title: COL10A1 nonsense and frame-shift mutations have a gain-of-function effect on the growth plate in human and mouse metaphyseal chondrodysplasia type Schmid.
abstract: Missense, nonsense and frame-shift mutations in the collagen X gene (COL10A1) result in metaphyseal chondrodysplasia type Schmid (MCDS). Complete degradation of mutant COL10A1 mRNA by nonsense-mediated decay in human MCDS cartilage implicates haploinsufficiency in the pathogenesis for nonsense mutations in vivo. However, the mechanism is unclear in situations where the mutant mRNA persist. We show that nonsense/frame-shift mutations can elicit a gain-of-function effect, affecting chondrocyte differentiation in the growth plate. In an MCDS proband, heterozygous for a p.Y663X nonsense mutation, the growth plate cartilage contained 64% wild-type and 36% mutant mRNA and the hypertrophic zone was disorganized and expanded. The in vitro translated mutant collagen X chains, which are truncated, were misfolded, unable to assemble into trimers and interfered with the assembly of normal alpha1(X) chains into trimers. Unlike Col10a1 null mutants, transgenic mice (FCdel) bearing the mouse equivalent of a human MCDS p.P620fsX621 mutation, displayed typical characteristics of MCDS with disproportionate shortening of limbs and early onset coxa vara. In FCdel mice, the degree of expansion of the hypertrophic zones was transgene-dosage dependent, being most severe in mice homozygous for the transgene. Chondrocytes in the lower region of the expanded hypertrophic zone expressed markers uncharacteristic of hypertrophic chondrocytes, indicating that differentiation was disrupted. Misfolded FCdel alpha1(X) chains were retained within the endoplasmic reticulum of hypertrophic chondrocytes, activating the unfolded protein response. Our findings provide strong in vivo evidence for a gain-of-function effect that is linked to the activation of endoplasmic reticulum-stress response and altered chondrocyte differentiation, as a possible molecular pathogenesis for MCDS.
authors.affiliation: Department of Biochemistry, The University of Hong Kong, Pokfulam, Hong Kong, China.
authors.forename: Matthew S P
authors.initials: MS
authors.lastname: Ho
authors.forename: Kwok Yeung
authors.initials: KY
authors.lastname: Tsang
authors.forename: Rebecca L K
authors.initials: RL
authors.lastname: Lo
authors.forename: Miki
authors.initials: M
authors.lastname: Susic
authors.forename: Outi
authors.initials: O
authors.lastname: Mäkitie
authors.forename: Tori W Y
authors.initials: TW
authors.lastname: Chan
authors.forename: Vivian C W
authors.initials: VC
authors.lastname: Ng
authors.forename: David O
authors.initials: DO
authors.lastname: Sillence
authors.forename: Raymond P
authors.initials: RP
authors.lastname: Boot-Handford
authors.forename: Gary
authors.initials: G
authors.lastname: Gibson
authors.forename: Kenneth M C
authors.initials: KM
authors.lastname: Cheung
authors.forename: William G
authors.initials: WG
authors.lastname: Cole
authors.forename: Kathryn S E
authors.initials: KS
authors.lastname: Cheah
authors.forename: Danny
authors.initials: D
authors.lastname: Chan
mesh_terms: D000293:Adolescent; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D019902:Chondrocytes / Q000378:metabolism; D018389:Codon, Nonsense; D024121:Collagen Type X / Q000096:biosynthesis / Q000235:genetics*; D004247:DNA / Q000235:genetics; D016368:Frameshift Mutation; D006132:Growth Plate / Q000473:pathology; D006801:Humans; D008297:Male; D051379:Mice; D008817:Mice, Mutant Strains; D008822:Mice, Transgenic; D010009:Osteochondrodysplasias / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D010641:Phenotype; D012333:RNA, Messenger / Q000235:genetics; D017384:Sequence Deletion
chemical_list: D018389:Codon, Nonsense; D024121:Collagen Type X; D012333:RNA, Messenger; D004247:DNA