Growth hormone suppresses the expression of IGFBP-5, and promotes the IGF-I-induced phosphorylation of Akt in bovine mammary epithelial cells

lncRNA MPFAST Promotes Proliferation and Fatty Acid Synthesis of Bovine Mammary Epithelial Cell by Sponging miR-103 Regulating PI3K-AKT Pathway

Long noncoding RNAs (lncRNAs) have an essential role in mammary gland development and lactation. Our earlier study showed that the lncRNA mammary proliferation and fatty acid synthesis-associated transcript (MPFAST) is highly expressed in the Holstein cow mammary gland during the middle lactation period compared to the dry period, which indicates its potential role in lactation. Therefore, gain- and loss-of-function experiments were performed on bovine mammary epithelial cells (BMECs) by cell counting kit 8 (CCK8), 5-ethynyl-2'-deoxyuridine (EdU), real-time quantitative polymerase chain reaction (RT-qPCR), and western blot. The results indicated that MPFAST promoted the viability and proliferation of BMECs. The oil red O staining and cellular triglyceride assay further showed that MPFAST promoted the number of lipid droplets and cellular triglyceride synthesis in BMECs. Bioinformatics analysis showed that MPFAST could act as a molecular sponge for miR-103, and PIK3R1 was a potential target of miR-103, which was further confirmed by the dual-luciferase reporter assay, RT-qPCR, and western blot. The overexpression of MPFAST promoted the expression of PIK3R1 at mRNA and protein levels. It also significantly increased the mRNA relative expression levels of AKT, mTOR, and SREBP1, and the protein relative expression levels of AKT and p-AKT in the PI3K-AKT signaling pathway. In contrast, the inhibition of MPFAST resulted in the downregulation of the PI3K-AKT signaling pathway genes. These results indicated that MPFAST regulates the expression of the genes in the PI3K-AKT signaling pathway through sponging miR-103 and promotes the proliferation and synthesis of fatty acids of BMECs. Our results would provide a new direction for further exploring the regulatory mechanism of lncRNA in the mammary gland.

Effect of acute stressors, adrenocorticotropic hormone administration, and cortisol release on milk yield, the expression of key genes, proliferation, and apoptosis in goat mammary epithelial cells

Cortisol is essential to milk synthesis; however, different acute stressors and the exogenous administration of adrenocorticotropic hormone (ACTH) decrease milk yield. Therefore, the effect of cortisol on milk yield and its influence on the survival of mammary epithelial cells have not been fully elucidated. In this context, the objective of this study was to evaluate the effect of cortisol on the expression of growth hormone receptor (GHR), insulin-like growth factor type 1 (IGF1), insulin-like growth factor type 1 receptor (IGF1R), insulin-like growth factor-binding protein 3 and 5 (IGFBP3 and IGFBP5), BAX, and BCL2 genes on the proliferation and apoptotic rates of mammary epithelial cells, and on milk yield in Saanen goats. In the present study, 3 experiments were conducted: (1) comparing the in vivo effects of first milking, vaccination, vermifugation, preventive hoof trimming, and the administration of ACTH or a placebo on cortisol release in dairy goats; (2) studying the in vivo effects of immediate increases in cortisol on the mammary gland of lactating goats; and (3) studying the in vitro effects of a prolonged increase in cortisol on mammary epithelial cells obtained from lactating goats. Cortisol release by goats increased significantly after ACTH administration compared with that observed after a placebo, and the cortisol profiles after first milking, vaccination, vermifugation, hoof trimming, and ACTH administration were similar. However, there was no effect of the immediate increase in cortisol in vivo on IGF-1 release, milk yield, milk quality, or the apoptosis and proliferation rates, nor was there any effect on the expression of the target genes. Furthermore, no interaction was observed between IGF-1 and cortisol in either the in vivo or in vitro experiments. However, the addition of cortisol in vitro significantly increased the expression of the GHR and IGF1R genes, which stimulate cell proliferation, and the BAX gene, which causes apoptosis. These contrasting results can explain why cortisol did not change the rates of proliferation or apoptosis in epithelial cells. Indeed, cortisol supplementation in vitro did not change the number or apoptotic rate of epithelial cells over the course of 5 d. Finally, further studies must be performed to understand the effect of cortisol on the expression of the GHR, IGF1R, and BAX genes by epithelial cells and the roles of these genes in milk synthesis during early lactation.

Mammary transcriptome analysis of lactating dairy cows following administration of bovine growth hormone

The galactopoietic effect of growth hormone (GH) in lactating ruminants is well established; however the mechanisms that mediate these effects are not well understood. The first objective of this study was to determine the effect of GH on the synthesis of the major casein and whey proteins. The second objective was to identify the genes and pathways that may be involved in mediating the effect of GH on milk synthesis. A single subcutaneous injection of a commercially available slow release formulation of GH (Lactatropin®), or physiological saline solution (control) was administered to non-pregnant dairy cows (n=4/group) in mid-late lactation. Milk samples were collected for composition analysis and mammary lobulo-alveolar tissue was collected postmortem 6 days post injection. Gene expression profiles were evaluated using either a 22 000 bovine complementary DNA microarray or quantitative PCR (qPCR), and microarrays were validated by qPCR. The yield of all the major casein and whey proteins was increased 32% to 41% in GH-treated cows, with the exception of α-lactalbumin yield which was elevated by 70% relative to controls. Treatment with GH treatment tended to increase the concentration of α-lactalbumin but had no effect on the concentration of any of the major milk proteins. Messenger RNA (mRNA) abundance of the major whey and casein genes, with the exception of α-s2-casein, was increased in response to GH compared with controls, which is consistent with the positive effect of GH on milk production. Treatment with GH treatment influenced the mRNA abundance of genes involved in cell growth and proliferation, transcriptional and translational regulation, actin cytoskeleton signalling, lipid metabolism and cell death. This study has provided new insights into the cell signalling that may be involved in mediating the effect of GH on milk production in the mammary gland of lactating dairy cows.

Up-regulation of integrin α6β4 expression by mitogens involved in dairy cow mammary development

In dairy cows, the extracellular microenvironment varies significantly from the virgin state to lactation. The function of integrin α6β4 is dependent on cell type and extracellular microenvironment, and the precise expression profile of α6β4 and its effects on mammary development remain to be determined. In the present study, real-time PCR and immunohistochemistry were used to analyze the expression and localization of integrin α6β4 in Holstein dairy cow mammary glands. The effects of integrin α6β4 on the proliferation induced by mammogenic mitogens were identified by blocking integrin function in purified dairy cow mammary epithelial cells (DCMECs). The results showed that the localization of β4 subunit and its exclusive partner the α6 subunit were not consistent but were co-localized in basal luminal cells and myoepithelial cells, appearing to prefer the basal surface of the plasma membrane. Moreover, α6 and β4 subunit messenger RNA (mRNA) levels changed throughout the stages of dairy cow mammary development, reflected well by protein levels, and remained higher in the virgin and pregnancy states, with duct/alveolus morphogenesis and active cell proliferation, than during lactation, when growth arrest is essential for mammary epithelial cell differentiation. Finally, the upregulation of integrin expression by both mammogenic growth hormone and insulin-like growth factor-1 and the inhibited growth of DCMECs by function-blocking integrin antibodies confirmed that integrin α6β4 was indeed involved in dairy cow mammary development.

Increased milk protein synthesis in response to exogenous growth hormone is associated with changes in mechanistic (mammalian) target of rapamycin (mTOR)C1-dependent and independent cell signaling

The objective of this study was to determine if increased milk protein synthesis observed in lactating dairy cows treated with growth hormone (GH) was associated with mechanistic (or mammalian) target of rapamycin complex 1 (mTORC1) regulation of downstream factors controlling nucleocytoplasmic export and translation of mRNA. To address this objective, biochemical indices of mammary growth and secretory activity and the abundance and phosphorylation status of mTORC1 pathway factors were measured in mammary tissues harvested from nonpregnant lactating dairy cows 6 d after treatment with a slow-release formulation of GH or saline (n=4/group). Treatment with GH increased mammary parenchymal weight and total protein content and tended to increase ribosome number and cell size, whereas protein synthetic efficiency, capacity, and cell number were unchanged. Cellular abundance of the mTORC1 components mTOR and (phosphorylated) mTOR(Ser2448) increased, as did complex eukaryotic initiation factor 4E:eukaryotic initiation factor 4E binding protein 1 (eIF4E:4EBP1), whereas no change was observed for mTORC1-downstream targets 4EBP1, 4EBP1(Ser65), p70/p85(S6K) and p70(S6K)Thre389/p85(S6K)Thre412. Changes in activation were not observed for any of the targets measured. These results indicate that GH treatment influences signaling to mTORC1 but not downstream targets involved in the nucleocytoplasmic export and translation of mRNA. Increased eIF4E:4EBP1 complex formation indicates involvement of the mitogen-activated protein kinase (MAPK) pathway. Abundance of MAPK pathway components eIF4E, eIF4E(Ser209), eIF4E:eIF4G complex, MAP kinase-interacting serine/threonine-protein kinase 1 (MKNK1), MKNK1(Thr197202), and ribosomal protein S6 kinase, 90kDa, polypeptide 1 (RPS6KA1) increased significantly in response to GH, whereas relative activation of the proteins was unchanged. Expression of IGFBP3 and IGFBP5 increased, that of IGF1R decreased, and that of IGF1 remained unchanged in response to GH. PatSearch analysis of the milk caseins αS1-casein, αS2-casein, and β-casein, MAPK signaling target RPS6KA1, and proliferation gene IGFBP3 mRNA indicated that all contained putative eIF4E-sensitivity elements. In response to GH, these genes were all upregulated, suggesting that increased abundance of eIF4E and eIF4E(Ser209) plays a role in mediating their nucleocytoplasmic export. We propose that, in response to GH, the IGF1-IGF1R-MAPK signaling cascade regulates eIF4E-mediated nucleocytoplasmic export and translation of mRNA, whereas mTOR controls cell renewal, cell turnover, and rRNA transcription through an alternative signaling cascade.

MiR-15a decreases bovine mammary epithelial cell viability and lactation and regulates growth hormone receptor expression

MicroRNAs (miRNAs) are a class of small non-coding RNAs that regulate the expression of target genes at the post-transcriptional level by transcript degradation or translational inhibition. The role of bta-miR-15a in bovine mammary gland hasn’t been reported. Using miRNAs prediction software, GHR gene was predicted to be a potential target of bta-miR-15a. In this study, bovine mammary epithelial cell line was used as an in vitro cell model to address the function of bta-miR-15a on bovine mammary epithelial cells. The expression changes of bta-miR-15a and Ghr after bta-miR-15a transfection were detected by qRT-PCR; the expression of GHR protein and casein was detected by western blotting. To determine whether bta-miR-15a can affect cell viability, cells were examined using an electronic Coulter counter (CASY-TT). In conclusion, bta-miR-15a inhibited the expression of casein of bovine mammary epithelial cells, and cell number and viability were reduced by bta-miR-15a expression. Bta-miR-15a inhibited the viability of mammary epithelial cells as well as the expression of GHR mRNA and protein level, therefore suggesting that bta-miR-15a may play an important role in mammary gland physiology.

Effects of growth hormone treatment on the expression of somatotropic axis genes in the skeletal muscle of lactating Holstein cows

This study focused on the expression of somatotropic axis genes in the skeletal muscle of dairy cattle. A slow-release recombinant bovine growth hormone (GH) (rbGH) formulation was administered to 5 cows, and saline solution (control) was administered to another 5 cows every 2 wk for a total of 10 wk, starting from the peak of lactation. Tissue and blood samples were collected on days 2 and 14 after each rbGH injection. As target genes insulin-like growth factor (IGF)-1, IGF-2, IGFBPs (1, 2, 3, 4, 5, 6), acute labile subunit (ALS), IGF-1 receptor (IGF-1R), GH receptor (GHR), and the known GHR 5'-UTR variants were selected as target genes, and their relative expression was measured using real-time polymerase chain reaction. In GH-treated cows, an increase in expression was observed for GHR 5'-UTR variant 1I on day 14 (P < 0.05), whereas a significant down-regulation of GHR (P < 0.05) was found after comparing values of treated cows between day 2 and day 14. However, only IGF binding proteins (BP)-5 was found to be appreciably up-regulated in GH-treated cows (P < 0.001), which may indicate the importance of this gene in the overall molecular response to GH administration. Our study indicated that GH treatment did not affect the expression of most somatotropic axis genes, despite the marked increase in GH and IGF-1 in blood (P < 0.001). Nor did it have a large impact on the proportion of GHR 5'-UTR variants in the skeletal muscle of lactating cows. Finally, although we observed a significant variation in the expression of some genes, it would appear that the differences between GH-treated cows and controls were not great enough to be considered as reliable indirect indicators of GH treatment in dairy cattle.

Experimental arthritis inhibits the insulin-like growth factor-I axis and induces muscle wasting through cyclooxygenase-2 activation

Chronic arthritis induces cachexia associated with an inhibition of the growth hormone (GH)-insulin-like growth factor-I (IGF-I) system and an activation of the E3 ubiquitin-ligating enzymes muscle atrophy F-box (MAFbx) and muscle Ring finger 1 (MuRF1) in the skeletal muscle. The aim of this work was to study the role of cyclooxygenase (COX)-2 in chronic arthritis-induced cachexia. Arthritis was induced in rats by Freund's adjuvant injection, and the effects of two COX inhibitors (indomethacin, a nonspecific inhibitor, and meloxicam, a selective COX-2 inhibitor on pituitary GH and on liver and serum IGF-I levels) were tested. Arthritis decreased body weight gain and GH and liver IGF-I gene expression. In the arthritic rats, both inhibitors, indomethacin and meloxicam, prevented the inhibitory effect of arthritis on body weight gain. Indomethacin and meloxicam administration to arthritic rats increased pituitary GH and liver IGF-I mRNA as well as serum levels of IGF-I. These data suggest that induction of COX-2 during chronic inflammation is involved in the inhibition of the GH-IGF-I axis and in the body weight loss. In the gastrocnemius muscle, arthritis increased the gene expression of tumor necrosis factor (TNF)-alpha, the E3 ubiquitin-ligating enzymes MAFbx and MuRF1, as well as of IGF-I and IGF-binding protein-5 (IGFBP-5). Inhibition of COX-2 by meloxicam administration increased gastrocnemius weight and decreased MAFbx, MuRF1, TNF-alpha, and IGFBP-5 gene expression. In summary, our data indicate that chronic arthritis-induced cachexia and muscle wasting are mediated by the COX-2 pathway resulting in a decreased GH-IGF-I secretion and increased expression of MAFbx and MuRF1 mRNA.

The fur seal-a model lactation phenotype to explore molecular factors involved in the initiation of apoptosis at involution

Mammary gland involution requires co-ordination of milk production, immune responses, apoptosis and remodeling. Initiation and progression of each of these components involves integral control by the mammary gland. Although cell-based culture models and genetically manipulated animals have shed light on these processes, the factors controlling each step in the involution cascade are still poorly understood. The fur seal displays a unique lactation phenotype. During the lactation cycle the mammary gland downregulates milk production and initiates an immune response but fails to initiate the apoptotic phase of involution, allowing the female fur seal to undertake long foraging trips of up to 28 days between suckling bouts. Upon return to shore the female continues feeding her pup following resumption of lactation and milk production. Expression profiling of genes involved in this lactation cycle provides valuable tools for investigation of the factors responsible for the initiation of apoptosis at involution.