Mechanism of stimulation of prostaglandin synthesis by a factor from rheumatoid synovial tissue.

Abstract

[1-14C]AA levels in cultures of untreated cells. These observations are inconsistent with a mechanism of prostaglandin stimulation consisting of an increase in phospholipase activity, because this mechanism would increase free AA levels as well as prostaglandins. A mechanism is proposed in which free AA is maintained at low steady-state levels by reacylation of free AA into phospholipids at a rate more rapid than its reaction with cyclooxygenase to form prostaglandins. In this mechanism, stimulation ofthe rate ofthe cyclooxygenase step by RSF accounts for increased prostaglandin synthesis as well as the decreased release of AA. On the basis of data previously reported by others, it is suggested that this mechanism may also be applicable to the stimulation of prostaglandin synthesis by several other agents. Preliminary characterization of the RSF indicates that it is a protein, and molecular seive chromatography indicates that its molecular weight is about 18,000. The production of RSF by rheumatoid synovial tissue is suppressed to undetectable levels by 1 F.M dexamethasone.It has been generally believed that the rate-limiting step in prostaglandin (PG) synthesis is the phospholipase-catalyzed hydrolysis of phospholipids and that the mechanisms of action ofvarious factors stimulating PG synthesis involve the activation of phospholipases. These hypotheses have been in part based on the facts that the quantities of free arachidonic acid (AA) within cells and tissue are insufficient to account for quantities of PGs synthesized and that stimulation of PG synthesis may be accompanied by variable increases in the concentrations of free AA (1-6).We report here the results ofstudies ofsome ofthe properties and the mechanism of action of a PG-stimulating factor produced by rheumatoid synovial tissue (RSF). In these experiments, the stimulation of PGE2 synthesis is generally accompanied by decreases in free AA concentrations. We conclude that these observations are inconsistent with a mechanism based on stimulation of phospholipase activity. A mechanism is proposed in which RSF stimulates the rate of the cyclooxygenase step. A preliminary report of some of this has appeared (7).MATERIALS AND METHODS Rheumatoid Synovial Cell Strains. Cells were grown from explants ofrheumatoid synovial tissue by using methods similar to those described by others (8, 9). Confluent cells were passaged using 0.05% trypsin/0.02% EDTA solution (GIBCO no. 530), and new plates were seeded at a density of 1.9 X 105 cells growing to =7 X 106 per 60-mm plate when confluent. For some experiments cells were passaged into multiwell plates at a similar density. Cells were stored in liquid N2 in a freezing mixture of minimal essential medium with 25% fetal bovine serum and 8% dimethyl sulfoxide. Cells were used for these experiments after 4 to 10 passages; no dependence of PG production on passage number was observed.Rheumatoid Synovial Explant Cultures. Explant cultures of rheumatoid synovial tissue were prepared (10). Approximately 60 mg of tissue (wet...

Cytokines and other mediators in rheumatoid arthritis

“…Although PGE 2 is present, its levels are substantially lower than in adherent stellate dendritic cells. Other investigators and ourselves have subsequently found that media from cultured fragments of synovium (containing all cells including monocytemacrophages) can also stimulate PGE 2 production by synovial cell culture [160]. Furthermore, the same culture media can stimulate chondrocytes, bone-derived cells, and to a lesser extent certain skin fibroblasts.…”

Production of C5a antagonist by synovial and peritoneal tissue fibroblasts

“…Informed consent was obtained from every subject before the tissue samples were taken. Cultures were made by a modification of the method of Robinson et al (1975Robinson et al ( ,1981. The biopsy material was excised aseptically and immersed in Dulbecco minimal essential medium (DMEM) containing 25% fetal calf serum (FCS) (Gibco, Grand Island, NY), 100 U/ml penicillin, and 100 mg/ml streptomycin.…”

Lymphocytes induce resorption of cartilage by producing catabolin

“…connective-tissue cells (fibroblasts and chondrocytes) to secrete proteinases and prostaglandins have been suggested to cause resorption of connectivetissue matrix, and their relationship to catabolin must be considered. Generally these factors have come from monocytes or macrophages (Deshmukh-Phadke et al, 1978, 1980Dayer et al, 1979;Ridge et al, 1980;Hamilton & Slywka, 1981) and synovial explants (Meats et al, 1980;Robinson et al, 1981). The best characterized is the monokine described by Dayer et al (1979), which stimulates synovial fibroblasts to produce collagenase and prostaglandins, and which is now thought to be interleukin 1 .…”