Function of SREBP1 in the milk fat synthesis of dairy cow mammary epithelial cells

Regulatory impacts of PPARGC1A gene expression on milk production and cellular metabolism in buffalo mammary epithelial cells

The PPARGC1A gene plays a fundamental role in regulating cellular energy metabolism, including adaptive thermogenesis, mitochondrial biogenesis, adipogenesis, gluconeogenesis, and glucose/fatty acid metabolism. In a previous study, our group investigated seven SNPs in Mediterranean buffalo associated with milk production traits, and the current study builds on this research by exploring the regulatory influences of the PPARGC1A gene in buffalo mammary epithelial cells (BuMECs). Our findings revealed that knockdown of PPARGC1A gene expression significantly affected the growth of BuMECs, including proliferation, cell cycle, and apoptosis. Additionally, we observed downregulated triglyceride secretion after PPARGC1A knockdown. Furthermore, the critical genes related to milk production, including the STATS, BAD, P53, SREBF1, and XDH genes were upregulated after RNAi, while the FABP3 gene, was downregulated. Moreover, Silencing the PPARGC1A gene led to a significant downregulation of β-casein synthesis in BuMECs. Our study provides evidence of the importance of the PPARGC1A gene in regulating cell growth, lipid, and protein metabolism in the buffalo mammary gland. In light of our previous research, the current study underscores the potential of this gene for improving milk production efficiency and overall dairy productivity in buffalo populations.

ALG5 Regulates STF-62247-Induced Milk Fat Synthesis via the mTOR Signaling Pathway

Milk fat content is a critical indicator of milk quality. Exploring the key regulatory genes involved in milk fat synthesis is essential for enhancing milk fat content. STF-62247 (STF), a thiazolamide compound, has the potential to bind with ALG5 and upregulate lipid droplets in fat synthesis. However, the effect of STF on the process of milk fat synthesis and whether it acts through ALG5 remains unknown. In this study, the impact of ALG5 on milk fat synthesis and its underlying mechanism were investigated using bovine mammary epithelial cells (BMECs) and mouse models through real-time PCR, western blotting, Oil Red O staining, and triglyceride analysis. Experimental findings revealed a positive correlation between STF and ALG5 with the ability to synthesize milk fat. Silencing ALG5 led to decreased expression of FASN, SREBP1, and PPARγ in BMECs, as well as reduced phosphorylation levels in the PI3K/AKT/mTOR signaling pathway. Moreover, the phosphorylation levels of the PI3K/AKT/mTOR signaling pathway were restored when ALG5 silencing was followed by the addition of STF. These results suggest that STF regulates fatty acid synthesis in BMECs by affecting the PI3K/AKT/mTOR signaling pathway through ALG5. ALG5 is possibly a new factor in milk fat synthesis.

The Role of Progesterone in Elf5 Activation and Milk Component Synthesis for Cell-Cultured Milk Production in MAC-T Cells

Prolactin is essential for mammary gland development and lactation. Progesterone also induces ductal branching and alveolar formation via initial secretory differentiation within the mammary gland. Herein, we aimed to evaluate the role of progesterone as a prolactin substitute for the production of cell-cultured milk components in MAC-T cells. Cells were treated with various hormones such as prolactin (PRL), progesterone (P4), 17β-estradiol (E2), cortisol (COR), and insulin (INS) for 5 d. MAC-T cells cultured in a P4 differentiation media (2500 ng/mL of P4, 25 ng/mL of E2, 25 ng/mL of COR, and 25 ng/mL of INS) showed similar levels of E74-like factor 5 (Elf5) and milk component synthesis (α-casein, β-casein, α-lactalbumin, β-lactoglobulin, and triglycerides) compared to those cultured in a PRL differentiation media (5000 ng/mL of PRL, 500 ng/mL of CORT, and 50 ng/mL of INS). The levels of α-casein and triglycerides in the optimal P4 differentiation media were present at comparable levels to those in the PRL differentiation media. Our results demonstrated that P4 induces the activation of Elf5 and the synthesis of milk components in MAC-T cells, similar to PRL. Therefore, P4 may be used as an effective substitute of PRL for cell-cultured milk production in in vitro frameworks.

Acylated Ghrelin Activates PI3K/mTOR Signaling Pathway by Promoting ThPOK Acetylation to Promote Milk Fat Synthesis in Bovine Mammary Epithelial Cells

Ghrelin regulates diverse physiological activities. However, the effects of this hormone on the milk fat synthesis remain unknown. This study aimed to investigate the effect of acylated ghrelin (AG) on milk fat synthesis by modifying the expression (knockdown or overexpression) of growth hormone secretagogue receptor 1a (GHSR1a) and Th-inducing POK (ThPOK) in primary bovine mammary epithelial cells (BMECs). The results showed that AG significantly increased the triglyceride relative content from 260.83 ± 9.87 to 541.67 ± 8.38 in BMECs via GHSR1a. ThPOK functions as a key regulatory target downstream of AG, activating the PI3K and mTOR signaling pathways to promote milk fat synthesis in BMECs. Moreover, AG-regulated ThPOK by increasing the EP300 activity, which promoted ThPOK acetylation to protect it from proteasomal degradation. In conclusion, AG increases ThPOK acetylation and stabilizes ThPOK through GHSR1a, thereby activating the PI3K/mTOR signaling pathway and ultimately promoting the milk fat synthesis in BMECs.

DNAJA1 positively regulates amino acid-stimulated milk protein and fat synthesis in bovine mammary epithelial cells

Several cellular processes, including the recovery of misfolded proteins, the folding of polypeptide chains, transit of polypeptides across the membrane, construction and disassembly of protein complexes, and modulation of protein control, are carried out by DnaJ homolog subfamily A member 1 (DNAJA1), which belongs to the DnaJ heat-shock protein family. It is unknown if DNAJA1 regulates the production of milk in bovine mammary epithelium cells (BMECs). Methionine and leucine increased DNAJA1 expression and nuclear location, as seen by us. In contrast to DNAJA1 knockdown, overexpression of DNAJA1 boosted the production of milk proteins and fats as well as mammalian target of rapamycin (mTOR) and sterol regulatory element binding protein-1c (SREBP-1c). As a result of amino acids, mTOR and SREBP-1c gene expression are stimulated, and DNAJA1 is a positive regulator of BMECs' amino acid-induced controlled milk protein and fat production.

MicroRNA-19a regulates milk fat metabolism by targeting SYT1 in bovine mammary epithelial cells

MicroRNAs (miRNAs) are important post-transcriptional factors involved in the regulation of gene expression and play crucial roles in biological processes related to milk fat metabolism. Our previous study revealed that miR-19a expression was significantly higher in the mammary epithelial cells of high-milk fat cows than in those of low-milk fat cows. However, the precise molecular mechanisms underlying these differences remain unclear. In this study, we found a high expression of miR-19a in the mammary tissues of dairy cows. The regulatory effects of miR-19a on bovine mammary epithelial cells (BMECs) were analyzed using cell counting kit-8 and 5-ethynyl-2'-deoxyuridine assays, which demonstrated that miR-19a significantly inhibited BMEC proliferation. Transfection of the miR-19a mimic into BMECs significantly upregulated the expression of milk fat marker genes LPL, SCAP, and SREBP1, promoting triglyceride (TG) synthesis and lipid droplet formation, whereas the miR-19a inhibitor exhibited the opposite function. TargetScan and miRWalk predictions revealed that synaptotagmin 1 (SYT1) is a target gene of miR-19a. A dual luciferase reporter gene assay, RT-qPCR, and western blot analyses revealed that miR-19a directly targets the 3'-untranslated region (UTR) of SYT1 and negatively regulates SYT1 expression. Functional validation revealed that overexpression of SYT1 in BMECs significantly downregulated the expression of LPL, SCAP, and SREBP1, and inhibited TG synthesis and lipid droplet formation. Conversely, the knockdown of SYT1 had the opposite effect. Altogether, miR-19a plays a crucial role in regulating the proliferation and differentiation of BMECs and regulates biological processes related to TG synthesis and lipid droplet formation by suppressing SYT1 expression. These findings provide a strong foundation for further research on the functional mechanisms underlying milk fat metabolism in dairy cows.

Stearic acid promotes lipid synthesis through CD36/Fyn/FAK/mTORC1 axis in bovine mammary epithelial cells

Stearic acid (C18:0, SA) is a saturated long-chain fatty acid (LCFA) that has a prominent function in lactating dairy cows. It is obtained primarily from the diet and is stored in the form of triacylglycerol (TAG) molecules. The transmembrane glycoprotein cluster of differentiation 36 (CD36) is also known as fatty acid translocase, but whether SA promotes lipid synthesis through CD36 and FAK/mTORC1 signaling is unknown. In this study, we examined the function and mechanism of CD36-mediated SA-induced lipid synthesis in bovine mammary epithelial cells (BMECs). SA-enriched supplements enhanced lipid synthesis and the FAK/mTORC1 pathway in BMECs. SA-induced lipid synthesis, FAK/mTORC1 signaling, and the expression of lipogenic genes were impaired by anti-CD36 and the CD36-specific inhibitor SSO, whereas overexpression of CD36 effected the opposite results. Inhibition of FAK/mTORC1 by TAE226/Rapamycin attenuated SA-induced TAG synthesis, inactivated FAK/mTORC1 signaling, and downregulated the lipogenic genes PPARG, CD36, ACSL1, SCD, GPAT4, LIPIN1, and DGAT1 at the mRNA and protein levels in BMECs. By coimmunoprecipitation and yeast two-hybrid screen, CD36 interacted directly with Fyn but not Lyn, and Fyn bound directly to FAK; FAK also interacted directly with TSC2. CD36 linked FAK through Fyn, and FAK coupled mTORC1 through TSC2 to form the CD36/Fyn/FAK/mTORC1 signaling axis. Thus, stearic acid promotes lipogenesis through CD36 and Fyn/FAK/mTORC1 signaling in BMECs. Our findings provide novel insights into the underlying molecular mechanisms by which LCFA supplements promote lipid synthesis in BMECs.

TWAS revealed significant causal loci for milk production and its composition in Murrah buffaloes

Milk yield is the most complex trait in dairy animals, and mapping all causal variants even with smallest effect sizes has been difficult with the genome-wide association study (GWAS) sample sizes available in geographical regions with small livestock holdings such as Indian sub-continent. However, Transcriptome-wide association studies (TWAS) could serve as an alternate for fine mapping of expression quantitative trait loci (eQTLs). This is a maiden attempt to identify milk production and its composition related genes using TWAS in Murrah buffaloes (Bubalus bubalis). TWAS was conducted on a test (N = 136) set of Murrah buffaloes genotyped through ddRAD sequencing. Their gene expression level was predicted using reference (N = 8) animals having both genotype and mammary epithelial cell (MEC) transcriptome information. Gene expression prediction was performed using Elastic-Net and Dirichlet Process Regression (DPR) model with fivefold cross-validation and without any cross-validation. DPR model without cross-validation predicted 80.92% of the total genes in the test group of Murrah buffaloes which was highest compared to other methods. TWAS in test individuals based on predicted gene expression, identified a significant association of one unique gene for Fat%, and two for SNF% at Bonferroni corrected threshold. The false discovery rates (FDR) corrected P-values of the top ten SNPs identified through GWAS were comparatively higher than TWAS. Gene ontology of TWAS-identified genes was performed to understand the function of these genes, it was revealed that milk production and composition genes were mainly involved in Relaxin, AMPK, and JAK-STAT signaling pathway, along with CCRI, and several key metabolic processes. The present study indicates that TWAS offers a lower false discovery rate and higher significant hits than GWAS for milk production and its composition traits. Hence, it is concluded that TWAS can be effectively used to identify genes and cis-SNPs in a population, which can be used for fabricating a low-density genomic chip for predicting milk production in Murrah buffaloes.

Evolutionary analysis of buffalo sterol regulatory element-binding factor (SREBF) family genes and their affection on milk traits

The sterol regulatory element-binding factor (SREBF) genes are a vital group of proteins binding to the sterol regulatory element 1 (SRE-1) regulating the synthesis of fatty acid. Two potential candidate genes (SREBF1 and SREBF2) have been identified as affecting milk traits. This study aims to identify the SREBF family of genes and find candidate markers or SREBF genes influencing lactation production in buffalo. A genome-wide study was performed and identified seven SREBF genes randomly distributed on 7 chromosomes and 24 protein isoforms in buffalos. The SREBF family of genes were also characterized in cattle, goat, sheep and horse, and using these all-protein sequences, a phylogenetic tree was built. The SREBF family genes were homologous between each other in the five livestock. Eight single nucleotide polymorphisms (SNPs) within or near the SREBF genes in the buffalo genome were identified and at least one milk production trait was associated with three of the SNP. The expression of SREBF genes at different lactation stages in buffalo and cattle from published data were compared and the SREBF genes retained a high expression throughout lactation with the trend being the same for buffalo and cattle. These results provide valuable information for clarifying the evolutionary relationship of the SREBF family genes and determining the role of SREBF genes in the regulation of milk production in buffalo.

Progress of Conjugated Linoleic Acid on Milk Fat Metabolism in Ruminants and Humans

As a valuable nutrient in milk, fat accounts for a significant proportion of the energy requirements of ruminants and is largely responsible for determining milk quality. Fatty acids (FAs) are a pivotal component of milk fat. Conjugated linoleic acid (CLA) is one of the naturally occurring FAs prevalent in ruminant dairy products and meat. Increasing attention has been given to CLA because of its anti-cancer, anti-inflammatory, immune regulation, and lipid metabolism regulation properties, and these benefits potentially contribute to the growth and health of infants. In breast milk, CLA is present in trace amounts, mainly in the form of cis-9, trans-11 CLA. Notably, cis-9, trans-11 CLA improves the milk fat rate while trans-10, cis-12 CLA inhibits it. Apart from having multiple physiological functions, CLA is also a pivotal factor in determining the milk quality of ruminants, especially milk fat rate. In response to growing interest in green and healthy functional foods, more and more researchers are exploring the potential of CLA to improve the production performance of animals and the nutritional value of livestock products. Taken together, it is novel and worthwhile to investigate how CLA regulates milk fat synthesis. It is the purpose of this review to clarify the necessity for studying CLA in ruminant milk fat and breast milk fat.

Leucine and arginine enhance milk fat and milk protein synthesis via the CaSR/Gi/mTORC1 and CaSR/Gq/mTORC1 pathways

BACKGROUND AND AIMS

Amino acids (AAs) not only constitute milk protein but also stimulate milk synthesis through the activation of mTORC1 signaling, but which amino acids that have the greatest impact on milk fat and protein synthesis is still very limited. In this study, we aimed to identify the most critical AAs involved in the regulation of milk synthesis and clarify how these AAs regulate milk synthesis through the G-protein-coupled receptors (GPCRs) signaling pathway.

METHODS

In this study, a mouse mammary epithelial cell line (HC11) and porcine mammary epithelial cells (PMECs) were selected as study subjects. After treatment with different AAs, the amount of milk protein and milk fat synthesis were detected. Activation of mTORC1 and GPCRs signaling induced by AAs was also investigated.

RESULTS

In this study, we demonstrate that essential amino acids (EAAs) are crucial to promote lactation by increasing the expression of genes and proteins related to milk synthesis, such as ACACA, FABP4, DGAT1, SREBP1, α-casein, β-casein, and WAP in HC11 cells and PMECs. In addition to activating mTORC1, EAAs uniquely regulate the expression of calcium-sensing receptor (CaSR) among all amino-acid-responsive GPCRs, which indicates a potential link between CaSR and the mTORC1 pathway in mammary gland epithelial cells. Compared with other EAAs, leucine and arginine had the greatest capacity to trigger GPCRs (p-ERK) and mTORC1 (p-S6K1) signaling in HC11 cells. In addition, CaSR and its downstream G proteins Gi, Gq, and Gβγ are involved in the regulation of leucine- and arginine-induced milk synthesis and mTORC1 activation. Taken together, our data suggest that leucine and arginine can efficiently trigger milk synthesis through the CaSR/Gi/mTORC1 and CaSR/Gq/mTORC1 pathways.

CONCLUSION

We found that the G-protein-coupled receptor CaSR is an important amino acid sensor in mammary epithelial cells. Leucine and arginine promote milk synthesis partially through the CaSR/Gi/mTORC1 and CaSR/Gq/mTORC1 signaling systems in mammary gland epithelial cells. Although this mechanism needs further verification, it is foreseeable that this mechanism may provide new insights into the regulation of milk synthesis.

Maternal sodium acetate supplementation promotes lactation performance of sows and their offspring growth performance

Milk yield and composition are critical determining factors for the early growth and development of neonates. The objective of this experiment was to comprehensively evaluate the effects of dietary sodium acetate (SA) supplementation on the milk yield and composition of sows and the growth performance of their offspring. A total of 80 sows (Landrace × Yorkshire, 3 to 6 parity) were randomly assigned to 2 groups (with or without 0.1% SA) from d 85 of gestation to d 21 of lactation. The result shows that maternal 0.1% SA supplementation significantly increased sows milk yield, milk fat, immunoglobulin A (IgA) and IgG content in milk (P < 0.05), with the up-regulation of short-chain fatty acids receptors (GPR41 and GPR43) expression and the activation of mammalian target of rapamycin complex C1 (mTORC1) signaling pathway. Consistently, in our in vitro experiment, SA also activated mTORC1 signaling in porcine mammary epithelial cells (P < 0.05). Furthermore, the improvement of milk quality and quantity caused by maternal SA supplementation led to the increase in body weight (BW) and average daily weight gain (ADG) of weaning piglets, with the improvement of gut health and colonization of the beneficial bacteria (P < 0.05). In conclusion, maternal supplementation of 0.1% SA improved the lactation performance (milk yield and milk fat) of sows, possibly with the activation of GPR41/GPR43-mTORC1 signaling. Furthermore, enhanced milk quality improved growth performance, gut health and the colonization of beneficial microbial flora of their piglets.

Genetics, environmental stress, and amino acid supplementation affect lactational performance via mTOR signaling pathway in bovine mammary epithelial cells

Mammary glands are known for their ability to convert nutrients present in the blood into milk contents. In cows, milk synthesis and the proliferation of cow mammary epithelial cells (CMECs) are regulated by various factors, including nutrients such as amino acids and glucose, hormones, and environmental stress. Amino acids, in particular, play a crucial role in regulating cell proliferation and casein synthesis in mammalian epithelial cells, apart from being building blocks for protein synthesis. Studies have shown that environmental factors, particularly heat stress, can negatively impact milk production performance in dairy cattle. The mammalian target of rapamycin complex 1 (mTORC1) pathway is considered the primary signaling pathway involved in regulating cell proliferation and milk protein and fat synthesis in cow mammary epithelial cells in response to amino acids and heat stress. Given the significant role played by the mTORC signaling pathway in milk synthesis and cell proliferation, this article briefly discusses the main regulatory genes, the impact of amino acids and heat stress on milk production performance, and the regulation of mTORC signaling pathway in cow mammary epithelial cells.

Review: Effect of essential fatty acids and conjugated linoleic acid on the adaptive physiology of dairy cows during the transition period

Cows fed total mixed rations (silage-based) may not receive as much essential fatty acids (EFAs) and conjugated linoleic acids (CLAs) as cows fed pasture-based rations (fresh grass) containing rich sources of polyunsaturated fatty acids. CLA-induced milk fat depression allows dairy cows to conserve more metabolisable energy, thereby shortening the state of negative energy balance and reducing excessive fat mobilisation at early lactation. EFAs, particularly α-linolenic acid, exert anti-inflammatory and antioxidative properties, thereby modulating immune functions. Thus, combined EFA and CLA supplementation seems to be an effective nutritional strategy to relieve energy metabolism and to improve immune response, which are often compromised during the transition from late pregnancy to lactation in high-yielding dairy cows. There has been extensive research on this idea over the last two decades, and despite promising results, several interfering factors have led to varying findings, making it difficult to conclude whether and under what conditions EFA and CLA supplementations are beneficial for dairy cows during the transition period. This article reviews the latest studies on the effects of EFA and CLA supplementation, alone or in combination, on dairy cow metabolism and health during various stages around parturition. Our review article summarises and provides novel insights into the mechanisms by which EFA and/or CLA influence markers of metabolism, energy homeostasis and partitioning, immunity, and inflammation revealed by a deep molecular phenotyping.

Transcriptome Profile in Dairy Cows Resistant or Sensitive to Milk Fat Depression

Feeding linseed to dairy cows results in milk fat depression (MFD), but there is a wide range of sensitivity among cows. The objectives of this study were to identify target genes containing SNP that may play a key role in the regulation of milk fat synthesis in cows resistant or sensitive to MFD. Four cows were selected from a dairy farm after a switch from a control diet to a linseed-rich diet; two were resistant to MFD with a high milk fat content in the control (4.06%) and linseed-rich (3.90%) diets; and two were sensitive to MFD with the milk fat content decreasing after the change from the control (3.87%) to linseed-rich (2.52%) diets. Transcriptome and SNP discovery analyses were performed using RNA-sequencing technology. There was a large number of differentially expressed genes in the control (n = 1316) and linseed-rich (n = 1888) diets. Of these, 15 genes were detected as key gene regulators and harboring SNP in the linseed-rich diet. The selected genes MTOR, PDPK1, EREG, NOTCH1, ZNF217 and TGFB3 may form a network with a principal axis PI3K/Akt/MTOR/SREBP1 involved in milk fat synthesis and in the response to diets that induced MFD. These 15 genes are novel candidate genes to be involved in the resistance or sensitivity of dairy cows to milk fat depression.

Overexpression of DGAT2 Regulates the Differentiation of Bovine Preadipocytes

Triacylglycerols (TAGs) are a major component of intramuscular fat. Diacylglycerol O-acyltransferase 2(DGAT2) expression determines the rate of TAG synthesis. The purpose of this study was to investigate the role of DGAT2 in the differentiation of Yanbian cattle preadipocytes and lipid metabolism-related signalling pathways. Bovine preadipocytes were infected with overexpression and interfering adenovirus vectors of DGAT2. The effects on the differentiation of Yanbian cattle preadipocytes were examined using molecular and transcriptomic techniques, including differentially expressed genes (DEGs) and Kyoto Encyclopaedia of Genes and Genomes (KEGG) pathway analysis. DGAT2 overexpression significantly increased (p < 0.05) intracellular TAG, adiponectin, and lipid droplet (LD) contents. Moreover, it upregulated (p < 0.05) peroxisome proliferator-activated receptor γ (PPARγ), CCAAT/enhancer binding protein α, and fatty acid binding protein 4 mRNA expression. In contrast, DGAT2 knockdown reduced intracellular TAG and LD content and downregulated (p < 0.05) C/EBPβ, mannosyl (alpha-1,3-)-glycoproteinbeta-1,2-N-acetylglucosaminyltransferase, lipin 1,1-acylglycerol-3-phosphate O-acyltransferase 4, and acetyl-CoA carboxylase alpha mRNA expression. Between DGAT2-overexpressing preadipocytes and normal cells, 208 DEGs were identified, including 106 upregulated and 102 downregulated genes. KEGG pathway analysis revealed DEGs mainly enriched in PPAR signalling and AMP-activated protein kinase pathways, cholesterol metabolism, and fatty acid biosynthesis. These results demonstrated that DGAT2 regulated preadipocyte differentiation and LD and TAG accumulation by mediating the expression of adipose differentiation-, lipid metabolism-, and fatty acid synthesis-related genes.

Niacin/β-hydroxybutyrate regulates milk fat and milk protein synthesis via the GPR109A/Gi/mTORC1 pathway

As a crucial receptor of BHBA and niacin, GPR109A is largely expressed in the mammary gland. However, the role of GPR109A in milk synthesis and its underlying mechanism is still largely unknown. In this study, we first investigated the effect of GPR109A agonists (niacin/BHBA) on milk fat and milk protein synthesis in a mouse mammary epithelial cell line (HC11) and PMECs (porcine mammary epithelial cells). The results showed that both niacin and BHBA promote milk fat and milk protein synthesis with the activation of mTORC1 signaling. Importantly, knockdown GPR109A attenuated the niacin-induced increase of milk fat and protein synthesis and the niacin-induced activation of mTORC1 signaling. Furthermore, we found that GPR109A downstream G protein-G_αi and -G_βγ participated in the regulation of milk synthesis and the activation of mTORC1 signaling. Consistent with the finding in vitro, dietary supplementation with niacin increases milk fat and protein synthesis in mice with the activation of GPR109A-mTORC1 signaling. Collectively, GPR109A agonists promote the synthesis of milk fat and milk protein through the GPR109A/G_i/mTORC1 signaling pathway.

Sodium acetate regulates milk fat synthesis through the activation of GPR41/GPR43 signaling pathway

Background

Fat is a critical component in milk, which provided energy for the early growth and development of mammals. Milk fat is positively related to the concentration of acetate in the blood, while the underlying mechanism is still unclear.

Objective

This study is to investigate the effects of sodium acetate (NaAc) on milk fat synthesis in the mammary gland, and explored the underlying mechanism.

Methods

In vitro experiments were carried out in mouse mammary epithelial cell line (HC11) cells cultured with NaAc to explore the potential pathway of NaAc on milk fat synthesis. Furthermore, 24 pregnant mice (from d 18.5 of gestation to d 7 of lactation, exposed to 200 mM NaAc drinking water) were used as an in vivo model to verify the results.

Results

In this study, we found that NaAc promoted milk fat synthesis and the expression of related genes and proteins in HC11 mammary epithelial cells with the activation of GPCR and mTORC1 signaling pathways (p &lt; 0.05). Pretreatment with the mTORC1 inhibitors and G protein inhibitors attenuated the NaAc-induced milk fat synthesis in HC11 mammary epithelial cells (p &lt; 0.05). Importantly, the effect of NaAc on milk synthesis was attenuated in GPR41 and GPR43 knockdown HC11 mammary epithelial cells (p &lt; 0.05). This evidence indicates that NaAc might regulate milk fat synthesis through the GPR41/GPR43-mTORC1 pathway. Consistently, in in vivo experiment, dietary supplementation with NaAc significantly increased milk fat content and fat synthesis-related proteins in mice mammary glands with the activation of mTORC1 and GPCR signaling pathways at peak lactation (p &lt; 0.05).

Conclusion

The addition of NaAc promoted the increase of milk fat synthesis in HC11 mammary epithelial cells and mice mammary glands at peak lactation. Mechanistically, NaAc activates GPR41 and GPR43 receptors, leading to the activation of the mTORC1 signaling pathway to promote the synthesis of milk fat.

Comparative Genomic Analysis of the Thiolase Family and Functional Characterization of the Acetyl-Coenzyme A Acyltransferase-1 Gene for Milk Biosynthesis and Production of Buffalo and Cattle

Cattle and buffalo served as the first and second largest dairy animals, respectively, providing 96% milk products worldwide. Understanding the mechanisms underlying milk synthesis is critical to develop the technique to improve milk production. Thiolases, also known as acetyl-coenzyme A acetyltransferases (ACAT), are an enzyme family that plays vital roles in lipid metabolism, including ACAT1, ACAT2, ACAA1, ACAA2, and HADHB. Our present study showed that these five members were orthologous in six livestock species including buffalo and cattle. Transcriptomic data analyses derived from different lactations stages showed that ACAA1 displayed different expression patterns between buffalo and cattle. Immunohistochemistry staining revealed that ACAA1 were dominantly located in the mammary epithelial cells of these two dairy animals. Knockdown of ACAA1 inhibited mammary epithelial cell proliferation and triglyceride and β-casein secretion by regulating related gene expressions in cattle and buffalo. In contrast, ACAA1 overexpression promoted cell proliferation and triglyceride secretion. Finally, three novel SNPs (g.-681A>T, g.-23117C>T, and g.-24348G>T) were detected and showed significant association with milk production traits of Mediterranean buffaloes. In addition, g.-681A>T mutation located in the promoter region changed transcriptional activity significantly. Our findings suggested that ACAA1 play a key role in regulating buffalo and cattle milk synthesis and provided basic information to further understand the dairy animal lactation physiology.

Novel Insight into the Role of Squalene Epoxidase (SQLE) Gene in Determining Milk Production Traits in Buffalo

Understanding the genetic mechanisms underlying milk production traits contribute to improving the production potential of dairy animals. Squalene epoxidase (SQLE) is one of the rate-limiting enzymes for cholesterol biosynthesis and was highly expressed in the buffalo mammary. The objectives of the present study were to detect the polymorphisms within SQLE in buffalo, the genetic effects of these mutations on milk production traits, and to understand the gene regulatory effects on buffalo mammary epithelial cells (BuMECs). A total of five SNPs were identified by sequencing, g.18858G > A loci were significantly associated with fat yield, and g.22834C > T loci were significantly associated with peak milk yield, milk yield, fat yield, and protein yield. Notably, linkage disequilibrium analysis indicated that 2 SNPs (g.18858G > A and g.22834C > T) formed one haplotype block, which was found to be significantly associated with milk fat yield, fat percentage, and protein yield. Furthermore, expression of SQLE was measured in different tissues of buffalo and was found to be higher in the mammary. Knockdown of SQLE gene expression significantly affected the growth of BuMECs, including proliferation, cell cycle, and apoptosis, and significantly downregulated the expression of related genes MYC, PCNA, and P21. In addition, knockdown of the SQLE gene significantly reduces triglyceride concentrations and the signal intensity of oil red O staining. In addition, silencing of SQLE was also found to regulate the synthesis and secretion of β-casein and κ-casein negatively. Furthermore, SQLE knockdown is accompanied by the downregulation of critical genes (RPS6KB1, JAK2, eIF4E, and SREBP1) related to milk fat and protein synthesis. The current study showed the potential of the SQLE gene as a candidate for buffalo milk production traits. It provides a new understanding of the physiological mechanisms underlying buffalo milk production regulation.

Enhancing Milk Production by Nutrient Supplements: Strategies and Regulatory Pathways

The enhancement of milk production is essential for dairy animals, and nutrient supplements can enhance milk production. This work summarizes the influence of nutrient supplements-including amino acids, peptides, lipids, carbohydrates, and other chemicals (such as phenolic compounds, prolactin, estrogen and growth factors)-on milk production. We also attempt to provide possible illuminating insights into the subsequent effects of nutrient supplements on milk synthesis. This work may help understand the strategy and the regulatory pathway of milk production promotion. Specifically, we summarize the roles and related pathways of nutrients in promoting milk protein and fat synthesis. We hope this review will help people understand the relationship between nutritional supplementation and milk production.

Nuciferine Ameliorates Nonesterified Fatty Acid-Induced Bovine Mammary Epithelial Cell Lipid Accumulation, Apoptosis, and Impaired Migration via Activating LKB1/AMPK Signaling Pathway

High blood concentrations of nonesterified fatty acids (NEFAs) provoke various metabolic disorders and are associated with mammary tissue injury and decreased milk production in dairy cows. Nuciferine, an alkaloid found in Nelumbo nucifera leaves, has great potential for correcting lipid metabolism derangements and lipotoxicity. In this study, we evaluated the lipotoxicity induced by excessive NEFA in bovine mammary epithelial cells (bMECs) and investigated whether nuciferine alleviates NEFA-induced lipotoxicity and the underlying molecular mechanisms. We found that excessive NEFA (1.2 and 2.4 mM) induced lipid accumulation, apoptosis, and migration ability impairment in bMECs, whereas nuciferine could ameliorate these disarrangements, as indicated by decreasing triglyceride content, protein abundance of SREBP-1c, cytoplasmic cytochrome c, and cleaved caspase-3 and increasing protein abundance of PPARα and migration ability. Moreover, nuciferine could reverse NEFA-induced LKB1/AMPK signaling inhibition, and the protective effect of nuciferine on lipotoxicity caused by NEFA was abrogated by AMPK inhibitor dorsomorphin. Furthermore, transfection with LKB1 siRNA (si-LKB1) largely abolished the activation effect of nuciferine on AMPK. Overall, nuciferine can protect bMECs from excessive NEFA-induced lipid accumulation, apoptosis, and impaired migration by activating LKB1/AMPK signaling pathway.

Sodium acetate promotes fat synthesis by suppressing TATA element modulatory factor 1 in bovine mammary epithelial cells

Short-chain fatty acids are important nutrients that regulate milk fat synthesis. They regulate milk synthesis via the sterol regulatory element binding protein 1 (SREBP1) pathway; however, the details are still unknown. Here, the regulation and mechanism of sodium acetate (SA) in milk fat synthesis in bovine mammary epithelial cells (BMECs) were assessed. BMECs were treated with SA supplementation (SA+) or without SA supplementation (SA-), and milk fat synthesis and activation of the SREBP1 pathway were increased (P = 0.0045; P = 0.0042) by SA+ and decreased (P = 0.0068; P = 0.0031) by SA-, respectively. Overexpression or inhibition of SREBP1 demonstrated that SA promoted milk fat synthesis (P = 0.0045) via the SREBP1 pathway. Overexpression or inhibition of TATA element modulatory factor 1 (TMF1) demonstrated that TMF1 suppressed activation of the SREBP1 pathway (P = 0.0001) and milk fat synthesis (P = 0.0022) activated by SA+. Overexpression or inhibition of TMF1 and SREBP1 showed that TMF1 suppressed milk fat synthesis (P = 0.0073) through the SREBP1 pathway. Coimmunoprecipitation analysis revealed that TMF1 interacted with SREBP1 in the cytoplasm and suppressed the nuclear localization of SREBP1 (P = 0.0066). The absence or presence of SA demonstrated that SA inhibited the expression of TMF1 (P = 0.0002) and the interaction between TMF1 and SREBP1 (P = 0.0001). Collectively, our research suggested that TMF1 was a new negative regulator of milk fat synthesis. In BMECs, SA promoted the SREBP1 pathway and milk fat synthesis by suppressing TMF1. This study enhances the current understanding of the regulation of milk fat synthesis and provides new scientific data for the regulation of milk fat synthesis.

Lithium Chloride Promotes Milk Protein and Fat Synthesis in Bovine Mammary Epithelial Cells via HIF-1α and β-Catenin Signaling Pathways

Lithium is one of the trace elements with many physiological properties, such as being anti-cancer, anti-viral, and anti-inflammatory. However, little is known about its effect on milk synthesis during lactation. Therefore, we selected different concentrations (5 mM, 10 mM, and 20 mM) of lithium chloride (LiCl) and assessed the effect of LiCl on bovine mammary epithelial (MAC-T) cells that underwent 4 days of differentiation induction. Moreover, we analyzed the effect of LiCl on the expression of genes related to milk fat and milk protein synthesis. Herein, LiCl (5-20 mM) significantly increased the expression of β-casein, promoted mRNA expression and phosphorylated protein expression of the signal transduction molecule and activator of transcription 5β (STAT5-β), and inhibited mRNA and protein expression of suppressor of cytokine signaling 2 (SOCS2). In contrast, 5 and 10 mM LiCl significantly inhibited expression of SOCS3. LiCl at concentration of 5-20 mM enhanced phosphorylation level of mTOR protein; at 10 mM and 20 mM, LiCl significantly promoted expression and phosphorylation of downstream ribosomal protein S6 kinase beta-1 (S6K1) protein. Considering milk fat synthesis, mRNA expression of acetyl CoA carboxylase (ACC) and lipoprotein lipase (LPL) genes was considerably increased in the presence of LiCl (5-20 mM). Additionally, increased protein expression levels of stearoyl-CoA desaturase (SCD), peroxisome proliferator-activated receptor-γ (PPARγ), and sterol regulatory element-binding protein 1 (SREBP1) were observed at all LiCl concentrations tested. Subsequently, LiCl (5-20 mM) significantly promoted protein expression and phosphorylation of β-catenin, while 10 mM and 20 mM of LiCl significantly promoted protein expression of hypoxia-inducible factor-1α (HIF-1α). Collectively, it has been shown that 10 mM LiCl can effectively activate HIF-1α, β-catenin, and β-catenin downstream signaling pathways. Conversely, at 10 mM, LiCl inhibited SOCS2 and SOCS3 protein expression through JAK2/STAT5, mTOR, and SREBP1 signaling pathways, improving synthesis of milk protein and fat. Therefore, LiCl can be used as a potential nutrient to regulate milk synthesis in dairy cows.

Acetate-Induced Milk Fat Synthesis Is Associated with Activation of the mTOR Signaling Pathway in Bovine Mammary Epithelial Cells

Acetate is a precursor substance for fatty acid synthesis in bovine mammary epithelial cells (BMECs), and the mTOR signaling pathway plays an important role in milk fat synthesis. However, the mechanism of the regulatory effects of acetate on lipogenic genes via the mTOR signaling pathway in BMEC remains unknown. We hypothesized that acetate can enhance the expression of lipogenic genes and triglyceride (TG) production by activating the mTOR signaling pathway in BMECs. Therefore, the aim of this study was to investigate the network of acetate-regulated lipid metabolism by the mTOR signaling pathway in BMECs. These results showed that TG synthesis was elevated (p < 0.01) in BMECs with acetate treatment. The lipid droplets were increased in the acetate-treated groups compared with those in the control group through the Bodipy staining of the lipids. In addition, the fatty acid profile in BMECs treated with acetate was affected, with an elevation in the proportions of C14:0, C16:0, and C18:0. The mRNA levels of the sterol-response-element-binding protein 1 (SREBP1), stearoyl-CoA desaturase 1 (SCD1), and fatty acid synthase (FAS) genes involved in the lipogenesis and transcriptional factors were upregulated (p < 0.05) in BMECs with acetate treatment. Remarkably, the expression of acetyl-CoA carboxylase α (ACCα) and FAS rate-limiting enzymes involved in lipogenesis was upregulated in BMECs with acetate treatment. Moreover, the addition of acetate enhanced the key protein expression of S6K1, which is related to the mTOR signaling pathway. Taken together, our data suggest that TG accumulation and expression of lipogenic genes induced by acetate are associated with the activation of the mTOR signaling pathway, which provides new insights into the understanding of the molecular mechanism in the expression of mTOR-signaling-pathway-regulated lipogenic genes.

CIDEA Regulates De Novo Fatty Acid Synthesis in Bovine Mammary Epithelial Cells by Targeting the AMPK/PPARγ Axis and Regulating SREBP1

Cell-death-inducing DNA fragmentation factor-α-like effector A (CIDEA) is a lipid-droplet-associated protein that helps to promote lipid metabolism in adipocytes of mice and humans. However, studies on the regulatory mechanism of CIDEA on lipid metabolism in the mammary glands of dairy cows are rare. Therefore, the role of CIDEA in bovine mammary epithelial cells (bMECs) was investigated in this study. The CIDEA expression levels in the mammary glands of high-fat-milk-producing cows were significantly higher compared to those in low-fat-milk-producing cows. Results of in vitro studies in bMECs showed that the inhibition of CIDEA inhibited the expression of fatty acid synthesis-related genes and triglyceride (TAG) synthesis-related genes. Conversely, the overexpression of CIDEA leads to an increase in the content of TAG and fatty acid. The results of mechanistic studies indicated that the overexpression of CIDEA inhibits AMP-activated protein kinase (AMPK) activity, which enhances the expression of peroxisome proliferator-activated receptor-γ (PPARγ) and consequently increases the TAG content. Furthermore, the overexpression of CIDEA promoted the nuclear translocation of sterol regulatory element-binding protein 1 (SREBP1). Therefore, a theoretical framework is provided by this study for the regulation of lipid metabolism in dairy cows by means of nutrition and the hormone targeting of CIDEA.

AMPK-ChREBP axis mediates de novo milk fatty acid synthesis promoted by glucose in the mammary gland of lactating goats

To investigate the role of glucose in regulating milk fatty acid synthesis, 6 lactating Guanzhong dairy goats were infused with 0, 60, or 100 g/d glucose via the external pubic artery in a 3 × 3 repeated Latin square experiment. A concomitant in vitro experiment was conducted to investigate possible mechanisms whereby glucose regulates milk fatty acid synthesis. RNA sequencing was used for cellular transcriptome analysis. Drugs, MK-2206, rapamycin, and dorsomorphin were used to block cellular mammalian AMP-activated protein kinase (AMPK), AKT serine/threonine kinase 1, and mechanistic target of rapamycin kinase signaling pathways, respectively. Carbohydrate response element binding protein (ChREBP) was knockdown and overexpressed to investigate its role in regulating milk fatty acid synthesis in mammary epithelial cells. Glucose infusion linearly elevated the concentration of C8:0 (P = 0.039) and C10:0 (P = 0.041) in milk fat while it linearly decreased (P = 0.049) that of C16:0. This result was in agreement with the upregulation of genes related to de novo synthesis of fatty acids and lipid droplet formation, including adipose differentiation-related protein, butyrophilin subfamily 1 member A1, fatty acid synthase (FASN) and ChREBP. Their expression increased (P < 0.05) linearly in the lactating goat mammary gland. In vitro, glucose linearly stimulated the expression of genes related to de novo synthesis of fatty acids and cellular triacylglycerol in cultured mammary epithelial cells. RNA sequencing and inhibition studies revealed that glucose induced transcriptomic changes increasing lipogenic pathways, with AMPK responding to glucose by controlling ChREBP and FASN. Knockdown and overexpression of ChREBP highlighted its essential role in lipogenesis. The knockdown and overexpression of ChREBP protein also revealed an essential role in regulating the de novo synthesis of fatty acids. Collectively, our data highlight that glucose supplementation promotes de novo fatty acid synthesis via the AMPK-ChREBP axis, hence increasing milk fat yield in the goat mammary gland. Results from the current study provide possible strategies to manipulate the fatty acid composition as well as improve ruminant milk quality.

GPRC6A is a key mediator of palmitic acid regulation of lipid synthesis in bovine mammary epithelial cells

Fatty acids (FAs) can promote lipid synthesis in the mammary gland via stimulating lipogenic gene expression, but the underlying molecular mechanism is still not fully understood. Here, we showed the dose-dependent effects of palmitic acid (PA) on lipid synthesis in primary bovine mammary epithelial cells (BMECs) and explored the corresponding molecular mechanism. BMECs were treated with PA (0, 50, 100, 150, and 200 μM), and the 100 μM treatment had the best stimulatory effect on lipid synthesis and expression and maturation of sterol regulatory element-binding protein 1c (SREBP-1c) in cells. Inhibition of phosphatidylinositol 3-kinase (PI3K) almost totally blocked the stimulation of PA on SREBP-1c expression, whereas protein kinase Cα (PKCα) knockdown only partially decreased the stimulation of PA on SREBP-1c expression but abolished the stimulation of PA on its maturation. Knockdown of GPR120 did not change the stimulation of PA on the SREBP-1c signaling. G protein-coupled receptor family C group 6 member A  (GPRC6A) knockdown almost totally blocked the stimulation of FA on PI3K and PKCα phosphorylation as well as SREBP-1c expression and maturation. Furthermore, PA dose-dependently promoted GPRC6A expression and plasma membrane localization. Together, these above results reveal that GPRC6A is a key mediator of PA signaling to lipid synthesis in BMECs via the PI3K/PKCα-SREBP-1c pathways.

Tissue-Specific Expression of Circ_015343 and Its Inhibitory Effect on Mammary Epithelial Cells in Sheep

Circular RNAs (circRNAs) are a kind of non-coding RNA that have an important molecular function in mammary gland development and lactation of mammals. In our previous study, circ_015343 was found to be highly expressed in the ovine mammary gland tissue at the peak-lactation period by using RNA sequencing (RNA-seq). In the present study, the authenticity of circ_015343 was confirmed by using reverse transcriptase-polymerase chain reaction (RT-PCR) analysis and Sanger sequencing. The circ_015343 was derived from the complete 10 exons of aminoadipic semialdehyde synthase (AASS), ranging from exon 2 to exon 11 and mainly located in cytoplasm of ovine mammary epithelial cells. The circRNA was found to be expressed in eight ovine tissues, with the highest expression level in the mammary gland and the least expression in Longissimus dorsi muscle. The circ_015343 had a lower level of expression in a sheep breed with higher milk yield and milk fat content. The disturbed circ_015343 increased the viability and proliferation of the ovine mammary epithelial cells. The inhibition of circ_015343 also increased the expression levels of three milk fat synthesis marker genes: acetyl-coenzyme A carboxylase alpha (ACACA), fatty acid-binding protein 4 (FABP4), and sterol regulatory element-binding protein 1 (SREBP1), as well as three proliferation-related genes: cyclin dependent kinase 2 (CDK2), cyclin dependent kinase 4 (CDK4) and proliferating cell nuclear antigen (PCNA), but decreased the expression level of its parent gene AASS. A circRNA-miRNA-mRNA interaction network showed that circ_015343 would bind some microRNAs (miRNAs) to regulate the expression of functional genes related to the development of mammary gland and lactation. This study contributes to a better understanding of the roles of circ_015343 in the mammary gland of sheep.

Isoleucine stimulates mTOR and SREBP-1c gene expression for milk synthesis in mammary epithelial cells through BRG1-mediated chromatin remodelling

Several amino acids can stimulate milk synthesis in mammary epithelial cells (MEC); however, the regulatory role of isoleucine (Ile) and underlying molecular mechanism remain poorly understood. In this study, we aimed to evaluate the regulatory effects of Ile on milk protein and fat synthesis in MEC and reveal the mediation mechanism of Brahma-related gene 1 (BRG1) on this regulation. Ile dose dependently affected milk protein and fat synthesis, mechanistic target of rapamycin (mTOR) phosphorylation, sterol regulatory element binding protein 1c (SREBP-1c) expression and maturation, and BRG1 protein expression in bovine MEC. Phosphatidylinositol 3 kinase (PI3K) inhibition by LY294002 treatment blocked the stimulation of Ile on BRG1 expression. BRG1 knockdown and gene activation experiments showed that it mediated the stimulation of Ile on milk protein and fat synthesis, mTOR phosphorylation, and SREBP-1c expression and maturation in MEC. ChIP-PCR analysis detected that BRG1 bound to the promoters of mTOR and SREBP-1c, and ChIP-qPCR further detected that these bindings were increased by Ile stimulation. In addition, BRG1 positively regulated the binding of H3K27ac to these two promoters, while it negatively affected the binding of H3K27me3 to these promoters. BRG1 knockdown blocked the stimulation of Ile on these two gene expressions. The expression of BRG1 was higher in mouse mammary gland in the lactating period, compared with that in the puberty or dry period. Taken together, these experimental data reveal that Ile stimulates milk protein and fat synthesis in MEC via the PI3K-BRG1-mTOR/SREBP-1c pathway.

14-3-3β is essential for milk composition stimulated by Leu/IGF-1 via IGF1R signaling pathway in BMECs

The cell proliferation of bovine mammary epithelial cells (BMECs) and consequent milk synthesis are regulated by multiple factors. The purpose of this study was to examine the effect of 14-3-3β on cellular proliferation and milk fat/β-casein synthesis in BMECs and reveal its underlying mechanisms. In this study, we employed gene function analysis to explore the regulatory effect and molecular mechanisms of 14-3-3β on milk synthesis and proliferation in BMECs. We found that leucine and IGF-1 enhance cell proliferation and milk synthesis in a 14-3-3β-dependent manner and only exhibiting such effect in the presence of 14-3-3β. We further determined that 14-3-3β interacts with the IGF1R self-phosphorylation site and it additionally mediated leucine and IGF-1 to stimulate the synthesis of milk through the IGF1R-AKT-mTORC1 signaling pathway. In summary, our data indicated that 14-3-3β mediates the expression of milk fat and protein stimulated by leucine and IGF-1, leading to lactogenesis through IGF1R signaling pathway in BMECs.

Stearic Acid Activates the PI3K-mTOR-4EBP1/S6K and mTOR-SREBP-1 Signaling Axes through FATP4-CDK1 To Promote Milk Synthesis in Primary Bovine Mammary Epithelial Cells

Stearic acid (SA), an 18-carbon long-chain saturated fatty acid, has great potential for promoting lactation. Therefore, this study investigates the effects and mechanism of SA on milk synthesis in primary bovine mammary epithelial cells (BMECs). In our study, we found that SA significantly increased β-casein and triglycerides, and the effect was most significant at 100 μM. Signaling pathway studies have found that SA affects milk synthesis by upregulating cyclin-dependent kinase 1 (CDK1) to activate PI3K-mTOR-4EBP1/S6K and mTOR-SREBP-1 pathways. Furthermore, we detected fatty acid transport proteins (FATPs) when BMECs were treated with SA; the mRNA levels of FATP3 (3.713 ± 0.583) and FATP4 (40.815 ± 8.959) were significantly upregulated at 100 μM. Subsequently, we constructed FATP4-siRNA and found that SA was transported by FATP4 into BMECs, promoting milk synthesis. Collectively, these results revealed that SA activated PI3K-mTOR-4EBP1/S6K and mTOR-SREBP-1 signaling axes through FATP4-CDK1 to promote milk synthesis in BMECs.

Energy deprivation-induced AMPK activation inhibits milk synthesis by targeting PrlR and PGC-1α

Background

The mammary gland is responsible for milk production and secretion, which is critical for neonatal health during lactation. Lactation efficiency is largely affected by energy status with unclear mechanism.

Results

In the current study, we found that synthesis of milk fat and protein was significantly inhibited under energy-deficient conditions, which is accompanied with AMP-activated protein kinase (AMPK) activation. Modulating the AMPK signaling pathway directly or indirectly affects the synthesis of milk fat and protein. Besides mammalian target of rapamycin complex 1 (mTORC1) signaling in the regulation of milk synthesis, we discovered that AMPK mainly regulates the synthesis of milk protein through prolactin signaling. Mechanistically, AMPK triggers the ubiquitination of prolactin receptor (PrlR) through regulating the activity of β-transducin repeat-containing protein (β-TrCP, an E3 ligase). Subsequently, PrlR is degraded by the endocytosis process of lysosomes, which further attenuates prolactin signaling. In addition, our results revealed that AMPK activation inhibits milk fat synthesis through decreasing and accelerating de novo synthesis and β-oxidation of fatty acids, respectively. To be precise, AMPK activation inhibits rate limiting enzymes and transcriptional regulatory factors involved in de novo fatty acid synthesis and decreases the acetylation process of peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α) to strengthen the oxidation of fatty acids.

Conclusions

Taken together, AMPK regulates the synthesis of milk not only depends on canonical mTORC1 signaling and key rate-limiting enzymes, but also through manipulating the degradation of PrlR and the acetylation of PGC-1α.

Regulation of Key Genes for Milk Fat Synthesis in Ruminants

Milk fat is the most important and energy-rich substance in milk and plays an important role in the metabolism of nutrients during human growth and development. It is mainly used in the production of butter and yogurt. Milk fat not only affects the flavor and nutritional value of milk, but also is the main target trait of ruminant breeding. There are many key genes involve in ruminant milk fat synthesis, including ACSS2, FASN, ACACA, CD36, ACSL, SLC27A, FABP3, SCD, GPAM, AGPAT, LPIN, DGAT1, PLIN2, XDH, and BTN1A1. Taking the de novo synthesis of fatty acids (FA) and intaking of long-chain fatty acids (LCFA) in blood to the end of lipid droplet secretion as the mainline, this manuscript elucidates the complex regulation model of key genes in mammary epithelial cells (MECs) in ruminant milk fat synthesis, and constructs the whole regulatory network of milk fat synthesis, to provide valuable theoretical basis and research ideas for the study of milk fat regulation mechanism of ruminants.

Circadian Gene PER2 Silencing Downregulates PPARG and SREBF1 and Suppresses Lipid Synthesis in Bovine Mammary Epithelial Cells

Simple Summary

The present study was constructed to determine the effects of the core circadian clock gene, Period 2 (PER2), on lipid synthesis in bovine mammary epithelial cells (BMECs). Data revealed that PER2-regulated genes were involved in fatty acid de novo synthesis, desaturation, TAG accumulation, and lipid droplet secretion in primary BMECs, partly by inhibiting PPARG and SREBF1. Our overall data suggests that PER2 in bovine mammary cells plays a role in regulating milk fat synthesis directly, or via the activation of the transcription regulators PPARG and SREBF1. This study provides molecular evidence underscoring a link between the circadian clock and lipid metabolism in bovines.

Abstract

PER2, a circadian clock gene, is associated with mammary gland development and lipid synthesis in rodents, partly via regulating peroxisome proliferator-activated receptor gamma (PPARG). Whether such a type of molecular link existed in bovines was unclear. We hypothesized that PER2 was associated with lipid metabolism and regulated cell cycles and apoptosis in bovine mammary epithelial cells (BMECs). To test this hypothesis, BMECs isolated from three mid-lactation (average 110 d postpartum) cows were used. The transient transfection of small interfering RNA (siRNA) was used to inhibit PER2 transcription in primary BMECs. The silencing of PER2 led to lower concentrations of cellular lipid droplets and triacylglycerol along with the downregulation of lipogenic-related genes such as ACACA, FASN, LPIN1, and SCD, suggesting an overall inhibition of lipogenesis and desaturation. The downregulation of PPARG and SREBF1 in response to PER2 silencing underscored the importance of circadian clock signaling and the transcriptional regulation of lipogenesis. Although the proliferation of BMECs was not influenced by PER2 silencing, the number of cells in the G2/GM phase was upregulated. PER2 silencing did not affect cell apoptosis. Overall, the data provided evidence that PER2 participated in the coordination of mammary lipid metabolism and was potentially a component of the control of lipid droplets and TAG synthesis in ruminant mammary cells. The present data suggested that such an effect could occur through direct effects on transcriptional regulators.

Multi-Omics Analysis of Mammary Metabolic Changes in Dairy Cows Exposed to Hypoxia

Hypoxia exposure can cause a series of physiological and biochemical reactions in the organism and cells. Our previous studies found the milk fat rate increased significantly in hypoxic dairy cows, however, its specific metabolic mechanism is unclear. In this experiment, we explored and verified the mechanism of hypoxia adaptation based on the apparent and omics results of animal experiments and in vitro cell model. The results revealed that hypoxia exposure was associated with the elevation of AGPAT2-mediated glycerophospholipid metabolism. These intracellular metabolic disorders consequently led to the lipid disorders associated with apoptosis. Our findings update the existing understanding of increased adaptability of dairy cows exposure to hypoxia at the metabolic level.

Liver X receptor α promotes milk fat synthesis in buffalo mammary epithelial cells by regulating the expression of FASN

Liver X receptor α (LXRα; NR1H3) is an important transcription factor that can facilitate milk fat synthesis by regulating the transcription of FASN in mice and goats. Nevertheless, the lipid synthesis related to LXRα and its regulation on FASN in the buffalo mammary gland remain elusive. Here, we demonstrated that the mRNA and protein expression of LXRα in buffalo mammary tissue increased in lactation compared with that in the dry-off period. Overexpression of NR1H3 enhanced the lipid droplet formation and triacylglycerol concentration in buffalo mammary epithelial cells (BuMEC), whereas the knockdown of NR1H3 resulted in a decrease in the number of lipid droplets. At the same time, NR1H3 also affected the expression of regulatory factors (INSIG1, INSIG2, SREBF1, and PPARG) related to milk fat synthesis and that of genes involved in de novo synthesis (FASN, ACACA, and SCD), and uptake and transport (LPL, CD36, and FABP3) of fatty acids as well as triacylglycerol synthesis (GPAM, APGAT6, and DGAT1). Luciferase reporter assays indicated that overexpression of NR1H3 resulted in an increase in the activity of FASN promoter, whereas the knockdown of NR1H3 had an opposite effect. When NR1H3 was overexpressed, mutations in LXRE or SRE could decrease the promoter activity of FASN. Furthermore, mutagenesis of both LXRE and SRE within the FASN promoter completely eliminated the induced activity of LXRα. Our results reveal that buffalo LXRα promotes milk fat synthesis through regulating the expression of FASN by directly interacting with FASN promoter and affecting the SREBF1 expression. This study underscores a crucial role of LXRα in regulating lipid synthesis of the buffalo mammary gland.

The regulatory mechanism of amino acids on milk protein and fat synthesis in mammary epithelial cells: a mini review

Mammary epithelial cell (MEC) is the basic unit of the mammary gland that synthesizes milk components including milk protein and milk fat. MECs can sense to extracellular stimuli including nutrients such as amino acids though different sensors and signaling pathways. Here, we review recent advances in the regulatory mechanism of amino acids on milk protein and fat synthesis in MECs. We also highlight how these mechanisms reflect the amino acid requirements of MECs and discuss the current and future prospects for amino acid regulation in milk production.

UFL1 regulates milk protein and fat synthesis-related gene expression of bovine mammary epithelial cells probably via the mTOR signaling pathway

UFL1 is an ufmylation (a novel post-translational modification) E3 ligase, mainly located in the endoplasmic reticulum (ER), that has emerged as a significant regulator of several physiological and pathological processes. Yet its physiological function in milk synthesis in bovine mammary epithelial cells (BMECs) remains unknown. In this study, we investigated the effects of UFL1 in milk protein and fat synthesis-related gene expression, with a particular emphasis on the role of UFL1 in LPS-treated BMECs. Results showed that UFL1 depletion significantly reduced the expression of milk protein and fat synthesis-related gene and mTOR phosphorylation in both normal and LPS-treated BMECs. Overexpression of UFL1 enhanced the activation of the mTOR and milk protein and fat synthesis-related gene expression. Collectively, these above results strongly demonstrate that UFL1 could regulate milk protein and fat synthesis-related gene expression of BMECs probably via the mTOR signaling pathway.

Novel advances in understanding fatty acid-binding G protein-coupled receptors and their roles in controlling energy balance

Diabetes, obesity, and other metabolic diseases have been recognized as the main factors that endanger human health worldwide. Most of these metabolic syndromes develop when the energy balance in the body is disrupted. Energy balance depends upon the systemic regulation of food intake, glucose homeostasis, and lipid metabolism. Fatty acid-binding G protein-coupled receptors (GPCRs) are widely expressed in various types of tissues and cells involved in energy homeostasis regulation. In this review, the distribution and biological functions of fatty acid-binding GPCRs are summarized, particularly with respect to the gut, pancreas, and adipose tissue. A systematic understanding of the physiological functions of the fatty acid-binding GPCRs involved in energy homeostasis regulation will help in identifying novel pharmacological targets for metabolic diseases.

Improving dairy performance through molecular characterization of SREBP-1 gene in Sarda sheep breed

This research has two aims: (i) to characterize the coding sequence of the SREBP-1 gene in dairy sheep in order to investigate possible relationships between single nucleotide polymorphisms (SNPs) and milk traits; and (ii) to investigate possible relationship between SREBP-1 gene expression and nucleotide variation. Four hundred adult and multiparous lactating Sarda breed ewes were selected from two farms. Milk samples were collected from Day 30 to Day 150 of lactation to determine the mean yield, somatic cell count, lactose, fat, and protein content of the milk. RNA was extracted from the milk samples, after which the SREBP-1 gene coding regions were amplified and sequenced to scan mutations. Whilst eight SNPs were identified, none had statistically significant association with the analysed milk traits. Moreover, the identified expression patterns were not affected by the SNP or combined genotypes. High SREBP-1 gene expression levels were found to be correlated with high milk fat content (P < 0.01), indicating the crucial role of this gene in the milk fat synthesis. In conclusion, the polymorphisms found within SREBP-1 gene exhibited no significant associations with milk traits or with individual SREBP-1 mRNA expression patterns. The findings thus suggest that this small genetic variability may derive from the selection carried out in Sarda breed to improve milk yield.

Metabolic Transition of Milk Triacylglycerol Synthesis in Response to Varying Levels of Three 18-Carbon Fatty Acids in Porcine Mammary Epithelial Cells

This study aimed to examine the effects of increasing levels of three 18-carbon fatty acids (stearate, oleate and linoleate) on mammary lipogenesis, and to evaluate their effects on the milk lipogenic pathway in porcine mammary epithelial cells (pMECs). We found that increasing the three of 18-carbon fatty acids enhanced the cellular lipid synthesis in a dose-dependent manner, as reflected by the increased (triacylglycerol) TAG content and cytosolic lipid droplets in pMECs. The increased lipid synthesis by the three 18-carbon fatty acids was probably caused by the up-regulated expression of major genes associated with milk fat biosynthesis, including CD36 (long chain fatty acid uptake); GPAM, AGPAT6, DGAT1 (TAG synthesis); PLIN2 (lipid droplet formation); and PPARγ (regulation of transcription). Western blot analysis of CD36, DGAT1 and PPARγ proteins confirmed this increase with the increasing incubation of 18-carbon fatty acids. Interestingly, the mRNA expressions of ACSL3 and FABP3 (fatty acids intracellular activation and transport) were differentially affected by the three 18-carbon fatty acids. The cellular mRNA expressions of ACSL3 and FABP3 were increased by stearate, but were decreased by oleate or linoleate. However, the genes involved in fatty acid de novo synthesis (ACACA and FASN) and the regulation of transcription (SREBP1) were decreased by incubation with increasing concentrations of 18-carbon fatty acids. In conclusion, our findings provided evidence that 18-carbon fatty acids (stearate, oleate and linoleate) significantly increased cytosolic TAG accumulation in a dose-dependent manner, probably by promoting lipogenic genes and proteins that regulate the channeling of fatty acids towards milk TAG synthesis in pMECs.

Effect of acetate, β-hydroxybutyrate and their interaction on lipogenic gene expression, triglyceride contents and lipid droplet formation in dairy cow mammary epithelial cells

The purpose of this study was to assess the effects of acetate and β-hydroxybutyrate alone or in combination on lipogenic genes and their associated regulatory proteins in dairy cow mammary epithelial cells (DCMEC) using quantitative reverse transcription polymerase chain reaction (qRT-PCR), western blotting, lipid droplet staining and a triglyceride content detection kit, to determine whether SCFA are related to milk fat synthesis regulation in DCMEC. Our experiment shows that addition of different concentrations of acetate, β-hydroxybutyrate and their combinations to DCMEC increase in relative mRNA abundance of lipogenic genes and key transcription factors suggest an increase in lipogenic capacity, which is supported by an increased in cytosolic triglyceride content. Similarly, the protein expression level of acetyl-coenzyme A carboxylase (ACACA), fatty acid synthase (FASN) and sterol-coenzyme desaturase-1 (SCD1) genes and the transcription factor sterol regulatory element-binding protein-1 (SREBP1) were found to be increased by addition of acetate, β-hydroxybutyrate and their combinations. The expression pattern of fat-related genes and proteins showed similar trends in almost all treatments, suggesting that common transcription factor are regulating these genes. These results show that acetate and β-hydroxybutyrate regulate fat synthesis, further confirming that SCFAs work by targeting genes to activate the SREBP1 and insulin-induced gene 1 protein (INSIG1) signalling pathways in DCMEC.

Advances in fatty acids nutrition in dairy cows: from gut to cells and effects on performance

High producing dairy cows generally receive in the diet up to 5-6% of fat. This is a relatively low amount of fat in the diet compared to diets in monogastrics; however, dietary fat is important for dairy cows as demonstrated by the benefits of supplementing cows with various fatty acids (FA). Several FA are highly bioactive, especially by affecting the transcriptome; thus, they have nutrigenomic effects. In the present review, we provide an up-to-date understanding of the utilization of FA by dairy cows including the main processes affecting FA in the rumen, molecular aspects of the absorption of FA by the gut, synthesis, secretion, and utilization of chylomicrons; uptake and metabolism of FA by peripheral tissues, with a main emphasis on the liver, and main transcription factors regulated by FA. Most of the advances in FA utilization by rumen microorganisms and intestinal absorption of FA in dairy cows were made before the end of the last century with little information generated afterwards. However, large advances on the molecular aspects of intestinal absorption and cellular uptake of FA were made on monogastric species in the last 20 years. We provide a model of FA utilization in dairy cows by using information generated in monogastrics and enriching it with data produced in dairy cows. We also reviewed the latest studies on the effects of dietary FA on milk yield, milk fatty acid composition, reproduction, and health in dairy cows. The reviewed data revealed a complex picture with the FA being active in each step of the way, starting from influencing rumen microbiota, regulating intestinal absorption, and affecting cellular uptake and utilization by peripheral tissues, making prediction on in vivo nutrigenomic effects of FA challenging.

Daidzein stimulates fatty acid-induced fat deposition in C2C12 myoblast cells via the G protein-coupled receptor 30 pathway

Fat deposition in skeletal muscle is an important aspect of improving meat quality. Isoflavones can promote animal anabolism, but whether and how they regulate muscle fat deposition remain largely unclear. In this study, we explored the role and corresponding molecular mechanism of one of the major isoflavones, daidzein, in fat deposition in C2C12 myoblast cells. In the absence of fatty acids (FAs), daidzein did not promote triglyceride synthesis and lipid droplet formation in cells but increased sterol regulatory element-binding protein 1c (SREBP-1c) expression and maturation. In the presence of FAs, daidzein enhanced FAs-induced fat deposition and the SREBP-1c signaling. Daidzein promoted FAs-induced nuclear factor κB1 (NFκB1) phosphorylation and activated the SREBP-1c signaling in a PI3K-dependent manner. G protein-coupled receptor 30 (GPR30) knockdown but not estrogen receptor α (ERα) knockdown blocked the stimulation of daidzein on the PI3K-NFκB1-SREBP-1c signaling pathway, while both knockdown did not affect the stimulation of FAs on this signaling. qRT-PCR and ChIP-qPCR further detected that daidzein stimulated NFκB1-targeted SREBP-1c transcription. Daidzein did not affect ERα expression in cells, but it stimulated GPR30 expression and cytoplasmic localization. These results reveal that daidzein promotes FAs-induced fat deposition through the GPR30 signaling in C2C12 myoblast cells.

Effects of 25-hydroxycholecalciferol supplementation in maternal diets on reproductive performance and the expression of genes that regulate lactation in sows

One hundred Yorkshire × Landrace sows were randomly assigned to one of two dietary treatments (diet ND: 6,000 IU vitamin D₃ /d feed; diet 25-D: 200 μg/day 25OHD₃ feed). The experiment began on d 90 of gestation and continued until weaning on day 21 of lactation. In sows that received 25OHD₃ , the growth rate of the piglets before weaning was significantly accelerated (0.266 kg/day, p < .05). Sow serum was collected after weaning, and those in the 25OHD₃ group were found to have significantly higher serum calcium (CA) and phosphorus (PI) levels (p < .05). Interestingly, the oestrus cycle of sows fed 25OHD₃ was significantly shortened (p < .05), the oestrus time was concentrated on the fifth day after weaning, and the piglets were born with a higher degree of uniformity (p < .05). Colostrum was collected on the day of delivery, and the colostrum of sows fed 25OHD₃ contained higher milk fat content than the control group (p < .05). 25OHD₃ supplementation increased the mRNA and protein expression of INSIG1 and SREBP1, which regulate milk fat synthesis, in the mammary gland of lactating sows (p < .05). In conclusion, 25OHD₃ supplementation in maternal diets improved reproductive performance, milk fat content and the mRNA and protein levels of genes regulating milk fat synthesis in lactating sows.

Niacin inhibits the synthesis of milk fat in BMECs through the GPR109A-mediated downstream signalling pathway

AIMS

Previous studies have shown the effect of niacin on dairy cow production, but no study on the role of niacin in milk fat synthesis has been performed. Therefore, the purpose of this study was to examine the effect of niacin on milk fat synthesis and its specific mechanism in BMECs.

MAIN METHODS

In this study, 0.5 mM niacin, a GPR109A-inhibiting plasmid, and an AMPK inhibitor were added to BMECs. Milk fat was measured by a triglyceride kit and BODIPY staining. The protein expression of GPR109A, FASN, SREBP1, AMPK, ACC, mTOR and S6K was measured by Western blotting. The gene expression of GPR109A, FASN, and SREBP1 was analysed by RT-PCR.

KEY FINDINGS

Our results showed that 0.5 mM niacin could significantly reduce milk fat synthesis in BMECs and activate the AMPK/ACC signalling pathway by stimulating GPR109A, reducing the protein expression of p-mTOR and p-S6K, and reducing the expression of SREBP1 and FASN in BMECs.

SIGNIFICANCE

The present study clarified the effect of niacin on milk fat synthesis. The results show that niacin inhibits the synthesis of milk fat in BMECs through the downstream signalling pathway mediated by GPR109A. The function of niacin has been expanded, and knowledge of the new mechanism and signalling pathway will help improve the biosynthesis of milk fat.

Valine increases milk fat synthesis in mammary gland of gilts through stimulating AKT/MTOR/SREBP1 pathway†

Lactating mammary glands are among the most active lipogenic organs and provide a large percentage of bioactive lipids and calories for infant growth. The branched-chain amino acid (BCAA) valine is known to modulate fatty acids synthesis in adipose tissue; however, its effects on fat metabolism and the underlying mechanisms in mammary glands remain to be determined. Valine supplementation during late pregnancy significantly increased the contents of total milk fat, triglyceride, sphingomyelin, and polyunsaturated fatty acids in the colostrum of gilts. Further study in porcine mammary epithelial cells (PMECs) confirmed that valine upregulated the phosphorylation levels of AKT-activated MTOR and subsequently induced the nuclear accumulation of sterol regulatory element binding protein 1 (SREBP1), thus increasing the expression of proteins related to fatty acids synthesis and intracellular triacylglycerol content. Inhibition of AKT/MTOR signaling or silencing of SREBP1 in PMECs downregulates the expression of proteins related to fatty acids synthesis and intracellular triacylglycerol content. Our findings indicated that valine enhanced milk fat synthesis of colostrum in porcine mammary glands via the AKT/MTOR/SREBP1 signaling pathway.