clinical implications for the development of new therapeutic strategies for osteoporosis and other bone disorders.

Impdh2 deficiency suppresses osteoclastogenesis through mitochondrial oxidative phosphorylation and alleviates ovariectomy-induced osteoporosis.

Abnormalities in osteoclastic generation or activity disrupt bone homeostasis and are highly involved in many pathologic bone-related diseases, including rheumatoid arthritis, osteopetrosis, and osteoporosis. Control of osteoclast-mediated bone resorption is crucial for treating these bone diseases. However, the mechanisms of control of osteoclastogenesis are incompletely understood. In this study, we identified that inosine 5'-monophosphate dehydrogenase type II (Impdh2) positively regulates bone resorption. By histomorphometric analysis, Impdh2 deletion in mouse myeloid lineage cells (Impdh2LysM-/- mice) showed a high bone mass due to the reduced osteoclast number. qPCR and western blotting results demonstrated that the expression of osteoclast marker genes, including Nfatc1, Ctsk, Calcr, Acp5, Dcstamp, and Atp6v0d2, was significantly decreased in the Impdh2LysM-/- mice. Furthermore, the Impdh inhibitor MPA treatment inhibited osteoclast differentiation and induced Impdh2-cytoophidia formation. The ability of osteoclast differentiation was recovered after MPA deprivation. Interestingly, genome-wide analysis revealed that the osteoclastic mitochondrial biogenesis and functions, such as oxidative phosphorylation, were impaired in the Impdh2LysM-/- mice. Moreover, the deletion of Impdh2 alleviated ovariectomy-induced bone loss. In conclusion, our findings revealed a previously unrecognized function of Impdh2, suggesting that Impdh2-mediated mechanisms represent therapeutic targets for osteolytic diseases.

New mechanistic understanding of osteoclast differentiation and bone resorption mediated by P2X7 receptors and PI3K-Akt-GSK3ß signaling.

OBJECTIVE: Osteoporosis is a global health issue characterized by decreased bone mass and microstructural degradation, leading to an increased risk of fractures. This study aims to explore the molecular mechanism by which P2X7 receptors influence osteoclast formation and bone resorption through the PI3K-Akt-GSK3ß signaling pathway. METHODS: An osteoporosis mouse model was generated through ovariectomy (OVX) in normal C57BL/6 and P2X7f/f; LysM-cre mice. Osteoclasts were isolated for transcriptomic analysis, and differentially expressed genes were selected for functional enrichment analysis. Metabolite analysis was performed using liquid chromatography-tandem mass spectrometry (LC-MS/MS), and multivariate statistical analysis and pattern recognition were used to identify differential lipid metabolism markers and their distribution. Bioinformatics analyses were conducted using the Encyclopedia of Genes and Genomes database and the MetaboAnalyst database to assess potential biomarkers and create a metabolic pathway map. Osteoclast precursor cells were used for in vitro cell experiments, evaluating cell viability and proliferation using the Cell Counting Kit 8 (CCK-8) assay. Osteoclast precursor cells were induced to differentiate into osteoclasts using macrophage colony-stimulating factor (M-CSF) and receptor activator of nuclear factor kappa-beta ligand (RANKL), and tartrate-resistant acid phosphatase (TRAP) staining was performed to compare differentiation morphology, size, and quantity between different groups. Western blot analysis was used to assess the expression of differentiation markers, fusion gene markers, and bone resorption ability markers in osteoclasts. Immunofluorescence staining was employed to examine the spatial distribution and quantity of osteoclast cell skeletons, P2X7 protein, and cell nuclei, while pit assay was used to evaluate osteoclast bone resorption ability. Finally, in vivo animal experiments, including micro computed tomography (micro-CT), hematoxylin and eosin (HE) staining, TRAP staining, and immunohistochemistry, were conducted to observe bone tissue morphology, osteoclast differentiation, and the phosphorylation level of the PI3K-Akt-GSK3ß signaling pathway. RESULTS: Transcriptomic and metabolomic data collectively reveal that the P2X7 receptor can impact the pathogenesis of osteoporosis through the PI3K-Akt-GSK3ß signaling pathway. Subsequent in vitro experiments showed that cells in the Sh-P2X7 + Recilisib group exhibited increased proliferative activity (1.15 versus 0.59), higher absorbance levels (0.68 versus 0.34), and a significant increase in resorption pit area (13.94 versus 3.50). Expression levels of osteoclast differentiation-related proteins MMP-9, CK, and NFATc1 were markedly elevated (MMP-9: 1.72 versus 0.96; CK: 2.54 versus 0.95; NFATc1: 3.05 versus 0.95), along with increased fluorescent intensity of F-actin rings. In contrast, the OE-P2X7 + LY294002 group showed decreased proliferative activity (0.64 versus 1.29), reduced absorbance (0.34 versus 0.82), and a significant decrease in resorption pit area (5.01 versus 14.96), accompanied by weakened expression of MMP-9, CK, and NFATc1 (MMP-9: 1.14 versus 1.79; CK: 1.26 versus 2.75; NFATc1: 1.17 versus 2.90) and decreased F-actin fluorescent intensity. Furthermore, in vivo animal experiments demonstrated that compared with the wild type (WT) + Sham group, mice in the WT + OVX group exhibited significantly increased levels of CTX and NTX in serum (CTX: 587.17 versus 129.33; NTX: 386.00 versus 98.83), a notable decrease in calcium deposition (19.67 versus 53.83), significant reduction in bone density, increased trabecular separation, and lowered bone mineral density (BMD). When compared with the KO + OVX group, mice in the KO + OVX + recilisib group showed a substantial increase in CTX and NTX levels in serum (CTX: 503.50 versus 209.83; NTX: 339.83 versus 127.00), further reduction in calcium deposition (29.67 versus 45.33), as well as decreased bone density, increased trabecular separation, and reduced BMD. CONCLUSION: P2X7 receptors positively regulate osteoclast formation and bone resorption by activating the PI3K-Akt-GSK3ß signaling pathway.

Gut-bone axis research: unveiling the impact of gut microbiota on postmenopausal osteoporosis and osteoclasts through Mendelian randomization.

Background: Postmenopausal osteoporosis is a prevalent disease that affects the bone health of middle-aged and elderly women. The link between gut microbiota and bone health, known as the gut-bone axis, has garnered widespread attention. Methods: We employed a two-sample Mendelian randomization approach to assess the associations between gut microbiota with osteoclasts and postmenopausal osteoporosis, respectively. Single nucleotide polymorphisms associated with the composition of gut microbiota were used as instrumental variables. By analyzing large-scale multi-ethnic GWAS data from the international MiBioGen consortium, and combining data from the eQTLGen consortium and the GEFOS consortium, we identified microbiota related to osteoclasts and postmenopausal osteoporosis. Key genes were further identified through MAGMA analysis, and validation was performed using single-cell data GSE147287. Results: The outcomes of this study have uncovered significant associations within the gut microbiome community, particularly with the Burkholderiales order, which correlates with both an increase in osteoclasts and a reduced risk of postmenopausal osteoporosis. with an odds ratio (OR) of 0.400, and a P-value of 0.011. Further analysis using single-cell data allowed us to identify two key genes, FMNL2 and SRBD1, that are closely linked to both osteoclasts and osteoporosis. Conclusion: This study utilizing Mendelian randomization and single-cell data analysis, provides new evidence of a causal relationship between gut microbiota and osteoclasts, as well as postmenopausal osteoporosis. It was discovered that the specific microbial group, the Burkholderiales order, significantly impacts both osteoporosis and osteoclasts. Additionally, key genes FMNL2 and SRBD1 were identified, offering new therapeutic strategies for the treatment of postmenopausal osteoporosis.

Differential Gene Expression Involved in Bone Turnover of Mice Expressing Constitutively Active TGFß Receptor Type I.

Transforming growth factor beta (TGF-ß) is ubiquitously found in bone and plays a key role in bone turnover. Mice expressing constitutively active TGF-ß receptor type I (Mx1;TßRICA mice) are osteopenic. Here, we identified the candidate genes involved in bone turnover in Mx1;TßRICA mice using RNA sequencing analysis. A total of 285 genes, including 87 upregulated and 198 downregulated genes, were differentially expressed. According to the KEGG analysis, some genes were involved in osteoclast differentiation (Fcgr4, Lilrb4a), B cell receptor signaling (Cd72, Lilrb4a), and neutrophil extracellular trap formation (Hdac7, Padi4). Lilrb4 is related to osteoclast inhibition protein, whereas Hdac7 is a Runx2 corepressor that regulates osteoblast differentiation. Silencing Lilrb4 increased the number of osteoclasts and osteoclast marker genes. The knocking down of Hdac7 increased alkaline phosphatase activity, mineralization, and osteoblast marker genes. Therefore, our present study may provide an innovative idea for potential therapeutic targets and pathways in TßRI-associated bone loss.

Caffeine regulates both osteoclast and osteoblast differentiation via the AKT, NF-κB, and MAPK pathways.

Background: Although caffeine generally offers benefits to human health, its impact on bone metabolism remains unclear. Aim and Methods: This study aimed to systematically evaluate the long-term effects of caffeine administration on osteoclasts, osteoblasts, and ovariectomy-induced postmenopausal osteoporosis (OP). Results: Our in vitro findings revealed that 3.125 and 12.5 µg/mL caffeine inhibited RANKL-mediated osteoclastogenesis in RAW 264.7 cells through the MAPK and NF-κB pathways, accompanied by the inactivation of nuclear translocation of nuclear factor NFATc1. Similarly, 3.125 and 12.5 µg/mL of caffeine modulated MC3T3-E1 osteogenesis via the AKT, MAPK, and NF-κB pathways. However, 50 µg/mL of caffeine promoted the phosphorylation of IκBα, P65, JNK, P38, and AKT, followed by the activation of NFATc1 and the inactivation of Runx2 and Osterix, ultimately disrupting the balance between osteoblastogenesis and osteoclastogenesis. In vivo studies showed that gavage with 55.44 mg/kg caffeine inhibited osteoclastogenesis, promoted osteogenesis, and ameliorated bone loss in ovariectomized mice. Conclusion: Conversely, long-term intake of high-dose caffeine (110.88 mg/kg) disrupted osteogenesis activity and promoted osteoclastogenesis, thereby disturbing bone homeostasis. Collectively, these findings suggest that a moderate caffeine intake (approximately 400 mg in humans) can regulate bone homeostasis by influencing both osteoclasts and osteoblasts. However, long-term high-dose caffeine consumption (approximately 800 mg in humans) could have detrimental effects on the skeletal system.

Immunostimulatory nucleic acid nanoparticles (NANPs) augment protective osteoblast and osteoclast type I interferon responses to Staphylococcus aureus.

Recalcitrant staphylococcal osteomyelitis may be due, in part, to the ability of Staphylococcus aureus to invade bone cells. However, osteoclasts and osteoblasts are now recognized to shape host responses to bacterial infection and we have recently described their ability to produce IFN-ß following S. aureus infection and limit intracellular bacterial survival/propagation. Here, we have investigated the ability of novel, rationally designed, nucleic acid nanoparticles (NANPs) to induce the production of immune mediators, including IFN-ß, following introduction into bone cells. We demonstrate the successful delivery of representative NANPs into osteoblasts and osteoclasts via endosomal trafficking when complexed with lipid-based carriers. Their delivery was found to differentially induce immune responses according to their composition and architecture via discrete cytosolic pattern recognition receptors. Finally, the utility of this nanoparticle technology was supported by the demonstration that immunostimulatory NANPs augment IFN-ß production by S. aureus infected bone cells and reduce intracellular bacterial burden.

Destruxin E backbone modification effects on osteoclast Morphology: Synthesis and SAR study of N-Desmethyl and N-Methyl analogs.

The design and synthesis of N-desmethyl and N-methyl destruxin E analogs have been demonstrated. The X-ray single crystal structure of destruxin E (1a) revealed a stable three-dimensional (3D) structure, including a s-cis amide bond at the MeVal-MeAla moiety and two intramolecular hydrogen bonds between NH(ß-Ala) and OC(Ile) and between NH(Ile) and OC(ß-Ala). N-Desmethyl analogs 2a (MeAla â†’ Ala) and 2b (MeVal â†’ Val) were synthesized through macrolactonization similar to our previously reported synthesis of 1a. Conversely, for the synthesis of N-methyl analogs 2c (Ile â†’ MeIle) and 2d (ß-Ala â†’ Meß-Ala), macrolactonization did not proceed; therefore, cyclization precursors 10c and 10d were designed to maintain the intramolecular hydrogen bonds described above during their cyclization. The macrolactamization proceeded despite the presence of a less reactive N-methylamino group at the N-terminus in both cases. Analog 2a, which exhibits multiple conformers in solutions, was inactive at 50 µM, whereas analog 2b, which exhibits a conformation similar to that of 1a in solutions, exhibited morphological changes against osteoclast-like multinuclear cells at 1.6 µM. The activity of the MeIle analog 2c, which cannot take the intramolecular hydrogen bond (Ile)NH•••OC(ß-Ala) in 1a, was markedly diminished compared with that of 1a, and that of the Meß-Ala analog 2d, which cannot take the intramolecular hydrogen bond (ß-Ala)NH•••OC(Ile) in 1a, was further reduced to one-fourth of that of 2c. The overall results indicate that both the s-cis amide bond at the MeVal-MeAla moiety and two intramolecular hydrogen bonds (ß-Ala)NH•••OC(Ile) and (Ile)NH•••OC(ß-Ala) are important for constraining the conformation of the macrocyclic peptide backbone in destruxin E, thereby exhibiting its potent biological activity.

Two Weeks of Continuous Opioid Treatment in an Adenine-Induced Mouse Model of Chronic Kidney Disease Exacerbates the Bone Inflammatory State and Increases Osteoclasts.

Patients with chronic kidney disease (CKD) report high pain levels, but reduced renal clearance eliminates many analgesic options; therefore, 30-50% of CKD patients have chronic opioid prescriptions. Opioid use in CKD is associated with higher fracture rates. Opioids may directly alter bone turnover directly through effects on bone cells and indirectly via increasing inflammation. We hypothesized that continuous opioid exposure would exacerbate the high bone turnover state of CKD and be associated with elevated measures of inflammation. Male C57Bl/6J mice after 8 weeks of adenine-induced CKD (AD) and non-AD controls (CON) had 14-day osmotic pumps (0.25-µL/hr release) containing either saline or 50-mg/mL oxycodone (OXY) surgically implanted in the subscapular region. After 2 weeks, all AD mice had elevated blood urea nitrogen, parathyroid hormone, and serum markers of bone turnover compared to controls with no effect of OXY. Immunohistochemical staining of the distal femur showed increased numbers of osteocytes positive for the mu opioid and for toll-like receptor 4 (TLR4) due to OXY. Osteocyte protein expression of tumor necrosis factor-α (TNF-α) and RANKL were higher due to both AD and OXY so that AD + OXY mice had the highest values. Trabecular osteoclast-covered surfaces were also significantly higher due to both AD and OXY, resulting in AD + OXY mice having 4.5-fold higher osteoclast-covered surfaces than untreated CON. These data demonstrate that opioids are associated with a pro-inflammatory state in osteocytes which increases the pro-resorptive state of CKD.

TGF-ß Signaling in Cranial Neural Crest Affects Late-Stage Mandibular Bone Resorption and Length.

Malocclusions are common craniofacial malformations which cause quality of life and health problems if left untreated. Unfortunately, the current treatment for severe skeletal malocclusion is invasive surgery. Developing improved therapeutic options requires a deeper understanding of the cellular mechanisms responsible for determining jaw bone length. We have recently shown that neural crest mesenchyme (NCM) can alter jaw length by controlling recruitment and function of mesoderm-derived osteoclasts. Transforming growth factor beta (TGF-ß) signaling is critical to craniofacial development by directing bone resorption and formation, and heterozygous mutations in TGF-ß type I receptor (TGFBR1) are associated with micrognathia in humans. To identify what role TGF-ß signaling in NCM plays in controlling osteoclasts during mandibular development, mandibles of mouse embryos deficient in the gene encoding Tgfbr1 specifically in NCM were analyzed. Our lab and others have demonstrated that Tgfbr1fl/fl;Wnt1-Cre mice display significantly shorter mandibles with no condylar, coronoid, or angular processes. We hypothesize that TGF-ß signaling in NCM can also direct later bone remodeling and further regulate late embryonic jaw bone length. Interestingly, analysis of mandibular bone through micro-computed tomography and Masson's trichrome revealed no significant difference in bone quality between the Tgfbr1fl/fl;Wnt1-Cre mice and controls, as measured by bone perimeter/bone area, trabecular rod-like diameter, number and separation, and gene expression of Collagen type 1 alpha 1 (Col1α1) and Matrix metalloproteinase 13 (Mmp13). Though there was not a difference in localization of bone resorption within the mandible indicated by TRAP staining, Tgfbr1fl/fl;Wnt1-Cre mice had approximately three-fold less osteoclast number and perimeter than controls. Gene expression of receptor activator of nuclear factor kappa-ß (Rank) and Mmp9, markers of osteoclasts and their activity, also showed a three-fold decrease in Tgfbr1fl/fl;Wnt1-Cre mandibles. Evaluation of osteoblast-to-osteoclast signaling revealed no significant difference between Tgfbr1fl/fl;Wnt1-Cre mandibles and controls, leaving the specific mechanism unresolved. Finally, pharmacological inhibition of Tgfbr1 signaling during the initiation of bone mineralization and resorption significantly shortened jaw length in embryos. We conclude that TGF-ß signaling in NCM decreases mesoderm-derived osteoclast number, that TGF-ß signaling in NCM impacts jaw length late in development, and that this osteoblast-to-osteoclast communication may be occurring through an undescribed mechanism.

Physiological occlusal force attenuates replacement root resorption of replanted teeth: an experimental animal study.

BACKGROUND: Tooth avulsion represents the most severe form of dental trauma, necessitating tooth replantation as the primary treatment. However, the risk of replacement root resorption (RRR) poses a significant threat to tooth retention following replantation. This study preliminarily aimed to investigate the effect of physiological occlusal force on RRR after the replantation of avulsed teeth and to explore the potential underlying mechanisms. METHODS: Thirty-six 4-week-old male Sprague-Dawley rats underwent extraction and immediate replantation of their left maxillary molars. The rats were randomly divided into two major groups: the occluded (n = 18) group, where the opposite mandibular teeth were preserved; non-occluded (n = 18) group, where the opposite mandibular teeth were extracted. Within each major group, there were three subgroups corresponding to 7 days, 14 days, and 2 months, resulting in a total of six subgroups, (n = 6 per subgroup). The right maxillary first molars served as the normal control. Various periodontal characteristics were assessed using haematoxylin-eosin (H&E), tartrate-resistant acid phosphatase (TRAP) staining, and micro-computed tomography (micro-CT). RESULTS: Histological staining revealed that under occlusal force, the early stage (day 7) after tooth replantation mainly manifested as root surface resorption, especially in the non-occluded group, which gradually diminished over time. Cementum and periodontal ligament (PDL) repair was observed on day 14. Micro-CT analysis indicated a significant decrease in PDL width in the non-occluded group two months after replantation, consistent with the histological findings, signifying severe RRR in the non-occluded group. CONCLUSIONS: This study provides preliminary evidence that physiological occlusal force may attenuate osteoclastogenesis during the early stage of tooth replantation, thereby reducing the occurrence of RRR and promoting periodontal healing.

Etiological Mechanisms and Genetic/Biological Modulation Related to PTH1R in Primary Failure of Tooth Eruption.

Primary failure of eruption (PFE) is a rare disorder that is characterized by the inability of a molar tooth/teeth to erupt to the occlusal plane or to normally react to orthodontic force. This condition is related to hereditary factors and has been extensively researched over many years. However, the etiological mechanisms of pathogenesis are still not fully understood. Evidence from studies on PFE cases has shown that PFE patients may carry parathyroid hormone 1 receptor (PTH1R) gene mutations, and genetic detection can be used to diagnose PFE at an early stage. PTH1R variants can lead to altered protein structure, impaired protein function, and abnormal biological activities of the cells, which may ultimately impact the behavior of teeth, as observed in PFE. Dental follicle cells play a critical role in tooth eruption and root development and are regulated by parathyroid hormone-related peptide (PTHrP)-PTH1R signaling in their differentiation and other activities. PTHrP-PTH1R signaling also regulates the activity of osteoblasts, osteoclasts and odontoclasts during tooth development and eruption. When interference occurs in the PTHrP-PTH1R signaling pathway, the normal function of dental follicles and bone remodeling are impaired. This review provides an overview of PTH1R variants and their correlation with PFE, and highlights that a disruption of PTHrP-PTH1R signaling impairs the normal process of tooth development and eruption, thus providing insight into the underlying mechanisms related to PTH1R and its role in driving PFE.

Corrigendum: Quercetin suppresses ovariectomy-induced osteoporosis in rat mandibles by regulating autophagy and the NLRP3 pathway.

[This corrects the article DOI: 10.1177/15353702231211977.].