Background: Breast tissue remodeling occurs with age and is marked by a progressive increase in stromal tissue. Advancing age is also associated with increased senescence among stromal cells that promote a protumorigenic microenvironment by adopting a senescence-associated secretory phenotype (SASP). In previous studies, calorie restriction has been effective in cancer prevention through inhibiting cellular senescence and SASP. However, obesity has shown to be cancer promoting with inconsistent findings on its role in cellular senescence.

Purpose: We tested the hypothesis that calorie restriction is protective to the protumorigenic, age-related changes that occur within the mammary microenvironment while diet-induced obesity accelerates these changes.

Methods: Six week old female mice were randomized to receive either a low-fat control regimen (10 kcal% fat), a 30% calorie restricted (CR) regimen relative to control, or a high-fat diet induced obesity (DIO, 60 kcal% fat) regimen, resulting in control, CR, and DIO mice respectively. A subset of mice was sacrificed at 1, 3, 5, 12 and 20 months following diet initiation with mammary fat pads (MFP) harvested and serum stored for further analysis. H&E staining was analyzed using a digital algorithm to quantify the composition of adipose, epithelia and stoma in the MFP tissue. RNA was extracted from MFP sections and rt-PCR was preformed to analyze gene expression of CDKN2a, the gene encoding p16(INK4a) a well known marker for senescence.

Results: CR significantly decreased body weight and decreased serum IGF-1, insulin, leptin and estradiol and significantly increased adiponectin relative to control and DIO mice at all time points. MFP composition remained relatively stable from 1 and 12-month time points. However, there was an apparent non-significant trend from 12 and 20-month time points, with increasing stromal tissue and a decrease in adipose tissue, which was most drastic in CR mice. Gene expression analysis showed an increase in CDKN2a expression in control mice relative to CR mice at 5 and 20-month time points. Additionally, control and CR mice demonstrated an increase in CDKN2a expression with age from 5 months to 20-months.

Conclusions: Stromal composition of murine MFP displayed an age-related increase that is consistent with findings in human breast tissue. Despite this uniform increase, we see a decrease in the age-related acquisition of a senescence phenotype in CR mice relative to control supporting the notion that CR is protective to this protumorigenic change that occurs with advancing age. Ongoing analysis of gene expression in DIO mice will determine the role of obesity in MFP cellular senescence and confirmation of senescent phenotypes via β-galactosidase staining and analysis of SASP associated gene expression.

Citation Format: Laura A. Smith, Emily L. Rossi, Laura W. Bowers, Emma H. Allot, Sarah Dunlap, Liza Makowski, Bentley Midkiff, Melissa Troester, Stephen D. Hursting. Metabolic and microenvironment changes in the mammary of calorie restricted, normal weight, and obese mice throughout the lifespan. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4090.