| Research Abstract |
Background-Tie2, an essential tyrosine kinase receptor for angiogenesis, is overexpressed in many cellular components of synovial tissues of rheumatoid arthritis (RA).
Objectives- To evaluate that angiopoietin- 1, -2 (Ang1, Ang2), ligands for Tie2, are also expressed in RA synovium, and to study the functional role of Ang1 and Ang2 in the cell proliferation and chemotaxis of the RA synoviocytes.
Methods- Immunohistochemistry and in situ hybridization of Ang1, Ang2 and Tie2 were performed to 10 RA synovial tissues. In the presence of recombinant Ang1 and Ang2, [3H] thymidine incorporation and transwell assays were carried out to the cultured fibroblastic synoviocytes obtained from two RA patients and cultured separately.
Results- Like Tie2, immunoreactivity of Ang1 and Ang2 was observed in all RA samples, in which synovial lining and stromal cells as well as small vessels on actively proliferating region showed intense staining. Double staining demonstrated that these Ang ligands positive cells were highly expressed proliferating cell nuclear antigen, and exclusively costained by Tie2 antibody.
Incubation of cultured synoviocytes with Ang1 or Ang2 resulted in a slight decrease of DNA synthesis in the synoviocytes from one patient, while another patient- derived cells exhibited no response to these ligands. Chemotaxic migration of these synoviocytes, however, was enhanced by Ang1 and Ang2 in both RA synoviocytes, whereby Ang2 showed more potent stimulator compared to Ang1.
Conclusions- These results demonstrate that Ang1 and Ang2 are involved in pathophysiology of RA by an autocrine/paracrine mechanism, in which Ang1 and Ang2 play an important role for cell migration rather than cell proliferation of not only vascular system but also of synovial lining and stromal cells.
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