AMPK活化劑-AICAR對iNOS及COX-2基因表現的調節作用

Abstract

AMP-activated protein kinase (AMPK), an energy-sensing enzyme that is activated in response to cellular stress, is a critical signaling molecule for the regulation of energy homeostasis and might play a part in protecting the body from metabolic diseases. AMPK is activated by the cellular stresses causing ATP depletion. At the molecular level, AMPK activation is associated with Thr172 phosphorylation on the catalytic α subunit by AMPK kinase (AMPKK). Besides, AMPK might be a novel anti-inflammatory signaling pathway. Recent observations in cultured cells as well as in the animal model suggest the regulatory role of AMPK signaling pathway in inflammatory process, and 5-aminoimidazole-4-carboxamide riboside (AICAR), an AMPK activator, of therapeutic value in treating inflammatory diseases. In this study, we examined the possible role of AMPK in the lipopolysaccharide (LPS)-induced inflammatory process in cultured cells and demonstrated that AICAR inhibits LPS-induced NO and PGE2 production in RAW264.7 macrophages and BV-2 microglia through downregulation of iNOS and COX-2 gene transcription. Moreover, AICAR could block LPS-mediated NFKB, AP-1, CREB and C/EBPβ activation. Conversely, AICAR fails to inhibit LPS-mediated IKK phosphorylation, IKB degradation and p65 nuclear translocation. In vitro direct addition of AICAR in EMSA assays reveals the interruption of NFKB, CREB and C/EBP binding to specific DNA element. Despite the ability of AICAR to enhance AMPK phosphorylation, these effects of AICAR are not associated with AMPK, as 5’-iodotubercidin, an inhibitor of adenosine kinase which blocks AICAR conversion to AMPK activator, fails to change AICAR action. Notably in the absence of LPS challenge we also observed a weak stimulatory effect of AICAR on iNOS and COX-2 protein expression in macrophages, microglia and human umbilical vein endothelial cells (HUVEC). This action of AICAR can be blocked by 5’-iodotubercidin, and might result from the activation of IKK, PKC, p38, ERK and/or Akt. These results imply AMPK might be involved in the upstream regulation of multiple signaling pathways, and in turn exerts diverse cellular functions which open a new research interest. Taken together, our current study documents the dual roles of AICAR on iNOS and COX-2 gene transcription through different action mechanisms, and suggests AICAR may be of therapeutic value in treating inflammatory diseases.