The role of TNF-alpha and its receptors in the production of beta-1,4-galactosyltransferase I mRNA by rat primary type-2 astrocytes.

Abstract

beta-1,4-galactosyltransferase I (beta-1,4-GalT I) plays an important role in the synthesis of the backbone structure of adhesion molecules involved in leukocyte-endothelial cell interaction. The expression of beta-1,4-GalT I mRNA increased in primary human endothelial cells after exposure to tumor necrosis factor-alpha (TNF-alpha). In the central nervous system (CNS), astrocytes play a pivotal role in immunity as immunocompetent cells by secreting cytokines and inflammatory mediators, there are two types of astrocytes. Type-1 astrocytes can secrete TNF-alpha when stimulated with Lipopolysaccharide (LPS), while the responses of type-2 astrocytes during inflammation are unknown. So we examined the expression change of beta-1,4-GalT I mRNA in type-2 astrocytes after exposure to TNF-alpha and LPS. Real-time PCR showed that TNF-alpha or LPS affected beta-1,4-GalT I mRNA expression in a time- and dose-dependent manner. RT-PCR analysis revealed that TNFR1 and TNFR2 were present in normal untreated type-2 astrocytes, and that TNF-alpha, TNFR1 and TNFR2 increased in type-2 astrocytes after exposure to TNF-alpha or LPS. Immunocytochemistry showed that TNFR1 was expressed in the cytoplasm, nucleus and processes of normal untreated type-2 astrocytes, and distributed mainly in the cytoplasm and processes after exposure to LPS. TNFR2 was mainly expressed in the nucleus of normal untreated type-2 astrocytes, and distributed mainly in the processes of type-2 astrocytes after exposure to LPS. Both anti-TNFR1 and anti-TNFR2 antibodies suppressed beta-1,4-GalT I mRNA expression induced by TNF-alpha or LPS. From these results, we conclude that TNF-alpha signaling via both TNFR1 and TNFR2 translocated from nucleus to cytoplasm or processes is sufficient to induce beta-1,4-GalT I mRNA. In addition, we observed that not only exogenous TNF-alpha but also TNF-alpha produced by type-2 astrocytes affected beta-1,4-GalT I mRNA production in type-2 astrocytes. These results suggest that an autocrine loop involving TNF-alpha contributes to the production of beta-1,4-GalT I mRNA in response to inflammation.