Sp1 is Involved in Vertebrate LC-PUFA Biosynthesis by Upregulating the Expression of Liver Desaturase and Elongase Genes

Research Note: Identification of core promoter region of the polyunsaturated fatty acid synthesis-related gene family in chicken

Chicken is considered an ideal model species to study the synthesis of polyunsaturated fatty acids (PUFAs) due to its appropriate proportions of fatty acids and abundant content of PUFAs, suitable for human consumption. However, the molecular mechanisms regulating poultry PUFA synthesis remain unclear. Here, we systematically explored the transcriptional regulation activity of the gene family related to PUFA synthesis in chicken by carrying out the Dual-Luciferase Reporter Assay. We identified the core promoter regions of members of the chicken PUFA synthesis-related gene family, including ELOVL1, ELOVL2, ELOVL3, ELOVL4, ELOVL5, ELOVL6, ELOVL7, FADS1, FADS2, FADS6, SCD, and SCD5. Additionally, changes in relative fluorescence values of different truncated segments in the upstream regulatory region of these genes indicate the existence of regulatory regions. Furthermore, we predicted the transcription factors that bind to the identified core promoter regions of multiple genes, including Sp1, NF-1, C/EBPalpha, etc. These findings provide a basis for the molecular mechanisms regulating poultry PUFA synthesis and offer new scientific insight into the potential improvement of poultry meat quality in the future.

The Promoter SNPs Were Associated with Both the Contents of Poly-Unsaturated Fatty Acids (PUFAs) and the Expressions of PUFA-Related Genes in Common Carp

The allo-tetraploid common carp encodes two duplicated fads2 genes (fads2a and fads2b) and two duplicated elovl5 genes (elovl5a and elovl5b). The coding SNPs (cSNPs) of these genes were reported to be significantly associated with the PUFA contents. Whether the promoter SNPs (pSNPs) were associated with the PUFA contents has not been reported yet. In this study, after sequencing the promoters of these four genes, we identified six pSNPs associated with the contents of PUFAs in common carp, including one elovl5a pSNP, one elovl5b pSNP, and four fads2b pSNPs. The pSNPs were predicted in the locations of transcriptional factor binding sites. Together with previously identified cSNPs in fads2b and elovl5b, the pSNPs and cSNPs of these two genes had the joint effects on the PUFA contents with higher explained percentage of phenotypic variation of the PUFA contents than single gene. The expression levels of both fads2a and fads2b were significantly positively correlated with the contents of six PUFAs. The fads2b pSNPs corresponding to higher fads2b expression levels were associated with higher PUFA contents. The pSNPs and cSNPs will be useful for the future selection breeding of common carp with higher PUFA contents.

Circ_0000253 promotes the progression of osteosarcoma via the miR-1236-3p/SP1 axis

OBJECTIVE

Circular RNAs (circRNAs) play important roles in modulating tumour progression. This study investigated the role of circ_0000253 in osteosarcoma (OS).

METHODS

We downloaded the chip dataset GSE140256 from the Gene Expression Omnibus database and the circRNAs differentially expressed in OS tissue and normal tissue samples were analysed. Quantitative real-time PCR (qRT-PCR) was carried out to examine circ_0000253 expression in OS tissues and cells. Cell counting kit-8, BrdU and flow cytometry assays were performed to verify the effects of circ_0000253 on OS cell growth and apoptosis. Bioinformatics analysis was conducted to predict, and RNA immunoprecipitation assay and dual-luciferase reporter gene assay were performed to verify the targeted relationships of miR-1236-3p with circ_0000253 and Sp1 transcription factor (SP1) mRNA 3'UTR. The effects of miR-1236-3p and circ_0000253 on SP1 expression in OS cells were detected through Western blot.

KEY FINDINGS

Circ_0000253 was upregulated in OS tissues and cell lines. Circ_0000253 overexpression facilitated OS cell growth and suppressed apoptosis, whereas knocking down circ_0000253 inhibited OS cell growth and facilitated apoptosis. Circ_0000253 targeted miR-1236-3p directly and negatively modulated its expression. SP1 was miR-1236-3p's target gene and positively regulated by circ_0000253.

CONCLUSION

Circ_0000253 promotes OS cell proliferation and suppresses cell apoptosis via regulating the miR-1236-3p/SP1 molecular axis.

Transcriptional analysis of microRNAs related to unsaturated fatty acid synthesis by interfering bovine adipocyte ACSL1 gene

Long-chain fatty acyl-CoA synthase 1 (ACSL1) plays a vital role in the synthesis and metabolism of fatty acids. The proportion of highly unsaturated fatty acids in beef not only affects the flavor and improves the meat’s nutritional value. In this study, si-ACSL1 and NC-ACSL1 were transfected in bovine preadipocytes, respectively, collected cells were isolated on the fourth day of induction, and then RNA-Seq technology was used to screen miRNAs related to unsaturated fatty acid synthesis. A total of 1,075 miRNAs were characterized as differentially expressed miRNAs (DE-miRNAs), of which the expressions of 16 miRNAs were upregulated, and that of 12 were downregulated. Gene ontology analysis indicated that the target genes of DE-miRNAs were mainly involved in biological regulation and metabolic processes. Additionally, KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway analysis identified that the target genes of DE-miRNAs were mainly enriched in metabolic pathways, fatty acid metabolism, PI3K-Akt signaling pathway, glycerophospholipid metabolism, fatty acid elongation, and glucagon signaling pathway. Combined with the previous mRNA sequencing results, several key miRNA-mRNA targeting relationship pairs, i.e., novel-m0035-5p—ACSL1, novel-m0035-5p—ELOVL4, miR-9-X—ACSL1, bta-miR-677—ACSL1, miR-129-X—ELOVL4, and bta-miR-485—FADS2 were screened via the miRNA-mRNA interaction network. Thus, the results of this study provide a theoretical basis for further research on miRNA regulation of unsaturated fatty acid synthesis in bovine adipocytes.

Molecular Regulation of Biosynthesis of Long Chain Polyunsaturated Fatty Acids in Atlantic Salmon

Salmon is a rich source of health-promoting omega-3 long chain polyunsaturated fatty acids (n-3 LC-PUFA), such as eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3). The LC-PUFA biosynthetic pathway in Atlantic salmon is one of the most studied compared to other teleosts. This has largely been due to the massive replacement of LC-PUFA-rich ingredients in aquafeeds with terrestrial plant oils devoid of these essential fatty acids (EFA) which ultimately pushed dietary content towards the minimal requirement of EFA. The practice would also reduce tissue content of n-3 LC-PUFA compromising the nutritional value of salmon to the human consumer. These necessitated detailed studies of endogenous biosynthetic capability as a contributor to these EFA. This review seeks to provide a comprehensive and concise overview of the current knowledge about the molecular genetics of PUFA biosynthesis in Atlantic salmon, highlighting the enzymology and nutritional regulation as well as transcriptional control networks. Furthermore, we discuss the impact of genome duplication on the complexity of salmon LC-PUFA pathway and highlight probable implications on endogenous biosynthetic capabilities. Finally, we have also compiled and made available a large RNAseq dataset from 316 salmon liver samples together with an R-script visualization resource to aid in explorative and hypothesis-driven research into salmon lipid metabolism.

Dynamics of TCR repertoire and T cell function in COVID-19 convalescent individuals

SARS-CoV-2 outbreak has been declared by World Health Organization as a worldwide pandemic. However, there are many unknowns about the antigen-specific T-cell-mediated immune responses to SARS-CoV-2 infection. Here, we present both single-cell TCR-seq and RNA-seq to analyze the dynamics of TCR repertoire and immune metabolic functions of blood T cells collected from recently discharged COVID-19 patients. We found that while the diversity of TCR repertoire was increased in discharged patients, it returned to basal level ~1 week after becoming virus-free. The dynamics of T cell repertoire correlated with a profound shift of gene signatures from antiviral response to metabolism adaptation. We also demonstrated that the top expanded T cell clones (~10% of total T cells) display the key anti-viral features in CD8⁺ T cells, confirming a critical role of antigen-specific T cells in fighting against SARS-CoV-2. Our work provides a basis for further analysis of adaptive immunity in COVID-19 patients, and also has implications in developing a T-cell-based vaccine for SARS-CoV-2.

Regulation of long-chain polyunsaturated fatty acid biosynthesis in teleost fish

Omega-3 (n-3) long-chain polyunsaturated fatty acids (LC-PUFA, C_20-24), including eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3), are involved in numerous biological processes and have a range of health benefits. Fish have long been considered as the main source of n-3 LC-PUFA in human diets. However, the capacity for endogenous biosynthesis of LC-PUFA from C₁₈ PUFA varies in fish species based on the presence, expression and activity of key enzymes including fatty acyl desaturases (Fads) and elongation of very long-chain fatty acids (Elovl) proteins. In this article, we review progress on the identified Fads and Elovl, as well as the regulatory mechanisms of LC-PUFA biosynthesis both at transcriptional and post-transcriptional levels in teleosts. The most comprehensive advances have been obtained in rabbitfish Siganus canaliculatus, a marine teleost demonstrated to have the entire pathway for LC-PUFA biosynthesis, including the roles of transcription factors hepatocyte nuclear factor 4α (Hnf4α), liver X receptor alpha (Lxrα), sterol regulatory element-binding protein 1 (Srebp-1), peroxisome proliferator-activated receptor gamma (Pparγ) and stimulatory protein 1 (Sp1), as well as post-transcriptional regulation by individual microRNA (miRNA) or clusters. This research has, for the first time, demonstrated the involvement of Hnf4α, Pparγ and miRNA in the regulation of LC-PUFA biosynthesis in vertebrates. The present review provides readers with a relatively comprehensive overview of the progress made into understanding LC-PUFA biosynthetic systems in teleosts, and some insights into improving endogenous LC-PUFA biosynthesis capacity aimed at reducing the dependence of aquafeeds on fish oil while maintaining or increasing flesh LC-PUFA content and the nutritional quality of farmed fish.

Identification of miR-145 as a Key Regulator Involved in LC-PUFA Biosynthesis by Targeting hnf4α in the Marine Teleost Siganus canaliculatus

Fish, particularly marine species, are considered as the major source of long-chain polyunsaturated fatty acids (LC-PUFA) in the human diet. The extent to which fish can synthesize LC-PUFA varies with species and is regulated by dietary fatty acids and ambient salinity. Therefore, to enable fish to produce more LC-PUFA, comprehending the mechanisms underlying the regulation of LC-PUFA biosynthesis is necessary. Here, the regulatory roles of miR-145 were investigated in the marine teleost rabbitfish Siganus canaliculatus. The hepatic abundance of miR-145 was lower in rabbitfish reared in low salinity (10 ppt) in comparison with that of those cultured in seawater (32 ppt), while the opposite pattern was observed for the transcripts of the transcription factor hepatocyte nuclear factor 4 alpha (Hnf4α), known to affect rabbitfish LC-PUFA biosynthesis. Rabbitfish hnf4α was identified as a target of miR-145 by luciferase reporter assays, and overexpression of miR-145 in the S. canaliculatus hepatocyte line (SCHL) markedly reduced the expression of Hnf4α and its target genes involved in LC-PUFA biosynthesis, namely, Δ4 fads2, Δ6Δ5 fads2, and elovl5. The opposite pattern was observed when miR-145 was knocked down in SCHL cells, with these effects being attenuated by subsequent hnf4α knockdown. Moreover, increasing endogenous Hnf4α by the knockdown of miR-145 increased the expression of LC-PUFA biosynthesis genes and enhanced the synthesis of LC-PUFA in both SCHL cells and rabbitfish in vivo. This is the first report to identify miR-145 as a key effector of LC-PUFA biosynthesis by targeting hnf4α, providing a novel insight into the mechanisms of the regulation of LC-PUFA biosynthesis in vertebrates.

miR-26a mediates LC-PUFA biosynthesis by targeting the Lxrα-Srebp1 pathway in the marine teleost Siganus canaliculatus

MicroRNAs have been recently shown to be important regulators of lipid metabolism. However, the mechanisms of microRNA-mediated regulation of long-chain polyunsaturated fatty acid (LC-PUFA) biosynthesis in vertebrates remain largely unknown. Herein, we for the first time addressed the role of miR-26a in LC-PUFA biosynthesis in the marine rabbitfish Siganus canaliculatus The results showed that miR-26a was significantly down-regulated in liver of rabbitfish reared in brackish water and in S. canaliculatus hepatocyte line (SCHL) incubated with the LC-PUFA precursor α-linolenic acid, suggesting that miR-26a may be involved in LC-PUFA biosynthesis because of its abundance being regulated by factors affecting LC-PUFA biosynthesis. Opposite patterns were observed in the expression of liver X receptor α (lxrα) and sterol regulatory element-binding protein-1 (srebp1), as well as the LC-PUFA biosynthesis-related genes (Δ4 fads2, Δ6Δ5 fads2, and elovl5) in SCHL cells incubated with α-linolenic acid. Luciferase reporter assays revealed rabbitfish lxrα as a target of miR-26a, and overexpression of miR-26a in SCHL cells markedly reduced protein levels of Lxrα, Srebp1, and Δ6Δ5 Fads2 induced by the agonist T0901317. Moreover, increasing endogenous Lxrα by knockdown of miR-26a facilitated Srebp1 activation and concomitant increased expression of genes involved in LC-PUFA biosynthesis and consequently promoted LC-PUFA biosynthesis both in vitro and in vivo These results indicate a critical role of miR-26a in regulating LC-PUFA biosynthesis through targeting the Lxrα-Srebp1 pathway and provide new insights into the regulatory network controlling LC-PUFA biosynthesis and accumulation in vertebrates.

The requirements for sterol regulatory element-binding protein (Srebp) and stimulatory protein 1 (Sp1)-binding elements in the transcriptional activation of two freshwater fish Channa striata and Danio rerio elovl5 elongase

Fish are a major source of beneficial n-3 LC-PUFA in human diet, and there is considerable interest to elucidate the mechanism and regulatory aspects of LC-PUFA biosynthesis in farmed species. Long-chain polyunsaturated fatty acid (LC-PUFA) biosynthesis involves the activities of two groups of enzymes, the fatty acyl desaturase (Fads) and elongase of very long-chain fatty acid (Elovl). The promoters of elovl5 elongase, which catalyses the rate-limiting reaction of elongating polyunsaturated fatty acid (PUFA), have been previously described and characterized from several marine and diadromous teleost species. We report here the cloning and characterization of elovl5 promoter from two freshwater fish species, the carnivorous snakehead fish (Channa striata) and zebrafish. Results show the presence of sterol-responsive elements (SRE) in the core regulatory region of both promoters, suggesting the importance of sterol regulatory element-binding protein (Srebp) in the regulation of elovl5 for both species. Mutagenesis luciferase and electrophoretic mobility shift assays further validate the role of SRE for basal transcriptional activation. In addition, several Sp1-binding sites located in close proximity with SRE were present in the snakehead promoter, with one having a potential synergy with SRE in the regulation of elovl5 expression. The core zebrafish elovl5 promoter fragment also directed in vivo expression in the yolk syncytial layer of developing zebrafish embryos.

Molecular Cloning, Characterization, and Expression Regulation of Acyl-CoA Synthetase 6 Gene and Promoter in Common Carp Cyprinus carpio

Omega-3 long chain polyunsaturated fatty acids (n-3 LC-PUFA), particularly docosahexaenoic acids (22:6n-3, DHA), have positive effects on multiple biologic and pathologic processes. Fish are the major dietary source of n-3 LC-PUFA for humans. Growing evidence supports acyl-coenzyme A (acyl-CoA) synthetase 6 (acsl6) being involved in cellular DHA uptake and lipogenesis in mammals, while its molecular function and regulatory mechanism remain unknown in fish. The present study focused on investigating the molecular characterization and transcription regulation of the acsl6 gene in the freshwater teleost common carp (Cyprinus carpio). First, the full length of acsl6 cDNA contained a coding region of 2148 bp for 715 amino acids, which possessed all characteristic features of the acyl-CoA synthetase (ACSL) family. Its mRNA expression was the highest in the brain, followed by in the heart, liver, kidney, muscle, and eyes, but little expression was detected in the ovary and gills. Additionally, a candidate acsl6 promoter region of 2058 bp was cloned, and the sequence from -758 bp to -198 bp was determined as core a promoter by equal progressive deletion and electrophoretic mobility shift assay. The binding sites for important transcription factors (TFs), including stimulatory protein 1 (SP1), CCAAT enhancer-binding protein (C/EBPα), sterol-regulatory element binding protein 1c (SREBP1c), peroxisome proliferator activated receptor α (PPARα), and PPARγ were identified in the core promoter by site-directed mutation and functional assays. Furthermore, the intraperitoneal injection of PPARγ agonists (balaglitazone) increased the expression of acsl6 mRNA, coupling with an increased proportion of DHA in the muscle, while opposite results were obtained in the injection of the SREBP1c antagonist (betulin). However, the expression of acsl6 and DHA content in muscle were largely unchanged by PPARα agonist (fenofibrate) treatment. These results indicated that acsl6 may play an important role for the muscular DHA uptake and deposition in common carp, and PPARγ and SREBP-1c are the potential TFs involved in the transcriptional regulation of acsl6 gene. To our knowledge, this is the first report of the characterization of acsl6 gene and its promoter in teleosts.