Transcript abundance of hormone receptors, mammalian target of rapamycin pathway-related kinases, insulin-like growth factor I, and milk proteins in porcine mammary tissue1

Abstract

Prolactin, glucocorticoids, and insulin are commonly used to induce milk protein synthesis in bovine mammary cell cultures. In addition, administration of GH increases milk yield in dairy cows, likely via the mammalian target of rapamycin (mTOR) pathway and IGF-I synthesis. As such, the hypothesis of this study was that mRNA abundance of hormone receptors, mammalian target of mTOR pathway-related kinases, IGF-I, and milk protein-encoding genes increases in the porcine mammary gland in response to greater lactation demand. Selected genes included those encoding for receptors of GH (GHR), insulin (INSR), glucocorticoid (NR3C1), prolactin (PRLR), IGF-I (IGF-I), mTOR (FRAP1), and p70S6 kinases (RPS6KB1), and the milk proteins α-lactalbumin (LALBA) and β-casein (CSN2). Mammary tissue was biopsied from 4 sows on d 110 of gestation (prepartum), d 5 and 17 of lactation, and d 5 after weaning (postweaning), and gene expression was quantified by reverse-transcription quantitative PCR. Compared with prepartum, d 5 of lactation increased (P < 0.001) NR3C1, tended to increase (P = 0.06) GHR, and decreased (P < 0.001) PRLR mRNA abundance. Compared with d 5 of lactation, d 17 of lactation increased PRLR (P < 0.001) and decreased GHR (P < 0.01). Expression of INR and FRAP1 did not differ when comparing either prepartum or d 17 of lactation with d 5 of lactation. Compared with d 17 of lactation, postweaning decreased (P < 0.001) PRLR, did not affect INSR, and increased both IGF-I and GHR (P < 0.05) mRNA abundance. From prepartum to d 17 of lactation, NR3C1 mRNA abundance was positively correlated with CSN2 (r = 0.85; P < 0.001) and LALBA mRNA abundance (r = 0.79; P = 0.002), whereas mRNA abundance of GHR tended to be positively correlated with that of IGF-I (r = 0.46; P = 0.06). In conclusion, expression of the genes NR3C1, PRLR, GHR, and IGF-I changed in the porcine mammary gland during the prepartum to postweaning periods, but only NR3C1 mRNA abundance was positively correlated with expression of CSN2 and LALBA.

Milk Protein Synthesis in the Lactating Mammary Gland: Insights from Transcriptomics Analyses

“…Studies discussed above provide support for such an approach but the exclusive use of AA in this case is not enough and might be detrimental if there is not also a concomitant increase in energy in the diet in the form of carbohydrates [28]. Contrary to observations in the bovine, there is not significant increase in expression of insulin receptor and FRAP during lactation in the porcine mammary gland [171]; however, phosphorylation studies are not available in this species to provide conclusions about the activity of mTOR during lactation.…”

Production of free glutamate in milk requires the leucine transporter LAT1

“…This expression pattern for LAT1 is similar to the one reported previously by Aleman et al (3) in rats and Manjarin et al (20) in pigs and probably respond to the specific hormonal changes that occur during pregnancy and lactation. Recent studies have shown that Leu transamination and decarboxylation are stimulated by cortisol in rat mammary tissue and the glucocorticoid receptor NR3C1 curiously overlaps with the expression of the major milk proteins ␣-lactalbumin and ␤-casein in the porcine mammary gland (15,19). In contrast, the expression of the growth hormone receptor (growth hormone inhibits Leu transamination) tended to decreases with lactation.…”

Trans-10,cis-12 conjugated linoleic acid reduces milk fat content and lipogenic gene expression in the mammary gland of sows without altering litter performance

“…As milk protein concentration is positively associated with dietary energy content (35) , the CLA-induced reduction in energy level may have reduced milk protein synthesis. In addition, trans-10, cis-12-CLA, but not the cis-9, trans-11 isomer, stimulates expression of the mammalian target of rapamycin in the mammary gland of the sows before initiating lactation, and it effects protein synthesis in this species (36,37) . As a mixture of these isomers was used, the milk protein reduction in the CLA-treated animals may be due to the isomer-specific action of cis-9, trans-11-CLA on mammalian target of rapamycin expression.…”