Membrane-associated IL-1 contributes to chronic synovitis and cartilage destruction in human IL-1 alpha transgenic mice.
IL-1 molecules are encoded by two distinct genes, IL-1alpha and IL-1beta. Both isoforms possess essentially identical activities and potencies, whereas IL-1alpha, in contrast to IL-1beta, is known to act as a membrane-associated IL-1 (MA-IL-1) and plays an important role in a variety of inflammatory situations. The transgenic (Tg) mouse line (Tg1706), which was generated in our laboratory, overexpresses human IL-1alpha (hIL-1alpha) and exhibits a severe arthritic phenotype characterized by autonomous synovial proliferation with subsequent cartilage destruction. Because the transgene encoded Lys(64) to Ala(271) of the hIL-1alpha amino acid sequence, Tg mice may overproduce MA-IL-1 as well as soluble IL-1alpha. The present study investigated whether MA-IL-1 contributes to synovial proliferation and cartilage destruction in the development of arthritis. Flow cytometric analysis revealed that both macrophage-like and fibroblast-like synoviocytes constitutively produce MA-IL-1. D10 cell proliferation assay revealed MA-IL-1 bioactivity of paraformaldehyde-fixed synoviocytes and the further induction of endogenous mouse MA-IL-1 via autocrine mechanisms. MA-IL-1 expressed on synoviocytes triggered synoviocyte self-proliferation through cell-to-cell (i.e., juxtacrine) interactions and also promoted proteoglycan release from the cartilage matrix in chondrocyte monolayer culture. Interestingly, the severity of arthritis was significantly correlated with MA-IL-1 activity rather than with soluble IL-1alpha activity or concentration of serum hIL-1alpha. Moreover, when the Tg1706 line was compared with the Tg101 line, which selectively overexpresses the 17-kDa mature hIL-1alpha, the severity of arthritis was significantly higher in the Tg1706 line than in the Tg101 line. These results suggest that MA-IL-1 contributes to synoviocyte self-proliferation and subsequent cartilage destruction in inflammatory joint disease such as rheumatoid arthritis.
Niki
Yasuo
Y
Department of Orthopedic Surgery, Keio University, 35 Shinanomachi, Shinjuku-ku, Tokyo 160-8582, Japan. y.niki@lib.bekkoame.ne.jp
Yamada
Harumoto
H
Kikuchi
Toshiyuki
T
Toyama
Yoshiaki
Y
Matsumoto
Hideo
H
Fujikawa
Kyosuke
K
Tada
Norihiro
N
D000818:Animals; D001169:Arthritis, Experimental / Q000235:genetics* / Q000276:immunology* / Q000473:pathology; D002358:Cartilage, Articular / Q000276:immunology / Q000378:metabolism / Q000473:pathology*; D002450:Cell Communication / Q000235:genetics / Q000276:immunology; D002455:Cell Division / Q000235:genetics / Q000276:immunology; D002462:Cell Membrane / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D002478:Cells, Cultured; D002908:Chronic Disease; D005109:Extracellular Matrix / Q000378:metabolism; D005434:Flow Cytometry; D005786:Gene Expression Regulation / Q000276:immunology; D006801:Humans; D007375:Interleukin-1 / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D007700:Kinetics; D008565:Membrane Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D051379:Mice; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D011233:Precipitin Tests; D011509:Proteoglycans / Q000378:metabolism; D012720:Severity of Illness Index; D012995:Solubility; D013583:Synovial Membrane / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D013585:Synovitis / Q000235:genetics* / Q000276:immunology* / Q000473:pathology
D007375:Interleukin-1; D008565:Membrane Proteins; D011509:Proteoglycans