Microenvironment-contextual cell signaling is attenuated with age

Post-menopausal women are more prone to breast cancer than younger women. The increased frequency of age-related breast cancers is likely due to interactions between acquired mutations and age-dependent epigenetic changes that affect mammary epithelial lineage fidelity. We hypothesized that the aging process fundamentally affects how human mammary epithelial cells (HMEC) respond to microenvironmental signals, resulting in increased susceptibility to oncogenic transformation. In order to measure microenvironmental cell signaling in normal finite lifespan HMEC, we applied a novel microsphere-based flow cytometry technology. The microsphere cytometry allows multiparametric single cell quantification of signaling pathway activity and lineage-specific marker expression in cells adhered to surface-functionalized microspheres that mimic specific microenvironments. Using this approach, we analyzed age-dependent changes in human mammary myoepithelial and luminal epithelial cells exposed to different ECM and growth factors. We found that ECM-mediated MAP kinase and PI3 kinase activation levels in HMEC were attenuated with age. Older luminal cells displayed higher surface integrin levels consistent with acquired basal identity, albeit with decreased integrin activation and increased Src-signaling relative to myoepithelial cells. We show that the diminished signaling magnitude in HMEC from older women correlated with reduced probability of activating oncogene-induced senescence. We propose that age-related changes in ECM-mediated epithelial cell regulation may impair protective tumor suppression mechanisms and increase breast cancer susceptibility.