Effects of dietary energy restriction on gene regulation in mammary epithelial cells

The objective of this study was to determine whether dietary energy restriction (DER) affects the pattern of gene expression in three interrelated energy metabolism pathways: glycolysis, gluconeogenesis, and the citric acid cycle. Mammary carcinogenesis was initiated by the i.p. injection of female Sprague-Dawley rats with 50 mg of 1-methyl-1-nitrosourea per kilogram of body weight. Five days following 1-methyl-1-nitrosourea administration, animals were fed ad libitum or 80% or 60% of the ad libitum intake. Epithelial cells were harvested from histologically confirmed adenocarcinomas (adenocarcinoma epithelial cell; ACEC) and uninvolved mammary gland (mammary gland epithelial cells; MGEC) via laser capture microdissection, whereas isolated RNA was arrayed on Affymetrix R230 2.0 genome chips. Principal components analysis revealed complete separation of the patterns of gene expression between ACEC versus MGEC. Further examination of the data set revealed an up-regulated pattern of expression in the ACEC of genes involved in glycolysis, whereas gluconeogenesis was suppressed. In general, genes involved in the citric acid cycle were not differentially expressed; however, pyruvate dehydrogenase expression was down-regulated and lactate dehydrogenase expression was increased in ACEC versus MGEC. Collectively, the observed patterns of expression were consistent with the Warburg effect. DER exerted no effect on the Warburg pattern of gene expression or on other aspects of these energy metabolism pathways. These findings imply that efforts to target the Warburg effect for cancer prevention are mechanistically distinct from those modulated by DER and provide a rationale for the combination of approaches that target basic defects in energy metabolism and energy-sensing pathways for the prevention of breast cancer.