Parenterally Delivered Methionyl-Methionine Dipeptide During Pregnancy Enhances Mammogenesis and Lactation Performance Over Free Methionine by Activating PI3K-AKT Signaling in Methionine-Deficient Mice

BACKGROUND: Pregnancy-induced hypoaminoacidemia, l-methionine (Met) included, disturbs embryogenesis and may also affect breast function. Supplementation with the dipeptide l-methionyl-Met (Met-Met) may improve lactation performance. OBJECTIVE: We compared the effects of supplemental Met or Met-Met during pregnancy on mammogenesis and lactogenesis and investigated underlying mechanisms. METHODS: In experiment 1, 9-wk-old ICR mice (n = 72, approximately 30 g) were divided into 3 groups. During the first 17 days of pregnancy (DP), the Control group was fed a diet with Met (8.2 g/kg) and saline was intraperitoneally injected, the Met group was fed a Met-devoid diet and 35% of the Met (92-mmo l Met) as contained in the Control diet was intraperitoneally injected, and the Met-Met group was fed the same diet and 70-mmo l Met plus 11-mmo l Met-Met was intraperitoneally injected. All animals were fed the Control diet after DP17 and during lactation. Mammogenesis, lactogenesis, transcriptome at DP17, and milk performance during lactation were examined. In experiment 2, 9-wk-old ICR mice (n = 55, approximately 30 g) at DP0 were injected through the teat with adeno-associated virus for overexpression/inhibition of phosphoinositide-3-kinase regulatory subunit 1 (Pik3r1), divided into the Control, Met, and Met-Met groups and received the same treatment as experiment 1 to examine mammogenesis and lactogenesis at DP17. RESULTS: In experiment 1, compared with the Met group, the Met-Met group showed higher (P < 0.05) mammary epithelium percentage (42%) and alphaS1-casein expression (84%) at DP17, milk yield (34%) and energy concentrations (8.7%) during lactation; transcriptomic analysis illustrated activated phosphatidylinositol-3 kinase (PI3K)/protein kinase B (AKT) signaling in the mammary glands of the Met-Met group (P-adj < 0.001). In experiment 2, overexpression of Pik3r1 enhanced (P < 0.05) the protective effect of Met-Met over Met on mammogenesis and beta-casein expression. CONCLUSION: Met-Met is more effective than Met in promoting mammogenesis and lactogenesis mainly by activation of PI3K-AKT signaling in Met-deficient mice.