Abstract P5-03-09: Cell composition changes in healthy breast tissue is associated with advancing age and epigenetic age acceleration

Abstract Introduction: Risk factors for breast cancer include advancing age, lifetime estrogen exposure, and breast density. DNA methylation-based estimates of age are elevated in breast tissue of healthy women compared with paired blood samples, and the degree of age acceleration is associated with lifetime estrogen exposure. However, no prior work has examined cell compositional changes associated with breast epigenetic aging. In this study we estimated the abundance of different cell types in healthy breast, computed using gene expression data, and investigate cell composition changes that accompany advancing chronologic age and breast epigenetic age acceleration. Methods: DNA/RNA were extracted (AllPrep, Qiagen) from breast tissue specimens from 192 healthy women aged 19-90 years who donated breast tissue to the Susan G. Komen Tissue Bank at the Indiana University Simon Comprehensive Cancer Center. Transcriptome analysis was performed using the QuantSeq 3’mRNA-SeqFWD kit to generate RNA sequencing libraries. DNA methylation age was estimated using beta-values from Illumina EPIC 850K array platform. Age acceleration is defined using the residual of a linear regression of methylation age on chronologic age. Cell deconvolution was performed using CIBERSORTx to estimate the abundance of adipocytes, luminal epithelial cells, basal myoepithelial cells, vascular endothelial cells, lymphatic endothelial cells, immune cells (dendritic cells & macrophages), pericytes & smooth muscle cells, and fibroblasts. We examined cell composition changes with chronologic age, and with age-adjusted measures of acceleration in 6 epigenetic clocks: the Horvath Pan-tissue, Hannum, Phenotypic, Grim, Skin & Blood, and Epigenetic Pacemaker clocks, as well as the DNA methylation-based estimate of telomere length, DNAmTL. Results: Advancing chronologic age was associated with an increase in the imputed proportion of adipocytes (R=0.40, p< 0.0001), vascular endothelial cells (R=0.23, p=0.0033), and immune cells (dendritic cells & macrophages) (R=0.29, p=0.00016), and a decrease in the proportion of luminal epithelial cells (R=-0.43, p< 0.0001), and basal myoepithelial cells (R=-0.27, p=0.00047). Epigenetic age acceleration was significantly associated with increases in proportions of luminal epithelial cells (p< 0.0001 for age-adjusted Hannum, Phenotypic, Grim, and Skin & Blood clocks, p< 0.05 for Pan-tissue) and basal myoepithelial cells (p< 0.0001 for Phenotypic and Skin & Blood clocks), and decreased proportions of adipocytes and vascular endothelial cells (p< 0.0001 for Hannum, Phenotypic, Grim, and Skin & Blood clocks, p< 0.05 for Pan-tissue). Conclusion: Using gene expression data in healthy female breast tissue, we identified significant changes in cell-type-specific abundance that accompany advancing chronologic age, with an increase in adipocytes and immune cells, and a decline in luminal epithelial cells and basal myoepithelial cells. By contrast, epigenetic age acceleration in breast tissue is associated with decreasing proportions of adipocytes and vascular endothelial cells and a rise in basal myoepithelial cells and luminal epithelial cells. Our findings suggest distinct patterns of cellular composition changes that accompany normal aging compared with accelerated aging in breast tissue. Citation Format: Mary E. Sehl, Wenbin Guo, Collin Farrell, Natascia Marino, Jill Henry, Anna Maria Storniolo, Jeanette Papp, Jingyi Li, Steve Horvath, Matteo Pellegrini, Patricia A. Ganz. Cell composition changes in healthy breast tissue is associated with advancing age and epigenetic age acceleration [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P5-03-09.