Connective tissue activation. XXI. Regulation of glycosaminoglycan metabolism by lymphocyte (CTAP-I) and platelet (CTAP-III) growth factors.

The quantitative radiochemical methodology described in this report allows a major increase in information generation, increased experimental flexibility, improved statistical control, and increased diversity of information per culture. Other advantages relate to economies of technical time, supplies, cells, and test materials per individual culture. Microcultures of human synovial cells incorporate [14C]glucosamine into hyaluronic acid that accumulated primarily in the media and to a lesser extent in the cell mass. CTAP-I (from lymphoid cells), CTAP-III (from human platelets), PGE2, dibutyryl cAMP, and poly(I) . poly(C) markedly stimulated hyaluronate synthesis, whereas cortisol, cycloheximide, and tunicamycin inhibited stimulated synthesis. Time studies with cycloheximide indicated that translation, essential for the activation of synovial cells, was completed by 17 h postexposure to CTAP-I. Tunicamycin also seemed to inhibit CTAP-I induced activation primarily by interfering with translation; however, tunicamycin also caused modest post-translation inhibition of hyaluronate synthesis in activated adult human synovial cells.

Connective tissue activation. XXXVII. Effects of cytokine combinations, implications for an integrated cytokine network.

OBJECTIVE: Since many cytokines have been identified in chronically inflamed human synovium, it is possible that particular cytokines or combinations of cytokines play dominant roles in driving or inhibiting metabolic processes important to inflammation. To assess these possibilities, we compared selected effects of individual cytokines and their binary, ternary, and higher combinations in human synovial cell cultures. METHODS: Cytokines studied known to occur in human synovial tissue included: interleukin 1beta (IL-1beta), IL-6, tumor necrosis factor-alpha, granulocyte macrophage colony stimulating factor, interferon-gamma, acidic fibroblast growth factor (aFGF), basic FGF (bFGF), platelet derived growth factor, transforming growth factor-beta1, connecting tissue activating peptide-III, and epidermal growth factor. The growth related effects of these agents singly and in combinations were assessed by measuring newly synthesized [3H]DNA and [14C]GAG (glycosaminoglycan) in human synovial cell cultures. Cytokine induced synthesis of prostaglandin E2 (PGE2) was measured by ELISA. RESULTS: Most cytokine combinations resulted in additive/synergistic anabolic effects, except when IL-1beta was present; IL-1beta was markedly antagonistic to the mitogenic effects of other cytokines tested. Combinations of platelet derived cytokines were the most potent stimulators of DNA synthesis, while combinations of synovial derived cytokines were more active in stimulating GAG synthesis. Synovial cells exposed simultaneously to both platelet and synovial derived cytokines produced large quantities of [14C]GAG and showed a modest increase in [3H]DNA synthesis. IL-1beta, alone or in combinations, was dominant with respect to stimulation of PGE2 synthesis. Acetylsalicylic acid substantially interfered with all the effects of cytokine combinations measured. CONCLUSION: Quantitative alterations in synovial cell synthesis of GAG and DNA varied greatly depending on the ambient mixture of cytokines. Virtually all combinations of cytokines tested gave rise to large increases in synovial cell synthesis of GAG. Four platelet derived cytokines, a "physiologic combination," appeared to be dominant agents in stimulating DNA synthesis. This effect was profoundly reduced by the antagonistic effect of IL-1beta, mediated in part by PGE2. The patterns of cytokine combination induced metabolic effects suggest that the "cytokine network" has a significant measure of redundancy with respect to control of synovial cell metabolism.

Connective tissue activation. XXV. Regulation of proteoglycan synthesis in human synovial cells.

In this study, virtually all sulfated glycosaminoglycan (GAG) synthesized and secreted by human synovial cells, both normal and rheumatoid, was detected in the form of proteoglycans of monomeric size. Enzyme hydrolysis studies that were performed demonstrated dermatan sulfate to be the dominant GAG in the proteoglycan, with lesser amounts of chondroitin 4/6 sulfate. Exposure to beta-xyloside, used as a false "core protein," resulted in marked enhancement of GAG chain formation, suggesting that the synthesis of the sulfated carbohydrate chain itself was not rate limiting. Proteoglycan synthesis and secretion were stimulated by several types of connective tissue activating peptides (CTAP); CTAP-III stimulation of incremental core protein and glycosaminoglycan was shown to be of a similar magnitude. Since chain synthesis was not rate limiting, it is suggested that stimulated proteoglycan formation caused by the CTAP peptides may be primarily modulated through increased formation of core protein.

Connective tissue activation. XXXV. Detection of connective tissue activating peptide-III isoforms in synovium from osteoarthritis and rheumatoid arthritis patients: patterns of interaction with other synovial cytokines in cell culture.

OBJECTIVE: To determine whether extracts of unincubated osteoarthritis (OA) and rheumatoid arthritis (RA) synovial tissue contain connective tissue activating peptide-III (CTAP-III) isoforms and prostaglandin E2 (PGE2), and whether such extracts have growth-promoting activity, and to determine whether binary combinations of CTAP-III with other cytokines reported to be present in synovial tissue lead to synergistic, additive, or inhibitory effects on growth. METHODS: Acid-ethanol extracts of human synovium were examined for growth-promoting activity by measuring formation of 14C-glycosaminoglycan (14C-GAG) and 3H-DNA in synovial cell cultures; PGE2 was measured by enzyme immunoassay, and CTAP-III isoforms were identified by Western blotting of extracted proteins separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Growth-promoting activity of CTAP-III and other cytokines was tested in synovial cultures treated with the agonists singly and in binary combination, by measuring changes in synthesis of 14C-GAG and 3H-DNA. RESULTS: Platelet-derived CTAP-III and a cleavage isoform with the electrophoretic mobility of CTAP-III-des 1-15/neutrophil-activating peptide-2 (NAP-2) and PGE2 were found in biologically active extracts of synovial samples from patients with RA and OA. Five growth factors (recombinant epidermal growth factor [rEGF], recombinant interleukin-1 beta [rIL-1 beta], basic fibroblast growth factor [bFGF], PGE1, and PGE2) in binary combination with CTAP-III showed synergism in stimulating GAG synthesis; two (recombinant platelet-derived growth factor type BB [rPDGE-BB] and recombinant transforming growth factor beta [rTGF beta]) had an additive effect. In combination with CTAP-III, rEGF and rPDGF-BB had a synergistic effect in promoting DNA synthesis, rTGF beta and rbFGF had an additive effect, and rIL-1 beta, PGE1, and PGE2 were antagonistic. CONCLUSIONS: The results suggest that, in addition to endogenous factors, CTAP-III and other platelet-derived cytokines may play roles in regulating synovial cell metabolism in RA and OA, and that combinations of growth factors may be more significant than single agents in amplification or suppression of important cell functions.

Connective tissue activation. XXXIII. Biologically active cleavage products of CTAP-III from human platelets.

Evidence for three new isoforms of CTAP-III from human platelets is presented; two NH2-terminal cleavage products were identified, CTAP-III (des 1-13) and CTAP-III (des 1-15). CTAP-III (des 1-13) has a pI of 8.6 and is a relatively stable proteolytic cleavage product that retains the capacity to stimulate [14C]GAG synthesis in human synovial cell cultures. CTAP-III (des 1-15) appears to be an elastase or chymotrypsin cleavage product and identical to NAP-2, an entity thought to have neutrophil activating properties.

Connective tissue activation. XXXIV: Effects of proteolytic processing on the biologic activities of CTAP-III.

Microheterogeneity of connective tissue activation peptide III (CTAP-III) was revealed by preparative and analytical isoelectric focusing. Proteolytic activities in human platelet preparations resulted in four cleavage products of platelet-derived CTAP-III. Three isoforms (CTAP-III des 1-13, des 1-14, and des 1-15/NAP-2) stimulate [14C]glycosaminoglycan synthesis; two isoforms also promote [3H]DNA synthesis in human fibroblast cultures. Elastase (from porcine pancreas) cleavage of human platelet-derived CTAP-III and rCTAP-III-Leu-21 to the des 1-15 isoforms was associated with either preservation of specific anabolic biologic activity or an actual increase in specific activity. Nonenzymatic glycosylation of lysyl residues and deamination of the NH2-terminal asparagine of platelet-derived CTAP-III were commonly present, but did not correlate with the biologic activities that were measured. Protein sequence homology shows CTAP-III and its isoforms to be members of a family of proteins (including NAP-1/II-8, MGSA, and platelet factor-4) known to be associated with growth, wound repair, inflammation, and neoplasia. The consequences of proteolytic processing reported here for CTAP-III may be characteristic of the other proteins in this group.