Local and Circulating Endothelial Cells Undergo Endothelial to Mesenchymal Transition (EndMT) in Response to Musculoskeletal Injury

Jaggeds/Notches promote endothelial-mesenchymal transition-mediated pulmonary arterial hypertension via upregulation of the expression of GATAs

This study tested the hypothesis that Jagged2/Notches promoted the endothelial-mesenchymal transition (endMT)-mediated pulmonary arterial hypertension (PAH) (i.e. induction by monocrotaline [MCT]/63 mg/kg/subcutaneous injection) through increasing the expression of GATA-binding factors which were inhibited by propylthiouracil (PTU) (i.e. 0.1% in water for daily drinking since Day 5 after PAH induction) in rodent. As compared with the control (i.e. HUVECs), the protein expressions of GATAs (3/4/6) and endMT markers (Snail/Zeb1/N-cadherin/vimentin/fibronectin/α-SMA/p-Smad2) were significantly reduced, whereas the endothelial-phenotype markers (CD31/E-cadherin) were significantly increased in silenced JAG2 gene or in silenced GATA3 gene of HUVECs (all p < 0.001). As compared with the control, the protein expressions of intercellular signallings (GATAs [3/4/6], Jagged1/2, notch1/2 and Snail/Zeb1/N-cadherin/vimentin/fibronectin/α-SMA/p-Smad2) were significantly upregulated in TGF-ß/monocrotaline-treated HUVECs that were significantly reversed by PTU treatment (all p < 0.001). By Day 42, the results of animal study demonstrated that the right-ventricular systolic-blood-pressure (RVSBP), RV weight (RVW) and lung injury/fibrotic scores were significantly increased in MCT group than sham-control (SC) that were reversed in MCT + PTU groups, whereas arterial oxygen saturation (%) and vasorelaxation/nitric oxide production of PA exhibited an opposite pattern of RVW among the groups (all p < 0.0001). The protein expressions of hypertrophic (ß-MHC)/pressure-overload (BNP)/oxidative-stress (NOX-1/NOX-2) biomarkers in RV and the protein expressions of intercellular signalling (GATAs3/4/6, Jagged1/2, notch1/2) and endMT markers (Snail/Zeb1/N-cadherin/vimentin/fibronectin/TGF-ß/α-SMA/p-Smad2) in lung parenchyma displayed an identical pattern of RVW among the groups (all p < 0.0001). Jagged-Notch-GATAs signalling, endMT markers and RVSBP that were increased in PAH were suppressed by PTU.

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.

Pathophysiology and Emerging Molecular Therapeutic Targets in Heterotopic Ossification

The term heterotopic ossification (HO) describes bone formation in tissues where bone is normally not present. Musculoskeletal trauma induces signalling events that in turn trigger cells, probably of mesenchymal origin, to differentiate into bone. The aetiology of HO includes extremely rare but severe, generalised and fatal monogenic forms of the disease; and as a common complex disorder in response to musculoskeletal, neurological or burn trauma. The resulting bone forms through a combination of endochondral and intramembranous ossification, depending on the aetiology, initiating stimulus and affected tissue. Given the heterogeneity of the disease, many cell types and biological pathways have been studied in efforts to find effective therapeutic strategies for the disorder. Cells of mesenchymal, haematopoietic and neuroectodermal lineages have all been implicated in the pathogenesis of HO, and the emerging dominant signalling pathways are thought to occur through the bone morphogenetic proteins (BMP), mammalian target of rapamycin (mTOR), and retinoic acid receptor pathways. Increased understanding of these disease mechanisms has resulted in the emergence of several novel investigational therapeutic avenues, including palovarotene and other retinoic acid receptor agonists and activin A inhibitors that target both canonical and non-canonical signalling downstream of the BMP type 1 receptor. In this article we aim to illustrate the key cellular and molecular mechanisms involved in the pathogenesis of HO and outline recent advances in emerging molecular therapies to treat and prevent HO that have had early success in the monogenic disease and are currently being explored in the common complex forms of HO.

Endothelial Heterogeneity in Development and Wound Healing

The vasculature is comprised of endothelial cells that are heterogeneous in nature. From tissue resident progenitors to mature differentiated endothelial cells, the diversity of these populations allows for the formation, maintenance, and regeneration of the vascular system in development and disease, particularly during situations of wound healing. Additionally, the de-differentiation and plasticity of different endothelial cells, especially their capacity to undergo endothelial to mesenchymal transition, has also garnered significant interest due to its implication in disease progression, with emphasis on scarring and fibrosis. In this review, we will pinpoint the seminal discoveries defining the phenotype and mechanisms of endothelial heterogeneity in development and disease, with a specific focus only on wound healing.

Burn-induced heterotopic ossification from incidence to therapy: key signaling pathways underlying ectopic bone formation

Burn injury is one of the potential causes of heterotopic ossification (HO), which is a rare but debilitating condition. The incidence ranges from 3.5 to 5.6 depending on body area. Burns that cover a larger percentage of the total body surface area (TBSA), require skin graft surgeries, or necessitate pulmonary intensive care are well-researched risk factors for HO. Since burns initiate such complex pathophysiological processes with a variety of molecular signal changes, it is essential to focus on HO in the specific context of burn injury to define best practices for its treatment. There are numerous key players in the pathways of burn-induced HO, including neutrophils, monocytes, transforming growth factor-β1-expressing macrophages and the adaptive immune system. The increased inflammation associated with burn injuries is also associated with pathway activation. Neurological and calcium-related contributions are also known. Endothelial-to-mesenchymal transition (EMT) and vascularization are known to play key roles in burn-induced HO, with hypoxia-inducible factor-1 (HIF-1) and vascular endothelial growth factor (VEGF) as potential initiators. Currently, non-steroidal anti-inflammatory drugs (NSAIDs) and radiotherapy are effective prophylaxes for HO. Limited joint motion, ankylosis and intolerable pain caused by burn-induced HO can be effectively tackled via surgery. Effective biomarkers for monitoring burn-induced HO occurrence and bio-prophylactic and bio-therapeutic strategies should be actively developed in the future.

An oxidative stress-responsive electrospun polyester membrane capable of releasing anti-bacterial and anti-inflammatory agents for postoperative anti-adhesion

Peritendinous adhesion, secondary to the repair surgery of tendon rupture or injury, is one of the most common causes of reoperation, owing to the proliferation of fibrous tissue and excessive collagen synthesis caused by the residing inflammatory cells. In this study, a smart oxidative stress-responsive electrospun polyester membrane (EPM) was fabricated as both physical barrier and reservoir of curcumin/celecoxib (CUR/CEL) to prevent peritendinous adhesion. The multicomponent EPM was designed to release the encapsulated drugs in response to oxidative stress of the local microenvironment induced by inflammation. Specifically, sulfides in the EPM were able to react with reactive oxygen species (ROS) and become hydrophilic sulfoxide or sulfone to accelerate the release rate of drugs and regulate oxidative stress level in the inflammatory site intelligently. The oxidation-sensitive multicomponent EPM loaded with CUR and CEL was tested for anti-adhesion capacity in vitro and in vivo. An excellent ROS-sensitive degradation behavior and good cytocompatibility with cell viability of above 85% were presented with the fabricated EPM. The CUR- or CEL-loaded EPM possessed a better anti-adhesion ability compared with EPM without the drugs. Nevertheless, they were inferior to the EPM simultaneously loaded with both drugs, where the adhesion rate and fibrous adhesion number in the EPM+CUR/CEL group were close to extremely low values of about zero, demonstrating that CUR and CEL could synergistically prevent peritendinous adhesion. More interestingly, the multicomponent EPM was able to react with the local oxidative stress, leading to a smart and sustained behavior of releasing approximately 80% of the drug within 20 days. Overall, the smart multicomponent EPM offers a promising barrier strategy to prevent peritendinous adhesion.

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.

Heterotopic ossification of tendon and ligament

Much of the similarities of the tissue characteristics, pathologies and mechanisms of heterotopic ossification (HO) formation are shared between HO of tendon and ligament (HOTL). Unmet need and no effective treatment has been developed for HOTL, primarily attributable to poor understanding of cellular and molecular mechanisms. HOTL forms via endochondral ossification, a common process of most kinds of HO. HOTL is a dynamic pathologic process that includes trauma/injury, inflammation, mesenchymal stromal cell (MSC) recruitment, chondrogenic differentiation and, finally, ossification. A variety of signal pathways involve HOTL with multiple roles in different stages of HO formation, and here in this review, we summarize the progress and provide an up‐to‐date understanding of HOTL.

The histone demethylase JMJD2B regulates endothelial-to-mesenchymal transition

Here we show that the histone demethylase JMJD2B is induced in endothelial cells by EndMT provoking stimuli and thereby contributes to the acquirement of a mesenchymal/smooth muscle phenotype. Silencing of JMJD2B inhibited EndMT in vitro and reduced the induction of EndMT after myocardial infarction in vivo. Inhibition of JMJD2B prevents the demethylation of repressive trimethylated histone H3 at lysine 9 (H3K9me3) at promoters of mesenchymal and EndMT-controlling genes, thereby reducing EndMT. Together, our study reports a crucial role for JMJD2B in controlling histone modifications during the transition of endothelial cells toward a mesenchymal phenotype.

Endothelial cells play an important role in maintenance of the vascular system and the repair after injury. Under proinflammatory conditions, endothelial cells can acquire a mesenchymal phenotype by a process named endothelial-to-mesenchymal transition (EndMT), which affects the functional properties of endothelial cells. Here, we investigated the epigenetic control of EndMT. We show that the histone demethylase JMJD2B is induced by EndMT-promoting, proinflammatory, and hypoxic conditions. Silencing of JMJD2B reduced TGF-β2-induced expression of mesenchymal genes, prevented the alterations in endothelial morphology and impaired endothelial barrier function. Endothelial-specific deletion of JMJD2B in vivo confirmed a reduction of EndMT after myocardial infarction. EndMT did not affect global H3K9me3 levels but induced a site-specific reduction of repressive H3K9me3 marks at promoters of mesenchymal genes, such as Calponin (CNN1), and genes involved in TGF-β signaling, such as AKT Serine/Threonine Kinase 3 (AKT3) and Sulfatase 1 (SULF1). Silencing of JMJD2B prevented the EndMT-induced reduction of H3K9me3 marks at these promotors and further repressed these EndMT-related genes. Our study reveals that endothelial identity and function is critically controlled by the histone demethylase JMJD2B, which is induced by EndMT-promoting, proinflammatory, and hypoxic conditions, and supports the acquirement of a mesenchymal phenotype.

Mesenchymal VEGFA induces aberrant differentiation in heterotopic ossification

Heterotopic ossification (HO) is a debilitating condition characterized by the pathologic formation of ectopic bone. HO occurs commonly following orthopedic surgeries, burns, and neurologic injuries. While surgical excision may provide palliation, the procedure is often burdened with significant intra-operative blood loss due to a more robust contribution of blood supply to the pathologic bone than to native bone. Based on these clinical observations, we set out to examine the role of vascular signaling in HO. Vascular endothelial growth factor A (VEGFA) has previously been shown to be a crucial pro-angiogenic and pro-osteogenic cue during normal bone development and homeostasis. Our findings, using a validated mouse model of HO, demonstrate that HO lesions are highly vascular, and that VEGFA is critical to ectopic bone formation, despite lacking a contribution of endothelial cells within the developing anlagen.

rhBMP‑7 suppresses TGF‑β1‑induced endothelial to mesenchymal transition in circulating endothelial cells by regulating Smad5

Endothelial to mesenchymal transition (EndMT) has been confirmed to participate in several cardiovascular diseases. In addition, EndMT of circulating endothelial cells (CECs) contributes to the pathology of musculoskeletal injury. However, little is known about the molecular mechanism of CECs undergoing EndMT. In the present study, human CECs were isolated and identified using anti‑CD146‑coupled magnetic beads. CECs were exposed to transforming growth factor (TGF)‑β1 or TGF‑β1 + recombinant human bone morphogenetic protein 7 (rhBMP‑7) or TGF‑β1 + rhBMP‑7 + Smad5 antagonist Jun activation domain‑binding protein 1. Vascular endothelial (VE)‑cadherin and vimentin expression were detected by immunofluorescence staining in TGF‑β1‑treated CECs. The expression levels of von Willebrand factor (vWF), E‑selectin, VE‑cadherin, vimentin, fibronectin, α smooth muscle actin (α‑SMA) and Smad2/3 were detected by reverse transcription‑quantitative PCR or western blot analysis. It was identified that rhBMP‑7 attenuated TGF‑β1‑induced endothelial cell injury. TGF‑β1 could induce the EndMT process in CECs, as confirmed by the co‑expression of VE‑cadherin and vimentin. TGF‑β1 significantly reduced the expression of VE‑cadherin, and induced the expression of vimentin, fibronectin and α‑SMA. rhBMP‑7 reversed the effects of TGF‑β1 on the expression of these genes. Additionally, Smad5 antagonist reversed the effects of rhBMP‑7 on TGF‑β1‑induced EndMT, and upregulated rhBMP‑7‑inhibited Smad2/3 expression. In conclusion, TGF‑β1 could induce EndMT in CECs and rhBMP‑7 may suppress this process by regulating Smad5.

Severe Heterotopic Ossification in the Skeletal Muscle and Endothelial Cells Recruitment to Chondrogenesis Are Enhanced by Monocyte/Macrophage Depletion

Altered macrophage infiltration upon tissue damage results in inadequate healing due to inappropriate remodeling and stem cell recruitment and differentiation. We investigated in vivo whether cells of endothelial origin phenotypically change upon heterotopic ossification induction and whether infiltration of innate immunity cells influences their commitment and alters the ectopic bone formation. Liposome-encapsulated clodronate was used to assess macrophage impact on endothelial cells in the skeletal muscle upon acute damage in the ECs specific lineage-tracing Cdh5CreER^T2:R26REYFP/dtTomato transgenic mice. Macrophage depletion in the injured skeletal muscle partially shifts the fate of ECs toward endochondral differentiation. Upon ectopic stimulation of BMP signaling, monocyte depletion leads to an enhanced contribution of ECs chondrogenesis and to ectopic bone formation, with increased bone volume and density, that is reversed by ACVR1/SMAD pathway inhibitor dipyridamole. This suggests that macrophages contribute to preserve endothelial fate and to limit the bone lesion in a BMP/injury-induced mouse model of heterotopic ossification. Therefore, alterations of the macrophage-endothelial axis may represent a novel target for molecular intervention in heterotopic ossification.

Endothelial to Mesenchymal Transition: Role in Physiology and in the Pathogenesis of Human Diseases

Numerous studies have demonstrated that endothelial cells are capable of undergoing endothelial to mesenchymal transition (EndMT), a newly recognized type of cellular transdifferentiation. EndMT is a complex biological process in which endothelial cells adopt a mesenchymal phenotype displaying typical mesenchymal cell morphology and functions, including the acquisition of cellular motility and contractile properties. Endothelial cells undergoing EndMT lose the expression of endothelial cell-specific proteins such as CD31/platelet-endothelial cell adhesion molecule, von Willebrand factor, and vascular-endothelial cadherin and initiate the expression of mesenchymal cell-specific genes and the production of their encoded proteins including α-smooth muscle actin, extra domain A fibronectin, N-cadherin, vimentin, fibroblast specific protein-1, also known as S100A4 protein, and fibrillar type I and type III collagens. Transforming growth factor-β1 is considered the main EndMT inducer. However, EndMT involves numerous molecular and signaling pathways that are triggered and modulated by multiple and often redundant mechanisms depending on the specific cellular context and on the physiological or pathological status of the cells. EndMT participates in highly important embryonic development processes, as well as in the pathogenesis of numerous genetically determined and acquired human diseases including malignant, vascular, inflammatory, and fibrotic disorders. Despite intensive investigation, many aspects of EndMT remain to be elucidated. The identification of molecules and regulatory pathways involved in EndMT and the discovery of specific EndMT inhibitors should provide novel therapeutic approaches for various human disorders mediated by EndMT.

Function of cAMP scaffolds in obstructive lung disease: Focus on epithelial-to-mesenchymal transition and oxidative stress

Over the past decades, research has defined cAMP as one of the central cellular nodes in sensing and integrating multiple pathways and as a pivotal role player in lung pathophysiology. Obstructive lung disorders, such as chronic obstructive pulmonary disease (COPD), are characterized by a persistent and progressive airflow limitation and by oxidative stress from endogenous and exogenous insults. The extent of airflow obstruction depends on the relative deposition of different constituents of the extracellular matrix, a process related to epithelial-to-mesenchymal transition, and which subsequently results in airway fibrosis. Oxidative stress from endogenous and also from exogenous sources causes a profound worsening of COPD. Here we describe how cAMP scaffolds and their different signalosomes in different subcellular compartments may contribute to COPD. Future research will require translational studies to alleviate disease symptoms by pharmacologically targeting the cAMP scaffolds. LINKED ARTICLES: This article is part of a themed section on Adrenoceptors-New Roles for Old Players. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.14/issuetoc.

The therapeutic potential of targeting the endothelial-to-mesenchymal transition

Endothelial cells (ECs) have been found to be capable of acquiring a mesenchymal phenotype through a process known as endothelial-to-mesenchymal transition (EndMT). First seen in the developing embryo, EndMT can be triggered postnatally under certain pathological conditions. During this process, ECs dedifferentiate into mesenchymal stem-like cells (MSCs) and subsequently give rise to cell types belonging to the mesoderm lineage. As EndMT contributes to a multitude of diseases, pharmacological modulation of the signaling pathways underlying EndMT may prove to be effective as a therapeutic treatment. Additionally, EndMT in ECs could also be exploited to acquire multipotent MSCs, which can be readily re-differentiated into various distinct cell types. In this review, we will consider current models of EndMT, how manipulation of this process might improve treatment of clinically important pathologies and how it could be harnessed to advance regenerative medicine and tissue engineering.

Epithelial mesenchymal transition (EMT): a universal process in lung diseases with implications for cystic fibrosis pathophysiology

Cystic Fibrosis (CF) is a genetic disorder that arises due to mutations in the Cystic Fibrosis Transmembrane Conductance Regulator gene, which encodes for a protein responsible for ion transport out of epithelial cells. This leads to a disruption in transepithelial Cl-, Na + and HCO₃− ion transport and the subsequent dehydration of the airway epithelium, resulting in infection, inflammation and development of fibrotic tissue. Unlike in CF, fibrosis in other lung diseases including asthma, chronic obstructive pulmonary disease and idiopathic pulmonary fibrosis has been well characterised. One of the driving forces behind fibrosis is Epithelial Mesenchymal Transition (EMT), a process where epithelial cells lose epithelial proteins including E-Cadherin, which is responsible for tight junctions. The cell moves to a more mesenchymal phenotype as it gains mesenchymal markers such as N-Cadherin (providing the cells with migration potential), Vimentin and Fibronectin (proteins excreted to help form the extracellular matrix), and the fibroblast proliferation transcription factors Snail, Slug and Twist. This review paper explores the EMT process in a range of lung diseases, details the common links that these have to cystic fibrosis, and explores how understanding EMT in cystic fibrosis may open up novel methods of treating patients with cystic fibrosis.

Endothelial smoothened-dependent hedgehog signaling is not required for sonic hedgehog induced angiogenesis or ischemic tissue repair

Sonic Hedgehog (Shh) signaling induces neovascularization and angiogenesis. It is not known whether the hedgehog signaling pathway in endothelial cells is essential to angiogenesis. Smoothened (Smo) transduces hedgehog signaling across the cell membrane. This study assessed whether endothelial Smoothened-dependent Shh signaling is required for Shh-mediated angiogenesis and ischemic tissue repair. Endothelial-specific smoothened knockout mice, eSmo^Null were created using Cre-lox recombination system. eSmo^Null mice had no observable phenotype at baseline and showed normal cardiac function. Smoothened in CD31+ cells isolated from eSmo^Null hearts was significantly reduced compared to CD31+ cells from eSmo^WT littermate control hearts. Fluorescence immunostaining of eSmo^Null heart sections showed Smo expression in endothelial cells was abolished. The hind-limb ischemia (HLI) model was used to assess the response to ischemic injury. Perfusion ratio, limb motor function, and limb necrosis were not significantly different after HLI between eSmo^Null mice and eSmo^WT. Capillary densities in the ischemic limb in eSmo^Null mice were also similar to eSmo^WT at 4 weeks after HLI. Next, response to exogenous Shh was assessed in the corneal angiogenesis model. There was no significant difference in corneal angiogenesis induced by administration of Shh pellets between eSmo^WT and eSmo^Null mice. Furthermore, in vitro experiments demonstrated that direct Shh had limited effects on endothelial cell proliferation and migration. However, conditioned media from Shh-treated fibroblasts had a more potent effect on endothelial cell proliferation and migration than non-treated conditioned media. Furthermore, Shh treatment of fibroblasts dramatically stimulated angiogenic growth factor expression, including PDGF-B, VEGF-A, HGF and IGF. PDGF-B was the most upregulated and may contribute to the large neo-vessels associated with Shh-induced angiogenesis. Taken together, these data demonstrate that Shh signaling via Smoothened in endothelial cells is not required for angiogenesis and ischemic tissue repair. Shh signaling via stromal cells likely mediates its angiogenic effects.

Heterotopic ossification and the elucidation of pathologic differentiation

Tissue regeneration following acute or persistent inflammation can manifest a spectrum of phenotypes ranging from the adaptive to the pathologic. Heterotopic Ossification (HO), the endochondral formation of bone within soft-tissue structures following severe injury serves as a prominent example of pathologic differentiation; and remains a persistent clinical issue incurring significant patient morbidity and expense to adequately diagnose and treat. The pathogenesis of HO provides an intriguing opportunity to better characterize the cellular and cell-signaling contributors to aberrant differentiation. Indeed, recent work has continued to resolve the unique cellular lineages, and causative pathways responsible for ectopic bone development yielding promising avenues for the development of novel therapeutic strategies shown to be successful in analogous animal models of HO development. This review details advances in the understanding of HO in the context of inciting inflammation, and explains how these advances inform the current standards of diagnosis and treatment.

Stem cells and heterotopic ossification: Lessons from animal models

Put most simply, heterotopic ossification (HO) is the abnormal formation of bone at extraskeletal sites. HO can be classified into two main subtypes, genetic and acquired. Acquired HO is a common complication of major connective tissue injury, traumatic central nervous system injury, and surgical interventions, where it can cause significant pain and postoperative disability. A particularly devastating form of HO is manifested in the rare genetic disorder, fibrodysplasia ossificans progressiva (FOP), in which progressive heterotopic bone formation occurs throughout life, resulting in painful and disabling cumulative immobility. While the central role of stem/progenitor cell populations in HO is firmly established, the identity of the offending cell type(s) remains to be conclusively determined, and little is known of the mechanisms that direct these progenitor cells to initiate cartilage and bone formation. In this review, we summarize current knowledge of the cells responsible for acquired HO and FOP, highlighting the strengths and weaknesses of animal models used to interrogate the cellular origins of HO.

Activin-dependent signaling in fibro/adipogenic progenitors causes fibrodysplasia ossificans progressiva

Fibrodysplasia ossificans progressiva (FOP) is a rare autosomal-dominant disorder characterized by progressive and profoundly disabling heterotopic ossification (HO). Here we show that fibro/adipogenic progenitors (FAPs) are a major cell-of-origin of HO in an accurate genetic mouse model of FOP (Acvr1^tnR206H). Targeted expression of the disease-causing type I bone morphogenetic protein (BMP) receptor, ACVR1(R206H), to FAPs recapitulates the full spectrum of HO observed in FOP patients. ACVR1(R206H)-expressing FAPs, but not wild-type FAPs, activate osteogenic signaling in response to activin ligands. Conditional loss of the wild-type Acvr1 allele dramatically exacerbates FAP-directed HO, suggesting that mutant and wild-type ACVR1 receptor complexes compete for activin ligands or type II BMP receptor binding partners. Finally, systemic inhibition of activin A completely blocks HO and restores wild-type-like behavior to transplanted Acvr1^R206H/+ FAPs. Understanding the cells that drive HO may facilitate the development of cell-specific therapeutic approaches to inhibit catastrophic bone formation in FOP.

Fibrodysplasia ossificans progressiva is a severe disorder characterized by heterotopic ossification, and is caused by mutations in ACVR1. Here, the authors show that expression of mutant ACVR1 in fibro/adipogenic progenitors recapitulates disease progression, and that this can be halted by systemic inhibition of activin A in mice.

The mechanism of TGF-β/miR-155/c-Ski regulates endothelial-mesenchymal transition in human coronary artery endothelial cells

Human coronary artery endothelial cells (HCAECs) have the potential to undergo fibrogenic endothelial–mesenchymal transition (EndMT), which results in matrix-producing fibroblasts and thereby contributes to the pathogenesis of cardiac fibrosis. Recently, the profibrotic cytokine transforming growth factor-β (TGF-β) is shown to be the crucial pathogenic driver which has been verified to induce EndMT. C-Ski is an important regulator of TGF-β signaling. However, the detailed role of c-Ski and the molecular mechanisms by which c-Ski affects TGF-β-induced EndMT in HCAECs are not largely elucidated. In the present study, we treated HCAECs with TGF-β of different concentrations to induce EndMT. We found that overexpression of c-Ski in HCAECs either blocked EndMT via hindering Vimentin, Snail, Slug, and Twist expression while enhancing CD31 expression, with or without TGF-β treatment. In contrast, suppression of c-Ski further enhanced EndMT. Currently, miRNA expression disorder has been frequently reported associating with cardiac fibrosis. By using online tools, we regarded miR-155 as a candidate miRNA that could target c-Ski, which was verified using luciferase assays. C-Ski expression was negatively regulated by miR-155. TGF-β-induced EndMT was inhibited by miR-155 silence; the effect of TGF-β on Vimentin, CD31, Snail, Slug, and Twist could be partially restored by miR-155. Altogether, these findings will shed light on the role and mechanism by which miR-155 regulates TGF-β-induced HCAECs EndMT via c-Ski to affect cardiac fibrosis, and miR-155/c-Ski may represent novel biomarkers and therapeutic targets in the treatment of cardiac fibrosis.

The traumatic bone: trauma-induced heterotopic ossification

Heterotopic ossification (HO) is a common occurrence after multiple forms of extensive trauma. These include arthroplasties, traumatic brain and spinal cord injuries, extensive burns in the civilian setting, and combat-related extremity injuries in the battlefield. Irrespective of the form of trauma, heterotopic bone is typically endochondral in structure and is laid down via a cartilaginous matrix. Once formed, the heterotopic bone typically needs to be excised surgically, which may result in wound healing complications, in addition to a risk of recurrence. Refinements of existing diagnostic modalities, like micro- and nano-CT are being adapted toward early intervention. Trauma-induced HO is a consequence of aberrant wound healing, systemic and local immune system activation, infections, extensive vascularization, and innervation. This intricate molecular crosstalk culminates in activation of stem cells that initiate heterotopic endochondral ossification. Development of animal models recapitulating the unique traumatic injuries has greatly facilitated the mechanistic understanding of trauma-induced HO. These same models also serve as powerful tools to test the efficacy of small molecules which specifically target the molecular pathways underlying ectopic ossification. This review summarizes the recent advances in the molecular understanding, diagnostic and treatment modalities in the field of trauma-induced HO.