Superinduction of IL-6 synthesis in human peritoneal mesothelial cells is related to the induction and stabilization of IL-6 mRNA.
The initiation of peritonitis is accompanied by a massive increase in intraperitoneal levels of IL-6. The source of this cytokine and the mechanism by which its levels are increased so dramatically are unknown. We examined the mechanism of IL-6 secretion by HPMC exposed to the milicu present in the peritoneal cavity during the initiation of inflammation. Exposure of HPMC to spent peritoneal dialysis effluent (PDE) or IL-1 beta resulted in a time- and dose-dependent increase in IL-6 secretion. After 24 hours the IL-6 release (pg/microgram cell protein) was increased from 5.0 +/- 0.8 in control cells to 16.0 +/- 2.4 and to 83.8 +/- 17.4 in HPMC treated with PDE and IL-1 beta (1000 pg/ml), respectively (N = 5, P < 0.05). If, however, PDE and IL-1 beta were combined, then the secretion of IL-6 was synergistically increased to 747.7 +/- 349.9 (P < 0.05 vs. expected additive value). The same effect was evident when PDE was combined with TNF alpha or mixed with peritoneal macrophage conditioned medium. These changes were not a reflection of HPMC proliferation as estimated by 3H-thymidine incorporation. The "superinduction" of IL-6 release was associated both with the induction and stabilization of IL-6 mRNA. Competitive PCR demonstrated that the amount of IL-6 mRNA (fM/microgram total RNA) was increased from 0.35 +/- 0.13 in control cells to 11.66 +/- 3.89 and to 10.83 +/- 5.17 in HPMC treated with PDE and IL-1 beta (100 pg/ml), respectively (N = 5, P < 0.05). The combination of PDE + IL-1 beta synergistically increased IL-6 mRNA levels to 56.33 +/- 8.79 (P < 0.05 vs. additive value). RNA stability experiments using actinomycin D revealed that the half life of IL-6 mRNA (hours) was increased from 2.8 hours in control cells to 6.7 and 9.4 in HPMC exposed to PDE and IL-1 beta, respectively. The combination of PDE together with IL-1 beta resulted in a prolonged stabilization of IL-6 mRNA with levels remaining constant over the 12 hours of the experiment. These data demonstrate that HPMC IL-6 synthesis can be synergistically amplified in the presence of peritoneal dialysis effluent and PMO-derived cytokines. The results suggest that the peritoneal mesothelium may be responsible for the dramatic rise in IL-6 levels seen during the initial stages of CAPD peritonitis.
Witowski
J
J
Institute of Nephrology, University of Wales College of Medicine, Cardiff, United Kingdom.
Jörres
A
A
Coles
G A
GA
Williams
J D
JD
Topley
N
N
D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D017077:Culture Media, Conditioned / Q000494:pharmacology; D003513:Cycloheximide / Q000494:pharmacology; D003609:Dactinomycin / Q000494:pharmacology; D015314:Dialysis Solutions / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004587:Electrophoresis, Agar Gel; D004847:Epithelial Cells; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism*; D005786:Gene Expression Regulation; D006801:Humans; D007375:Interleukin-1 / Q000494:pharmacology; D015850:Interleukin-6 / Q000096:biosynthesis* / Q000235:genetics*; D017737:Macrophages, Peritoneal / Q000378:metabolism; D008954:Models, Biological; D010529:Peritoneal Cavity / Q000166:cytology; D010538:Peritonitis / Q000209:etiology; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000032:analysis; D017472:Receptors, Interleukin-1 / Q000037:antagonists & inhibitors; D013997:Time Factors
D017077:Culture Media, Conditioned; D015314:Dialysis Solutions; D007375:Interleukin-1; D015850:Interleukin-6; D012333:RNA, Messenger; D017472:Receptors, Interleukin-1; D003609:Dactinomycin; D003513:Cycloheximide