ABSTRACT
We investigated the role of interferon regulatory factor 8 (IRF8) in a model of chronic pain in which repeated cold stress (RCS) exposure produces tactile allodynia. RCS exposure produced a decrease in paw withdrawal threshold (PWT) to mechanical stimulation. Spinal microglia of RCS-exposed mice were morphologically activated. Expression of IRF8 was significantly increased in the spinal cord of RCS-exposed mice and was localized in microglia. IRF8-knockout mice failed to show the RCS-induced decrease in PWT. Thus, RCS exposure activates spinal microglia and upregulation of IRF8 in these cells is involved in the development of tactile allodynia after RCS exposure.
Subject(s)
Cold-Shock Response/physiology , Gene Expression/physiology , Hyperalgesia/etiology , Interferon Regulatory Factors/genetics , Interferon Regulatory Factors/metabolism , Microglia/metabolism , Animals , Chronic Disease , Differential Threshold , Disease Models, Animal , Extremities/physiopathology , Interferon Regulatory Factors/physiology , Male , Mice, Inbred C57BL , Spinal Cord/cytology , Spinal Cord/metabolism , Up-RegulationABSTRACT
Although a large number of microbial metabolites have been discovered as inhibitors of bacterial peptidoglycan biosynthesis, only a few inhibitors were reported for the pathway of UDP-MurNAc-pentapeptide formation, partly because of the lack of assays appropriate for natural product screening. Among the pathway enzymes, D-Ala racemase (Alr), D-Ala:D-Ala ligase (Ddl) and UDP-MurNAc-tripeptide:D-Ala-D-Ala transferase (MurF) are particularly attractive as antibacterial targets, because these enzymes are essential for growth and utilize low-molecular-weight substrates. Using dansylated UDP-MurNAc-tripeptide and L-Ala as the substrates, we established a cell-free assay to measure the sequential reactions of Alr, Ddl and MurF coupled with translocase I. This assay is sensitive and robust enough to screen mixtures of microbial metabolites, and enables us to distinguish the inhibitors for D-Ala-D-Ala formation, MurF and translocase I. D-cycloserine, the D-Ala-D-Ala pathway inhibitor, was successfully detected by this assay (IC(50)=1.7 microg ml(-1)). In a large-scale screening of natural products, we have identified inhibitors for D-Ala-D-Ala synthesis pathway, MurF and translocase I.
