Distinct effects of calorie restriction and exercise on mammary gland gene expression in C57BL/6 mice

Energy balance, including diet, weight, adiposity, and physical activity, is associated with carcinogenesis. Epidemiologic studies indicate that obesity and sedentary and/or active behavior are risk factors for breast cancer in postmenopausal women and survival in both premenopausal and postmenopausal breast cancer patients. Thus, understanding the influence of energy balance modulation on changes in gene expression patterns in the normal mammary gland is important for understanding mechanisms linking energy balance and breast cancer. In a 6-week-long study, female C57BL/6 mice (9-week-old) were randomized into four groups: (a) food consumed ad libitum (AL), (b) AL with access to running wheels (AL+EX), (c) 30% calorie restricted (CR), and (d) 30% CR with access to running wheels (CR+EX). CR mice received 70% of calories but 100% of all other nutrients compared with AL mice. Diet and exercise treatments, individually and combined, had significant effects on body composition and physical activity. Affymetrix oligomicroarrays were used to explore changes in gene expression patterns in total RNA samples from excised whole mammary glands. Contrasting AL versus CR resulted in 425 statistically significant expression changes, whereas AL versus AL+EX resulted in 45 changes, with only 3 changes included among the same genes, indicating that CR and EX differentially influence expression patterns in noncancerous mammary tissue. Differential expression was observed in genes related to breast cancer stem cells, the epithelial-mesenchymal transition, and the growth and survival of breast cancer cells. Thus, CR and EX seem to exert their effects on mammary carcinogenesis through distinct pathways.