Expression of cyclooxygenase 2 and cytosolic phospholipase A2 in the liver tissue of patients with chronic hepatitis and liver cirrhosis
Introduction
Cyclooxgenase (COX) and phospholipase A2 (PLA2) are crucial rate-limiting enzymes involved in the conversion of arachidonic acid to prostaglandin H2, the precursor of various compounds including prostaglandins (PGs), prostacyclin, and thromboxanes in the process of PGs' synthesis. PLA2 plays a key role in numerous cellular processes by regulating the release of arachidonic acid (AA) from membrane phospholipids. AA is then converted to a prostanoid by cyclooxygenase (COX). There are at least two isoforms of COX: COX1 and COX2. COX1 is constitutively expressed in a wide variety of tissues while COX2 is a highly inducible gene that is expressed in response to a variety of proinflammatory agents and cytokines [1], [2]. Over-expression of COX2 has been demonstrated in various chronic inflammatory diseases and tumor tissues such as rheumatoid arthritis, ulcerative colitis, colon cancer and pancreatic cancer [3], [4], [5], [6], [7]. Although several studies have shown the up-regulation of COX2 in adjacent cirrhotic tissue of hepatocellular carcinoma and well-differentiated hepatocellular carcinoma [8], [9], the precise role of COX2 in hepatopathology remains unclear. Previous reports have shown that COX2 and cPLA2 expression were involved in various pathologic course [10], [11], [12], [13], [14], but there is little evidence whether the expression of COX2 and cytosolic phospholipase A2 (cPLA2) coordinately regulate the process of liver fibrogenesis. In this study, we investigated the relationship between the expression of COX2 or cPLA2 and liver fibrosis using immunohistochemistry, western blotting and image analysis.
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Tissue samples
We used 45 formalin-fixed, paraffin-embedded liver tissue samples for immunohistochemistry obtained by needle biopsies from patients with chronic hepatitis, consisting of 7 cases of F0, 10 cases of F1, 10 cases of F2, 9 cases of F3, and 9 cases of liver cirrhosis (LC) according to the New Inuyama Classification [15] of the staging of liver fibrosis. All paraffin-embedded liver tissue samples came from patients of the Third Department of Internal Medicine, Hyogo College of Medicine during
The expression of COX2 and cPLA2 in the progression of liver fibrosis
Cytoplasmic staining for COX2 in liver cell was observed (Fig. 1). The relative amount of COX2 was 1.24±0.11 D.U. (mean±SD) in group F0, 1.33±0.09 D.U. in group F1, 1.42±0.11 D.U in group F2, 1.44±0.09 D.U. in group F3 and 1.51±0.07 D.U. in group LC. The signal intensity of COX2 increased significantly with the progression of liver fibrosis (P<0.001) (Fig. 2). The positive signals of cPLA2 were observed in liver cytoplasm (Fig. 1). In some cells, cPLA2 staining was observed in the cytoplasm
Discussion
Prostaglandins have been recognized as important mediators of hepatic, renal, cardiovascular and pulmonary normal functions and their synthesis alters during the courses of several physiopathological situations [16], [17]. Biochemical and genetic studies have pointed out COX2 and cPLA2 expression as the main contributor of prostanoid synthesis under pathological circumstances [10], [11], [12], [13], [14]. COX2 and cPLA2 expression has not been described previously in relation to liver fibrosis.
References (31)
- et al.
Induction of cyclooxygenase-2 by interleukin-1 α; evidence for post-transcriptional regulation
J. Biol. Chem.
(1994) - et al.
Cyclooxygenase 2 expression is increased in the stroma of colon carcinomas from IL-10 (−/−) mice
Gastroenterology
(2000) - et al.
Alterations in cellular adhesion and apoptosis in epithelial cells overexpressing prostaglandin endoperoxide synthase 2
Cell
(1995) - et al.
Differential regulation of inducible and constitutive prostaglandin endoperoxide synthase in osteoblastic MC3T3-E1 cells
J. Biol. Chem.
(1993) - et al.
Cytosolic phospholipase A2 is required for cytokine-induced expression of type II A secretory phospholipase A2 that mediates optimal cyclooxygenase-2 dependent delayed prostaglandin E2 generation in rat 3Y1 fibroblasts
J. Biol. Chem.
(1998) - et al.
Enhancement of prostaglandin E2 production by epidermal growth factor requires the coordinate activation of cytosolic phospholipase A2 and cyclooxygenase 2 in human squamous carcinoma A431 cells
Prostaglandins
(1997) - et al.
New Inuyama Classification; new criteria for histological assessment of chronic hepatitis
Int. Hepatol. Commun.
(1996) Prostagladin endoperoxide synthase: regulation of enzyme expression
Biochim. Biophys. Acta
(1991)- et al.
Differential regulation of cyclooxygenases 1 and 2 interleukin-1β, tumor necrosis factor-α, and transforming growth factor-β1 in human lung fibroblasts
Exp. Cell. Res.
(1998) - et al.
Transforming growth factor-β1 enhances Ha-ras-induced expression of cyclooxygenase-2 in intestinal epithelial cell via stabilization of mRNA
J. Biol. Chem.
(2000)