Runjun Yang

Background: Exosomes are crucial mediators of intercellular communication. As a key component of milk, milk-derived exosomes are abundant in genetic cargo, particularly microRNAs (miRNAs), indicating their potential role in regulating mammary gland physiology. Therefore, this study aimed to investigate the specificity of miRNAs in milk-derived exosomes and their regulatory roles in lipid synthesis in bovine mammary epithelial cells (BMECs). Results: Based on 17,838 DHI records showing a significantly higher milk fat percentage (MFP) in late lactation (4.24% ± 1.07%), 10 high- (5.96% ± 0.26%, HMF) and 10 low-MFP (1.68% ± 0.23%, LMF) cows were selected during this stage for milk-derived exosome isolation and miRNA profiling. Exosomes isolated via differential ultracentrifugation were verified as 50–150 nm vesicles expressing CD9, CD81, and TSG101. miRNA sequencing identified 1,320 differentially expressed miRNAs (496 upregulated and 824 downregulated) between the HMF_EXO and LMF_EXO groups. Uptake assays confirmed that BMECs internalized these exosomes, and qRT-PCR validation showed that miR-423-5p and miR-125b were significantly upregulated and downregulated in HMF_EXO- and LMF_EXO-treated BMECs, respectively. Functionally, exosomal miR-423-5p promoted intracellular lipid accumulation and TG synthesis in BMECs by targeting APOA5 , whereas miR-125b inhibited lipolysis and fatty acid oxidation by repressing SLC27A1 . Conclusions: This study demonstrates that milk-derived exosomal miRNAs represent a novel mechanism for regulating milk fat synthesis. Specifically, miR-423-5p and miR-125b directly modulated lipid metabolism in BMECs via the miR-423-5p/ APOA5 and miR-125b/ SLC27A1 pathways. These findings provide new insights into the molecular regulation of milk fat synthesis and highlight the importance of exosome-mediated intercellular communication in the lactating mammary gland. Graphical

Background Exosomes have recently been considered as major players in cell-cell communication. Milk-derived exosomes contained abundant genetic cargos and the potential biological functions in the synthesis of milk fat remain poorly understood. Milk fat percentage is a crucial trait that influences dairy quality and consumer preference. This study focused on the regulatory role of milk-derived exosomal miRNAs in lipid synthesis within BMECs. Results Initially, based on 17,838 DHI milk production performance data collected from January 2021 to February 2023, compared with early lactation , mid-lactation from 100 to 199 days, late lactation from 200 to 299 days, duration lactation the milk fat percentage (MFP) of late lactation (4.24±1.07%) significant higher than other stages. The milk protein percentage during this stage (3.43±0.36) is significantly higher compared to other stages. The heritability estimates for milk fat and milk protein percentage show a positive correlation. Subsequently, 10 cows with high MFP （5.96±0.26 ) and ten cows with low MFP (1.68±0.23) were selected during the late lactation stage, and milk samples were collected for further analysis. Milk-derived exosomes isolated via differential ultracentrifugation exhibited a spherical vesicle structure ranging in size from 50 to 150 nm and were enriched in exosome-specific protein markers CD9, CD81, and TSG101. Through miRNA-seq, 1320 differentially expressed miRNAs were identified including 496 up-regulated and 824 down-regulated miRNAs by high-throughput miRNA sequencing. Furthermore, the exosome uptake experiment revealed that upon BMECs, exosomes predominantly localized in the cytoplasm.The results of exosomal q-PCR demonstrated that miR-423-5p and miR-125b were significantly up-regulated and down-regulated in HMF_EXO and LMF_EXO groups, respectively. Conclusions Milk-derived exosomal miRNAs associated with lipid metabolism can provide preliminary insights into the effects of exosomes on lactation mechanisms and potentially identify biomarkers for distinguishing molecular markers and loci related to high or low milk fat content in dairy cattle.

Background/Objectives: Breast milk provides essential nutrition and immune protection to support infant growth and development. However, insufficient breast milk remains a serious issue, and bioactive peptides represent a potential strategy to promote lactation. In this study, we investigated the impact of a methionine-containing dipeptide, EM, on MCF-10A mammary epithelial cells. Methods: MCF-10A cells were treated with EM, and cell proliferation and the expression of key milk protein genes were assessed. Integrated transcriptomic and untargeted metabolomic analyses were performed to identify EM-induced changes in metabolic and gene expression pathways. Results: EM treatment significantly enhanced cell proliferation and upregulated the expression of key milk protein genes (CSN1S1 (casein alpha-S1, encoding alpha-S1 casein), CSN2 (casein beta, encoding beta-casein), and CSN3 (casein kappa, encoding kappa-casein)) at both transcriptional and protein levels compared to controls. Integrated transcriptomic and metabolomic analyses revealed that EM reprogrammed amino acid metabolism, lipid biosynthesis, and nutrient transport pathways. Core genes such as SLC7A11, APOE, and ABCA1 were identified as critical nodes linking metabolic and transcriptional networks. Conclusions: These findings indicate that EM may promote lactogenic activity by modulating metabolic and transcriptional networks in vitro, highlighting the potential of dipeptide-based nutritional interventions, which warrants further in vivo validation.

The CD44 gene is a critical factor in animal physiological processes and has been shown to affect insulin resistance and fat accumulation in mammals. Nevertheless, little research has been conducted on its precise functions in lipid metabolism and adipogenic differentiation in beef cattle. This study analyzed the expression of CD44 and miR-199a-3p during bovine preadipocyte differentiation. The luciferase reporter assay demonstrated that CD44 was a direct target of miR-199a-3p. Increased accumulation of lipid droplets and triglyceride levels, altered fatty acid metabolism, and accelerated preadipocyte differentiation were all caused by the upregulation of miR-199a-3p or a reduction in CD44 expression. CD44 knockdown upregulated the expression of adipocyte-specific genes (LPL and FABP4) and altered the levels of lipid metabolites (SOPC, l-arginine, and heptadecanoic acid). Multiomics highlights enriched pathways involved in energy metabolism (MAPK, cAMP, and calcium signaling) and shifts in mitochondrial respiration and glycolysis, indicating that CD44 plays a regulatory role in lipid metabolism. The findings show that intracellular lipolysis, glycolysis, mitochondrial respiration, fat deposition, and lipid droplet composition are all impacted by miR-199a-3p, which modulates CD44 in bovine adipocytes.

Stearoyl-CoA desaturase-1 (SCD1) is a key enzyme in the biosynthesis of monounsaturated fatty acids and is considered a candidate gene for improving milk and meat quality traits. Sanger sequencing was employed to investigate the genetic polymorphism of the fifth exon and intron of bovine SCD1, revealing four SNPs, g.21272246 A>G, g.21272306 T>C, g.21272422 C>T, and g.21272529 A>G. Further variance analysis and multiple comparisons were conducted to examine the relationship between variation sites and economic traits in Chinese Simmental cattle, as well as milk production traits in Holstein cows. The findings revealed these four loci exhibited significant associations with carcass traits (carcass weight, carcass length, backfat thickness, and waist meat thickness), meat quality (pH value, rib eye area, and marbling score), adipogenic traits (fat score and carcass fat coverage rate), and fatty acid composition (linoleic acid and α-linolenic acid). Furthermore, these loci were additionally found to be significantly associated with average milk yield and milk fat content in cows. In addition, a haplotype analysis of combinations of SNPs showed that H2H3 has a significant association with adipogenic traits and H2H2 was associated with higher levels of linoleic acid and α-linolenic acid than the other combinations. These results suggest that the four SNPs are expected to be prospective genetic markers for the above economic traits. In addition, the function of SNPs in exon 5 of SCD1 on gene expression and protein structure needs to be explored in the future.

Delta-like non-canonical Notch ligand 1 (DLK1), which inhibits the differentiation of precursor adipocytes, is a recognized marker gene for precursor adipocytes. Lipids play a crucial role in energy storage and metabolism as a vital determinant of beef quality. In this study, we investigated the mechanism of the DLK1 gene in lipid metabolism by constructing adipose tissue-specific knockout mice. We examined some phenotypic traits, including body weight, liver coefficient, fat index, the content of triglyceride (TG) and cholesterol (CHOL) in abdominal white adipose tissue (WAT) and blood. Subsequently, the fatty acid content and genes related to lipid metabolism expression were detected in DLK1^−/− and wild-type mice via GC-MS/MS analysis and quantitative real-time PCR (qRT-PCR), respectively. The results illustrated that DLK1^−/− mice exhibited significant abdominal fat deposition compared to wild-type mice. HE staining and immunohistochemistry (IHC) results showed that the white adipocytes of DLK1^−/− mice were larger, and the protein expression level of DLK1^−/− was significantly lower. Regarding the blood biochemical parameters of female mice, DLK1^−/− mice had a strikingly higher triglyceride content (p < 0.001). The fatty acid content in DLK1^−/− mice was generally reduced. There was a significant reduction in the expression levels of the majority of genes that play a crucial role in lipid metabolism. This study reveals the molecular regulatory mechanism of fat metabolism in mice and provides a molecular basis and reference for the future application of the DLK1 gene in the breeding of beef cattle with an excellent meat quality traits. It also provides a molecular basis for unravelling the complex and subtle relationship between adipose tissue and health.

Breast milk is widely considered to be the most natural, safe, and complete food for infants. However, current breastfeeding rates fall short of the recommendations established by the World Health Organization. Despite this, there are few studies that have focused on the promotion of human lactation through nutrient supplementation. Therefore, the aim of this study was to investigate the effect of methionine on milk synthesis in human mammary epithelial cells (MCF-10A cells) and to explore the underlying mechanisms. To achieve this, MCF-10A cells were cultured with varying concentrations of methionine, ranging from 0 to 1.2 mM. Our results indicated that 0.6 mM of methionine significantly promoted the synthesis of milk protein. An RNA-seq analysis revealed that methionine acted through the PI3K pathway. This finding was validated through real-time quantitative polymerase chain reaction (RT-qPCR) and Western blotting. In addition, PI3K inhibition assays confirmed that methionine upregulated the expression of both mTOR and p-mTOR through activation of PI3K. Taken together, these findings suggest that methionine positively regulates milk protein synthesis in MCF-10A cells through the PI3K-mTOR signaling pathway.

Meat quality has a close relationship with fat and connective tissue; therefore, screening and identifying functional genes related to lipid metabolism is essential for the production of high-grade beef. The transcriptomes of the Longissimus dorsi muscle in Wagyu and Chinese Red Steppe cattle, breeds with significant differences in meat quality and intramuscular fat deposition, were analyzed using RNA-seq to screen for candidate genes associated with beef quality traits. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that the 388 differentially expressed genes (DEGs) were involved in biological processes such as short-chain fatty acid metabolism, regulation of fatty acid transport and the peroxisome proliferator-activated receptor (PPAR) signaling pathway. In addition, crystallin alpha B (CRYAB), ankyrin repeat domain 2 (ANKRD2), aldehyde dehydrogenase 9 family member A1 (ALDH9A1) and enoyl-CoA hydratase and 3-hydroxyacyl CoA dehydrogenase (EHHADH) were investigated for their effects on intracellular triglyceride and fatty acid content and their regulatory effects on genes in lipogenesis and fatty acid metabolism pathways. This study generated a dataset from transcriptome profiling of two cattle breeds, with differing capacities for fat-deposition in the muscle, and revealed molecular evidence that CRYAB, ANKRD2, ALDH9A1 and EHHADH are related to fat metabolism in bovine fetal fibroblasts (BFFs). The results provide potential functional genes for maker-assisted selection and molecular breeding to improve meat quality traits in beef cattle.

Acyl-CoA synthetase family member 3 (ACSF3) carries out the first step of mitochondrial fatty acid synthesis II, which is the linkage of malonate and, to a lesser extent, methylmalonate onto CoA. Malonyl-coenzyme A (malonyl-CoA) is a central metabolite in mammalian fatty acid biochemistry that is generated and utilized in the cytoplasm. In this research, we verified the relationship between expression of the ACSF3 and the production of triglycerides (TGs) at the cellular level by silencing and over-expressing ACSF3. Subsequently, through Sanger sequencing, five polymorphisms were found in the functional domain of the bovine ACSF3, and the relationship between ACSF3 polymorphism and the economic traits and fatty acid composition of Chinese Simmental cattle was analyzed by a means of variance analysis and multiple comparison. The results illustrated that the expression of ACSF3 promoted triglyceride synthesis in bovine mammary epithelial cells and bovine fetal fibroblast cells. Further association analysis also indicated that individuals with the AG genotype (g.14211090 G > A) of ACSF3 were significantly associated with the fatty acid composition of intramuscular fat (higher content of linoleic acid, α-linolenic acid, and arachidonic acid), and that CTCAG haplotype individuals were significantly related to the fatty acid composition of intramuscular fat (higher linoleic acid content). Individuals with the AA genotypes of g.14211055 A > G and g.14211090 G > A were substantially associated with a larger eye muscle area in the Chinese Simmental cattle population. ACSF3 played a pivotal role in the regulation of cellular triacylglycerol and long-chain polyunsaturated fatty acid levels, and polymorphism could serve as a useful molecular marker for future marker-assisted selection in the breeding of intramuscular fat deposition traits in beef cattle.

This study aims to screen potential regulators and regulate fecundity networks between microRNAs (miRNAs) and target genes. The bovine testes of immature and mature Chinese Red Steppes were performed by genome-wide analysis of mRNAs and miRNAs. Compared with testicular tissues of newborns, 6051 upregulated genes and 7104 downregulated genes in adult cattle were identified as differentially expressed genes (DEGs). The DEGs were significantly enriched in 808 GO terms (p < 0.05) including male gonad development, male genitalia development, spermatogenesis, and sperm motility. Moreover, DEGs were also significantly enriched in 105 KEGG pathways (p < 0.05), including cGMP-PKG signaling pathway and calcium signaling pathway. To explore the expression of miRNA-regulated gene expression, 896 differentially expressed target genes negatively regulated with the expression levels of 31 differentially expressed miRNAs (DERs) were predicted and analyzed, and a network-integrated analysis was constructed. Furthermore, real-time PCR was performed to verify the expression levels of DEGs and DERs. Our results identified novel candidate DEGs and DERs correlated with male reproduction and intricate regulating networks between miRNAs and genes, which will be valuable for future genetic and epigenetic studies of sperm development and maturity, as well as providing valuable insights into the molecular mechanisms of male fertility and spermatogenesis in cattle.