Thyroid hormone responsive protein spot 14 enhances lipogenesis in bovine mammary epithelial cells

PI3K/AKT/mTORC1 signalling pathway regulates MMP9 gene activation via transcription factor NF-κB in mammary epithelial cells of dairy cows

Matrix metalloproteinase 9 (MMP9) plays a pivotal role in mammary ductal morphogenesis, angiogenesis and glandular tissue architecture remodeling. However, the molecular mechanism of MMP9 expression in mammary epithelial cells of dairy cows remains unclear. This study aimed to explore the underlying mechanism of MMP9 expression. In this study, to determine whether the PI3K/AKT/mTORC1/NF-κB signalling pathway participates in the regulation of MMP9 expression, we treated mammary epithelial cells with specific pharmacological inhibitors of PI3K (LY294002), mTORC1 (Rapamycin) or NF-κB (Celastrol), respectively. Western blotting results indicated that LY294002, Rapamycin and Celastrol markedly decreased MMP9 expression and P65 nuclear translocation. Furthermore, we found that NF-κB (P65) overexpression resulted in elevated expression of MMP9 protein and activation of MMP9 promoter. In addition, we observed that Celastrol markedly decreases P65-overexpression-induced MMP9 promoter activity. Moreover, the results of the promoter assay indicated that the core regulation sequence for MMP9 promoter activation may be located at -420 ∼ -80 bp downstream from the transcription start site. These observations indicated that the PI3K/AKT/mTORC1 signalling pathway is involved in MMP9 expression by regulating MMP9 promoter activity via NF-κB in the mammary epithelial cells of dairy cows.

Effect of dietary phosphorus deprivation during the dry period on the liver transcriptome of high-yielding periparturient dairy cows

Although dietary phosphorus (P) deprivation extending from the dry period into early lactation impairs health and productivity of cows, restricting dietary P supply during the dry period not only appears to be innocuous but rather effectively mitigates hypocalcemia during the first wk of lactation. To investigate possible negative metabolic effects of P deprivation during the dry period, the present study tested the hypothesis that restricted dietary P supply during the dry period alters the liver transcriptome of dairy cows during the periparturient period. Thirty late-pregnant multiparous Holstein-Friesian dairy cows entering their second, third, or fourth lactation were assigned to either a dry cow ration with low (LP, 0.16% P in DM) or adequate P content (AP, 0.35% in DM) during the last 4 wk of the dry period (n = 15/group). Liver transcriptomics, which was carried out in a subset of 5 second-parity cows of each group (n = 5), and determination of selected hormones and metabolites in blood of all cows, was performed ∼1 wk before calving and on d 3 postpartum. Liver tissue specimens and blood samples were obtained by a micro-invasive biopsy technique from the right tenth intercostal space and puncture of a jugular vein, respectively. One hundred seventy-five hepatic transcripts were expressed differentially between LP versus AP cows in late pregnancy, and 165 transcripts differed between LP versus AP cows in early lactation (fold change >1.3 and <-1.3, P < 0.05). In late pregnancy, the enriched biological processes of the upregulated and the downregulated transcripts were mainly related to immune processes and signal transduction (P < 0.05), respectively. In early lactation, the enriched biological processes of the upregulated and the downregulated transcripts were involved in mineral transport and biotransformation (P < 0.05), respectively. The plasma concentrations of the hormones and acute-phase proteins (progesterone, insulin-like growth factor 1, serum amyloid α, haptoglobin, and 17β-estradiol) determined were not affected by P supply. These results suggest that P deprivation during the dry period moderately affects the liver transcriptome of cows in late pregnancy and early lactation, and causes no effects on important plasma hormones and acute-phase proteins indicating no obvious impairment of health or metabolism of the cows.

Research Progress on the Mechanism of Milk Fat Synthesis in Cows and the Effect of Conjugated Linoleic Acid on Milk Fat Metabolism and Its Underlying Mechanism: A Review

Milk fat synthesis in cows mainly includes the synthesis of short- and medium-chain fatty acids, the uptake, transport, and activation of long-chain fatty acids (LCFAs), the synthesis of triglycerides, and the synthesis of the genes, transcription factors, and signaling pathways involved. Although the various stages of milk fat synthesis have been outlined in previous research, only partial processes have been revealed. CLA consists of an aggregation of positional and geometric isomers of linoleic fatty acid, and the accumulated evidence suggests that the two isomers of the active forms of CLA (cis-9, trans-11 conjugated linoleic acid and trans-10, cis-12 conjugated linoleic acid, abbreviated as c9, t11-CLA and t10, c12-CLA) can reduce the fat content in milk by regulating lipogenesis, fatty acid (FA) uptake, oxidation, and fat synthesis. However, the mechanism through which CLA inhibits milk fat synthesis is unique, with most studies focusing only on the effects of CLA on one of the genes, transcription factors, or signaling pathways involved. In this study, we summarized the structure and function of classic genes and pathways (mTOR, SREBP, AMPK, and PPARG) and new genes or pathways (THRSP, METTL3, ELOVL, and LPIN1) involved in each stage of milk fat synthesis and demonstrated the interactions between genes and pathways. We also examined the effects of other substances (melanin, nicotinic acid, SA, etc.). Furthermore, we evaluated the influence of β-sitosterol, sodium butyrate, Met arginine, and Camellia oleifera Abel on milk fat synthesis to improve the mechanism of milk fat synthesis in cows and provide a mechanistic reference for the use of CLA in inhibiting milk fat biosynthesis.

Thyroid hormone-responsive protein mediates the response of chicken liver to fasting mainly through the cytokine-cytokine receptor interaction pathway

1. The objective of this study was to explore the mediating role of thyroid hormone-responsive protein (THRSP) in the response of chicken liver to fasting.2. A batch of 7-d-old chicks with similar body weights were randomly divided into the control group and the fasting group (n = 10). The control group was fed ad libitum, while the test group fasted for 24 h. The liver and pectoral muscle tissues were collected. Chicken primary hepatocytes or myocytes were treated with different concentrations of thyroxine, glucose, insulin, oleic acid and palmitic acid, separately. Chicken primary hepatocytes were transfected with THRSP overexpression vector vs. empty vector, and the cells were used for transcriptome analysis. The mRNA expression of THRSP and other genes was determined by quantitative PCR.3. The expression of THRSP in chicken liver and pectoral muscle tissues was significantly inhibited by fasting (P < 0.05). In chicken primary hepatocytes, the expression of THRSP was significantly induced by thyroxine (0.25, 0.5, 1 mmol/l), glucose (50, 100 mmol/l), and insulin (20 nmol/l), and was significantly inhibited by palmitic acid (0.125, 0.25 mmol/l). In the myocytes, expression of THRSP was significantly induced by thyroxine (0.25, 0.5, 1 mmol/l), glucose (50 mmol/l) and oleic acid (0.125, 0.25 mmol/l), was significantly inhibited by insulin (5 nmol/l) and was not significantly affected by palmitic acid.4. Transcriptome analysis showed that overexpression of THRSP significantly affected the expression of 1411 DEGs, of which 1007 were up-regulated and 404 were down-regulated. The GO term and KEGG pathway enrichment analyses showed that these DEGs were mainly enriched in the interaction between cytokine and cytokine receptor and its regulation and signal transduction, cell growth and apoptosis and its regulation, immune response and retinol metabolism.5. In conclusion, the THRSP gene mediates biological effects of fasting by influencing the expressional regulation of the genes related to biological processes such as cytokine-cytokine receptor interaction, cell growth and apoptosis, immune response, retinol metabolism, including TGM2, HSD17B2, RUNX3, IRF1, ANKRD6, UPP2, IKBKE, and PYCR1 genes, in chicken liver.

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.

Review: genetic background of milk fatty acid synthesis in bovines

Milk fat composition is an important trait for the dairy industry as it directly influences the nutritional and technological properties of milk and other dairy products. The synthesis of milk fat is a complex process regulated by a network of genes. Thus, understanding the genetic variation and molecular mechanisms regulating milk fat synthesis will help to improve the nutritional quality of dairy products. In this review, we provide an overview of milk fat synthesis in bovines along with the candidate genes involved in the pathway. We also discuss de novo synthesis of fatty acids (ACSS, ACACA, FASN), uptake of FAs (FATP, FAT, LPL), intracellular activation and channelling of FAs (ACSL, FABP), elongation (EVOLV6), desaturation (SCD, FADS), formation of triglycerides (GPAM, AGPAT, LIPIN, DGAT), and milk lipid secretion (BTN1A1, XDH, PLIN2). The genetic variability of individual fatty acids will help to develop selection strategies for obtaining a healthier milk fat profile in bovines. Thus, this review will offer a potential understanding of the molecular mechanisms that regulate milk fat synthesis in bovines.

Gene co-expression network and differential expression analyses of subcutaneous white adipose tissue reveal novel insights into the pathological mechanisms underlying ketosis in dairy cows

Ketosis is a common nutritional metabolic disease during the perinatal period in dairy cows. Although various risk factors have been identified, the molecular mechanism underlying ketosis remains elusive. In this study, subcutaneous white adipose tissue (sWAT) was biopsied for transcriptome sequencing on 10 Holstein cows with type II ketosis [blood β-hydroxybutyric acid (BHB) >1.4 mmol/L; Ket group] and another 10 cows without type II ketosis (BHB ≤1.4 mmol/L; Nket group) at d 10 after calving. Serum concentrations of nonesterified fatty acids (NEFA) and BHB, as indicators of excessive fat mobilization and circulating ketone bodies, respectively, were significantly higher in the Ket group than in the Nket group. Aspartate transaminase (AST) and total bilirubin (TBIL), as indicators of liver damage, were higher in the Ket group than in the Nket group. Weighted gene co-expression network analysis (WGCNA) of the sWAT transcriptome revealed modules significantly correlated with serum BHB, NEFA, AST, TBIL, and total cholesterol. The genes in these modules were enriched in the regulation of the lipid biosynthesis process. Neurotrophic tyrosine kinase receptor type 2 (NTRK2) was identified as the key hub gene by intramodular connectivity, gene significance, and module membership. Quantitative reverse transcription PCR analyses for these samples, as well as a set of independent samples, validated the downregulation of NTRK2 expression in the sWAT of dairy cows with type II ketosis. NTRK2 encodes tyrosine protein kinase receptor B (TrkB), which is a high-affinity receptor for brain-derived neurotrophic factor, suggesting that abnormal lipid mobilization in cows with type II ketosis might be associated with impaired central nervous system regulation of adipose tissue metabolism, providing a novel insight into the pathogenesis underlying type II ketosis in dairy cows.

Prolactin regulates RANKL expression via signal transducer and activator of transcription 5a signaling in mammary epithelial cells of dairy cows

Receptor of activated nuclear factor kappa B ligand (RANKL) is regulated by prolactin in the mammary gland. However, the intrinsic molecular mechanism is not well understood. Herein, mammary epithelial cells (MECs) of dairy cows were isolated to characterize the molecular mechanism of prolactin in vitro. We demonstrated that prolactin stimulation increased the expression of RANKL in MECs. Moreover, the expression of RANKL induced by prolactin was inhibited by the prolactin receptor or signal transducer and activator of transcription 5A (STAT5a) knockdown. Furthermore, prolactin markedly increased RANKL-Luciferase reporter activity in MECs. We identified a putative gamma-interferon activated site (GAS) in the region between residues -883 to -239 bp of the RANKL promoter. Subsequently, we found that the mutated GAS sequence failed to respond to prolactin stimulation. In addition, STAT5a knockdown markedly decreased prolactin-stimulated RANKL promoter activity. Western blot results revealed that RANKL overexpression markedly decreased the STAT5a phosphorylation level in MECs. These findings indicate that prolactin could regulate RANKL promoter activity via STAT5a, contributing to increased RANKL expression in MECs. RANKL may have a negative regulatory effect on STAT5a activity.

METTL3 is a key regulator of milk synthesis in mammary epithelial cells

The enzyme m⁶ A methyltransferase-like 3 (METTL3) catalyzes N⁶ -methyladenosine (m⁶ A) modification in eukaryotic messenger RNAs (mRNAs). However, the physiological function and molecular mechanism of METTL3 in mammalian cells have not been fully understood. Here we showed that METTL3 was highly expressed in mouse mammary gland of the lactation period. METTL3 was located in the nucleus of bovine mammary epithelial cells (MECs), and methionine (Met) and β-estrodial (E2) upregulated METTL3 protein level. METTL3 knockdown decreased milk protein and fat synthesis, whereas its overexpression had the opposite effects. METTL3 overexpression stimulated mRNA expression and protein phosphorylation of the mechanistic target of rapamycin (mTOR) and mRNA and protein expression of sterol regulatory element binding protein 1 (SREBP1), whereas METTL3 knockdown blocked the stimulatory effects of Met and E2 on these processes. Furthermore, METTL3 overexpression led to increased mRNA m⁶ A methylation of mTOR and SREBP1, whereas METTL3 knockdown suppressed the stimulatory effects of Met and E2 on these processes. The interaction between METTL3 and glycyl-tRNA synthetase (GlyRS) was confirmed by Co-immunoprecipitation and fluorescence resonance energy transfer approaches, and colocalization observation further showed that Met and E2 treatment increased this interaction. GlyRS knockdown abolished METTL3 protein levels upregulated by Met and E2, and METTL3 knockdown markedly decreased the effects of GlyRS overexpression on mTOR expression and phosphorylation and SREBP1 expression. In summary, we demonstrate that METTL3 is a key positive regulator of Met and E2-stimulated and GlyRS-mediated mTOR and SREBP1 signaling pathways and milk protein and fat synthesis in mammary epithelial cells.

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.

Activation of Endogenous H2S Biosynthesis or Supplementation with Exogenous H2S Enhances Adipose Tissue Adipogenesis and Preserves Adipocyte Physiology in Humans

Aims: To investigate the impact of exogenous hydrogen sulfide (H₂S) and its endogenous biosynthesis on human adipocytes and adipose tissue in the context of obesity and insulin resistance. Results: Experiments in human adipose tissue explants and in isolated preadipocytes demonstrated that exogenous H₂S or the activation of endogenous H₂S biosynthesis resulted in increased adipogenesis, insulin action, sirtuin deacetylase, and PPARγ transcriptional activity, whereas chemical inhibition and gene knockdown of each enzyme generating H₂S (CTH, CBS, MPST) led to altered adipocyte differentiation, cellular senescence, and increased inflammation. In agreement with these experimental data, visceral and subcutaneous adipose tissue expression of H₂S-synthesising enzymes was significantly reduced in morbidly obese subjects in association with attenuated adipogenesis and increased markers of adipose tissue inflammation and senescence. Interestingly, weight-loss interventions (including bariatric surgery or diet/exercise) improved the expression of H₂S biosynthesis-related genes. In human preadipocytes, the expression of CTH, CBS, and MPST genes and H₂S production were dramatically increased during adipocyte differentiation. More importantly, the adipocyte proteome exhibiting persulfidation was characterized, disclosing that different proteins involved in fatty acid and lipid metabolism, the citrate cycle, insulin signaling, several adipokines, and PPAR, experienced the most dramatic persulfidation (85-98%). Innovation: No previous studies investigated the impact of H₂S on human adipose tissue. This study suggests that the potentiation of adipose tissue H₂S biosynthesis is a possible therapeutic approach to improve adipose tissue dysfunction in patients with obesity and insulin resistance. Conclusion: Altogether, these data supported the relevance of H₂S biosynthesis in the modulation of human adipocyte physiology. Antioxid. Redox Signal. 35, 319-340.

Association between THRSP Gene Polymorphism and Fatty Acid Composition in Milk of Dairy Cows

Thyroid hormone-inducible hepatic protein is involved in the de novo synthesis of fatty acids in the lactating mammary gland. Different variants of the gene that encodes this protein may be associated with its different activity. The primary aim of this study was to find polymorphism in the THRSP gene and estimate the relationship between individual genotypes and fatty acid composition in milk. Investigations were carried out on 224 cows represented by two breeds-Jersey (n = 80) and Polish Holstein-Friesian (n = 144). Polymorphism in THRSP was detected by Sanger sequencing; however, genotypes were determined by the PCR-RFLP method. It was shown that the analyzed variant had a significant (p < 0.05) influence on palmitic and stearic fatty acids as well as on fatty acids with a chain length of 14, 16, and 6-16 in Jersey breed and on caproic, palmitic, myristoleic, and palmitoleic fatty acids in H-F. Obtained results indicated that analyzed SNP in bovine THRSP gene (rs42714482) may be considered as a potential marker for fatty acid composition in milk.

Effects of Dietary Vegetable Oils on Mammary Lipid-Related Genes in Holstein Dairy Cows

Simple Summary

This study analyzed effects of vegetable oils fed to dairy cows on abundance of genes related to lipid metabolism in milk somatic cells (MSC). During 63 days (9 weeks), 15 cows were allocated to 3 treatments: a control diet with no added lipid and the same diet supplemented with olive oil (OO, 30 g/kg DM) or hydrogenated vegetable oil (HVO, 30 g/kg DM). Dietary oil supplementation (3% DM) had a modest nutrigenomic effect on biological functions such as acetate and FA activation and intra-cellular transport, lipid droplet formation, and transcription regulation in MSC. Results suggest that long-term dietary monounsaturated and saturated lipids could alter mRNA abundance in MSC from mid-lactating cows.

Abstract

This study analyzed effects of vegetable oils fed to dairy cows on abundance of genes related to lipid metabolism in milk somatic cells (MSC). During 63 days, 15 cows were allocated to 3 treatments: a control diet with no added lipid the same diet supplemented with olive oil (OO, 30 g/kg DM) or hydrogenated vegetable oil (HVO, 30 g/kg DM). On days 21, 42 and 63, MSC were obtained from all cows. Relative abundance of genes involved in lipid metabolism in MSC from cows fed control on days 42 and 63 was compared with relative abundance at day 21 to evaluate fold-changes. Those genes without changes over the time were selected to analyze effects of OO and HVO. Compared with control, on day 42, PLIN2 and THRSP were upregulated by OO. Compared with control, on day 21, HVO up regulated ACACA, down regulated FABP3, and on day 63 THRSP and FABP4 were down regulated. Dietary oil supplementation (3% DM) had a modest nutrigenomic effect on different biological functions such as acetate and FA activation and intra-cellular transport, lipid droplet formation, and transcription regulation in MSC.

GRP78 regulates milk biosynthesis and the proliferation of bovinemammaryepithelial cells through the mTOR signaling pathway

BACKGROUND

Glucose-regulated protein 78 (GRP78) is a member of the HSP70 protein family and a key endoplasmic reticulum chaperone. It has been revealed to play important roles both in the maturation, folding and transport of proteins and in cellproliferation. However, its involvement in milk biosynthesis or the proliferation of bovine primary mammary epithelial cells (BMECs) has yet to be established.

METHODS

The expressions of GRP78 in BMECs stimulated with methionine, leucine, estrogen and prolactin were determined using western blotting and immunofluorescence assays. To explore the function of GRP78 in BMECs, the protein was overexpressed or knocked down, respectively using an overexpression vector or an siRNA mixture transfected into cells cultured in vitro. Flow cytometry was used to analyze cell proliferation and cell activity. The contents of lactose and triglyceride (TG) secreted from the treated BMECs were measured using lactose and TG assay kits, respectively. Western blotting analysis was used to measure the β-casein content and the protein levels of the signaling molecules known to be involved in milk biosynthesis and cell proliferation.

RESULTS

GRP78overexpression significantly stimulated milk protein and milk fat synthesis, enhanced cell proliferation, positively regulated the phosphorylation of mammalian target of rapamycin (mTOR), and increased the amount of protein of cyclinD1andsterol regulatory element-binding protein 1c (SREBP-1c). GRP78 knockdown after siRNA transfection had the opposite effects. We further found that GRP78 was located in the cytoplasm of BMECs, and that stimulating methionine, leucine, estrogen and prolactin expression led to a significant increase in the protein expression of GRP78 in BMECs.

CONCLUSIONS

These data reveal that GRP78 is an important regulator of milk biosynthesis and the proliferation of BMECs through the mTOR signaling pathway.

The mTORC1/4EBP1/PPARγ Axis Mediates Insulin-Induced Lipogenesis by Regulating Lipogenic Gene Expression in Bovine Mammary Epithelial Cells

4EBP1 is a chief downstream factor of mTORC1, and PPARγ is a key lipogenesis-related transcription factor. mTORC1 and PPARγ are associated with lipid metabolism. However, it is unknown which effector protein connects mTORC1 and PPARγ. This study investigated the interaction between 4EBP1 with PPARγ as part of the underlying mechanism by which insulin-induced lipid synthesis and secretion are regulated by mTORC1 in primary bovine mammary epithelial cells (pBMECs). Rapamycin, a specific inhibitor of mTORC1, downregulated 4EBP1 phosphorylation and the expression of PPARγ and the following lipogenic genes: lipin 1, DGAT1, ACC, and FAS. Rapamycin also decreased the levels of intracellular triacylglycerol (TAG); 10 types of fatty acid; and the accumulation of TAG, palmitic acid (PA), and stearic acid (SA) in the cell culture medium. Inactivation of mTORC1 by shRaptor or shRheb attenuated the synthesis and secretion of TAG and PA. In contrast, activation of mTORC1 by Rheb overexpression promoted 4EBP1 phosphorylation and PPARγ expression and upregulated the mRNA and protein levels of lipin 1, DGAT1, ACC, and FAS, whereas the levels of intracellular and extracellular TAG, PA, and SA also rose. Further, 4EBP1 interacted directly with PPARγ. Inactivation of mTORC1 by shRaptor prevented the nuclear location of PPARγ. These results demonstrate that mTORC1 regulates lipid synthesis and secretion by inducing the expression of lipin 1, DGAT1, ACC, and FAS, which is likely mediated by the 4EBP1/PPARγ axis. This finding constitutes a novel mechanism by which lipid synthesis and secretion are regulated in pBMECs.

mTORC2 Regulates Lipogenic Gene Expression through PPARγ to Control Lipid Synthesis in Bovine Mammary Epithelial Cells

The mechanistic target of rapamycin complex 2 (mTORC2) primarily functions as an effector of insulin/PI3K signaling to regulate cell proliferation and is associated with cell metabolism. However, the function of mTORC2 in lipid metabolism is not well understood. In the present study, mTORC2 was inactivated by the ATP-competitive mTOR inhibitor AZD8055 or shRNA targeting RICTOR in primary bovine mammary epithelial cells (pBMECs). MTT assay was performed to examine the effect of AZD8055 on cell proliferation. ELISA assay and GC-MS analysis were used to determine the content of lipid. The mRNA and protein expression levels were investigated by RT/real-time PCR and western blot analysis, respectively. We found that cell proliferation, mTORC2 activation, and lipid secretion were inhibited by AZD8055. RICTOR was knocked down and mTORC2 activation was specifically attenuated by the shRNA. Compared to control cells, the expression of the transcription factor gene PPARG and the lipogenic genes LPIN1, DGAT1, ACACA, and FASN was downregulated in RICTOR silencing cells. As a result, the content of intracellular triacylglycerol (TAG), palmitic acid (PA), docosahexaenoic acid (DHA), and other 16 types of fatty acid was decreased in the treated cells; the accumulation of TAG, PA, and DHA in cell culture medium was also reduced. Overall, mTORC2 plays a critical role in regulating lipogenic gene expression, lipid synthesis, and secretion in pBMECs, and this process probably is through PPARγ. This finding provides a model by which lipogenesis is regulated in pBMECs.

Taurine Promotes Milk Synthesis via the GPR87-PI3K-SETD1A Signaling in BMECs

Taurine, a β-aminosulfonic acid, exerts many cellular physiological functions. It is still unknown whether taurine can regulate milk synthesis in the mammary gland. Therefore, in this study we investigated the effects and mechanism of taurine on milk synthesis in mammary epithelial cells (MECs). Bovine MECs (BMECs) cultured in FBS-free OPTI-MEMImedium were treated with taurine (0, 0.08, 0.16, 0.24, 0.32, and 0.4 mM). Taurine treatment led to increased milk protein and fat synthesis, mTOR phosphorylation, and SREBP-1c protein expression, in a dose-dependent manner, with an apparent maximum at 0.24 mM. Gene function study approaches revealed that the GPR87-PI3K-SETD1A signaling was required for taurine to increase the mTOR and SREBP-1c mRNA levels. Taurine stimulated GPR87 expression and cell membrane localization in a dose dependent manner, suggesting a sensing mechanism of GPR87 to extracellular taurine. Collectively, these data demonstrate that taurine promotes milk synthesis via the GPR87-PI3K-SETD1A signaling.

Methionine Promotes Milk Protein and Fat Synthesis and Cell Proliferation via the SNAT2-PI3K Signaling Pathway in Bovine Mammary Epithelial Cells

Methionine (Met) plays a critical regulatory role in milk production, however, the molecular mechanism of action of Met is largely unknown. This study therefore aimed to investigate the influence of Met on milk synthesis in and proliferation of bovine mammary epithelial cells (BMECs) and explore the underlying mechanism. BMECs cultured in fetal bovine serum (FBS) free Dulbecco's modified eagle's medium (DMEM)/F-12 medium were treated with Met (0, 0.3, 0.6, 0.9, and 1.2 mM). Results showed that Met (0.6 mM) significantly increased milk protein and fat synthesis and cell proliferation. Met stimulation also increased mTOR phosphorylation and protein expression of SREBP-1c and Cyclin D1. Gene function study approaches further revealed that SNAT2 is a key regulator of these signaling pathways. PI3K inhibition experiments demonstrated that SNAT2 stimulates these pathways through regulating PI3K activity, and SNAT2 inhibition experiments further revealed that SNAT2 is required for Met to activate PI3K. Furthermore, immunofluorescence observation detected that Met stimulates SNAT2 cytoplasmic expression. Collectively, these findings demonstrate that Met positively regulates milk protein and fat synthesis and cell proliferation via the SNAT2-PI3K signaling pathway in BMECs.

MiR-451a attenuates free fatty acids-mediated hepatocyte steatosis by targeting the thyroid hormone responsive spot 14 gene

The thyroid hormone responsive spot 14 (THRSP) gene is a de novo lipogenesis-related gene that plays a significant role in the initiation and development of nonalcoholic fatty liver disease (NAFLD). Several previous studies had shown that endogenous and environmental factors could regulate the expression of THRSP. The role of microRNAs (miRNAs), however, in controlling THRSP expression has not been investigated. In this study, we first constructed the hepatic steatosis cell model by using a mixture of free fatty acids (FFAs; oleate/palmitate, 2:1 ratio) to treat and demonstrate the promotive role of THRSP in lipid accumulation in hepatic cells. By analyzing the photoactivatable ribonucleoside-enhanced crosslinking and immunoprecipitation (PAR-CLIP) database and performing a luciferase reporter assay, we confirmed that microRNA-451a specifically binds to mouse and human THRSP 3'UTR and inhibits its activity. Overexpression of miR-451a efficiently reduced THRSP mRNA and protein expression as well as triglyceride (TG) accumulation in cultured hepatic cells (AML12 and HepG2). Moreover, overexpression of miR-451a significantly decreases TG accumulation in the livers of mice injected with an miR-451a agomir. All these results demonstrated that miR-451a might participate in the FFA-induced hepatic steatosis by regulating the expression of the THRSP gene which represents a new potential target for NAFLD therapy.

Time-dependent effect of trans-10,cis-12 conjugated linoleic acid on gene expression of lipogenic enzymes and regulators in mammary tissue of dairy cows

Trans-10,cis-12 conjugated linoleic acid (CLA) has been identified as an intermediate of rumen fatty acid biohydrogenation that caused milk fat depression (MFD) in the dairy cow. Previous studies in cows experiencing CLA- and diet-induced MFD have identified reduced mammary expression of the master lipogenic regulator sterol response element transcription factor 1 (SREBF1) and many of its dependent genes. To distinguish between primary mechanisms regulating milk fat synthesis and secondary adaptations to the reduction in milk fat, we conducted a time-course experiment. Eleven dairy cows received by abomasal infusion an initial priming dose of 6.25 g of CLA followed by 12.5 g/d delivered in multiple pulses per day for 5 d. Cows were milked 3×/d and mammary biopsies were obtained under basal condition (prebolus control) and 12, 30, and 120 h relative to initiation of CLA infusion. Milk fat concentration and yield decreased progressively reaching a nadir at 69 h (1.82% and 38.2 g/h) and averaged 2.03 ± 0.19% and 42.1 ± 4.10 g/h on the last day of treatment (±standard deviation). Expression of fatty acid synthase (FASN) and lipoprotein lipase (LPL) were decreased at 30 and 120 h compared with control. Expression of SREBF1 and THRSP were also decreased at 30 and 120 h compared with control. Additionally, we failed to observe changes in other factors, including peroxisome proliferator-activated receptor γ and liver × receptor β and milk fat globular membrane proteins, during CLA treatment. However, expression of milk fat globular membrane proteins were decreased after 14 d of diet-induced MFD in samples from a previous experiment, indicating a possible long-term response. The rapid decrease in lipogenic enzymes, SREBF1, and THRSP provide strong support for their transcriptional regulation as a primary mechanism of milk fat depression.

MiR-139 suppresses β-casein synthesis and proliferation in bovine mammary epithelial cells by targeting the GHR and IGF1R signaling pathways

BACKGROUND

MicroRNAs have important roles in many biological processes. However, the role of miR-139 in healthy mammary gland remains unclear. The objective of this study was to investigate the effects of miR-139 on lactation in dairy cows.

RESULTS

Here, we found that miR-139 was down-regulated in mid-lactation dairy cow mammary tissues compared with mid-pregnancy tissues. Then, we prioritized two of potential target genes of miR-139 in cow, growth hormone receptor (GHR) and type I insulin-like growth factor receptor (IGF1R) for further functional studies based on their roles in lactation processes. Dual luciferase reporter assays validated direct binding of miR-139 to the 3'- untranslated region (UTR) of GHR and IGF1R. Moreover, over-expression or silencing of miR-139 affected mRNA levels of GHR and IGF1R in cultured bovine mammary epithelial cells (BMECs). Furthermore, over-expression of miR-139 decreased protein levels of β-casein, proliferation in mammary epithelial cell, and the protein levels of IGF1R and key members of the GHR or IGF1R pathways as well, whereas silencing miR-139 produced the opposite result. Among these signal molecules, signal transducer and activator of transcription-5 (STAT5), protein kinase B (also known as AKT1), mammalian target of rapamycin (mTOR), and p70-S6 Kinase (p70S6K) are involed in β-casein synthesis, and Cyclin D1 is involved in cell proliferation. In addition, silencing GHR decreased protein levels of β-casein, IGF1R, and key members of the IGF1R pathway, whereas co-silencing miR-139 and GHR rescued the expression of GHR and reversed GHR silencing effects.

CONCLUSIONS

Our results demonstrate that GHR and IGF1R are target genes of miR-139 in dairy cow. MiR-139 suppresses β-casein synthesis and proliferation in BMECs by targeting the GHR and IGF1R signaling pathways.

Expression of Thyroid Hormone Responsive SPOT 14 Gene Is Regulated by Estrogen in Chicken (Gallus gallus)

Thyroid hormone responsive spot 14 (THRSP) is a small nuclear protein that responds rapidly to thyroid hormone. It has been shown that THRSP is abundant in lipogenic tissues such as liver, fat and the mammary gland in mammals. The THRSP gene acts as a key lipogenic activator and can be activated by thyroid hormone triiodothyronine (T3), glucose, carbohydrate and insulin. Here we report that chicken THRSP is also abundant in lipogenic tissues including the liver and the abdominal fat, and its expression levels increased with sex maturation and reached the highest level at the peak of egg production. Structure analysis of the THRSP gene indicates that there is a conscious estrogen response element (ERE) located in the −2390 – −2402 range of the gene promoter region. Further studies by ChIP-qPCR proved that the ERα interacts with the putative ERE site. In addition, THRSP was significantly upregulated (P < 0.05) when chickens or chicken primary hepatocytes were treated with 17β-estradiol in both the in vivo and in vitro conditions. We therefore conclude that THRSP is directly regulated by estrogen and is involved in the estrogen regulation network in chicken.

Sebaceous Gland Atrophy in Psoriasis: An Explanation for Psoriatic Alopecia?

In a transcriptome study of lesional psoriatic skin (PP) versus normal skin, we found a coexpressed gene module (N5) enriched 11.5-fold for lipid biosynthetic genes. We also observed fewer visible hairs in PP skin, compared with uninvolved nonlesional psoriatic skin or normal skin (P < 0.0001). To ask whether these findings might be due to abnormalities of the pilosebaceous unit, we carried out three-dimensional morphometric analysis of paired PP and nonlesional psoriatic skin biopsies. Sebaceous glands were markedly atrophic in PP versus nonlesional psoriatic skin (91% average reduction in volume, P = 0.031). Module N5 genes were strongly downregulated in PP versus normal skin (fold change < 0.25, 44.4-fold) and strongly upregulated in sebaceous hyperplasia (fold change > 4, 54.1-fold). The intersection of PP-downregulated and sebaceous hyperplasia-upregulated gene lists generated a gene expression signature consisting solely of module N5 genes, whose expression in PP versus normal skin was inversely correlated with the signature of IL17-stimulated keratinocytes. Despite loss of visible hairs, morphometry identified elongated follicles in PP versus nonlesional psoriatic skin (average 1.7 vs. 1.2 μm, P = 0.020). These results document sebaceous gland atrophy in nonscalp psoriasis, identify a cytokine-regulated set of sebaceous gland signature genes, and suggest that loss of visible hair in PP skin may result from abnormal sebaceous gland function.

Biosynthesis of milk fat, protein, and lactose: roles of transcriptional and posttranscriptional regulation

The demand for high-quality milk is increasing worldwide. The efficiency of milk synthesis can be improved by taking advantage of the accumulated knowledge of the transcriptional and posttranscriptional regulation of genes coding for proteins involved in the synthesis of fat, protein, and lactose in the mammary gland. Research in this area is relatively new, but data accumulated in the last 10 years provide a relatively clear picture. Milk fat synthesis appears to be regulated, at least in bovines, by an interactive network between SREBP1, PPARγ, and LXRα, with a potential role for other transcription factors, such as Spot14, ChREBP, and Sp1. Milk protein synthesis is highly regulated by insulin, amino acids, and amino acid transporters via transcriptional and posttranscriptional routes, with the insulin-mTOR pathway playing a central role. The transcriptional regulation of lactose synthesis is still poorly understood, but it is clear that glucose transporters play an important role. They can also cooperatively interact with amino acid transporters and the mTOR pathway. Recent data indicate the possibility of nutrigenomic interventions to increase milk fat synthesis by feeding long-chain fatty acids and milk protein synthesis by feeding amino acids. We propose a transcriptional network model to account for all available findings. This model encompasses a complex network of proteins that control milk synthesis with a cross talk between milk fat, protein, and lactose regulation, with mTOR functioning as a central hub.

Thyroid hormone responsive (THRSP) promotes the synthesis of medium-chain fatty acids in goat mammary epithelial cells

In nonruminants, thyroid hormone responsive (THRSP) is a crucial protein for cellular de novo lipogenesis. However, the role of THRSP in regulating the synthesis of milk fatty acid composition in goat mammary gland remains unknown. In the present study, we compared gene expression of THRSP among different goat tissues. Results revealed that THRSP had the highest expression in subcutaneous fat, and expression was higher during lactation compared with the dry period. Overexpression of THRSP upregulated the expression of fatty acid synthase (FASN), stearoyl-coenzyme A desaturase 1 (SCD1), diacylglycerol acyltransferase 2 (DGAT2), and glycerol-3-phosphate acyltransferase (GPAM) in goat mammary epithelial cells. In contrast, overexpression of THRSP led to downregulation of thrombospondin receptor (CD36) and had no effect on the expression of acetyl-coenzyme A carboxylase α (ACACA) and sterol regulatory element binding transcription factor1 (SREBF1). In addition, overexpressing THRSP in vitro resulted in a significant increase in triacylglycerol (TAG) concentration and the concentrations of C12:0 and C14:0. Taken together, these results highlight an important role of THRSP in regulating lipogenesis in goat mammary epithelial cells.