Over-expression of wild-type ACVR1 in fibrodysplasia ossificans progressiva mice rescues perinatal lethality and inhibits heterotopic ossification

Fibrodysplasia ossificans progressiva (FOP) is a devastating disease of progressive heterotopic bone formation for which effective treatments are currently unavailable. FOP is caused by dominant gain-of-function mutations in the receptor ACVR1 (also known as ALK2), which render the receptor inappropriately responsive to activin ligands. In previous studies, we developed a genetic mouse model of FOP that recapitulates most clinical aspects of the disease. In this model, genetic loss of the wild-type Acvr1 allele profoundly exacerbated heterotopic ossification, suggesting the hypothesis that the stoichiometry of wild-type and mutant receptors dictates disease severity. Here, we tested this model by producing FOP mice that conditionally over-express human wild-type ACVR1. Injury-induced heterotopic ossification (HO) was completely blocked in FOP mice when expression of both the mutant and wild-type receptor were targeted to Tie2-positive cells, which includes fibro/adipogenic progenitors (FAPs). Perinatal lethality of Acvr1R206H/+ mice was rescued by constitutive ACVR1 over-expression and these mice survived to adulthood at predicted Mendelian frequencies. Constitutive over-expression of ACVR1 also provided protection from spontaneous HO, and the incidence and severity of injury-induced HO in these mice was dramatically reduced. Analysis of pSMAD1/5/8 signaling both in cultured cells and in vivo indicates that ACVR1 over-expression functions cell-autonomously by reducing osteogenic signaling in response to activin A. Manipulating the stoichiometry of FOP-causing and wild-type ACVR1 receptors may provide the foundation for novel therapeutic strategies to treat this devastating disease.

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Post-COVID-19 exacerbation of fibrodysplasia ossificans progressiva with multiple flare-ups and extensive heterotopic ossification in a 45-year-old female patient

Rheumatology International ◽

10.1007/s00296-021-04911-6 ◽

2021 ◽

Author(s):

Lovorka Grgurevic ◽

Rudjer Novak ◽

Stela Hrkac ◽

Grgur Salai ◽

Simeon Grazio

Keyword(s):

Heterotopic Ossification ◽

Female Patient ◽

Soft Tissues ◽

Hereditary Disease ◽

Fibrodysplasia Ossificans Progressiva ◽

Heterotopic Bone ◽

Heterotopic Bone Formation ◽

Cytokine Analysis ◽

Viral Illness ◽

First Time

AbstractFibrodyplasia ossificans progressiva (FOP) is a rare hereditary disease, which has a variable course characterized by occasional flare-ups of heterotopic ossification (HO) in soft tissues that are followed by swelling, stiffness, pain and warmth. Here, we report for the first time a case of a 45-year-old female patient with known FOP recovering from COVID-19 with disease progression potentially linked with the viral illness. In December 2020 the patient contracted a mild form of COVID-19 infection without need for hospital admission. Since January 2021, the patient felt unwell, with occasional abdominal pain which progressively intensified. In March 2021 she presented with new onset of HO, complaining of pain, swelling and thickening sensation in the lower abdomen and left part of the neck. Computerized tomography (CT) and cytokine analysis were performed. CT scan revealed new heterotopic bone formation in multiple soft tissue areas of the neck indicating clear radiological progression. Radiotherapy, which has proven to be an efficient tool to control HO in this patient, was not able to halt HO formation after COVID-19 infection. Cytokine analysis of a plasma sample obtained during a flare-up after COVID-19 infection showed a significantly elevated pro-inflammatory cytokines compared to a flare-up panel prior to infection. Of the 23 analyzed levels of cytokines, a staggering number of 21 were above normal levels. This case is the first confirmation of uncontrolled post-COVID-19 effects in a FOP patient, which manifested with flare-ups followed by progressive HO, possibly caused by a thus far, never described form of post-COVID syndrome.

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ACVR1 antibodies exacerbate heterotopic ossification in fibrodysplasia ossificans progressiva (FOP) by activating FOP-mutant ACVR1

10.1101/2021.07.18.452865 ◽

2021 ◽

Author(s):

Senem Aykul ◽

Lily Huang ◽

Lili Wang ◽

Nanditha Das ◽

Sandra Reisman ◽

...

Keyword(s):

Heterotopic Ossification ◽

Genetic Disorder ◽

Activin A ◽

Bmp Signaling ◽

Fibrodysplasia Ossificans Progressiva ◽

Bone Lesions ◽

Type I ◽

Heterotopic Bone ◽

Wild Type ◽

Blocking Antibodies

Fibrodysplasia ossificans progressiva (FOP) is a rare genetic disorder whose most debilitating pathology is progressive and cumulative heterotopic ossification (HO) of skeletal muscles, ligaments, tendons, and fascia. FOP is caused by amino acid-altering mutations in ACVR1, a type I BMP receptor. The mutations occur in the region encoding the intracellular domain of ACVR1 and bestow FOP-mutant ACVR1 with the neofuction of recognizing Activin A as an agonistic ligand. (In contrast, Activin A antagonizes BMP signaling from wild type ACVR1.) This neofuction is required for HO in FOP as inhibition of Activin A stops the initiation and progression of heterotopic bone lesions in FOP. These results unequivocally demonstrated that HO in FOP is dependent on activation of FOP-mutant ACVR1 by ligand and set the stage to explore ACVR1-blocking antibodies as an additional potential therapeutic for FOP. Surprisingly, ACVR1 antibodies stimulate - rather than inhibit - HO and induce Smad1/5/8 phosphorylation of FOP-mutant ACVR1. This property is restricted to FOP-mutant ACVR1, as signaling by wild type ACVR1 is inhibited by these antibodies, as is trauma-induced HO. These results uncover yet an additional novel property of FOP-mutant ACVR1 and indicate that anti-ACVR1 antibodies should not be considered as a therapeutic strategy for FOP

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Synostosis Between Pubic Bones due to Neurogenic, Heterotopic Ossification

The Scientific World JOURNAL ◽

10.1100/tsw.2006.387 ◽

2006 ◽

Vol 6 ◽

pp. 2486-2490 ◽

Cited By ~ 1

Author(s):

Subramanian Vaidyanathan ◽

Peter L. Hughes ◽

Bakul M. Soni

Keyword(s):

Bone Formation ◽

Heterotopic Ossification ◽

Foley Catheter ◽

Symphysis Pubis ◽

Heterotopic Bone ◽

Heterotopic Bone Formation ◽

Suprapubic Catheter ◽

Suprapubic Cystostomy ◽

Urine Leak ◽

Irregular Margin

Neurogenic, heterotopic ossification is characterised by the formation of new, extraosseous (ectopic) bone in soft tissue in patients with neurological disorders. A 33-year-old female, who was born with spina bifida, paraplegia, and diastasis of symphysis pubis, had indwelling urethral catheter drainage and was using oxybutynin bladder instillations. She was prescribed diuretic for swelling of feet, which aggravated bypassing of catheter. Hence, suprapubic cystostomy was performed. Despite anticholinergic therapy, there was chronic urine leak around the suprapubic catheter and per urethra. Therefore, the urethra was mobilised and closed. After closure of the urethra, there was no urine leak from the urethra, but urine leak persisted around the suprapubic catheter. Cystogram confirmed the presence of a Foley balloon inside the bladder; there was no urinary fistula. The Foley balloon ruptured frequently, leading to extrusion of the Foley catheter. X-ray of abdomen showed heterotopic bone formation bridging the gap across diastasis of symphysis pubis. CT of pelvis revealed heterotopic bone lying in close proximity to the balloon of the Foley catheter; the sharp edge of heterotopic bone probably acted like a saw and led to frequent rupture of the balloon of the Foley catheter. Unique features of this case are: (1) temporal relationship of heterotopic bone formation to suprapubic cystostomy and chronic urine leak; (2) occurrence of heterotopic ossification in pubic region; (3) complications of heterotopic bone formation viz. frequent rupture of the balloon of the Foley catheter by the irregular margin of heterotopic bone and difficulty in insertion of suprapubic catheter because the heterotopic bone encroached on the suprapubic track; (4) synostosis between pubic bones as a result of heterotopic ossification..Common aetiological factors for neurogenic, heterotopic ossification, such as forceful manipulation, trauma, or spasticity, were absent in this patient. Since heterotopic bone formation was observed in the pubic region after suprapubic cystostomy and chronic urine leak, it is possible that risk factors related to the urinary tract might have played a role in heterotopic bone formation, which resulted in synostosis between pubic bones.

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Clinical Aspects and Current Therapeutic Approaches for FOP

Biomedicines ◽

10.3390/biomedicines8090325 ◽

2020 ◽

Vol 8 (9) ◽

pp. 325

Author(s):

Hiroshi Kitoh

Keyword(s):

Heterotopic Ossification ◽

Fibrodysplasia Ossificans Progressiva ◽

Clinical Aspects ◽

Type I ◽

Gene Encoding ◽

Neck Stiffness ◽

Skeletal Malformations ◽

Morphogenetic Protein ◽

Heritable Disorder ◽

Ossification Centers

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.

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Saracatinib is an efficacious clinical candidate for fibrodysplasia ossificans progressiva

10.1101/2020.10.29.360370 ◽

2020 ◽

Author(s):

Eleanor Williams ◽

Jana Bagarova ◽

Georgina Kerr ◽

Dong-Dong Xia ◽

Elsie S. Place ◽

...

Keyword(s):

Heterotopic Ossification ◽

Soft Tissues ◽

Kinase Inhibitor ◽

Tissue Injury ◽

Soft Tissue Injury ◽

Biologically Active ◽

Fibrodysplasia Ossificans Progressiva ◽

Heterotopic Bone ◽

Transgenic Mouse Line ◽

Clinical Candidate

AbstractCurrently, no effective therapies exist for fibrodysplasia ossificans progressiva (FOP), a rare congenital syndrome in which heterotopic bone is formed in soft tissues due to dysregulated activity of the bone morphogenetic protein (BMP) receptor kinase ALK2/ACVR1. From a screen of known biologically active compounds, we identified saracatinib as a potent ALK2 kinase inhibitor. In enzymatic and cell-based assays, saracatinib preferentially inhibited ALK2 compared with other receptors of the BMP/TGFβ signaling pathway, and induced dorsalization in zebrafish embryos consistent with BMP antagonism. We further tested the efficacy of saracatinib using an inducible ACVR1Q207D transgenic mouse line, which provides a model of heterotopic ossification, as well as an inducible ACVR1R206H knock-in, which serves as a genetically and physiologically faithful model of FOP. In both models, saracatinib was well tolerated and potently inhibited the development of heterotopic ossification even when administered transiently following soft tissue injury. Together, these data suggest that saracatinib is an efficacious clinical candidate for repositioning in the treatment of FOP, offering an accelerated path to clinical proof of efficacy studies and potentially significant benefits to individuals with this devastating condition.

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A self-amplifying loop of YAP and SHH drives formation and expansion of heterotopic ossification

Science Translational Medicine ◽

10.1126/scitranslmed.abb2233 ◽

2021 ◽

Vol 13 (599) ◽

pp. eabb2233

Author(s):

Qian Cong ◽

Yuchen Liu ◽

Taifeng Zhou ◽

Yaxing Zhou ◽

Ruoshi Xu ◽

...

Keyword(s):

Heterotopic Ossification ◽

Mouse Models ◽

Sonic Hedgehog ◽

Osteoblast Differentiation ◽

Feedback Loop ◽

Genetic Disorders ◽

Fibrodysplasia Ossificans Progressiva ◽

Bone Homeostasis ◽

Wild Type ◽

Necessary And Sufficient

Heterotopic ossification (HO) occurs as a common complication after injury or in genetic disorders. The mechanisms underlying HO remain incompletely understood, and there are no approved prophylactic or secondary treatments available. Here, we identify a self-amplifying, self-propagating loop of Yes-associated protein (YAP)–Sonic hedgehog (SHH) as a core molecular mechanism underlying diverse forms of HO. In mouse models of progressive osseous heteroplasia (POH), a disease caused by null mutations in GNAS, we found that Gnas−/− mesenchymal cells secreted SHH, which induced osteoblast differentiation of the surrounding wild-type cells. We further showed that loss of Gnas led to activation of YAP transcription activity, which directly drove Shh expression. Secreted SHH further induced YAP activation, Shh expression, and osteoblast differentiation in surrounding wild-type cells. This self-propagating positive feedback loop was both necessary and sufficient for HO expansion and could act independently of Gnas in fibrodysplasia ossificans progressiva (FOP), another genetic HO, and nonhereditary HO mouse models. Genetic or pharmacological inhibition of YAP or SHH abolished HO in POH and FOP and acquired HO mouse models without affecting normal bone homeostasis, providing a previously unrecognized therapeutic rationale to prevent, reduce, and shrink HO.

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

Nature Communications ◽

10.1038/s41467-021-24643-2 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Dali Zhang ◽

Junlan Huang ◽

Xianding Sun ◽

Hangang Chen ◽

Shuo Huang ◽

...

Keyword(s):

Bone Formation ◽

Heterotopic Ossification ◽

Growth Factor Receptor ◽

Lineage Tracing ◽

Conditional Knockout ◽

Heterotopic Bone ◽

Dependent Manner ◽

Heterotopic Bone Formation ◽

Inflammatory Microenvironment ◽

Achilles Tenotomy

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

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Identification of the Identical Human Mutation in ACVR1 in 2 Cats With Fibrodysplasia Ossificans Progressiva

Veterinary Pathology ◽

10.1177/0300985819835585 ◽

2019 ◽

Vol 56 (4) ◽

pp. 614-618 ◽

Cited By ~ 1

Author(s):

Margret L. Casal ◽

Julie B. Engiles ◽

Maja Zakošek Pipan ◽

Asaf Berkowitz ◽

Yael Porat-Mosenco ◽

...

Keyword(s):

Heterotopic Ossification ◽

Fibrodysplasia Ossificans Progressiva ◽

Heterozygous Mutation ◽

Type I ◽

Heterotopic Bone ◽

Intact Male ◽

Shoulder Joints ◽

Pelvic Limb ◽

Human Mutation ◽

Reduced Mobility

Two domestic shorthair cats, 1 intact female and 1 intact male, presented with progressive limb lameness and digital deformities at 4 and 6 months of age. Stiffness and swelling of the distal thoracic and pelvic limb joints progressed to involve hip and shoulder joints, resulting in reduced mobility. Radiographs in both cats and computed tomography of the male cat revealed ankylosing, polyarticular deposits of extracortical heterotopic bone spanning multiple axial and appendicular joints, extending into adjacent musculotendinous tissues. All findings supported fibrodysplasia ossificans progressiva (FOP), a disorder characterized by toe malformations and progressive heterotopic ossification in humans. In both cats, molecular analyses revealed the same heterozygous mutation in the activin A receptor type I ( ACVR1) gene that occurs in humans with FOP. Several reports of heterotopic ossification in cats exist, but this is the first one to identify clinical FOP in 2 cats with the identical mutation that occurs in >95% of humans with FOP.

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The role of Activin A in fibrodysplasia ossificans progressiva: a prominent mediator

Bioscience Reports ◽

10.1042/bsr20190377 ◽

2019 ◽

Vol 39 (8) ◽

Cited By ~ 3

Author(s):

Hui Lin ◽

Fuli Shi ◽

Jiayu Gao ◽

Ping Hua

Keyword(s):

Signaling Pathway ◽

Genetic Disorder ◽

Activin A ◽

Bmp Signaling ◽

The Body ◽

Fibrodysplasia Ossificans Progressiva ◽

Type I ◽

Heterotopic Bone ◽

Heterotopic Bone Formation

Abstract Heterotopic ossification (HO) is the aberrant formation of mature, lamellar bone in nonosseous tissue. Fibrodysplasia ossificans progressiva (FOP) is a rare and devastating genetic disorder that causes progressive HO in the ligaments, tendons, and muscles throughout the body. FOP is attributed to an autosomal mutation in activin receptor-like kinase 2 (ALK2), a bone morphogenetic protein (BMP) type I receptor. Initial studies show that mutant ALK2 drives HO by constitutively activating the BMP signaling pathway. Recently, mutant ALK2 has been shown to transduce Smad1/5 signaling and enhance chondrogenesis, calcification in response to Activin A, which normally signals through Smad2/3 and inhibits BMP signaling pathway. Furthermore, Activin A induces heterotopic bone formation via mutant ALK2, while inhibition of Activin A blocks spontaneous and trauma-induced HO. In this manuscript, we describe the molecular mechanism of the causative gene ALK2 in FOP, mainly focusing on the prominent role of Activin A in HO. It reveals a potential strategy for prevention and treatment of FOP by inhibition of Activin A. Further studies are needed to explore the cellular and molecular mechanisms of Activin A in FOP in more detail.

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The unique activity of bone morphogenetic proteins in bone: a critical role of the Smad signaling pathway

Biological Chemistry ◽

10.1515/hsz-2012-0310 ◽

2013 ◽

Vol 394 (6) ◽

pp. 703-714 ◽

Cited By ~ 40

Author(s):

Takenobu Katagiri ◽

Sho Tsukamoto

Keyword(s):

Skeletal Muscle ◽

Transcription Factors ◽

Bone Formation ◽

Bone Morphogenetic Proteins ◽

Fibrodysplasia Ossificans Progressiva ◽

Type I ◽

Heterotopic Bone ◽

Heterotopic Bone Formation ◽

Smad Signaling ◽

Smad Signaling Pathway

Abstract Bone morphogenetic proteins (BMPs) are multifunctional cytokines that belong to the transforming growth factor-β family. BMPs were originally identified based on their unique activity, inducing heterotopic bone formation in skeletal muscle. This unique BMP activity is transduced by specific type I and type II transmembrane kinase receptors. Among the downstream pathways activated by these receptors, the Smad1/5/8 transcription factors appear to play critical roles in BMP activity. Smad1/5/8 transcription factors are phosphorylated at the C-terminal SVS motif by BMP type I receptors and then induce the transcription of early BMP-responsive genes by binding to conserved sequences in their enhancer regions. The linker regions of Smad1/5/8 contain multiple kinase phosphorylation sites, and phosphorylation and dephosphorylation of these sites regulate the transcriptional activity of Smad proteins. Gain-of-function mutations in one BMP type I receptor have been identified in patients with fibrodysplasia ossificans progressiva, a rare genetic disorder that is characterized by progressive heterotopic bone formation in the skeletal muscle. The mutant receptors activate the Smad signaling pathway even in the absence of BMPs, therefore novel inhibitors for the BMP receptor – Smad axis are being developed to prevent heterotopic bone formation in fibrodysplasia ossificans progressiva. Taken together, the data in the literature show that the BMP type I receptor – Smad signaling axis is the critical pathway for the unique activity of BMPs and is a potential therapeutic target for pathological conditions caused by inappropriate BMP activity.

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