Abstract A045: Elevated PGC1α during abrupt mammary gland involution leads to long-term metabolic reprogramming and genomic instability; hallmarks of breast cancer

Abstract

Abstract Epidemiological data links higher parity and lack of breastfeeding with increased risk of breast cancer, specifically aggressive triple negative breast cancer, and associated higher mortality rate. 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 show several precancerous changes, such as increased collagen deposition, inflammation, and hyperplasia in the mammary gland (MG) of mice after AI1. Recent studies indicate peroxisome proliferator-activated receptor-gamma coactivator 1-apha (PGC1α) as a regulator of involution and energy metabolism. As metabolic reprogramming is a hallmark of cancer, metabolic changes in the MG related to involution warrant investigation. Objective: Our objective was to evaluate the metabolic effects of AI in MG. We hypothesized that AI leads to marked alteration in mammary lipid metabolism, mitochondrial biogenesis, and oxidative stress through elevations of PGC1α, which cause long-term metabolic reprogramming and genomic instability. Methods: FVB/n mice were paired for breeding. At partum, dams were randomized to AI or GI cohort and standardized to 6 pups per dam. AI mice had pups removed on day 7 postpartum (PPM). For GI mice 3 pups each were removed on day 28 and 31ppm. Tissues were harvested on day 28, 56, and 120 PPM. MG were subjected to Affymetrix, Gene Set Enrichment Analysis (GSEA), Seahorse Analysis, and lipidomics. Results were validated by qPCR and Western Blot. Superoxide species were detected by flow cytometry. DNA damage was analyzed via 8-hydroxy-2’-deoxygnuanosine (8-OHdG) ELISA. Results: Day 28 AI glands had significantly higher PGC1α expression than GI glands (p=0.006). Affymetrix and GSEA data showed day 28 AI glands to have enriched pathways related to fatty acid metabolism (p=0.004) and oxidative phosphorylation (p<0.001). Lipidomics showed elevated levels of oxidized sphingolipids and production of prostaglandin J2 (PGJ2) in day 28 AI glands (all p<0.02). Day 56 AI glands had higher levels of mitochondria superoxide species (p<0.0001) and higher PGJ2 synthesis (p=0.01). Day 120 AI MG had upregulation of an oxidized lipid (p=0.0476). Day 120 AI glands had significantly higher 8-OHdG levels (p=0.02), higher reliance of fatty acid substrates for energy (p=0.0185), and elevated extracellular acidification rates (p=0.0194). Conclusion: Although histologically both GI and AI MG return to near pre-pregnancy state within a month, our data shows long-term metabolic reprogramming in the AI MG similar to what is shown in breast cancer cells. These metabolic changes link to early elevations in PGC1α. Addressing the metabolic changes by targeting PGC1α provide a potential option to reduce the risk of developing breast cancer if a woman is unable to breastfeed. PMID6637535 *Fellowship T32CA229114 Citation Format: Kate S Ormiston, Kirti Kaul, Neelam Shinde, Gautam Sarathy, Morgan Bauer, Djawed Bennouna, Rachel Kopec, Ramesh Ganju, Sarmila Majumder, Bhuvaneswari Ramaswamy. Elevated PGC1α during abrupt mammary gland involution leads to long-term metabolic reprogramming and genomic instability; hallmarks of breast cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Breast Cancer Research; 2023 Oct 19-22; San Diego, California. Philadelphia (PA): AACR; Cancer Res 2024;84(3 Suppl_1):Abstract nr A045.