OR18-02 Mammary Insulin Sensitivity Increases At The Onset Of Lactation And Promotes Metabolic Pathways Supporting Breast Milk Synthesis

Disclosure: X. Meng: None. H. Rostom: None. A. Fry: None. T. Elajnaf: None. F. Hannan: None. The initiation of lactation during postpartum days 1-4 is hormonally regulated and critical for successful breastfeeding. Insulin represents a key lactogenic hormone as evidenced by women with diabetes mellitus who have delayed lactation onset. However, the role of insulin in lactation and its influence on mammary cells are unclear. We utilised clinical and cellular approaches to investigate this, and recruited n=38 healthy pregnant women (age range 26-42 years) following informed consent and measured serum insulin at 36 weeks’ gestation and during post-partum days 1-4 (1). Serum insulin progressively decreased from 36 weeks’ gestation to day 4 post-partum (244±33pmol/L vs 37±4pmol/L, p<0.0001). Moreover, reverse transcription-quantitative PCR (RT-qPCR) of lactating human mammary epithelial cells (HMECs) isolated from breast milk showed a >20-fold increase in insulin receptor expression compared to non-lactating HMECs (p<0.01, n=4). These findings indicated an increase in both systemic and mammary insulin sensitivity at lactation onset. We hypothesised that insulin promotes lactation by influencing mammary metabolism and used cultured HMECs to evaluate this. Stimulation of HMECs with 10nM insulin caused a >7-fold increase (p=0.001, n=5) in the phosphorylation of Akt, a signalling protein required for initiating lactation. Akt influences oxidative phosphorylation and glycolysis, and we assessed these processes by measuring oxygen consumption rate (OCR) and extracellular acidification rate (ECAR), respectively. Cultured HMECs treated with 10nM insulin for ≤18hrs showed increased OCR (22±0.9 vs. 17±0.4pmol O(2)/min/10(6) cells for control HMECs, p<0.05, n=4) and ECAR (0.23±0.003 vs. 0.18±0.002mpH/min/10(6) cells for control HMECs, p<0.001, n=4), consistent with increased oxidative phosphorylation and glycolysis. HMECs treated with 10nM insulin for 8hrs had significant upregulation of genes encoding glycolytic enzymes, namely hexokinase 2 (>4-fold increase, p<0.0001, n=4) and pyruvate kinase M1/2 (1.4-fold increase, p<0.05, n=4). However, RT-qPCR analysis of HMECs showed that insulin did not increase expression of genes mediating oxidative phosphorylation, suggesting an Akt-mediated post-transcriptional mechanism. In summary, increased mammary insulin sensitivity together with insulin-stimulated oxidative phosphorylation and glycolysis may support mammary function and milk component synthesis at the onset of lactation. Reference: (1) Rostom, H. et al. Protocol for an observational study investigating hormones triggering the onset of sustained lactation: the INSIGHT study. BMJ Open 12, e062478. Presentation: Saturday, June 17, 2023