Adipocyte-Derived Exosomes Increase the Growth of Breast Tumors in Obese Mice

Abstract

Abstract Objectives 1) We assessed whether the secretion and cargos of exosomes are distinct in obese and lean mice. 2) We assessed whether adipocyte-derived exosomes increase the size of tumors of the mammary gland in mice. Methods Female tamoxifen-inducible adipose-specific TSG101 conditional knockout mice (TSG KO) were initiated on an AIN-93G-based 50% high fat (HFD) or 15.8% low fat (LFD) at age 3 weeks and continued on these diets for 10 weeks. At age 4 weeks, mice were injected with tamoxifen or vehicle (TSG+), followed by the injection of 1.8*106 murine breast adenocarcinoma E0771 cells into the mammary gland fat pad 10 days after tamoxifen injection. Loss and gain of TSG101 and Cre, respectively, in inguinal subcutaneous adipose tissue were confirmed by RT-qPCR. Tumors were excised and their size was assessed using a caliper and by weight. H&E staining was used to assess the tumor type. Exosomes were isolated from plasma by an ExoQuick Plasma Prep kit, authenticated by western blot analysis and counted using a Nanosight tracker. The statistical analysis was performed by one-way ANOVA and Least Significant Differences posthoc test using a significance level of P < 0.05. Results HFD led to an increase in breast tumor size, which was diminished in adipose-specific TSG101 KO fed HFD: The size of mammary tumors in TSG+ fed HFD increased by 198% compared to TSG+ fed LFD (P < 0.05), whereas tumor size decreased by 58% TSG101 KO fed HFD compared to TSG+ fed HFD (P < 0.05). HFD led to an increase in adipose-derived exosomes that was reduced by TSG101 KO: The expression of ASC-1, a marker for adipose-derived exosomes in plasma exosomes increased by 58% in TSG+ fed HFD compared to TSG+ fed LFD, and decreased by 29% in TSG KO fed HFD compared to TSG+ fed HFD (P < 0.05). Plasma exosomes tested positive for exosome markers, CD63, CD81 and HSP70 and negative for a non-exosome marker, calnexin. H&E staining suggested that the tumors observed in all mice were adenocarcinomas. Tumor numbers were not affected by TSG101 and diet. Conclusions HFD increases the growth of mammary tumors in mice and the diet effect depends on exosome biogenesis in adipose tissue. We speculate that adipose-derived exosomes promote tumor growth but not metastasis. Funding Sources NIFA, NIH, and USDA. J.Z. is a consultant for PureTech Health.