Biomodulatory role of ceramide in basic fibroblast growth factor-induced proliferation of cerebellar astrocytes in primary culture

Journal of Biological Chemistry

et al. 2001

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We recently reported that the marked decrease in cellular ceramide in primary astrocytes is an early event associated with the mitogenic activity of basic fibroblast growth factor (bFGF) (Riboni, L., Viani, P., Bassi, R., Stabieini, A., and Tettamanti, G. (2000) GLIA 32, 137-145). Here we show that a rapid activation of sphingomyelin biosynthesis appears to be the major mechanism responsible for the fall in ceramide levels induced by bFGF. When quiescent astrocytes were treated with bFGF, an increased amount of newly synthesized ceramide (from either L-[ 3 H]serine or [ 3 H]sphingosine) was directed toward the biosynthesis of sphingomyelin. Conversely, bFGF did not appear to affect ceramide levels by other metabolic pathways involved in ceramide turnover such as sphingomyelin degradation and ceramide biosynthesis, degradation, and glucosylation. Enzymatic studies demonstrating a relevant and rapid increase in sphingomyelin synthase activity after bFGF treatment have provided a convincing explanation for the activation of sphingomyelin biosynthesis. The bFGF-induced increase in sphingomyelin synthase appears to depend on a post-translational activation mechanism. Moreover, in the presence of brefeldin A, the activation of sphingomyelin biosynthesis was abolished, suggesting that the enzyme is located in a compartment other than the Golgi apparatus. Also the phosphatidylcholine-specific phospholipase C inhibitor D609 exerted a potent inhibitory effect on sphingomyelin biosynthesis. Finally, we demonstrate that inhibition of sphingomyelin biosynthesis by brefeldin A or D609 led to a significant inhibition of bFGF-stimulated mitogenesis. All this supports that, in primary astrocytes, the early activation of sphingomyelin synthase is involved in the bFGF signaling pathway leading to proliferation.Ceramide, a key sphingolipid metabolite in both the biosynthesis and degradation of complex sphingolipids, is involved in the signal transduction of different extracellular stimuli that lead to cell proliferation, cell differentiation, cell cycle arrest, and apoptotic cell death (reviewed in Refs. 1-3). In all these events, the ceramide concentration, possibly at specific subcellular sites, is crucial. There is evidence that different activators such as cytokines, growth factors, and hormones elicit their biological effect by modulating the activity of sphingomyelinases, ceramide synthase, or neutral ceramidase (reviewed in Refs. 1 and 3-5) and thus affect ceramide levels.A role of ceramide as an intracellular mediator of specific extracellular agents has been recognized also in cells from the central nervous system (reviewed in Refs. 6 -8). In neuronal and glial cells, the administration of differentiating or apoptotic agents results in increased cellular levels of ceramide, which, in turn, participate in the cascade of events producing the final effects (9 -12). In a recent study (13), we demonstrated that ceramide plays a role in the growth control of glial cells by basic fibroblast growth factor (bFGF), 1 a factor stimul...

Section: Discussioncontrasting

confidence: 46%

Section: Discussionmentioning

confidence: 75%

“…This apparent contradiction could be explained by the evidence that the cellular concentration of SM in rat cerebellar astrocytes is 20-fold higher than that of ceramide (13,27).…”

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 97%

mentioning

confidence: 99%

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Basic Fibroblast Growth Factor-induced Proliferation of Primary Astrocytes

Riboni

Viani

Journal of Biological Chemistry

et al. 2001

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Ceramide levels are inversely associated with malignant progression of human glial tumors

Riboni

Campanella

et al. 2002

Glia

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114

Ceramide represents an important sphingoid mediator involved in the signaling pathways that control cell proliferation, differentiation, and death. To determine whether ceramide levels correlate with the malignant progression of human astrocytomas, we investigated these levels in surgical specimens of glial tumors of low-grade and high-grade malignancy. Tumor samples obtained from 52 patients who underwent therapeutic removal of primary brain tumors were used. The tumors were classified according to standard morphologic criteria and were grouped into tumors of low-grade and high-grade malignancy. Sections of normal brain tissue adjacent to the tumor were also analyzed in 11 of the 52 patients. After extraction and partial purification, ceramide was measured by quantitative derivatization to ceramide-1-phosphate using diacylglycerol kinase and [gamma-(32)P]ATP. Ceramide levels were significantly lower in the combined high-grade tumors compared with low-grade tumors and in both tumor groups compared with peritumoral tissue. The results indicate an inverse correlation between the amount of ceramide and tumor malignancy as assessed by both the histological grading and ganglioside pattern. Moreover, overall survival analysis of 38 patients indicates that ceramide levels are significantly associated with patient survival. The present findings indicate that ceramide is inversely associated with malignant progression of human astrocytomas and poor prognosis. The downregulation of ceramide levels in human astrocytomas emerges as a novel alteration that may contribute to glial neoplastic transformation. The low ceramide levels in high-grade tumors may provide an advantage for their rapid growth and apoptotic resistant features. This study appears to support the rationale for the potential benefits of a ceramide-based chemotherapy.

Sphingosine‐1‐phosphate is released by cerebellar astrocytes in response to bFGF and induces astrocyte proliferation through G_i‐protein‐coupled receptors

Anelli

Giussani

et al. 2006

Glia

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120

105

The mitogenic role of sphingosine-1-phosphate (S1P) and its involvement in basic fibroblast growth factor (bFGF)-induced proliferation were examined in primary cultures of cerebellar astrocytes. Exposure to bFGF resulted in a rapid increase of extracellular S1P formation, bFGF inducing astrocytes to release S1P, but not sphingosine kinase, in the extracellular milieu. The SK inhibitor N,N-dimethylsphingosine inhibited S1P release as well as bFGF-induced growth stimulation. S1P application in quiescent astrocytes caused a dose-dependent increase in DNA synthesis. This gliotrophic effect was induced by a brief exposure to low nanomolar S1P, mimicked by the S1P receptor agonist dihydro-S1P, and inhibited by pertussis toxin (PTX), an inactivator of G(i)/G(o)-proteins. S1P also induced activation of extracellular signal-regulated kinase that was inhibited again by PTX. Moreover, the S1P lyase inhibitor 4-deoxypyridoxine induced the cellular accumulation of S1P but did not affect DNA synthesis. These results support the view that S1P exerted a mitogenic effect on cerebellar astrocytes extracellularly, most likely through cell surface S1P receptors. In agreement, mRNAs for S1P1, S1P2, and S1P3 receptors are expressed in cerebellar astrocytes (Anelli et al., 2005. J Neurochem 92:1204-1215). Ceramide, a negative regulator of astrocyte proliferation and down-regulated by bFGF (Riboni et al., 2002. Cerebellum 1:129-135), efficiently inhibited S1P-induced proliferation. The S1P action appears to be part of an autocrine/paracrine cascade stimulated by bFGF and, together with ceramide down-regulation, essential for astrocytes to respond to bFGF. The results suggest that S1P and bFGF/S1P may play an important role in physiopathological glial proliferation, such as brain development, reactive gliosis and brain tumor formation.