Osteoarthritis-related fibrosis is associated with both elevated pyridinoline cross-link formation and lysyl hydroxylase 2b expression.
OBJECTIVE
Fibrosis is a major contributor to joint stiffness in osteoarthritis (OA). We investigated several factors associated with the persistence of transforming growth factor beta (TGF-β)-induced fibrosis and whether these factors also play a role in OA-related fibrosis.


METHODS
Mice were injected intra-articularly (i.a.) with an adenovirus encoding either TGF-β or connective tissue growth factor (CTGF). In addition, we induced OA by i.a. injection of bacterial collagenase into the right knee joint of C57BL/6 mice. mRNA was isolated from the synovium for Q-PCR analysis of the gene expression of various extracellular matrix (ECM) components, ECM degraders, growth factors and collagen cross-linking-related enzymes. Sections of murine knee joints injected with Ad-TGF-β or Ad-CTGF or from experimental OA were stained for lysyl hydroxylase 2 (LH2). The number of pyridinoline cross-links per triple helix collagen in synovium biopsies was determined with high-performance liquid chromatography (HPLC).


RESULTS
Expression of collagen alpha-1(I) chain precursor (Col1a1), tissue inhibitor of metalloproteinases 1 (TIMP1) and especially procollagen-lysine, 2-oxoglutarate 5-dioxygenase 2b (Plod2b) were highly upregulated by TGF-β but not by CTGF. Elevated expression of Plod2b mRNA was associated with high lysyl hydroxylase 2 (LH2) protein staining after TGF-β overexpression and in experimental OA. Furthermore, in experimental OA the number of hydroxypyridinoline cross-links was significant increased compared to control knee joints.


CONCLUSIONS
Our data show that elevated LH2b expression is associated with the persistent nature of TGF-β-induced fibrosis. Also in experimental OA, LH2b expression as well as the number of hydroxypyridinoline cross-link were significantly upregulated. We propose that LH2b, and the subsequent increase in pyridinoline cross-links, is responsible for the persistent fibrosis in experimental OA.
Rheumatology Research and Advanced Therapeutics, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands. D.Remst@reuma.umcn.nl
D F G
DF
Remst
E N
EN
Blaney Davidson
E L
EL
Vitters
A B
AB
Blom
R
R
Stoop
J M
JM
Snabel
R A
RA
Bank
W B
WB
van den Berg
P M
PM
van der Kraan
D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D001169:Arthritis, Experimental; D002853:Chromatography, Liquid; D003094:Collagen / Q000235:genetics / Q000378:metabolism; D055513:Connective Tissue Growth Factor / Q000494:pharmacology; D005109:Extracellular Matrix / Q000235:genetics; D005355:Fibrosis; D015870:Gene Expression; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D020370:Osteoarthritis, Knee / Q000378:metabolism*; D008240:Procollagen-Lysine, 2-Oxoglutarate 5-Dioxygenase / Q000378:metabolism*; D020871:RNA Stability; D013264:Stifle / Q000473:pathology; D013583:Synovial Membrane / Q000378:metabolism / Q000473:pathology*; D016212:Transforming Growth Factor beta / Q000494:pharmacology
D000596:Amino Acids; D036341:Intercellular Signaling Peptides and Proteins; D016212:Transforming Growth Factor beta; D055513:Connective Tissue Growth Factor; C015484:pyridinoline; D003094:Collagen; D008240:Procollagen-Lysine, 2-Oxoglutarate 5-Dioxygenase; C582419:lysyl hydroxylase 2, mouse