sirolimus and Acute-Phase-Reaction

Interleukin-6 (IL-6) is the major activator of the acute phase response (APR). One important regulator of IL-6-activated APR is peroxisome proliferator-activated receptor alpha (PPARα). Currently, there is a growing interest in determining the role of PPARα in regulating APR; however, studies on the molecular mechanisms and signaling pathways implicated in mediating the effects of IL-6 on the expression of PPARα are limited. We previously revealed that IL-6 inhibits PPARα gene expression through CAAT/enhancer-binding protein transcription factors in hepatocytes. In this study, we determined that STAT1/3 was the direct downstream molecules that mediated the Janus kinase 2 (JAK2) and phosphatidylinositol-3 kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) signaling pathways in IL-6-induced repression of PPARα. Treatment of cells with pharmacological inhibitors of JAK2, PI3K, AKT, and mTOR attenuated the inhibitory effect of IL-6 on PPARα protein in a dose-dependent manner. These inhibitors also decreased the IL-6-induced repression of PPARα mRNA expression and promoter activity. Overexpression of STAT1 and STAT3 in HepG2 cells cotransfected with a reporter vector containing this PPARα promoter region revealed that both the expression plasmids inhibited the IL-6-induced repression of PPARα promoter activity. In the presence of inhibitors of JAK2 and mTOR (AG490 and rapamycin, respectively), IL-6-regulated protein expression and DNA binding of STAT1 and STAT3 were either completely or partially inhibited simultaneously, and the IL-6-induced repression of PPARα protein and mRNA was also inhibited. This study has unraveled novel pathways by which IL-6 inhibits PPARα gene transcription, involving the modulation of JAK2/STAT1-3 and PI3K/AKT/mTOR by inducing the binding of STAT1 and STAT3 to STAT-binding sites on the PPARα promoter. Together, these findings represent a new model of IL-6-induced suppression of PPARα expression by inducing STAT1 and STAT3 phosphorylation and subsequent down-regulation of PPARα mRNA expression.

Topics: Acute-Phase Reaction; Androstadienes; Binding Sites; Cell Line, Tumor; Hep G2 Cells; Hepatocytes; Humans; Interleukin-6; Janus Kinase 2; Phosphatidylinositol 3-Kinases; Phosphorylation; PPAR alpha; Promoter Regions, Genetic; Protein Binding; RNA, Messenger; Sirolimus; STAT1 Transcription Factor; STAT3 Transcription Factor; TOR Serine-Threonine Kinases; Transcription, Genetic; Tyrphostins; Wortmannin

Rapamycin (RAPA), a potent immunosuppressive agent that prevents organ graft rejection in animal models of transplantation, possesses a mechanism of action different than that of cyclosporin A and FK-506. In this study, the pharmacological activity of RAPA in a variety of immune and inflammatory models was assessed in order to define better its potential utility as an antiarthritic agent. RAPA inhibited T cell-mediated inflammation in mouse methylated bovine serum albumin-induced delayed-type hypersensitivity (ED40 = 4.7 mg/kg p.o.) and produced oral ED50 of 2.0 mg/kg against developing adjuvant arthritis in rats (3-day dosing schedule) and 9.5 mg/kg in established adjuvant arthritis in rats (daily dosing schedule). In both models of adjuvant arthritis, effects of RAPA were maintained even after cessation of drug dosing. In contrast, after discontinuation of cyclosporin A (5- and 10-mg/kg doses), disease activity returned. RAPA was also effective in another T cell-mediated model, experimental allergic encephalomyelitis (ED50 approximately 5 mg/kg p.o.). At higher doses, RAPA significantly inhibited carrageenan paw edema in rats, a model of acute inflammation (ED40, 56 mg/kg p.o.), without increasing serum corticosterone levels. In this model, doses approximately 10 to 20 times greater than active doses in T cell-mediated models were required. RAPA at 1 to 50 microM did not inhibit in vitro human synovial phospholipase A2 or 5-lipoxygenase and cyclo-oxygenase activity in the human blood leukocyte assay. The total profile of RAPA suggests that it may be effective in the treatment of rheumatoid arthritis, multiple sclerosis and other autoimmune diseases.

Topics: Acute-Phase Reaction; Animals; Arthritis, Experimental; Eicosanoids; Hypersensitivity, Delayed; Immunosuppressive Agents; Leukocytes; Male; Mice; Phospholipases A; Phospholipases A2; Polyenes; Rats; Rats, Inbred Lew; Sirolimus