title: Follistatin in chondrocytes: the link between TRPV4 channelopathies and skeletal malformations.
abstract: Point mutations in the calcium-permeable TRPV4 ion channel have been identified as the cause of autosomal-dominant human motor neuropathies, arthropathies, and skeletal malformations of varying severity. The objective of this study was to determine the mechanism by which TRPV4 channelopathy mutations cause skeletal dysplasia. The human TRPV4(V620I) channelopathy mutation was transfected into primary porcine chondrocytes and caused significant (2.6-fold) up-regulation of follistatin (FST) expression levels. Pore altering mutations that prevent calcium influx through the channel prevented significant FST up-regulation (1.1-fold). We generated a mouse model of the TRPV4(V620I) mutation, and found significant skeletal deformities (e.g., shortening of tibiae and digits, similar to the human disease brachyolmia) and increases in Fst/TRPV4 mRNA levels (2.8-fold). FST was significantly up-regulated in primary chondrocytes transfected with 3 different dysplasia-causing TRPV4 mutations (2- to 2.3-fold), but was not affected by an arthropathy mutation (1.1-fold). Furthermore, FST-loaded microbeads decreased bone ossification in developing chick femora (6%) and tibiae (11%). FST gene and protein levels were also increased 4-fold in human chondrocytes from an individual natively expressing the TRPV4(T89I) mutation. Taken together, these data strongly support that up-regulation of FST in chondrocytes by skeletal dysplasia-inducing TRPV4 mutations contributes to disease pathogenesis.
authors.affiliation: Department of Orthopaedic Surgery.
authors.forename: Holly A
authors.initials: HA
authors.lastname: Leddy
authors.affiliation: Department of Orthopaedic Surgery.
authors.forename: Amy L
authors.initials: AL
authors.lastname: McNulty
authors.affiliation: Department of Neurology.
authors.forename: Suk Hee
authors.initials: SH
authors.lastname: Lee
authors.affiliation: Department of Orthopaedic Surgery.
authors.forename: Nicole E
authors.initials: NE
authors.lastname: Rothfusz
authors.affiliation: Department of Neurobiology.
authors.forename: Bernd
authors.initials: B
authors.lastname: Gloss
authors.affiliation: Department of Pediatrics, and.
authors.forename: Margaret L
authors.initials: ML
authors.lastname: Kirby
authors.affiliation: Department of Pediatrics, and.
authors.forename: Mary R
authors.initials: MR
authors.lastname: Hutson
authors.affiliation: Department of Molecular, Cell, and Developmental Biology and Department of Orthopaedic Surgery, Orthopaedic Hospital Research Center, University of California at Los Angeles, Los Angeles, California, USA.
authors.forename: Daniel H
authors.initials: DH
authors.lastname: Cohn
authors.affiliation: Department of Orthopaedic Surgery, guilak@duke.edu wolfgang@neuro.duke.edu.
authors.forename: Farshid
authors.initials: F
authors.lastname: Guilak
authors.affiliation: Department of Neurology, Duke University Clinics for Pain and Palliative Care, Duke University Medical Center, Durham, North Carolina, USA; and guilak@duke.edu wolfgang@neuro.duke.edu.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Liedtke
mesh_terms: D000818:Animals; D001848:Bone Diseases, Developmental / Q000196:embryology* / Q000235:genetics; D053447:Channelopathies / Q000503:physiopathology*; D002642:Chick Embryo; D019902:Chondrocytes / Q000378:metabolism; D038681:Follistatin / Q000502:physiology*; D006801:Humans; D051379:Mice; D009154:Mutation; D010009:Osteochondrodysplasias; D010012:Osteogenesis / Q000235:genetics; D013552:Swine; D050916:TRPV Cation Channels / Q000235:genetics*; D015854:Up-Regulation
chemical_list: D038681:Follistatin; D050916:TRPV Cation Channels; C416986:TRPV4 protein, human
keywords: bone morphogenetic protein; calcium signaling; cartilage; growth plate