title: Increase in ALK1/ALK5 ratio as a cause for elevated MMP-13 expression in osteoarthritis in humans and mice.
abstract: During osteoarthritis (OA) chondrocytes show deviant behavior resembling terminal differentiation of growth-plate chondrocytes, characterized by elevated MMP-13 expression. The latter is also a hallmark for OA. TGF-beta is generally thought to be a protective factor for cartilage, but it has also displayed deleterious effects in some studies. Recently, it was shown that besides signaling via the ALK5 (activin-like kinase 5) receptor, TGF-beta can also signal via ALK1, thereby activating Smad1/5/8 instead of Smad2/3. The Smad1/5/8 route can induce chondrocyte terminal differentiation. Murine chondrocytes stimulated with TGF-beta activated the ALK5 receptor/Smad2/3 route as well as the ALK1/Smad1/5/8 route. In cartilage of mouse models for aging and OA, ALK5 expression decreased much more than ALK1. Thus, the ALK1/ALK5 ratio increased, which was associated with changes in the respective downstream markers: an increased Id-1 (inhibitor of DNA binding-1)/PAI-1 (plasminogen activator inhibitor-1) ratio. Transfection of chondrocytes with adenovirus overexpressing constitutive active ALK1 increased MMP-13 expression, while small interfering RNA against ALK1 decreased MMP-13 expression to nondetectable levels. Adenovirus overexpressing constitutive active ALK5 transfection increased aggrecan expression, whereas small interfering RNA against ALK5 resulted in increased MMP-13 expression. Moreover, in human OA cartilage ALK1 was highly correlated with MMP-13 expression, whereas ALK5 correlated with aggrecan and collagen type II expression, important for healthy cartilage. Collectively, we show an age-related shift in ALK1/ALK5 ratio in murine cartilage and a strong correlation between ALK1 and MMP-13 expression in human cartilage. A change in balance between ALK5 and ALK1 receptors in chondrocytes caused changes in MMP-13 expression, thereby causing an OA-like phenotype. Our data suggest that dominant ALK1 signaling results in deviant chondrocyte behavior, thereby contributing to age-related cartilage destruction and OA.
authors.affiliation: Rheumatology Research and Advanced Therapeutics, Radboud University Nijmegen Medical Center, Nijmegen, the Netherlands. e.blaneydavidson@reuma.umcn.nl
authors.forename: Esmeralda N
authors.initials: EN
authors.lastname: Blaney Davidson
authors.forename: Dennis F G
authors.initials: DF
authors.lastname: Remst
authors.forename: Elly L
authors.initials: EL
authors.lastname: Vitters
authors.forename: Henk M
authors.initials: HM
authors.lastname: van Beuningen
authors.forename: Arjen B
authors.initials: AB
authors.lastname: Blom
authors.forename: Marie-Jose
authors.initials: MJ
authors.lastname: Goumans
authors.forename: Wim B
authors.initials: WB
authors.lastname: van den Berg
authors.forename: Peter M
authors.initials: PM
authors.lastname: van der Kraan
mesh_terms: D030201:Activin Receptors, Type I / Q000235:genetics / Q000378:metabolism*; D030301:Activin Receptors, Type II / Q000235:genetics / Q000378:metabolism*; D000375:Aging / Q000502:physiology; D000818:Animals; D002356:Cartilage / Q000201:enzymology; D002478:Cells, Cultured; D019902:Chondrocytes / Q000201:enzymology; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D051798:Inhibitor of Differentiation Protein 1 / Q000378:metabolism; D008297:Male; D053509:Matrix Metalloproteinase 13 / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D010003:Osteoarthritis / Q000201:enzymology* / Q000235:genetics; D017395:Plasminogen Activator Inhibitor 1 / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D012333:RNA, Messenger / Q000235:genetics; D000077293:Receptor, Transforming Growth Factor-beta Type I; D018125:Receptors, Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: C497455:Idb1 protein, mouse; D051798:Inhibitor of Differentiation Protein 1; D017395:Plasminogen Activator Inhibitor 1; D012333:RNA, Messenger; D018125:Receptors, Transforming Growth Factor beta; D017346:Protein Serine-Threonine Kinases; C425364:ACVRL1 protein, human; D030201:Activin Receptors, Type I; D030301:Activin Receptors, Type II; C498931:Acvrl1 protein, mouse; D000077293:Receptor, Transforming Growth Factor-beta Type I; C000625841:TGFBR1 protein, human; C000625842:Tgfbr1 protein, mouse; C507079:MMP13 protein, human; D053509:Matrix Metalloproteinase 13; C507081:Mmp13 protein, mouse