CpG Methylation of Receptor Activator NF-κB (RANK) Gene Promoter Region Delineates Senescence-Related Decrease of RANK Gene Expression.

While the rapid decrease in estrogen is well known as the main cause of postmenopausal osteoporosis in women, the precise pathogenesis of senile osteoporosis in the elderly regardless of gender is largely unknown. The age-related epigenetic regulation of receptor activator NF-κB (RANK) gene expression was investigated with the use of a high-passaged mouse osteoclast progenitor cell line, RAW264.7, as an in vitro model of aging. In the RAW264.7 cells after repeated passages, receptor RANK expression was downregulated, resulting in decreased soluble RANK ligand (sRANKL)-induced osteoclastogenesis, expression of tartrate-resistant acid phosphatase-5b (TRAcP) and cathepsin K (CTSK). Methylation-specific PCR and bisulfite mapping revealed hypermethylation of CpG-loci located in the RANK gene promoter in multiple-passaged cells. ICON probe-mediated in situ assessment of methylated-cytosine at the CpG loci revealed an increase in the percentage of methylated RAW264.7 cells in the RANK gene in a passage-dependent manner. Conversely, upon treatment with demethylating agent 5-aza-2-deoxycytidine (5-aza-dC), high-passaged RAW264.7 cells displayed restored expression of the RANK gene, osteoclastogenesis, TRAcP and CTSK. Ex vivo cultures of splenic macrophages from young (10.5 W) and aged (12 M) mice also showed that CpG methylation was predominant in the aged animals, resulting in reduced RANK expression and osteoclastogenesis. Reduced RANK expression by age-related accumulation of DNA methylation, albeit in a limited population of osteoclast precursor cells, might be, at least in part, indicative of low-turnover bone characteristic of senile osteoporosis.

Inhibition of 12/15-lipoxygenase reduces orthodontically induced root resorption in rats.

OBJECTIVES: To investigate whether the inhibition of 12/15-lipoxygenase (12/15-LOX), one of the core enzymes of the arachidonic acid cascade, suppresses orthodontically induced root resorption (OIRR), and examine the involvement of the hyaline degeneration of periodontal ligament cells and odontoclast differentiation. MATERIALS AND METHODS: The left maxillary first molars of 10-week-old male Wistar rats were moved mesially for 14 days using a closed-coil spring (25 cN) inserted between the first molar and incisor. The rats were intraperitoneally administered with a 12/15-LOX specific inhibitor (ML-351; 0.05 mmol/kg) daily in the experimental group or vehicle (dimethyl sulfoxide) in the control group. Tooth movement was measured using microcomputed tomography on day 14. The appearance of OIRR, hyaline degeneration, osteoclasts, and odontoclasts was evaluated via histological analysis. Immunohistochemical staining for receptor-activated NF-kB ligand (RANKL) and osteoprotegerin was performed. RESULTS: OIRR observed on day 14 in the control group was strongly suppressed by ML-351 treatment. Hyaline degeneration observed on the compression side on day 3 and the appearance of osteoclasts and odontoclasts on days 3 and 14 were significantly suppressed by ML-351. RANKL expression on day 3 was significantly suppressed by ML-351. These key processes in OIRR were substantially suppressed by ML-351 treatment. CONCLUSIONS: Inhibition of 12/15-LOX reduced OIRR by suppressing hyaline degeneration and subsequent odontoclast differentiation.

Tunneling Nanotubes in Myeloid Cells: Perspectives for Health and Infectious Diseases.

Tunneling nanotubes (TNTs) are cellular connections, which represent a novel route for cell-to-cell communication. Strong evidence points to a role for TNTs in the intercellular transfer of signals, molecules, organelles, and pathogens, involving them in many cellular functions. In myeloid cells (e.g., monocytes/macrophages, dendritic cells, and osteoclasts), intercellular communication via TNT contributes to their differentiation and immune functions, by favoring material and pathogen transfer, as well as cell fusion. This chapter addresses the complexity of the definition and characterization of TNTs in myeloid cells, the different processes involved in their formation, their existence in vivo, and finally their function(s) in health and infectious diseases, with the example of HIV-1 infection.

Influence of vitamin D in orthodontic tooth movement-a systematic review and meta-analysis of randomized controlled trials in humans.

BACKGROUND: Orchestration of tooth movement necessitates an equilibrium of bone synthesis and resorption. Vitamin D, through receptor-mediated actions, regulates the differentiation and maturation of osteoblasts and also induces osteoclastogenesis, maintaining this equilibrium. OBJECTIVE: To analyze the impact of vitamin D in orthodontic tooth movement (OTM). SEARCH METHOD: A comprehensive exploration of the existing literature was conducted by systematic search through seven e-databases. SELECTION CRITERIA: The criteria for inclusion were established using the PICO format: Orthodontic patients treated with fixed appliance (P), administered with vitamin D3 (I), collated with appropriate control groups (C), with tooth movement as the primary outcome and root resorption, anchorage loss, gingival crevicular fluid (GCF) volume, pain perception, and alveolar bone density as the secondary outcome (O). DATA COLLECTION AND ANALYSIS: After an extensive database search, 251 articles were obtained. Six articles were chosen following a stringent selection using Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. The critical appraisal of randomized control trials (RCTs) involved the meticulous application of the RoB 2 tool. The quantitative synthesis incorporated a subset of six articles only. RESULTS: In the meta-analysis investigating the influence of vitamin D on OTM, a notable disparity was evident between the vitamin D and control groups. Specifically, the standardized mean difference (SMD) stood at 1.43, accompanied by a 95% confidence interval (CI) ranging from 0.691 to 2.169 (P = .00154). For root resorption, the SMD was recorded at -0.51, with a 95% CI spanning from -3.051 to 2.031 (P = .11). CONCLUSIONS: The rate of tooth movement was enhanced by systemic and local administration of vitamin D. However, the inadequacy of available data is a hindrance in determining conclusively the impact of vitamin D on the extent of root resorption. The resolution of this quandary needs future human studies devoted toward investigating the influence of vitamin D in the realms of OTM and associated root resorption, thereby providing a definitive elucidation. REGISTRATION DETAILS: Prospero- CRD42023491783.

Saikosaponin A attenuates osteoclastogenesis and bone loss by inducing ferroptosis.

To alleviate bone loss, most current drugs target osteoclasts. Saikosaponin A (Ssa), a triterpene saponin derived from Bupleurum falcatum (also known as Radix bupleuri), has immunoregulatory, neuromodulatory, antiviral, anticancer, anti-convulsant, anti-inflammatory, and anti-proliferative effects. Recently, modulation of bone homeostasis was shown to involve ferroptosis. Herein, we aimed to determine Ssa's inhibitory effects on osteoclastogenesis and differentiation, whether ferroptosis is involved, and the underlying mechanisms. Tartrate-resistant acid phosphatase (TRAP) staining, F-actin staining, and pit formation assays were conducted to confirm Ssa-mediated inhibition of RANKL-induced osteoclastogenesis in vitro. Ssa could promote osteoclast ferroptosis and increase mitochondrial damage by promoting lipid peroxidation, as measured by iron quantification, FerroOrange staining, Dichloro-dihydro-fluorescein diacetate, MitoSOX, malondialdehyde, glutathione, and boron-dipyrromethene 581/591 C11 assays. Pathway analysis showed that Ssa can promote osteoclasts ferroptosis by inhibiting the Nrf2/SCL7A11/GPX4 axis. Notably, we found that the ferroptosis inhibitor ferrostatin-1 and the Nrf2 activator tert-Butylhydroquinone reversed the inhibitory effects of Ssa on RANKL-induced osteoclastogenesis. In vivo, micro-computed tomography, hematoxylin and eosin staining, TRAP staining, enzyme-linked immunosorbent assays, and immunofluorescence confirmed that in rats with periodontitis induced by lipopolysaccharide, treatment with Ssa reduced alveolar bone resorption dose-dependently. The results suggested Ssa as a promising drug to treat osteolytic diseases.

Bone niches in the regulation of tumour cell dormancy.

Secondary metastases, accounting for 90 % of cancer-related deaths, pose a formidable challenge in cancer treatment, with bone being a prevalent site. Importantly, tumours may relapse, often in the skeleton even after successful eradication of the primary tumour, indicating that tumour cells may lay dormant within bone for extended periods of time. This review summarises recent findings in the mechanisms underlying tumour cell dormancy and the role of bone cells in this process. Hematopoietic stem cell (HSC) niches in bone provide a model for understanding regulatory microenvironments. Dormant tumour cells have been shown to exploit similar niches, with evidence suggesting interactions with osteoblast-lineage cells and other stromal cells via CXCL12-CXCR4, integrins, and TAM receptor signalling, especially through GAS6-AXL, led to dormancy, with exit of dormancy potentially regulated by osteoclastic bone resorption and neuronal signalling. A comprehensive understanding of dormant tumour cell niches and their regulatory mechanisms is essential for developing targeted therapies, a critical step towards eradicating metastatic tumours and stopping disease relapse.

α-IRAK-4 Suppresses the Activation of RANK/RANKL Pathway on Macrophages Exposed to Endodontic Microorganisms.

Periapical lesions are common pathologies affecting the alveolar bone, often initiated by intraradicular lesions resulting from microbial exposure to dental pulp. These microorganisms trigger inflammatory and immune responses. When endodontic treatment fails to eliminate the infection, periapical lesions persist, leading to bone loss. The RANK/RANKL/OPG pathway plays a crucial role in both the formation and the destruction of the bone. In this study, the objective was to inhibit the RANK/RANKL pathway in vitro within exposed Thp-1 macrophages to endodontic microorganisms, specifically Enterococcus faecalis, which was isolated from root canals of 20 patients with endodontic secondary/persistent infection, symptomatic and asymptomatic, and utilizing an α-IRAK-4 inhibitor, we introduced endodontic microorganisms and/or lipoteichoic acid from Streptococcus spp. to cellular cultures in a culture plate, containing thp-1 cells and/or PBMC from patients with apical periodontitis. Subsequently, we assessed the percentages of RANK+, RANKL+, and OPG+ cells through flow cytometry and measured the levels of several inflammatory cytokines (IL-1ß, TNF-α, IL-6, IL-8, IL-10, and IL-12p70) in the cellular culture supernatant through a CBA kit and performed analysis by flow cytometry. A significant difference was observed in the percentages of RANK+RANKL+, OPG+ RANKL+ cells in thp-1 cells and PBMCs from patients with apical periodontitis. The findings revealed significant differences in the percentages of the evaluated cells, highlighting the novel role of the IRAK-4 inhibitor in addressing this oral pathology, apical periodontitis, where bone destruction is observed.

Osteoclast-Driven Polydopamine-to-Dopamine Release: An Upgrade Patch for Polydopamine-Functionalized Tissue Engineering Scaffolds.

Polydopamine, a mussel-inspired self-adherent polymer of dopamine, has impressive adhesive properties and thus is one of the most versatile approaches to functionalize tissue engineering scaffolds. To date, many types of polydopamine-functionalized scaffolds have been manufactured and extensively applied in bone tissue engineering at the preclinical stage. However, how polydopamine is biodegraded and metabolized during the bone healing process and the side effects of its metabolite remain largely unknown. These issues are often neglected in the modern manufacture of polydopamine-functionalized materials and restrict them from stepping forward to clinical applications. In this study, using our bioinspired polydopamine-laced hydroxyapatite collagen calcium silicate material as a representative of polydopamine-functionalized tissue engineering scaffolds, we discovered that polydopamine can be metabolized to dopamine specifically by osteoclasts, which we termed "osteoclast-driven polydopamine-to-dopamine release". The released dopamine showed an osteoinductive effect in vitro and promoted bone regeneration in calvarial critical-sized defects. The concept of "osteoclast-driven polydopamine-to-dopamine release" has considerable application potential. It could be easily adopted by other existing polydopamine-functionalized scaffolds: just by recruiting osteoclasts. Once adopted, scaffolds will obtain a dopamine-releasing function, which enables their modulation of osteoblast activity and hence elevates the osteoinductive effect. Thus, "osteoclast-driven polydopamine-to-dopamine release" serves as an upgrade patch, which is useful for many existing polydopamine-functionalized materials.

The Case for Bisphosphonate Use in Astronauts Flying Long-Duration Missions.

Changes in the structure of bone can occur in space as an adaptive response to microgravity and on Earth due to the adaptive effects to exercise, to the aging of bone cells, or to prolonged disuse. Knowledge of cell-mediated bone remodeling on Earth informs our understanding of bone tissue changes in space and whether these skeletal changes might increase the risk for fractures or premature osteoporosis in astronauts. Comparisons of skeletal health between astronauts and aging humans, however, may be both informative and misleading. Astronauts are screened for a high level of physical fitness and health, are launched with high bone mineral densities, and perform exercise daily in space to combat skeletal atrophy as an adaptive response to reduced weight-bearing function, while the elderly display cellular and tissue pathology as a response to senescence and disuse. Current clinical testing for age-related bone change, applied to astronauts, may not be sufficient for fully understanding risks associated with rare and uniquely induced bone changes. This review aims to (i) highlight cellular analogies between spaceflight-induced and age-related bone loss, which could aid in predicting fractures, (ii) discuss why overreliance on terrestrial clinical approaches may miss potentially irreversible disruptions in trabecular bone microarchitecture induced by spaceflight, and (iii) detail how the cellular effects of the bisphosphonate class of drugs offer a prophylactic countermeasure for suppressing the elevated bone resorption characteristically observed during long-duration spaceflights. Thus the use of the bisphosphonate will help protect the bone from structural changes while in microgravity either along with exercise or alone when exercise is not performed, e.g. after an injury or illness.

Developing long bones respond to surrounding tissues by trans-pairing of periosteal osteoclasts and endocortical osteoblasts.

Developing long bones alter their shape while maintaining uniform cortical thickness via coordinated activity of bone-forming osteoblasts and bone-resorbing osteoclasts at periosteal and endosteal surfaces, a process we designate trans-pairing. Two types of trans-pairing shift cortical bone in opposite orientations: peri-forming trans-pairing (peri-t-p) increases bone marrow space and endo-forming trans-pairing (endo-t-p) decreases it, via paired activity of bone resorption and formation across the cortex. Here, we focused on endo-t-p in growing bones. Analysis of endo-t-p activity in the cortex of mouse fibulae revealed osteoclasts under the periosteum compressed by muscles, and expression of RANKL in periosteal cells of the cambium layer. Furthermore, mature osteoblasts were localized on the endosteum, while preosteoblasts were at the periosteum and within cortical canals. X-ray tomographic microscopy revealed the presence of cortical canals more closely associated with endo- than with peri-t-p. Sciatic nerve transection followed by muscle atrophy and unloading induced circumferential endo-t-p with concomitant spread of cortical canals. Such canals likely supply the endosteum with preosteoblasts from the periosteum under endo-t-p, allowing bone shape to change in response to mechanical stress or nerve injury.

Pharmacological impacts of tanshinone on osteogenesis and osteoclastogenesis: a review.

Tanshinone, a lipophilic component of Salvia miltiorrhiza, is used to treat diseases like atherosclerosis, hypertension, Alzheimer's disease, and diabetes mellitus through its pharmacological activities like anti-inflammatory, anti-oxidant, and anti-tumor. Excessive inflammation is the primary cause of bone diseases such as osteoporosis and rheumatoid arthritis, affecting more than millions of people across the globe. Recently, tanshinone has shown potential benefits against bone diseases by modulating signaling pathways accountable for the proliferation and differentiation of bone cells. In vitro and in vivo studies reported that tanshinone promotes osteoblast formation and mineralization and suppresses excessive bone resorption during disease conditions. In this review, we have summarized the beneficial effects of tanshinone and other extracts of Salvia miltiorrhiza for bone health and their potential molecular targets in signaling.

S100P binds to RAGE and activates ERK/NF-κB signaling to promote osteoclast differentiation and activity.

S100 calcium-binding protein P (S100P) is a secretory protein that is expressed in various healthy tissues and tumors. Megakaryocyte-secreted S100P promotes osteoclast differentiation and function; however, its receptor and cellular signaling in osteoclasts remain unclear. Receptor for advanced glycation end products (RAGE), which is the receptor for S100P on cancer cells, was expressed in osteoclast precursors, and S100P-RAGE binding was confirmed through co-immunoprecipitation. Additionally, the phosphorylation of ERK and NF-κB was increased in S100P-stimulated osteoclast precursors but was inhibited by addition of the RAGE antagonistic peptide (RAP). S100P-induced osteoclast differentiation and excessive bone resorption activity were also reduced by the addition of RAP. This study demonstrates that S100P, upon binding with RAGE, activates the ERK and NF-κB signaling pathways in osteoclasts, leading to increased cell differentiation and bone resorption activity.

Urinary biomarkers in metastatic bone pain: Results from a multicentre randomized trial of ibandronate compared to single dose radiotherapy for localized metastatic bone pain in prostate cancer (RIB).

Background: The Radiotherapy IBandronate (RIB) trial compared single dose radiotherapy and a single infusion of ibandronate in 470 bisphosphonate naïve patients with metastatic bone pain from prostate cancer randomised into a non-inferiority two arm study. Results for the primary endpoint of pain score response at 4 weeks showed that the ibandronate arm was non-inferior to single dose radiotherapy. Patients and method: In addition to pain assessments including analgesic use made at baseline, 4, 8, 12, 26 and 52 weeks, urine was collected at baseline, 4 and 12 weeks. It was subsequently analysed for urinary N-telopeptide (NTx) and cystatin C. Linear regression models were used to compare the continuous outcome measures for urinary markers within treatment arms and baseline measurements were included as covariates. Interaction terms were fitted to allow for cross-treatment group comparisons. Results: The primary endpoint of the RIB trial was worst pain response at 4 weeks and there was no treatment difference seen. Urine samples and paired pain scores at 4 weeks were available for 273 patients (radiotherapy 168; ibandronate 159)The baseline samples measured for the RIB trial had an average concentration of 193 nM BCE/mM creatinine (range of 7.3-1871) compared to the quoted normal range of 33 nM BCE/mM creatinine (3 to 63). In contrast the average value of Cystatin C was 66 ng/ml (ranges ND - 1120 ng/ml) compared to the quoted normal range of 62.9 ng/ml (ranges 12.6-188 ng/ml). A statistically significant reduction in NTx concentrations between baseline and 4 weeks was seen in the ibandronate arm but not in the radiotherapy arm. No correlation between pain response and urinary marker concentration was seen in either the ibandronate or radiotherapy cohort at any time point. Conclusion: NTx was significantly raised compared to the normal range consistent with a role as a biomarker for bone metastases from prostate cancer. A significant reduction in NTx 4 weeks after ibandronate is consistent with its action in osteoclast inhibition which was not seen after radiotherapy implying a different mode of action for radiation. There was no correlation between bone biomarker levels and pain response.

The emerging role of osteoclasts in the treatment of bone metastases: rationale and recent clinical evidence.

The occurrence of bone metastasis is a grave medical concern that substantially impacts the quality of life in patients with cancer. The precise mechanisms underlying bone metastasis remain unclear despite extensive research efforts, and efficacious therapeutic interventions are currently lacking. The ability of osteoclasts to degrade the bone matrix makes them a crucial factor in the development of bone metastasis. Osteoclasts are implicated in several aspects of bone metastasis, encompassing the formation of premetastatic microenvironment, suppression of the immune system, and reactivation of quiescent tumor cells. Contemporary clinical interventions targeting osteoclasts have proven effective in mitigating bone-related symptoms in patients with cancer. This review comprehensively analyzes the mechanistic involvement of osteoclasts in bone metastasis, delineates potential therapeutic targets associated with osteoclasts, and explores clinical evidence regarding interventions targeting osteoclasts.

Periosteum response to static forces stimulates cortical drifting: A new orthopedic target.

BACKGROUND: The mechanism of cortical bone adaptation to static forces is not well understood. This is an important process because static forces are applied to the cortical bone in response to the growth of soft tissues and during Orthodontic and Orthopedic corrections. The aim of this study was to investigate the cortical bone response to expanding forces applied to the maxilla. METHODS: Overall, 375 adult Sprague-Dawley rats were divided into three groups: 1) static force group, 2) static force plus stimulation group, and 3) sham group. In addition to static force across the maxilla, some animals were exposed to anti-inflammatory medication. Samples were collected at different time points and evaluated by micro-computed tomography, fluorescence microscopy, immunohistochemistry, and gene and protein analyses. RESULTS: The application of expansion forces to the maxilla increased inflammation in the periosteum and activated osteoclasts on the surface of the cortical plate. This activation was independent of the magnitude of tooth movement but followed the pattern of skeletal displacement. Bone formation on the surface of the cortical plate occurred at a later stage and resulted in the relocation of the cortical boundary of the maxilla and cortical drifting. CONCLUSIONS: This study demonstrates that cortical bone adaptation to static forces originates from the periosteum, and it is an inflammatory-based phenomenon that can be manipulated by the clinician. Our findings support a new theory for cortical adaptation to static forces and an innovative clinical approach to promote cortical drifting through periosteal stimulation. Being able to control cortical drift can have a significant impact on clinical orthodontic and dentofacial orthopedics by allowing corrections of severe deformities without the need for maxillofacial surgery.

A natural agent, 5-deoxycajanin, mitigates estrogen-deficiency bone loss via modulating osteoclast-osteoblast homeostasis.

Hyperactive osteoclasts and hypoactive osteoblasts usually result in osteolytic conditions such as estrogen-deficiency bone loss. Few natural compounds that both attenuating bone resorption and enhancing bone formation could exert effects on this imbalance. 5-Deoxycajanin (5-D), an isoflavonoid extracted from Cajan leaf with estrogen-like properties, were found to have beneficial pharmacological effects on rebalancing the activities of osteoclasts and osteoblasts. This study revealed that 5-D at the same concentration could inhibit osteoclastogenesis of BMMs and promoted osteoblast differentiation of BMSCs. 5-D not only attenuated the fluorescent formation of RANKL-induced F-actin belts and NFATc1, but also activated ALP and RUNX2 expressions. As to downstream factor expressions, 5-D could block osteoclast-specific genes and proteins including NFATc1 and CTSK, while increased osteogenic genes and proteins including OPG and OCN, as confirmed by Real-time PCR and Western Blotting. Additionally, the network pharmacology and molecular docking identified the involvement of 5-D in the MIF and MAPK signaling pathways and the stable binding between 5-D and MAPK2K1. Further Western blot studies showed that 5-D decreased the phosphorylation of p38 and ERK in osteoclasts, but promoted these phosphorylations in osteoblasts. In a female C57BL/6J mouse model of estrogen deficiency-induced bone loss, 5-D demonstrated efficacy in enhancing BMD through attenuating osteoclast activities and promoting osteogenesis. These results underscore the potential application of 5-D on treating osteolysis resulting from hyperactive osteoclasts and hypoactive osteoblasts, shedding light on modulating osteoclast-osteoblast homeostasis.

Annexin A family: A new perspective on the regulation of bone metabolism.

Osteoblast-mediated bone formation and osteoclast-mediated bone resorption are critical processes in bone metabolism. Annexin A, a calcium-phospholipid binding protein, regulates the proliferation and differentiation of bone cells, including bone marrow mesenchymal stem cells, osteoblasts, and osteoclasts, and has gradually become a marker gene for the diagnosis of osteoporosis. As calcium channel proteins, the annexin A family members are closely associated with mechanical stress, which can target annexins A1, A5, and A6 to promote bone cell differentiation. Despite the significant clinical potential of annexin A family members in bone metabolism, few studies have reported on these mechanisms. Therefore, based on a review of relevant literature, this article elaborates on the specific functions and possible mechanisms of annexin A family members in bone metabolism to provide new ideas for their application in the prevention and treatment of bone diseases, such as osteoporosis.

PTHrP participates in the bone destruction of middle ear cholesteatoma via promoting macrophage differentiation into osteoclasts induced by RANKL. / PTHrP促进RANKLè¯±å¯¼å·¨å™¬ç»†èƒžåˆ†åŒ–ä¸ºç ´éª¨ç»†èƒžå‚ä¸Žä¸­è€³èƒ†è„‚ç˜¤éª¨ç ´å.

OBJECTIVES: Progressive bone resorption and destruction is one of the most critical clinical features of middle ear cholesteatoma, potentially leading to various intracranial and extracranial complications. However, the mechanisms underlying bone destruction in middle ear cholesteatoma remain unclear. This study aims to explore the role of parathyroid hormone-related protein (PTHrP) in bone destruction associated with middle ear cholesteatoma. METHODS: A total of 25 cholesteatoma specimens and 13 normal external auditory canal skin specimens were collected from patients with acquired middle ear cholesteatoma. Immunohistochemical staining was used to detect the expressions of PTHrP, receptor activator for nuclear factor-kappa B ligand (RANKL), and osteoprotegerin (OPG) in cholesteatoma and normal tissues. Tartrate-resistant acid phosphatase (TRAP) staining was used to detect the presence of TRAP positive multi-nucleated macrophages in cholesteatoma and normal tissues. Mono-nuclear macrophage RAW264.7 cells were subjected to interventions, divided into a RANKL intervention group and a PTHrP+ RANKL co-intervention group. TRAP staining was used to detect osteoclast formation in the 2 groups. The mRNA expression levels of osteoclast-related genes, including TRAP, cathepsin K (CTSK), and nuclear factor of activated T cell cytoplasmic 1 (NFATc1), were measured using real-time polymerase chain reaction (real-time PCR) after the interventions. Bone resorption function of osteoclasts was assessed using a bone resorption pit analysis. RESULTS: Immunohistochemical staining showed significantly increased expression of PTHrP and RANKL and decreased expression of OPG in cholesteatoma tissues (all P<0.05). PTHrP expression was significantly positively correlated with RANKL, the RANKL/OPG ratio, and negatively correlated with OPG expression (r=0.385, r=0.417, r=-0.316, all P<0.05). Additionally, the expression levels of PTHrP and RANKL were significantly positively correlated with the degree of bone destruction in cholesteatoma (r=0.413, r=0.505, both P<0.05). TRAP staining revealed a large number of TRAP-positive cells, including multi-nucleated osteoclasts with three or more nuclei, in the stroma surrounding the cholesteatoma epithelium. After 5 days of RANKL or PTHrP+RANKL co-intervention, the number of osteoclasts was significantly greater in the PTHrP+RANKL co-intervention group than that in the RANKL group (P<0.05), with increased mRNA expression levels of TRAP, CTSK, and NFATc1 (all P<0.05). Scanning electron microscopy of bone resorption pits showed that the number (P<0.05) and size of bone resorption pits on bone slices were significantly greater in the PTHrP+RANKL co-intervention group compared with the RANKL group. CONCLUSIONS: PTHrP may promote the differentiation of macrophages in the surrounding stroma of cholesteatoma into osteoclasts through RANKL induction, contributing to bone destruction in middle ear cholesteatoma.

Age-related increase of CD38 directs osteoclastogenic potential of monocytic myeloid-derived suppressor cells through mitochondrial dysfunction in male mice.

An aged immune system undergoes substantial changes where myelopoiesis dominates within the bone marrow. Monocytic-MDSCs (M-MDSCs) have been found to play an important role in osteoclastogenesis and bone resorption. In this study, we sought to provide a more comprehensive understanding of the osteoclastogenic potential of bone marrow M-MDSCs during normal aging through transcriptomic and metabolic changes. Using young mature and aged mice, detailed immunophenotypic analyses of myeloid cells revealed that the M-MDSCs were not increased in bone marrow, however M-MDSCS were significantly expanded in peripheral tissues. Although aged mice exhibited a similar number of M-MDSCs in bone marrow, these M-MDSCs had significantly higher osteoclastogenic potential and greater demineralization activity. Intriguingly, osteoclast progenitors from aged bone marrow M-MDSCs exhibited greater mitochondrial respiration rate and glucose metabolism. Further, transcriptomic analyses revealed the upregulation of mitochondrial oxidative phosphorylation and glucose metabolism genes. Interestingly, there was 8-fold increase in Cd38 mRNA gene expression, consistent with the Mouse Aging Cell Atlas transcriptomic database, and confirmed by qRT-PCR. CD38 regulates NAD+ availability, and 78c, a small molecule inhibitor of CD38, reduced the mitochondrial oxygen consumption rate and glucose metabolism and inhibited the osteoclastogenic potential of aged mice bone marrow-derived M-MDSCs. These results indicate that the age-related increase in Cd38 expression in M-MDSCs bias the transcriptome of M-MDSCs towards osteoclastogenesis. This enhanced understanding of the mechanistic underpinnings of M-MDSCs and their osteoclastogenesis during aging could lead to new therapeutic approaches for age-related bone loss and promote healthy aging.

ENPP1 enzyme replacement therapy improves ectopic calcification but does not rescue skeletal phenotype in a mouse model for craniometaphyseal dysplasia.

Craniometaphyseal dysplasia (CMD) is a rare genetic bone disorder, characterized by progressive thickening of craniofacial bones and flared metaphyses of long bones. Craniofacial hyperostosis leads to the obstruction of neural foramina and neurological symptoms such as facial palsy, blindness, deafness, or severe headache. Mutations in ANKH (mouse ortholog ANK), a transporter of small molecules such as citrate and ATP, are responsible for autosomal dominant CMD. Knock-in (KI) mice carrying an ANKF377del mutation (AnkKI/KI ) replicate many features of human CMD. Pyrophosphate (PPi) levels in plasma are significantly reduced in AnkKI/KI mice. PPi is a potent inhibitor of mineralization. To examine the extent to which restoration of circulating PPi levels may prevent the development of a CMD-like phenotype, we treated AnkKI/KI mice with the recombinant human ENPP1-Fc protein IMA2a. ENPP1 hydrolyzes ATP into AMP and PPi. Male and female Ank+/+ and AnkKI/KI mice (n ≥ 6/group) were subcutaneously injected with IMA2a or vehicle weekly for 12 wk, starting at the age of 1 wk. Plasma ENPP1 activity significantly increased in AnkKI/KI mice injected with IMA2a (Vehicle/IMA2a: 28.15 ± 1.65/482.7 ± 331.2 mOD/min; p <.01), which resulted in the successful restoration of plasma PPi levels (Ank+/+ /AnkKI/KI vehicle treatment/AnkKI/KI IMA2a: 0.94 ± 0.5/0.43 ± 0.2/1.29 ± 0.8 µM; p <.01). We examined the skeletal phenotype by X-Ray imaging and µCT. IMA2a treatment of AnkKI/KI mice did not significantly correct CMD features such as the abnormal shape of femurs, increased bone mass of mandibles, hyperostotic craniofacial bones, or the narrowed foramen magnum. However, µCT imaging showed ectopic calcification near basioccipital bones at the level of the foramen magnum and on joints of AnkKI/KI mice. Interestingly, IMA2a treatment significantly reduced the volume of calcified nodules at both sites. Our data demonstrate that IMA2a is sufficient to restore plasma PPi levels and reduce ectopic calcification but fails to rescue skeletal abnormalities in AnkKI/KI mice under our treatment conditions.