Fat-1 transgenic cattle as a model to study the function of ω-3 fatty acids

Genome-wide association and genomic prediction for a reproductive index summarizing fertility outcomes in U.S. Holsteins

Subfertility represents one major challenge to enhancing dairy production and efficiency. Herein, we use a reproductive index (RI) expressing the predicted probability of pregnancy following artificial insemination (AI) with Illumina 778K genotypes to perform single and multi-locus genome-wide association analyses (GWAA) on 2,448 geographically diverse U.S. Holstein cows and produce genomic heritability estimates. Moreover, we use genomic best linear unbiased prediction (GBLUP) to investigate the potential utility of the RI by performing genomic predictions with cross validation. Notably, genomic heritability estimates for the U.S. Holstein RI were moderate (h2 = 0.1654 ± 0.0317-0.2550 ± 0.0348), while single and multi-locus GWAA revealed overlapping quantitative trait loci (QTL) on BTA6 and BTA29, including the known QTL for the daughter pregnancy rate (DPR) and cow conception rate (CCR). Multi-locus GWAA revealed seven additional QTL, including one on BTA7 (60 Mb) which is adjacent to a known heifer conception rate (HCR) QTL (59 Mb). Positional candidate genes for the detected QTL included male and female fertility loci (i.e. spermatogenesis and oogenesis), meiotic and mitotic regulators, and genes associated with immune response, milk yield, enhanced pregnancy rates, and the reproductive longevity pathway. Based on the proportion of the phenotypic variance explained (PVE), all detected QTL (n = 13; P ≤ 5e - 05) were estimated to have moderate (1.0% < PVE ≤ 2.0%) or small effects (PVE ≤ 1.0%) on the predicted probability of pregnancy. Genomic prediction using GBLUP with cross validation (k = 3) produced mean predictive abilities (0.1692-0.2301) and mean genomic prediction accuracies (0.4119-0.4557) that were similar to bovine health and production traits previously investigated.

Invited review: Cytochrome P450 enzyme involvement in health and inflammatory-based diseases of dairy cattle

Dairy cattle are at the greatest risk of developing diseases around the time of calving because of compromised immune responses and the occurrence of oxidative stress. Both the development of compromised immunity and oxidative stress are influenced directly or indirectly by the metabolism of polyunsaturated fatty acids (PUFA) and fat-soluble vitamins. The cytochrome P450 (CYP450) family of enzymes is central to the metabolism of both classes of these compounds, but to date, the importance of CYP450 in the health of dairy cattle is underappreciated. As certain CYP450 isoforms metabolize both PUFA and fat-soluble vitamins, potential interactions may occur between PUFA and fat-soluble vitamins that are largely unexplored. For example, one CYP450 that generates anti-inflammatory oxylipids from arachidonic acid additionally contributes to the activation of vitamin D. Other potential substrate interactions between PUFA and vitamins A and E may exist as well. The intersection of PUFA and fat-soluble vitamin metabolism by CYP450 suggest that this enzyme system could provide an understanding of how immune function and oxidant status interconnect, resulting in increased postpartum disease occurrence. This review will detail the known contributions of bovine CYP450 to the regulation of oxylipids with a focus on enzymes that may also be involved in the metabolism of fat-soluble vitamins A, D, and E that contribute to antioxidant defenses. Although the activity of specific CYP450 is generally conserved among mammals, important differences exist in cattle, such as the isoforms primarily responsible for activation of vitamin D that makes their specific study in cattle of great importance. Additionally, a CYP450-driven inflammatory positive feedback loop is proposed, which may contribute to the dysfunctional inflammatory responses commonly found during the transition period. Establishing the individual enzyme isoform contributions to oxylipid biosynthesis and the regulation of vitamins A, D, and E may reveal how the CYP450 family of enzymes can affect inflammatory responses during times of increased susceptibility to disease. Determining the potential effect of each CYP450 on disease susceptibility or pathogenesis may allow for the targeted manipulation of the CYP450 pathways to influence specific immune responses and antioxidant defenses during times of increased risk for health disorders.

Alpha-Linolenic Acid-Enriched Butter Promotes Fatty Acid Remodeling and Thermogenic Activation in the Brown Adipose Tissue

Supplementation with n-3 long-chain (LC) polyunsaturated fatty acids (PUFA) is known to promote thermogenesis via the activation of brown adipose tissue (BAT). Agricultural products that are biofortified with α-linolenic acid (ALA), the precursor of n-3 LC PUFA, have been launched to the market, but their impact on BAT function is unknown. This study aimed to evaluate the effects of ALA-biofortified butter on lipid metabolism and thermogenic functions in the BAT. C57BL/6 mice were fed a high-fat diet containing ALA-biofortified butter (n3Bu, 45% calorie from fat) for ten weeks in comparison with the isocaloric high-fat diets prepared from conventional butter or margarine. The intake of n3Bu significantly reduced the whitening of BAT and increased the thermogenesis in response to acute-cold treatment. Also, n3Bu supplementation is linked with the remodeling of BAT by promoting bioconversion into n-3 LC PUFA, FA elongation and desaturation, and mitochondrial biogenesis. Taken together, our results support that ALA-biofortified butter is a novel source of n-3 PUFA, which potentiates the BAT thermogenic function.

The ω-3 polyunsaturated fatty acids prevented colitis-associated carcinogenesis through blocking dissociation of β-catenin complex, inhibiting COX-2 through repressing NF-κB, and inducing 15-prostaglandin dehydrogenase

Numerous studies have demonstrated that diets containing an increased ratio of ω-6 : ω-3 polyunsaturated fatty acids (PUFAs) are a risk factor for colon cancer and might affect tumorigenesis. Therefore, dietary ω-3 PUFA administration may be a preventive strategy against colon cancer. Until now, the exact molecular mechanisms and required dietary doses of ω-3 PUFAs for cancer prevention were unknown. In this study, we explored the anti-tumorigenic mechanisms of ω-3 PUFAs against a colitis-associated cancer (CAC) model. Through in vitro cell models involving docosahexaenoic acid (DHA) administration, down-regulation of survivin and Bcl-2, and up-regulation of Bax, accompanied by blockage of β-catenin complex dissociation, the main mechanisms responsible for DHA-induced apoptosis in HCT116 cells were determined. Results included significant reduction in azoxymethane-initiated, dextran sodium sulfate-promoted CACs, as well as significant preservation of 15-hydroxyprostaglandin dehydrogenase (15-PGDH) and significant inhibition of Cyclooxyganase-2 (COX-2) and Prostaglandin E₂(P < 0.01). Additional mechanisms and significant induction of apoptosis in both tumor and non-tumor tissues were also noted in fat-1 transgenic (TG) mice. The lipid profiles of colon tissues measured in all specimens revealed that intake greater than 3 g ω-3 PUFA/60 kg of body weight showed tissue levels similar to those seen in fat-1 TG mice, preventing cancer. Our study concluded that COX-2 inhibition, 15-PGDH preservation, apoptosis induction, and blockage of β-catenin complex dissociation contributed to the anti-tumorigenesis effect of ω-3 PUFAs, and an intake higher than 3g ω-3 PUFAs/60 kg of body weight can assist in CAC prevention.

MicroRNA profiles of fibroblasts derived from in vivo fertilized and fat-1 transgenic cattle

Fat-1 transgenic cattle have high levels of ω-3 fatty acids, which regulate several genes in fatty acid metabolism. In the current study, fibroblasts derived from in vivo fertilized (Ferti) and fat-1 transgenic (TG) Luxi cattle (Bos taurus), a local breed in China, were cultured and their miRNA expression was characterized. Expression of 352 known miRNAs differed in cells from Ferti and TG cattle: 83 miRNAs were found to be specifically expressed in cells from Ferti cattle while 23 miRNAs were found to be specifically expressed in cells from TG cattle. Novel differences in miRNA expression were also found in cells from Ferti and TG cattle. The identity of seven differentially expressed miRNAs was verified using quantitative real-time PCR, and target genes were identified computationally. GO and KEGG analysis revealed that these miRNAs were involved in seven major biological pathways, including metabolism, MAPK signaling, calcium signaling, purine metabolism, ubiquitin mediated proteolysis, pyrimidine metabolism, and the cell cycle. Overexpression of one of these miRNAs, miR-21-5p, was found to suppress expression of fibroblast growth factor 10 (FGF10) and adipose triglyceride lipase (ATGL) in fibroblasts from TG cattle and 3T3-L1 pre-adipocytes. Conversely, knockdown of miR-21-5p stimulated expression. Together, these results suggest that miRNAs potentially play a role in expression of lipogenic and lipolytic genes as well as in synthesis of ω-3 fatty acids facilitated by fat-1.

Efficient generation of sFat-1 transgenic rabbits rich in n-3 polyunsaturated fatty acids by intracytoplasmic sperm injection

N-3 polyunsaturated fatty acids (n-3 PUFAs) have their first double bond at the third carbon from the methyl end of the fatty-acid chain and had been proven to be beneficial to human health. However, mammals cannot produce n-3 PUFAs by themselves because they lack the n-3 fatty-acid desaturase (Fat-1) gene. Thus, the possibility of producing sFat-1 transgenic rabbits was explored in this study. The transgenic cassette of pPGK1-sFat-1-CMV-EGFP was constructed and transgenic rabbit embryos were produced by intracytoplasmic sperm injection (ICSI). When 123 EGFP-positive embryos at the 2-8-cell stage were transplanted into the oviduct of four oestrous-synchronised recipients, two of them became pregnant and gave birth to seven pups. However, transfer of embryos into the uterus of oestrous-synchronised recipients and oviduct or uterus of oocyte donor rabbits did not result in pregnancy. The integration of the sFat-1 gene was confirmed in six of the seven live pups by PCR and Southern blot. The expression of the sFat-1 gene in the six transgenic pups was also detected by reverse transcription polymerase chain reaction (RT-PCR). Gas chromatography-mass spectrometry analysis revealed that transgenic rabbits exhibited an ~15-fold decrease in the ratio of n-6:n-3 PUFAs in muscle compared with wild-type rabbits and non-transgenic rabbits. These results demonstrate that sFat-1 transgenic rabbits can be produced by ICSI and display a low ratio of n-6:n-3 PUFAs.

DNMT 1 maintains hypermethylation of CAG promoter specific region and prevents expression of exogenous gene in fat-1 transgenic sheep

Methylation is an important issue in gene expression regulation and also in the fields of genetics and reproduction. In this study, we created fat-1 transgenic sheep, investigated the fine-mapping and the modulatory mechanisms of promoter methylation. Sheep fetal fibroblasts were transfected by pCAG-fat1-IRES-EGFP. Monoclonal cell line was screened as nuclear donor and carried out nuclear transfer (441 transgenic cloned embryos, 52 synchronism recipient sheep). Six offsprings were obtained. Expressions of exogenous genes fat-1 and EGFP were detectable in 10 examined tissues and upregulated omega-3 fatty acid content. Interestingly, more or less EGFP negative cells were detectable in the positive transgenic fetal skin cells. EGFP negative and positive cells were sorted by flow cytometry, and their methylation status in the whole promoter region (1701 nt) were investigated by bisulphate sequencing. The fine-mapping of methylation in CAG promoter were proposed. The results suggested that exogenous gene expression was determined by the methylation status from 721–1346 nt and modulated by methylation levels at 101, 108 and 115 nt sites in CAG promoter. To clarify the regulatory mechanism of methylation, examination of four DNA methyltransferases (DNMTs) demonstrated that hypermethylation of CAG promoter is mainly maintained by DNMT 1 in EGFP negative cells. Furthermore, investigation of the cell surface antigen CD34, CD45 and CD166 indicated that EGFP positive and negative cells belong to different types. The present study systematically clarified methylation status of CAG promoter in transgenic sheep and regulatory mechanism, which will provide research strategies for gene expression regulation in transgenic animals.

Using Caenorhabditis elegans to Uncover Conserved Functions of Omega-3 and Omega-6 Fatty Acids

The nematode Caenorhabditis elegans is a powerful model organism to study functions of polyunsaturated fatty acids. The ability to alter fatty acid composition with genetic manipulation and dietary supplementation permits the dissection of the roles of omega-3 and omega-6 fatty acids in many biological process including reproduction, aging and neurobiology. Studies in C. elegans to date have mostly identified overlapping functions of 20-carbon omega-6 and omega-3 fatty acids in reproduction and in neurons, however, specific roles for either omega-3 or omega-6 fatty acids are beginning to emerge. Recent findings with importance to human health include the identification of a conserved Cox-independent prostaglandin synthesis pathway, critical functions for cytochrome P450 derivatives of polyunsaturated fatty acids, the requirements for omega-6 and omega-3 fatty acids in sensory neurons, and the importance of fatty acid desaturation for long lifespan. Furthermore, the ability of C. elegans to interconvert omega-6 to omega-3 fatty acids using the FAT-1 omega-3 desaturase has been exploited in mammalian studies and biotechnology approaches to generate mammals capable of exogenous generation of omega-3 fatty acids.

Microarray Analysis of the Gene Expression Profile and Lipid Metabolism in Fat-1 Transgenic Cattle

Long-chain n-3 polyunsaturated fatty acids (n-3 PUFAs) are beneficial for human health. However, humans and mammals are unable to synthesize n-3 PUFAs because they lack the n-3 desaturase gene fat-1 and must therefore obtain this type of fatty acid through their diet. Through the production of fat-1 transgenic animals, it is possible to obtain animal products that are rich in n-3 PUFAs, such as meat and milk. The aim of this study was to analyze the gene expression profile and the mechanism of lipid metabolism in fat-1 transgenic cattle and to accumulate important basic data that are required to obtain more efficient fat-1 transgenic cattle. Transcriptome profiling of fat-1 transgenic and wild-type cattle identified differentially expressed genes that are involved in 90 biological pathways, eight pathways of which were related to lipid metabolism processes 36 genes of which were related to lipid metabolism. This analysis also identified 11 significantly enriched genes that were involved in the peroxisome proliferator-activated receptor signaling pathway. These findings were verified by quantitative polymerase chain reaction. The information obtained in this study indicated that the introduction of an exogenous fat-1 gene into cattle affects the gene expression profile and the process of lipid metabolism in these animals. These results may provide important insights into how an exogenous fat-1 gene synthesizes n-3 PUFAs in transgenic cattle and other mammals.

Cloning and in vitro function analysis of codon-optimized FatI gene

Currently, n-3 polyunsaturated fatty acids (n-3 PUFAs) have attracted great attention because of their biological significance to organisms. In addition, PUFAs show an obvious impact on prevention and treatment of various diseases. Because n-3 PUFAs cannot be endogenously synthesized by mammals, mammals have to rely on a dietary supplement for sufficient supply. The finding and application of the fatty acid dehydrogenase I (FatI) gene are expected to change the current situation because it can convert n-6 polyunsaturated fatty acids (n-6 PUFAs) to n-3 PUFAs. Meanwhile, the gradual maturation of transgenic technology makes it possible to produce transgenic animals that can synthesize n-3 PUFAs by themselves. In this study, the DNA coding sequence of FatI was synthesized by a chemical method after codon optimization according to the mammal's codon bias. The synthesized DNA sequence was introduced into Boer goat fetal fibroblasts by the constructed recombinant eukaryotic expression vector pcDNA3.1(+)-FatI. Boer goat fetal fibroblasts were transfected by electroporation, and the stable transfected cell lines were obtained by G418 selection. Genomic DNA PCR and Southern blot were applied to verify that the foreign gene FatI was integrated into the genome of the Boer goat fibroblasts. RT-PCR results showed the expression of FatI gene at the mRNA level. The fatty acid profile of cells carrying the FatI gene revealed an increase in total n-3 PUFAs (from 0.61 to 0.95), but a decrease in n-6 PUFAs (from 10.34 to 9.85), resulting in a remarkable increase in the n-3:n-6 ratio (from 0.059 to 0.096). The n-3:n-6 ratio had a 63.49 percent increase, which is a precursor of the response of n-3 desaturase activity of the FatI gene. The study may provide a practical tool for producing transgenic animals that can produce n-3 PUFAs by themselves, and we hope that the application will lay the foundation for animals producing n-3 PUFAs, which will benefit human nutrition and wellness.