Investigating the Role of the Gut Microbiota in a Mouse Model of Obesity-driven Breast Cancer
Creators: name: Chen, Fangxin
Publisher: name: The University of North Carolina at Chapel Hill University Libraries
Year: 2024

description: Background: Both breast cancer and obesity are characterized by low-grade inflammation and obesity is associated with an increased risk of breast cancer development. Weight loss interventions, such as intermittent energy restriction (IER), have been suggested to exert an anti-tumor effect. Additionally, homeostasis of the intestinal microbial community plays a critical role in the host’s immunity. Breast cancer, obesity, and IER can lead to changes in the intestinal microbial community. However, whether gut microbiota remodeling associated with obesity and IER mediates breast cancer outcomes remains unclear. Thus, the goal of this Honors thesis was to determine the contribution of microbial communities associated with different dietary patterns to breast cancer progression, achieved by developing a protocol for antibiotic treatment, assessing colonizing efficiency, and profiling microbial communities.

Methods: Female C57BL/6NCrl donor mice were maintained on either a control diet, 10% kcal, or a diet-induced obesity (DIO) diet, 60 kcal% fat for 15 weeks. Then, donor mice fed on the control diet remained the same (Control) and those fed on the DIO diet were randomized to either continue the DIO diet (DIO) or receive an intermittent energy restriction (IER) diet (DIO-IER). Cecal microbial transplant (CMT) recipient mice were maintained on a control diet throughout the study. The intestinal microbial communities of recipient mice were depleted by 10-day antibiotic treatment and replenished by cecal slurries from donor mice. After 8 days of microbial recolonization, E0771 mammary cancer cells were injected orthotopically into recipient mice. To assess the depletion and repopulation of gut microbiota in recipient mice, DNA extraction and qPCR were performed on fecal pellets collected from recipient mice before and after antibiotic treatments, and after 8 days of microbial recolonization. Cecal microbial communities were analyzed via 16S rRNA amplicon sequencing. Serum was collected to assess circulating hormones and intestinal permeability. 

Results: No anaerobic or aerobic microbial growth was detected and a significant reduction in 16S rRNA gene copies was observed after 10 days of antibiotic treatment. The intestinal tract was successfully recolonized by cecal contents from donor mice but further optimization on the proportions of sequence variants (SVs) shared by donors and corresponding CMT recipients is required. Tumor mass and intestinal permeability were not significantly different across recipient mice. Cecal microbial communities diverged across control, DIO, and DIO-IER recipient groups. Microbial diversity was lower in DIO recipient mice relative to control and DIO-IER recipient mice. The relative abundance of 4 genera was associated with circulating levels of metabolic hormones. 

Conclusions: This study presented reproducible protocols for depleting and replenishing the gut microbiota of specific pathogen-free mice. Data suggest that the composition of intestinal microbiota may be remodeled and distinct microbial communities may be formed in response to different diets. The abundance of certain genera may be associated with metaboendocrine hormones. Understanding the link between the intestinal microbial community and obesity-driven breast cancer outcomes and identifying genera or species that could promote antitumor immunity would be clinically beneficial.