Dysregulated BMP signaling and enhanced osteogenic differentiation of connective tissue progenitor cells from patients with fibrodysplasia ossificans progressiva (FOP).
The study of FOP, a disabling genetic disorder of progressive heterotopic ossification, is hampered by the lack of readily available connective tissue progenitor cells. We isolated such cells from discarded primary teeth of patients with FOP and controls and discovered dysregulation of BMP signaling and rapid osteoblast differentiation in FOP cells compared with control cells.


BACKGROUND
Fibrodysplasia ossificans progressiva (FOP), the most disabling condition of progressive heterotopic ossification in humans, is caused by a recurrent heterozygous missense mutation in activin receptor IA (ACVR1), a bone morphogenetic protein (BMP) type I receptor, in all classically affected individuals. A comprehensive understanding of FOP has been limited, in part, by a lack of readily available connective tissue progenitor cells in which to study the molecular pathology of this disorder.


METHODS
We derived connective tissue progenitor cells from discarded primary teeth (SHED cells) of patients with FOP and controls and examined BMP signaling and osteogenic differentiation in these cells.


RESULTS
SHED cells transmitted BMP signals through both the SMAD and p38 mitogen-activated protein kinase (MAPK) pathways and responded to BMP4 treatment by inducing BMP responsive genes. FOP cells showed ligand-independent BMP signaling and ligand-dependent hyper-responsiveness to BMP stimulation. Furthermore, FOP cells showed more rapid differentiation to an osteogenic phenotype than control cells.


CONCLUSIONS
This is the first study of BMP signaling and osteogenic differentiation in connective tissue progenitor cells from patients with FOP. Our data strongly support both basal and ligand-stimulated dysregulation of BMP signaling consistent with in silico studies of the mutant ACVR1 receptor in this condition. This study substantially extends our understanding of dysregulated BMP signaling in a progenitor cell population relevant to the pathogenesis of this catastrophic disorder of progressive ectopic ossification.
Billings
Paul C
PC
The Center for Research in FOP and Related Disorders, The University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA.
Fiori
Jennifer L
JL
Bentwood
Jennifer L
JL
O'Connell
Michael P
MP
Jiao
Xiangyang
X
Nussbaum
Burton
B
Caron
Robert J
RJ
Shore
Eileen M
EM
Kaplan
Frederick S
FS
D030201:Activin Receptors, Type I / Q000378:metabolism; D055415:Bone Morphogenetic Protein 4; D052005:Bone Morphogenetic Protein Receptors, Type I / Q000378:metabolism*; D019485:Bone Morphogenetic Proteins / Q000378:metabolism* / Q000494:pharmacology; D002454:Cell Differentiation / Q000187:drug effects; D002478:Cells, Cultured; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D020935:MAP Kinase Signaling System / Q000187:drug effects; D009221:Myositis Ossificans / Q000378:metabolism* / Q000473:pathology; D010012:Osteogenesis / Q000187:drug effects; D051785:Smad Proteins / Q000378:metabolism; D013234:Stem Cells / Q000378:metabolism* / Q000473:pathology; D014070:Tooth / Q000378:metabolism* / Q000473:pathology; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
C525809:BMP4 protein, human; D055415:Bone Morphogenetic Protein 4; D019485:Bone Morphogenetic Proteins; D051785:Smad Proteins; D048051:p38 Mitogen-Activated Protein Kinases; C425423:ACVR1 protein, human; D030201:Activin Receptors, Type I; D052005:Bone Morphogenetic Protein Receptors, Type I