We applied the same modeling and simulation methods to established FOP variants, to identify the detailed effects that they have on the ACVR1 protein, as well as to act as positive controls against which the effects of p.K400E could be evaluated.
By comparison to known mutations in genetic conditions of HO such as fibrodysplasia ossificans progressiva (FOP) and progressive osseous heteroplasia (POH), DNA sequencing analysis demonstrated the presence of a commonly occurring heterozygous synonymous polymorphism (c.690G>A; E230E) in the causative gene for FOP (ACVR1/ALK2).
By comparison to known mutations in genetic conditions of HO such as fibrodysplasia ossificans progressiva (FOP) and progressive osseous heteroplasia (POH), DNA sequencing analysis demonstrated the presence of a commonly occurring heterozygous synonymous polymorphism (c.690G>A; E230E) in the causative gene for FOP (ACVR1/ALK2).
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.
ALK2 R206H mutation linked to fibrodysplasia ossificans progressiva confers constitutive activity to the BMP type I receptor and sensitizes mesenchymal cells to BMP-induced osteoblast differentiation and bone formation.
While the recurrent c.617G>A; p.R206H mutation was found in all cases of classic FOP and most cases of FOP-plus, novel ACVR1 mutations occur in the FOP variants and two cases of FOP-plus.
We found that the Acvr1 R206H mutation caused increased BMP signaling in posttraumatic FOP lesions and early divergence from the normal skeletal muscle repair program with elevated and prolonged immune cell infiltration.
Gene transfer of Smad7 or inhibition of type I receptors with dorsomorphin may represent strategies for blocking the activity induced by ALK2(R206H) in FOP.
All patients with classic clinical features of FOP (great toe malformations and progressive heterotopic ossification) have previously been found to carry the same heterozygous mutation (c.617G>A; p.R206H) in the glycine and serine residue (GS) activation domain of activin A type I receptor/activin-like kinase 2 (ACVR1/ALK2), a bone morphogenetic protein (BMP) type I receptor.
The 617G>A (R206H) mutation in the activin receptor type IA (ACVR1) gene has been identified in all examined individuals with FOP of various ethnic groups, including Caucasian and Chinese descents.
We mapped FOP to chromosome 2q23-24 by linkage analysis and identified an identical heterozygous mutation (617G --> A; R206H) in the glycine-serine (GS) activation domain of ACVR1, a BMP type I receptor, in all affected individuals examined.
FOP is caused by a recurrent heterozygous activating mutation (c.617G>A; R206H) of Activin receptor type IA/Activin-like kinase-2 (ACVR1/ALK2), a bone morphogenetic protein (BMP) type I receptor that occurs in all classically affected individuals.
Most patients with fibrodysplasia ossificans progressiva (FOP), a rare genetic disorder of heterotopic ossification, have the same causative mutation in ACVR1, R206H.
Overall, our ES cells are useful for studying the molecular mechanisms of heterotopic ossification in FOP in vitro and for developing novel inhibitors of chondrogenesis induced by mutant ALK2(R206H) associated with FOP.
The activities of ALK2(L196P) were higher than those of ALK2(G356D), another mutant ALK2 allele found in patients with FOP and were equivalent to those of ALK2(R206H), a typical mutation found in patients with FOP.
In addition, an RAR-γ agonist blocked heterotopic ossification in transgenic mice expressing activin receptor-like kinase-2 (ALK2) Q207D, a constitutively active form of the receptor that is related to ALK2 R206H found in individuals with fibrodysplasia ossificans progressiva.
Fibrodysplasia ossificans progressiva is characterized by extensive ossification within muscle tissues, and its molecular pathogenesis is responsible for the constitutively activating mutation (R206H) of the bone morphogenetic protein type 1 receptor, activin-like kinase 2 (ALK2).
All familial and sporadic cases with a classic clinical presentation of FOP carry a gain-of-function mutation (R206H; c.617 G > A) in ACVR1, a cell surface receptor that mediates bone morphogenetic protein (BMP) signaling.