title: A syndrome of joint laxity and impaired tendon integrity in lumican- and fibromodulin-deficient mice.
abstract: Lumican and fibromodulin regulate the assembly of collagens into higher order fibrils in connective tissues. Here, we show that mice deficient in both of these proteoglycans manifest several clinical features of Ehlers-Danlos syndrome. The Lum(-/-)Fmod(-/-) mice are smaller than their wild type littermates and display gait abnormality, joint laxity, and age-dependent osteoarthritis. Misaligned knee patella, severe knee dysmorphogenesis, and extreme tendon weakness are the likely causes for joint laxity in the double-nulls. Fibromodulin deficiency alone leads to significant reduction in tendon stiffness in the Lum(+/+)Fmod(-/-) mice, with further loss in stiffness in a Lum gene dose-dependent way. At the protein level, we show marked increase of lumican in Fmod(-/-) tendons, which may partially rescue the tendon phenotype in this genotype. These results establish fibromodulin as a key regulator and lumican as a modulator of tendon strength. A disproportionate increase in small diameter immature collagen fibrils and a lack of progression to mature, large diameter fibrils in the Fmod(-/-) background may constitute the underlying cause of tendon weakness and suggest that fibromodulin aids fibril maturation. This study demonstrates that the collagen fibril-modifying proteoglycans, lumican and fibromodulin, are candidate genes and key players in the pathogenesis of certain types of Ehlers-Danlos syndrome and other connective tissue disorders.
authors.affiliation: Department of Orthopedics, Mount Sinai School of Medicine, New York, New York 10029, USA.
authors.forename: Karl J
authors.initials: KJ
authors.lastname: Jepsen
authors.forename: Feng
authors.initials: F
authors.lastname: Wu
authors.forename: Jason H
authors.initials: JH
authors.lastname: Peragallo
authors.forename: Jennifer
authors.initials: J
authors.lastname: Paul
authors.forename: Luke
authors.initials: L
authors.lastname: Roberts
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Ezura
authors.forename: Ake
authors.initials: A
authors.lastname: Oldberg
authors.forename: David E
authors.initials: DE
authors.lastname: Birk
authors.forename: Shukti
authors.initials: S
authors.lastname: Chakravarti
mesh_terms: D000818:Animals; D001483:Base Sequence; D002352:Carrier Proteins / Q000235:genetics / Q000502:physiology*; D011508:Chondroitin Sulfate Proteoglycans / Q000235:genetics / Q000502:physiology*; D017931:DNA Primers; D016326:Extracellular Matrix Proteins; D000071235:Fibromodulin; D007593:Joint Instability / Q000235:genetics*; D007632:Keratan Sulfate / Q000235:genetics / Q000502:physiology*; D000071234:Lumican; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008854:Microscopy, Electron; D011509:Proteoglycans; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013577:Syndrome; D013710:Tendons / Q000503:physiopathology* / Q000648:ultrastructure
chemical_list: D002352:Carrier Proteins; D011508:Chondroitin Sulfate Proteoglycans; D017931:DNA Primers; D016326:Extracellular Matrix Proteins; C000604332:Fmod protein, mouse; C000604307:Lum protein, mouse; D000071234:Lumican; D011509:Proteoglycans; D000071235:Fibromodulin; D007632:Keratan Sulfate