Transforming Growth Factor β1 Regulates the Expression of Cyclooxygenase in Cultured Cortical Astrocytes and Neurons

Abstract

Abstract:The hypothesis that transforming growth factor ßl (TGFß1) regulates the synthesis of prostaglandins by CNS tissue was tested by using purified cultures of cortical astrocytes or neurons that were obtained from rat pups on postnatal day 4 or 5 or fetuses on gestational day 16, respectively. The cells were exposed to TGFß1 for 2 days. The synthesis of prostaglandins depends upon the production and conversion of arachidonic acid, steps that are catalyzed by phospholipase A 2 (PLA2) and cyclooxygenase (COX), respectively. Prostaglandin E2 (PGE2) concentration was determined by radioimmunoassay. The expression of cytosolic PLA2 and COX (the constitutive COX1 and the inducible COX2) was assessed by using immunohistochemical and quantitative immunoblotting procedures. Astrocytes produced much more PGE2 than neurons, suggesting that glial cells are an important source of PGE2 in the CNS. TGF/31 increased the production of PGE2 by astrocytes and neurons in a concentration-dependent manner. Furthermore, TGFß1 enhanced COX activity; the inhibitor indomethacin completely blocked TGF/31-mediated PGE2 synthesis. Cultured astrocytes and neurons expressed the three enzymes: cytosolic PLA2, COX1, and COX2. Cytosolic PLA2 expression was unaffected by TGFf31 treatment. In contrast, COX expression was altered by TGF~31treatment in a concentration-dependent fashion. COX1 was increased by TGFß1, but only in astrocytes. TGFß1 increased COX2 expression in astrocytes and neurons. Thus, TGFß1 -induced increases in PGE2 concentration are regulated by COX. This study suggests that TGF/31 is an important regulator of immune and inflammatory processes in the CNS. Key Words: Cell culture-Cerebral cortex-Cytokine-Phospholipase A2-Prostaglandin. J. Neurochem. 71, 526-534 (1998).Prostaglandins, thromboxanes, and prostacyclin, collectively called prostanoids, are metabolites of arachidonic acid (AA). The initial step of prostanoid synthesis, the production of AA from fatty acids, is catalyzed by phospholipases, primarily phospholipase A2 (PLA2). AA is then converted to a prostanoid by cyclooxygenase (COX). There are at least two isoforms of COX: the constitutive COX1 and the inducible COX2.Prostanoids are commonly known as pivotal regulators of immune and inflammatory processes (Plescia and Racis, 1988). They are also present in the CNS, where they play important roles in the regulation of diverse CNS functions, i.e., cerebral blood flow, the sleep/wake cycle, and temperature regulation (Wolfe, 1982;Rothwell, 1992; Hayaishi, 1994). Although prostanoid concentrations are low in brain under normal conditions, they are increased in pathological states, such as ischemia, seizures, multiple sclerosis, acquired immunodeficiency syndrome, alcohol intoxication, and inflammation (Chen et al., 1986;George et al., 1986;Shimizu and Wolfe, 1990;Fretland, 1992;Griffin et al., 1994).Various growth factors, e.g., transforming growth factor ß (TGFß), have functions that parallel those of the prostanoids. Three isoforms of TGFß (TGF/31, TGF/32, and TGFß3...

Prostaglandin E 2 release from astrocytes triggers gonadotropin-releasing hormone (GnRH) neuron firing via EP2 receptor activation

“…This finding suggests that eicosanoids sustaining spontaneous GnRH neuronal activity are mostly COX-2-derived products, a conclusion consistent with evidence that COX-2 is the most abundant COX form expressed in astrocytes (42,43). Because endocannabinoids, such as 2-arachidonoyl glycerol (2-AG) and arachidonoyl ethanolamide (AEA or anandamide) were re- Fig.…”

Regulation of Transforming Growth Factor-β-dependent Cyclooxygenase-2 Expression in Fibroblasts

“…Although the complexity of TGF-␤ signaling is very challenging to analyze, a differential proteomic approach allowed us to discover both positive and negative components of TGF-␤-stimulated regulation of COX-2 expression. Although few previous reports have described that TGF-␤ induces COX-2 in several cell lines (18,36,37), surprisingly, almost nothing has been described about underlying molecular mechanisms. This is the first report that shows that HNRPAB is a TGF-␤-induced factor that directly increases the expression level of COX-2 protein.…”

Inhibitors of Cyclooxygenase-2, but Not Cyclooxygenase-1 Provide Structural and Functional Protection against Quinolinic Acid-Induced Neurodegeneration

“…In addition to suppressing necrosis, reducing free-radical damage to the mitochondria by COX-2 inhibition would reduce the probability of neuronal apoptosis manifested many days after the initial insult (Luetjens et al, 2000). Subsequent to this initial insult, cellular inflammatory processes would increase the amount of active COX-2 available at the lesion site (Luo et al, 1998), expanding the neurodegeneration beyond the initial area impacted (Barone and Feuerstein, 1999). Based on our observations, rapid suppression of the initial, glutamate receptor-stimulated activation of COX-2 expression by inhaled flurbiprofen seems sufficient to reduce the immediate neuronal damage that would trigger subsequent neurodegeneration by inflammatory mechanisms.…”

“…COX-2 expression is constitutive in some neurons (Seibert et al, 1994) but is induced by glutamate (Manev et al, 2000) and proinflammatory stimuli (Bazan et al, 1994) in migratory immune cells, glia, and neurons (Nogawa et al, 1997;Luo et al, 1998;Hurley et al, 2002). The resulting increase in COX-2 activity may contribute to neurodegeneration either by oxidative stress, or the neurotoxic actions of prostaglandins such as PGA 1 and PGE 1 (Kukreja et al, 1986;Bezzi et al, 1998).…”