Cloning and expressions of peroxisome proliferator activated receptor alpha1 and alpha2 (PPARα1 and PPARα2) in loach (Misgurnus anguillicaudatus) and in response to different dietary fatty acids

The Peroxisome Proliferator-Activated Receptors of Ray-Finned Fish: Unique Structures, Elusive Functions

The Actinopterygian and specifically the Teleostean peroxisome proliferator-activated receptors (PPARs) present an impressive variability and complexity in their structures, both at the gene and protein levels. These structural differences may also reflect functional divergence from their mammalian homologs, or even between fish species. This review, taking advantage of the data generated from the whole-genome sequencing of several fish species, highlights the differences in the primary structure of the receptors, while discussing results from the literature pertaining to the functions of fish PPARs and their activation by natural and synthetic compounds.

Evolution and Functional Characteristics of the Novel elovl8 That Play Pivotal Roles in Fatty Acid Biosynthesis

Elongation of very long-chain fatty acid (Elovl) proteins are key enzymes that catalyze the rate-limiting step in the fatty acid elongation pathway. The most recently discovered member of the Elovl family, Elovl8, has been proposed to be a fish-specific elongase with two gene paralogs described in teleosts. However, the biological functions of Elovl8 are still to be elucidated. In this study, we showed that in contrast to previous findings, elovl8 is not unique to teleosts, but displays a rather unique and ample phylogenetic distribution. For functional determination, we generated elovl8a (elovl8a^−/−) and elovl8b (elovl8b^−/−) zebrafish using CRISPR/Cas9 technology. Fatty acid composition in vivo and zebrafish liver cell experiments suggest that the substrate preference of Elovl8 overlapped with other existing Elovl enzymes. Zebrafish Elovl8a could elongate the polyunsaturated fatty acids (PUFAs) C18:2n-6 and C18:3n-3 to C20:2n-6 and C20:3n-3, respectively. Along with PUFA, zebrafish Elovl8b also showed the capacity to elongate C18:0 and C20:1. Gene expression quantification suggests that Elovl8a and Elovl8b may play a potentially important role in fatty acid biosynthesis. Overall, our results provide novel insights into the function of Elovl8a and Elovl8b, representing additional fatty acid elongases not previously described in chordates.

Integrated transcriptome and phosphoproteome analyses reveal that fads2 is critical for maintaining body LC-PUFA homeostasis

Fatty acid desaturate 2 (Fads2) is associated with many chronic diseases. Nevertheless, comprehensive researches on its role have not been performed. We here conducted an integrated analysis of long-chain polyunsaturated fatty acid (LC-PUFA) metabolism of fads2-deletion zebrafish (fads2^-/-) by transcriptomics, proteomics and phosphoproteomics. Compared with wild type zebrafish (WT), fads2^-/- showed significantly higher contents of hepatic linoleic acid (all-cis-9,12-C18:2), α-linolenic acid (all-cis-9,12,15-C18:3) and docosapetaenoic acid (all-cis-7,10,13,16,19-C22:5), and lower contents of γ-linolenic acid (all-cis-6,9,12-C18:3), stearidonic acid (all-cis-6,9,12,15-C18:4) and docosahexaenoic acid (all-cis-4,7,10,13,16,19-C22:6), accompanied by an increased n-6/n-3 PUFA level. In total, we identified 1608 differentially expressed genes (DEGs), 209 differentially expressed proteins (DEPs) and 153 differentially expressed phosphorylated proteins (DEPPs) with 190 sites between fads2^-/- and WT. Transcriptome and proteome analysis simultaneously aggregated these DEGs and DEPs into LC-PUFA synthesis and PPAR signaling pathways. Further interaction network analysis of the DEPPs showed that spliceosome and protein processing in endoplasmic reticulum pathway were critical groups. Additionally, we determined seven highly phosphorylated kinases and a highly expressed phosphatase in fads2^-/- zebrafish. These results give insights into the mechanism by which fads2 affects metabolic disease occurrence, and provide datasets for target selections for human disease treatment. SIGNIFICANCE: Balanced LC-PUFA composition was deeply associated with body health, while changes of LC-PUFAs usually induced serious diseases such as cardiovascular disease, type 2 diabetes and inflammatory disease. Fatty acid desaturase 2 (Fads2), subordinating to the fatty acid desaturase protein family, catalyzes the first desaturation reaction in LC-PUFA synthesis. Although Fads2 is associated with many chronic diseases including metabolic abnormalities, type 2 diabetes and obesity, comprehensive researches on its role have not been performed. On the basis of the integrated transcriptome, proteome and phosphoproteome analysis, we identified that fads2 was critical for maintaining body LC-PUFA homeostasis. Moreover, the crucial pathways including PPAR signaling pathway, spliceosome and protein processing in endoplasmic reticulum pathway, and candidate kinase targets associated with LC-PUFA metabolism were determined. These findings will contribute to the revealing of the mechanism and supply possible datasets for target selection for human disease treatment.

Inefficient ATP synthesis by inhibiting mitochondrial respiration causes lipids to decrease in MSTN-lacking muscles of loach Misgurnus anguillicaudatus

Myostatin (MSTN) lacking could lead to enhanced muscle growth and lipid metabolism disorder in animals. Plenty of researches have been performed to warrant a better understanding of the mechanisms underlying the enhanced muscle growth; however, mechanisms for lipid metabolic changes are poorly understood. In this study, MSTN-depletion loaches Misgurnus anguillicaudatus (MU for short) were firstly generated by CRISPR/Cas9 technique. Based on histological observation, we found that skeletal muscle fat accumulation in MU sharply reduced compared with wild-type loaches (WT for short). To further investigate the fat change, muscle lipidomic analysis was performed. There were no significant differences in three membrane phospholipid contents between WT and MU. The contents of six other major lipid species in MU muscles were all significantly lower than those in WT muscles, indicating that MSTN deficiency could obviously decrease muscle lipid production in the loach. Meanwhile, it was also supported by results of three lipogenesis-related genes' expressions. And then combined with muscle ATP determination and gene expression profiles of the five mitochondrial respiration chain complexes, we speculated that MSTN lacking may cause the weak of mitochondrial respiration functions in the loach muscles, leading to ATP synthesis decreasing and finally reducing the production of lipids.

Genetic polymorphisms of PPAR genes and human cancers: evidence for gene-environment interactions

Peroxisome proliferator-activated receptors (PPARs) are nuclear transcription factors that play a role in lipid metabolism, cell proliferation, terminal differentiation, apoptosis, and inflammation. Although several cancer models have been suggested to explain PPARs' involvement in tumorigenesis, however, their role is still unclear. In this review, we examined associations of the different PPARs, polymorphisms and various types of cancer with a focus on gene-environment interactions. Reviewed evidence suggests that functional genetic variants of the different PPARs may modulate the relationship between environmental exposure and cancer risk. In addition, this report unveils the scarcity of reliable quantitative environmental exposure data when examining these interactions, and the current gaps in studying gene-environment interactions in many types of cancer, particularly colorectal, prostate, and bladder cancers.

The Transcriptional Factor PPARαb Positively Regulates Elovl5 Elongase in Golden Pompano Trachinotus ovatus (Linnaeus 1758)

The nuclear peroxisome proliferator-activated receptors (PPARs) regulate the transcription of elongases of very long-chain fatty acids (Elovl), which are involved in polyunsaturated fatty acid (PUFA) biosynthesis in mammals. In the present study, we first characterized the function of Elovl5 elongase in Trachinotus ovatus. The functional study showed that ToElovl5 displayed high elongation activity toward C18 and C20 PUFA. To investigate whether PPARαb was a regulator of Elovl5, we also reported the sequence of T. ovatus PPARαb (ToPPARαb). The open reading frame (ORF) sequence encoded 469 amino acids possessing four typical characteristic domains, including an N-terminal hypervariable region, a DNA-binding domain (DBD), a flexible hinge domain and a ligand-binding domain (LBD). Thirdly, promoter activity experiments showed that the region from PGL3-basic-Elovl5-5 (-146 bp to +459 bp) was defined as the core promoter by progressive deletion mutation of Elovl5. Moreover, PPARαb overexpression led to a clear time-dependent enhancement of ToElovl5 promoter expression in HEK 293T cells. Fourth, the agonist of PPARαb prominently increased PPARαb and Elovl5 expression, while PPARαb depletion by RNAi or an inhibitor was correlated with a significant reduction of Elovl5 transcription in T. ovatus caudal fin cells (TOCF). In conclusion, the present study provides the first evidence of the positive regulation of Elovl5 transcription by PPARαb and contributes to a better understanding of the transcriptional mechanism of PPARαb in fish.

In Vivo Effects of Lipopolysaccharide on Peroxisome Proliferator-Activated Receptor Expression in Juvenile Gilthead Seabream (Sparus Aurata)

Fish are constantly exposed to microorganisms in the aquatic environment, many of which are bacterial pathogens. Bacterial pathogens activate the innate immune response in fish involving the production of pro-inflammatory molecules that, in addition to their immune-related role, can affect non-immune tissues. In the present study, we aimed at investigating how inflammatory responses can affect metabolic homeostasis in the gilthead seabream (Sparus aurata), a teleost of considerable economic importance in Southern European countries. Specifically, we mimicked a bacterial infection by in vivo administration of lipopolysaccharide (LPS, 6 mg/kg body weight) and measured metabolic parameters in the blood and, importantly, the mRNA expression levels of the three isotypes of peroxisome proliferator activated receptors (PPARα, β, and γ) in metabolically-relevant tissues in seabream. PPARs are nuclear receptors that are important for lipid and carbohydrate metabolism in mammals and that act as biological sensors of altered lipid metabolism. We show here that LPS-induced inflammatory responses result in the modulation of triglyceride plasma levels that are accompanied most notably by a decrease in the hepatic mRNA expression levels of PPARα, β, and γ and by the up-regulation of PPARγ expression only in adipose tissue and the anterior intestine. In addition, LPS-induced inflammation results in an increase in the hepatic mRNA expression and protein activity levels of members of the mitogen-activated protein kinase (MAPK) family, known in mammals to regulate the transcription and activity of PPARs. Our results provide evidence for the involvement of PPARs in the metabolic response to inflammatory stimuli in seabream and offer insights into the molecular mechanisms underlying the redirection of metabolic activities under inflammatory conditions in vertebrates.