Macrophage-derived oncostatin M contributes to human and mouse neurogenic heterotopic ossifications

Tailoring surface stiffness to modulate senescent macrophage immunomodulation: Implications for osteo-/angio-genesis in aged bone regeneration

The application of biomaterials in bone regeneration is a prevalent clinical practice. However, its efficacy in elderly patients remains suboptimal, necessitating further advancements. While biomaterial properties are known to orchestrate macrophage (MΦ) polarization and local immune responses, the role of biomaterial cues, specifically stiffness, in directing the senescent macrophage (S-MΦ) is still poorly understood. This study aimed to elucidate the role of substrate stiffness in modulating the immunomodulatory properties of S-MΦ and their role in osteo-immunomodulation. Our results demonstrated that employing collagen-coated polyacrylamide hydrogels with varying stiffness values (18, 76, and 295 kPa) as model materials, the high-stiffness hydrogel (295 kPa) steered S-MΦs towards a pro-inflammatory M1 phenotype, while hydrogels with lower stiffness (18 and 76 kPa) promoted an anti-inflammatory M2 phenotype. The immune microenvironment created by S-MΦs promoted the bioactivities of senescent endothelial cells (S-ECs) and senescent bone marrow mesenchymal stem cells BMSCs (S-BMSCs). Furthermore, the M2 S-MΦs, particularly incubated on the 76 kPa hydrogel matrices, significantly enhanced the ability of angiogenesis of S-ECs and osteogenic differentiation of S-BMSCs, which are crucial and interrelated processes in bone healing. This modulation aided in reducing the accumulation of reactive oxygen species in S-ECs and S-BMSCs, thereby significantly contributing to the repair and regeneration of aged bone tissue.

Matrine reduces traumatic heterotopic ossification in mice by inhibiting M2 macrophage polarization through the MAPK pathway

In this study, the role of matrine, a component derived from traditional Chinese medicine, in modulating macrophage polarization and its effects on traumatic heterotopic ossification (HO) in mice was investigated. Traumatic HO is a pathological condition characterized by abnormal bone formation in nonskeletal tissues, often following severe trauma or surgery. The mechanisms underlying HO involve an enhanced inflammatory response and abnormal bone formation, with macrophages playing a crucial role. Our study demonstrated that matrine effectively inhibits the polarization of bone marrow-derived macrophages (BMDMs) toward the M2 phenotype, a subtype associated with anti-inflammatory processes and implicated in the progression of HO. Using in vitro assays, we showed that matrine suppresses key M2 markers and inhibits the MAPK signaling pathway in BMDMs. Furthermore, in vivo experiments revealed that matrine treatment significantly reduced HO formation in the Achilles tendons of mice and downregulated the expression of markers associated with M2 macrophages and the MAPK pathway. Our findings suggest that the ability of matrine to modulate macrophage polarization and inhibit the MAPK pathway has therapeutic potential for treating traumatic HO, providing a novel approach to managing this complex condition.

The Role of Neuromodulation and Potential Mechanism in Regulating Heterotopic Ossification

Heterotopic ossification (HO) is a pathological process characterized by the aberrant formation of bone in muscles and soft tissues. It is commonly triggered by traumatic brain injury, spinal cord injury, and burns. Despite a wide range of evidence underscoring the significance of neurogenic signals in proper bone remodeling, a clear understanding of HO induced by nerve injury remains rudimentary. Recent studies suggest that injury to the nervous system can activate various signaling pathways, such as TGF-β, leading to neurogenic HO through the release of neurotrophins. These pathophysiological changes lay a robust groundwork for the prevention and treatment of HO. In this review, we collected evidence to elucidate the mechanisms underlying the pathogenesis of HO related to nerve injury, aiming to enhance our understanding of how neurological repair processes can culminate in HO.

The significance of heterotopic ossification following total ankle arthroplasty: a systematic review and meta-analysis

PURPOSE

The purpose of this systematic review and meta-analysis was to evaluate the prevalence and clinical significance of heterotopic ossification (HO) following total ankle replacement (TAR).

METHODS

During August 2023, the PubMed, Embase and Cochrane library databases were systematically reviewed to identify clinical studies reporting HO following TAR. Data regarding surgical characteristics, pathological characteristics, subjective clinical outcomes, ankle range of motion, radiographic outcomes, reoperation rates were extracted and analysed.

RESULTS

Twenty-seven studies with 2639 patients (2695 ankles) at a weighed mean follow-up time of 52.8 ± 26.9 months were included. The pooled prevalence rate was 44.6% (0.25; 0.66). The implant with the highest rate of HO was the INBONE I (100%) and BOX (100%) implants. The most common modified Brooker staging was grade 1 (132 patients, 27.0%). Random effects models of standardized mean differences found no difference in American orthopedic foot and ankle society (AOFAS) scores, visual analog scale scores (VAS) and ankle range of motion (ROM) between patients with HO and patients without HO. Random effects models of correlation coefficients found no correlation between AOFAS, VAS and ROM and the presence of HO. The surgical intervention rate for symptomatic HO was 4.2%.

CONCLUSION

This systematic review and meta-analysis found that HO is a common finding following TAR that is not associated with inferior clinical outcomes. Surgical intervention was required only for moderate-to-severe, symptomatic HO following TAR. This study is limited by the marked heterogeneity and low level and quality of evidence of the included studies. Further higher quality studies are warranted to determine the precise prevalence and impact of HO on outcomes following TAR.

LEVEL OF EVIDENCE III

Roles of Plasminogen Activator Inhibitor-1 in Heterotopic Ossification Induced by Achilles Tenotomy in Thermal Injured Mice

Heterotopic ossification (HO) is the process by which ectopic bone forms at an extraskeletal site. Inflammatory conditions induce plasminogen activator inhibitor 1 (PAI-1), an inhibitor of fibrinolysis, which regulates osteogenesis. In the present study, we investigated the roles of PAI-1 in the pathophysiology of HO induced by trauma/burn treatment using PAI-1-deficient mice. PAI-1 deficiency significantly promoted HO and increased the number of alkaline phosphatase (ALP)-positive cells in Achilles tendons after trauma/burn treatment. The mRNA levels of inflammation markers were elevated in Achilles tendons of both wild-type and PAI-1-deficient mice after trauma/burn treatment and PAI-1 mRNA levels were elevated in Achilles tendons of wild-type mice. PAI-1 deficiency significantly up-regulated the expression of Runx2, Osterix, and type 1 collagen in Achilles tendons 9 weeks after trauma/burn treatment in mice. In in vitro experiments, PAI-1 deficiency significantly increased ALP activity and mineralization in mouse osteoblasts. Moreover, PAI-1 deficiency significantly increased ALP activity and up-regulated osteocalcin expression during osteoblastic differentiation from mouse adipose-tissue-derived stem cells, but suppressed the chondrogenic differentiation of these cells. In conclusion, the present study showed that PAI-1 deficiency promoted HO in Achilles tendons after trauma/burn treatment partly by enhancing osteoblast differentiation and ALP activity in mice. Endogenous PAI-1 may play protective roles against HO after injury and inflammation.

M1 macrophage-derived oncostatin M induces osteogenic differentiation of ligamentum flavum cells through the JAK2/STAT3 pathway

Background

M1 macrophages (Mφs) are involved in osteogenic differentiation of ligamentum flavum (LF) cells and play an important role in heterotopic ossification. However, the mechanism by which M1 Mφs influence osteogenic differentiation of LF cells has not been studied.

Methods

The effect of conditioned medium including secretions of M1 Mφs (CM-M1) on LF cells was analyzed by GeneChip profiling and ingenuity pathway analysis (IPA). THP-1 cells were polarized into M1 Mφs and CM-M1 was used to induce LF cells. In addition, LF cells were induced by CM-M1 in the presence of cyclooxygenase 2 (COX-2) inhibitors or oncostatin M (OSM)-neutralizing antibodies. Based on the presence of OSM, knockout of OSMR or GP130 receptors, or addition of the Janus kinase 2 (JAK2) inhibitor AZD1480 or signal transducer and activator of transcription 3 (STAT3) inhibitor Stattic were examined for effects on osteogenic differentiation of LF cells. OSM secretion was quantified by ELISA, while qPCR and western blot were used to evaluate expression of osteogenic genes and receptor and signaling pathway-related proteins, respectively.

Results

GeneChip and IPA results indicate that the OSM signaling pathway and its downstream signaling molecules JAK2 and STAT3 are significantly activated. ELISA results indicate that OSM is highly expressed in cells treated with CM-M1 and lowly expressed in cells treated with CM-M1 and a COX-2 inhibitor. Besides, CM-M1 induces osteogenic differentiation of LF cells, which is weakened when COX-2 inhibitors or OSM-neutralizing antibody are added to it. Recombinant OSM could induce osteogenic differentiation of LF cells and upregulate expression of OSMR, GP130, phosphorylated (P)-JAK2, and P-STAT3. Upon knockdown of OSMR or GP130, or the addition of AZD1480 or Stattic, P-JAK2 and P-STAT3 expression were decreased and osteogenic differentiation was reduced.

Conclusion

M1 Mφ-derived OSM induces osteogenic differentiation of LF cells and the JAK2/STAT3 signaling pathway plays an important role.

The neutrophil-osteogenic cell axis promotes bone destruction in periodontitis

The immune-stromal cell interactions play a key role in health and diseases. In periodontitis, the most prevalent infectious disease in humans, immune cells accumulate in the oral mucosa and promote bone destruction by inducing receptor activator of nuclear factor-κB ligand (RANKL) expression in osteogenic cells such as osteoblasts and periodontal ligament cells. However, the detailed mechanism underlying immune-bone cell interactions in periodontitis is not fully understood. Here, we performed single-cell RNA-sequencing analysis on mouse periodontal lesions and showed that neutrophil-osteogenic cell crosstalk is involved in periodontitis-induced bone loss. The periodontal lesions displayed marked infiltration of neutrophils, and in silico analyses suggested that the neutrophils interacted with osteogenic cells through cytokine production. Among the cytokines expressed in the periodontal neutrophils, oncostatin M (OSM) potently induced RANKL expression in the primary osteoblasts, and deletion of the OSM receptor in osteogenic cells significantly ameliorated periodontitis-induced bone loss. Epigenomic data analyses identified the OSM-regulated RANKL enhancer region in osteogenic cells, and mice lacking this enhancer showed decreased periodontal bone loss while maintaining physiological bone metabolism. These findings shed light on the role of neutrophils in bone regulation during bacterial infection, highlighting the novel mechanism underlying osteoimmune crosstalk.

Oncostatin M: Dual Regulator of the Skeletal and Hematopoietic Systems

PURPOSE OF THE REVIEW

The bone and hematopoietic tissues coemerge during development and are functionally intertwined throughout mammalian life. Oncostatin M (OSM) is an inflammatory cytokine of the interleukin-6 family produced by osteoblasts, bone marrow macrophages, and neutrophils. OSM acts via two heterodimeric receptors comprising GP130 with either an OSM receptor (OSMR) or a leukemia inhibitory factor receptor (LIFR). OSMR is expressed on osteoblasts, mesenchymal, and endothelial cells and mice deficient for the Osm or Osmr genes have both bone and blood phenotypes illustrating the importance of OSM and OSMR in regulating these two intertwined tissues.

RECENT FINDINGS

OSM regulates bone mass through signaling via OSMR, adaptor protein SHC1, and transducer STAT3 to both stimulate osteoclast formation and promote osteoblast commitment; the effect on bone formation is also supported by action through LIFR. OSM produced by macrophages is an important inducer of neurogenic heterotopic ossifications in peri-articular muscles following spinal cord injury. OSM produced by neutrophils in the bone marrow induces hematopoietic stem and progenitor cell proliferation in an indirect manner via OSMR expressed by bone marrow stromal and endothelial cells that form hematopoietic stem cell niches. OSM acts as a brake to therapeutic hematopoietic stem cell mobilization in response to G-CSF and CXCR4 antagonist plerixafor. Excessive OSM production by macrophages in the bone marrow is a key contributor to poor hematopoietic stem cell mobilization (mobilopathy) in people with diabetes. OSM and OSMR may also play important roles in the progression of several cancers. It is increasingly clear that OSM plays unique roles in regulating the maintenance and regeneration of bone, hematopoietic stem and progenitor cells, inflammation, and skeletal muscles. Dysregulated OSM production can lead to bone pathologies, defective muscle repair and formation of heterotopic ossifications in injured muscles, suboptimal mobilization of hematopoietic stem cells, exacerbated inflammatory responses, and anti-tumoral immunity. Ongoing research will establish whether neutralizing antibodies or cytokine traps may be useful to correct pathologies associated with excessive OSM production.

The future of artificial hibernation medicine: protection of nerves and organs after spinal cord injury

Spinal cord injury is a serious disease of the central nervous system involving irreversible nerve injury and various organ system injuries. At present, no effective clinical treatment exists. As one of the artificial hibernation techniques, mild hypothermia has preliminarily confirmed its clinical effect on spinal cord injury. However, its technical defects and barriers, along with serious clinical side effects, restrict its clinical application for spinal cord injury. Artificial hibernation is a future-oriented disruptive technology for human life support. It involves endogenous hibernation inducers and hibernation-related central neuromodulation that activate particular neurons, reduce the central constant temperature setting point, disrupt the normal constant body temperature, make the body "adapt" to the external cold environment, and reduce the physiological resistance to cold stimulation. Thus, studying the artificial hibernation mechanism may help develop new treatment strategies more suitable for clinical use than the cooling method of mild hypothermia technology. This review introduces artificial hibernation technologies, including mild hypothermia technology, hibernation inducers, and hibernation-related central neuromodulation technology. It summarizes the relevant research on hypothermia and hibernation for organ and nerve protection. These studies show that artificial hibernation technologies have therapeutic significance on nerve injury after spinal cord injury through inflammatory inhibition, immunosuppression, oxidative defense, and possible central protection. It also promotes the repair and protection of respiratory and digestive, cardiovascular, locomotor, urinary, and endocrine systems. This review provides new insights for the clinical treatment of nerve and multiple organ protection after spinal cord injury thanks to artificial hibernation. At present, artificial hibernation technology is not mature, and research faces various challenges. Nevertheless, the effort is worthwhile for the future development of medicine.

Neutrophil and NETosis Modulation in Traumatic Heterotopic Ossification

OBJECTIVE

To characterize the role of neutrophil extracellular traps (NETs) in heterotopic ossification (HO) formation and progression and to use mechanical and pharmacological methods to decrease NETosis and mitigate HO formation.

BACKGROUND

Traumatic HO is the aberrant osteochondral differentiation of mesenchymal progenitor cells after traumatic injury, burns, or surgery. While the innate immune response has been shown to be necessary for HO formation, the specific immune cell phenotype and function remain unknown. Neutrophils, one of the earliest immune cells to respond after HO-inducing injuries, can extrude DNA, forming highly inflammatory NETs. We hypothesized that neutrophils and NETs would be diagnostic biomarkers and therapeutic targets for the detection and mitigation of HO.

METHODS

C57BL6J mice underwent burn/tenotomy (a well-established mouse model of HO) or a non-HO-forming sham injury. These mice were either (1) ambulated ad libitum, (2) ambulated ad libitum with daily intraperitoneal hydroxychloroquine, ODN-2088 (both known to affect NETosis pathways), or control injections, or (3) had the injured hind limb immobilized. Single-cell analysis was performed to analyze neutrophils, NETosis, and downstream signaling after the HO-forming injury. Immunofluorescence microscopy was used to visualize NETosis at the HO site and neutrophils were identified using flow cytometry. Serum and cell lysates from HO sites were analyzed using enzyme-linked immunosorbent assay for myeloperoxidase-DNA and ELA2-DNA complexes to identify NETosis. Micro-computerized tomography was performed on all groups to analyze the HO volume.

RESULTS

Molecular and transcriptional analyses revealed the presence of NETs within the HO injury site, which peaked in the early phases after injury. These NETs were highly restricted to the HO site, with gene signatures derived from both in vitro NET induction and clinical neutrophil characterizations showing a high degree of NET "priming" at the site of injury, but not in neutrophils in the blood or bone marrow. Cell-cell communication analyses revealed that this localized NET formation coincided with high levels of toll-like receptor signaling specific to neutrophils at the injury site. Reducing the overall neutrophil abundance within the injury site, either pharmacologically through treatment with hydroxychloroquine, the toll-like receptor 9 inhibitor OPN-2088, or mechanical treatment with limb offloading, results in the mitigation of HO formation.

CONCLUSIONS

These data provide a further understanding of the ability of neutrophils to form NETs at the injury site, clarify the role of neutrophils in HO, and identify potential diagnostic and therapeutic targets for HO mitigation.

Coding and noncoding RNA profile of human heterotopic ossifications - Risk factors and biomarkers

Heterotopic ossification (HO) means the formation of bone in muscles and soft tissues, such as ligaments or tendons. HO could have a genetic history or develop after a traumatic event, as a result of muscle injury, fractures, burns, surgery, or neurological disorders. Many lines of evidence suggest that the formation of HO is related to the pathological differentiation of stem or progenitor cells present within soft tissues or mobilized from the bone marrow. The cells responsible for the initiation and progression of HO are generally called HO precursor cells. The exact mechanisms behind the development of HO are not fully understood. However, several factors have been identified as potential contributors. For example, local tissue injury and inflammation disturb soft tissue homeostasis. Inflammatory cells release growth factors and cytokines that promote osteogenic or chondrogenic differentiation of HO precursor cells. The bone morphogenetic protein (BMP) is one of the main factors involved in the development of HO. In this study, next-generation sequencing (NGS) and RT-qPCR were performed to analyze the differences in mRNA, miRNA, and lncRNA expression profiles between muscles, control bone samples, and HO samples coming from patients who underwent total hip replacement (THR). As a result, crucial changes in the level of gene expression between HO and healthy tissues were identified. The bioinformatic analysis allowed to describe the processes most severely impacted, as well as genes which level differed the most significantly between HO and control samples. Our analysis showed that the level of transcripts involved in leukocyte migration, differentiation, and activation, as well as markers of chronic inflammatory diseases, that is, miR-148, increased in HO, as compared to muscle. Furthermore, the levels of miR-195 and miR-143, which are involved in angiogenesis, were up-regulated in HO, as compared to bone. Thus, we suggested that inflammation and angiogenesis play an important role in HO formation. Importantly, we noticed that HO is characterized by a higher level of TLR3 expression, compared to muscle and bone. Thus, we suggest that infection may also be a risk factor in HO development. Furthermore, an increased level of transcripts coding proteins involved in osteogenesis and signaling pathways, such as ALPL, SP7, BGLAP, BMP8A, BMP8B, SMPD3 was noticed in HO, as compared to muscles. Interestingly, miR-99b, miR-146, miR-204, and LINC00320 were up-regulated in HO, comparing to muscles and bone. Therefore, we suggested that these molecules could be important biomarkers of HO formation and a potential target for therapies.

Bacterial Lipopolysaccharides Exacerbate Neurogenic Heterotopic Ossification Development

Neurogenic heterotopic ossifications (NHO) are heterotopic bones that develop in periarticular muscles after severe central nervous system (CNS) injuries. Several retrospective studies have shown that NHO prevalence is higher in patients who suffer concomitant infections. However, it is unclear whether these infections directly contribute to NHO development or reflect the immunodepression observed in patients with CNS injury. Using our mouse model of NHO induced by spinal cord injury (SCI) between vertebrae T11 to T13 , we demonstrate that lipopolysaccharides (LPS) from gram-negative bacteria exacerbate NHO development in a toll-like receptor-4 (TLR4)-dependent manner, signaling through the TIR-domain-containing adapter-inducing interferon-β (TRIF/TICAM1) adaptor rather than the myeloid differentiation primary response-88 (MYD88) adaptor. We find that T11 to T13 SCI did not significantly alter intestinal integrity nor cause intestinal bacteria translocation or endotoxemia, suggesting that NHO development is not driven by endotoxins from the gut in this model of SCI-induced NHO. Relevant to the human pathology, LPS increased expression of osteoblast markers in cultures of human fibro-adipogenic progenitors isolated from muscles surrounding NHO biopsies. In a case-control retrospective study in patients with traumatic brain injuries, infections with gram-negative Pseudomonas species were significantly associated with NHO development. Together these data suggest a functional association between gram-negative bacterial infections and NHO development and highlights infection management as a key consideration to avoid NHO development in patients. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Multifaceted oncostatin M: novel roles and therapeutic potential of the oncostatin M signaling in rheumatoid arthritis

Rheumatoid arthritis (RA) is a self-immune inflammatory disease characterized by joint damage. A series of cytokines are involved in the development of RA. Oncostatin M (OSM) is a pleiotropic cytokine that primarily activates the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) signaling pathway, the mitogen-activated protein kinase (MAPK) signaling pathway, and other physiological processes such as cell proliferation, inflammatory response, immune response, and hematopoiesis through its receptor complex. In this review, we first describe the characteristics of OSM and its receptor, and the biological functions of OSM signaling. Subsequently, we discuss the possible roles of OSM in the development of RA from clinical and basic research perspectives. Finally, we summarize the progress of clinical studies targeting OSM for the treatment of RA. This review provides researchers with a systematic understanding of the role of OSM signaling in RA, which can guide the development of drugs targeting OSM for the treatment of RA.

Spinal cord injury dysregulates fibro-adipogenic progenitors miRNAs signaling to promote neurogenic heterotopic ossifications

Neurogenic heterotopic ossifications are intramuscular bone formations developing following central nervous system injury. The pathophysiology is poorly understood and current treatments for this debilitating condition remain unsatisfying. Here we explored the role of miRNAs in a clinically relevant mouse model that combines muscle and spinal cord injury, and in patients' cells. We found an osteo-suppressive miRNAs response in injured muscle that was hindered when the spinal cord injury was associated. In isolated fibro-adipogenic progenitors from damaged muscle (cells at the origin of ossification), spinal cord injury induced a downregulation of osteo-suppressive miRNAs while osteogenic markers were overexpressed. The overexpression of selected miRNAs in patient's fibro-adipogenic progenitors inhibited mineralization and osteo-chondrogenic markers in vitro. Altogether, we highlighted an osteo-suppressive mechanism involving multiple miRNAs in response to muscle injury that prevents osteogenic commitment which is ablated by the neurologic lesion in heterotopic ossification pathogenesis. This provides new research hypotheses for preventive treatments.

Genetic insights into ossification of the posterior longitudinal ligament of the spine

Ossification of the posterior longitudinal ligament of the spine (OPLL) is an intractable disease leading to severe neurological deficits. Its etiology and pathogenesis are primarily unknown. The relationship between OPLL and comorbidities, especially type 2 diabetes (T2D) and high body mass index (BMI), has been the focus of attention; however, no trait has been proven to have a causal relationship. We conducted a meta-analysis of genome-wide association studies (GWASs) using 22,016 Japanese individuals and identified 14 significant loci, 8 of which were previously unreported. We then conducted a gene-based association analysis and a transcriptome-wide Mendelian randomization approach and identified three candidate genes for each. Partitioning heritability enrichment analyses observed significant enrichment of the polygenic signals in the active enhancers of the connective/bone cell group, especially H3K27ac in chondrogenic differentiation cells, as well as the immune/hematopoietic cell group. Single-cell RNA sequencing of Achilles tendon cells from a mouse Achilles tendon ossification model confirmed the expression of genes in GWAS and post-GWAS analyses in mesenchymal and immune cells. Genetic correlations with 96 complex traits showed positive correlations with T2D and BMI and a negative correlation with cerebral aneurysm. Mendelian randomization analysis demonstrated a significant causal effect of increased BMI and high bone mineral density on OPLL. We evaluated the clinical images in detail and classified OPLL into cervical, thoracic, and the other types. GWAS subanalyses identified subtype-specific signals. A polygenic risk score for BMI demonstrated that the effect of BMI was particularly strong in thoracic OPLL. Our study provides genetic insight into the etiology and pathogenesis of OPLL and is expected to serve as a basis for future treatment development.

Ethyl caffeate inhibits macrophage polarization via SIRT1/NF-κB to attenuate traumatic heterotopic ossification in mice

Heterotopic ossification (HO) denotes the presence of mature bone tissue in soft tissues or around joints. Inflammation is a key driver of traumatic HO, and macrophages play an important role in this process. Ethyl caffeate (ECF), a critical active compound found in Petunia, exerts significant anti-inflammatory effects. Herein, we established a mouse model of HO by transection of the Achilles tendon and back burn and found abundant macrophage infiltration in the early stage of HO, which decreased with time. In vitro and in vivo experiments indicated that ECF inhibited macrophage polarization, and mechanistic studies showed that it inhibited the SIRT1/NF-κB signalling pathway, thereby suppressing the release of downstream inflammatory cytokines. ECF reduced HO in mice, and its effect was comparable to indomethacin (INDO). In vitro studies revealed that ECF did not directly affect the mineralization of mesenchymal stem cells (MSCs) or osteogenic differentiation but inhibited these processes by reducing the level of inflammatory cytokines in the conditioned medium (CM). Thus, M1 macrophages may play a crucial role in the pathogenesis of HO, and ECF is a prospective candidate for the prevention of trauma-induced HO. DATA AVAILABILITY: Data will be made available on request.

Enoxaparin attenuates pyrrolizidine alkaloids-induced hepatic sinusoidal obstruction syndrome by inhibiting oncostatin M expression

BACKGROUND AND AIMS

The definitive treatment for pyrrolizidine alkaloids (PAs)-induced hepatic sinusoidal obstruction syndrome (HSOS) is not available. The effectiveness of anticoagulation therapy remains controversial. The efficacy of low molecular weight heparin (LMWH) should be investigated in patients and animal models, and the underlying mechanism should be explored.

METHODS

The prognosis of patients with PAs-HSOS who received anticoagulation therapy was retrospectively analysed. The effect of enoxaparin on the liver injury was determined in animal models of monocrotaline (MCT)-induced HSOS was determined, and the underlying mechanism was investigated using a murine model.

RESULTS

The cumulative survival rate of patients with PAs-induced HSOS was 60.00% and 90.90% in the non-anticoagulation group and anticoagulation group. Enoxaparin attenuated liver injury effectively in a rat model of MCT-induced HSOS. Additionally, the improvement of severe liver injury was observed in MCT-treated mice after the administration of enoxaparin (40 mg/kg). The alleviation of liver injury was observed in mice with hepatocyte-specific deletion of oncostatin M (Osm^△Hep ). In MCT-treated mice administrated with enoxaparin, no significant differences in liver injury were observed between Osm^△Hep mice and Osm^flox/flox mice. Additionally, adenovirus-mediated overexpression of Osm resulted in severe liver injury in MCT-induced mice after the administration of enoxaparin.

CONCLUSIONS

LMWH attenuated severe liver injury in patients with PAs-Induced HSOS and animal models of MCT-induced HSOS, which provides a rationale for the application of anticoagulation therapy.

Macrophage-Derived TGF-β and VEGF Promote the Progression of Trauma-Induced Heterotopic Ossification

Heterotopic ossification (HO) is a pathological bone formation process caused by musculoskeletal trauma. HO is characterized by aberrant endochondral ossification and angiogenesis. Our previous studies have indicated that macrophage inflammation is involved in traumatic HO formation. In this study, we found that macrophage infiltration and TGF-β signaling activation are presented in human HO. Depletion of macrophages effectively suppressed traumatic HO formation in a HO mice model, and macrophage depletion significantly inhibited the activation of TGF-β/Smad2/3 signaling. In addition, the TGF-β blockade created by a neutralizing antibody impeded ectopic bone formation in vivo. Notably, endochondral ossification and angiogenesis are attenuated following macrophage depletion or TGF-β inhibition. Furthermore, our observations on macrophage polarization revealed that M2 macrophages, rather than M1 macrophages, play a critical role in supporting HO development by enhancing the osteogenic and chondrogenic differentiation of mesenchymal stem cells. Our findings on ectopic bone formation in HO patients and the mice model indicate that M2 macrophages are an important contributor for HO development, and that inhibition of M2 polarization or TGF-β activity may be a potential method of therapy for traumatic HO.

Fetuin-A is an immunomodulator and a potential therapeutic option in BMP4-dependent heterotopic ossification and associated bone mass loss

Heterotopic ossification (HO) is the abnormal formation of bone in extraskeletal sites. However, the mechanisms linking HO pathogenesis with bone mass dysfunction remain unclear. Here, we showed that mice harboring injury-induced and BMP4-dependent HO exhibit bone mass loss similar to that presented by patients with HO. Moreover, we found that injury-induced hyperinflammatory responses at the injury site triggered HO initiation but did not result in bone mass loss at 1 day post-injury (dpi). In contrast, a suppressive immune response promoted HO propagation and bone mass loss by 7 dpi. Correcting immune dysregulation by PD1/PDL1 blockade dramatically alleviated HO propagation and bone mass loss. We further demonstrated that fetuin-A (FetA), which has been frequently detected in HO lesions but rarely observed in HO-adjacent normal bone, acts as an immunomodulator to promote PD1 expression and M2 macrophage polarization, leading to immunosuppression. Intervention with recombinant FetA inhibited hyperinflammation and prevented HO and associated bone mass loss. Collectively, our findings provide new insights into the osteoimmunological interactions that occur during HO formation and suggest that FetA is an immunosuppressor and a potential therapeutic option for the treatment of HO.

Oncostatin M: Risks and Benefits of a Novel Therapeutic Target for Atherosclerosis

BACKGROUND

Cardiovascular disease (CVD) is a leading cause of death worldwide. It is predicted that approximately 23.6 million people will die from CVDs annually by 2030. Therefore, there is a great need for an effective therapeutic approach to combat this disease. The European Cardiovascular Target Discovery (CarTarDis) consortium identified Oncostatin M (OSM) as a potential therapeutic target for atherosclerosis. The benefits of modulating OSM - an interleukin (IL)-6 family cytokine - have since been studied for multiple indications. However, as decades of high attrition rates have stressed, the success of a drug target is determined by the fine balance between benefits and the risk of adverse events. Safety issues should therefore not be overlooked.

OBJECTIVE

In this review, a risk/benefit analysis is performed on OSM inhibition in the context of atherosclerosis treatment. First, OSM signaling characteristics and its role in atherosclerosis are described. Next, an overview of in vitro, in vivo, and clinical findings relating to both the benefits and risks of modulating OSM in major organ systems is provided. Based on OSM's biological function and expression profile as well as drug intervention studies, safety concerns of inhibiting this target have been identified, assessed, and ranked for the target population.

CONCLUSION

While OSM may be of therapeutic value in atherosclerosis, drug development should also focus on de-risking the herein identified major safety concerns: tissue remodeling, angiogenesis, bleeding, anemia, and NMDA- and glutamate-induced neurotoxicity. Close monitoring and/or exclusion of patients with various comorbidities may be required for optimal therapeutic benefit.

G-CSF Receptor Deletion Amplifies Cortical Bone Dysfunction in Mice With STAT3 Hyperactivation in Osteocytes

Bone strength is determined by the structure and composition of its thickened outer shell (cortical bone), yet the mechanisms controlling cortical consolidation are poorly understood. Cortical bone maturation depends on SOCS3-mediated suppression of IL-6 cytokine-induced STAT3 phosphorylation in osteocytes, the cellular network embedded in bone matrix. Because SOCS3 also suppresses granulocyte-colony-stimulating factor receptor (G-CSFR) signaling, we here tested whether global G-CSFR (Csf3r) ablation altereed bone structure in male and female mice lacking SOCS3 in osteocytes, (Dmp1^Cre :Socs3^f/f mice). Dmp1^Cre :Socs3^f/f :Csf3r^-/- mice were generated by crossing Dmp1^Cre :Socs3^f/f mice with Csf3r^-/- mice. Although G-CSFR is not expressed in osteocytes, Csf3r deletion further delayed cortical consolidation in Dmp1^Cre :Socs3^f/f mice. Micro-CT images revealed extensive, highly porous low-density bone, with little true cortex in the diaphysis, even at 26 weeks of age; including more low-density bone and less high-density bone in Dmp1^Cre :Socs3^f/f :Csf3r^-/- mice than controls. By histology, the area where cortical bone would normally be found contained immature compressed trabecular bone in Dmp1^Cre :Socs3^f/f :Csf3r^-/- mice and greater than normal levels of intracortical osteoclasts, extensive new woven bone formation, and the presence of more intracortical blood vessels than the already high levels observed in Dmp1^Cre :Socs3^f/f controls. qRT-PCR of cortical bone from Dmp1^Cre :Socs3^f/f :Csf3r^-/- mice also showed more than a doubling of mRNA levels for osteoclasts, osteoblasts, RANKL, and angiogenesis markers. The further delay in cortical bone maturation was associated with significantly more phospho-STAT1 and phospho-STAT3-positive osteocytes, and a threefold increase in STAT1 and STAT3 target gene mRNA levels, suggesting G-CSFR deletion further increases STAT signaling beyond that of Dmp1^Cre :Socs3^f/f bone. G-CSFR deficiency therefore promotes STAT1/3 signaling in osteocytes, and when SOCS3 negative feedback is absent, elevated local angiogenesis, bone resorption, and bone formation delays cortical bone consolidation. This points to a critical role of G-CSF in replacing condensed trabecular bone with lamellar bone during cortical bone formation. © 2022 American Society for Bone and Mineral Research (ASBMR).

Effectiveness of Prophylactic Interventions in Neurogenic Heterotopic Ossification (NHO): A Systematic Review

Neurogenic heterotopic ossification (NHO) is the formation of mature lamellar bone in peri-articular tissues following a neurological insult, most commonly traumatic brain injury (TBI) or spinal cord injury (SCI). NHO is a debilitating condition associated with significant morbidity and reduced quality of life. However, its pathophysiology remains poorly understood. While surgery is the mainstay of treatment once NHO has been diagnosed, prophylactic options are limited and not well studied. This review aimed to determine the efficacy of various interventions used in the primary prevention of NHO. We conducted an electronic literature search using five databases (PubMed, Embase, ScienceDirect, Cochrane Library, and Cumulative Index to Nursing and Allied Health Literature (CINAHL)) for records published until April 10, 2022. We identified 2,610 potentially eligible records across all databases. Nine reports met our eligibility criteria and were included in this review. Four were clinical trials (three randomized control trials, one nonrandomized trial), four were observational studies, and one was a systematic review/meta-analysis. The medications/interventions used included: warfarin, pulse low-intensity electromagnetic field therapy (PLIMF), bisphosphonates, and nonsteroidal anti-inflammatory drugs (NSAIDs). We did not find conclusive evidence to recommend the use of bisphosphonates and warfarin in the prevention of NHO. On the contrary, we found NSAIDs and PLIMF as effective prophylactic options based on the results of high-quality randomized control trials. Further prospective randomized studies with prolonged follow-ups are needed to confirm the long-term efficacy of these preventive interventions.

Contemporary perspectives on heterotopic ossification

Heterotopic ossification (HO) is the formation of ectopic bone that is primarily genetically driven (fibrodysplasia ossificans progressiva [FOP]) or acquired in the setting of trauma (tHO). HO has undergone intense investigation, especially over the last 50 years, as awareness has increased around improving clinical technologies and incidence, such as with ongoing wartime conflicts. Current treatments for tHO and FOP remain prophylactic and include NSAIDs and glucocorticoids, respectively, whereas other proposed therapeutic modalities exhibit prohibitive risk profiles. Contemporary studies have elucidated mechanisms behind tHO and FOP and have described new distinct niches independent of inflammation that regulate ectopic bone formation. These investigations have propagated a paradigm shift in the approach to treatment and management of a historically difficult surgical problem, with ongoing clinical trials and promising new targets.

Stimulation of Osteoclast Formation by Oncostatin M and the Role of WNT16 as a Negative Feedback Regulator

Oncostatin M (OSM), which belongs to the IL-6 family of cytokines, is the most potent and effective stimulator of osteoclast formation in this family, as assessed by different in vitro assays. Osteoclastogenesis induced by the IL-6 type of cytokines is mediated by the induction and paracrine stimulation of the osteoclastogenic cytokine receptor activator of nuclear factor κ-B ligand (RANKL), expressed on osteoblast cell membranes and targeting the receptor activator of nuclear factor κ-B (RANK) on osteoclast progenitor cells. The potent effect of OSM on osteoclastogenesis is due to an unusually robust induction of RANKL in osteoblasts through the OSM receptor (OSMR), mediated by a JAK-STAT/MAPK signaling pathway and by unique recruitment of the adapter protein Shc1 to the OSMR. Gene deletion of Osmr in mice results in decreased numbers of osteoclasts and enhanced trabecular bone caused by increased trabecular thickness, indicating that OSM may play a role in physiological regulation of bone remodeling. However, increased amounts of OSM, either through administration of recombinant protein or of adenoviral vectors expressing Osm, results in enhanced bone mass due to increased bone formation without any clear sign of increased osteoclast numbers, a finding which can be reconciled by cell culture experiments demonstrating that OSM can induce osteoblast differentiation and stimulate mineralization of bone nodules in such cultures. Thus, in vitro studies and gene deletion experiments show that OSM is a stimulator of osteoclast formation, whereas administration of OSM to mice shows that OSM is not a strong stimulator of osteoclastogenesis in vivo when administered to adult animals. These observations could be explained by our recent finding showing that OSM is a potent stimulator of the osteoclastogenesis inhibitor WNT16, acting in a negative feedback loop to reduce OSM-induced osteoclast formation.

Interleukin-1 Is Overexpressed in Injured Muscles Following Spinal Cord Injury and Promotes Neurogenic Heterotopic Ossification

Neurogenic heterotopic ossifications (NHOs) form in periarticular muscles after severe spinal cord (SCI) and traumatic brain injuries. The pathogenesis of NHO is poorly understood with no effective preventive treatment. The only curative treatment remains surgical resection of pathological NHOs. In a mouse model of SCI-induced NHO that involves a transection of the spinal cord combined with a muscle injury, a differential gene expression analysis revealed that genes involved in inflammation such as interleukin-1β (IL-1β) were overexpressed in muscles developing NHO. Using mice knocked-out for the gene encoding IL-1 receptor (IL1R1) and neutralizing antibodies for IL-1α and IL-1β, we show that IL-1 signaling contributes to NHO development after SCI in mice. Interestingly, other proteins involved in inflammation that were also overexpressed in muscles developing NHO, such as colony-stimulating factor-1, tumor necrosis factor, or C-C chemokine ligand-2, did not promote NHO development. Finally, using NHO biopsies from SCI and TBI patients, we show that IL-1β is expressed by CD68⁺ macrophages. IL-1α and IL-1β produced by activated human monocytes promote calcium mineralization and RUNX2 expression in fibro-adipogenic progenitors isolated from muscles surrounding NHOs. Altogether, these data suggest that interleukin-1 promotes NHO development in both humans and mice. © 2021 American Society for Bone and Mineral Research (ASBMR).

Spinal cord injury reprograms muscle fibroadipogenic progenitors to form heterotopic bones within muscles

The cells of origin of neurogenic heterotopic ossifications (NHOs), which develop frequently in the periarticular muscles following spinal cord injuries (SCIs) and traumatic brain injuries, remain unclear because skeletal muscle harbors two progenitor cell populations: satellite cells (SCs), which are myogenic, and fibroadipogenic progenitors (FAPs), which are mesenchymal. Lineage-tracing experiments using the Cre recombinase/LoxP system were performed in two mouse strains with the fluorescent protein ZsGreen specifically expressed in either SCs or FAPs in skeletal muscles under the control of the Pax7 or Prrx1 gene promoter, respectively. These experiments demonstrate that following muscle injury, SCI causes the upregulation of PDGFRα expression on FAPs but not SCs and the failure of SCs to regenerate myofibers in the injured muscle, with reduced apoptosis and continued proliferation of muscle resident FAPs enabling their osteogenic differentiation into NHOs. No cells expressing ZsGreen under the Prrx1 promoter were detected in the blood after injury, suggesting that the cells of origin of NHOs are locally derived from the injured muscle. We validated these findings using human NHO biopsies. PDGFRα⁺ mesenchymal cells isolated from the muscle surrounding NHO biopsies could develop ectopic human bones when transplanted into immunocompromised mice, whereas CD56⁺ myogenic cells had a much lower potential. Therefore, NHO is a pathology of the injured muscle in which SCI reprograms FAPs to undergo uncontrolled proliferation and differentiation into osteoblasts.

Ossifying pilomatricoma and a novel hypothesis for its pathogenesis: A case report and comprehensive literature review

RATIONALE

Pilomatricoma is a benign skin appendageal tumor derived from hair follicle matrix cells that commonly affects the head, neck, and upper extremities of the pediatric population. Since the original tumor description, diverse variants have been reported in the literature. Pilomatricoma with florid osseous metaplasia is described as an ossifying pilomatricoma and is recognized as a distinct variant of this benign tumor. However, the pathogenesis of this variant remains unclear. In this study, we present an uncommon case of ossifying pilomatricoma and address the pathogenesis of metaplastic ossification through a comprehensive literature review.

PATIENT CONCERNS

A 14-year-old boy presented with an asymptomatic protuberant mass in the preauricular region.

DIAGNOSIS

Based on its clinicopathological features, we diagnosed the lesion as an ossifying pilomatricoma.

INTERVENTIONS AND OUTCOMES

The lesion was surgically removed under local anesthesia. The postoperative course was uneventful during the 6-month postoperative follow-up.

LESSONS

We suggest that metaplastic ossification in ossifying pilomatricoma represents another feature of foreign body reaction to keratinous materials containing shadow cells in old lesions and a walling-off phenomenon to prevent exposure of surrounding tissues to keratinous materials.

Lymphocytes Are Not Required for Neurogenic Heterotopic Ossification Development after Spinal Cord Injury

Neurogenic heterotopic ossifications (NHOs) are incapacitating complications of traumatic brain and spinal cord injuries (SCI) that manifest as abnormal bone formation in periarticular muscles. Using a unique model of NHO after SCI in genetically unmodified mice, we have previously established that the innate immune system plays a key driving role in NHO pathogenesis. The role of adaptive immune cells in NHO pathogenesis, however, remains unexplored in this model. Here we established that B lymphocytes were reduced in the spleen and blood after SCI and increased in muscles of mice in which NHO develops, whereas minimal changes in T cell frequencies were noted. Interestingly, Rag1^-/- mice lacking mature T and B lymphocytes, developed NHO, similar to wild-type mice. Finally, mice that underwent splenectomy before SCI and muscle damage also developed NHO to the same extent as non-splenectomized SCI controls. Overall, our findings show that functional T and B lymphocytes have minimal influence or dispensable contributions to NHO development after experimental SCI in mice.

Biomarkers from Secondary Complications in Spinal Cord Injury

PURPOSE OF REVIEW

In the USA, spinal cord injury (SCI) occurs in 40 people per million every year due to events such as car accidents, falls, violence, or sports injury. Secondary complications that arise from SCI are life-threatening and should be treated as early as possible. In some cases, it is not completely obvious what complication a patient may have until it is too late. Therefore, biomarkers are required to assess the levels of secondary complications after SCI. As there are several complications that pose different warning signs, different biomarkers may be beneficial in early detection, maintenance, and long-term care for patients with SCI.

RECENT FINDINGS

Numerous studies have been conducted on biomarkers in various SCI and its related complications, such as neuropathic pain and deep vein thrombosis. In recent years, research has expanded with biomarkers discovered by cellular and molecular, genome-wide transcriptomic analysis, bioinformatics, and clinical studies. Biomarkers have allowed early prediction of the severity of secondary complications due to SCI.

SUMMARY

In this review, we summarize recent studies on the common biomarkers for the secondary complications related to SCI. We highlight the reliable biomarkers that have been tested, e.g., sclerostin, NGF, D-dimer, oncostatin M (OSM), microbiota, and C-reactive protein, which are valuable and with clinical importance. This review also emphasizes continuing research in biomarkers as they can provide valuable cellular and molecular insight into secondary complications after SCI.

Oncostatin M regulates hematopoietic stem cell (HSC) niches in the bone marrow to restrict HSC mobilization

We show that pro-inflammatory oncostatin M (OSM) is an important regulator of hematopoietic stem cell (HSC) niches in the bone marrow (BM). Treatment of healthy humans and mice with granulocyte colony-stimulating factor (G-CSF) dramatically increases OSM release in blood and BM. Using mice null for the OSM receptor (OSMR) gene, we demonstrate that OSM provides a negative feed-back acting as a brake on HSPC mobilization in response to clinically relevant mobilizing molecules G-CSF and CXCR4 antagonist. Likewise, injection of a recombinant OSM molecular trap made of OSMR complex extracellular domains enhances HSC mobilization in poor mobilizing C57BL/6 and NOD.Cg-Prkdc^scidIl2rg^tm1Wjl/SzJ mice. Mechanistically, OSM attenuates HSC chemotactic response to CXCL12 and increases HSC homing to the BM signaling indirectly via BM endothelial and mesenchymal cells which are the only cells expressing OSMR in the BM. OSM up-regulates E-selectin expression on BM endothelial cells indirectly increasing HSC proliferation. RNA sequencing of HSCs from Osmr^-/- and wild-type mice suggest that HSCs have altered cytoskeleton reorganization, energy usage and cycling in the absence of OSM signaling in niches. Therefore OSM is an important regulator of HSC niche function restraining HSC mobilization and anti-OSM therapy combined with current mobilizing regimens may improve HSPC mobilization for transplantation.

Changes of Migration, Immunoregulation and Osteogenic Differentiation of Mesenchymal Stem Cells in Different Stages of Inflammation

Bone infection has always been the focus of orthopedic research. Mesenchymal stem cells (MSCs) are the natural progenitors of osteoblasts, and the process of osteogenesis is triggered in response to different signals from the extracellular matrix. MSCs exert important functions including secretion and immune regulation and also play a key role in bone regeneration. The biological behavior of MSCs in acute and chronic inflammation, especially the transformation between acute inflammation and chronic inflammation, has aroused great interest among researchers. This paper reviews the recent literature and summarizes the behavior and biological characteristics of MSCs in acute and chronic inflammation to stimulate further research on MSCs and treatment of bone diseases.

Murine Oncostatin M Has Opposing Effects on the Proliferation of OP9 Bone Marrow Stromal Cells and NIH/3T3 Fibroblasts Signaling through the OSMR

The IL-6 family cytokine Oncostatin M (OSM) is involved in cell development, growth, hematopoiesis, inflammation, and cancer. Intriguingly, OSM has proliferative and antiproliferative effects depending on the target cell. The molecular mechanisms underlying these opposing effects are not fully understood. Previously, we found OSM upregulation in different myeloproliferative syndromes. However, OSM receptor (OSMR) expression was detected on stromal cells but not the malignant cells themselves. In the present study, we, therefore, investigated the effect of murine OSM (mOSM) on proliferation in stromal and fibroblast cell lines. We found that mOSM impairs the proliferation of bone marrow (BM) stromal cells, whereas fibroblasts responded to mOSM with increased proliferation. When we set out to reveal the mechanisms underlying these opposing effects, we detected increased expression of the OSM receptors OSMR and LIFR in stromal cells. Interestingly, Osmr knockdown and Lifr overexpression attenuated the OSM-mediated effect on proliferation in both cell lines indicating that mOSM affected the proliferation signaling mainly through the OSMR. Furthermore, mOSM induced activation of the JAK-STAT, PI3K-AKT, and MAPK-ERK pathways in OP9 and NIH/3T3 cells with differences in total protein levels between the two cell lines. Our findings offer new insights into the regulation of proliferation by mOSM.

Macrophages in heterotopic ossification: from mechanisms to therapy

Heterotopic ossification (HO) is the formation of extraskeletal bone in non-osseous tissues. It is caused by an injury that stimulates abnormal tissue healing and regeneration, and inflammation is involved in this process. It is worth noting that macrophages are crucial mediators of inflammation. In this regard, abundant macrophages are recruited to the HO site and contribute to HO progression. Macrophages can acquire different functional phenotypes and promote mesenchymal stem cell (MSC) osteogenic differentiation, chondrogenic differentiation, and angiogenesis by expressing cytokines and other factors such as the transforming growth factor-β1 (TGF-β1), bone morphogenetic protein (BMP), activin A (Act A), oncostatin M (OSM), substance P (SP), neurotrophin-3 (NT-3), and vascular endothelial growth factor (VEGF). In addition, macrophages significantly contribute to the hypoxic microenvironment, which primarily drives HO progression. Thus, these have led to an interest in the role of macrophages in HO by exploring whether HO is a "butterfly effect" event. Heterogeneous macrophages are regarded as the "butterflies" that drive a sequence of events and ultimately promote HO. In this review, we discuss how the recruitment of macrophages contributes to HO progression. In particular, we review the molecular mechanisms through which macrophages participate in MSC osteogenic differentiation, angiogenesis, and the hypoxic microenvironment. Understanding the diverse role of macrophages may unveil potential targets for the prevention and treatment of HO.

Macrophage-Mediated Bone Formation in Scaffolds Modified With MSC-Derived Extracellular Matrix Is Dependent on the Migration Inhibitory Factor Signaling Pathway

The positive role of macrophages in the osteogenesis of mesenchymal stem cells (MSCs) has been a recent research focus. On the other hand, MSCs could carefully regulate the paracrine molecules derived from macrophages. Human umbilical cord mesenchymal stem cells (hucMSCs) can reduce the secretion of inflammatory factors from macrophages to improve injury healing. hucMSC-derived extracellular matrix (hucMSC-ECM) has the similar effect to hucMSCs, which could combat the inflammatory response of macrophages. Additionally, MSC-derived extracellular matrix also enhanced bone regeneration by inhibiting osteoclastic differentiation of monocyte/macrophage lineage. However, whether hucMSC-ECM could improve bone formation by guiding macrophage-induced osteogenic differentiation of MSCs is unknown. Here, we present decalcified bone scaffolds modified by hucMSC-derived extracellular matrix (DBM-ECM), which maintained multiple soluble cytokines from hucMSCs, including macrophage migration inhibitory factor (MIF). Compared with DBM, the DBM-ECM scaffolds induced bone formation in an improved heterotopic ossification model of severe combined immunodeficiency (SCID) mice in a macrophage-dependent manner. Macrophages cocultured with DBM-ECM expressed four osteoinductive cytokines (BMP2, FGF2, TGFβ3 and OSM), which were screened out by RNA sequencing and measured by qPCR and western blot. The conditioned medium from macrophages cocultured with DBM-ECM improved the osteogenic differentiation of hBMSCs. Furthermore, DBM-ECM activated CD74/CD44 (the typical MIF receptors) signal transduction in macrophages, including phosphorylation of P38 and dephosphorylation of c-jun. On the other side, the inhibitory effects of the DBM-ECM scaffolds with a deficient of MIF on osteogenesis in vitro and in vivo revealed that macrophage-mediated osteogenesis depended on MIF/CD74 signal transduction. The results of this study indicate that the coordinated crosstalk of macrophages and MSCs plays a key role on bone regeneration, with an emphasis on hucMSC-ECM constructing a macrophage-derived osteoinductive microenvironment.

Low expression of TCP1 (T-Complex 1) and PSMC1 (Proteasome 26S subunit, ATPase 1) in heterotopic ossification during ankylosing spondylitis

Heterotopic ossification (HO) is frequently seen in patients with spinal injuries. Therefore, this study aimed to characterize the association of HO with ankylosing spondylitis (AS) through gene expression profiling. The human transcriptomic datasets (GSE73754 and GSE94683) were obtained from the Gene Expression Omnibus database for analysis. Overlapping differentially expressed genes (DEGs) were identified between AS and HO disease states. Subsequently, weighted gene co-expression network analysis (WGCNA) was performed for constructing and identifying hub genes for each condition. Finally, a consensus of the overlapping DEGs and the hub genes in AS and HO was taken for determining the key genes involved in AS-induced HO. Quantitative real-time polymerase chain reaction and western blotting were used to detect the mRNA and protein expression levels in mesenchymal stem cells of AS patients and controls. Additionally, immunohistochemistry was performed on interspinous ligament samples for experimental validation of genes. DEG analysis identified 355 overlapping genes between HO and AS. WGCNA indicated that the salmon module of the 22 modules constructed, was most significantly correlated with AS-induced HO. Subsequently, Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analysis of the salmon module indicated the presence of genes enriched in proteasome regulatory particle and proteasome pathways. mRNA expression analysis identified TCP1 and PSMC1 as the key genes in AS-induced HO. Further validation of these genes could help elucidate their role in the complex association of AS and HO.

Senescent immune cells release grancalcin to promote skeletal aging

Skeletal aging is characterized by low bone turnover and marrow fat accumulation. However, the underlying mechanism for this imbalance is unclear. Here, we show that during aging in rats and mice proinflammatory and senescent subtypes of immune cells, including macrophages and neutrophils, accumulate in the bone marrow and secrete abundant grancalcin. The injection of recombinant grancalcin into young mice was sufficient to induce premature skeletal aging. In contrast, genetic deletion of Gca in neutrophils and macrophages delayed skeletal aging. Mechanistically, we found that grancalcin binds to the plexin-b2 receptor and partially inactivates its downstream signaling pathways, thus repressing osteogenesis and promoting adipogenesis of bone marrow mesenchymal stromal cells. Heterozygous genetic deletion of Plexnb2 in skeletal stem cells abrogated the improved bone phenotype of Gca-knockout mice. Finally, we developed a grancalcin-neutralizing antibody and showed that its treatment of older mice improved bone health. Together, our data suggest that grancalcin could be a potential target for the treatment of age-related osteoporosis.

WNT16 is Robustly Increased by Oncostatin M in Mouse Calvarial Osteoblasts and Acts as a Negative Feedback Regulator of Osteoclast Formation Induced by Oncostatin M

Background

Bone loss is often observed adjacent to inflammatory processes. The WNT signaling pathways have been implicated as novel regulators of both immune responses and bone metabolism. WNT16 is important for cortical bone mass by inhibiting osteoclast differentiation, and we have here investigated the regulation of WNT16 by several members of the pro-inflammatory gp130 cytokine family.

Methods

The expression and regulation of Wnt16 in primary murine cells were studied by qPCR, scRNAseq and in situ hybridization. Signaling pathways were studied by siRNA silencing. The importance of oncostatin M (OSM)-induced WNT16 expression for osteoclastogenesis was studied in cells from Wnt16-deficient and wild-type mice.

Results

We found that IL-6/sIL-6R and OSM induce the expression of Wnt16 in primary mouse calvarial osteoblasts, with OSM being the most robust stimulator. The induction of Wnt16 by OSM was dependent on gp130 and OSM receptor (OSMR), and downstream signaling by the SHC1/STAT3 pathway, but independent of ERK. Stimulation of the calvarial cells with OSM resulted in enhanced numbers of mature, oversized osteoclasts when cells were isolated from Wnt16 deficient mice compared to cells from wild-type mice. OSM did not affect Wnt16 mRNA expression in bone marrow cell cultures, explained by the finding that Wnt16 and Osmr are expressed in distinctly different cells in bone marrow, nor was osteoclast differentiation different in OSM-stimulated bone marrow cell cultures isolated from Wnt16^−/- or wild-type mice. Furthermore, we found that Wnt16 expression is substantially lower in cells from bone marrow compared to calvarial osteoblasts.

Conclusion

These findings demonstrate that OSM is a robust stimulator of Wnt16 mRNA in calvarial osteoblasts and that WNT16 acts as a negative feedback regulator of OSM-induced osteoclast formation in the calvarial bone cells, but not in the bone marrow.

Neurogenic heterotopic ossification in the upper limb

Neurogenic heterotopic ossifications (NHOs) are periarticular ectopic ossifications that frequently develop after a central nervous system injury, most often a traumatic one. They limit range of motion and cause pain, interfering with limb positioning and function, whether active or passive. Highly described in the lower limbs, NHOs can also develop in the upper limb, with specific characteristics depending on their location. This article provides a summary of the diagnostic and therapeutic management of NHOs in the upper limb, based on the current literature.

Beyond the Brain: Peripheral Interactions after Traumatic Brain Injury

Traumatic brain injury (TBI) is a leading cause of death and disability, and there are currently no pharmacological treatments known to improve patient outcomes. Unquestionably, contributing toward a lack of effective treatments is the highly complex and heterogenous nature of TBI. In this review, we highlight the recent surge of research that has demonstrated various central interactions with the periphery as a potential major contributor toward this heterogeneity and, in particular, the breadth of research from Australia. We describe the growing evidence of how extracranial factors, such as polytrauma and infection, can significantly alter TBI neuropathology. In addition, we highlight how dysregulation of the autonomic nervous system and the systemic inflammatory response induced by TBI can have profound pathophysiological effects on peripheral organs, such as the heart, lung, gastrointestinal tract, liver, kidney, spleen, and bone. Collectively, this review firmly establishes TBI as a systemic condition. Further, the central and peripheral interactions that can occur after TBI must be further explored and accounted for in the ongoing search for effective treatments.

Intratumoral injection of caerin 1.1 and 1.9 peptides increases the efficacy of vaccinated TC-1 tumor-bearing mice with PD-1 blockade by modulating macrophage heterogeneity and the activation of CD8+ T cells in the tumor microenvironment

OBJECTIVES

Developing a vaccine formula that alters the tumor-infiltrating lymphocytes to be more immune active against a tumor is key to the improvement of clinical responses to immunotherapy. Here, we demonstrate that, in conjunction with E7 antigen-specific immunotherapy, and IL-10 and PD-1 blockade, intratumoral administration of caerin 1.1/1.9 peptides improves TC-1 tumor microenvironment (TME) to be more immune active than injection of a control peptide.

METHODS

We compared the survival time of vaccinated TC-1 tumor-bearing mice with PD-1 and IL-10 blockade, in combination with a further injection of caerin 1.1/1.9 or control peptides. The tumor-infiltrating haematopoietic cells were examined by flow cytometry. Single-cell transcriptomics and proteomics were used to quantify changes in cellular activity across different cell types within the TME.

RESULTS

The injection of caerin 1.1/1.9 increased the efficacy of vaccinated TC-1 tumor-bearing mice with anti-PD-1 treatment and largely expanded the populations of macrophages and NK cells with higher immune activation level, while reducing immunosuppressive macrophages. More activated CD8+ T cells were induced with higher populations of memory and effector-memory CD8+ T subsets. Computational integration of the proteome with the single-cell transcriptome supported activation of Stat1-modulated apoptosis and significant reduction in immune-suppressive B-cell function following caerin 1.1 and 1.9 treatment.

CONCLUSIONS

Caerin 1.1/1.9-containing treatment results in improved antitumor responses. Harnessing the novel candidate genes preferentially enriched in the immune active cell populations may allow further exploration of distinct macrophages, T cells and their functions in TC-1 tumors.

Potential genes and pathways associated with heterotopic ossification derived from analyses of gene expression profiles

Background

Heterotopic ossification (HO) represents pathological lesions that refer to the development of heterotopic bone in extraskeletal tissues around joints. This study investigates the genetic characteristics of bone marrow mesenchymal stem cells (BMSCs) from HO tissues and explores the potential pathways involved in this ailment.

Methods

Gene expression profiles (GSE94683) were obtained from the Gene Expression Omnibus (GEO), including 9 normal specimens and 7 HO specimens, and differentially expressed genes (DEGs) were identified. Then, protein–protein interaction (PPI) networks and Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were performed for further analysis.

Results

In total, 275 DEGs were differentially expressed, of which 153 were upregulated and 122 were downregulated. In the biological process (BP) category, the majority of DEGs, including EFNB3, UNC5C, TMEFF2, PTH2, KIT, FGF13, and WISP3, were intensively enriched in aspects of cell signal transmission, including axon guidance, negative regulation of cell migration, peptidyl-tyrosine phosphorylation, and cell-cell signaling. Moreover, KEGG analysis indicated that the majority of DEGs, including EFNB3, UNC5C, FGF13, MAPK10, DDIT3, KIT, COL4A4, and DKK2, were primarily involved in the mitogen-activated protein kinase (MAPK) signaling pathway, Ras signaling pathway, phosphatidylinositol-3-kinase/protein kinase B (PI3K/Akt) signaling pathway, and Wnt signaling pathway. Ten hub genes were identified, including CX3CL1, CXCL1, ADAMTS3, ADAMTS16, ADAMTSL2, ADAMTSL3, ADAMTSL5, PENK, GPR18, and CALB2.

Conclusions

This study presented novel insight into the pathogenesis of HO. Ten hub genes and most of the DEGs intensively involved in enrichment analyses may be new candidate targets for the prevention and treatment of HO in the future.

Local and Systemic Factors Drive Ectopic Osteogenesis in Regenerating Muscles of Spinal-Cord-Injured Mice in a Lesion-Level-Dependent Manner

Neuroimmune dysfunction is thought to promote the development of several acute and chronic complications in spinal cord injury (SCI) patients. Putative roles for adrenal stress hormones and catecholamines are increasingly being recognized, yet how these adversely affect peripheral tissue homeostasis and repair under SCI conditions remains elusive. Here, we investigated their influence in a mouse model of SCI with acquired neurogenic heterotopic ossification. We show that spinal cord lesions differentially influence muscular regeneration in a level-dependent manner and through a complex multi-step process that creates an osteopermissive environment within the first hours of injury. This cascade of events is shown to critically involve adrenergic signals and drive the acute release of the neuropeptide, substance P. Our findings generate new insights into the kinetics and processes that govern SCI-induced deregulations in skeletal muscle homeostasis and regeneration, thereby aiding the development of sequential therapeutic strategies that can prevent or attenuate neuromusculoskeletal complications in SCI patients.

Role of macrophages and phagocytes in orchestrating normal and pathologic hematopoietic niches

The bone marrow (BM) contains a mosaic of niches specialized in supporting different maturity stages of hematopoietic stem and progenitor cells such as hematopoietic stem cells and myeloid, lymphoid, and erythroid progenitors. Recent advances in BM imaging and conditional gene knockout mice have revealed that niches are a complex network of cells of mesenchymal, endothelial, neuronal, and hematopoietic origins, together with local physicochemical parameters. Within these complex structures, phagocytes, such as neutrophils, macrophages, and dendritic cells, all of which are of hematopoietic origin, have been found to be important in regulating several niches in the BM, including hematopoietic stem cell niches, erythropoietic niches, and niches involved in endosteal bone formation. There is also increasing evidence that these macrophages have an important role in adapting hematopoiesis, erythropoiesis, and bone formation in response to inflammatory stressors and play a key part in maintaining the integrity and function of these. Likewise, there is also accumulating evidence that subsets of monocytes, macrophages, and other phagocytes contribute to the progression and response to treatment of several lymphoid malignancies such as multiple myeloma, Hodgkin lymphoma, and non-Hodgkin lymphoma, as well as lymphoblastic leukemia, and may also play a role in myelodysplastic syndrome and myeloproliferative neoplasms associated with Noonan syndrome and aplastic anemia. In this review, the potential functions of macrophages and other phagocytes in normal and pathologic niches are discussed, as are the challenges in studying BM and other tissue-resident macrophages at the molecular level.

Targeting local lymphatics to ameliorate heterotopic ossification via FGFR3-BMPR1a pathway

Acquired heterotopic ossification (HO) is the extraskeletal bone formation after trauma. Various mesenchymal progenitors are reported to participate in ectopic bone formation. Here we induce acquired HO in mice by Achilles tenotomy and observe that conditional knockout (cKO) of fibroblast growth factor receptor 3 (FGFR3) in Col2⁺ cells promote acquired HO development. Lineage tracing studies reveal that Col2⁺ cells adopt fate of lymphatic endothelial cells (LECs) instead of chondrocytes or osteoblasts during HO development. FGFR3 cKO in Prox1⁺ LECs causes even more aggravated HO formation. We further demonstrate that FGFR3 deficiency in LECs leads to decreased local lymphatic formation in a BMPR1a-pSmad1/5-dependent manner, which exacerbates inflammatory levels in the repaired tendon. Local administration of FGF9 in Matrigel inhibits heterotopic bone formation, which is dependent on FGFR3 expression in LECs. Here we uncover Col2⁺ lineage cells as an origin of lymphatic endothelium, which regulates local inflammatory microenvironment after trauma and thus influences HO development via FGFR3-BMPR1a pathway. Activation of FGFR3 in LECs may be a therapeutic strategy to inhibit acquired HO formation via increasing local lymphangiogenesis.

Different types of mesenchymal progenitors participate in ectopic bone formation. Here, the authors show Col2⁺ lineage cells adopt a lymphatic endothelium cell fate, which regulates local inflammatory microenvironment after trauma, thus influencing heterotopic ossification (HO) development via a FGFR3-BMPR1a pathway.

Quercetin Attenuates Trauma-Induced Heterotopic Ossification by Tuning Immune Cell Infiltration and Related Inflammatory Insult

Heterotopic ossification (HO) is one of the most intractable disorders following musculoskeletal injury and is characterized by the ectopic presence of bone tissue in the soft tissue leading to severe loss of function in the extremities. Recent studies have indicated that immune cell infiltration and inflammation are involved in aberrant bone formation. In this study, we found increased monocyte/macrophage and mast cell accumulation during early HO progression. Macrophage depletion by clodronate liposomes and mast cell stabilization by cromolyn sodium significantly impeded HO formation. Therefore, we proposed that the dietary phytochemical quercetin could also suppress immune cell recruitment and related inflammatory responses to prevent HO. As expected, quercetin inhibited the monocyte-to-macrophage transition, macrophage polarization, and mast cell activation in vitro in a dose-dependent manner. Using a murine burn/tenotomy model, we also demonstrated that quercetin attenuated inflammatory responses and HO in vivo. Furthermore, elevated SIRT1 and decreased acetylated NFκB p65 expression were responsible for the mechanism of quercetin, and the beneficial effects of quercetin were reversed by the SIRT1 antagonist EX527 and mimicked by the SIRT agonist SRT1720. The findings in this study suggest that targeting monocyte/macrophage and mast cell activities may represent an attractive approach for therapeutic intervention of HO and that quercetin may serve as a promising therapeutic candidate for the treatment of trauma-induced HO by modulating SIRT1/NFκB signaling.

Neurogenic Heterotopic Ossifications Recapitulate Hematopoietic Stem Cell Niche Development Within an Adult Osteogenic Muscle Environment

Hematopoiesis and bone interact in various developmental and pathological processes. Neurogenic heterotopic ossifications (NHO) are the formation of ectopic hematopoietic bones in peri-articular muscles that develop following severe lesions of the central nervous system such as traumatic cerebral or spinal injuries or strokes. This review will focus on the hematopoietic facet of NHO. The characterization of NHO demonstrates the presence of hematopoietic marrow in which quiescent hematopoietic stem cells (HSC) are maintained by a functional stromal microenvironment, thus documenting that NHOs are neo-formed ectopic HSC niches. Similarly to adult bone marrow, the NHO permissive environment supports HSC maintenance, proliferation and differentiation through bidirectional signaling with mesenchymal stromal cells and endothelial cells, involving cell adhesion molecules, membrane-bound growth factors, hormones, and secreted matrix proteins. The participation of the nervous system, macrophages and inflammatory cytokines including oncostatin M and transforming growth factor (TGF)-β in this process, reveals how neural circuitry fine-tunes the inflammatory response to generate hematopoietic bones in injured muscles. The localization of NHOs in the peri-articular muscle environment also suggests a role of muscle mesenchymal cells and bone metabolism in development of hematopoiesis in adults. Little is known about the establishment of bone marrow niches and the regulation of HSC cycling during fetal development. Similarities between NHO and development of fetal bones make NHOs an interesting model to study the establishment of bone marrow hematopoiesis during development. Conversely, identification of stage-specific factors that specify HSC developmental state during fetal bone development will give more mechanistic insights into NHO.

Oncostatin M Is a Prognostic Biomarker and Inflammatory Mediator for Sepsis

BACKGROUND

Oncostatin M (OSM) is a pleiotropic cytokine of the interleukin-6 family. The role of OSM in sepsis remains unknown.

METHODS

Serum OSM level was determined and analyzed in septic patients on the day of intensive care unit (ICU) admission. Furthermore, the effects of OSM on polymicrobial sepsis induced by cecal ligation and puncture (CLP) were assessed.

RESULTS

On the day of ICU admission, septic patients had significantly higher serum OSM levels when compared with ICU patient controls and healthy volunteers, which were related to the severity of sepsis, including parameters such as the sequential (sepsis-related) organ failure assessment score, procalcitonin level, and white blood cell number. A high serum OSM level on ICU admission was associated with 28-day mortality in septic patients. In CLP-induced polymicrobial sepsis, anti-OSM antibody decreased tissue inflammation and injury, and thus improved survival, while local and systemic bacterial dissemination was almost constant. Complementarily, supplementation with recombinant OSM protein in septic mice increased tissue injury, amplified inflammation, and worsened mortality after CLP, while it did not affect bacterial dissemination in septic mice.

CONCLUSIONS

Sepsis results in an increased production of OSM, which might be a potential prognostic biomarker and therapeutic target for sepsis.

Novel Lineage-Tracing System to Identify Site-Specific Ectopic Bone Precursor Cells

Heterotopic ossification (HO) is a form of pathological cell-fate change of mesenchymal stem/precursor cells (MSCs) that occurs following traumatic injury, limiting range of motion in extremities and causing pain. MSCs have been shown to differentiate to form bone; however, their lineage and aberrant processes after trauma are not well understood. Utilizing a well-established mouse HO model and inducible lineage-tracing mouse (Hoxa11-CreER^T2;ROSA26-LSL-TdTomato), we found that Hoxa11-lineage cells represent HO progenitors specifically in the zeugopod. Bioinformatic single-cell transcriptomic and epigenomic analyses showed Hoxa11-lineage cells are regionally restricted mesenchymal cells that, after injury, gain the potential to undergo differentiation toward chondrocytes, osteoblasts, and adipocytes. This study identifies Hoxa11-lineage cells as zeugopod-specific ectopic bone progenitors and elucidates the fate specification and multipotency that mesenchymal cells acquire after injury. Furthermore, this highlights homeobox patterning genes as useful tools to trace region-specific progenitors and enable location-specific gene deletion.

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Lineage tracing, single-cell RNA-seq and single cell ATAC enable cell specific analysis of in vivo cell fate

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Hoxa11 lineage marks distinct mesenchymal precursors in the zeugopod

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Hoxa11 lineage mesenchymal precursors undergo an aberrant cell fate change towards ectopic bone and cartilage

Characterization of traumatized muscle-derived multipotent progenitor cells from low-energy trauma

Background

Multipotent progenitor cells have been harvested from different human tissues, including the bone marrow, adipose tissue, and umbilical cord blood. Previously, we identified a population of mesenchymal progenitor cells (MPCs) isolated from the traumatized muscle of patients undergoing reconstructive surgery following a war-related blast injury. These cells demonstrated the ability to differentiate into multiple mesenchymal lineages. While distal radius fractures from a civilian setting have a much lower injury mechanism (low-energy trauma), we hypothesized that debrided traumatized muscle near the fracture site would contain multipotent progenitor cells with the ability to differentiate and regenerate the injured tissue.

Methods

The traumatized muscle was debrided from the pronator quadratus in patients undergoing open reduction and internal fixation for a distal radius fracture at the Walter Reed National Military Medical Center. Using a previously described protocol for the isolation of MPCs from war-related extremity injuries, cells were harvested from the low-energy traumatized muscle samples and expanded in culture. Isolated cells were characterized by flow cytometry and q-RT-PCRs and induced to adipogenic, osteogenic, and chondrogenic differentiation. Downstream analyses consisted of lineage-specific staining and q-RT-PCR.

Results

Cells isolated from low-energy traumatized muscle samples were CD73+, CD90+, and CD105+ that are the characteristic of adult human mesenchymal stem cells. These cells expressed high levels of the stem cell markers OCT4 and NANOG 1-day after isolation, which was dramatically reduced over-time in monolayer culture. Following induction, lineage-specific markers were demonstrated by each specific staining and confirmed by gene expression analysis, demonstrating the ability of these cells to differentiate into adipogenic, osteogenic, and chondrogenic lineages.

Conclusions

Adult multipotent progenitor cells are an essential component for the success of regenerative medicine efforts. While MPCs have been isolated and characterized from severely traumatized muscle from high-energy injuries, here, we report that cells with similar characteristics and multipotential capacity have been isolated from the tissue that was exposed to low-energy, community trauma.

Genetic and Acquired Heterotopic Ossification: A Translational Tale of Mice and Men

Heterotopic ossification is defined as an aberrant formation of bone in extraskeletal soft tissue, for which both genetic and acquired conditions are known. This pathologic process may occur in many different sites such as the skin, subcutaneous tissue, skeletal muscle and fibrous tissue adjacent to joints, ligaments, walls of blood vessels, mesentery and other. The clinical spectrum of this disorder is wide: lesions may range from small foci of ossification to massive deposits of bone throughout the body, typical of the progressive genetically determined conditions such as fibrodysplasia ossificans progressiva, to mention one of the most severe and disabling forms. The ectopic bone formation may be regarded as a failed tissue repair process in response to a variety of triggers and evolving towards bone formation through a multistage differentiation program, with several steps common to different clinical presentations and distinctive features. In this review, we aim at providing a comprehensive view of the genetic and acquired heterotopic ossification disorders by detailing the clinical and molecular features underlying the different human conditions in comparison with the corresponding, currently available mouse models.