Implication of S-adenosylhomocysteine hydrolase in inhibition of TNF-alpha- and IL-1beta-induced expression of inflammatory mediators by AICAR in RPE cells.
OBJECTIVE
AMP-activated protein kinase (AMPK) has been suggested to be a novel signaling pathway in regulating inflammation. The role of AMPK in retinal pigment epithelial cell inflammatory response is addressed using AMPK activator 5-aminoimidazole-4-carboxamide riboside (AICAR).


METHODS
Protein expression and activation of signaling molecules were detected by immunoblotting. Cytokines were determined by ELISA kits. AMPKalpha expression was knockdown by siRNAs.


RESULTS
AICAR inhibited tumor necrosis factor (TNF)-alpha- or interleukin (IL)-1beta-induced production of IL-6, IL-8, and monocyte chemotactic protein (MCP)-1 and of intercellular adhesion molecule (ICAM)-1 expression in human RPE cells. The inhibitory effect on cytokine production and ICAM-1 expression persisted in the RPE cells in which AMPK was knocked down by AMPK siRNA. Moreover, an adenosine kinase inhibitor 5'-iodotubercidin, which effectively abolished AMPK activation caused by AICAR, did not reverse the anti-inflammatory effect of AICAR. In comparison, anti-inflammatory effects of AICAR were mimicked by adenosine but not inosine, the metabolites of AICAR. Finally, with the exception of TNF-alpha-induced IL-6 production, adenosine dialdehyde, an inhibitor of S-adenosylhomocysteine hydrolase, was found to block cytokine production and ICAM-1 expression.


CONCLUSIONS
Regardless of the ability of AICAR to activate AMPK, the inhibitory effects of AICAR on cytokine production and ICAM-1 expression were not associated with AMPK. The mechanism of AICAR inhibition may be attributed to the interference of adenosylmethionine-dependent methylation.
Qin
Suofu
S
Retinal Disease Research, Department of Biological Sciences, Allergan, Inc., Irvine, California 92612-1599,USA. qin_suofu@allergan.com
Ni
Ming
M
De Vries
Gerald W
GW
D055372:AMP-Activated Protein Kinases; D000241:Adenosine / Q000031:analogs & derivatives / Q000494:pharmacology; D043383:Adenosylhomocysteinase / Q000502:physiology*; D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives* / Q000494:pharmacology; D002478:Cells, Cultured; D018932:Chemokine CCL2 / Q000378:metabolism; D018925:Chemokines / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D015151:Immunoblotting; D018799:Intercellular Adhesion Molecule-1 / Q000378:metabolism; D053583:Interleukin-1beta / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D015850:Interleukin-6 / Q000378:metabolism; D016209:Interleukin-8 / Q000378:metabolism; D009097:Multienzyme Complexes / Q000378:metabolism; D010857:Pigment Epithelium of Eye / Q000187:drug effects* / Q000201:enzymology; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D012265:Ribonucleotides / Q000494:pharmacology*; D014162:Transfection; D014409:Tumor Necrosis Factor-alpha / Q000037:antagonists & inhibitors* / Q000494:pharmacology
C491768:Ccl2 protein, mouse; D018932:Chemokine CCL2; D018925:Chemokines; D053583:Interleukin-1beta; D015850:Interleukin-6; D016209:Interleukin-8; D009097:Multienzyme Complexes; D034741:RNA, Small Interfering; D012265:Ribonucleotides; D014409:Tumor Necrosis Factor-alpha; D018799:Intercellular Adhesion Molecule-1; C027579:periodate-oxidized adenosine; D000620:Aminoimidazole Carboxamide; D017346:Protein Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases; D043383:Adenosylhomocysteinase; C031143:AICA ribonucleotide; D000241:Adenosine