Monocyte Chemoattractant Protein-1 (MCP-1/CCL2) Drives Activation of Bone Remodelling and Skeletal Metastasis.

PURPOSE OF REVIEW: The purpose of this review is to explore the role of monocyte chemoattractant protein-1 (MCP-1 or CCL2) in the processes that underpin bone remodelling, particularly the action of osteoblasts and osteoclasts, and its role in the development and metastasis of cancers that target the bone. RECENT FINDINGS: MCP-1 is a key mediator of osteoclastogenesis, being the highest induced gene during intermittent treatment with parathyroid hormone (iPTH), but also regulates catabolic effects of continuous PTH on bone including monocyte and macrophage recruitment, osteoclast formation and bone resorption. In concert with PTH-related protein (PTHrP), MCP-1 mediates the interaction between tumour-derived factors and host-derived chemokines to promote skeletal metastasis. In breast and prostate cancers, an osteolytic cascade is driven by tumour cell-derived PTHrP that upregulates MCP-1 in osteoblastic cells. This relationship between PTHrP and osteoblastic expression of MCP-1 may drive the colonisation of disseminated breast cancer cells in the bone. There is mounting evidence to suggest a pivotal role of MCP-1 in many diseases and an important role in the establishment of comorbidities. Coupled with its role in bone remodelling and the regulation of bone turnover, there is the potential for pathological relationships between bone disorders and bone-related cancers driven by MCP-1. MCP-1's role in bone remodelling and bone-related cancers highlights its potential as a novel anti-resorptive and anti-metastatic target.

CCL2 and CCR2 are Essential for the Formation of Osteoclasts and Foreign Body Giant Cells.

Osteoclasts are multinucleated cells responsible for bone resorption. They are derived from the fusion of cells in the monocyte/macrophage lineage. Monocytes and macrophages can also fuse to form foreign body giant cells (FBGC). Foreign body giant cells are observed at the interface between a host and a foreign body such as implants during a foreign body reaction. Macrophages are attracted to the site of bone resorption and foreign body reactions by different cytokines. Chemokine (C-C) ligand-2 (CCL2) is an important chemotactic factor and binds to a receptor CCR2. In this study we investigated the importance of CCL2 and the receptor CCR2 in the formation of osteoclasts and FBGC. CCL2 mRNA was more highly expressed in giant cell culture than macrophages, being 9-fold and 16-fold more abundant in osteoclasts and FBGC respectively. Significantly fewer osteoclasts and FBGC were cultured from the bone marrow of CCL2 and CCR2 knockout mice, when compared to wild type. Not only were the number of giant cells reduced but there was a significant reduction in the number of nuclei and the size of these cells in the cultures of CCL2 and CCR2 knockout mice. Formation of osteoclasts and FBGC were recovered in cultures by addition of exogenous CCL2 to the media containing marrow cells from CCL2-/- mice. We conclude that CCL2 and its receptor CCR2 are important for the formation of osteoclasts and FBGC and absence of these genes causes inhibition of osteoclast and FBGC formation.

Pentosan Polysulfate: a Novel Glycosaminoglycan-Like Molecule for Effective Treatment of Alphavirus-Induced Cartilage Destruction and Inflammatory Disease.

UNLABELLED: Arthritogenic alphaviruses such as Ross River virus (RRV) and chikungunya virus (CHIKV) cause large-scale epidemics of severe musculoskeletal disease and have been progressively expanding their global distribution. Since its introduction in July 2014, CHIKV now circulates in the United States. The hallmark of alphavirus disease is crippling pain and inflammation of the joints, a similar immunopathology to rheumatoid arthritis. The use of glycans as novel therapeutics is an area of research that has increased in recent years. Here, we describe the promising therapeutic potential of the glycosaminoglycan (GAG)-like molecule pentosan polysulfate (PPS) to alleviate virus-induced arthritis. Mouse models of RRV and CHIKV disease were used to characterize the extent of cartilage damage in infection and investigate the potential of PPS to treat disease. This was assessed using histological analysis, real-time PCR, and fluorescence-activated cell sorting (FACS). Alphaviral infection resulted in cartilage destruction, the severity of which was alleviated by PPS therapy during RRV and CHIKV clinical disease. The reduction in cartilage damage corresponded with a significant reduction in immune infiltrates. Using multiplex bead arrays, PPS treatment was found to have significantly increased the anti-inflammatory cytokine interleukin-10 and reduced proinflammatory cytokines, typically correlated with disease severity. Furthermore, we reveal that the severe RRV-induced joint pathology, including thinning of articular cartilage and loss of proteoglycans in the cartilage matrix, was diminished with treatment. PPS is a promising new therapy for alphavirus-induced arthritis, acting to preserve the cartilage matrix, which is damaged during alphavirus infection. Overall, the data demonstrate the potential of glycotherapeutics as a new class of treatment for infectious arthritis. IMPORTANCE: The hallmark of alphavirus disease is crippling pain and joint arthritis, which often has an extended duration. In the past year, CHIKV has expanded into the Americas, with approximately 1 million cases reported to date, whereas RRV continues to circulate in the South Pacific. Currently, there is no licensed specific treatment for alphavirus disease, and the increasing spread of infection highlights an urgent need for therapeutic intervention strategies. Pentosan polysulfate (PPS) is a glycan derivative that is orally bioavailable, has few toxic side effects, and is currently licensed under the name Elmiron for the treatment of cystitis in the United States. Our findings show that RRV infection damages the articular cartilage, including a loss of proteoglycans within the joint. Furthermore, treatment with PPS reduced the severity of both RRV- and CHIKV-induced musculoskeletal disease, including a reduction in inflammation and joint swelling, suggesting that PPS is a promising candidate for drug repurposing for the treatment of alphavirus-induced arthritis.

Bindarit, an inhibitor of monocyte chemotactic protein synthesis, protects against bone loss induced by chikungunya virus infection.

UNLABELLED: The recent global resurgence of arthritogenic alphaviruses, in particular chikungunya virus (CHIKV), highlights an urgent need for the development of therapeutic intervention strategies. While there has been significant progress in defining the pathophysiology of alphaviral disease, relatively little is known about the mechanisms involved in CHIKV-induced arthritis or potential therapeutic options to treat the severe arthritic symptoms associated with infection. Here, we used microcomputed tomographic (µCT) and histomorphometric analyses to provide previously undescribed evidence of reduced bone volume in the proximal tibial epiphysis of CHIKV-infected mice compared to the results for mock controls. This was associated with a significant increase in the receptor activator of nuclear factor-κB ligand/osteoprotegerin (RANKL/OPG) ratio in infected murine joints and in the serum of CHIKV patients. The expression levels of the monocyte chemoattractant proteins (MCPs), including MCP-1/CCL2, MCP-2/CCL8, and MCP-3/CCL7, were also highly elevated in joints of CHIKV-infected mice, accompanied by increased cellularity within the bone marrow in tibial epiphysis and ankle joints. Both this effect and CHIKV-induced bone loss were significantly reduced by treatment with the MCP inhibitor bindarit. Collectively, these findings demonstrate a unique role for MCPs in promoting CHIKV-induced osteoclastogenesis and bone loss during disease and suggest that inhibition of MCPs with bindarit may be an effective therapy for patients affected with alphavirus-induced bone loss. IMPORTANCE: Arthritogenic alphaviruses, including chikungunya virus (CHIKV) and Ross River virus (RRV), cause worldwide outbreaks of polyarthritis, which can persist in patients for months following infection. Previous studies have shown that host proinflammatory soluble factors are associated with CHIKV disease severity. Furthermore, it is established that chemokine (C-C motif) ligand 2 (CCL2/MCP-1) is important in cellular recruitment and inducing bone-resorbing osteoclast (OC) formation. Here, we show that CHIKV replicates in bone and triggers bone loss by increasing the RANKL/OPG ratio. CHIKV infection results in MCP-induced cellular infiltration in the inflamed joints, and bone loss can be ameliorated by treatment with an MCP-inhibiting drug, bindarit. Taken together, our data reveal a previously undescribed role for MCPs in CHIKV-induced bone loss: one of recruiting monocytes/OC precursors to joint sites and thereby favoring a pro-osteoclastic microenvironment. This suggests that bindarit may be an effective treatment for alphavirus-induced bone loss and arthritis in humans.

Integrating gross pathology into teaching of undergraduate medical science students using human cadavers.

Human cadavers offer a great opportunity for histopathology students for the learning and teaching of tissue pathology. In this study, we aimed to implement an integrated learning approach by using cadavers to enhance students' knowledge and to develop their skills in gross tissue identification, handling and dissection techniques. A total of 35 students enrolled in the undergraduate medical science program participated in this study. A 3-hour laboratory session was conducted that included an active exploration of cadaveric specimens to identify normal and pathological tissues as well as tissue dissection. The majority of the students strongly agreed that the integration of normal and morbid anatomy improved their understanding of tissue pathology. All the students either agreed or strongly agreed that this laboratory session was useful to improve their tissue dissection and instrument handling skills. Furthermore, students from both cohorts rated the session as very relevant to their learning and recommended that this approach be added to the existing histopathology curriculum. To conclude, an integrated cadaver-based practical session can be used effectively to enhance the learning experience of histopathology science students, as well as improving their manual skills of tissue treatment, instrument handling and dissection.

EphrinB2 signaling in osteoblasts promotes bone mineralization by preventing apoptosis.

Cells that form bone (osteoblasts) express both ephrinB2 and EphB4, and previous work has shown that pharmacological inhibition of the ephrinB2/EphB4 interaction impairs osteoblast differentiation in vitro and in vivo. The purpose of this study was to determine the role of ephrinB2 signaling in the osteoblast lineage in the process of bone formation. Cultured osteoblasts from mice with osteoblast-specific ablation of ephrinB2 showed delayed expression of osteoblast differentiation markers, a finding that was reproduced by ephrinB2, but not EphB4, RNA interference. Microcomputed tomography, histomorphometry, and mechanical testing of the mice lacking ephrinB2 in osteoblasts revealed a 2-fold delay in bone mineralization, a significant reduction in bone stiffness, and a 50% reduction in osteoblast differentiation induced by anabolic parathyroid hormone (PTH) treatment, compared to littermate sex- and age-matched controls. These defects were associated with significantly lower mRNA levels of late osteoblast differentiation markers and greater levels of osteoblast and osteocyte apoptosis, indicated by TUNEL staining and transmission electron microscopy of bone samples, and a 2-fold increase in annexin V staining and 7-fold increase in caspase 8 activation in cultured ephrinB2 deficient osteoblasts. We conclude that osteoblast differentiation and bone strength are maintained by antiapoptotic actions of ephrinB2 signaling within the osteoblast lineage.

Differential expression of chemokines, chemokine receptors and proteinases by foreign body giant cells (FBGCs) and osteoclasts.

Osteoclasts and foreign body giant cells (FBGCs) are both derived from the fusion of macropahges. These cells are seen in close proximity during foreign body reactions, therefore it was assumed that they might interact with each other. The aim was to identify important genes that are expressed by osteoclasts and FBGCs which can be used to understand peri-implantitis and predict the relationship of these cells during foreign body reactions. Bone marrow macrophages (BMM) were treated with receptor activator of nuclear factor kappa B ligand (RANKL) to produce osteoclasts. Quantitative PCR (qPCR) was used to identify the genes that were expressed by osteoclasts and FBGCs compared to macrophage controls. TRAP staining was used to visualise the cells while gelatine zymography and western blots were used for protein expression. Tartrate-resistant acid phosphatase (TRAP), matrix metallo proteinase 9 (MMP9), nuclear factor of activated T cells 1 (NFATc1), cathepsin K (CTSK) and RANK were significantly lower in FBGCs compared to osteoclasts. Inflammation specific chemokines such as monocyte chemotactic protein (MCP1 also called CCL2), macrophage inflammatory protein 1 alpha (MIP1α), MIP1ß and MIP1γ, and their receptors CCR1, CCR3 and CCR5, were highly expressed by FBGCs. FBGCs were negative for osteoclast specific markers (RANK, NFATc1, CTSK). FBGCs expressed chemokines such as CCL2, 3, 5 and 9 while osteoclasts expressed the receptors for these chemokines i.e. CCR1, 2 and 3. Our findings show that osteoclast specific genes are not expressed by FBGCs and that FBGCs interact with osteoclasts during foreign body reaction through chemokines.

Foreign body giant cells and osteoclasts are TRAP positive, have podosome-belts and both require OC-STAMP for cell fusion.

Macrophages have the ability to fuse and form multinucleated giant cells such as Osteoclast (OCs) and FBGCs. Osteoclast stimulatory transmembrane protein (OC-STAMP) is an important cell surface protein involved in the formation of OCs. This study sought to determine if OC-STAMP also regulates formation of FBGCs using expression analysis and subsequent inhibition studies. qPCR and Western blot analysis showed that OC-STAMP expression is significantly higher in FBGCs compared to control monocytes (P < 0.05). Four days following cell culture, OCs were positive for TRAP and F-actin ring formation, but FBGCs were not. In contrast, FBGCs were positive for TRAP and showed podosome belts comprised of F-actin on Day 8. FBGCs were subsequently plated onto dentine, but despite presenting some morphologic features of OCs (OC-STAMP expression, TRAP reactivity, and podosome belts) they failed to resorb bone. To evaluate a role for OC-STAMP in FBGCs, we inhibited this cell surface protein with anti-OC-STAMP antibody and observed that cell fusion and podosome belt formation was inhibited in both OCs and FBGCs. Our data support the hypothesis that OC-STAMP is a regulatory molecule for FBGCs; and that they are functionally distinct from OCs, despite similarities in gene expression profile, podosome belt formation, and TRAP expression.

Association of change in fat and lean mass with incident cardiovascular events for women in midlife and beyond: A prospective study using dual-energy x-ray absorptiometry (DXA).

OBJECTIVE: To determine whether changes in fat and lean mass over time, quantified using dual-energy x-ray absorptiometry (DXA), are related to incident cardiovascular events. Previous studies using surrogate anthropometric methods have had inconsistent findings. STUDY DESIGN: Prospective, longitudinal observational study of women aged 40 to 80 randomly selected from the electoral roll and stratified into decades: 40-49, 50-59, 60-69 and 70-79 years. MAIN OUTCOME MEASURES: Changes in anthropometric measurements (body mass index and waist-to-hip ratio) and DXA-quantified fat mass and lean mass between the first and fifth years of the study. Incident cardiovascular events recorded from the sixth to the 12th year. RESULTS: In total 449 participants (87.9 %) were analyzed. A 10 % or greater decrease in total fat mass index was associated with a 67 % lower likelihood of any cardiovascular event (OR = 0.33, 95%CI 0.15-0.71); no association was observed for an increase. A 10 % or greater decrease in abdominal fat mass index was associated with a 62 % lower likelihood of incident stroke (OR = 0.38, 95%CI 0.16-0.91); no association was observed for an increase. A 10 % or greater decrease in appendicular lean mass index resulted in increased odds ratio of 2.91 for incident peripheral artery events (OR = 2.91, 95%CI 1.18-7.20). CONCLUSIONS: Reducing fat mass for women in midlife and beyond may decrease the risk of cardiovascular events. An increase in fat mass may not contribute to additional cardiovascular events. A reduction in limb muscle mass may provide an independent marker for cardiometabolic risk and peripheral artery disease. No independent association was found using anthropometric measurements and incident cardiovascular events.

MCP-1 expression in breast cancer and its association with distant relapse.

BACKGROUND: Distant relapse of breast cancer complicates management of the disease and accounts for 90% of breast cancer-related deaths. Monocyte chemoattractant protein-1 (MCP-1) has critical roles in breast cancer progression and is widely accepted as a pro-metastatic chemokine. METHODS: This study explored MCP-1 expression in the primary tumour of 251 breast cancer patients. A simplified 'histoscore' was used to determine if each tumour had high or low expression of MCP-1. Patient breast cancers were retrospectively staged based on available patient data. p < 0.05 was used to determine significance and changes in hazard ratios between models were considered. RESULTS: Low MCP-1 expression in the primary tumour was associated with breast cancer-related death with distant relapse in ER- breast cancers (p < 0.01); however, this was likely a result of most low MCP-1-expressing ER- breast cancers being Stage III or Stage IV, with high MCP-1 expression in the primary tumour significantly correlated with Stage I breast cancers (p < 0.05). Expression of MCP-1 in the primary ER- tumours varied across Stage I, II, III and IV and we highlighted a switch in MCP-1 expression from high in Stage I ER- cancers to low in Stage IV ER- cancers. CONCLUSION: This study has emphasised a critical need for further investigation into MCP-1's role in breast cancer progression and improved characterisation of MCP-1 in breast cancers, particularly in light of the development of anti-MCP-1, anti-metastatic therapies.

Effects of PTH glandular and external dosing patterns on bone cell activity using a two-state receptor model-Implications for bone disease progression and treatment.

Temporal aspects of ligand specificity have been shown to play a significant role in the case of pulsatile hormone secretion, as exemplified by parathyroid hormone (PTH) binding to its receptor (PTH1R), a G-protein-coupled receptor expressed on surfaces of osteoblasts and osteocytes. The latter binding reaction regulates intracellular signalling and subsequently modulates skeletal homeostasis via bone remodelling. PTH glandular secretion patterns dictate bone cellular activity. In healthy humans, 70% of PTH is secreted in a tonic fashion, whereas 30% is secreted in low-amplitude and high-frequency bursts occurring every 10-20 min, superimposed on the tonic secretion. Changes in the PTH secretion patterns have been associated with various bone diseases. In this paper, we analyse PTH glandular secretion patterns for healthy and pathological states and their link to bone cellular responsiveness (αR). We utilise a two-state receptor ligand binding model of PTH to PTH1R together with a cellular activity function which is able to distinguish various aspects of the stimulation signal including peak dose, time of ligand exposure, and exposure period. Formulating and solving several constrained optimisation problems, we investigate the potential of pharmacological manipulation of the diseased glandular secretion and via clinical approved external PTH injections to restore healthy bone cellular responsiveness. Based on the mean experimentally reported data, our simulation results indicate cellular responsiveness in healthy subjects is sensitive to the tonic baseline stimulus and it is 28% of the computed maximum responsiveness. Simulation results for pathological cases of glucocorticoid-induced osteoporosis, hyperparathyroidism, initial and steady state hypocalcemia clamp tests indicate αR values significantly larger than the healthy baseline (1.7, 2.2, 4.9 and 1.9-times, respectively). Manipulation of the pulsatile glandular secretion pattern, while keeping the mean PTH concentration constant, allowed restoration of healthy baseline values from these catabolic bone diseases. Conversely, PTH glandular diseases that led to maximum bone cellular responsiveness below the healthy baseline value can't be restored to baseline via glandular manipulation. However, external PTH injections allowed restoration of these latter cases.

Monocyte Chemotactic Protein-1 (MCP1) Accumulation in Human Osteoclast Precursor Cultures.

In vitro osteoclast methods require constant treatment with macrophage colony stimulating factor (M-CSF) to support precursor survival and addition of the differentiation agent receptor activator of NF-κB ligand (RANKL). Constant exposure to granulocyte macrophage colony stimulating factor (GM-CSF) suppresses human osteoclast formation in vitro. Addition of the chemokine monocyte chemotactic protein-1 (MCP1) to such cultures dramatically increases osteoclast formation and overcomes GM-CSF mediated suppression. We investigated the effect of M-CSF, GM-CSF and the combination of M-CSF and GM-CSF treatment on the expression of chemokines in human CD14+ cells in culture. Of assayed chemokines, MCP1 was the most abundant in terms of mRNA transcript and protein in M-CSF treated cultures and was suppressed by GM-CSF. MCP1 protein accumulated up to 50 ng/mL in culture medium, greatly exceeding other assayed chemokines. C-C chemokine receptor-2 (CCR2) is the receptor for MCP1: the formation of osteoclast-like cells was inhibited by constant exposure to the CCR2 antagonist RS102895, in part by decreasing expression of RANK, the receptor for RANKL.

Sponge swabs increase sensitivity of sterility testing of processed bone and tendon allografts.

Sterility testing is the final, and critical, step in quality control of tissue banking. It informs the decision whether to release the tissue allografts for clinical use, or not. The most common method for sterility testing of structural bone and tendon allografts is to swab using cotton tip streaks. This method provides low recovery efficiency; and therefore may pass allografts with low bioburden, providing false negatives. Our pilot data revealed organism recovery efficiencies of 60, 30 and 100% from cotton swab, membrane filtration and sponge swaps, respectively. Our aim was to develop a high sensitivity sterility test for structural bone and tendon allografts using a sponge sampling method. Eighty-one bone and tendon allograft samples were inoculated with organism suspensions (10(2) or less organisms per 0.1 mL) of Clostridium sporogenes, Staphylococcus aureus, Pseudomonas aeruginosa, Candida albicans, Bacillus subtilis, Aspergillus niger, Staphylococcus epidermidis and Micrococcus spp. Nasco sponges (4 × 8 cm) were used to aseptically sample the whole surface of allograft samples. The sponges were cut in half and cultured in either tryptone soya or fluid thioglycollate broths for 14 days. Positive culture samples were further examined for microbial morphology. The results showed that the sensitivity of the method, and negative predictive value, is 100% for all inoculated organisms incubated with thioglycollate. We conclude that this sponge sampling method should be applied as the standard for sterility testing of structural bone and tendon allografts.

Validation of 11 kGy as a radiation sterilization dose for frozen bone allografts.

A radiation sterilization dose (RSD) of 25 kGy is deleterious to bone allografts. This study aimed to establish a lower RSD for bone allografts using method 1 of International Standard Organisation 11137.2:2006. This provides a database to select an RSD corresponding to an allograft's bioburden, given that the bioburden's gamma resistance is equal to or less than the standard. This can be verified by irradiating 100 allografts at a dose selected to provide a sterility assurance level of 10(-2). The bioburden of our allografts was 0, which prescribed a verification dose of 1.3 kGy. After irradiating 100 allografts, sterility tests returned no positive cultures. We therefore validated an RSD of 11 kGy for allografts with that bioburden. According to the standard, this RSD provides a sterility assurance level of 10(-6) for bone allografts.

Comparison of obesity and metabolic syndrome prevalence using fat mass index, body mass index and percentage body fat.

BACKGROUND: Accurate obesity classification is important so that appropriate intervention can be instituted to modify metabolic risk factors. Commonly utilized body mass index (BMI) and percentage body fat (PBF) are influenced by lean mass whereas fat mass index (FMI) measures only body fat. This study compares the prevalence of obesity and metabolic risk factors with FMI, BMI and PBF using DXA (dual-energy x-ray absorptiometry). METHODS: 489 women randomly recruited from the electoral roll were stratified into 4 age groups; 40-49, 50-59, 60-69 and 70-79 years from 2000 to 2001. Clinical data and DXA body composition were obtained. Statistical analyses were performed using Medcalc v15 (Ostend, Belgium) with significance level at p = 0.05 (two-tailed). RESULTS: There was higher prevalence of obesity using PBF compared to BMI and FMI (p<0.001). This difference was greater from age 50-59 (p<0.05) which may be explained by age-related lean mass loss. PBF over-classified obesity in over 35% of normal and 95% of overweight categories compared to FMI and BMI. BMI has a sensitivity of 78.9% and specificity of 98.3% for obesity using FMI as the standard. BMI under-classified obesity in the overweight category by 14.9% compared to FMI. There was no difference in diabetes, dyslipidemia, hypertension and metabolic syndrome prevalence within the BMI-obesity and FMI-obesity categories (p>0.05). CONCLUSION: PBF classified more obesity than BMI and FMI because of its low pre-determined threshold. The greater difference with PBF compared to BMI and FMI from the 50-59 decade onwards can be attributed to age-related lean mass loss. BMI had the lowest sensitivity for obesity diagnosis. BMI under-classified obesity in the overweight category compared to FMI due to its inability to differentiate lean mass. However, there was no significant difference in the prevalence of metabolic risk factors between BMI and FMI-obesity categories indicating that fat location may influence metabolic dysregulation.

Dmp1Cre-directed knockdown of parathyroid hormone-related protein (PTHrP) in murine decidua is associated with a life-long increase in bone mass, width, and strength in male progeny.

Parathyroid hormone-related protein (PTHrP, gene name Pthlh) is a pleiotropic regulator of tissue homeostasis. In bone, Dmp1Cre-targeted PTHrP deletion in osteocytes causes osteopenia and impaired cortical strength. We report here that this outcome depends on parental genotype. In contrast to our previous report using mice bred from heterozygous (flox/wild type) Dmp1Cre.Pthlhf/w parents, adult (16-week-old and 26-week-old) flox/flox (f/f) Dmp1Cre.Pthlhf/f mice from homozygous parents (Dmp1Cre.Pthlhf/f(hom) ) have stronger bones, with 40% more trabecular bone mass and 30% greater femoral width than controls. This greater bone size was observed in Dmp1Cre.Pthlhf/f(hom) mice as early as 12 days of age, when greater bone width was also found in male and female Dmp1Cre.Pthlhf/f(hom) mice compared to controls, but not in gene-matched mice from heterozygous parents. This suggested a maternal influence on skeletal size prior to weaning. Although Dmp1Cre has previously been reported to cause gene recombination in mammary gland, milk PTHrP protein levels were normal. The wide-bone phenotype was also noted in utero: Dmp1Cre.Pthlhf/f(hom) embryonic femurs were more mineralized and wider than controls. Closer examination revealed that Dmp1Cre caused PTHrP recombination in placenta, and in the maternal-derived decidual layer that resides between the placenta and the uterus. Decidua from mothers of Dmp1Cre.Pthlhf/f(hom) mice also exhibited lower PTHrP levels by immunohistochemistry and were smaller than controls. We conclude that Dmp1Cre leads to gene recombination in decidua, and that decidual PTHrP might, through an influence on decidual cells, limit embryonic bone radial growth. This suggests a maternal-derived developmental origin of adult bone strength. © 2021 American Society for Bone and Mineral Research (ASBMR).

Heterogeneity in microstructural deterioration following spinal cord injury.

BACKGROUND: Modelling and remodelling adapt bone morphology to accommodate strains commonly encountered during loading. If strains exceed a threshold threatening fracture, modelling-based bone formation increases bone volume reducing these strains. If unloading reduces strains below a threshold that inhibits resorption, increased remodelling-based bone resorption reduces bone volume restoring strains, but at the price of compromised bone volume and microstructure. As weight-bearing regions are adapted to greater strains, we hypothesized that microstructural deterioration will be more severe than at regions commonly adapted to low strains following spinal cord injury. METHODS: We quantified distal tibial, fibula and radius volumetric bone mineral density (vBMD) using high-resolution peripheral quantitative computed tomography in 31 men, mean age 43.5 years (range 23.5-75.0), 12 with tetraplegia and 19 with paraplegia of 0.7 to 18.6 years duration, and 102 healthy age- and sex-matched controls. Differences in morphology relative to controls were expressed as standardized deviation (SD) scores (mean ± SD). Standardized between-region differences in vBMD were expressed as SDs (95% confidence intervals, CI). RESULTS: Relative to controls, men with tetraplegia had deficits in total vBMD of -1.72 ± 1.38 SD at the distal tibia (p < 0.001) and - 0.68 ± 0.69 SD at distal fibula (p = 0.041), but not at the distal radius, despite paralysis. Deficits in men with paraplegia were -2.14 ± 1.50 SD (p < 0.001) at the distal tibia and -0.83 ± 0.98 SD (p = 0.005) at the distal fibula while distal radial total vBMD was 0.23 ± 1.02 (p = 0.371), not significantly increased, despite upper limb mobility. Comparing regions, in men with tetraplegia, distal tibial total vBMD was 1.04 SD (95%CI 0.07, 2.01) lower than at the distal fibula (p = 0.037) and 1.51 SD (95%CI 0.45, 2.57) lower than at the distal radius (p = 0.007); the latter two sites did not differ from each other. Results were similar in men with paraplegia, but total vBMD at the distal fibula was 1.06 SD (95%CI 0.35, 1.77) lower than at the distal radius (p = 0.004). CONCLUSION: Microarchitectural deterioration following spinal cord injury is heterogeneous, perhaps partly because strain thresholds regulating the cellular activity of mechano-transduction are region specific.

Assessment of romosozumab efficacy in the treatment of postmenopausal osteoporosis: Results from a mechanistic PK-PD mechanostat model of bone remodeling.

This paper introduces a theoretical framework for the study of the efficacy of romosozumab, a humanized monoclonal antibody targeting sclerostin for the treatment of osteoporosis. We developed a comprehensive mechanistic pharmacokinetic-pharmacodynamic (PK-PD) model of the effect of drug treatment on bone remodeling in postmenopausal osteoporosis (PMO). We utilized a one-compartment PK model to represent subcutaneous injections of romosozumab and subsequent absorption into serum. The PD model is based on a recently-developed bone cell population model describing the bone remodeling process at the tissue scale. The latter accounts for mechanical feedback by incorporating nitric oxide (NO) and sclerostin (Scl) as biochemical feedback molecules. Utilizing a competitive binding model, where Wnt and Scl compete for binding to LRP5/6, allows to regulate anabolic bone remodeling responses. Here, we extended this model with respect to romosozumab binding to sclerostin. For the currently approved monthly injections of 210 mg, the model predicted a 6.59%, 10.38% and 15.25% increase in BMD at the lumbar spine after 6, 12 and 24 months, respectively. These results are in good agreement with the data reported in the literature. Our model is also able to distinguish the bone-site specific drug effects. For instance, at the femoral neck, our model predicts a BMD increase of 3.85% after 12 months of 210 mg injections, which is consistent with literature observations. Finally, our simulations indicate rapid bone loss after treatment discontinuation, indicating that some additional interventions such as use of bisphosphonates are required to maintain bone mass.

Intermittent Parathyroid Hormone Accelerates Stress Fracture Healing More Effectively Following Cessation of Bisphosphonate Treatment.

Parathyroid hormone (PTH) and bisphosphonates (BPs), including alendronate (ALN), have opposing effects on bone dynamics. The extent to which PTH remains effective in the treatment of stress fracture (SFx) in the presence of an ongoing BP treatment has not been tested. SFx was induced in 150 female Wistar rats, divided into five equal groups (n = 30). All rats were pretreated with ALN (1 µg/kg-1/day-1) for 14 days prior to SFx induction, followed by ALN cessation or continuation for the duration of the experiment; this was combined with daily PTH (8 µg/100 g-1/day-1) on SFx induction for 14 days, followed by cessation or continuation of ALN after SFx induction or an equivalent vehicle as a control. Ulnas were examined 2 weeks or 6 weeks following SFx. Two toluidine blue- and two tartrate-resistant acid phosphatase-stained sections were examined for histomorphometric analysis using Osteomeasure software. There was a significant interaction between the effects of time and treatment type on the woven bone width and apposition rate, as well as an improvement in the woven bone architecture. However, woven bone variables remained unaffected by the cessation or continuation of ALN. Cessation of ALN increased osteoclast number when compared with the ALN-PTH continuation group (p = 0.006), and vehicle (p = 0.024) after 2 weeks. There was a significant interaction between the effects of time and treatment type on the number of osteoclasts per unit BMU area and length. The number of osteoclasts per unit BMU area and length was significantly greater in ALN cessation groups. It was concluded that intermittent short-duration iPTH treatment effectively increased remodeling of SFx with a concurrent BP treatment, provided that BP was ceased at the time of SFx. Our results could help develop shorter iPTH treatment protocols for the clinical management of SFxs and guide clinical decision-making to cease BP treatment in cases of SFx. © 2020 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.