A newly discovered member of the fatty acid desaturase gene family: a non-coding, antisense RNA gene to delta5-desaturase

Influence of the nutritional status and oxidative stress in the desaturation and elongation of n-3 and n-6 polyunsaturated fatty acids: Impact on non-alcoholic fatty liver disease

Polyunsaturated fatty acids (PUFA) play essential roles in cell membrane structure and physiological processes including signal transduction, cellular metabolism and tissue homeostasis to combat diseases. PUFA are either consumed from food or synthesized by enzymatic desaturation, elongation and peroxisomal β-oxidation. The nutritionally essential precursors α-linolenic acid (C18:3n-3; ALA) and linoleic acid (C18:2n-6; LA) are subjected to desaturation by Δ6D/Δ5D desaturases and elongation by elongases 2/5, enzymes that are induced by insulin and repressed by PUFA. Maintaining an optimally low n-6/n-3 PUFA ratio is linked to prevention of the development of several diseases, including nonalcoholic fatty liver disease (NAFLD) that is characterized by depletion of PUFA promoting hepatic steatosis and inflammation. In this context, supplementation with n-3 PUFA revealed significant lowering of hepatic steatosis in obese patients, whereas prevention of fatty liver by high-fat diet in mice is observed in n-3 PUFA and hydroxytyrosol co-administration. The aim of this work is to review the role of nutritional status and nutrient availability on markers of PUFA biosynthesis. In addition, the impact of oxidative stress developed as a result of NAFLD, a redox imbalance that may alter the expression and activity of the enzymes involved, and diminished n-3 PUFA levels by free-radical dependent peroxidation processes will be discussed.

Chromatin-remodeling factors mediate the balance of sense-antisense transcription at the FGF2 locus

Antisense transcription is prevalent in mammalian genomes, yet the function of many antisense transcripts remains elusive. We have previously shown that the fibroblast growth factor 2 (FGF2) gene is regulated endogenously by an overlapping antisense gene called Nudix-type motif 6 (NUDT6). However, the molecular mechanisms that determine the balance of FGF2 and NUDT6 transcripts are not yet well understood. Here we demonstrate that there is a strong negative correlation between FGF2 and NUDT6 across 7 different cell lines. Small interfering RNA-mediated knockdown of NUDT6 causes an increase in nascent FGF2 transcripts, including a short FGF2 variant that lacks sequence complementarity with NUDT6, indicating the involvement of transcriptional mechanisms. In support of this, we show that changes in histone acetylation by trichostatin A treatment, histone deacetylase inhibition, or small interfering RNA knockdown of the histone acetyltransferase CSRP2BP, oppositely affect NUDT6 and FGF2 mRNA levels. A significant increase in histone acetylation with trichostatin A treatment was only detected at the genomic region where the 2 genes overlap, suggesting that this may be an important regulatory region for determining the balance of NUDT6 and FGF2. Knockdown of the histone demethylase KDM4A similarly causes a shift in the balance of NUDT6 and FGF2 transcripts. Expression of CSRP2BP and KDM4A correlates positively with NUDT6 expression and negatively with FGF2 expression. The results presented here indicate that histone acetylation and additional chromatin modifiers are important in determining the relative levels of FGF2 and NUDT6 and support a model in which epigenetic remodeling contributes to their relative expression levels.

LncRNA pathway involved in premature preterm rupture of membrane (PPROM): an epigenomic approach to study the pathogenesis of reproductive disorders

Preterm birth (PTB) is a live birth delivered before 37 weeks of gestation (GW). About one-third of PTBs result from the preterm premature rupture of membranes (PPROM). Up to the present, the pathogenic mechanisms underlying PPROM are not clearly understood. Here, we investigated the differential expression of long chain non-coding RNAs (lncRNAs) in placentas of PTBs with PPROM, and their possible involvement in the pathogenic pathways leading to PPROM. A total number of 1954, 776, and 1050 lncRNAs were identified with a microarray from placentas of PPROM (group A), which were compared to full-term birth (FTB) (group B), PTB (group C), and premature rupture of membrane (PROM) (group D) at full-term, respectively. Instead of investigating the individual pathogenic role of each lncRNA involved in the molecular mechanism underlying PPROM, we have focused on investigating the metabolic pathways and their functions to explore what is the likely association and how they are possibly involved in the development of PPROM. Six groups, including up-regulation and down-regulation in the comparisons of A vs. B, A vs. C, and A vs. D, of pathways were analyzed. Our results showed that 22 pathways were characterized as up-regulated 7 down-regulated in A vs. C, 18 up-regulated and 15 down-regulated in A vs. D, and 33 up-regulated and 7 down-regulated in A vs. B. Functional analysis showed pathways of infection and inflammatory response, ECM-receptor interactions, apoptosis, actin cytoskeleton, and smooth muscle contraction are the major pathogenic mechanisms involved in the development of PPROM. Characterization of these pathways through identification of lncRNAs opened new avenues for further investigating the epigenomic mechanisms of lncRNAs in PPROM as well as PTB.

Long non-coding RNAs and human disease

The central dogma of molecular biology states that DNA is transcribed into RNA, which in turn is translated into proteins. We now know, however, that as much as 50% of the transcriptome has no protein-coding potential, but rather represents an important class of regulatory molecules responsible for the fine-tuning of gene expression. Although the role of small regulatory RNAs [microRNAs and siRNAs (small interfering RNA)] is well defined, another much less characterized category of non-coding transcripts exists, namely lncRNAs (long non-coding RNAs). Pervasively expressed by eukaryotic genomes, lncRNAs can be kilobases long and regulate their targets by influencing the epigenetic control, chromatin status, mRNA processing or translation capacity of their targets. In the present review, I outline the potential mechanisms of action of lncRNAs, the cellular processes that have been associated with them, and also explore some of the emerging evidence for their involvement in common human disease.

Regulation of FADS2 expression and activity in European sea bass (Dicentrarchus labrax, L.) fed a vegetable diet

Supplies of marine fish oils are limited, and continued growth in aquaculture production dictates that lipid substitutes in fish diets must be used without compromising fish health and product quality. In this study, the total substitution of a fish meal and fish oil by a blend of vegetable meals (corn, soybean, wheat and lupin) and linseed oil in the diet of European sea bass (Dicentrachus labrax) was investigated. Two groups of European sea bass were fed with fish diet (FD) or vegetable diet (VD) for 9months. VD, totally deprived of eicosapentaenoate (EPA; 20:5n-3) and docosahexaenoate (DHA; 22:6n-3), revealed a nutritional deficiency and affected growth performance. Whilst VD induced a significant increase in fatty acid desaturase 2 (FADS2) and sterol binding regulatory element-binding protein 1 (SREBP-1) mRNA levels, the desaturation rate of [1-(14)C]18:3n-3 into [1-(14)C]18:4n-3, analysed in microsomal preparations using HPLC method, did not show an upregulation of FADS2 activities in liver and intestine of fish fed VD. Moreover Western-blot analysis did not revealed any significant difference of FADS2 protein amount between the two dietary groups. These data demonstrate that sea bass exhibits a desaturase (FADS2) activity whatever their diet, but a post-transcriptional regulation of fads2 RNA prevents an increase of enzyme in fish fed a HUFA-free diet. This led to a lower fish growth and poor muscle HUFA content.

The key roles of elongases and desaturases in mammalian fatty acid metabolism: Insights from transgenic mice

In mammalian cells, elongases and desaturases play critical roles in regulating the length and degree of unsaturation of fatty acids and thereby their functions and metabolic fates. In the past decade, a great deal has been learnt about these enzymes and the first part of this review summarizes our current knowledge concerning these enzymes. More recently, several transgenic mouse models lacking either an elongase (Elovl3(-/-), Elovl4(-/-), Elovl5(-/-), Elovl6(-/-)) or a desaturase (Scd-1(-/-), Scd-2(-/-), Fads2(-/-)) have been developed and the second part of this review focuses on the insights gained from studies with these mice, as well as from investigations on cell cultures.