Opioid signaling in mast cells regulates injury responses associated with heterotopic ossification

Estrogen Deficiency Exacerbates Traumatic Heterotopic Ossification in Mice

Background

Traumatic heterotopic ossification (HO) is a devastating sequela of orthopedic surgeries and traumatic injuries; however, few studies have explored the effects of the estrogen-deficient state on HO formation. In the present study, we investigated the impact of estrogen deficiency on ectopic cartilage and bone formation in tendon after Achilles tenotomy in an ovariectomized mouse model.

Methods

A total of 45 female C57BL/6 mice were randomly divided into three groups: sham-operated (control), estrogen depletion by ovariectomy (OVX) and OVX with 17β-estradiol supplementation (OVX + E2), with 15 animals in each group. Three weeks after OVX, all mice were subjected to an Achilles tenotomy using a posterior midpoint approach to induce HO. At 1, 3 and 9 weeks after tenotomy, the left hind limbs were harvested for histology, immunohistochemistry and immunofluorescence evaluations. The volume of ectopic bone was assessed by micro-CT.

Results

Mice in the OVX group formed more ectopic cartilage 3 weeks after tenotomy, as well as ectopic bone 9 weeks after tenotomy, compared to the control group. Estrogen deficiency resulted in more severe inflammatory infiltration at the injury sites 1 week after tenotomy, involving the recruitment of more macrophages and mast cells, as well as increasing the expressions of pro-inflammatory mediators, including IL-1β, IL-6, and TNF-α. Moreover, the local TGF-β/SMAD signaling pathway was dysregulated after OVX, which manifested as upregulated expressions of TGF-β and pSMAD2/3. E2 supplementation protected against OVX-induced HO deterioration, inhibited inflammatory infiltration, and downregulated the TGF-β/SMAD signaling pathway.

Conclusion

Estrogen deficiency exacerbated HO formation in the Achilles tenotomy model. These findings might be attributable to the disturbance of the inflammatory response and the activation of TGF-β/SMAD signaling at the injury sites during the early stages of HO development.

Metformin alleviates genetic and traumatic heterotopic ossification by inhibiting infiltration and mitochondrial metabolism of myeloid cells

OBJECTIVES

Heterotopic ossification (HO), whether hereditary or traumatic, refers to the abnormal formation of bone in extraskeletal sites, often triggered by inflammation or flare-ups. Unfortunately, there are currently no effective treatments for HO. Metformin is well-known for its anti-diabetic, anti-inflammatory, anti-aging, and anti-cancer effects. However, its potential role in treating HO remains uncertain.

METHODS

Metformin was dissolved into water and given to mice. All the mice in this study were examined by microCT and myeloid cell quantification using flow cytometry. Complex activity kit was used to examine the activity of mitochondrial complexes of myeloid cells.

RESULTS

In this study, we discovered that metformin effectively inhibits genetic and traumatic HO formation and progression. Additionally, we observed a significant increase in myeloid cells in the genetic and traumatic HO mouse model compared to uninjured mice. Notably, metformin specifically reduced the infiltration of myeloid cells into the injured sites of the genetic and traumatic HO model mice. Further investigations revealed that metformin targets mitochondrial complex I and suppresses mitochondrial metabolism in myeloid cells.

CONCLUSION

These findings suggest that metformin suppresses HO development by potentially downregulating the mitochondrial metabolism of myeloid cells, offering a promising therapeutic option for HO treatment.

ACVR1-activating mutation causes neuropathic pain and sensory neuron hyperexcitability in humans

ABSTRACT

Altered bone morphogenetic protein (BMP) signaling is associated with many musculoskeletal diseases. However, it remains unknown whether BMP dysfunction has direct contribution to debilitating pain reported in many of these disorders. Here, we identified a novel neuropathic pain phenotype in patients with fibrodysplasia ossificans progressiva (FOP), a rare autosomal-dominant musculoskeletal disorder characterized by progressive heterotopic ossification. Ninety-seven percent of these patients carry an R206H gain-of-function point mutation in the BMP type I receptor ACVR1 (ACVR1 R206H ), which causes neofunction to Activin A and constitutively activates signaling through phosphorylated SMAD1/5/8. Although patients with FOP can harbor pathological lesions in the peripheral and central nervous system, their etiology and clinical impact are unclear. Quantitative sensory testing of patients with FOP revealed significant heat and mechanical pain hypersensitivity. Although there was no major effect of ACVR1 R206H on differentiation and maturation of nociceptive sensory neurons (iSNs) derived from FOP induced pluripotent stem cells, both intracellular and extracellular electrophysiology analyses of the ACVR1 R206H iSNs displayed ACVR1-dependent hyperexcitability, a hallmark of neuropathic pain. Consistent with this phenotype, we recorded enhanced responses of ACVR1 R206H iSNs to TRPV1 and TRPA1 agonists. Thus, activated ACVR1 signaling can modulate pain processing in humans and may represent a potential target for pain management in FOP and related BMP pathway diseases.

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.

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.

RNA Sequencing Evidences the Prevention of Oxidative Stress is Effective in Injury-Induced Heterotopic Ossification Treatment

Heterotopic ossification is a bona fide bone formation outside the normal skeleton. Traumatic injury and genetic mutations are the important risk factors of HO. Both injury-induced HO and hereditary HO severely affect human life quality. However, there were no effect therapies treating HO. Here, we performed the RNA-sequencing assay to examine dynamic process during HO initiation and development. Moreover, we found that oxidation-reduction process were significantly dysregulated following HO formation. Further, we characterized that Nuclear factor erythroid 2-related factor 2 (NRF2) expression conferred antioxidant property in macrophages and then helped chondrocytes formation. Instead, 3-Nitrotyrosine is expressed by T-lymphocytes, but not macrophages, causing deficient adaptive immunity. Inhibition of NRF2 markedly alleviated HO. Finally, we identified that PI3K/AKT signaling pathway is responsible for whole HO process, but ERK signaling is activated only in early stage. ERK pathway blockade effectively prevented HO. These findings revealed that oxidative stress induced by early immune response can be targeted in HO treatment.

Dermorphin [D-Arg2, Lys4] (1-4) amide inhibits below-level heat hypersensitivity in mice after contusive thoracic spinal cord injury

Opioid use for chronic pain is limited by severe central adverse effects. We examined whether activating mu-opioid receptors (MORs) in the peripheral nervous system attenuates spinal cord injury (SCI) pain-like behavior in mice. We produced a contusive SCI at the T10 vertebral level and examined motor and sensory dysfunction for 6 weeks. At 6 weeks, we tested the effect of subcutaneous (s.c.) injection of dermorphin [D-Arg2, Lys4] (1-4) amide (DALDA), a peripherally acting MOR-preferring agonist, on mechanical and heat hypersensitivity. Basso mouse scale score was significantly decreased after SCI, and mice showed hypersensitivity to mechanical and heat stimulation at the hind paw beginning at 2 weeks, as indicated by increased paw withdrawal frequency to mechanical stimulation and decreased paw withdrawal latency to heat stimulation. In wild-type SCI mice, DALDA (1 mg/kg, s.c.) attenuated heat but not mechanical hypersensitivity. The effect was blocked by pretreatment with an intraperitoneal injection of methylnaltrexone (5 mg/kg), a peripherally restricted opioid receptor antagonist, and was also diminished in Pirt-MOR conditional knockout mice. DALDA did not adversely affect exploratory activity or induced preference to drug treatment in SCI mice. In vivo calcium imaging showed that DALDA (1, 10 mg/kg, s.c.) inhibited responses of small dorsal root ganglion neurons to noxious heat stimulation in Pirt-GCaMP6s mice after SCI. Western blot analysis showed upregulation of MOR in the lumbar spinal cord and sciatic nerves at 6 weeks after SCI. Our findings suggest that peripherally acting MOR agonist may inhibit heat hypersensitivity below the injury level with minimal adverse effects.

Osteoimmunology: A Current Update of the Interplay Between Bone and the Immune System

Immunology, already a discipline in its own right, has become a major part of many different medical fields. However, its relationship to orthopedics and trauma surgery has unfortunately, and perhaps unjustly, been developing rather slowly. Discoveries in recent years have emphasized the immense breadth of communication and connection between both systems and, importantly, the highly promising therapeutic opportunities. Recent discoveries of factors originally assigned to the immune system have now also been shown to have a significant impact on bone health and disease, which has greatly changed how we approach treatment of bone pathologies. In case of bone fracture, immune cells, especially macrophages, are present throughout the whole healing process, assure defense against pathogens and discharge a complex variety of effectors to regulate bone modeling. In rheumatoid arthritis and osteoporosis, the immune system contributes to the formation of the pathological and chronic conditions. Fascinatingly, prosthesis failure is not at all solely a mechanical problem of improper strain but works in conjunction with an active contribution of the immune system as a reaction to irritant debris from material wear. Unraveling conjoined mechanisms of the immune and osseous systems heralds therapeutic possibilities for ailments of both. Contemplation of the bone as merely an unchanging support pillar is outdated and obsolete. Instead it is mandatory that this highly diverse network be incorporated in our understanding of the immune system and hematopoiesis.

Inhibition of immune checkpoints prevents injury-induced heterotopic ossification

Heterotopic ossification (HO), true bone formation in soft tissue, is closely associated with abnormal injury/immune responses. We hypothesized that a key underlying mechanism of HO might be injury-induced dysregulation of immune checkpoint proteins (ICs). We found that the earliest stages of HO are characterized by enhanced infiltration of polarized macrophages into sites of minor injuries in an animal model of HO. The non-specific immune suppressants, Rapamycin and Ebselen, prevented HO providing evidence of the central role of the immune responses. We examined the expression pattern of ICs and found that they are dysregulated in HO lesions. More importantly, loss of function of inhibitory ICs (including PD1, PD-L1, and CD152) markedly inhibited HO, whereas loss of function of stimulatory ICs (including CD40L and OX-40L) facilitated HO. These findings suggest that IC inhibitors may provide a therapeutic approach to prevent or limit the extent of HO.

BMP-dependent, injury-induced stem cell niche as a mechanism of heterotopic ossification

Background

Heterotopic ossification (HO), either acquired (aHO) or hereditary, such as fibrodysplasia ossificans progressiva (FOP), is a serious condition without effective treatment. Understanding of the core process of injury-induced HO is still severely limited.

Methods

Double-pulse thymidine analog labeling was used to explore the distinctive domains evolved in injury-induced lesions in an animal model of HO (Nse-BMP4). Histological studies were performed to see whether a similar zonal pattern is also consistently found in biopsies from patients with aHO and FOP. In vivo clonal analysis with Rainbow mice, genetic loss-of-function studies with diphtheria toxin A (DTA)-mediated depletion and lineage tracing with Zsgreen reporter mice were used to obtain further evidence that Tie2-cre-, Gli1-creERT-, and Glast-creERT-labeled cells contribute to HO as niche-dwelling progenitor/stem cells. Immunohistochemistry was used to test whether vasculature, neurites, macrophages, and mast cells are closely associated with the proposed niche and thus are possible candidate niche supportive cells. Similar methods also were employed to further understand the signaling pathways that regulate the niche and the resultant HO.

Results

We found that distinctive domains evolved in injury-induced lesions, including, from outside-in, a mesenchymal stem cell (MSC) niche, a transient domain and an inner differentiated core in an animal model of HO (Nse-BMP4). A similar zonal structure was found in patients with aHO and FOP. In vivo clonal analysis with Rainbow mice and genetic loss-of-function studies with DTA provided evidence that Tie2-cre-, Gli1-creERT-, and Glast-creERT-labeled cells contribute to HO as niche-dwelling progenitor/stem cells; consistently, vasculature, neurites, macrophages, and mast cells are closely associated with the proposed niche and thus are possible candidate niche supportive cells. Further mechanistic study found that BMP and hedgehog (Hh) signaling co-regulate the niche and the resultant HO.

Conclusions

Available data provide evidence of a potential core mechanism in which multiple disease-specific cellular and extracellular molecular elements form a unique local microenvironment, i.e., an injury-induced stem cell niche, which regulates the proliferation and osteogenic differentiation of mesenchymal stem cells (MSCs). The implication for HO is that therapeutic approaches must consider several different disease specific factors as parts of a functional unit, instead of treating one factor at a time.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-1107-7) contains supplementary material, which is available to authorized users.

A Pharmacological Rationale to Reduce the Incidence of Opioid Induced Tolerance and Hyperalgesia: A Review

Chronic pain is an important health and social problem. Misuse and abuse of opioids in chronic non-cancer pain management seem to be a huge problem, in some countries. This could probably affect the normal use of such analgesics in patients in need of them. Basic and clinical researches should find the solution to mitigate the potential damage. Dysregulation of mast cell and microglia activation plays an important role in the pathogenesis and management of chronic pain. Persistent mast cell activation sensitizes nociceptors and initiates central nervous system inflammatory processes, involving microglial cell activation and sensitization of spinal somatosensory neurons. Exposure of mast cells and microglia to opioids is well known to provoke activation of these non-neuronal immune cell populations, thereby contributing to an exacerbation of pro-inflammatory and pro-nociceptive processes and promoting, over the long-term, opioid-induced hyperalgesia and tolerance. This review is intended to provide the reader with an overview of the role for these non-neuronal cells in opioid-induced chronic pain and tolerance as a consequence of prolonged exposure to these drugs. In addition, we will examine a potential strategy with the aim to modulate opioid-induced over-activation of glia and mast cells, based on endogenous defense mechanisms and fatty acid amide signaling molecules.

Mast cell inhibition as a therapeutic approach in fibrodysplasia ossificans progressiva (FOP)

BACKGROUND

Episodic flare-ups of fibrodysplasia ossificans progressiva (FOP) are characterized clinically by severe, often posttraumatic, connective tissue swelling and intramuscular edema, followed histologically by an intense and highly angiogenic fibroproliferative reaction. This early inflammatory and angiogenic fibroproliferative response is accompanied by the presence of abundant mast cells far in excess of other reported myopathies.

RESULTS

Using an injury-induced, constitutively-active transgenic mouse model of FOP we show that mast cell inhibition by cromolyn, but not aprepitant, results in a dramatic reduction of heterotopic ossification. Cromolyn, but not aprepitant, significantly decreases the total number of mast cells in FOP lesions. Furthermore, cromolyn specifically diminishes the number of degranulating and resting degranulated mast cells in pre-osseous lesions.

CONCLUSIONS

This work demonstrates that consideration of FOP as a type of localized mastocytosis may offer new therapeutic interventions for treatment of this devastating condition.

The role of the adaptive immune system in burn-induced heterotopic ossification and mesenchymal cell osteogenic differentiation

BACKGROUND

Heterotopic ossification (HO) is the pathologic process of extraskeletal bone formation. Although the exact etiology remains unknown, inflammation appears to catalyze disease progression. The goal of this study is to determine the impact of the adaptive immune system on HO.

METHODS

HO was induced in 8-wk-old control C57BL/6 and immunocompromised Rag1tm1Mom (Rag1 KO) male mice deficient in B- and T-lymphocytes via combined Achilles tenotomy and burn injury. Microcomputed tomography quantified the extent of HO formation at the tenotomy site. Adipose-derived mesenchymal stem cells were harvested to evaluate osteogenic differentiation potential.

RESULTS

Areas of developing HO demonstrated substantial enrichment of CD45 + leukocytes at 3 wk after injury. HO from Rag1 KO mice was substantially less mature with foci of cartilage and disorganized trabecular bone present 12 wk after injury. Rag1 KO mice formed 60% less bone compared to immunocompetent controls (4.67 ± 1.5 mm versus 7.76 ± 0.65 mm; P = 0.001). Tartrate-resistant acid phosphatase staining and immunofluorescent analysis of osteoprotegerin and nuclear factor kappa-light-chain-enhancer of activated B cells demonstrated no appreciable difference in osteoclast number or activation. Alizarin red staining in vitro demonstrated a significant decrease in osteogenic potential in immunocompromised mice compared to controls (29.1 ± 0.54 mm versus 12.1 ± 0.14 mm; P < 0.001).

CONCLUSIONS

We demonstrate a prominent role for the adaptive immune system in the development of HO. In the absence of mature B- and T-lymphocytes, HO growth and development are attenuated. Furthermore, we demonstrate that mesenchymal populations from B- and T-cell deficient mice are inherently less osteogenic. This study identifies a potential therapeutic role for modulation of the adaptive immune system in the treatment of HO.

Endogenous opiates and behavior: 2014

This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants). This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants).

Myositis Ossificans in the Thigh of a Lacrosse Player

An 18-year-old man presented with mid left thigh pain after sequential lacrosse injuries 1 month and 2 weeks prior. Physical examination was significant for a tender mass in the mid left thigh.

The immunological contribution to heterotopic ossification disorders

The formation of bone outside the endogenous skeleton is a significant clinical event, rendering affected individuals with immobility and a diminished quality of life. This bone, termed heterotopic ossification (HO), can appear in patients following invasive surgeries and traumatic injuries, as well as progressively manifest in several congenital disorders. A unifying feature of both genetic and nongenetic episodes of HO is immune system involvement at the early stages of disease. Activation of the immune system sets the stage for the downstream anabolic events that eventually result in ectopic bone formation, rendering the immune system a particularly appealing site of early therapeutic intervention for optimal management of disease. In this review, we will discuss the immunological contributions to HO disorders, with specific focus on contributing cell types, signaling pathways, relevant in vivo animal models, and potential therapeutic targets.