Fatty acid exposure promotes age-related mammary tissue alterations with pro-tumorigenic potential

Introduction . Exposure of non-transformed breast cells and breast microstructures to the medium-chain (MC) fatty acid (FA) octanoic acid (OA) induces a metabolic shift toward the serine, one-carbon, glycine and methionine pathways (SOG/methionine), enhancing epigenetic plasticity, increasing reactive oxygen species (ROS), promoting cell survival and disrupting cell-cell communication. Similarly, the aged mammary gland is characterized by disrupted cell-cell communication, epigenetic plasticity and increased ROS. We hypothesize that FA-induced metabolic reprogramming leads to biological aging of the mammary gland, contributing to pro-tumorigenic alterations observed during chronologic aging. Methods . MCF-10A cells were exposed to OA for proteomics. Breast microstructures exposed to ± OA were analyzed by scRNAseq. Breast microstructures and 3D mammary spheres derived from primary cells were embedded in Matrigel, exposed to ± OA for 7 days, stained for luminal and basal markers, F-actin, and nuclei, and imaged by confocal microscopy to assess migration/invasion. Migratory cell populations enriched in OA-containing media were identified with scRNAseq. Raman spectroscopy (RS) was used to characterize the lipid content in normal breast tissue. Results . OA treatment induced changes previously reported in aging and tumorigenic contexts, including: (1) upregulation (p < 0.01) of aging-related genes ( GDF15, MDK, PLIN2 ), and downregulation (p < 0.01) of lineage markers and MMP7 , a gene whose downregulation promotes mammary epithelial aging; (2) upregulation (p < 0.01) of Senescence-Associated Secretory Phenotype (SASP) genes, including AREG (reprogramming) and ANGPTL4 (migration); (3) increased secreted signaling via AREG , GDF15 , and MDK; and (4) reduced extracelular matrix (ECM)-receptor and cell-cell interactions. Ex vivo , OA altered tissue architecture disrupting the basal barrier and promoting cellular migration. BMYO1, LASP1, and LHS1 epithelial subtypes were among the migratory cells in OA media and expressed SASP, cancer ( MYC , EGFR , SREBF1 ), migration ( S100A4 , NCAM1 ), aging and SOG/methionine genes. FB1 fibroblasts dominated in vehicle media, but OA favored ECM-disassembling FB2 cells. RS analysis demonstrates the presence of both saturated and unsaturated FAs and revealed the presence of MCFAs, such as OA, with higher intensities observed in the postmenopausal tissue supporting the in vivo plausibility of our in vitro/ex vivo findings . Conclusions. Our data supports a model suggesting that chronological and biological aging processes increase the release of free FAs, due to elevated GDF15-induced lipolysis. The rise in FAs drives mammary gland remodeling and accelerates aging of the gland. Chronological and biological aging increase vulnerability to breast cancer. This model suggests potential preventive strategies such as targeting GDF15 and SOG/methionine.