Acetate Upregulates GPR43 Expression and Function via PI3K-AKT-SP1 Signaling in Mammary Epithelial Cells during Milk Fat Synthesis

This study investigated the mechanism underlying acetate-induced orphan G-protein-coupled receptor 43 (GPR43) expression and milk fat production. The mammary epithelial cells of dairy cows were treated with acetate, and the effects of GPR43 on acetate uptake and the expression of lipogenesis-related genes were determined by gas chromatography and quantitative polymerase chain reaction (qPCR), respectively. RNAi, inhibitor treatment, and luciferase assay were used to determine the effect of phosphoinositide 3-kinase-protein kinase B-specificity protein 1 (PI3K-AKT-SP1) signaling on acetate-induced GPR43 expression and function. The results showed that GPR43 was highly expressed in lactating cow mammary tissues, which was related to milk fat synthesis. 12 mM acetate significantly increased the GPR43 expression in mammary epithelial cells of dairy cows. In acetate-treated cells, GPR43 overexpression significantly increased the cellular uptake of acetate, the intracellular triacylglycerol (TAG) content, and acetate-induced lipogenesis gene expression. Acetate activated PI3K-AKT signaling and promoted SP1 translocation from the cytosol into the nucleus, where SP1 bound to the GPR43 promoter and upregulated GPR43 transcription. Moreover, the activation of PI3K-AKT-SP1 by acetate facilitated the trafficking of GPR43 from the cytosol to the plasma membrane. In conclusion, acetate upregulated GPR43 expression and function via PI3K-AKT-SP1 signaling in mammary epithelial cells, thereby increasing milk fat synthesis. These results provide an experimental strategy for improving milk lipid synthesis, which is important to the dairy industry.

A MDM2 inhibitor MX69 inhibits adipocytes adipogenesis and differentiation

Adipose tissue, a key regulator of systemic energy homeostasis, can synthesize and store triglycerides to meet long-term energy demands. In response to nutrient overload, adipose tissue expands by hypertrophy or hyperplasia. As an oncogene, MDM2 has exerted diverse biological activities including human development, tissue regeneration, and inflammation, in addition to major oncogenic activities. Recently, some studies indicated that MDM2 plays an important role in adipose tissue function. However, the role of MX69, a MDM2 inhibitor, in adipose tissue function has not been fully elucidated. Here, we administered MX69 intraperitoneally to high-fat diet-induced obesity (DIO) wild type C57BL/6 mice and found that MX69 could promote the body weight and white adipose tissue weight of DIO mice. Moreover, MX69 had no effects on glucose tolerance and insulin sensitivity in DIO mice. And MX69 treatment decreased the size of adipocytes and fat deposition in adipose tissue and inhibited 3T3-L1 preadipocytes differentiation. Mechanistically, MX69 inhibited the protein levels of MDM2 and the mRNA levels of genes related to adipogenesis and differentiation. In summary, our results indicated that MDM2 has a crucial and complex role in regulating adipose tissue function.

Transcriptome analysis of CRISPR/Cas9-mediated GPAM-/- in bovine mammary epithelial cell-line unravelled the effects of GPAM gene on lipid metabolism

Glycerol-3-phosphate acyltransferase mitochondrial (GPAM) is an enzyme in animal lipid metabolism pathways that catalyzes the initial and most committed step of glycerolipid biosynthesis. The present study mainly focused on exploring the relationship between the GPAM gene and the lipid metabolism of mammary epithelial cells and the effect of GPAM on the related pathways of lipid metabolism. The GPAM gene was knocked out entirely in bovine mammary epithelial cells(BMECs) using CRISPR/Cas9 technology, and the mechanism by which the GPAM gene regulates lipid metabolism in BMECs was confirmed. Furthermore, after the complete loss of GPAM, BMECs' triglycerides (TGs) and cholesterol (CHOL) levels were significantly decreased (p < 0.05). Concurrently, the content of octanoic acid, a medium-chain saturated fatty acid, increased substantially in BMECs. RNA-seq of GPAM^-/- BMECs revealed that GPAM could affect the expression of genes related to lipid metabolism, downregulated the expression of Acyl-CoA synthetase long-chain family member 5 (ACSL5), Fatty Acid Binding Protein 3 (FABP3), Hormone-sensitive lipase (HSL), Protease, serine-2 (PRSS2), 1-Acylglycerol-3-Phosphate O Acyltransferase 4 (AGPAT4), and regulated the milk synthesis metabolism pathway.The findings revealed that a number of genes were expressed, a number of genes were differentially expressed genes (DEGs), and a number of GO terms were enriched, with a number of GO terms considerably increased. Further, the differentially expressed genes (DEGs) were significantly enriched in Fat digestion and absorption pathway, Fatty acid metabolic pathway, Biosynthesis of unsaturated fatty acids, Biosynthesis of unsaturated fatty acids and steroids, NF-kappa B signalling pathway, MAPK signalling pathway. In conclusion, the current research results show that GPAM is a crucial regulator of BMEC lipid metabolism. GPAM^-/- BMEC may also become useful genetic materials and tools for future research on gene functions related to lipid and fatty acid metabolism. This study will contribute to the discovery of gene regulation and molecular mechanisms in milk fat synthesis.

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.

CIDEC silencing attenuates diabetic nephropathy via inhibiting apoptosis and promoting autophagy

OBJECTIVE

The role of cell death-inducing DFF45-like effector C (CIDEC) in insulin resistance has been established, and it is considered to be an important trigger factor for the progression of diabetic nephropathy (DN). We intend to explore whether CIDEC plays an important role in the regulation of DN and its potential mechanism.

METHODS

High-fat diet and low dose streptozotocin were used to establish type 2 diabetic rat model. We investigate the role of CIDEC in the pathogenesis and process of DN through histopathological analysis, western blot and gene silencing. Meanwhile, the effect of CIDEC on renal tubular epithelial cells stimulated by high glucose was also verified.

RESULTS

DM group exhibited glucose and lipid metabolic disturbance, with hypertrophy of kidneys, damaged renal function, increased apoptosis, decreased autophagy, glomerulosclerosis and interstitial fibrosis. CIDEC gene silencing improved metabolic disorder and insulin resistance, alleviated renal hypertrophy and renal function damage, decreased glomerular and tubular apoptosis, increased autophagy and inhibited renal fibrosis. At the cellular level, high glucose stimulation increased CIDEC expression in renal tubular epithelial cells, accompanied by increased apoptosis and decreased autophagy. CIDEC gene silencing can improve autophagy and reduce apoptosis. At the molecular level, CIDEC gene silencing also decreased the expression of early growth response factor (EGR)1 and increased the expression of adipose triglyceride lipase (ATGL).

CONCLUSION

CIDEC gene silencing may delay the progression of DN by restoring autophagy activity and inhibiting apoptosis with the participation of EGR1and ATGL.

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.

MiR-485 targets the DTX4 gene to regulate milk fat synthesis in bovine mammary epithelial cells

MicroRNAs (miRNAs) are mRNA suppressors that regulate a variety of cellular and physiological processes, including cell proliferation, apoptosis, triglyceride synthesis, fat formation, and lipolysis, by post-transcriptional processing. In previous studies, we isolated and sequenced miRNAs from mammary epithelial cells from Chinese Holstein cows with high and low milk fat percentages. MiR-485 was one of the significantly differentially expressed miRNAs that were identified. In the present study, the relationship between the candidate target gene DTX4 and miR-485 was validated by bioinformatics and real-time fluorescent quantitative PCR (qRT-PCR) and Western blot (WB) analyses in bovine mammary epithelial cells (bMECs). The results indicated that miR-485 negatively regulated the mRNA expression of the target gene DTX4. Furthermore, an shRNA interference vector for the target gene DTX4 was constructed successfully, and it increased the triglyceride content and reduced the cholesterol content of transfected cells. These results suggest that miR-485 may affect the contents of triglycerides (TGs) and cholesterol (CHOL) by targeting the DTX4 gene. This study indicates that miR-485 has a role in regulating milk fat synthesis and that miR-485 targets the DTX4 gene to regulate lipid metabolism in bMECs. These findings contribute to the understanding of the functional significance of miR-485 in milk fat synthesis.

Cell death-inducing DNA fragmentation factor-α-like effector C (CIDEC) regulates acetate- and β-hydroxybutyrate-induced milk fat synthesis by increasing FASN expression in mammary epithelial cells of dairy cows

Increasing acetate and β-hydroxybutyrate (BHB) supply to lactating cows will increase milk fat synthesis. However, the underlying molecular mechanism remains largely unknown. Cell death-inducing DNA fragmentation factor-α-like effector C (CIDEC) is a lipid droplet-associated protein that promotes intracellular triacylglycerol accumulation. In the present study, using gene overexpression and knockdown, we detected the contributions of CIDEC on milk fat synthesis in mammary epithelial cells of dairy cows in the presence of acetate and BHB. The results showed that knockdown of CIDEC decreased fatty acid synthase (FASN) expression and intracellular triacylglycerol content, whereas overexpression of CIDEC had the opposite effect. The transcription factor CCAAT/enhancer-binding protein β (C/EBPβ) regulates cell growth and differentiation in the mammary gland. We demonstrated that the FASN promoter had a canonical C/EBPβ binding sequence. CEBPB overexpression upregulated FASN expression and milk fat synthesis, whereas CEBPB knockdown had the opposite effect. Moreover, knockdown of CEBPB attenuated the promoting effects of CIDEC on acetate- and BHB-induced FASN transcription. Taken together, our data showed that acetate and BHB induced FASN expression in mammary epithelial cells of dairy cows in a CIDEC-C/EBPβ-dependent manner, which provides new insights into the understanding of the molecular events involved in milk fat synthesis.

Nutrigenomic Role of Acetate and β-Hydroxybutyrate in Bovine Mammary Epithelial Cells

Acetate and β-hydroxybutyrate (BHBA) are the predominant substrates for de novo fatty acid (FA) synthesis in mammary gland of dairy cow. To investigate the nutrigenomic role of acetate and BHBA in bovine mammary epithelial cells during milk fat production, RNA sequencing (RNA-seq) transcriptomic analysis was used to identify differentially expressed genes (DEGs) between acetate- and BHBA-treated cells (high-milk fat cells) and control cells. A total of 625 DEGs (358 upregulated and 267 downregulated) were identified between the high-milk fat cells and control cells. Gene ontology enrichment analysis revealed that the upregulated genes in high-milk fat cells were mainly involved in lipid biosynthetic process, steroid biosynthetic process, oxidation-reduction process, receptor binding, and vesicle and small molecule biosynthetic process. The downregulated genes were mainly associated with immune response, cytokine production, negative regulation of biological process, and peptidyl-threonine modification. Pathway analysis indicated that FA metabolism and steroid biosynthesis were significantly enriched for the upregulated genes in the high-milk fat cells, while apoptosis was enriched for the downregulated genes. This work provides a profile of gene expression changes that occur during acetate- and BHBA-induced milk fat synthesis in bovine mammary epithelial cells, which furthers our understanding of the molecular regulation of lipid metabolism.