Matrix metalloproteinase-9 (MMP-9) plays a critical role in tissue remodeling under both physiological and pathological conditions. Although MMP-9 expression is low in most cells and is tightly controlled, the mechanism of its regulation is poorly understood. We utilized mouse embryonic fibroblasts (MEFs) that were nullizygous for the catalytic a-subunit of AMP-activated protein kinase (AMPK), which is a key regulator of energy homeostasis, to identify AMPK as a suppressor of MMP-9 expression. Total AMPKa deletion significantly elevated MMP-9 expression compared with WT MEFs, whereas single knockout of the isoforms AMPKa1 and AMPKa2 caused minimal change in the level of MMP-9 expression. The suppressive role of AMPK on MMP-9 expression was mediated both through its activity and presence. The AMPK activators 5-amino-4-imidazole carboxamide riboside (AICAR) and A769662 suppressed MMP-9 expression in WT MEFs, and AMPK inhibition by the over-expression of dominant negative (DN) AMPKa elevated MMP-9 expression. However, in AMPKa–/– MEFs transduced with DN AMPKa, MMP-9 expression was suppressed. AMPKa–/– MEFs showed increased phosphorylation of I¿Ba, expression of I¿Ba mRNA, nuclear localization of nuclear factor-¿B (NF-¿B), and DNA-binding activity of NF-¿B compared with WT. Consistently, selective NF-¿B inhibitors BMS-345541 and SM-7368 decreased MMP-9 expression in AMPKa–/– MEFs. Overall, our results suggest that both AMPKa isoforms suppress MMP-9 expression, and that both the activity and presence of AMPKa contribute to its function as a regulator of MMP-9 expression by inhibiting the NF-¿B pathway.

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