title: The secreted glycoprotein lubricin protects cartilage surfaces and inhibits synovial cell overgrowth.
abstract: The long-term integrity of an articulating joint is dependent upon the nourishment of its cartilage component and the protection of the cartilage surface from friction-induced wear. Loss-of-function mutations in lubricin (a secreted glycoprotein encoded by the gene PRG4) cause the human autosomal recessive disorder camptodactyly-arthropathy-coxa vara-pericarditis syndrome (CACP). A major feature of CACP is precocious joint failure. In order to delineate the mechanism by which lubricin protects joints, we studied the expression of Prg4 mRNA during mouse joint development, and we created lubricin-mutant mice. Prg4 began to be expressed in surface chondrocytes and synoviocytes after joint cavitation had occurred and remained strongly expressed by these cells postnatally. Mice lacking lubricin were viable and fertile. In the newborn period, their joints appeared normal. As the mice aged, we observed abnormal protein deposits on the cartilage surface and disappearance of underlying superficial zone chondrocytes. In addition to cartilage surface changes and subsequent cartilage deterioration, intimal cells in the synovium surrounding the joint space became hyperplastic, which further contributed to joint failure. Purified or recombinant lubricin inhibited the growth of these synoviocytes in vitro. Tendon and tendon sheath involvement was present in the ankle joints, where morphologic changes and abnormal calcification of these structures were observed. We conclude that lubricin has multiple functions in articulating joints and tendons that include the protection of surfaces and the control of synovial cell growth.
authors.affiliation: Department of Genetics, Center for Human Genetics, Case Western Reserve University School of Medicine and University Hospitals of Cleveland, Cleveland, Ohio 44106, USA.
authors.forename: David K
authors.initials: DK
authors.lastname: Rhee
authors.forename: Jose
authors.initials: J
authors.lastname: Marcelino
authors.forename: MacArthur
authors.initials: M
authors.lastname: Baker
authors.forename: Yaoqin
authors.initials: Y
authors.lastname: Gong
authors.forename: Patrick
authors.initials: P
authors.lastname: Smits
authors.forename: Véronique
authors.initials: V
authors.lastname: Lefebvre
authors.forename: Gregory D
authors.initials: GD
authors.lastname: Jay
authors.forename: Matthew
authors.initials: M
authors.lastname: Stewart
authors.forename: Hongwei
authors.initials: H
authors.lastname: Wang
authors.forename: Matthew L
authors.initials: ML
authors.lastname: Warman
authors.forename: John D
authors.initials: JD
authors.lastname: Carpten
mesh_terms: D000818:Animals; D002356:Cartilage / Q000166:cytology / Q000378:metabolism*; D002448:Cell Adhesion; D049109:Cell Proliferation; D002478:Cells, Cultured; D019902:Chondrocytes / Q000166:cytology / Q000378:metabolism; D006614:Hindlimb / Q000000981:diagnostic imaging / Q000473:pathology; D006801:Humans; D017403:In Situ Hybridization; D007592:Joint Diseases / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D007596:Joints / Q000166:cytology / Q000254:growth & development / Q000378:metabolism / Q000473:pathology; D051379:Mice; D018345:Mice, Knockout; D010641:Phenotype; D017433:Protein Structure, Secondary; D011509:Proteoglycans / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011859:Radiography; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D013499:Surface Properties; D013577:Syndrome; D013582:Synovial Fluid; D013583:Synovial Membrane / Q000166:cytology* / Q000378:metabolism; D000099158:Proteoglycan 4
chemical_list: D011509:Proteoglycans; D011994:Recombinant Proteins; C419197:PRG4 protein, human; D000099158:Proteoglycan 4; C498837:Prg4 protein, mouse
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