Search

Milk fat globule membrane (MFGM) proteins surround the triacylglycerol core comprising milk fat globules (MFG). We previously detected a decrease in the size of fat globules during conjugated linoleic acid (CLA)-induced milk fat depression (MFD), and other studies have reported that some MFGM proteins play a central role in regulating mammary cellular lipid droplet size. However, little is known about the relationship between MFD, MFG size, and MFGM proteins in bovine milk. The aim of this study was to investigate the profile of MFGM proteins during MFD induced by CLA. Sixteen mid-lactating Holstein cows (145 ± 24 d in milk) with similar body condition and parity were divided into control and CLA groups over a 10-d period. Cows were fed a basal diet (control, n = 8) or control plus 15 g/kg of dry matter (DM) CLA (n = 8) to induce MFD. Cow performance, milk composition, and MFG size were measured daily. On d 10, MFGM proteins were extracted and identified by quantitative proteomic analysis, and western blotting was used to verify a subset of the identified MFGM proteins. Compared with controls, supplemental CLA did not affect milk production, DM intake, or milk protein and lactose contents. However, CLA reduced milk fat content (3.73 g/100 mL vs. 2.47 g/100 mL) and the size parameters volume-related diameter D

Metabolism in most organisms can show variations between the day and night. These variations may also affect the composition of products derived from livestock. The aim of the present study was to investigate the difference in composition between the day milk and night milk of dairy cows. Ten multiparous Holstein cows (milk yield = 25.2 ± 5.00 kg/d) were randomly selected during mid lactation. Milk samples were collected at 0500 h (“night milk”) and 1500 h (“day milk”) and analyzed to determine their composition. Mid-infrared spectroscopy was used to analyze macronutrient content of milk. Metabolomics and lipidomics were used to detect and analyze small molecules and fatty acids, respectively. An automatic biochemical analyzer and ELISA kits were used to determine biochemical indicators, as well as antioxidant and immune parameters in the milk. Though milk fat, protein, lactose, and total milk solids were not different between day milk and night milk, small molecules, metabolites and lipids, and hormones and cytokines differed between day milk and night milk. Regarding biochemical and immune-related indicators, the concentrations of malondialdehyde, HSP70, and HSP90 in night milk were lower than that in day milk. However, interferon-γ levels were higher in night milk. Additionally, night milk was naturally rich in melatonin. Lipidomics analyses showed that the levels of some lipids in night milk were higher than those in day milk. Metabolomics analyses identified 36 different metabolites between day milk and night milk. Higher concentrations of N-acetyl- d -glucosamine, cis-aconitate, and d -sorbitol were observed in day milk. However, the other 33 metabolites analyzed, including carbohydrates, lipids, AA, and aromatic compounds, showed lower concentrations in day milk than in night milk. The present findings show that the composition of night milk differs considerably from that of day milk. Notable changes in the circadian rhythm also altered milk composition. These results provide evidence to support the strategic use and classification of day milk and night milk.

Subacute ruminal acidosis (SARA) can cause rapid lipopolysaccharide (LPS) elevation and milk yield decline in lactating ruminants. LPS has been shown to promote apoptosis and reduce the proliferation of mammary epithelial cells. Previous studies have shown that γ- amino butyric acid (GABA) can enhance production performance, regulating β-cell apoptosis and proliferation. Whether GABA can regulate apoptosis and proliferation induced by LPS in mammary epithelial cells is unknown. In this paper, we detected the role of GABA on proliferation and apoptosis as well as inflammation induced by LPS in bovine mammary epithelial cells (MAC-T cell line). In addition, we explored the role mechanism of GABA in LPS-induced MAC-T cells response through detecting the NFκB signaling pathway key molecules. The results suggested that GABA reduced the effects of cell apoptosis induced by LPS. Furthermore, GABA inhibited the expression of inflammatory cytokines activated by LPS. More importantly, blocking GABA receptors with its antagonist, GABA could not reduce the expression of inflammatory and pro-apoptotic factors activated by LPS. Notably, GABA significantly decreased the TLR4, NFκB p65, and MyD88 mRNA expression levels that were elevated by LPS. Our data indicated that GABA can improve cell viability and decrease apoptosis induced by LPS, while exerting an anti-inflammatory effect through the NFκB signaling pathway.

This study aimed to evaluate the effects of a high dose of conjugated linoleic acid (CLA) on lactating mice. In one experiment, Kunming mice were separated into four groups (n = 6 per group); the control (CON) group received 3.0% linoleic acid (LA) oil, the L-CLA group received a mixture of 2.0% LA and 1.0% CLA, the M-CLA group received a mixture of 1.0% LA and a 2.0% CLA, and the H-CLA group received 3.0% CLA. Feeding proceeded from day 4 to day 10 of lactation. In a second experiment, a CON group received 3.0% LA, and an H-CLA group received 3.0% CLA. Plasma parameters were analyzed for all groups, and insulin tolerance tests (ITTs) were conducted. CLA treatment did not affect dam weight but significantly decreased the food intake of dams during lactation. Furthermore, CLA decreased the weight of pups on day 10 of lactation; this effect was attributed to lower milk fat of dams in the CLA group than in those of the other groups. Relative to mice in the CON group, the mice in the H-CLA group displayed increased liver weight and liver triglyceride (TG) content as well as higher TG content and γ-glutamyl transferase (γ-GT) activity in the plasma. Moreover, high-dose CLA resulted in insulin resistance, possibly affecting the red blood cell (RBC) and hemoglobin (HCB) levels in the plasma. In conclusion, lactating mice receiving a high dose of CLA exhibited fatty liver, insulin resistance, and impaired lactation performance.

The periparturient period is the most critical period during the lactation cycle of dairy cows and is characterized by increased oxidative stress status. The objective of this experiment was to evaluate the effect of supplementing rumen-protected methionine on nuclear factor erythroid 2-like 2 (NFE2L2, formerly NRF2) protein and target gene expression in the mammary gland during the early postpartal period. Multiparous Holstein cows were used in a block design experiment with 30 cows per treatment. Treatments consisting of a basal control diet (control) or the basal diet plus rumen-protected methionine (methionine) were fed from d -28 to 60 relative to parturition. Mammary tissue biopsies were harvested on d 21 postpartum from 5 cows per treatment. Compared with control, methionine increased dry matter intake, milk yield, and milk protein content. Among plasma parameters measured, methionine led to greater methionine and lower reactive oxygen metabolites. Compared with control, methionine supply resulted in greater mRNA abundance of the NFE2L2 target genes glutamate-cysteine ligase catalytic subunit (GCLC), glutamate-cysteine ligase modifier subunit (GCLM), glutathione reductase (GSR), glutathione peroxidase 1 (GPX1), malic enzyme 1 (ME1), ferrochelatase (FECH), ferritin heavy chain 1 (FTH1), and NAD(P) H quinone dehydrogenase 1 (NQO1) in the mammary tissue. In addition, methionine upregulated the mRNA abundance of NFE2L2, NFKB1, MAPK14 and downregulated KEAP1. The ratio of phosphorylated NFE2L2 to total NFE2L2 protein, and total heme oxygenase 1 (HMOX1) protein were markedly greater in response to methionine supply. In contrast, total protein abundance of Kelch-like ECH-associated protein 1 (KEAP1), which sequesters NFE2L2 in the cytosol and reduces its activity, was lower with methionine. Besides the consistent positive effect of methionine supply on systemic inflammation and oxidative stress status, the present data indicate a positive effect also on antioxidant mechanisms within the mammary gland, which are regulated, at least in part, via phosphorylation of NFE2L2 and its target genes. The exact mechanisms for these responses merit further study.

To investigate the expression pattern of lipogenic genes in mammary gland of mouse in different lactation stages, the relative mRNA abundance and expression of 20 genes involved in milk fat synthesis and secretion of lactating mammary tissues were assessed using real-time PCR. Results revealed the significant upregulation of mRNA expression for both high abundant genes (abundance > 5%), such as LPL, ACACA, SCD, XDH, BTN, and ADFP and moderate abundant genes (5% > abundance > 1%), such as CD36, FASN, AGPAT6, and DGAT in lactation stages compared to pregnancy (P < 0.05). The mRNA expression of lipogenic enzyme genes for ACACA, SCD, FASN, AGPAT6, and DGAT exhibited lower expression lever in early (6 d) and late (18 d) lactation stages but higher expression level at middle stage (12 d), demonstrating a low-high-low pattern. Besides, the mRNA levels of some gene regulators were also measured. The mRNA expression of SREBF gene increased gradually along with the lactation, which showed a 10-fold elevation at middle stage (12 d). The expression pattern of SREBF gene was the same as lipogenic enzyme genes, suggesting that SREBF may play an important role in the regulation of lipogenic enzyme genes in the lactating mammary gland.

The functions of distinct isoforms of solute carrier family 27 transporters (SLC27A1-6), acetyl-CoA carboxylase (ACACA, ACACB), stearoyl-CoA desaturase (SCD1-4), fatty acid desaturase (FADS1-3), LPIN (LPIN1-3), insulin-induced gene (INSIG1, 2), and peroxisome proliferator-activated receptor gamma coactivator1 (PPARGC1A, B) were studied in the mouse mammary gland from pregnancy to lactation. The relative mRNA abundance and percent change in real-time PCR were determined. mRNA expression of SLC27A3 and SLC27A4 was 37- and 1.4-fold more upregulated at 12 days of lactation, respectively (P0.01). Transcripts of SCD isoforms were the most abundant, accounting for 59% of all genes measured, and PPARGC1 isoforms were the least (0.06% of all genes measured). The mRNA abundance from ACC, FADS and LPIN accounted for 29, 9 and 2.6%, respectively. INSIG1 mRNA expression was 32-fold more upregulated (P0.05), while PPARGC1B was 0.18-fold downregulated at 18 days of lactation (P0.01). We concluded that mRNA abundance and expression of these isoforms are affected by the stage of lactation.

Obtaining quantitative data concerning gene expression is important for understanding milk synthesis in mammary glands. Quantitative real-time PCR (qRT-PCR) is an efficient tool to calculate gene expression; however, it is necessary to find valid reference genes for normalization of qRT-PCR data. We applied the geNorm software to eight commonly used reference genes to identify the most stable and optimal genes for the mouse mammary gland. Based on this analysis, HPRT, RPL and GAPDH are the most appropriate reference genes for data normalization. We tested the expression of the alpha-lactalbumin and fatty acid synthase genes using these three reference genes, both normalized and non-normalized. The normalized mRNA expression ratio was significantly different from the non-normalized ratio. We recommend the use of these three reference genes for the normalization of qRT-PCR data in gene expression studies of mouse mammary glands.

The efficacy of conjugated linoleic acid (CLA) in diet supplements for milk fat reduction is well documented in several species. However, the mechanisms by which fatty acids regulate mammary lipogenesis remain largely unknown, especially with regard to gene expression of enzyme and regulators. In this study, 8 Holstein dairy cows in their mid-lactation period were randomly divided into 2 groups. Control cows received a Ca salt of palm oil fatty acid dietary supplement, and those in the CLA group were fed Ca salts of CLA (Ca-CLA), all in a dose of approximately 200 g∙cow(-1)∙day(-1) for 14 days. The milk yield was recorded daily, and protein, lactose, and fat in the milk were quantified every 3 days for 2 weeks. Fatty acids in the milk were analyzed with gas-liquid chromatography. Measurement of messenger RNA levels of the main lipogenic genes of lipoprotein lipase, acetyl-coenzyme A (CoA) carboxylase, fatty acid synthase, stearoyl-CoA desaturase, and transcription factors such as sterol response element binding protein 1 (SREBP1) and peroxisome proliferator-activated receptor γ was performed in biopsy samples of mammary tissue on the last day. The results indicated that dietary Ca-CLA caused a continuous reduction of milk fat (P < 0.01) with no effect on milk yield, milk protein, and lactose. The fatty acid profile in the milk from the CLA group differed from that from controls, and the yield of milk fatty acid decreased (P < 0.01) with Ca-CLA supplementation. The depressed expression of lipogenic genes (lipoprotein lipase, acetyl-CoA carboxylase, fatty acid synthase, and stearoyl-CoA desaturase) demonstrated inhibition of fatty acid de novo synthesis and uptake in the mammary gland of the CLA group. Furthermore, the gene expression of transcription factor SREBP1 was also downregulated (P < 0.01), but peroxisome proliferator-activated receptor γ was unchanged, suggesting that SREBP1 may play a key role in the regulation of lipogenic gene expression in the lactating mammary gland.

Leptin is expressed in various tissues, suggesting that this protein is effective not only at the central nervous system level, but also peripherically. Recent studies have shown leptin production by other tissues, including the placenta, stomach, and mammary tissues, but there is no information available concerning expression levels of leptin in the rat mammary gland at different activation stages. We used semi-quantitative RT-PCR to investigate leptin mRNA expression levels in the rat mammary gland at different activity stages. Rat mammary gland samples were collected from virgin females and on days 6, 12, 18 of pregnancy and of lactation (six rats per group). The expression levels of leptin mRNA were measured by semi-quantitative RT-PCR, with β-actin as an internal control. Leptin mRNA was highly expressed in virgin rat mammary glands (leptin(IOD)/β-actin(IOD) = 1.60). It decreased gradually during pregnancy, being lowest at 18 days of pregnancy, when the levels were significantly lower than in virgin mammary tissue. Leptin mRNA increased slightly during lactation, but the difference was not significant. By day 18 of lactation, expression levels of leptin mRNA reached the same values as in virgin mammary tissue (leptin(IOD)/β-actin(IOD) = 1.65). Based on these results, we suggest that leptin has an important regulation role in rat mammary gland activation.