Soluble factors from the tumor-adipocyte interplay stimulate morphological and metabolic changes in 3T3-L1 adipocytes

Priscila Ayelén Pagnotta¹,4, Mariana Gantov¹, Cecilia Lotufo¹, Rubén Dreszman², María Luján Crosbie³, Natalia Santiso³, Anabela Ursino³, Celeste Frascarolli³, Alicia Amato³, Juan Carlos Calvo¹,4, Judith Toneatto¹

Adipocytes are one of the primary stromal cells in mammary tissue, considered to play an active role in the tumor microenvironment. The aim of this work was to evaluate the effects of factors derived from conditioned media from human breast cancer adipose tissue (TCM) or normal breast adipose tissue explants (NCM) on lipolytic and mitochondrial changes and the expression of adipocyte markers. Adipocytes 3T3-L1 exposed to TCM showed an increase in the number of lipid droplets (LDs) but with reduced area, with a signal of discontinuous intensity for Plin1, and a reduction in cell area. Adipocytes exposed to NCM increased LDs size, without affecting HSL and Plin1 subcellular localization. Adipocytes incubated with TCM showed a tendency to increase expression of lipolytic proteins (HSL and Plin1) with a significant decrease in triglyceride level. 90% of the adipocytes incubated with TCM showed fragmented mitochondria, whereas only about 60% of those exposed to NCM presented this change. The highest percentage of mitochondrial fragmentation per cell was more frequent in adipocytes treated with TCM vs NCM. Adipocytes exposed to TCM showed a tendency to a decrease in white adipocyte (Caveolin, ATGL) and adipogenic (PPAR gamma) markers, and to an increase of immature (Pref-1) and beige adipocyte (UCP1) markers. These findings suggest that peritumoral adipocytes secrete factors which may induce morphologic and metabolic changes on adipocytes, that could contribute to tumor progression.