Fatty acid elongase 5 (ELOVL5) alters the synthesis of long-chain unsaturated fatty acids in goat mammary epithelial cells

tsRNA Landscape and Potential Function Network in Subcutaneous and Visceral Pig Adipose Tissue

Noncoding RNAs (ncRNAs) called tsRNAs (tRNA-derived short RNAs) have the ability to regulate gene expression. The information on tsRNAs in fat tissue is, however, limited. By sequencing, identifying, and analyzing tsRNAs using pigs as animal models, this research reports for the first time the characteristics of tsRNAs in subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT). A total of 474 tsRNAs, 20 and 21 of which were particularly expressed in VAT and SAT, respectively, were found in WAT. According to the analysis of the tsRNA/miRNA/mRNA co-expression network, the tsRNAs with differential expression were primarily engaged in the endocrine and immune systems, which fall under the classification of organic systems, as well as the global and overview maps and lipid metropolis, which fall under the category of metabolism. This research also discovered a connection between the activity of the host tRNA engaged in translation and the production of tsRNAs. This research also discovered that tRF-Gly-GCC-037/tRF-Gly-GCC-042/tRF-Gly-CCC-016 and miR-218a/miR281b may be involved in the regulation of fatty acid metabolism in adipose tissue through SCD based on the tsRNA/miRNA/mRNA/fatty acid network. In conclusion, our findings enrich the understanding of ncRNAs in WAT metabolism and health regulation, as well as reveal the differences between SAT and VAT at the level of tsRNAs.

The LXRB-SREBP1 network regulates lipogenic homeostasis by controlling the synthesis of polyunsaturated fatty acids in goat mammary epithelial cells

Background

In rodents, research has revealed a role of liver X receptors (LXR) in controlling lipid homeostasis and regulating the synthesis of polyunsaturated fatty acids (PUFA). Recent data suggest that LXRB is the predominant LXR subtype in ruminant mammary cells, but its role in lipid metabolism is unknown. It was hypothesized that LXRB plays a role in lipid homeostasis via altering the synthesis of PUFA in the ruminant mammary gland. We used overexpression and knockdown of LXRB in goat primary mammary epithelial cells (GMEC) to evaluate abundance of lipogenic enzymes, fatty acid profiles, content of lipid stores and activity of the stearoyl-CoA desaturase (SCD1) promoter.

Results

Overexpression of LXRB markedly upregulated the protein abundance of LXRB while incubation with siRNA targeting LXRB markedly decreased abundance of LXRB protein. Overexpression of LXRB plus T0901317 (T09, a ligand for LXR) dramatically upregulated SCD1 and elongation of very long chain fatty acid-like fatty acid elongases 5–7 (ELOVL 5–7), which are related to PUFA synthesis. Compared with the control, cells overexpressing LXRB and stimulated with T09 had greater concentrations of C16:0, 16:1, 18:1n7,18:1n9 and C18:2 as well as desaturation and elongation indices of C16:0. Furthermore, LXRB-overexpressing cells incubated with T09 had greater levels of triacylglycerol and cholesterol. Knockdown of LXRB in cells incubated with T09 led to downregulation of genes encoding elongases and desaturases. Knockdown of LXRB attenuated the increase in triacylglycerol and cholesterol that was induced by T09. In cells treated with dimethylsulfoxide, knockdown of LXRB increased the concentration of C16:0 at the expense of C18:0, while a significant decrease in C18:2 was observed in cells incubated with both siLXRB and T09. The abundance of sterol regulatory element binding transcription factor 1 precursor (pSREBP1) and its mature fragment (nSREBP1) was upregulated by T09, but not LXRB overexpression. In the cells cultured with T09, knockdown of LXRB downregulated the abundance for pSREBP1 and nSREBP1. Luciferase reporter assays revealed that the activities of wild type SCD1 promoter or fragment with SREBP1 response element (SRE) mutation were decreased markedly when LXRB was knocked down. Activity of the SCD1 promoter that was induced by T09 was blocked when the SRE mutation was introduced.

Conclusion

The current study provides evidence of a physiological link between the LXRB and SREBP1 in the ruminant mammary cell. An important role was revealed for the LXRB-SREBP1 network in the synthesis of PUFA via the regulation of genes encoding elongases and desaturases. Thus, targeting this network might elicit broad effects on lipid homeostasis in ruminant mammary gland.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40104-022-00774-4.

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.

The repertoire of the elongation of very long-chain fatty acids (Elovl) protein family is conserved in tambaqui (Colossoma macropomum): Gene expression profiles offer insights into the sexual differentiation process

Elongation of very long-chain fatty acids (Elovl) proteins are critical players in the regulation of the length of a fatty acid. At present, eight members of the Elovl family (Elovl1-8), displaying a characteristic fatty acid substrate specificity, have been identified in vertebrates, including teleost fish. In general, Elovl1, Elovl3, Elovl6 and Elovl7 exhibit a substrate preference for saturated and monounsaturated fatty acids, while Elovl2, Elovl4, Elovl5 and Elovl8 use polyunsaturated fatty acids (PUFA) as substrates. PUFA elongases have received considerable attention in aquatic animals due to their involvement in the conversion of C₁₈ PUFAs to long-chain polyunsaturated fatty acids (LC-PUFA). Here, we identified the full repertoire of elovl genes in the tambaqui Colossoma macropomum genome. A detailed phylogenetic and synteny analysis suggests a conservation of these genes among teleosts. Furthermore, based on RNAseq gene expression data, we discovered a gender bias expression of elovl genes during sex differentiation of tambaqui, toward future males. Our findings suggest a role of Elovl enzymes and fatty acid metabolism in tambaqui sexual differentiation.

circ01592 regulates unsaturated fatty acid metabolism through adsorbing miR-218 in bovine mammary epithelial cells

The composition of fatty acids plays a key role in regulating milk flavor and quality. Therefore, to improve the quality of milk, it is particularly important to study the regulatory mechanism of fatty acid metabolism in dairy cows. In this study, the expression profiles at non-lactation, peak-lactation, mid-lactation and late-lactation were constructed by high-throughput sequencing. Considering non-lactation as the control group and the other points as the experimental groups, the differentially expressed genes were screened. ELOVL5 was significantly upregulated and was selected for subsequent analyses. Bioinformatics prediction, a dual-luciferase assay, qPCR analysis and western blot analysis were used for verification. The results showed that ELOVL5 was a downstream target gene of miR-218 that regulated milk fat metabolism. A dual-luciferase assay and expression level analysis showed that circ01592 can directly bind to miR-218 and that overexpression of circ01592 (pcDNA-circ01592) significantly reduced the expression of miR-218 and enhanced the expression of ELOVL5, the target gene of miR-218 in BMECs. A functional study of BMECs showed that circ01592 promoted the synthesis of TAG and increased the content of UFA. The function of miR-218 was opposite to that of circ01592. Overall, the data showed that circ01592 promoted TAG synthesis and fatty acid composition by binding miR-218, alleviating the inhibitory effect of miR-218 on ELOVL5 expression. These mechanisms provide a new research approach and theoretical basis for improving milk quality.

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.

MicroRNA-193a-5p Regulates the Synthesis of Polyunsaturated Fatty Acids by Targeting Fatty Acid Desaturase 1 (FADS1) in Bovine Mammary Epithelial Cells

Cardiovascular diseases (CVDs) are seriously threatening to human life and health. Polyunsaturated fatty acids (PUFAs) are known for their role in preventing CVDs. It is beneficial to population health to promote the content of PUFAs in bovine milk. In recent years, limited research based on molecular mechanisms has focused on this field. The biological roles of numerous microRNAs (miRNAs) remain unknown. In this study, a promising and negatively correlated pair of the miRNA (miRNA-193a-5p) and a fatty acid desaturase 1 (FADS1) gene are identified and screened to explore whether they are potential factors of PUFAs’ synthesis in bovine milk. The targeted relationship between miRNA-193a-5p and FADS1 in bovine mammary epithelial cells (BMECs) is demonstrated by dual luciferase reporter assays. qRT-PCR and western blot assays indicate that both the expression of mRNA and the protein FADS1 show a negative correlation with miRNA-193a-5p expression in BMECs. Also, miR-193a-5p expression is positively correlated with the expression of genes associated with milk fatty acid metabolism, including ELOVL fatty acid elongase 6 (ELOVL6) and diacylglycerol O-acyltransferase 2 (DGAT2). The expression of fatty acid desaturase 2 (FADS2) is negatively correlated with miR-193a-5p expression in BMECs. The contents of triglycerides (TAG), eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA) and docosahexaenoic acid (DHA) have a significant positive correlation with the expression of FADS1 and a significant negative correlation with the expression of miR-193a-5p in BMECs. For the first time, this study confirms that miRNA-193a-5p regulates PUFAs metabolism in BMECs by targeting FADS1, indicating that miRNA-193a-5p and FADS1 are underlying factors that improve PUFAs content in bovine milk.

Supplementation with Seabuckthorn Oil Augmented in 16:1n-7t Increases Serum Trans-Palmitoleic Acid in Metabolically Healthy Adults: A Randomized Crossover Dose-Escalation Study

BACKGROUND

In animal models cis-palmitoleic acid (9-hexadecenoic acid; 16:1n-7c), a lipokine, improves insulin sensitivity, inflammation, and lipoprotein profiles; in humans trans-palmitoleic acid (16:1n-7t) has been associated with lower incidence of type 2 diabetes. The response to dose-escalation of supplements containing cis- and trans-palmitoleic acid has not been evaluated.

OBJECTIVES

We examined dose-escalation effects of oral supplementation with seabuckthorn oil and seabuckthorn oil augmented in 16:1n-7t on serum phospholipid fatty acids (PLFAs).

METHODS

Thirteen participants (7 women and 6 men; age 48 ± 16 y, BMI 30.4 ± 3.7 kg/m2) participated in a randomized, double-blind, crossover, dose-escalation trial of unmodified seabuckthorn oils relatively high in 16:1n-7c (380, 760, and 1520 mg 16:1n-7c/d) and seabuckthorn oils augmented in 16:1n-7t (120, 240, and 480 mg 16:1n-7t/d). Each of the 3 escalation doses was provided for 3 wk, with a 4-wk washout period between the 2 supplements. At the end of each dose period, fasting blood samples were used to determine the primary outcomes (serum concentrations of the PLFAs 16:1n-7t and 16:1n-7c) and the secondary outcomes (glucose homeostasis, serum lipids, and clinical measures). Trends across doses were evaluated using linear regression.

RESULTS

Compared with baseline, supplementation with seabuckthorn oil augmented in 16:1n-7t increased phospholipid 16:1n-7t by 26.6% at the highest dose (P = 0.0343). Supplementation with unmodified seabuckthorn oil resulted in a positive trend across the dose-escalations (P-trend = 0.0199). No significant effects of either supplement were identified on blood glucose, insulin, lipids, or other clinical measures, although this dosing study was not powered to detect such effects. No carryover or adverse effects were observed.

CONCLUSIONS

Supplementation with seabuckthorn oil augmented in 16:1n-7t and unmodified seabuckthorn oil moderately increased concentrations of their corresponding PLFAs in metabolically healthy adults, supporting the use of supplementation with these fatty acids to test potential clinical effects in humans.This trial was registered at clinicaltrials.gov as NCT02311790.

Genome-Wide Identification and Characterization of Long Noncoding RNAs of Brown to White Adipose Tissue Transformation in Goats

Long noncoding RNAs (lncRNAs) play an important role in the thermogenesis and energy storage of brown adipose tissue (BAT). However, knowledge of the cellular transition from BAT to white adipose tissue (WAT) and the potential role of lncRNAs in goat adipose tissue remains largely unknown. In this study, we analyzed the transformation from BAT to WAT using histological and uncoupling protein 1 (UCP1) gene analyses. Brown adipose tissue mainly existed within the goat perirenal fat at 1 day and there was obviously a transition from BAT to WAT from 1 day to 1 year. The RNA libraries constructed from the perirenal adipose tissues of 1 day, 30 days, and 1 year goats were sequenced. A total number of 21,232 lncRNAs from perirenal fat were identified, including 5393 intronic-lncRNAs and 3546 antisense-lncRNAs. Furthermore, a total of 548 differentially expressed lncRNAs were detected across three stages (fold change ≥ 2.0, false discovery rate (FDR) < 0.05), and six lncRNAs were validated by qPCR. Furthermore, trans analysis found lncRNAs that were transcribed close to 890 protein-coding genes. Additionally, a coexpression network suggested that 4519 lncRNAs and 5212 mRNAs were potentially in trans-regulatory relationships (r > 0.95 or r < -0.95). In addition, Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses showed that the targeted genes were involved in the biosynthesis of unsaturated fatty acids, fatty acid elongation and metabolism, the citrate cycle, oxidative phosphorylation, the mitochondrial respiratory chain complex, and AMP-activated protein kinase (AMPK) signaling pathways. The present study provides a comprehensive catalog of lncRNAs involved in the transformation from BAT to WAT and provides insight into understanding the role of lncRNAs in goat brown adipogenesis.

Fatty Acid Elongase 7 (ELOVL7) Plays a Role in the Synthesis of Long-Chain Unsaturated Fatty Acids in Goat Mammary Epithelial Cells

Simple Summary

Very-long-chain elongases are required for the synthesis of essential fatty acids in non-ruminants. Whether the fatty acid elongase 7 (ELOVL7) plays a role in ruminants is unclear. We demonstrated, in goat mammary epithelial cells, that ELOVL7 activation resulted in greater concentrations of vaccenic (C18:1n7) and linoleic (C18:2) acid, and lower concentrations of palmitoleic (C16:1n7) and oleic (C18:1n9) acid. Knockdown of ELOVL7 increased the concentration of C18:1n9. The data support a novel role of ELOVL7 in altering long-chain unsaturated fatty acids in goat mammary epithelial cells.

Abstract

In humans, fatty acid elongase 7 (ELOVL7) plays a role in synthesis of long-chain saturated fatty acids. Whether ELOVL7 protein plays a role in ruminants is unclear. The transcript abundance of ELOVL7 in goat mammary tissue was assessed at three stages of lactation. Results showed that ELOVL7 had the highest expression in the dry period compared with peak and late lactation period. Results revealed that ELOVL7 overexpression was correlated with lower expression in diacylglycerol O-acyltransferase 2 (DGAT2) and stearoyl-CoA desaturase 1 (SCD1), and had no significant effect on triacylglycerol concentration. Overexpression of ELOVL7 significantly decreased the concentration of palmitoleic (C16:1n7) and oleic (C18:1n9) acid, and increased the concentration of vaccenic (C18:1n7) and linoleic (C18:2) acid. Overexpression of ELOVL7 significantly upregulated the elongation index of C16:1 in goat epithelial mammary cells (GMEC), but had a minor effect on that of palmitate (C16:0). Knockdown of ELOVL7 decreased mRNA expression of fatty acid binding protein 3 (FABP3) and fatty acid desaturase 2 (FADS2) and had a minor effect on triacylglycerol concentration; however, it increased concentration of C18:1n9 in GMEC. The elongation indices of C16:0 and C16:1 did not differ due to knockdown of ELOVL7. The minor change for the C16:0 and stearate (C18:0) was observed after activation of ELOVL7, suggesting the two fatty acids are not the preferential substrates of ELOVL7 in cultured GMEC. However, changes in C18:1n9 and C18:2 after overexpression or knockdown of ELOVL7 indicated a biological functional role of ELOVL7. Collectively, our data highlighted a role of ELOVL7 in long-chain unsaturated fatty acid elongation in goat mammary epithelial cells.

gga-miRNA-18b-3p Inhibits Intramuscular Adipocytes Differentiation in Chicken by Targeting the ACOT13 Gene

Intramuscular fat (IMF) is the most important evaluating indicator of chicken meat quality, the content of which is positively correlated with tenderness, flavor, and succulence of the meat. Chicken IMF deposition process is regulated by many factors, including genetic, nutrition, and environment. Although large number of omics' studies focused on the IMF deposition process, the molecular mechanism of chicken IMF deposition is still poorly understood. In order to study the role of miRNAs in chicken intramuscular adipogenesis, the intramuscular adipocyte differentiation model (IMF-preadipocytes and IMF-adipocytes) was established and subject to miRNA-Seq. A total of 117 differentially expressed miRNAs between two groups were obtained. Target genes prediction and functional enrichment analysis revealed that eight pathways involved in lipid metabolism related processes, such as fatty acid metabolism and fatty acid elongation. Meanwhile a putative miRNA, gga-miR-18b-3p, was identified be served a function in the intramuscular adipocyte differentiation. Luciferase assay suggested that the gga-miR-18b-3p targeted to the 3'UTR of ACOT13. Subsequent functional experiments demonstrated that gga-miR-18b-3p acted as an inhibitor of intramuscular adipocyte differentiation by targeting ACOT13. Our findings laid a new theoretical foundation for the study of lipid metabolism, and also provided a potential target to improve the meat quality in the poultry industry.

CRISPR/Cas9-mediated Stearoyl-CoA Desaturase 1 (SCD1) Deficiency Affects Fatty Acid Metabolism in Goat Mammary Epithelial Cells

Stearoyl-CoA desaturase 1 (SCD1) is a fatty acid desaturase catalyzing cis-double-bond formation in the Δ9 position to produce monounsaturated fatty acids essential for the synthesis of milk fat. Previous studies using RNAi methods have provided support for a role of SCD1 in goat mammary epithelial cells (GMEC); however, RNAi presents several limitations that might preclude a truthful understanding of the biological function of SCD1. To explore the function of SCD1 on fatty acid metabolism in GMEC, we used CRISPR-Cas9-mediated SCD1 knockout through non-homologous end-joining (NHEJ) and homology-directed repair (HDR) pathways in GMEC. We successfully introduced nucleotide deletions and mutations in the SCD1 gene locus through the NHEJ pathway and disrupted its second exon via insertion of an EGFP-PuroR segment using the HDR pathway. In clones derived from the latter, gene- and protein-expression data indicated that we obtained a monoallelic SCD1 knockout. A T7EN1-mediated assay revealed no off-targets in the surveyed sites. The contents of triacylglycerol and cholesterol and the desaturase index were significantly decreased as a consequence of SCD1 knockout. The deletion of SCD1 decreased the expression of other genes involved in de novo fatty acid synthesis, including SREBF1 and FASN, as well the fatty acid transporters FABP3 and FABP4. The downregulation of these genes partly explains the decrease of intracellular triacylglycerols. Our results indicate a successful SCD1 knockout in goat mammary cells using CRISPR-Cas9. The demonstration of the successful use of CRISPR-Cas9 in GMEC is an important step to producing transgenic goats to study mammary biology in vivo.

Effect of different exogenous fatty acids on the cytosolic triacylglycerol content in bovine mammary cells

The objective of this study was to determine how cytosolic triacylglycerols (TAG) are stored in mammary cells and whether this depends on the individual chemical configuration of fatty acids (FA). This objective was accomplished by addition of different FA to a FA-free medium used to culture mammary alveolar cells-large T antigen cells (MAC-T). Treatments consisted of adding FA (palmitate, stearate, oleate, linoleate, rumenic acid [CLA], elaidate and vaccinate) solutions to the medium at 100, 200, 300 and 400 mmol/L concentrations for a 24-h incubation period. At the end of each incubation period, cytosolic TAG, DNA and protein contents were measured. Palmitate, vaccenate, linoleate and CLA increased (P < 0.05) cytosolic TAG (μg/mg protein). Palmitate and CLA increased (P < 0.05) cytosolic TAG adjusted for DNA content. Overall, effects on cytosolic TAG accumulation depended on individual FA structure (chain length, degree of saturation, and number and orientation of FA double bonds). In addition, the long-chain FA used in this study did not have a detrimental effect on MAC-T cells as indicated by cytosolic protein and DNA contents reflecting their biological role in lipid accumulation.