The role of <i>ESR1</i> in regulating lactation traits in buffalo mammary epithelial cells

Abstract. Buffalo milk is favoured by consumers due to its higher nutritional components, as well as its rich and mellow flavour. However, research on the molecular mechanisms underlying the formation of lactation traits in buffalo remains limited. In this study, we systematically investigated the regulatory effects of estrogen receptor alpha (ESR1) on lactation-related functions in buffalo mammary epithelial cells (BMECs) using overexpression and small interfering RNA (siRNA)-mediated silencing strategies. Our results demonstrated that ESR1 knockdown via siRNA significantly suppressed BMEC viability and proliferation and downregulated the expression of genes associated with lipid transport and secretion (PPARG, LPL, PLIN2, VLDLR, ADFP, CD36), milk protein synthesis (CSN1S1, CSN1S2, RPS6, RHEB, EIF4E, AKT1), and cell proliferation (STAT5A, MTOR, ELF5, CCND1, EGF, IGF1). Concurrently, silencing ESR1 markedly upregulated pro-apoptotic genes (BAX, CASP9) and downregulated the anti-apoptotic gene BCL2. Conversely, ESR1 overexpression exerted opposite effects on BMECs, further validating the critical role of ESR1 in modulating BMEC proliferation and milk component synthesis. In conclusion, ESR1 expression enhances buffalo lactation traits by promoting milk fat and milk protein synthesis, stimulating BMEC proliferation, and inhibiting cellular apoptosis. These findings provide novel insights into the molecular mechanisms governing buffalo lactation and offer valuable references for the development and utilization of lactation-related genetic resources in buffalo breeding.