Statins activate peroxisome proliferator-activated receptor gamma through extracellular signal-regulated kinase 1/2 and p38 mitogen-activated protein kinase-dependent cyclooxygenase-2 expression in macrophages

Both statins and peroxisome proliferator-activated receptor (PPAR)gamma ligands have been reported to protect against the progression of atherosclerosis. In the present study, we investigated the effects of statins on PPARgamma activation in macrophages. Statins increased PPARgamma activity, which was inhibited by mevalonate, farnesylpyrophosphate, or geranylgeranylpyrophosphate. Furthermore, a farnesyl transferase inhibitor and a geranylgeranyl transferase inhibitor mimicked the effects of statins. Statins inhibited the membrane translocations of Ras, RhoA, Rac, and Cdc42, and overexpression of dominant-negative mutants of RhoA (DN-RhoA) and Cdc42 (DN-Cdc42), but not of Ras or Rac, increased PPARgamma activity. Statins induced extracellular signal-regulated kinase (ERK)1/2 and p38 mitogen-activated protein kinase (MAPK) activation. However, DN-RhoA and DN-Cdc42 activated p38 MAPK, but not ERK1/2. ERK1/2- or p38 MAPK-specific inhibitors abrogated statin-induced PPARgamma activation. Statins induced cyclooxygenase (COX)-2 expression and increased intracellular 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)) levels through ERK1/2- and p38 MAPK-dependent pathways, and inhibitors or small interfering RNA of COX-2 inhibited statin-induced PPARgamma activation. Statins also activate PPARalpha via COX-2-dependent increases in 15d-PGJ(2) levels. We further demonstrated that statins inhibited lipopolysaccharide-induced tumor necrosis factor alpha or monocyte chemoattractant protein-1 mRNA expression, and these effects by statins were abrogated by the PPARgamma antagonist T0070907 or by small interfering RNA of PPARgamma or PPARalpha. Statins also induced ATP-binding cassette protein A1 or CD36 mRNA expression, and these effects were suppressed by small interfering RNAs of PPARgamma or PPARalpha. In conclusion, statins induce COX-2-dependent increase in 15d-PGJ(2) level through a RhoA- and Cdc42-dependent p38 MAPK pathway and a RhoA- and Cdc42-independent ERK1/2 pathway, thereby activating PPARgamma. Statins also activate PPARalpha via COX-2-dependent pathway. These effects of statins may explain their antiatherogenic actions.     

Distinct regulation of cyclooxygenase-2 by interleukin-1beta in normal and endometriotic stromal cells

Aberrant production of cyclooxygenase-2 (COX-2) plays pivotal roles in many pathological processes including tumorigenesis and endometriosis, although the underlying mechanism remains obscure. Herein we report evidence to demonstrate that COX-2 is distinctly regulated by IL-1beta in normal and endometriotic stroma. Ectopic endometriotic stromal cell is at least 100 times more sensitive to IL-1beta treatment, compared with its eutopic counterpart. Induction of COX-2 expression in normal endometrial stroma by IL-1beta is primary due to enhancement of COX-2 mRNA stability. In contrast, IL-1beta not only increases COX-2 mRNA stability but also up-regulates COX-2 promoter activity in ectopic endometriotic stroma. Induction of COX-2 promoter activity by IL-1beta is mediated via MAPK-dependent phosphorylation of cAMP-responding element binding protein. Promoter activity and EMSAs demonstrate that a cAMP response element site located at -571/-564 of COX-2 promoter is critical for IL-1beta-induced COX-2 gene expression. Our results indicate that elevation of COX-2 expression in endometriotic tissues may result from increased sensitivity to proinflammatory cytokines such as IL-1beta, which is consistently present in the peritoneal fluid of endometriosis patients. Distinct regulation of COX-2 gene by IL-1beta may play a critical role in pathophysiological processes such as cancer formation and endometriosis.     

Erythromycin suppresses the expression of cyclooxygenase-2 in rheumatoid synovial cells

OBJECTIVE: To investigate whether erythromycin (EM) can suppress the expression of cyclooxygenase-2 (COX-2) in rheumatoid synovial cells, and determine the mechanisms involved. Methods. Synovial tissues were obtained from 25 patients with rheumatoid arthritis (RA). Rheumatoid synovial cells were cultured with or without EM (0.1-1000 nM) in the presence of interleukin 1beta (IL-1beta) for various times. Protein expression of COX-2, and phosphorylation of extracellular signal regulated kinase 1/2 (ERK1/2) and p38 mitogen-activated protein kinase (p38 MAPK) were detected by Western blot. COX-2 messenger RNA (mRNA) was detected by RT-PCR. DNA binding activity of nuclear factor kappa B (NF-kB) was detected by ELISA. Results. IL-1beta-stimulated synovial cells expressed COX-2 protein. EM suppressed the IL-1beta-induced COX-2 protein expression in a dose-dependent manner and inhibited IL-1beta-induced p38 MAPK phosphorylation, which was correlated with COX-2 expression in synovial cells. In contrast, EM had no effect on DNA binding activity of NF-kB and ERK1/2 expression. CONCLUSION: Our results indicated that EM downregulated COX-2 expression by inhibiting the p38 MAPK cascade, but had no effect on NF-kB or ERK1/2, in rheumatoid synovial cells.     

Rosiglitazone induces interleukin-1 receptor antagonist in interleukin-1beta-stimulated rat synovial fibroblasts via a peroxisome proliferator-activated receptor beta/delta-dependent mechanism

OBJECTIVE: To study the potency of 2 peroxisome proliferator-activated receptor gamma (PPARgamma) agonists, 15-deoxy-Delta(12,14)-prostaglandin J(2) (15-deoxy-PGJ(2)) and rosiglitazone, to modulate the expression of interleukin-1 receptor antagonist (IL-1Ra) in rat synovial fibroblasts. METHODS: Levels of messenger RNA for IL-1Ra and PPAR isotypes (alpha, beta/delta, gamma) were assessed by real-time polymerase chain reaction in rat synovial fibroblasts exposed to 10 ng/ml of IL-1beta. PPAR levels were assessed by Western blotting and secreted IL-1Ra levels by immunoassay. The potency of PPARgamma agonists and the PPARbeta/delta agonist GW-501516 on IL-1Ra levels was tested in the range of 1-10 microM and at 100 pM, respectively. The contribution of PPARgamma to the effects of rosiglitazone on IL-1Ra secretion was examined either by its overexpression or by inhibition using wild-type or dominant-negative constructs and the antagonist GW-9662 (10 microM), respectively. The dominant-negative strategy was also performed to investigate the possible contribution of PPARbeta/delta and NF-kappaB activation. RESULTS: IL-1beta-induced IL-1Ra production was increased by 10 microM rosiglitazone but was reduced dose-dependently by 15-deoxy-PGJ(2). Both agonists lowered IL-1beta secretion, but rosiglitazone alone reduced the imbalance of IL-1beta/IL-1Ra toward basal levels. Enhancement of IL-1beta-induced IL-1Ra production by rosiglitazone was not affected by PPARgamma overexpression or by its inhibition with dominant-negative PPARgamma or GW-9662. Inhibition of NF-kappaB was also ineffective against rosiglitazone but abolished the stimulating effect of IL-1beta on IL-1Ra. All PPAR isotypes were expressed constitutively in rat synoviocytes, but PPARgamma decreased dramatically upon IL-1beta exposure, whereas PPARbeta/delta remained stable. Dominant-negative PPARbeta/delta abolished the enhancement of IL-1Ra by rosiglitazone, whereas GW-501516 reproduced the effect of rosiglitazone on IL-1Ra secretion. CONCLUSION: Rosiglitazone stimulates IL-1Ra production by a PPARbeta/delta mechanism in activated rat synovial fibroblasts, further contributing to its potential antiarthritic properties and opening new perspectives for the modulation of inflammatory genes by specific PPAR agonists in articular cells.     

Cyclooxygenase 2-dependent prostaglandin E2 modulates cartilage proteoglycan degradation in human osteoarthritis explants

OBJECTIVE: To examine cyclooxygenase-2 (COX-2) enzyme expression, its regulation by interleukin-1 beta (IL-1 beta), and the role of prostaglandin E(2) (PGE(2)) in proteoglycan degradation in human osteoarthritic (OA) cartilage. METHODS: Samples of human OA articular cartilage, meniscus, synovial membrane, and osteophytic fibrocartilage were obtained at knee arthroplasty and cultured ex vivo with or without IL-1 beta and COX inhibitors. COX expression was evaluated by immunohistochemistry and Western blot analysis. The enzymatic activity of COX was measured by conversion of arachidonic acid to PGE(2). Cartilage degradation was evaluated by measuring the accumulation of sulfated glycosaminoglycans in the medium. RESULTS: IL-1 beta induced robust expression of COX-2 and PGE(2) in OA meniscus, synovial membrane, and osteophytic fibrocartilage explants, whereas low levels were produced in OA articular cartilage. IL-1 beta also induced cartilage proteoglycan degradation in OA synovial membrane-cartilage cocultures. Increased proteoglycan degradation corresponded to the induction of COX-2 protein expression in, and PGE(2) production from, the synovial membrane. Dexamethasone, neutralizing IL-1 beta antibody, or the selective COX-2 inhibitor, SC-236, attenuated both the IL-1 beta-induced PGE(2) production and cartilage proteoglycan degradation in these cocultures. The addition of PGE(2) reversed the inhibition of proteoglycan degradation caused by SC-236. CONCLUSION: IL-1 beta-induced production of COX-2 protein and PGE(2) was low in OA articular cartilage compared with that in the other OA tissues examined. IL-1 beta-mediated degradation of cartilage proteoglycans in OA synovial membrane-cartilage cocultures was blocked by the selective COX-2 inhibitor, SC-236, and the effect of SC-236 was reversed by the addition of exogenous PGE(2). Our data suggest that induction of synovial COX-2-produced PGE(2) is one mechanism by which IL-1 beta modulates cartilage proteoglycan degradation in OA.