from C57BL/6 mice into the mammary

from C57BL/6 mice into the mammary fat pad and monitored tumour growth. We observed that development of obesity significantly increased TNBC growth, leading to tumours having twice the volumes of the ND group after 17 days (Figure 1D). In order to discriminate the impact of obesity-related disorders on TNBC growth from the impact of the HFD itself, we tested the growth of 4T1 TNBC cells derived from Balb/cJRj mice, which are described as an obesity-resistant model upon HFD feeding (Figure 1E). After 5 weeks of either ND or HFD, Balb/cJRj mice showed no difference of bodyweight gain or fat mass accumulation (Figure 1F,G), confirming resistance to obesity development. We followed 4T1 TNBC growth after orthotopic injection in Balb/cJRj mice and found that HFD alone had no impact on TNBC growth (Figure 1H), thereby showing the necessity to develop obesity and increase fat depots to favour tumour growth. To further explore whether apelin could be associated with these phenotypes, we measured apelin mRNA expression. We found that besides an increased TNBC growth, apelin mRNA expression increased by 120% in the subcutaneous adipose tissue of obese mice (Figure 1I). Interestingly, TNBC that is growing in obese mice also displays increased tumoral apelin expression by approximately 80% compared with TNBC harvested from mice fed a ND (Figure 1I). By contrast, the obesity-resistant mice showed no difference in apelin expression in the adipose tissue and had a tendency of only ±35% increase tumoral apelin (Figure 1J). Moreover, increased apelin expression in E0771 TNBC correlates with bigger TNBC volumes (Figure 1K), suggesting that increased apelin expression might be one of the mechanisms involved in the increase TNBC growth of obese mice.