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Ghrelin, glucagon-like peptide-1 (GLP-1), and peptide YY (PYY) are potent hormones mediating food intake according to the nutritional status in fish. However, limited information is available on these genes and their expression in response to nutrition in silver pomfret (Pampus argenteus). A comparison analysis revealed that ghrelin and GLP-1 were relatively conserved in marine fish. PYYa and PYYb shared a low identity and were clustered to different PYY branches. Ghrelin, pyya, and pyyb mRNAs were highly expressed in the brain, while glp-1 was highly expressed in the gills and liver. The ghrelin mRNA expression was relatively high an hour post-feeding and decreased after 3 to 72 h of fasting. The glp-1 mRNA expression was increased after 6 to 24 h of fasting. The pyya mRNA expression was increased after 72 h of fasting, while the pyyb expression remained stable during fasting. The diet with 14% lipid promoted the expressions of glp-1, pyya, and pyyb, but inhibited the ghrelin expression. The ghrelin expression in the intestine was increased after palmitic acid, oleic acid (OA), linoleic acid (LA), α-linolenic acid, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) incubation. OA decreased the expression of glp-1 and increased the expression of pyya. The expression of pyyb was downregulated by LA, DHA, and EPA. These results suggest the importance of ghrelin, glp-1, and pyy in coordinating food intake in response to fasting, dietary lipid concentration, and fatty acids in silver pomfret. [ABSTRACT FROM AUTHOR]

Understanding the metabolic effects of fatty acids on fish intestine is critical to the substitution of fish oil with vegetable oils in aquaculture. In this study, the effects of eicosapentaenoic acid (EPA) and palmitic acid (PA) on fish intestine were evaluated in vitro and in vivo. As the first step for in vitro study, an intestinal cell line (SPIF) was established from silver pomfret (Pampus argenteus). Thereafter, the effects of EPA and PA on cell viability, prostaglandin E2 (PGE2) production, and the expression of genes related to heat shock response, inflammation, extracellular matrix (ECM) formation and degradation were examined in SPIF cells. Finally, these metabolic effects of EPA and PA on the intestine were examined in zebrafish (Danio rerio) larvae. Results showed that all tested fatty acids (PA, oleic acid, linoleic acid, α-linolenic acid, arachidonic acid, and docosahexaenoic acid) except EPA reduced SPIF viability to distinct degrees at the same concentrations. PA decreased SPIF viability accompanied by an increase in PGE2 level. Meanwhile, PA increased the expression of genes related to heat shock response (grp78 , grp94 , hsp70 , and hsp90) and inflammation (nf-κb , il-1β , and cox2). Furthermore, PA reduced the expression of collagen type I (col1a1a and col1a1b) and extracellular matrix (ECM) degradation-related gene mmp2 , while up-regulating timp2 mRNA expression. In vivo , PA also increased hsp70 , il-1β , and cox2 mRNA levels and limited the expression of collagen type I in the larval zebrafish intestine. Interestingly, the combination of EPA and PA partially recovered the PA-induced changes in cell viability, PGE2 production, and mRNA expression in vitro and in vivo. These results suggest that PA may result in heat shock and inflammatory responses, as well as alter ECM formation and degradation in fish intestine, while EPA could at least partially mitigate these negative effects caused by PA. • An intestinal cell line from silver pomfret (SPIF) was developed as a study model. • Except for EPA, PA, OA, LA, ALA, ARA and DHA decreased SPIF viability to distinct degrees. • PA induced heat shock and inflammatory responses, and affected repair processes in fish intestine. • EPA mitigated PA-induced negative effects on fish intestine. [ABSTRACT FROM AUTHOR]

Highlights • Silver pomfret can biosynthesize DHA from endogenous EPA. • Cd exposure increases the brain-specific expression of genes required for DHA synthesis from EPA. • Pparα regulates LC-PUFA biosynthesis gene expression in response to Cd exposure. • Cd exposure reduces the DHA concentration and increases the malondialdehyde concentration in the brain of silver pomfret. Abstract Despite a close interaction between cadmium (Cd) and long-chain polyunsaturated fatty acid (LC-PUFA) metabolism, the influence of Cd exposure on the endogenous synthesis of LC-PUFA has received little attention. In the present study, we hypothesized that Cd exposure would affect the synthesis of LC-PUFA in the marine fish silver pomfret (Pampus argenteus). Therefore, the molecular basis of LC-PUFA biosynthesis and regulation was investigated as the first step to understanding the mechanisms underpinning the effects of Cd exposure. Thereafter, transcriptional regulation of the genes that participate in LC-PUFA biosynthesis and regulation by Cd exposure were also explored. Our results showed that fatty acyl desaturase 2 (Fads2) and elongases of very long-chain fatty acids 5 (Elovl5), two key enzymes involved in LC-PUFA biosynthesis, enabled silver pomfret to biosynthesize 20:3n–6 and 20:4n–3 from 18:2n-6 and 18:3n-3. The results also raise the possibility that silver pomfret may have the ability to produce docosahexaenoic acid (DHA, 22:6n-3) from endogenous eicosapentaenoic acid (EPA, 20:5n-3). The expression of silver pomfret fads2 and elovl5 was transcriptionally regulated by the peroxisome proliferator activated receptor α (Pparα). The expression of fads2 , elovl5 and pparα in the brain was significantly increased in response to Cd exposure. In addition, Cd exposure significantly reduced the DHA concentration and significantly increased the malondialdehyde concentration in the brain of silver pomfret. Cd exposure likely increases brain-specific DHA synthesis from EPA by transcriptionally activating fads2 and elovl5 via Pparα in silver pomfret. This regulation may be a coping mechanism for the reduction of DHA caused by Cd-oxidative stress in the brains of silver pomfret. [ABSTRACT FROM AUTHOR]

As an unusual economically important aquaculture species, Sinonovacula constricta possesses high levels of long-chain polyunsaturated fatty acids (LC-PUFA). Previously, our group identified fatty acyl desaturases (Fad) with Δ5 and Δ6 activities in S. constricta , which was the first report of Δ6 Fad in a marine mollusc. Here, we further successfully characterize elongases of very long-chain fatty acids (Elovl) in this important bivalve species, including one Elovl2/5, two Elovl4 isoforms (a and b) and a novel Elovl (c) with Elovl4 activity. In addition, we also determined the desaturation activity of S. constricta Δ6 Fad toward 24:5n-3 to give 24:6n-3, a key intermediate in docosahexaenoic acid (DHA) biosynthesis. Therefore, S. constricta is the first marine mollusc reported to possess all Fad and Elovl activities required for LC-PUFA biosynthesis via the 'Sprecher pathway'. This finding greatly increases our understanding of LC-PUFA biosynthesis in marine molluscs. Phylogenetic analysis by interrogating six marine molluscan genomes, and previously functionally characterized Elovl and Fad from marine molluscs, suggested that DHA biosynthetic ability was limited to a few species, due to the general lack of Δ4 or Δ6 Fad in most molluscs. • The S. constricta Elovl involved in LC-PUFA synthesis were investigated. • The desaturation ability of S. constricta Δ6 Fad toward 24:5n-3 was determined. • S. constricta is the first mollusc with capacity to operate the Sprecher pathway. • DHA biosynthetic ability was limited to certain marine molluscs. [ABSTRACT FROM AUTHOR]

Sinonovacula constricta is the first marine mollusc demonstrated to possess all fatty acyl desaturase (Fad) and elongase of very long chain fatty acids (Elovl) activities required for long-chain polyunsaturated fatty acids (LC-PUFA) biosynthesis via the Sprecher pathway, providing a good opportunity to investigate the essential fatty acids (FA) for its larval development. In the present study, we analyzed the Fad and Elovl expressions, FA compositions, and the feed effects of three representative microalgae (Chlorella sp. , Chaetoceros calcitrans and Isochrysis galbana) in S. constricta at early developmental stages. The results showed that S. constricta Fad and Elovl were all highly expressed in zygotes, which might occur from maternal transfer. Compared to transcripts of Elovl4 activity, Elovl2/5 was only expressed relatively high in zygotes, indicating that C ≥ 22 LC-PUFA were more important than C ≤ 20 LC-PUFA for S. constricta larval development. The zygotes accumulated abundant FA from parents, especially eicosapentaenoic acid (EPA), but with small amount of docosahexaenoic acid (DHA). Meanwhile, the trochophore larva fed with single or mixed microalgae with I. galbana (rich in DHA) exhibited significantly higher growth and survival rate compared to those fed with single Chlorella sp. (rich in 18:2n-6 and 18:3n-3) and C. calcitrans (rich in EPA) or both of them. Those findings suggested that the highly expressed Fad and Elovl might be largely responsible for DHA biosynthesis, but this capability was limited to meet the developmental requirement and the dietary DHA was necessary. Taken together, our results compellingly demonstrated that DHA was essential for S. constricta larval development, which is important to guide its breeding. • Fad and Elovl expressions were examined in developing S. constricta. • Fatty acid compositions were analyzed in developing S. constricta. • Trochophore larval growth and survival were evaluated by first-feeding diet. • DHA still appeared to be essential for S. constricta larval development. • Microalgae rich in EPA and DHA were critical for S. constricta breeding. [ABSTRACT FROM AUTHOR]