Transcriptional regulation of milk fat synthesis in dairy cattle

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.

The Effects of Two Selected Single Nucleotide Polymorphisms of the Fatty Acid Synthase Gene on the Fat Content and Fatty Acid Profile of Cow's Milk from the Polish Holstein-Friesian Red-and-White Breed versus Two Polish Red-and-White and Polish Red Conservation Breeds Kept in Poland

Fatty acid synthase (FASN) is a metabolic enzyme responsible for the synthesis of fatty acids in milk and meat. The SNPs g.841G/C and g.17924A/G of the FASN gene significantly influence the fat and fatty acid content of milk from cows of various breeds. Therefore, these SNPs were selected for this study. This study aimed to analyze the relationship of SNPs and their genotypes with the fat content and fatty acid profile of milk from Polish Red-and-White (ZR), Polish Red (RP), and Polish Holstein-Friesian Red-and-White (RW) cows. Milk samples were obtained during a milking trial. SNP genotyping was performed using the real-time PCR (HRM) method. It was shown that SNPs (with specific genotypes) were significantly associated with the presence of fatty acids such as C18:1n9t and C18:2n6c in milk. In addition, it was found that the milk fat from the ZR (genotypic variant A/G, AA) and RP (genotypic variant GG, A/G) breeds often exhibited a more attractive fatty acids profile than the milk fat from RW cows. This information can be used by both cattle breeders and people interested in consuming functional foods.

Bta-miR-200a Regulates Milk Fat Biosynthesis by Targeting IRS2 to Inhibit the PI3K/Akt Signal Pathway in Bovine Mammary Epithelial Cells

Milk fat synthesis has garnered significant attention due to its influence on the quality of milk. Recently, an increasing amount of proofs have elucidated that microRNAs (miRNAs) are important post-transcriptional factor involved in regulating gene expression and play a significant role in milk fat synthesis. MiR-200a was differentially expressed in the mammary gland tissue of dairy cows during different lactation periods, which indicated that miR-200a was a candidate miRNA involved in regulating milk fat synthesis. In our research, we investigated the potential function of miR-200a in regulating milk fat biosynthesis in bovine mammary epithelial cells (BMECs). We discovered that miR-200a inhibited cellular triacylglycerol (TAG) synthesis and suppressed lipid droplet formation; at the same time, miR-200a overexpression suppressed the mRNA and protein expression of milk fat metabolism-related genes, such as fatty acid synthase (FASN), peroxisome proliferator-activated receptor gamma (PPARγ), sterol regulatory element-binding protein 1 (SREBP1), CCAAT enhancer binding protein alpha (CEBPα), etc. However, knocking down miR-200a displayed the opposite results. We uncovered that insulin receptor substrate 2 (IRS2) was a candidate target gene of miR-200a through the bioinformatics online program TargetScan. Subsequently, it was confirmed that miR-200a directly targeted the 3'-untranslated region (3'-UTR) of IRS2 via real-time fluorescence quantitative PCR (RT-qPCR), western blot analysis, and dual-luciferase reporter gene assay. Additionally, IRS2 knockdown in BMECs has similar effects to miR-200a overexpression. Our research set up the mechanism by which miR-200a interacted with IRS2 and discovered that miR-200a targeted IRS2 and modulated the activity of the PI3K/Akt signaling pathway, thereby taking part in regulating milk fat synthesis in BMECs. Our research results provided valuable information on the molecular mechanisms for enhancing milk quality from the view of miRNA-mRNA regulatory networks.

Relationship between Selected SNPs (g.16024A/G, g.16039T/C and g.16060A/C) of the FASN Gene and the Fat Content and Fatty Acid Profile in the Milk of Three Breeds of Cows

Fat is an important energy and nutritional component of milk and consists of fatty acids. FASN (fatty acid synthase) is an enzyme that regulates the synthesis of fatty acids in the milk and meat of cattle. It was hypothesized that knowing the relationships between the genotypes of the tested single nucleotide polymorphisms (SNPs) and the content of fat and specific fatty acids would make it possible to improve milk quality in the selection process during cattle breeding. This study aimed to analyze the relationships of SNPs (g.16024A/G, g.16039T/C) of the FASN gene and their genotypes with the fat and fatty acid content of the milk of the following breeds: Polish Red-White (ZR), Polish Red (RP), and Polish Holstein-Friesian Red-White (RW). The SNP g.16060A/C was included in the study, although its effect on the fat composition of cow's milk has not yet been widely studied. Milk was obtained during test milkings. SNP genotyping was performed using the real-time PCR (HRM) method. The milk from ZR and RP cows was more often characterized by a more favorable fatty acid profile than the milk from RW cows. This information can be used by cattle breeders and consumers of so-called functional food.

Postnatal Growth and Development of the Rumen: Integrating Physiological and Molecular Insights

The rumen plays an essential role in the physiology and production of agriculturally important ruminants such as cattle. Functions of the rumen include fermentation, absorption, metabolism, and protection. Cattle are, however, not born with a functional rumen, and the rumen undergoes considerable changes in size, histology, physiology, and transcriptome from birth to adulthood. In this review, we discuss these changes in detail, the factors that affect these changes, and the potential molecular and cellular mechanisms that mediate these changes. The introduction of solid feed to the rumen is essential for rumen growth and functional development in post-weaning calves. Increasing evidence suggests that solid feed stimulates rumen growth and functional development through butyric acid and other volatile fatty acids (VFAs) produced by microbial fermentation of feed in the rumen and that VFAs stimulate rumen growth and functional development through hormones such as insulin and insulin-like growth factor I (IGF-I) or through direct actions on energy production, chromatin modification, and gene expression. Given the role of the rumen in ruminant physiology and performance, it is important to further study the cellular, molecular, genomic, and epigenomic mechanisms that control rumen growth and development in postnatal ruminants. A better understanding of these mechanisms could lead to the development of novel strategies to enhance the growth and development of the rumen and thereby the productivity and health of cattle and other agriculturally important ruminants.

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.

Effects of the timing of protein infusion on the daily rhythms of milk synthesis and plasma hormones and metabolites in dairy cows

Milk synthesis exhibits a daily rhythm that is modified by the timing of feed intake. However, it is unknown how specific nutrients entrain this daily rhythm. Amino acids have an important role in milk synthesis, and may have a role in entrainment of mammary circadian rhythms. The objective of this study was to determine the effects of intestinally absorbed protein on daily rhythms of milk and milk component synthesis and key plasma hormones and metabolites. Nine lactating Holstein cows were assigned to 1 of 3 treatment sequences in a 3 × 3 Latin square. Treatments included abomasal infusions of 500 g/d of sodium caseinate either continuously throughout the day (CON), for 8 h/d from 0900 to 1700 h (DAY), or for 8 h/d from 2100 to 0500 h (NGT). Cows were milked every 6 h during the final 8 d of each period. A 24-h rhythm was fit to data using cosine analysis and the amplitude and acrophase were determined. Night infusion of protein decreased the daily milk yield and milk protein yield by 8.2% and 9.2%, respectively. Milk fat yield was increased 5.5% by DAY and milk fat concentration was increased 8.8% by NGT. Milk yield exhibited a daily rhythm in all treatments, with NGT increasing the amplitude of the daily rhythm 33% compared with CON. Milk fat concentration fit a daily rhythm in CON and NGT, but not DAY, whereas milk protein concentration fit a daily rhythm in CON and DAY, but not NGT. Moreover, DAY abolished the daily rhythm of plasma glucose concentration, but induced rhythms of plasma insulin and nonesterified fatty acid concentrations. Results suggest that feeding increased protein levels during the early part of the day may increase milk fat yield and modify energy metabolism through increased daily variation in insulin-stimulated lipid release, but additional research focused on feeding multiple diets across the day is required.

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.

KRAS Affects the Lipid Composition by Regulating Mitochondrial Functions and MAPK Activation in Bovine Mammary Epithelial Cells

Kirsten rat sarcoma viral oncogene homolog (KRAS), or guanosine triphosphatase KRAS, is a proto-oncogene that encodes the small guanosine triphosphatase transductor protein. Previous studies have found that KRAS can promote cytokine secretion, cell chemotaxis, and survival. However, its effects on milk fat synthesis in bovine mammary epithelial cells are unclear. In this study, the effects of KRAS inhibition on cell metabolism, autophagy, oxidative stress, endoplasmic reticulum stress, mitochondrial function, and lipid composition as well as the potential mechanisms were detected in an immortalized dairy cow mammary epithelial cell line (MAC-T). The results showed that inhibition of KRAS changed the lipid composition (especially the triglyceride level), mitochondrial functions, autophagy, and endoplasmic reticulum stress in cells. Moreover, KRAS inhibition regulated the levels of the mammalian target of rapamycin and mitogen-activated protein kinase (extracellular regulated protein kinases, c-Jun N-terminal kinases, p38) activation. These results indicated that regulation of KRAS would affect the synthesis and composition of milk fat. These results are also helpful for exploring the synthesis and secretion of milk fat at the molecular level and provide a theoretical basis for improving the percentage of fat in milk and the yield of milk from cows.