This review aimed to provide a comprehensive analysis of the etiology, epidemiology, pathology, and conventional treatment of heterotopic ossification (HO), especially emerging potential therapies. HO is the process of ectopic bone formation at non-skeletal sites. HO can be subdivided into two major forms, acquired and hereditary, with acquired HO predominating. Hereditary HO is a rare and life-threatening genetic disorder, but both acquired and hereditary form can cause severe complications, such as peripheral nerve entrapment, pressure ulcers, and disability if joint ankylosis develops, which heavily contributes to a reduced quality of life. Modalities have been proposed to treat HO, but none have emerged as the gold standard. Surgical excision remains the only effective modality; however, the optimal timing is controversial and may cause HO recurrence. Recently, potential therapeutic strategies have emerged that focus on the signaling pathways involved in HO, and small molecule inhibitors have been shown to be promising. Moreover, additional specific targets, such as small interfering RNAs (siRNAs) and non-coding RNAs, could be used to effectively block HO or develop combinatorial therapies for HO.
Humans ; Ossification, Heterotopic/genetics*

Fibrodysplasia ossificans progressiva (FOP) is a rare genetic disorder characterized by congenital bilateral malformation of the large toe and progressive, extensive, and irreversible heterotopic ossification (HO) of soft tissues throughout the body, leading to severe disabilities. FOP is caused primarily by mutations in activin A receptor type 1 (ACVR1), also known as activin-like kinase 2 (ALK2), which encodes a receptor belonging to the bone morphogenetic protein (BMP) type I family. However, the continuous and complex process of HO in FOP is not yet fully understood, which has impeded the development of therapeutic drugs. Despite surgical removal of HO, which often results in recurrence and expansion of ossification, there is currently no definitive drug treatment available to completely prevent, halt, or reverse the progression of HO in FOP. Currently, researchers are intensively studying the pathogenesis of FOP at various stages and developing promising drug candidates, including saracatinib, palovarotene, and rapamycin. This review provides an overview of progress in understanding the mechanism of FOP and the development of therapeutic drugs, with the goal of providing insights for further research and the development of new treatment methods.
Myositis Ossificans/genetics* ; Humans ; Activin Receptors, Type I/genetics* ; Ossification, Heterotopic ; Mutation ; Sirolimus/therapeutic use* ; Quinolones/therapeutic use* ; Benzodioxoles/therapeutic use* ; Animals ; Quinazolines/therapeutic use*

Animals ; Cell Differentiation ; genetics ; physiology ; Humans ; MicroRNAs ; genetics ; Ossification, Heterotopic ; genetics ; Signal Transduction ; genetics ; physiology

Deletion or mutation of dentin matrix protein 1 (DMP1) leads to hypophosphatemic rickets and defects within the dentin. However, it is largely unknown if this pathological change is a direct role of DMP1 or an indirect role of phosphate (Pi) or both. It has also been previously shown that Klotho-deficient mice, which displayed a high Pi level due to a failure of Pi excretion, causes mild defects in the dentinal structure. This study was to address the distinct roles of DMP1 and Pi homeostasis in cell differentiation, apoptosis and mineralization of dentin and enamel. Our working hypothesis was that a stable Pi homeostasis is critical for postnatal tooth formation, and that DMP1 has an antiapoptotic role in both amelogenesis and dentinogenesis. To test this hypothesis, Dmp1-null (Dmp1(-/-)), Klotho-deficient (kl/kl), Dmp1/Klotho-double-deficient (Dmp1(-/-)/kl/kl) and wild-type (WT) mice were killed at the age of 6 weeks. Combinations of X-ray, microcomputed tomography (μCT), scanning electron microscopy (SEM), histology, apoptosis and immunohistochemical methods were used for characterization of dentin, enamel and pulp structures in these mutant mice. Our results showed that Dmp1(-/-) (a low Pi level) or kl/kl (a high Pi level) mice displayed mild dentin defects such as thin dentin and a reduction of dentin tubules. Neither deficient mouse line exhibited any apparent changes in enamel or pulp structure. However, the double-deficient mice (a high Pi level) displayed severe defects in dentin and enamel structures, including loss of dentinal tubules and enamel prisms, as well as unexpected ectopic ossification within the pulp root canal. TUNEL assay showed a sharp increase in apoptotic cells in ameloblasts and odontoblasts. Based on the above findings, we conclude that DMP1 has a protective role for odontoblasts and ameloblasts in a pro-apoptotic environment (a high Pi level).
Ameloblasts ; pathology ; Amelogenesis ; physiology ; Animals ; Apoptosis ; physiology ; Cell Differentiation ; physiology ; Dental Enamel ; pathology ; Dental Pulp ; pathology ; physiology ; Dental Pulp Cavity ; pathology ; Dentin ; abnormalities ; pathology ; Dentinogenesis ; physiology ; Extracellular Matrix Proteins ; genetics ; physiology ; Glucuronidase ; genetics ; Homeostasis ; physiology ; Hyperphosphatemia ; physiopathology ; Immunohistochemistry ; Mice ; Mice, Knockout ; Microscopy, Electron, Scanning ; Odontoblasts ; pathology ; Odontogenesis ; physiology ; Ossification, Heterotopic ; genetics ; pathology ; Phosphates ; physiology ; Tooth Calcification ; physiology ; X-Ray Microtomography

OBJECTIVETo investigate the clinical features, mutation of the GNAS1 and pathogenesis of progressive osseous heteroplasia (POH).

METHODThe typical clinical, pathological and radiographic features of a boy with POH were collected and summarized following family survey. The GNAS1 gene sequence of all family members were amplified by polymerase chain reaction (PCR) and the products were sequenced directly to identify the mutations. A literature review and long-term follow up were also conducted.

RESULTThe patient was an 11-year-old boy who had the onset in infancy, which indicates a chronic progressive cause of disease. The clinical features include the unsmooth local skin of the right shank where spread many rigid rice-like or irregular slabby uplifts, slabby bone-like sclerosis on the left lower mandible, left masticatory muscles, in lateral subcutaneous site of left hip joint and deep tissue, accompanied by gradually progressive difficulty in opening mouth. Histopathology showed that there were loosened hyperplasia of fibroblast and interstitial edema with punctiformed ossification. Radiographs showed flocculence hyperdense image in the subcutaneous tissues and muscles around left lower mandible, and the left masticatory muscles were obviously involved. The 3-dimensional computed tomography showed dislocations of the left temporomandibular joint. Sheeted hyperdense image with inequable density could be noted in lateral muscles of the left hip. And lamellar hyperdense image parallel to the long axis of the bone could be seen in the subcutaneous dorsum of the left foot and achilles tendon. Macro-thumb and of brachydactylia of the hands and feet were not present. The level of calcium, phosphorus and alkaline phosphatase in the blood were normal. Brother of same father but different mothers was free of the disease and no patient of the same disease was found in maternal line and paternal lines. A mutated allele in exon 7 and a polymorphism in exon 5 were found in GNAS1 gene in both of the patient and his father.

CONCLUSIONThere is possibility/likelihood/probability that Chinese children could develop POH. Translocated dermal ossification began in infancy and shows a progressive cause in childhood. The disease is characterized by the heterotopic ossification of the skin, deep tissue, muscles and facial surface tissues. The location of the mutation in this study was different from that reported in abroad studies although exist in the same exons.

Child ; Chromogranins ; DNA Mutational Analysis ; Exons ; GTP-Binding Protein alpha Subunits, Gs ; genetics ; Humans ; Male ; Mutation ; Ossification, Heterotopic ; diagnosis ; genetics ; pathology ; Pedigree

PURPOSE: The objective of this study was to determine the phenotypic characterization of ligamentum flavum cells from patients with ossification of the ligamentum flavum (OLF). MATERIALS AND METHODS: Ligamentum flavum tissues were harvested from OLF and non-OLF patients during surgery. OLF and non-OLF cells were isolated from explant cultures. Cultured cells were analyzed using immunofluorescence staining and reverse transcription-polymerase chain reaction. RESULTS: OLF cells exhibited various appearances compared with the typical fibroblast-like morphology of non-OLF cells. Expressions of collagen type I and collagen type III were observed in OLF and non-OLF cells. OLF cells uniquely expressed osteocalcin, which is a marker for osteoblasts, and collagen type II which is a marker for chondrocytes, whereas they were negative in non-OLF cells. CONCLUSION: These findings indicate that OLF cells have phenotypic characterization of osteoblasts and chondrocytes which could play a role in the pathophysiology of OLF.
Adolescent ; Adult ; Aged ; Cells, Cultured ; Collagen Type I/genetics/metabolism ; Collagen Type II/genetics/metabolism ; Collagen Type VI/genetics/metabolism ; Female ; Humans ; Ligamentum Flavum/metabolism/*pathology ; Male ; Microscopy, Fluorescence ; Middle Aged ; Ossification, Heterotopic/metabolism/*pathology ; Osteocalcin/genetics/metabolism ; Reverse Transcriptase Polymerase Chain Reaction ; Young Adult