ACVR1 p.Q207E causes classic fibrodysplasia ossificans progressiva and is functionally distinct from the engineered constitutively active ACVR1 p.Q207D variant.
Fibrodysplasia ossificans progressiva (FOP) is a disabling genetic disorder of progressive heterotopic ossification (HO). Here, we report a patient with an ultra-rare point mutation [c.619C>G, p.Q207E] located in a codon adjacent to the most common FOP mutation [c.617G>A, p.R206H] of Activin A Receptor, type 1 (ACVR1) and that affects the same intracellular amino acid position in the GS activation domain as the engineered constitutively active (c.a.) variant p.Q207D. It was predicted that both mutations at residue 207 have similar functional effects by introducing a negative charge. Transgenic p.Q207D-c.a. mice have served as a model for FOP HO in several in vivo studies. However, we found that the engineered ACVR1(Q207D-c.a.) is significantly more active than the classic FOP mutation ACVR1(R206H) when overexpressed in chicken limbs and in differentiation assays of chondrogenesis, osteogenesis and myogenesis. Importantly, our studies reveal that the ACVR1(Q207E) resembles the classic FOP receptor in these assays, not the engineered ACVR1(Q207D-c.a.). Notably, reporter gene assays revealed that both naturally occurring FOP receptors (ACVR1(R206H) and ACVR1(Q207E)) were activated by BMP7 and were sensitive to deletion of the ligand binding domain, whereas the engineered ACVR1(Q207D-c.a.) exhibited ligand independent activity. We performed an in silico analysis and propose a structural model for p.Q207D-c.a. that irreversibly relocates the GS domain into an activating position, where it becomes ligand independent. We conclude that the engineered p.Q207D-c.a. mutation has severe limitations as a model for FOP, whereas the naturally occurring mutations p.R206H and p.Q207E facilitate receptor activation, albeit in a reversible manner.
Berlin-Brandenburg Center for Regenerative Therapies (BCRT), Charité-Universitätsmedizin Berlin, 13353 Berlin, Germany, Department of Orthopaedic Surgery, Perelman School of Medicine.
Julia
J
Haupt
Berlin-Brandenburg Center for Regenerative Therapies (BCRT), Charité-Universitätsmedizin Berlin, 13353 Berlin, Germany, Berlin Brandenburg School for Regenerative Therapies (BSRT), Charité-Universitätsmedizin Berlin, 13353 Berlin, Germany.
Alexandra
A
Deichsel
Berlin-Brandenburg Center for Regenerative Therapies (BCRT), Charité-Universitätsmedizin Berlin, 13353 Berlin, Germany, Berlin Brandenburg School for Regenerative Therapies (BSRT), Charité-Universitätsmedizin Berlin, 13353 Berlin, Germany.
Katja
K
Stange
Research Group Development and Disease, Max-Planck-Institut für Molekulare Genetik, 14195 Berlin, Germany.
Cindy
C
Ast
Medical Genetics Unit, G. Gaslini Institute, and Department of Neuroscience, Rehabilitation, Ophthalmology, Genetics, Maternal and Child Health (DiNOGMI), University of Genova, 16147 Genova, Italy.
Renata
R
Bocciardi
Medical Genetics Unit, G. Gaslini Institute, and Department of Neuroscience, Rehabilitation, Ophthalmology, Genetics, Maternal and Child Health (DiNOGMI), University of Genova, 16147 Genova, Italy.
Roberto
R
Ravazzolo
Unit of Rare Diseases, G. Gaslini Institute, 16147 Genova, Italy.
Maja
M
Di Rocco
Department of Pediatrics, University of Modena and Reggio Emilia, 41100 Modena, Italy.
Paola
P
Ferrari
Hand Surgery and Microsurgery Unit, Policlinico of Modena, 41100 Modena, Italy.
Antonio
A
Landi
Department of Orthopaedic Surgery, Perelman School of Medicine, Center for Research in FOP and Related Disorders, Perelman School of Medicine, Department of Medicine, Perelman School of Medicine.
Frederick S
FS
Kaplan
Department of Orthopaedic Surgery, Perelman School of Medicine, Center for Research in FOP and Related Disorders, Perelman School of Medicine, Department of Genetics, Perelman School of Medicine, University of Pennsylvania, Philadelphia 19104 PA, USA.
Eileen M
EM
Shore
Institute of Anatomy and Molecular Neurobiology, Universitätsklinikum Münster, 48149 Münster, Germany.
Carsten
C
Reissner
Berlin-Brandenburg Center for Regenerative Therapies (BCRT), Charité-Universitätsmedizin Berlin, 13353 Berlin, Germany, Berlin Brandenburg School for Regenerative Therapies (BSRT), Charité-Universitätsmedizin Berlin, 13353 Berlin, Germany Research Group Development and Disease, Max-Planck-Institut für Molekulare Genetik, 14195 Berlin, Germany petra.seemann@charite.de.
Petra
P
Seemann
D030201:Activin Receptors, Type I / Q000737:chemistry* / Q000235:genetics*; D000595:Amino Acid Sequence; D000818:Animals; D002645:Chickens; D002648:Child; D004195:Disease Models, Animal; D014644:Genetic Variation; D018698:Glutamic Acid / Q000378:metabolism; D005973:Glutamine / Q000378:metabolism; D006614:Hindlimb / Q000378:metabolism; D006801:Humans; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000473:pathology*; D009221:Myositis Ossificans / Q000235:genetics* / Q000473:pathology*; D041681:NIH 3T3 Cells; D017354:Point Mutation; D020641:Polymorphism, Single Nucleotide; D016415:Sequence Alignment
D005973:Glutamine; D018698:Glutamic Acid; D030201:Activin Receptors, Type I