sFRP3 and DKK1 Regulate Fibroblast-Like Synoviocytes Markers and Wnt Elements Expression Depending on Cellular Context.
BACKGROUND
Fibroblast-like synoviocytes (FLS) from rheumatoid arthritis (RA) display pathogenic behavior. Various members of the Wnt pathway, especially the canonical Wnt/β-catenin cascade, may contribute to autonomous RA FLS activation. It has been shown that the two Wnt inhibitors: sFRP3 and DKK1 contribute to several critical aspects of joint biology. However, their effects on RA FLS are poorly characterized. The aim of our study was to investigate the effects of sFRP3 and DKK1 on FLS markers, Wnt components, and target oncogenes expression by RA FLS and compare the findings to osteoarthritic (OA) FLS.


METHODS
RA and OA FLS were treated with sFRP3 and DKK1 for 6 days. Wnt signaling components (Wnt5a, LRP5 and β-catenin), Wnt target oncogenes (cyclin E1 and WISP1), and FLS markers (fibronectin and MMP3) were analyzed using western blotting and/or qRT-PCR.


RESULTS
Our data indicated that sFRP3 down-regulated the key gene β-catenin in RA FLS. sFRP3 decreased fibronectin, a well-known downstream effectors gene of Wnt/β-catenin pathway, and LRP5 expression in both RA and OA FLS. In OA FLS, sFRP3 induced increased expression of Wnt5a and MMP3 but did not affect their levels in RA FLS. On the other hand, DKK1 increased fibronectin expression in RA FLS and decreased its expression in OA FLS.


CONCLUSIONS
Our results confirm the involvement of Wnt signaling in FLS transformation and show that two inhibitors of the same cascade can regulate differently the same elements and that a single inhibitor can initiate signaling depending on cellular context.


BACKGROUND
FLS: fibroblast-like synoviocytes; RA: rheumatoid arthritis; Wnt: Wingless; Fz: frizzled; LRP: Fz/low-density lipoprotein receptor protein; WISP1: Wnt1 inducible signaling pathway protein 1; sFRP: secreted Fz-related proteins; DKK: Dickkopf; OA: osteoarthritis; DMEM: Dulbecco's modified Eagle's medium; FBS: fetal bovine serum; PBS: phosphate buffered saline; SDS-PAGE: sodium dodecyl sulfate-polyacrylamide gel electrophoresis; ECL: enhanced chemiluminescence detection solution; MMP3: metaloproteinase 3; qRT-PCR: quantitative real-time polymerase chain reaction; S.D: standard deviation; CRD: cysteine-rich domain; MeCP2: methyl-CpG-binding protein; RANKL: nuclear factor-kappa B ligand.
a Immuno-Rheumatology Research laboratory, Rheumatology Department , La Rabta Hospital, University of Tunis-El Manar , Tunis , Tunisia.
Dorra
D
Elhaj Mahmoud
a Immuno-Rheumatology Research laboratory, Rheumatology Department , La Rabta Hospital, University of Tunis-El Manar , Tunis , Tunisia.
Nadia
N
Sassi
a Immuno-Rheumatology Research laboratory, Rheumatology Department , La Rabta Hospital, University of Tunis-El Manar , Tunis , Tunisia.|b Department of Orthopedic Surgery and Traumatology , La Rabta Hospital , Tunis , Tunisia.
Ghassen
G
Drissi
a Immuno-Rheumatology Research laboratory, Rheumatology Department , La Rabta Hospital, University of Tunis-El Manar , Tunis , Tunisia.|b Department of Orthopedic Surgery and Traumatology , La Rabta Hospital , Tunis , Tunisia.
Maher
M
Barsaoui
a Immuno-Rheumatology Research laboratory, Rheumatology Department , La Rabta Hospital, University of Tunis-El Manar , Tunis , Tunisia.|b Department of Orthopedic Surgery and Traumatology , La Rabta Hospital , Tunis , Tunisia.
Khaled
K
Zitouna
a Immuno-Rheumatology Research laboratory, Rheumatology Department , La Rabta Hospital, University of Tunis-El Manar , Tunis , Tunisia.
Hela
H
Sahli
a Immuno-Rheumatology Research laboratory, Rheumatology Department , La Rabta Hospital, University of Tunis-El Manar , Tunis , Tunisia.
Maryam
M
Kallel-Sellami
a Immuno-Rheumatology Research laboratory, Rheumatology Department , La Rabta Hospital, University of Tunis-El Manar , Tunis , Tunisia.|b Department of Orthopedic Surgery and Traumatology , La Rabta Hospital , Tunis , Tunisia.
Lassad
L
Kanoun
a Immuno-Rheumatology Research laboratory, Rheumatology Department , La Rabta Hospital, University of Tunis-El Manar , Tunis , Tunisia.
Elhem
E
Cheour
a Immuno-Rheumatology Research laboratory, Rheumatology Department , La Rabta Hospital, University of Tunis-El Manar , Tunis , Tunisia.
Lilia
L
Laadhar
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D001172:Arthritis, Rheumatoid / Q000276:immunology*; D049109:Cell Proliferation; D002478:Cells, Cultured; D060833:Cellular Microenvironment; D005260:Female; D005347:Fibroblasts / Q000502:physiology*; D005786:Gene Expression Regulation; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism*; D008297:Male; D009124:Muscle Proteins / Q000378:metabolism*; D010003:Osteoarthritis / Q000276:immunology*; D015398:Signal Transduction; D000070918:Synoviocytes / Q000502:physiology*; D051153:Wnt Proteins / Q000378:metabolism*
D048868:Adaptor Proteins, Signal Transducing; C501126:DKK1 protein, human; D036341:Intercellular Signaling Peptides and Proteins; C455624:MYOZ3 protein, human; D009124:Muscle Proteins; D051153:Wnt Proteins
Cell culture; Wnt pathway; osteroarthritis; rheumatoid arthritis; synoviocytes