Molecular Characterization, Nutritional and Insulin Regulation of Elovl6 in Rainbow Trout (Oncorhynchus mykiss)

Abstract

Elongation of very long-chain fatty acids protein 6 (Elovl6) is a crucial enzyme in the synthesis of endogenous fatty acids, which participates in the energy balance and metabolic diseases. The main objective of this study was to explore the molecular characterization of Elovl6 and the regulation of elovl6 expression in response to dietary fatty acids and insulin. In the present study, the ORF (open reading frame) of Elovl6 from rainbow trout was cloned and characterized, which showed a high identity (87%) with mammals and other teleost. The results of quantitative PCR showed that the transcriptional levels of elovl6 from rainbow trout that were fed diets containing soybean oil (enriched with 18:2n-6, linoleic acid (LA)) or linseed oil (enriched with 18:3n-3, α-linolenic acid (ALA)) were lower than those in the group that were fed diets containing fish oil (enriched with 20:5n-3, eicosapentaenoic acid (EPA) and 22:6n-3, docosahexaenoic acid (DHA)). Correspondingly, mRNA expression of elovl6 in hepatocytes treated with DHA was dramatically higher than that in LA and ALA groups. The transcriptional expression of elovl6 in hepatocytes treated with insulin was also significantly increased. Moreover, the dual luciferase assay showed the transcription factor CREB1 dramatically up-regulated the promoter activity of elovl6, while FOXO1 significantly down-regulated the elovl6 promoter activity in rainbow trout. The differences in transcriptional expression of crbe1 and foxo1 may contribute to the increase or decrease of elovl6 expression in rainbow trout in response to fatty acids or insulin. These findings revealed the molecular characterization of elovl6 and the regulation of elovl6 expression by CREB1 and FOXO1 in rainbow trout in response to dietary fatty acids or insulin.

Genome-wide identification and expression profile of Elovl genes in threadfin fish Eleutheronema

“…The elovl5 was present in virtually all teleosts that were specific for the elongation of C 18 and C 20 PUFAs, and also had capacity towards C 22 PUFA in some fish, such as Pegusa lascaris 16 and Scatophagus argus 17 . The elovl6 acted to convert C 16 saturated and monounsaturated fatty acids to C 18 fatty acids, similar to mammals, which has been reported in Larimichthys crocea 18 and Oncorhynchus mykiss 19 . The novel elongase, elovl8, including elovl8a and elovl8b, were apparently absent in mammals but shown to have elongation activity to C 18 and C 20 PUFA in teleosts such as Clarias gariepinus and Siganus canaliculatus 20 .…”

ELOVL6 promoter binding sites directly targeted by sterol regulatory element binding protein 1 in fatty acid synthesis of goat mammary epithelial cells

“…Further, conjugated linoleic acids reduce ELOVL6 mRNA levels in lactating dairy goats (Zhang et al, 2018). In contrast, dietary α-linolenic acid or linolenic acid upregulate ELOVL6 expression in marine fish by increasing the transcriptional expression of transcription factors (i.e., CREB1, RXRα; Li et al, 2019Li et al, , 2020. In addition, a previous study showed that the inhibiting effect of PUFA on milk fat synthesis mainly through suppressing the expression of SREBF1, and then blocking the expression of related genes in milk fat synthesis (Harvatine and Bauman, 2006).…”

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

“…Zebrafish possess two elovl1 genes, elovl1a and elovl1b, and knockdown of elovl1 increased levels of C14 to C20 SFA, MUFA and PUFA in zebrafish embryos, suggesting Elovl1 in zebrafish may also be involved in the elongation of PUFA [98], different from human ELOVL1 that has high activity toward C20 and C22 SFA and MUFA [99]. However, molecular characterization and nutritional regulation of Elovl6 was reported in loach (Misgurnus anguillicaudatus) [100], large yellow croaker (Larimichthys crocea) [101] and rainbow trout [102], with loach Elovl6 shown to elongate 16:0 and 16:1 to 18:0 and 18:1, respectively, similar to mammals [100]. While Elovl3 and Elovl7 have not yet been reported in fish, compared to mammalian Elovl7, Elovl7 from the marine crustacean orange mud crab (Scylla olivacea) had elongation activity towards 16:1n-7 and, to a lower extend, C18 PUFA [103].…”