title: Excess BMP Signaling in Heterotopic Cartilage Forming in Prg4-null TMJ Discs.
abstract: Heterotopic cartilage develops in certain pathologic conditions, including those affecting the human temporomandibular joint (TMJ), but the underlying molecular mechanisms remain obscure. This is in part due to the fact that a reliable animal model of such TMJ diseases is not available. Here, we show that aberrant chondrocyte differentiation and ectopic cartilage formation occur spontaneously in proteoglycan 4 (Prg4) mutant TMJ discs without further invasive procedure. By 2 mo of age, mutant disc cells displayed chondrocyte transdifferentiation, accompanied by strong expression of cartilage master gene Sox9 and matrix genes aggrecan and type II collagen. By 6 mo, heterotopic cartilage had formed in the discs and expressed cartilage hypertrophic markers Runx2 and ColX. The ectopic tissue grew in size over time and exhibited regional mineralization by 12 mo. Bone morphogenetic protein (BMP) signaling was activated with the ectopic chondrogenic cells and chondrocytes, as indicated by phosphorylated Smad 1/5/8 nuclear staining and by elevated expression of Bmp2, Bmpr1b, Bmpr2, and BMP signaling target genes. Likewise, we found that upon treatment with recombinant human BMP 2 in high-density micromass culture, mutant disc cells differentiated into chondrocytes and synthesized cartilage matrix more robustly than control cells. Importantly, a specific kinase inhibitor of BMP receptors drastically attenuated chondrogenesis in recombinant human BMP 2-treated mutant disc cultures. Unexpectedly, we found that Prg4 was expressed at joint-associated sites, including disc/muscle insertion and muscle/bone interface, and all these structures were abnormal in Prg4 mutants. Our data indicate that Prg4 is needed for TMJ disc integrity and function and that its absence leads to ectopic chondrogenesis and cartilage formation in conjunction with abnormal BMP signaling. Our findings imply that the BMP signaling pathway could be a potential therapeutic target for prevention or inhibition of ectopic cartilage formation in TMJ disease.
authors.affiliation: Division of Orthopaedic Surgery, Department of Surgery, The Children's Hospital of Philadelphia, Philadelphia, PA, USA Department of Orthodontics and Orofacial Orthopaedics, Center of Dentistry, Oral Medicine and Maxillofacial Surgery, University Hospital Tuebingen, Tuebingen, Germany.
authors.forename: T E
authors.initials: TE
authors.lastname: Bechtold
authors.affiliation: Division of Orthopaedic Surgery, Department of Surgery, The Children's Hospital of Philadelphia, Philadelphia, PA, USA.
authors.forename: C
authors.initials: C
authors.lastname: Saunders
authors.affiliation: Division of Orthopaedic Surgery, Department of Surgery, The Children's Hospital of Philadelphia, Philadelphia, PA, USA.
authors.forename: C
authors.initials: C
authors.lastname: Mundy
authors.affiliation: Division of Orthopaedic Surgery, Department of Surgery, The Children's Hospital of Philadelphia, Philadelphia, PA, USA.
authors.forename: H
authors.initials: H
authors.lastname: Um
authors.affiliation: Division of Orthopaedic Surgery, Department of Surgery, The Children's Hospital of Philadelphia, Philadelphia, PA, USA.
authors.forename: R S
authors.initials: RS
authors.lastname: Decker
authors.affiliation: Division of Plastic and Reconstructive Surgery, Department of Surgery, The Children's Hospital of Philadelphia, Philadelphia, PA, USA.
authors.forename: I
authors.initials: I
authors.lastname: Salhab
authors.affiliation: Division of Plastic and Reconstructive Surgery, Department of Surgery, The Children's Hospital of Philadelphia, Philadelphia, PA, USA.
authors.forename: N
authors.initials: N
authors.lastname: Kurio
authors.affiliation: Division of Orthopaedic Surgery, Department of Surgery, The Children's Hospital of Philadelphia, Philadelphia, PA, USA.
authors.forename: P C
authors.initials: PC
authors.lastname: Billings
authors.affiliation: Division of Orthopaedic Surgery, Department of Surgery, The Children's Hospital of Philadelphia, Philadelphia, PA, USA.
authors.forename: M
authors.initials: M
authors.lastname: Pacifici
authors.affiliation: Division of Plastic and Reconstructive Surgery, Department of Surgery, The Children's Hospital of Philadelphia, Philadelphia, PA, USA.
authors.forename: H D
authors.initials: HD
authors.lastname: Nah
authors.affiliation: Division of Orthopaedic Surgery, Department of Surgery, The Children's Hospital of Philadelphia, Philadelphia, PA, USA koyamae@email.chop.edu.
authors.forename: E
authors.initials: E
authors.lastname: Koyama
mesh_terms: D053674:Aggrecans / Q000032:analysis; D000818:Animals; D055396:Bone Morphogenetic Protein 2 / Q000494:pharmacology; D052005:Bone Morphogenetic Protein Receptors, Type I; D052006:Bone Morphogenetic Protein Receptors, Type II / Q000032:analysis; D019485:Bone Morphogenetic Proteins / Q000502:physiology*; D002113:Calcification, Physiologic / Q000502:physiology; D002454:Cell Differentiation / Q000235:genetics; D054338:Cell Transdifferentiation / Q000235:genetics; D019902:Chondrocytes / Q000502:physiology; D020219:Chondrogenesis / Q000502:physiology*; D002828:Choristoma / Q000503:physiopathology*; D024043:Collagen Type II / Q000032:analysis; D024121:Collagen Type X / Q000032:analysis; D050659:Core Binding Factor Alpha 1 Subunit / Q000032:analysis; D051379:Mice; D009154:Mutation / Q000235:genetics; D011509:Proteoglycans / Q000032:analysis / Q000235:genetics*; D011994:Recombinant Proteins / Q000494:pharmacology; D055758:SOX9 Transcription Factor / Q000032:analysis; D015398:Signal Transduction / Q000502:physiology*; D051898:Smad1 Protein / Q000032:analysis; D051902:Smad5 Protein / Q000032:analysis; D051904:Smad8 Protein / Q000032:analysis; D019224:Temporomandibular Joint Disc / Q000503:physiopathology*; D046509:Tissue Culture Techniques; D016212:Transforming Growth Factor beta / Q000494:pharmacology; D000099158:Proteoglycan 4
chemical_list: D053674:Aggrecans; D055396:Bone Morphogenetic Protein 2; D052005:Bone Morphogenetic Protein Receptors, Type I; D052006:Bone Morphogenetic Protein Receptors, Type II; D019485:Bone Morphogenetic Proteins; D024043:Collagen Type II; D024121:Collagen Type X; D050659:Core Binding Factor Alpha 1 Subunit; D011509:Proteoglycans; D011994:Recombinant Proteins; D055758:SOX9 Transcription Factor; D051898:Smad1 Protein; D051902:Smad5 Protein; D051904:Smad8 Protein; D016212:Transforming Growth Factor beta; C447413:Col2a1 protein, mouse; C498837:Prg4 protein, mouse; D000099158:Proteoglycan 4; C493716:Runx2 protein, mouse; C497401:Smad1 protein, mouse; C497798:Smad5 protein, mouse; C491621:Smad9 protein, mouse; C527933:Sox9 protein, mouse; C499469:recombinant human bone morphogenetic protein-2; C498215:Bmpr1b protein, mouse; C498219:Bmpr2 protein, mouse
keywords: TMJ disorder; articular disc; ectopic cartilage; joint lubrication; lubricin; temporomandibular joint