title: Reduced transforming growth factor-beta signaling in cartilage of old mice: role in impaired repair capacity.
abstract: Osteoarthritis (OA) is a common joint disease, mainly effecting the elderly population. The cause of OA seems to be an imbalance in catabolic and anabolic factors that develops with age. IL-1 is a catabolic factor known to induce cartilage damage, and transforming growth factor (TGF)-beta is an anabolic factor that can counteract many IL-1-induced effects. In old mice, we observed reduced responsiveness to TGF-beta-induced IL-1 counteraction. We investigated whether expression of TGF-beta and its signaling molecules altered with age. To mimic the TGF-beta deprived conditions in aged mice, we assessed the functional consequence of TGF-beta blocking. We isolated knee joints of mice aged 5 months or 2 years, half of which were exposed to IL-1 by intra-articular injection 24 h prior to knee joint isolation. Immunohistochemistry was performed, staining for TGF-beta1, -2 or -3, TGF-betaRI or -RII, Smad2, -3, -4, -6 and -7 and Smad-2P. The percentage of cells staining positive was determined in tibial cartilage. To mimic the lack of TGF-beta signaling in old mice, young mice were injected with IL-1 and after 2 days Ad-LAP (TGF-beta inhibitor) or a control virus were injected. Proteoglycan (PG) synthesis (35S-sulfate incorporation) and PG content of the cartilage were determined. Our experiments revealed that TGF-beta2 and -3 expression decreased with age, as did the TGF-beta receptors. Although the number of cells positive for the Smad proteins was not altered, the number of cells expressing Smad2P strongly dropped in old mice. IL-1 did not alter the expression patterns. We mimicked the lack of TGF-beta signaling in old mice by TGF-beta inhibition with LAP. This resulted in a reduced level of PG synthesis and aggravation of PG depletion. The limited response of old mice to TGF-beta induced-IL-1 counteraction is not due to a diminished level of intracellular signaling molecules or an upregulation of intracellular inhibitors, but is likely due to an intrinsic absence of sufficient TGF-beta receptor expression. Blocking TGF-beta distorted the natural repair response after IL-1 injection. In conclusion, TGF-beta appears to play an important role in repair of cartilage and a lack of TGF-beta responsiveness in old mice might be at the root of OA development.
authors.affiliation: Experimental Rheumatology and Advanced Therapeutics, St Radboud University Medical Centre Nijmegen, Geert Grooteplein 26, 6525 GA Nijmegen, The Netherlands. e.blaneydavidson@reuma.umcn.nl
authors.forename: E N
authors.initials: EN
authors.lastname: Blaney Davidson
authors.forename: A
authors.initials: A
authors.lastname: Scharstuhl
authors.forename: E L
authors.initials: EL
authors.lastname: Vitters
authors.forename: P M
authors.initials: PM
authors.lastname: van der Kraan
authors.forename: W B
authors.initials: WB
authors.lastname: van den Berg
mesh_terms: D000375:Aging; D000818:Animals; D002358:Cartilage, Articular / Q000166:cytology / Q000378:metabolism*; D002452:Cell Count; D019902:Chondrocytes / Q000166:cytology / Q000378:metabolism; D020219:Chondrogenesis / Q000502:physiology*; D004195:Disease Models, Animal; D006614:Hindlimb; D007091:Image Processing, Computer-Assisted; D007270:Injections, Intra-Articular; D007375:Interleukin-1 / Q000494:pharmacology; D007596:Joints / Q000378:metabolism / Q000473:pathology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D011509:Proteoglycans / Q000096:biosynthesis; D018125:Receptors, Transforming Growth Factor beta / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D051899:Smad2 Protein / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D007375:Interleukin-1; D011509:Proteoglycans; D018125:Receptors, Transforming Growth Factor beta; D051899:Smad2 Protein; C497783:Smad2 protein, mouse; D016212:Transforming Growth Factor beta