AMPKα1 Deficiency in Fibroblasts Promotes Angiogenesis in Athymic Nude Mice

Abstract

Angiogenesis is required and essential for tumor development. Increasing evidence suggests that adenosine monophosphate‐activated protein kinase (AMPK), an energy sensor and modulator of redox system, is associated with cancer development. However, the effect of AMPK on tumor development is controversial. Mouse embryo fibroblasts (MEF) were isolated from AMPKα1 knock out (AMPKα1‐KO), AMPKα2‐KO, and wild type (WT) C57BL/6J mouse embryos, and immortalized by using standard 3T3 protocol to investigate the mechanisms of fibroblast‐mediated angiogenesis. Xenograft model data revealed that knock out of AMPKα1, but not AMPKα2, stimulated the cellular proliferation of immortalized MEFs, angiogenesis, and tumor development in athymic nude mice in vivo. Consistent with this finding, the migration of human microvascular endothelial cells (hmvEC) was enhanced by co‐culturing with AMPKα1‐KO MEFs when compared to either WT or AMPKα2‐KO MEFs. Moreover, the network formation of hmvEC was stimulated by conditioned medium from AMPKα1‐KO MEFs, but not from WT or AMPKα2‐KO MEFs. Mechanistically, we found that the protein level of noncanonical nuclear factor kappa B2 (NF‐ĸB2)/p52 was elevated in AMPKα1‐KO MEFs and was responsible for induction of erythropoietin (Epo) expression. Finally, the most conclusive evidence for AMPKα1‐dependent inhibition of EC migration and consequent angiogenesis as well as tumor progression was that the xenograft growth of the inoculated AMPKα1‐KO MEFs was ameliorated by treatment with Epo neutralization antibody. This compelling evidence indicates that AMPKα1, rather than AMPKα2 deletion in fibroblasts, instigates EC migration, angiogenesis, and the resultant tumor development.