Recent Topics in Fibrodysplasia Ossificans Progressiva

BRCC3 Regulation of ALK2 in Vascular Smooth Muscle Cells: Implication in Pulmonary Hypertension

BACKGROUND

An imbalance of antiproliferative BMP (bone morphogenetic protein) signaling and proliferative TGF-β (transforming growth factor-β) signaling is implicated in the development of pulmonary arterial hypertension (PAH). The posttranslational modification (eg, phosphorylation and ubiquitination) of TGF-β family receptors, including BMPR2 (bone morphogenetic protein type 2 receptor)/ALK2 (activin receptor-like kinase-2) and TGF-βR2/R1, and receptor-regulated Smads significantly affects their activity and thus regulates the target cell fate. BRCC3 modifies the activity and stability of its substrate proteins through K63-dependent deubiquitination. By modulating the posttranslational modifications of the BMP/TGF-β-PPARγ pathway, BRCC3 may play a role in pulmonary vascular remodeling, hence the pathogenesis of PAH.

METHODS

Bioinformatic analyses were used to explore the mechanism by which BRCC3 deubiquitinates ALK2. Cultured pulmonary artery smooth muscle cells (PASMCs), mouse models, and specimens from patients with idiopathic PAH were used to investigate the rebalance between BMP and TGF-β signaling in regulating ALK2 phosphorylation and ubiquitination in the context of pulmonary hypertension.

RESULTS

BRCC3 was significantly downregulated in PASMCs from patients with PAH and animals with experimental pulmonary hypertension. BRCC3, by de-ubiquitinating ALK2 at Lys-472 and Lys-475, activated receptor-regulated Smad1/5/9, which resulted in transcriptional activation of BMP-regulated PPARγ, p53, and Id1. Overexpression of BRCC3 also attenuated TGF-β signaling by downregulating TGF-β expression and inhibiting phosphorylation of Smad3. Experiments in vitro indicated that overexpression of BRCC3 or the de-ubiquitin-mimetic ALK2-K472/475R attenuated PASMC proliferation and migration and enhanced PASMC apoptosis. In SM22α-BRCC3-Tg mice, pulmonary hypertension was ameliorated because of activation of the ALK2-Smad1/5-PPARγ axis in PASMCs. In contrast, Brcc3-/- mice showed increased susceptibility of experimental pulmonary hypertension because of inhibition of the ALK2-Smad1/5 signaling.

CONCLUSIONS

These results suggest a pivotal role of BRCC3 in sustaining pulmonary vascular homeostasis by maintaining the integrity of the BMP signaling (ie, the ALK2-Smad1/5-PPARγ axis) while suppressing TGF-β signaling in PASMCs. Such rebalance of BMP/TGF-β pathways is translationally important for PAH alleviation.

How Activin A Became a Therapeutic Target in Fibrodysplasia Ossificans Progressiva

Fibrodysplasia ossificans progressiva (FOP) is a rare genetic disorder characterized by episodic yet cumulative heterotopic ossification (HO) of skeletal muscles, tendons, ligaments, and fascia. FOP arises from missense mutations in Activin Receptor type I (ACVR1), a type I bone morphogenetic protein (BMP) receptor. Although initial findings implicated constitutive activity of FOP-variant ACVR1 (ACVR1FOP) and/or hyperactivation by BMPs, it was later shown that HO in FOP requires activation of ACVR1FOP by Activin A. Inhibition of Activin A completely prevents HO in FOP mice, indicating that Activin A is an obligate driver of HO in FOP, and excluding a key role for BMPs in this process. This discovery led to the clinical development of garetosmab, an investigational antibody that blocks Activin A. In a phase 2 trial, garetosmab inhibited new heterotopic bone lesion formation in FOP patients. In contrast, antibodies to ACVR1 activate ACVR1FOP and promote HO in FOP mice. Beyond their potential clinical relevance, these findings have enhanced our understanding of FOP's pathophysiology, leading to the identification of fibroadipogenic progenitors as the cells that form HO, and the discovery of non-signaling complexes between Activin A and wild type ACVR1 and their role in tempering HO, and are also starting to inform biological processes beyond FOP.

Fibrodysplasia Ossificans Progressiva Mimics Generalized Dystonia Disorder: A Case Report

Fibrodysplasia ossificans progressiva (FOP) is an autosomal dominant disorder characterized by congenital deformities of the big toes and the progressive formation of extra-skeletal bone within soft tissues. The underlying genetic cause of FOP is mostly due to gain-of-function mutations in the AVCR1/ALK2 genes. These mutations cause aberrant bone morphogenetic protein (BMP) signaling pathways and eventually result in cumulative musculoskeletal impairment. FOP has a prevalence of approximately one in every 2 million people worldwide, with nearly 90% of patients being misdiagnosed, possibly leading to an underestimation of its true prevalence. To the best of our knowledge, there are only three reported cases in Saudi Arabia. We report a case of a 21-year-old female patient, a product of a consanguineous marriage, referred to the neurology clinic for new-onset dysphagia and dysarthria in association with progressive painful muscle stiffness, which started at the age of four years. The diagnosis of generalized dystonia disorder was suspected, but eventually the whole exome sequencing showed a pathogenic missense mutation in the ACVR1 gene, confirming the diagnosis of FOP. FOP is a rare, debilitating disorder that can be difficult to diagnose and manage. Current research efforts are focused on early diagnosis and a high index of suspicion to help prevent unnecessary investigations and procedures, slow the progression of the disease, and promote patients' quality of life and long-term outcomes.

A Novel De Novo Frameshift Pathogenic Variant in the FAM111B Resulting in Progressive Osseous Heteroplasia Phenotype

INTRODUCTION

Progressive osseous heteroplasia (POH) is a rare, debilitating disorder characterized by heterotopic ossification in the skin and muscles, resulting in contractures of the joints and progressive loss of function. While 60-70% of the POH patients have paternally inherited, inactivating pathogenic variants in GNAS, the remaining 30-40% have no known etiology. FAM111B pathogenic variants, located on chromosome 11q12.1, cause POIKTMP (hereditary fibrosing poikiloderma with tendon contractures, myopathy, and pulmonary fibrosis), a very rare, autosomal-dominant disorder with high frequency of de novo missense pathogenic variants, which affects multiple tissues and organs, causing extensive fibrosis and muscle adiposis, though the exact mechanism is unknown. To our knowledge, there are no reports of FAM111B associated with POH. We describe the first case of POH phenotype associated with a novel de novo frameshift pathogenic variant in the FAM111B and present an analysis of the protein structure and function caused by this genomic disruption.

CASE

A 15-year-old African-American male presented with generalized calcific nodules, progressive contractures, and muscle weakness leading to immobility, beginning at 6 years of age. Cutaneous examination showed generalized hard nodules varying from small to plaque-like ulcerated erupted skin lesions. Biochemical evaluation revealed 25(OH) vitamin D insufficiency (20 ng/mL), and normal levels of parathyroid hormone, FGF-23, alkaline phosphatase, calcium, and phosphorus. Skeletal survey radiographs and computed tomography (CT) of the chest, abdomen, and pelvis showed extensive soft tissue and muscle heterotopic ossifications involving shoulders, axillae, trunk, abdomen, pelvis, upper and lower extremities, in a clumped, conglomerate distribution within muscle, subcutaneous fat, and in some areas extending to the skin. There was no pulmonary fibrosis on the chest CT. The clinical and radiographic findings were most consistent with POH. A trio-clinical exome sequencing revealed a de novo heterozygous likely pathogenic variant in the FAM111B (OMIM # 615584) (c.1462delT [p.Cys488Valfs*21]). The resulted frameshift change in exon 4 replaced C-terminal region with 21 alternative amino acids. Multiple, previously reported disease-associated variants appear to localize within the trypsin-like cysteine/serine peptidase domain in which this variant occurs, supporting the functional significance of this region, though none have been previously reported to be associated with POH phenotype. Our 3D protein modeling showed obliteration of predicted protein folding and structure, and elimination of the zinc-binding domain, likely severely affecting protein function.

CONCLUSION

This is the first case of POH phenotype associated with a novel de novo pathogenic frameshift variant in FAM111B. Whether the frameshift change in FAM111B predicts POH remains unclear. Further evaluations are necessary to fully elucidate this finding and the potential role and mechanism by which the FAM111B variants contributes to POH phenotype.

Cytoskeleton Reorganization in EndMT-The Role in Cancer and Fibrotic Diseases

Chronic inflammation promotes endothelial plasticity, leading to the development of several diseases, including fibrosis and cancer in numerous organs. The basis of those processes is a phenomenon called the endothelial–mesenchymal transition (EndMT), which results in the delamination of tightly connected endothelial cells that acquire a mesenchymal phenotype. EndMT-derived cells, known as the myofibroblasts or cancer-associated fibroblasts (CAFs), are characterized by the loss of cell–cell junctions, loss of endothelial markers, and gain in mesenchymal ones. As a result, the endothelium ceases its primary ability to maintain patent and functional capillaries and induce new blood vessels. At the same time, it acquires the migration and invasion potential typical of mesenchymal cells. The observed modulation of cell shape, increasedcell movement, and invasion abilities are connected with cytoskeleton reorganization. This paper focuses on the review of current knowledge about the molecular pathways involved in the modulation of each cytoskeleton element (microfilaments, microtubule, and intermediate filaments) during EndMT and their role as the potential targets for cancer and fibrosis treatment.

Exploration of marine natural resources in Indonesia and development of efficient strategies for the production of microbial halogenated metabolites

Nature is a prolific source of organic products with diverse scaffolds and biological activities. The process of natural product discovery has gradually become more challenging, and advances in novel strategic approaches are essential to evolve natural product chemistry. Our focus has been on surveying untouched marine resources and fermentation to enhance microbial productive performance. The first topic is the screening of marine natural products isolated from Indonesian marine organisms for new types of bioactive compounds, such as antineoplastics, antimycobacterium substances, and inhibitors of protein tyrosine phosphatase 1B, sterol O-acyl-transferase, and bone morphogenetic protein-induced osteoblastic differentiation. The unique biological properties of marine organohalides are discussed herein and attempts to efficiently produce fungal halogenated metabolites are documented. This review presents an overview of our recent work accomplishments based on the MONOTORI study.

Accumulated Knowledge of Activin Receptor-Like Kinase 2 (ALK2)/Activin A Receptor, Type 1 (ACVR1) as a Target for Human Disorders

Activin receptor-like kinase 2 (ALK2), also known as Activin A receptor type 1 (ACVR1), is a transmembrane kinase receptor for members of the transforming growth factor-β family. Wild-type ALK2/ACVR1 transduces osteogenic signaling in response to ligand binding. Fifteen years ago, a gain-of-function mutation in the ALK2/ACVR1 gene was detected in patients with the genetic disorder fibro-dysplasia ossificans progressiva, which is characterized by heterotopic ossification in soft tissues. Additional disorders, such as diffuse intrinsic pontin glioma, diffuse idiopathic skeletal hyperostosis, primary focal hyperhidrosis, and congenital heart defects, have also been found to be associated with ALK2/ACVR1. These findings further expand in vitro and in vivo model system research and promote our understanding of the molecular mechanisms of the pathogenesis and development of novel therapeutics and diagnosis for disorders associated with ALK2/ACVR1. Through aggressive efforts, some of the disorders associated with ALK2/ACVR1 will be overcome in the near future.

New insights on fibrodysplasia ossificans progressiva: discussion of an autoptic case report and brief literature review

Fibrodysplasia ossificans progressiva (FOP) is a rare genetic condition with soft tissue progressive ossification, leading to severe disability. We describe a 27-years-old female affected by FOP who died after a fall. An autopsy was performed. Upper and lower extremities resulted in fixed flexion, with kyphoscoliosis of the spine and chest wall deformity. Moreover, a cranial fracture was pointed out. At histology, atypical abundance of corpora amylacea in gray matter was observed. In a sample of macroscopically non-affected muscular tissue, small areas with necrosis of myocytes and hyperplasia of fibroblasts were seen in light microscopy, with intracellular inorganic dystrophic inclusions in transmission electron microscopy. Thyroid gland histology showed diffuse lymphocytic infiltration. Postmortem examination of FOP patients provided precious information about involvement of other tissues, suggesting an initial and widespread inflammatory/dystrophic phase, to be further investigated, because it might reveal new insights about a FOP mutation cascade.

Inhibitory effects of sesquiterpene lactones from the Indonesian marine sponge Lamellodysidea cf. herbacea on bone morphogenetic protein-induced osteoblastic differentiation

A new unique sesquiterpene lactone, bicyclolamellolactone A (1), was isolated together with two known monocyclofarnesol-type sesquiterpenes, lamellolactones A (2) and B (3), from the Indonesian marine sponge Lamellodysidea sp. (cf. L. herbacea). The planar structure of 1 was assigned based on its spectroscopic data (1D and 2D NMR, HRESIMS, UV, and IR spectra). The relative and absolute configuration of 1 was determined by comparison of its calculated and experimental electronic circular dichroism spectra in combination with NOESY correlations. Compounds 1-3 inhibited bone morphogenic protein (BMP)-induced alkaline phosphatase activity in mutant BMP receptor-carrying C2C12 cells with IC₅₀ values of 51, 4.6, and 20 μM, respectively.

Genomic Context and Mechanisms of the ACVR1 Mutation in Fibrodysplasia Ossificans Progressiva

Basic research in Fibrodysplasia Ossificans Progressiva (FOP) was carried out in the various fields involved in the disease pathophysiology and was important for designing therapeutic approaches, some of which were already developed as ongoing or planned clinical trials. Genetic research was fundamental in identifying the FOP causative mutation, and the astonishing progress in technologies for genomic analysis, coupled to related computational methods, now make possible further research in this field. We present here a review of molecular and cellular factors which could explain why a single mutation, the R206H in the ACVR1 gene, is absolutely prevalent in FOP patients. We also address the mechanisms by which FOP expressivity could be modulated by cis-acting variants in the ACVR1 genomic region in human chromosome 2q. Finally, we also discuss the general issue of genetic modifiers in FOP.

Screening for Small Molecule Inhibitors of BMP-Induced Osteoblastic Differentiation from Indonesian Marine Invertebrates

Fibrodysplasia ossificans progressiva (FOP) is a rare congenital disorder with heterotopic ossification (HO) in soft tissues. The abnormal activation of bone morphogenetic protein (BMP) signaling by a mutant activin receptor-like kinase-2 (ALK2) leads to the development of HO in FOP patients, and, thus, BMP signaling inhibitors are promising therapeutic applications for FOP. In the present study, we screened extracts of 188 Indonesian marine invertebrates for small molecular inhibitors of BMP-induced alkaline phosphatase (ALP) activity, a marker of osteoblastic differentiation in a C2C12 cell line stably expressing ALK2(R206H) (C2C12(R206H) cells), and identified five marine sponges with potent ALP inhibitory activities. The activity-guided purification of an EtOH extract of marine sponge Dysidea sp. (No. 256) resulted in the isolation of dysidenin (1), herbasterol (2), and stellettasterol (3) as active components. Compounds 1–3 inhibited ALP activity in C2C12(R206H) cells with IC₅₀ values of 2.3, 4.3, and 4.2 µM, respectively, without any cytotoxicity, even at 18.4–21.4 µM. The direct effects of BMP signaling examined using the Id1WT4F-luciferase reporter assay showed that compounds 1–3 did not decrease the reporter activity, suggesting that they inhibit the downstream of the Smad transcriptional step in BMP signaling.

Fibrodysplasia ossificans progressiva: current concepts from bench to bedside

Heterotopic ossification (HO) is a disorder characterised by the formation of ectopic bone in soft tissue. Acquired HO typically occurs in response to trauma and is relatively common, yet its aetiology remains poorly understood. Genetic forms, by contrast, are very rare, but provide insights into the mechanisms of HO pathobiology. Fibrodysplasia ossificans progressiva (FOP) is the most debilitating form of HO. All patients reported to date carry heterozygous gain-of-function mutations in the gene encoding activin A receptor type I (ACVR1). These mutations cause dysregulated bone morphogenetic protein (BMP) signalling, leading to HO at extraskeletal sites including, but not limited to, muscles, ligaments, tendons and fascia. Ever since the identification of the causative gene, developing a cure for FOP has been a focus of investigation, and studies have decoded the pathophysiology at the molecular and cellular levels, and explored novel management strategies. Based on the established role of BMP signalling throughout HO in FOP, therapeutic modalities that target multiple levels of the signalling cascade have been designed, and some drugs have entered clinical trials, holding out hope of a cure. A potential role of other signalling pathways that could influence the dysregulated BMP signalling and present alternative therapeutic targets remains a matter of debate. Here, we review the recent FOP literature, including pathophysiology, clinical aspects, animal models and current management strategies. We also consider how this research can inform our understanding of other types of HO and highlight some of the remaining knowledge gaps.

Summary: Fibrodysplasia ossificans progressiva is a rare disease characterised by progressive heterotopic bone formation. Here, we present a comprehensive summary of the recent literature on this debilitating condition and discuss approaches to solving this clinical puzzle.

Clinical Aspects and Current Therapeutic Approaches for FOP

Fibrodysplasia ossificans progressiva (FOP) is an extremely rare heritable disorder of connective tissues characterized by progressive heterotopic ossification in various skeletal sites. It is caused by gain-of-function mutations in the gene encoding activin A receptor type I (ACVR1)/activin-like kinase 2 (ALK2), a bone morphogenetic protein (BMP) type I receptor. Heterotopic ossification is usually progressive leading to severe deformities in the trunk and extremities. Early clinical diagnosis is important to prevent unnecessary iatrogenic harm or trauma. Clinicians should become aware of early detectable skeletal malformations, including great toe deformities, shortened thumb, neck stiffness associated with hypertrophy of the posterior elements of the cervical spine, multiple ossification centers in the calcaneus, and osteochondroma-like lesions of the long bones. Although there is presently no definitive medical treatment to prevent, stop or reverse heterotopic ossification in FOP, exciting advances of novel pharmacological drugs focusing on target inhibition of the activated ACVR1 receptor, including palovarotene, REGN 2477, rapamycin, and saracatinib, have developed and are currently in clinical trials.

Design of primers for direct sequencing of nine coding exons in the human ACVR1 gene

The human ACVR1 gene encodes a transmembrane protein consisting of 509 amino acids called activin A receptor, type I (ACVR1) or activin receptor-like kinase 2 (ALK2) and has nine coding exons. The ALK2 protein functions as a signaling receptor for ligands of the transforming growth factor-β family. In the human ACVR1 gene, approximately 20 types of heterozygotic mutations in the coding exons have been associated with congenital disorders and somatic cancer, such as fibrodysplasia ossificans progressiva (FOP), diffuse intrinsic pontine glioma, diffuse idiopathic skeletal hyperostosis and some congenital heart disorders. In the present study, we designed primers for direct sequencing of the nine coding exons in the human ACVR1 gene. The reliability of the primers was examined by PCR and DNA sequencing using genomic DNA prepared from peripheral blood or swab samples of three patients with FOP who had different mutations in the ACVR1 gene. A single nucleotide heterozygotic mutation was identified in each genomic sample without additional mutations in other regions. Therefore, the primers designed for the nine coding exons of the ACVR1 gene could be useful for the genetic diagnosis of patients who may have disorders associated with mutations in the ACVR1 gene.

Penicillic Acid Congener, a New Inhibitor of BMP-Induced Alkaline Phosphatase Activity in Myoblasts, Produced by the Fungus Penicillium sp. BF-0343

During our screening for microbial regulators of bone metabolism, a new compound, 6-ethoxy-5,6-dihydropenillic acid (1), was isolated together with a known and structurally related penicillic acid (2) from the culture broth of the soil-derived fungus Penicillium sp. BF-0343. The structure of 1 was elucidated by various spectroscopic data including nuclear magnetic resonance experiments. Compounds 1 and 2 dose-dependently inhibited bone morphogenetic protein–induced alkaline phosphatase activity in myoblasts with half-maximal inhibitory concentration values of 19.8 and 2.1 μM, respectively.

ALK2: A Therapeutic Target for Fibrodysplasia Ossificans Progressiva and Diffuse Intrinsic Pontine Glioma

Fibrodysplasia ossificans progressiva (FOP) and diffuse intrinsic pontine glioma (DIPG) are diseases that typically manifest in childhood and are associated with severely reduced life expectancy. However, there are currently no effective therapies for these diseases, which remain incurable. Activin receptor-like kinase-2 (ALK2), encoded by the ACVR1 gene, is a bone morphogenetic protein (BMP) type-I receptor subtype that plays an important physiological role in the development of bones, muscles, brain, and other organs. Constitutively active mutants of ALK2 have been identified as causative of FOP and involved in the tumorigenesis of DIPG owing to abnormal activation of BMP signaling, and therefore have emerged as promising treatment targets. Here, we describe these two diseases, along with the link to ALK2 signal transduction, and highlight potential ALK2 inhibitors that are under development to offer new hope for patients with FOP and DIPG.

Role of Signal Transduction Pathways and Transcription Factors in Cartilage and Joint Diseases

Osteoarthritis and rheumatoid arthritis are common cartilage and joint diseases that globally affect more than 200 million and 20 million people, respectively. Several transcription factors have been implicated in the onset and progression of osteoarthritis, including Runx2, C/EBPβ, HIF2α, Sox4, and Sox11. Interleukin-1 β (IL-1β) leads to osteoarthritis through NF-ĸB, IκBζ, and the Zn²⁺-ZIP8-MTF1 axis. IL-1, IL-6, and tumor necrosis factor α (TNFα) play a major pathological role in rheumatoid arthritis through NF-ĸB and JAK/STAT pathways. Indeed, inhibitory reagents for IL-1, IL-6, and TNFα provide clinical benefits for rheumatoid arthritis patients. Several growth factors, such as bone morphogenetic protein (BMP), fibroblast growth factor (FGF), parathyroid hormone-related protein (PTHrP), and Indian hedgehog, play roles in regulating chondrocyte proliferation and differentiation. Disruption and excess of these signaling pathways cause genetic disorders in cartilage and skeletal tissues. Fibrodysplasia ossificans progressive, an autosomal genetic disorder characterized by ectopic ossification, is induced by mutant ACVR1. Mechanistic target of rapamycin kinase (mTOR) inhibitors can prevent ectopic ossification induced by ACVR1 mutations. C-type natriuretic peptide is currently the most promising therapy for achondroplasia and related autosomal genetic diseases that manifest severe dwarfism. In these ways, investigation of cartilage and chondrocyte diseases at molecular and cellular levels has enlightened the development of effective therapies. Thus, identification of signaling pathways and transcription factors implicated in these diseases is important.

Alendronate disturbs femoral growth due to changes during immunolocalization of transforming growth factor-β1 and bone morphogenetic protein-2 in epiphyseal plate

BACKGROUND

The epiphyseal growth plate is an important anatomical segment localized on the ends of a long bone. Despite the abovementioned atractive reasons for alendronate’s use, few data on the effect of alendronate during epiphyseal growth exist.

AIM

Verify the effect of alendronate on the growth epiphyseal plate, and compare its effect with the size of the femur during the double-staining of the immunolocalization of transforming growth factor-β1 (TGF-β1) and bone morphogenetic protein-2 (BMP2) in endochondral ossifing in specimens that have received alendronate.

METHODS

Forty newborn rats were randomly divided into two groups: a control group (were given applications of 1 mg/kg physiologic saline) and a group that received Alendronate (a dose of 2.5 mg/kg). These groups were then divided into two subgroups for euthanasia in two and 12 d of life. After euthanasia, the femurs were removed, and the femoral bones were measured linearly between the apex of the greater trochanter until the lower intercondylar midlle face to verify the probable bone growth between 3 and 12 d in control and alednroanto treated rats. Posteriorly, the surgical pieces were also sent to the histopathology laboratory to produce histological slides. The obtained slides were stained with hematoxylin and eosin to measure each of the cartilage zones in endochondral development. and other slides were immunohistochemically tested for anti- TGF-β1 and BMP-2 antibodies to investigate the immunolocalization of these proteins in the epiphyseal plaque area.

RESULTS

On the third day, some diferences between the control group and specimens treated with alendronate were verified. Macroscopiccaly, we found similarities in size between the femoral bones when we compared the control group with the specimens that received alendronate. On the 12^th day, the bone size of the mice receiving the drug was significantly smaller than those of the control group. These results coincide with changes in the TGF-β1 and BMP-2 expression. In the specimens that received alendronate, the TGF-β1 was expressed in some sites of trabecular bone that was neoformed, peripherally to the bone marrow area. The BMP-2 was also positive in proliferative chondrocytes and hypertrofic chondrocytes. On the 12^th day, all layers of chondrocytes exhibited positivity for BMP-2 in the specimens that received alendronate. In the interface between the trabecular bone and cartilage, an area of disorganized bone deposition was evident. Neoformed bone also appeared to be different at 12 d. In the control group, BMP-2 was positive in an intense area of bone trabeculae, whereas the alendronate-treated group showed TGF-β1 positive trabeculae and a greater bone area.

CONCLUSION

Alendronate alters the immunolocalization of TGF-β1 and BMP-2 simultaneously, a condition that changes the usual histological aspects of the cartilage zone and impairs epiphysis growth and femur growth.

Fibrodysplasia ossificans progressiva: lessons learned from a rare disease

PURPOSE OF REVIEW

Fibrodysplasia ossificans progressiva (FOP) is an extremely rare and severely disabling autosomal dominant disease that is yet to be clearly understood. The purpose of this review is to present recent literature on pathophysiology, clinical features, diagnosis and treatment of FOP.

RECENT FINDINGS

FOP is characterized by congenital great toe deformity and progressive heterotopic ossifications in connective tissue. Heterotopic ossifications occur after painful flare-ups that can arise spontaneously or can be triggered by minor trauma. Each flare-up ultimately causes restriction of related-joint, and along with the others eventually leads to immobility. Death is usually caused by pulmonary complications because of chest wall involvement. The causative gene of FOP is activin A receptor type 1 (ACVR1), a bone morphogenetic protein-signalling component, which normally acts to inhibit osteoblastogenesis. The treatment of FOP is still preventive and supportive.

SUMMARY

Although there are still gaps in the underlying mechanism of FOP, effective treatment options, such as potential pharmacologic targets and cell-based therapies are promising for the future. Some of these were tested without a clinical trial setting, and are currently in the process of evidence-based research.

Propranolol and ascorbic acid in control of fibrodysplasia ossificans progressiva flare-ups due to accidental falls

Fibrodysplasia ossificans progressiva (FOP) is a rare, intractable and devastating genetic connective tissue disorder characterized by progressive ectopic ossification in the soft tissues and skeleton. Three patients, one teenage girl (P1), one male adult (P2) and one male child (P3), were studied and treated with FOPCON (combined formulation of 14 mg of propranolol and 250 mg of ascorbic acid), given three times per day. P1 started treatment in March 2012, P2 in October 2012 and P3 in July 2015. The clinical follow-up of these three patients, before initiating treatment with FOPCON, showed that FOP flare-ups used to occur frequently and that under FOPCON therapy, none of these patients had flare-ups. The striking feature of this treatment with FOPCON, is that, all three cases suffered accidental falls with documented injures until complete healing and that where major flare-ups should occur, injures or sequels, there was none. The present clinical observation shows that ascorbic acid plus the nonspecific beta blocker propranolol can be effectively useful, when administered previously and continually, in the prophylaxis of FOP flare-ups, especially for accidental falls. In this regard, FOPCON could be a prophylactic aid in cases of surgery of patients with FOP, hoping that it may benefit patients from having the severe sequels, characteristic of heterotopic bone formation. All three patients reported, to date, they no longer had flare-ups nor heterotopic ossification and showed normal scar healing.

Discovery of Heterotopic Bone-Inducing Activity in Hard Tissues and the TGF-β Superfamily

Bone is a unique organ because it can be experimentally induced in soft tissues by implanting a single growth factor, bone morphogenetic protein (BMP). Heterotopic bone-inducing activity was found in demineralized bone matrix in 1965. The characterization of this activity in bone enabled the purification and molecular cloning of BMPs and showed that they are members of the transforming growth factor-β (TGF-β) superfamily. Assay systems developed for this bone-inducing activity revealed the molecular mechanisms of the intracellular signaling of members of the superfamily, including BMPs. Moreover, they are being applied to elucidate molecular mechanisms and to develop novel therapeutics for a disease caused by an abnormality in BMP signaling.