Regulation of amino acid transporters in the mammary gland from late pregnancy to peak lactation in the sow

Abstract

BackgroundMilk protein is crucial for milk quality in sows and health of newborn piglets. Plasma amino acids (AA) in sows are important precursors for milk protein synthesis in the mammary gland. In order to study the regulation of AA transported in sow mammary glands and possible underlying mechanisms, we measured the expression of genes coding for milk proteins, AA transporter expressions, and plasma AA concentrations in sows at three different physiological stages (D-17, D1 and D17 of lactation), and then further investigated the regulation of AA transport across the cell membrane by adaptive mechanisms using pig mammary epithelial cells (PMEC) as an in vitro model. PMEC were cultured in DMEM:F12 with 4 amino acid concentrations (0 × AA complex, 1 × AA complex, 5 × AA complex, and 25 × AA complex). Classes of AA complexes evaluated in this study included neutral AAs (L-Ala + L-Ser + L-Cys), acidic AAs (L-Asp, L-Glu) and neutral + basic AAs (L-Ala + L-Ser + L-Cys + L-Lys).ResultsOur results indicated that mRNA expression of genes coding for milk protein (αs1-casein, αs2-casein, β-casein and κ-casein) increased significantly with the advance of physiological stage (P < 0.05), and plasma concentrations of most AAs including threonine, serine, glutamate, alanine, valine, cysteine, methionine, isoleucine and tyrosine were greater at D1 of lactation compared with D-17 and D17 of lactation (P < 0.05). Additionally, protein and gene expressions of AA transporters including excitatory AA transporter 3 (EAAT3), alanine/serine/cysteine/threonine transporter (ASCT1) and sodium-coupled neutral AA transporter 1 (SNAT2) were greater in lactating sow mammary glands compared with sow mammary glands in late pregnancy (P < 0.05). The mRNA expressions of SLC38A2, SLC1A1, SLC6A14 increased significantly in the cell mediums supplemented with 5 × and 25 × of AA complexes compared with those cells cultured in DMEM/F12 cell medium (P < 0.05). The mRNA expressions of SLC38A, SLC1A4, and SLC6A14 also increased in EBSS cell medium compared to DMEM/F12. However, only mRNA expression of SLC38A decreased when AA complex was added into EBSS (P < 0.05).ConclusionAA transportation was positively regulated in sow mammary glands with the advance of physiological stage from late pregnancy to peak of lactation and AA transporters in PMECs were adaptively regulated by changed AA concentrations.

Recent progress of porcine milk components and mammary gland function

“…ATB 0,+ and ASCT1 are significantly increased at peak lactation [ 80 ]. Our lab reported that either EAAC1 or EAAT3 (SLC1A1) is the predominant anionic amino acid transporter and is significantly increased during lactation [ 82 ]. Cationic amino acid transporters CAT-1 , CAT2-B , y + LAT1 and y + LAT2 are widely expressed in the mammary gland and y + LAT2 is significantly increased at peak lactation [ 82 ].…”

“…Our lab reported that either EAAC1 or EAAT3 (SLC1A1) is the predominant anionic amino acid transporter and is significantly increased during lactation [ 82 ]. Cationic amino acid transporters CAT-1 , CAT2-B , y + LAT1 and y + LAT2 are widely expressed in the mammary gland and y + LAT2 is significantly increased at peak lactation [ 82 ]. Neutral amino acid transporters ASCT1, ASCT2, LAT2 (SLC7A8) and SNAT2 (SLC38A2) are also expressed in the mammary gland [ 82 ].…”

“…Cationic amino acid transporters CAT-1 , CAT2-B , y + LAT1 and y + LAT2 are widely expressed in the mammary gland and y + LAT2 is significantly increased at peak lactation [ 82 ]. Neutral amino acid transporters ASCT1, ASCT2, LAT2 (SLC7A8) and SNAT2 (SLC38A2) are also expressed in the mammary gland [ 82 ]. Recently, a significant increase of B 0,+ AT and CAT-4 were observed in swine mammary gland during the transition from colostrogenesis to lactation [ 83 ].…”

Amino acid transportation, sensing and signal transduction in the mammary gland: key molecular signalling pathways in the regulation of milk synthesis

“…In rats, the gene expression of LAT1 in the mammary gland is greater than that of LAT2 during the lactation period (19) . The gene expression of LAT2, but not LAT1, is significantly increased with the progression of lactation in sows (21) . In bovine mammary glands, more research has been focused on the effects of LAT1 (20,22) .…”

“…These transporters are heterodimeric proteins, which comprise of a catalytic subunit (L-type amino acid transporter 1 (LAT1), encoded by SLC7A5, or L-type amino acid transporter 2 (LAT2), encoded by SLC7A6) and a glycoprotein 4F2 heavy chain (4F2hc). Both LAT1 and LAT2 are highly expressed in the mammary tissues (15) , but which subtype is predominately expressed in the mammary gland seems to be different among species (19)(20)(21) . In rats, the gene expression of LAT1 in the mammary gland is greater than that of LAT2 during the lactation period (19) .…”