Retinoid roles and action in skeletal development and growth provide the rationale for an ongoing heterotopic ossification prevention trial

A realistic mixture of ubiquitous persistent organic pollutants affects bone and cartilage development in zebrafish by interaction with nuclear receptor signaling

"Persistent organic pollutants (POPs)" have a plethora of deleterious effects on humans and the environment due to their bioaccumulative, persistent, and mimicking properties. Individually, each of these chemicals has been tested and its effects measured, however they are rather found as parts of complex mixtures of which we do not fully grasp the extent of their potential consequences. Here we studied the effects of realistic, environmentally relevant mixtures of 29 POPs on cartilage and bone development using zebrafish as a model species. We observed developmental issues in cartilage, in the form of diverse malformations such as micrognathia, reduced size of the Meckel's and other structures. Also, mineralized bone formation was disrupted, hence impacting the overall development of the larvae at later life stages. Assessment of the transcriptome revealed disruption of nuclear receptor pathways, such as androgen, vitamin D, and retinoic acid, that may explain the mechanisms of action of the compounds within the tested mixtures. In addition, clustering of the compounds using their chemical signatures revealed structural similarities with the model chemicals vitamin D and retinoic acid that can explain the effects and/or enhancing the phenotypes we witnessed. Further mechanistic studies will be required to fully understand this kind of molecular interactions and their repercussions in organisms. Our results contribute to the already existing catalogue of deleterious effects caused by exposure to POPs and help to understand the potential consequences in at risk populations.

Pay Attention to the Osteochondromas in Fibrodysplasia Ossificans Progressiva

BACKGROUND

Fibrodysplasia ossificans progressiva (FOP) is an extremely rare disease characterized by malformation of the bilateral great toes and progressive heterotopic ossification. The clinical features of FOP occur due to dysfunction of the bone morphogenetic protein (BMP) signaling pathway induced by the mutant activin A type I receptor/activin-like kinase-2 (ACVR1/ALK2) which contributes to the clinical features in FOP. Dysregulation of the BMP signaling pathway causes the development of osteochondroma. Poor awareness of the association between FOP and osteochondromas always results in misdiagnosis and unnecessary invasive operation.

CASE PRESENTATION

In this study, we present a case of classical FOP involving osteochondroma. An 18-year-old male adolescent, born with deformity of bilateral big toes, complained multiple masses on his back for 1 year. The mass initially emerged with a tough texture and did not cause pain. It was misdiagnosed as an osteochondroma. After two surgeries, the masses became hard and spread around the entire back region. Meanwhile, extensive heterotopic ossification was observed around the back, neck, hip, knee, ribs, and mandible during follow-up. Osteochondromas were observed around the bilateral knees. No abnormalities were observed in the laboratory blood test results. Whole exome sequencing revealed missense mutation of ACVR1/ALK2 (c.617G > A; p.R206H) in the patient and confirmed the diagnosis of FOP.

CONCLUSION

In summary, classical FOP always behaves as a bilateral deformity of the big toes, as well as progressive ectopic ossification and osteochondromas in the distal femur and proximal tibia. An understanding of the association between osteochondromas and FOP aids in diagnosis and avoids unnecessary invasive management in patients.

Effect of a retinoic acid analogue on BMP-driven pluripotent stem cell chondrogenesis

Osteoarthritis is the most common degenerative joint condition, leading to articular cartilage (AC) degradation, chronic pain and immobility. The lack of appropriate therapies that provide tissue restoration combined with the limited lifespan of joint-replacement implants indicate the need for alternative AC regeneration strategies. Differentiation of human pluripotent stem cells (hPSCs) into AC progenitors may provide a long-term regenerative solution but is still limited due to the continued reliance upon growth factors to recapitulate developmental signalling processes. Recently, TTNPB, a small molecule activator of retinoic acid receptors (RARs), has been shown to be sufficient to guide mesodermal specification and early chondrogenesis of hPSCs. Here, we modified our previous differentiation protocol, by supplementing cells with TTNPB and administering BMP2 at specific times to enhance early development (referred to as the RAPID-E protocol). Transcriptomic analyses indicated that activation of RAR signalling significantly upregulated genes related to limb and embryonic skeletal development in the early stages of the protocol and upregulated genes related to AC development in later stages. Chondroprogenitors obtained from RAPID-E could generate cartilaginous pellets that expressed AC-related matrix proteins such as Lubricin, Aggrecan, and Collagen II, but additionally expressed Collagen X, indicative of hypertrophy. This protocol could lay the foundations for cell therapy strategies for osteoarthritis and improve the understanding of AC development in humans.

Palovarotene Action Against Heterotopic Ossification Includes a Reduction of Local Participating Activin A-Expressing Cell Populations

Heterotopic ossification (HO) consists of extraskeletal bone formation. One form of HO is acquired and instigated by traumas or surgery, and another form is genetic and characterizes fibrodysplasia ossificans progressiva (FOP). Recently, we and others showed that activin A promotes both acquired and genetic HO, and in previous studies we found that the retinoid agonist palovarotene inhibits both HO forms in mice. Here, we asked whether palovarotene's action against HO may include an interference with endogenous activin A expression and/or function. Using a standard mouse model of acquired HO, we found that activin A and its encoding RNA (Inhba) were prominent in chondrogenic cells within developing HO masses in untreated mice. Single-cell RNAseq (scRNAseq) assays verified that Inhba expression characterized chondroprogenitors and chondrocytes in untreated HO, in addition to its expected expression in inflammatory cells and macrophages. Palovarotene administration (4 mg/kg/d/gavage) caused a sharp inhibition of both HO and amounts of activin A and Inhba transcripts. Bioinformatic analyses of scRNAseq data sets indicated that the drug had reduced interactions and cross-talk among local cell populations. To determine if palovarotene inhibited Inhba expression directly, we assayed primary chondrocyte cultures. Drug treatment inhibited their cartilaginous phenotype but not Inhba expression. Our data reveal that palovarotene markedly reduces the number of local Inhba-expressing HO-forming cell populations. The data broaden the spectrum of HO culprits against which palovarotene acts, accounting for its therapeutic effectiveness. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Berberine and aspirin prevent traumatic heterotopic ossification by inhibition of BMP signalling pathway and osteogenic differentiation

Heterotopic ossification (HO) is a pathological process that often occurs in soft tissues following severe trauma. There is no effective therapy for HO. The BMP signalling pathway plays an essential role in the pathogenesis of HO. Our previous study showed that AMPK negatively regulates the BMP signalling pathway and osteogenic differentiation. The present study aims to study the effect of two AMPK activators berberine and aspirin on osteogenic differentiation and HO induced by traumatic injury. The effects of two AMPK activators, berberine and aspirin, on BMP signalling and osteogenic differentiation were measured by western blot, ALP and Alizarin red S staining in C3H10T1/2 cells. A mouse model with Achilles tenotomy was employed to assess the effects of berberine and aspirin on HO using μCT and histological analysis. First, our study showed that berberine and aspirin inhibited phosphorylation of Smad1/5 induced by BMP6 and the inhibition was attributed to the down-regulation of ALK2 expression. Second, the combination of berberine and aspirin yielded more potent effects on BMP signalling. Third, we further found that there was an additive effect of berberine and aspirin combination on osteogenic differentiation. Finally, we found that berberine and aspirin blocked trauma-induced ectopic bone formation in mice, which may be through suppression of phosphorylation of Smad1/5 in injured tissues. Collectively, these findings indicate that berberine and aspirin inhibit osteogenic differentiation in C3H10T1/2 cells and traumatic HO in mice, possibly through the down-regulation of the BMP signalling pathway. Our study sheds a light on prevention and treatment of traumatic HO using AMPK pharmacological activators berberine and aspirin.

Reduction of New Heterotopic Ossification (HO) in the Open-Label, Phase 3 MOVE Trial of Palovarotene for Fibrodysplasia Ossificans Progressiva (FOP)

Fibrodysplasia ossificans progressiva (FOP) is an ultra-rare, severely disabling genetic disorder of progressive heterotopic ossification (HO). The single-arm, open-label, phase 3 MOVE trial (NCT03312634) assessed efficacy and safety of palovarotene, a selective retinoic acid receptor gamma agonist, in patients with FOP. Findings were compared with FOP natural history study (NHS; NCT02322255) participants untreated beyond standard of care. Patients aged ≥4 years received palovarotene once daily (chronic: 5 mg; flare-up: 20 mg for 4 weeks, then 10 mg for ≥8 weeks; weight-adjusted if skeletally immature). The primary endpoint was annualized change in new HO volume versus NHS participants (by low-dose whole-body computed tomography [WBCT]), analyzed using a Bayesian compound Poisson model (BcPM) with square-root transformation. Twelve-month interim analyses met futility criteria; dosing was paused. An independent Data Monitoring Committee recommended trial continuation. Post hoc 18-month interim analyses utilized BcPM with square-root transformation and HO data collapsed to equalize MOVE and NHS visit schedules, BcPM without transformation, and weighted linear mixed-effects (wLME) models, alongside prespecified analysis. Safety was assessed throughout. Eighteen-month interim analyses included 97 MOVE and 101 NHS individuals with post-baseline WBCT. BcPM analyses without transformation showed 99.4% probability of any reduction in new HO with palovarotene versus NHS participants (with transformation: 65.4%). Mean annualized new HO volume was 60% lower in MOVE versus the NHS. wLME results were similar (54% reduction fitted; nominal p = 0.039). All palovarotene-treated patients reported ≥1 adverse event (AE); 97.0% reported ≥1 retinoid-associated AE; 29.3% reported ≥1 serious AE, including premature physeal closure (PPC)/epiphyseal disorder in 21/57 (36.8%) patients aged <14 years. Post hoc computational analyses using WBCT showed decreased vertebral bone mineral density, content, and strength, and increased vertebral fracture risk in palovarotene-treated patients. Thus, post hoc analyses showed evidence for efficacy of palovarotene in reducing new HO in FOP, but high risk of PPC in skeletally immature patients. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Roles of Local Soluble Factors in Maintaining the Growth Plate: An Update

The growth plate is a cartilaginous tissue found at the ends of growing long bones, which contributes to the lengthening of bones during development. This unique structure contains at least three distinctive layers, including resting, proliferative, and hypertrophic chondrocyte zones, maintained by a complex regulatory network. Due to its soft tissue nature, the growth plate is the most susceptible tissue of the growing skeleton to injury in childhood. Although most growth plate damage in fractures can heal, some damage can result in growth arrest or disorder, impairing leg length and resulting in deformity. In this review, we re-visit previously established knowledge about the regulatory network that maintains the growth plate and integrate current research displaying the most recent progress. Next, we highlight local secretary factors, such as Wnt, Indian hedgehog (Ihh), and parathyroid hormone-related peptide (PTHrP), and dissect their roles and interactions in maintaining cell function and phenotype in different zones. Lastly, we discuss future research topics that can further our understanding of this unique tissue. Given the unmet need to engineer the growth plate, we also discuss the potential of creating particular patterns of soluble factors and generating them in vitro.

Osteochondroma formation is independent of heparanase expression as revealed in a mouse model of hereditary multiple exostoses

Hereditary multiple exostoses (HME) is a rare, pediatric disorder characterized by osteochondromas that form along growth plates and provoke significant musculoskeletal problems. HME is caused by mutations in heparan sulfate (HS)-synthesizing enzymes EXT1 or EXT2. Seemingly paradoxically, osteochondromas were found to contain excessive extracellular heparanase (Hpse) that could further reduce HS levels and exacerbate pathogenesis. To test Hpse roles, we asked whether its ablation would protect against osteochondroma formation in a conditional HME model consisting of mice bearing floxed Ext1 alleles in Agr-CreER background (Ext1f/f ;Agr-CreER mice). Mice were crossed with a new global Hpse-null (Hpse-/- ) mice to produce compound Hpse-/- ;Ext1f/f ;Agr-CreER mice. Tamoxifen injection of standard juvenile Ext1f/f ;Agr-CreER mice elicited stochastic Ext1 ablation in growth plate and perichondrium, followed by osteochondroma formation, as revealed by microcomputed tomography and histochemistry. When we examined companion conditional Ext1-deficient mice lacking Hpse also, we detected no major decreases in osteochondroma number, skeletal distribution, and overall structure by the analytical criteria above. The Ext1 mutants used here closely mimic human HME pathogenesis, but have not been previously tested for responsiveness to treatments. To exclude some innate therapeutic resistance in this stochastic model, tamoxifen-injected Ext1f/f ;Agr-CreER mice were administered daily doses of the retinoid Palovarotene, previously shown to prevent ectopic cartilage and bone formation in other mouse disease models. This treatment did inhibit osteochondroma formation compared with vehicle-treated mice. Our data indicate that heparanase is not a major factor in osteochondroma initiation and accumulation in mice. Possible roles of heparanase upregulation in disease severity in patients are discussed.

Retinoic Acid Receptor Activation Reduces Metastatic Prostate Cancer Bone Lesions by Blocking the Endothelial-to-Osteoblast Transition

Metastatic prostate cancer in the bone induces bone-forming lesions that contribute to progression and therapy resistance. Prostate cancer-induced bone formation originates from endothelial cells (EC) that have undergone endothelial-to-osteoblast (EC-to-OSB) transition in response to tumor-secreted BMP4. Current strategies targeting prostate cancer-induced bone formation are lacking. Here, we show that activation of retinoic acid receptor (RAR) inhibits EC-to-OSB transition and reduces prostate cancer-induced bone formation. Treatment with palovarotene, an RARγ agonist being tested for heterotopic ossification in fibrodysplasia ossificans progressiva, inhibited EC-to-OSB transition and osteoblast mineralization in vitro and decreased tumor-induced bone formation and tumor growth in several osteogenic prostate cancer models, and similar effects were observed with the pan-RAR agonist all-trans-retinoic acid (ATRA). Knockdown of RARα, β, or γ isoforms in ECs blocked BMP4-induced EC-to-OSB transition and osteoblast mineralization, indicating a role for all three isoforms in prostate cancer-induced bone formation. Furthermore, treatment with palovarotene or ATRA reduced plasma Tenascin C, a factor secreted from EC-OSB cells, which may be used to monitor treatment response. Mechanistically, BMP4-activated pSmad1 formed a complex with RAR in the nucleus of ECs to activate EC-to-OSB transition. RAR activation by palovarotene or ATRA caused pSmad1 degradation by recruiting the E3-ubiquitin ligase Smad ubiquitination regulatory factor1 (Smurf1) to the nuclear pSmad1/RARγ complex, thus blocking EC-to-OSB transition. Collectively, these findings suggest that palovarotene can be repurposed to target prostate cancer-induced bone formation to improve clinical outcomes for patients with bone metastasis.

SIGNIFICANCE

This study provides mechanistic insights into how RAR agonists suppress prostate cancer-induced bone formation and offers a rationale for developing RAR agonists for prostate cancer bone metastasis therapy. See related commentary by Bhowmick and Bhowmick, p. 2975.

Gene Therapy for Fibrodysplasia Ossificans Progressiva: Feasibility and Obstacles

Fibrodysplasia ossificans progressiva (FOP) is a rare and devastating genetic disease, in which soft connective tissue is converted into heterotopic bone through an endochondral ossification process. Patients succumb early as they gradually become trapped in a second skeleton of heterotopic bone. Although the underlying genetic defect is long known, the inherent complexity of the disease has hindered the discovery of effective preventions and treatments. New developments in the gene therapy field have motivated its consideration as an attractive therapeutic option for FOP. However, the immune system's role in FOP activation and the as-yet unknown primary causative cell, are crucial issues which must be taken into account in the therapy design. While gene therapy offers a potential therapeutic solution, more knowledge about FOP is needed to enable its optimal and safe application.

Categorize the existing clamps used for tensile test of human graft- a systematic review

Background

The use of tendon allografts for orthopedic repair has gained wide acceptance in recent years, most notably in anterior cruciate tendon reconstruction. Multiple studies support the use of tendon allografts and the benefits of its use are well accepted and understood. One of the important criteria of the use of tendon allografts is statistically similar histological and biomechanical properties to autographs. The aim of this systematic literature review is to investigate and categorize existing clamps used in the determination of the biomechanical properties of tendons such as maximum load, maximum strength, modulus of elasticity, ultimate strain, and stiffness. A variety of clamps for use during the endurance test of tendons were categorized according to the temperature used during the measurement. The clamps are divided into three groups: room temperature, cooled and heated clamps. The second goal of our review is to overview of clamps on the following aspects: name of clamp, author and date, type of clamps, type of endurance test (static or dynamic), type preloading (dynamic or static), type of tendon and measured and calculated parameters, and summarize in Table 3, as a comprehensive catalogue.

Methods

This systematic review was carried out in keeping with the PRISMA 2020 E&E and the PRISMA-S guidelines and checklists. A search was conducted for publications dating between 1991 and February 28th 2022 through three electronic databases (Web of Science, Scopus, and PubMed). We used Critical Appraisal Skills Program checklist to check the quality of included articles.

Results

The database search and additional sources resulted in 1725 records. 1635 records eliminated during the screening for various reasons (case report, other languages, book chapter, unavailable text/conference abstract, unrelated topic). The number of articles used in the final synthesis was 90. A variety of clamps for use during the endurance test of tendons were identified and categorized according to the temperature used during the measurement. Based on this, the clamps are divided into three groups: room temperature, cooled or heated clamps.

Conclusions

On the basis of the systematic literature review, mechanical parameters determined by usage with cooled clamps proved to be more reliable than with those at room temperature and with heated clamps. The collected information from the articles included name of clamp, author and date, type of clamps, type of endurance test (static or dynamic), type preloading (dynamic or static), type of tendon and measured and calculated parameters given in Table 3. summarized. The main advantage of the cooled clamps is that there is no limit to the type and length of the tendon. This study provides an overview of clamps and does not represent the modernity of any method.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-022-05650-w.

Recent progress in drug development for fibrodysplasia ossificans progressiva

Fibrodysplasia Ossificans Progressiva (FOP) is a rare genetic disease caused by heterozygous missense mutations in Activin A receptor type I which is also known as Activin-like kinase 2 (ALK2), a type I receptor of Bone Morphogenetic Proteins(BMP). Patients with FOP usually undergo episodic flare-ups and the heterotopic ossification in soft and connective tissues. Molecular mechanism study indicates that Activin A, the ligand which normally transduces Transforming Growth Factor Beta signaling, abnormally activates BMP signaling through ALK2 mutants in FOP, leading to heterotopic bone formation. To date, effective therapies to FOP are unavailable. However, significant advances have recently been made in the development of FOP drugs. In this article, we review the recent advances in understanding the FOP mechanism and drug development, with a focus on the small-molecular and antibody drugs currently in the clinical trials for FOP treatment.

Circadian rhythm modulates endochondral bone formation via MTR1/AMPKβ1/BMAL1 signaling axis

The circadian clock is a master regulator in coordinating daily oscillations of physiology and behaviors. Nevertheless, how the circadian rhythm affects endochondral ossification is poorly understood. Here we showed that endochondral bone formation exhibits circadian rhythms, manifested as fast DNA replication in the daytime, active cell mitosis, and matrix synthesis at night. Circadian rhythm disruption led to endochondral ossification deformities. The mechanistic dissection revealed that melatonin receptor 1 (MTR1) periodically activates the AMPKβ1 phosphorylation, which then orchestrates the rhythms of cell proliferation and matrix synthesis via destabilizing the clock component CRY1 and triggering BMAL1 expression. Accordingly, the AMPKβ1 agonist is capable of alleviating the abnormity of endochondral ossification caused by circadian dysrhythmias. Taken together, these findings indicated that the central circadian clock could control endochondral bone formation via the MTR1/AMPKβ1/BMAL1 signaling axis in chondrocytes. Also, our results suggested that the AMPKβ1 signaling activators are promising medications toward endochondral ossification deformities.

A Rapid and Cheap Method for Extracting and Quantifying Lycopene Content in Tomato Sauces: Effects of Lycopene Micellar Delivery on Human Osteoblast-Like Cells

Identifying and quantifying the beneficial molecules contained in nutraceuticals is essential to predict the effects derived from their consumption. This study explores a cheap and rapid method for quantifying lycopene content from a semi-solid matrix. In addition, it compares the in vitro effects of the extracts obtained from different tomato sauces available on the local market with Osteocol®, a patented tomato sauce from southern Italy. We performed a liquid extraction of lycopene using suitable solvents. The lycopene extracted was encapsulated in surfactant micelles and finally tested in vitro on Saos-2 cells. The effects exerted by lycopene on ALP and Wnt/β-catenin pathways were investigated by Western blotting. Hexane was found to be the best solvent for lycopene extraction. Spectrophotometrical and HPLC analyses showed similar trends. Osteocol® contained 39 ± 4 mg lycopene per 100 g of sauce, while the best commercial product contained 19 ± 1 mg/100 g. The Osteocol® lycopene extract increased ALP and β-catenin protein expressions in a dose-dependent manner, also showing statistically significant results (p < 0.05 respectively). In conclusion, despite both techniques showing similar final results, UV/VIS spectrophotometer is preferable to HPLC due to its cheap, rapid, and accurate results, as well as for the opportunity to analyze lycopene-loaded micelles. The extraction and release of lycopene to bone cells positively influences the differentiation of osteoblasts and increases the expression of the ALP and β-catenin proteins. As a consequence, as a lycopene-rich sauce, Osteocol® represents a useful supplement in the prevention of osteoporosis compared to its commercial competitors.

Retinoid Agonists in the Targeting of Heterotopic Ossification

Retinoids are metabolic derivatives of vitamin A and regulate the function of many tissues and organs both prenatally and postnatally. Active retinoids, such as all trans-retinoic acid, are produced in the cytoplasm and then interact with nuclear retinoic acid receptors (RARs) to up-regulate the transcription of target genes. The RARs can also interact with target gene response elements in the absence of retinoids and exert a transcriptional repression function. Studies from several labs, including ours, showed that chondrogenic cell differentiation and cartilage maturation require (i) the absence of retinoid signaling and (ii) the repression function by unliganded RARs. These and related insights led to the proposition that synthetic retinoid agonists could thus represent pharmacological agents to inhibit heterotopic ossification (HO), a process that recapitulates developmental skeletogenesis and involves chondrogenesis, cartilage maturation, and endochondral ossification. One form of HO is acquired and is caused by injury, and another severe and often fatal form of it is genetic and occurs in patients with fibrodysplasia ossificans progressiva (FOP). Mouse models of FOP bearing mutant ACVR1R206H, characteristic of most FOP patients, were used to test the ability of the retinoid agonists selective for RARα and RARγ against spontaneous and injury-induced HO. The RARγ agonists were found to be most effective, and one such compound, palovarotene, was selected for testing in FOP patients. The safety and effectiveness data from recent and ongoing phase II and phase III clinical trials support the notion that palovarotene may represent a disease-modifying treatment for patients with FOP. The post hoc analyses showed substantial efficacy but also revealed side effects and complications, including premature growth plate closure in some patients. Skeletally immature patients will need to be carefully weighed in any future regulatory indications of palovarotene as an important therapeutic option in FOP.

Unveiling the genetic variation of severe continuous/mixed-type ossification of the posterior longitudinal ligament by whole-exome sequencing and bioinformatic analysis

BACKGROUND CONTEXT

Ossification of the posterior longitudinal ligament (OPLL) in the cervical spine is known as a rare, complex genetic disease, its complexity being partly because OPLL is diagnosed by radiological findings regardless of clinical or genetic evaluations. Although many genes associated with susceptibility have been reported, the exact causative genes are still unknown.

PURPOSE

We performed an analysis using next-generation sequencing and including only patients with a clear involved phenotype.

STUDY DESIGN/SETTING

This was a case control study.

PATIENT SAMPLE

A total of 74 patients with severe OPLL and 26 healthy controls were included.

OUTCOME MEASURES

Causal single-nucleotide variant (SNV), gene-wise variant burden (GVB), and related pathway METHOD: We consecutively included the severe OPLL patients with continuous-/mixed-type and an occupying ratio of ≥ 40%, and performed whole-exome sequencing (WES) and bioinformatic analysis. Then, a validation test was performed for candidate variations. Participants were divided into 4 groups (rapidly-growing OPLL, growing rate ≥ 2.5%/y; slow-growing, < 2.5%/y; uncertain; and control).

RESULTS

WES was performed on samples from 74 patients with OPLL (rapidly-growing, 33 patients; slow-growing, 37; and uncertain, 4) with 26 healthy controls. Analysis of 100 participants identified a newly implicated SNV and 4candidate genes based on GVB. The GVB of CYP4B1 showed a more deleterious score in the OPLL than the control group. Comparison between the rapidly growing OPLL and control groups revealed seven newly identified SNVs. We found significant association for 2 rare missense variants; rs121502220 (odds ratio [OR] = infinite; minor allele frequency [MAF] = 0.034) in NLRP1 and rs13980628 (OR= infinite; MAF = 0.032) in SSH2. The 3 genes are associated with inflammation control and arthritis, and SSH2 and NLRP1 are also related to vitamin D modulation.

CONCLUSIONS

Identification of unique variants in novel genes such as CYP4B1 gene may induce the development of OPLL. In subgroup analysis, NLRP1 and SSH2 genes coding inflammation molecules may related with rapidly-growing OPLL.

Administration of a selective retinoic acid receptor-γ agonist improves neuromuscular strength in a rodent model of volumetric muscle loss

PURPOSE

Volumetric muscle loss is a uniquely challenging pathology that results in irrecoverable functional deficits. Furthermore, a breakthrough drug or bioactive factor has yet to be established that adequately improves repair of these severe skeletal muscle injuries. This study sought to assess the ability of an orally administered selective retinoic acid receptor-γ agonist, palovarotene, to improve recovery of neuromuscular strength in a rat model of volumetric muscle loss.

METHODS

An irrecoverable, full thickness defect was created in the tibialis anterior muscle of Lewis rats and animals were survived for 4 weeks. Functional recovery of the tibialis anterior muscle was assessed in vivo via neural stimulation and determination of peak isometric torque. Histological staining was performed to qualitatively assess fibrous scarring of the defect site.

RESULTS

Treatment with the selective retinoic acid receptor-γ agonist, palovarotene, resulted in a 38% improvement of peak isometric torque in volumetric muscle loss affected limbs after 4 weeks of healing compared to untreated controls. Additionally, preliminary histological assessment suggests that oral administration of palovarotene reduced fibrous scarring at the defect site.

CONCLUSIONS

These results highlight the potential role of selective retinoic acid receptor-γ agonists in the design of regenerative medicine platforms to maximize skeletal muscle healing. Additional studies are needed to further elucidate cellular responses, optimize therapeutic delivery, and characterize synergistic potential with adjunct therapies.

Premature Growth Plate Closure Caused by a Hedgehog Cancer Drug Is Preventable by Co-Administration of a Retinoid Antagonist in Mice

The growth plates are key engines of skeletal development and growth and contain a top reserve zone followed by maturation zones of proliferating, prehypertrophic, and hypertrophic/mineralizing chondrocytes. Trauma or drug treatment of certain disorders can derange the growth plates and cause accelerated maturation and premature closure, one example being anti-hedgehog drugs such as LDE225 (Sonidegib) used against pediatric brain malignancies. Here we tested whether such acceleration and closure in LDE225-treated mice could be prevented by co-administration of a selective retinoid antagonist, based on previous studies showing that retinoid antagonists can slow down chondrocyte maturation rates. Treatment of juvenile mice with an experimental dose of LDE225 for 2 days (100 mg/kg by gavage) initially caused a significant shortening of long bone growth plates, with concomitant decreases in chondrocyte proliferation; expression of Indian hedgehog, Sox9, and other key genes; and surprisingly, the number of reserve progenitors. Growth plate involution followed with time, leading to impaired long bone lengthening. Mechanistically, LDE225 treatment markedly decreased the expression of retinoid catabolic enzyme Cyp26b1 within growth plate, whereas it increased and broadened the expression of retinoid synthesizing enzyme Raldh3, thus subverting normal homeostatic retinoid circuitries and in turn accelerating maturation and closure. All such severe skeletal and molecular changes were prevented when LDE-treated mice were co-administered the selective retinoid antagonist CD2665 (1.5 mg/kg/d), a drug targeting retinoid acid receptor γ, which is most abundantly expressed in growth plate. When given alone, CD2665 elicited the expected maturation delay and growth plate expansion. In vitro data showed that LDE225 acted directly to dampen chondrogenic phenotypic expression, a response fully reversed by CD2665 co-treatment. In sum, our proof-of-principle data indicate that drug-induced premature growth plate closures can be prevented or delayed by targeting a separate phenotypic regulatory mechanism in chondrocytes. The translation applicability of the findings remains to be studied. © 2021 American Society for Bone and Mineral Research (ASBMR).

Different sterilization and disinfection methods used for human tendons - a systematic review using mechanical properties to evaluate tendon allografts

Background

It is important to know the biomechanical properties of an allograft. This is because when looking to do a transplant of a tendon, the tendon must have very similar biomechanical properties to the original tendon. To use tendon allografts, it is critical to properly sterilize the tendon before implantation. In past decades, several sterilization procedures have been used. This study aimed to systematically evaluate the existing literature to compare the values of failure load/ultimate strength and Young’s modulus of elasticity of different sterilization methods on commonly used tendon allografts. Five major scientific literature databases (Web of Science, Science Direct, Scopus, PLOS ONE, Hindawi) and additional sources were used.

Results

Studies used had to show a particular sterilization method. Studies were identified to meet the following inclusion criteria: is a controlled laboratory study, gamma irradiation (dose reported), and other sterilization methods. Search for publications dated between 1991 and March 31st, 2020. The database search and additional sources resulted in 284 records. Two hundred thirty records eliminated during the screening for various reasons. The number of articles used in the final synthesis was 54.

Conclusions

Identified sterilization methods (gamma irradiation, ethylene oxid, supercritical carbon dioxide (SCCO2), BioCleanse, Electron Beam) are offered as a catalog of potential methods.

As a result of the broadness of the present research, it provides an overview of sterilization methods and their effect on the mechanical properties (failure load and Young’s modulus of elasticity) of tendons. It does not stand for the state-of-the-art of any single process. Based on a systematic literature review, we recommend freezing and gamma irradiation or electron beam at 14.8–28.5 kGy. These methods are effective at keeping or improving the mechanical properties, while fully sterilizing the inside and the outside of the tendon. Other sterilization method (ethylene oxide, supercritical carbon dioxide (SCCO2), BioCleanse) deteriorated the mechanical properties. These methods are not recommended.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-021-04296-4.

Case Report: Two Monochorionic Twins With a Critically Different Course of Progressive Osseus Heteroplasia

Progressive osseous heteroplasia (POH; OMIM 166350) is a rare autosomal-dominant genetic disorder in which extra-skeletal bone forms within skin and muscle tissue. POH is one of the clinical manifestations of an inactivating mutation in the GNAS gene. GNAS gene alterations are difficult matter to address, as GNAS alleles show genetic imprinting and produce several transcript products, and the same mutation may lead to strikingly different phenotypes. Also, most of the publications concerning POH patients are either clinical depictions of a case (or a case series), descriptions of their genetic background, or a tentative correlation of both clinical and molecular findings. Treatment for POH is rarely addressed, and POH still lacks therapeutic options. We describe a unique case of POH in two monochorionic twins, who presented an almost asymptomatic vs. the severe clinical course, despite sharing the same mutation and genetic background. We also report the results of the therapeutic interventions currently available for heterotopic ossification in the patient with the severe course. This article not only critically supports the assumption that the POH course is strongly influenced by factors beyond genetic background but also remarks the lack of options for patients suffering an orphan disease, even after testing drugs with promising in vitro results.

Fibrodysplasia Ossificans Progressiva: What Have We Achieved and Where Are We Now? Follow-up to the 2015 Lorentz Workshop

Fibrodysplasia ossificans progressiva (FOP) is an ultra-rare progressive genetic disease effecting one in a million individuals. During their life, patients with FOP progressively develop bone in the soft tissues resulting in increasing immobility and early death. A mutation in the ACVR1 gene was identified as the causative mutation of FOP in 2006. After this, the pathophysiology of FOP has been further elucidated through the efforts of research groups worldwide. In 2015, a workshop was held to gather these groups and discuss the new challenges in FOP research. Here we present an overview and update on these topics.

Expression and Role of IL-1β Signaling in Chondrocytes Associated with Retinoid Signaling during Fracture Healing

The process of fracture healing consists of an inflammatory reaction and cartilage and bone tissue reconstruction. The inflammatory cytokine interleukin-1β (IL-1β) signal is an important major factor in fracture healing, whereas its relevance to retinoid receptor (an RAR inverse agonist, which promotes endochondral bone formation) remains unclear. Herein, we investigated the expressions of IL-1β and retinoic acid receptor gamma (RARγ) in a rat fracture model and the effects of IL-1β in the presence of one of several RAR inverse agonists on chondrocytes. An immunohistochemical analysis revealed that IL-1β and RARγ were expressed in chondrocytes at the fracture site in the rat ribs on day 7 post-fracture. In chondrogenic ATDC5 cells, IL-1β decreases the levels of aggrecan and type II collagen but significantly increased the metalloproteinase-13 (Mmp13) mRNA by real-time reverse transcription-polymerase chain reaction (RT-PCR) analysis. An RAR inverse agonist (AGN194310) inhibited IL-1β-stimulated Mmp13 and Ccn2 mRNA in a dose-dependent manner. Phosphorylated extracellular signal regulated-kinases (pERK1/2) and p-p38 mitogen-activated protein kinase (MAPK) were increased time-dependently by IL-1β treatment, and the IL-1β-induced p-p38 MAPK was inhibited by AGN194310. Experimental p38 inhibition led to a drop in the IL-1β-stimulated expressions of Mmp13 and Ccn2 mRNA. MMP13, CCN2, and p-p38 MAPK were expressed in hypertrophic chondrocytes near the invaded vascular endothelial cells. As a whole, these results point to role of the IL-1β via p38 MAPK as important signaling in the regulation of the endochondral bone formation in fracture healing, and to the actions of RAR inverse agonists as potentially relevant modulators of this process.

New perspectives on the treatment of skeletal dysplasia

The last few decades have been marked by the identification of numerous genes implicated in genetic disorders, helping in the elucidation of the underlying pathophysiology of these conditions. This has allowed new therapeutic approaches to emerge such as cellular therapy, gene therapy, or pharmacological therapy for various conditions. Skeletal dysplasias are good models to illustrate these scientific advances. Indeed, several therapeutic strategies are currently being investigated in osteogenesis imperfecta; there are ongoing clinical trials based on pharmacological approaches, targeting signaling pathways in achondroplasia and fibrodysplasia ossificans progressiva or the endoplasmic reticulum stress in metaphyseal dysplasia type Schmid or pseudoachondroplasia. Moreover, the treatment of hypophosphatasia or Morquio A disease illustrates the efficacy of enzyme drug replacement. To provide a highly specialized multidisciplinary approach, these treatments are managed by reference centers. The emergence of treatments in skeletal dysplasia provides new perspectives on the prognosis of these severe conditions and may change prenatal counseling in these diseases over the coming years.

Attenuation of Hypertrophy in Human MSCs via Treatment with a Retinoic Acid Receptor Inverse Agonist

In vitro chondrogenically differentiated mesenchymal stem cells (MSCs) have a tendency to undergo hypertrophy, mirroring the fate of transient “chondrocytes” in the growth plate. As hypertrophy would result in ossification, this fact limits their use in cartilage tissue engineering applications. During limb development, retinoic acid receptor (RAR) signaling exerts an important influence on cell fate of mesenchymal progenitors. While retinoids foster hypertrophy, suppression of RAR signaling seems to be required for chondrogenic differentiation. Therefore, we hypothesized that treatment of chondrogenically differentiating hMSCs with the RAR inverse agonist, BMS204,493 (further named BMS), would attenuate hypertrophy. We induced hypertrophy in chondrogenic precultured MSC pellets by the addition of bone morphogenetic protein 4. Direct activation of the RAR pathway by application of the physiological RAR agonist retinoic acid (RA) further enhanced the hypertrophic phenotype. However, BMS treatment reduced hypertrophic conversion in hMSCs, shown by decreased cell size, number of hypertrophic cells, and collagen type X deposition in histological analyses. BMS effects were dependent on the time point of application and strongest after early treatment during chondrogenic precultivation. The possibility of modifing hypertrophic cartilage via attenuation of RAR signaling by BMS could be helpful in producing stable engineered tissue for cartilage regeneration.

Lycopene and bone: an in vitro investigation and a pilot prospective clinical study

Background

There are several effective therapies for osteoporosis but these agents might cause serious adverse events. Lycopene intake could prevent bone loss, however studies on its effects on bone are scarce. Our aim was to investigate the effects of lycopene on osteoblast cells as well as bone mineral density and bone turnover markers in postmenopausal women.

Methods

We investigated the effect of lycopene on the Wnt/β-catenin and ERK 1/2 pathways, RUNX2, alkaline phosphatase, RANKL and COL1A of Saos-2. We also carried out a pilot controlled clinical study to verify the feasibility of an approach for bone loss prevention through the intake of a lycopene-rich tomato sauce in 39 postmenopausal women.

Results

Lycopene 10 µM resulted in higher β-catenin and phERK1/2 protein Vs the vehicle (p = 0.04 and p = 0.006). RUNX2 and COL1A mRNA was induced by both 5 and 10 µM doses (p = 0.03; p = 0.03 and p = 0.03; p = 0.05) while RANKL mRNA was reduced (p < 0.05). A significant bone density loss was not detected in women taking the tomato sauce while the control group had bone loss (p = 0.002). Tomato sauce intake resulted in a greater bone alkaline phosphatase reduction than the control (18% vs 8.5%, p = 0.03).

Conclusions

Lycopene activates the WNT/β-catenin and ERK1/2 pathways, upregulates RUNX2, alkaline phosphatase, COL1A and downregulates RANKL Saos-2. These processes contributed to prevent bone loss in postmenopausal women.

The evolving therapeutic landscape of genetic skeletal disorders

BACKGROUND

Rare bone diseases account for 5% of all birth defects yet very few have personalised treatments. Developments in genetic diagnosis, molecular techniques and treatment technologies however, are leading to unparalleled therapeutic advance. This review explores the evolving therapeutic landscape of genetic skeletal disorders (GSDs); the key conditions and there key differentials.

METHODS

A retrospective literature based review was conducted in December 2018 using a systematic search strategy for relevant articles and trials in Pubmed and clinicaltrials.gov respectively. Over 140 articles and 80 trials were generated for review.

RESULTS

Over 20 personalised therapies are discussed in addition to several novel disease modifying treatments in over 25 GSDs. Treatments discussed are at different stages from preclinical studies to clinical trials and approved drugs, including; Burosumab for X-linked hypophosphatemia, Palovarotene for Hereditary Multiple Exostoses, Carbamazepine for Metaphyseal Chondrodysplasia (Schmid type), Lithium carbonate and anti-sclerostin therapy for Osteoporosis Pseudoglioma syndrome and novel therapies for Osteopetrosis. We also discuss therapeutic advances in Achondroplasia, Osteogenesis Imperfecta (OI), Hypophosphotasia (HPP), Fibrodysplasia Ossificans Progressiva, and RNA silencing therapies in preclinical studies for OI and HPP.

DISCUSSION

It is an exciting time for GSD therapies despite the challenges of drug development in rare diseases. In discussing emerging therapies, we explore novel approaches to drug development from drug repurposing to in-utero stem cell transplants. We highlight the improved understanding of bone pathophysiology, genetic pathways and challenges of developing gene therapies for GSDs.

Simple and Robust Differentiation of Human Pluripotent Stem Cells toward Chondrocytes by Two Small-Molecule Compounds

A simple induction protocol to differentiate chondrocytes from pluripotent stem cells (PSCs) using small-molecule compounds is beneficial for cartilage regenerative medicine and mechanistic studies of chondrogenesis. Here, we demonstrate that chondrocytes are robustly induced from human PSCs by simple combination of two compounds, CHIR99021, a glycogen synthase kinase 3 inhibitor, and TTNPB, a retinoic acid receptor (RAR) agonist, under serum- and feeder-free conditions within 5-9 days. An excellent differentiation efficiency and potential to form hyaline cartilaginous tissues in vivo were demonstrated. Comprehensive gene expression and open chromatin analyses at each protocol stage revealed step-by-step differentiation toward chondrocytes. Genome-wide analysis of RAR and β-catenin association with DNA showed that retinoic acid and Wnt/β-catenin signaling collaboratively regulated the key marker genes at each differentiation stage. This method provides a promising cell source for regenerative medicine and, as an in vitro model, may facilitate elucidation of the molecular mechanisms underlying chondrocyte differentiation.

Vitamin A decreases the anabolic bone response to mechanical loading by suppressing bone formation

Increased vitamin A consumption is associated with decreased cortical bone mass and increased fracture risk in humans. Rodent studies have demonstrated that hypervitaminosis A increases cortical bone resorption, whereas the importance of the effects on bone formation is less well defined. We used an experimental model of increased bone formation by loading of the tibiae to investigate the effect of vitamin A on bone formation. Control [retinol activity equivalents (RAE) 4.5 µg/g chow] or vitamin A (RAE 60 µg/g chow) diets were given to female C57BL/6N mice for 4 wk, after which the tibiae were subjected to axial loading on alternate days for 2 wk, while the diets were continued. Vitamin A inhibited the loading-induced increase in trabecular and cortical bone volume. This was attributed to inhibition of loading-induced increase in osteoblast number and activity, and expression of osteoblastic genes Sp7, Alpl, and Col1a1 in cortical bone. Vitamin A, loading, and combination thereof also resulted in site-specific effects on bone composition measured by Raman spectroscopy. In summary, a clinically relevant dose of vitamin A suppresses the loading-induced gain of bone mass by decreasing bone formation. These observations may have implications for regulation of bone mass caused by physical activity and the risk of osteoporosis in humans.-Lionikaite, V., Henning, P., Drevinge, C., Shah, F. A., Palmquist, A., Wikström, P., Windahl, S. H., Lerner, U. H. Vitamin A decreases the anabolic bone response to mechanical loading by suppressing bone formation.

Therapeutic advances for blocking heterotopic ossification in fibrodysplasia ossificans progressiva

Fibrodysplasia ossificans progressiva (FOP) is a rare genetic disease in which heterotopic bone forms in muscle and soft tissue, leading to joint dysfunction and significant disability. FOP is progressive and many patients are wheelchair-bound by the 3rd decade of life. FOP is caused by an activating mutation in the ACVR1 gene, which encodes the activin A Type 1 receptor. Aberrant signalling through this receptor leads to abnormal activation of the pSMAD 1/5/8 pathway and triggers the formation of bone outside of the skeleton. There is no curative therapy for FOP; however, exciting advances in novel therapies have developed recently. Here, we review the clinical and translational pharmacology of three drugs that are currently in clinical trials (palovarotene, REGN 2477 and rapamycin) as well as other emerging treatment strategies for FOP.

Retinoic Receptor Signaling Regulates Hypertrophic Chondrocyte-specific Gene Expression

BACKGROUND/AIM

Retinoid signaling is important for the maturation of growth-plate chondrocytes. The effect of retinoid receptor gamma (RARγ) signaling on the expression of genes in hypertrophic chondrocytes is unclear. This study investigated the role of RARγ signaling in regulation of hypertrophic chondrocyte-specific genes.

MATERIALS AND METHODS

The gene expression in mouse E17.5 tibial cartilage was examined by in situ hybridization analysis. Real-time reverse transcription-polymerase chain reaction (RT-PCR) and immunoblotting were used for analysis of mRNA and phosphorylated mitogen-activated protein kinase (MAPK).

RESULTS

mRNA expression of Rarg and connective tissue growth factor (Ccn2) was detected in maturing chondrocytes throughout the cartilaginous skeletal elements. In chondrogenic ATDC5 cells, an RARγ agonist induced the gene expression of type-X collagen (Col10A1), transglutaminase-2 (Tg2), matrix metalloproteinase-13 (Mmp13), and Ccn2 mRNA, whereas a retinoic acid pan-agonist suppressed RARγ agonist-stimulated gene expression. Phosphorylated extracellular signal regulated-kinases (pERK1/2), p-p38, and phosphorylated c-Jun N-terminal kinase (pJNK) MAPK were time-dependently increased by RARγ agonist treatment. Experimental p38 inhibition led to a severe drop in the RARγ agonist-stimulated expressions of Col10A1, Tg2, Mmp13, and Ccn2 mRNA.

CONCLUSION

RARγ signaling is required for the differentiation of hypertrophic chondrocytes, with differential cooperation with p38 MAPK.

Hypoxia-selective allosteric destabilization of activin receptor-like kinases: A potential therapeutic avenue for prophylaxis of heterotopic ossification

Heterotopic ossification (HO), the pathological extraskeletal formation of bone, can arise from blast injuries, severe burns, orthopedic procedures and gain-of-function mutations in a component of the bone morphogenetic protein (BMP) signaling pathway, the ACVR1/ALK2 receptor serine-threonine (protein) kinase, causative of Fibrodysplasia Ossificans Progressiva (FOP). All three ALKs (-2, -3, -6) that play roles in bone morphogenesis contribute to trauma-induced HO, hence are well-validated pharmacological targets. That said, development of inhibitors, typically competitors of ATP binding, is inherently difficult due to the conserved nature of the active site of the 500+ human protein kinases. Since these enzymes are regulated via inherent plasticity, pharmacological chaperone-like drugs binding to another (allosteric) site could hypothetically modulate kinase conformation and activity. To test for such a mechanism, a surface pocket of ALK2 kinase formed largely by a key allosteric substructure was targeted by supercomputer docking of drug-like compounds from a virtual library. Subsequently, the effects of docked hits were further screened in vitro with purified recombinant kinase protein. A family of compounds with terminal hydrogen-bonding acceptor groups was identified that significantly destabilized the protein, inhibiting activity. Destabilization was pH-dependent, putatively mediated by ionization of a histidine within the allosteric substructure with decreasing pH. In vivo, nonnative proteins are degraded by proteolysis in the proteasome complex, or cellular trashcan, allowing for the emergence of therapeutics that inhibit through degradation of over-active proteins implicated in the pathology of diseases and disorders. Because HO is triggered by soft-tissue trauma and ensuing hypoxia, dependency of ALK destabilization on hypoxic pH imparts selective efficacy on the allosteric inhibitors, providing potential for safe prophylactic use.

Hereditary multiple exostoses: are there new plausible treatment strategies?

Introduction

Hereditary multiple exostoses (HME) is a rare congenital pediatric disorder characterized by osteochondromas forming next to the growth plates in young patients. The osteochondromas cause multiple health problems that include skeletal deformities and chronic pain. Surgery is used to remove the most symptomatic osteochondromas but because of their large number, many are left in place, causing life-long problems and increasing the probability of malignant transformation. There is no other treatment to prevent or reduce osteochondromas formation at present.

Areas covered

Recent studies reviewable through PubMed are providing new insights into cellular and molecular mechanisms of osteochondroma development. The resulting data are suggesting rational and plausible new therapeutic strategies for osteochondroma prevention some of which are being tested in HME animal models and one of which is part of a just announced clinical trial.

Expert Commentary

This section summarizes and evaluates such strategies and points also to possible future alternatives.

Acquired and congenital forms of heterotopic ossification: new pathogenic insights and therapeutic opportunities

Heterotopic ossification (HO) involves the formation and accumulation of extraskeletal bone tissue at the expense of local tissues including muscles and connective tissues. There are common forms of HO that are triggered by extensive trauma, burns and other bodily insults, and there are also rare congenital severe forms of HO that occur in children with Fibrodysplasia Ossificans Progressiva or Progressive Osseous Heteroplasia. Given that HO is often preceded by inflammation, current treatments usually involve anti-inflammatory drugs alone or in combination with local irradiation, but are not very effective. Recent studies have provided novel insights into the pathogenesis of acquired and genetic forms of HO and have used the information to conceive and test new and more specific therapies in animal models. In this review, I provide salient examples of these exciting and promising advances that are undoubtedly paving the way toward resolution of this debilitating and at times fatal disease.

The Horizon of a Therapy for Rare Genetic Diseases: A "Druggable" Future for Fibrodysplasia Ossificans Progressiva

Fibrodysplasia ossificans progressiva (FOP) is a rare genetic condition characterized by progressive extra-skeletal ossification leading to cumulative and severe disability. FOP has an extremely variable and episodic course and can be induced by trauma, infections, iatrogenic harms, immunization or can occur in an unpredictable way, without any recognizable trigger. The causative gene is ACVR1, encoding the Alk-2 type I receptor for bone morphogenetic proteins (BMPs). The signaling is initiated by BMP binding to a receptor complex consisting of type I and II molecules and can proceed into the cell through two main pathways, a canonical, SMAD-dependent signaling and a p38-mediated cascade. Most FOP patients carry the recurrent R206H substitution in the receptor Glycine-Serine rich (GS) domain, whereas a few other mutations are responsible for a limited number of cases. Mutations cause a dysregulation of the downstream BMP-dependent pathway and make mutated ACVR1 responsive to a non-canonical ligand, Activin A. There is no etiologic treatment for FOP. However, many efforts are currently ongoing to find specific therapies targeting the receptor activity and the downstream aberrant pathway at different levels or targeting cellular components and/or processes that are important in modifying the local environment leading to bone neo-formation.