Background: The incidence of colorectal cancer (CRC) is closely related to metabolic diseases. AMP-activated protein kinase (AMPK) is known as a key metabolic regulator. Recently, the regulartory function of AMPK in the perspective of cancer metabolic reprogramming have attracted increasingly attention.
Methods: To assess the regulatory role of AMPK in colonic tumorigenesis, we cross-bred AMPKα1-floxed mice with Lgr5Cre mice to specifically knockout AMPK α1 gene in intestinal stem cells, where Lgr5 is expressed, and their derived epithelial cells. The wild-type and AMPK knockout mice were subjected to azoxymethane-induced and dextran sulfate sodium promoted (AOM/DSS) colitis-associated CRC induction. Mechanisms were examined in Caco-2 cells. Stable AMPK knockout cell line was selected using G418.
Results: AMPK deficiency caused colonic hyperproliferation and pathological features, which was associated with accelerated CRC development including the augmentation of tumor number, tumor size, and hyperplasia in the AOM/DSS mouse model. The aggravated colorectal tumorigenesis induced by AMPK ablation likely resulted from the alteration of metabolites, as indicated by the reduced production of α-ketoglutarate, an obligate substrate for ten-eleven translocation hydroxylases (TETs) mediated DNA demethylation, in colonic tissues. Consistent with reduced α-ketoglutarate, the content of isocitrate dehydrogenase 1 and the activity of TET1 were markably decreased in AMPK deficient mice, correlated with reduced metastasis inhibitors, Adamts1 (A disintegrin and metalloproteinase with thrombospondin motif 1) and Mal (myelin and lymphocyte), as well as DNA hypermethylation of Mal and Mgmt (O-6-methylguanine-DNA methyltransferase) promotor regions. The mismatch repair (MMR) protein MLH1 or MSH2 levels were downregulated in AMPK deficient Caco-2 cells. AMPK activiation inhibited hypermethylation in promoter regions of Adamts1, Mal and p16ink4a in Caco-2 cells.
Conclusions: AMPK deficiency limits α-ketoglutarate concentration and aggregates suppressive epigenetic modifications of antioncogenes in gut epithelial cells, increasing risk of colorectal tumorigenesis. Because AMPK activity is ameable to change, AMPK may serve as a molecular target for colorectal cancer prevention and therapeutic.