Phosphodiesterase 4B2 gene is an effector of Toll-like receptor signaling in astrocytes.

ABSTRACT

Cyclic AMP is part of an endogenous mechanism that downregulates inflammatory response, and its intracellular concentration is regulated chiefly by cyclic nucleotide phosphodiesterases type 4. The goal of the present study was to determine whether phosphodiesterases 4 are involved in the inflammatory response of astrocytes mediated by Toll-like receptors. Astrocyte cultures established from newborn rat brain were challenged with lipoteichoic acid, a ligand of Toll-like receptor 2, polyinosinic-polycytidylic acid, a ligand of Toll-like receptor 3, or lipopolysaccharide, a ligand of Toll-like receptor 4. After 24 h the expression of genes encoding phosphodiesterase 4A, phosphodiesterase 4B and phosphodiesterase 4D was determined by real time reverse transcription polymerase chain reaction. The challenge of astrocytes with the ligands profoundly up-regulated expression of the phosphodiesterase 4B mRNA, while the phosphodiesterase 4A and 4D mRNA was either unaffected or downregulated. Moreover, Toll-like receptor ligation specifically up-regulated expression of the phosphodiesterase 4B2 transcriptional variant. Thus, polyinosinic-polycytidylic acid, lipopolysaccharide and lipoteichoic acid induced approximately 7-, 5- and 4-fold up-regulation of the message, respectively. Toll-like receptor ligation also led to an over 2-fold increase in the protein level of phosphodiesterase 4B2 as revealed by immunoblot analysis. The inactivation of Rho proteins by pretreatment with toxin B form C. difficile enhanced ligation-induced up-regulation of the phosphodiesterase 4B2 message by 4-9-fold. However, in spite of this increase in the message abundance, there was no increase in the protein level compared to cells challenged with the ligands alone. These results demonstrate that the phosphodiesterase 4B2 gene is an effector of Toll-like receptor signaling in astrocytes, and that its up-regulation at the protein level is controlled by complex mechanisms.