Obesity, palmitate, and senescence : investigating the role of fibroblasts in breast cancer progression

Obese breast cancer patients suffer a worse prognosis than their normoweight counterparts, including increased risks of recurrence and mortality. While the causative mechanisms remain to be fully uncovered, emerging evidence implicates the obesity-related factor palmitate in development of cellular senescence, an inflammatory state associated with proliferation, metastasis, and other hallmarks of cancer. To investigate the obesity-senescence axis, we utilized in vitro models in which palmitate or sera from non-obese or obese women were applied to fibroblasts, the most populous stromal cell type found in the breast tumor microenvironment, after which the cells were assessed for onset of senescence. Indirect co-culture was then used to assess the impact of these obesity- and palmitate-exposed fibroblasts on multiple breast cancer cell lines. Involvement of NF-κB was investigated using a pharmacological inhibitor, and the polyunsaturated omega-3 fatty acids EPA and DHA were tested as potential therapeutic agents. Obese conditions and palmitate exposure induced a senescent-like phenotype in fibroblasts, characterized by such measures as a proliferative arrest, senescence-associated beta-galactosidase activity, and pro-inflammatory gene and protein expression. The mechanism establishing senescent-like gene expression relied at least partially on NF-κB activity. While these effects were not abrogated by concurrent omega-3 fatty acid administration, the fibroblast phenotype induced by obese conditions and palmitate appeared of pathological significance, inducing cell non-autonomous effects in breast cancer cells. Specifically, senescent-like, palmitate-exposed fibroblasts imparted changes in tumorigenic measures, including cell viability, migration, and gene expression signatures related to EMT, angiogenesis, metabolism, cell cycle, and DNA damage repair. These studies are among the first to implicate the pathogenicity of palmitate-induced fibroblast senescence in the context of breast cancer. In informing our understanding of the connection between palmitate, senescence, and breast tumorigenesis, these studies will ultimately facilitate identification of a therapeutic target that can be used to improve the comparably worse outcomes of the obese breast cancer patient.