Abstract PO5-09-11: Abrupt involution of mouse mammary gland leads to inflammatory systemic changes along with mammary specific metabolic shifts that may enhance risk of breast cancer

Abstract Epidemiological data links higher parity and lack of breastfeeding with increased risk of breast cancer, specifically aggressive triple negative breast cancer (TNBC), and higher mortality rate. Following pregnancy and lactation, breast remodels to near pre-pregnancy stage through apoptotic cell death and adipocyte repopulation process. Long-term breastfeeding and gradual weaning of an infant leads to gradual involution (GI) of the breast, while lack of or abrupt discontinuation of breastfeeding after birth leads to abrupt involution (AI), when rapid and massive cell death takes place. Our studies have shown several precancerous changes, such as increased collagen deposition, inflammation, and hyperplasia in the mammary gland of mice after AI. However, the systemic impact of AI and how this increases risk of breast cancer is yet to be elucidated. Objectives: Our objective is to evaluate the systemic effects that are prompted by the AI mammary gland. We hypothesize that AI leads to marked alteration in lipid metabolism and systemic inflammation that enhances risk for breast cancer. Methods: FVB/n mice (8week old) were paired for breeding. At partum (day 0), dams were randomized to AI or GI cohort and standardized to 6 pups. AI mice had pups removed on day 7 postpartum (ppm) to mimic short-term breastfeeding. For GI mice 3 pups each were removed on day 28 and 31ppm to mimic gradual weaning. Tissues harvested on day 28, 56, and 120 postpartum. Body composition was measured by echo MRI. Glucose tolerance test (GTT) was performed after a 6 hour fast using a 2g/kg glucose intraperitoneal injection. Blood glucose was measured by glucometer. Serum insulin was analyzed by ELISA. HOMA-IR was calculated using blood glucose and serum insulin results. Serum was analyzed using multiplex ELISA by MesoScale Diagnostics. Mammary glands were subjected to untargeted lipidomics. Results: There were no significant differences in body weight, percent body fat or lean mass between AI and GI groups at any time point. However, at day 120 ppm (4 months after partum), we have observed significantly larger amount (1.29-fold increase) of perigonadal adipose tissue (visceral adipose) in AI mice than GI mice (p=0.0112; n=24-38/group). There were no significant differences in blood glucose, serum insulin, HOMA-IR, or GTT results between AI and GI groups at day 120. AI mice had significantly higher levels of cytokines IL-1β (3.1-fold increase, p=0.0417) and KC/GRO (1.5-fold increase, p=0.0196) than GI mice at day 120. At day 28, AI mammary glands had significantly higher amounts of level 3 identified oxidized ceramide containing sphingolipids that were linked to insulin resistance and diabetes. At day 56, GI mammary glands had significantly higher amounts of level 2 and 3 identified metabolites linked to cellular signaling and lipid metabolism. On day 120, there were no significant differences in lipid metabolites between groups. Conclusion: Although histologically GI and AI mammary glands return to near pre-pregnancy state within a month after partum, our data shows specific lipid changes in the AI mammary gland similar to what has been shown in women with TNBC. Furthermore, AI of the mammary gland leads to systemic effects on adiposity and inflammation that could be key to increased breast cancer risk. Further studies along these lines are in progress to understand the whole-body effects of AI and stratify preventive measures for women who cannot breast feed. Significance: Lack of breastfeeding is more prevalent in African American (AA) women and linked to higher risk of developing aggressive TNBC1. Our novel animal models of AI and GI help to link the impact of AI and systemic changes that may enhance breast cancer risk. In particular, we see an increase in visceral adiposity with AI. Understanding this mechanism will help identify strategies to reduce risk in women who are unable or choose not to breastfeed and ultimately help to reduce TNBC and TNBC-related mortality in AA women. Citation Format: Kate Ormiston, Kirti Kaul, Neelam Shinde, Djawed Bennouna, Rachel Kopec, Ramesh Ganju, Sarmila Majumder, Bhuvaneswari Ramaswamy. Abrupt involution of mouse mammary gland leads to inflammatory systemic changes along with mammary specific metabolic shifts that may enhance risk of breast cancer abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-09-11.