Large adipocytes alter mode of lipid release and promote breast cancer malignancy.

Primary adipocytes possess a dramatic capacity to expand and retract in volume, leading to high variability in cell size within and between individuals. Yet, how adipocyte size impacts cell function remains unclear as adipocyte size is not tunable with traditional experimental approaches, forcing previous work to rely on correlative studies. Here, we develop protocols to separate primary adipocytes from the same donor into large and small populations and maintain these size-sorted cells in culture. Using these methods, we perform transcriptomic, lipidomic, and functional analyses on large and small adipocytes across two orthogonal mouse models of obesity and validate our results with human clinical samples. Our findings indicate that changes to cell size, rather than global differences mediated by weight gain, drive the transcriptional response of primary adipocytes to obesity. Moreover, large adipocytes shift from a traditional, lipase-mediated mode of lipid release to a non-canonical, extracellular vesicle-mediated mechanism. In functional coculture studies, this change promotes lipid accumulation in neighboring breast cancer cells, increasing their migration and proliferation via enhanced tumor cell fatty acid oxidation. Consistent with our experimental data, human patients with large adipocytes present with greater rates of dyslipidemia and higher concentrations of fasting triglycerides, even when accounting for differences in body mass index. Collectively, our results provide direct evidence that large and small adipocytes from the same donor differ in gene expression, lipid composition, and function with implications for the management of adipose tissue-related pathologies such as breast cancer.