THU052 Serum Growth Hormone Increases At The Onset Of Lactation And Promotes Mitochondrial Activity In Human Mammary Cells

Disclosure: T. Elajnaf: None. H. Rostom: None. X. Meng: None. A. Fry: None. F. Hannan: None. Growth hormone (GH) administration is reported to increase milk yield in breastfeeding women. However, the role of endogenous GH in human lactation is unknown. We investigated whether serum GH is associated with the initiation of lactation after child birth, and recruited n=30 pregnant women (age range 24-41 years) following informed consent (1). Serum GH was measured at 36 weeks’ gestation and during postpartum days 1-4. All women had term births and initiated lactation between postpartum days 2-4. The mean maternal serum GH value progressively increased from 0.2±0.01 mIU/L at 36 weeks’ gestation to a peak value of 0.9±0.2 mIU/L on postpartum day-3 (p<0.0001), with serum GH then decreasing to 0.2±0.03 mIU/L by postpartum day-4. We hypothesised that this early postpartum rise in serum GH may increase mammary metabolism in order to stimulate milk synthesis after child-birth. Reverse transcription-quantitative PCR (RT-qPCR) demonstrated that lactating human mammary epithelial cells (HMECs) isolated from breast milk express the GH receptor. We next assessed the effects of GH in cultured HMECs. Recombinant human GH (rhGH) caused a dose-dependent increase in the phosphorylation of Akt, which is a key signalling protein required for initiating lactation. Thus, 50ng/mL and 500ng/ml rhGH caused ∼1.5-fold and ∼2-fold increases in Akt phosphorylation, respectively (p<0.05, n=4 experiments). We further evaluated the effects of rhGH on HMECs by untargeted proteomics involving nano liquid chromatography and tandem mass spectrometry. This demonstrated that the major mammary cell biological processes induced by GH involve the mitochondria. Indeed, HMECs treated with rhGH for 8 hours showed a significant upregulation of mitochondrial proteins involved in electron transport chain assembly, namely COQ9 (>4-fold increase, p<0.05) and IBA57 (>4-fold increase, p<0.05); and upregulation of CHCHD3 (6-fold increase, p<0.05), which influences mitochondrial cristae structure. We assessed whether these mitochondrial protein changes affect mammary cell respiration. Extracellular O(2), which is an indicator of oxidative phosphorylation, was measured in cultured HMECs treated with 50ng/mL rhGH for up to 5 days. Administration of 50ng/mL rhGH caused a significant increase in the rate of O(2) consumed by these cells (579±28 vs. 456±14 pmol O(2)/min/10(6) cells for control HMECs, p<0.01, n=4 experiments), consistent with increased oxidative phosphorylation. In summary, these clinical and cellular studies highlight a pivotal role for GH in promoting mammary cellular metabolism 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: Thursday, June 15, 2023