Abstract
Omega-3 long chain polyunsaturated fatty acids (n-3 LC-PUFA), particularly docosahexaenoic acids (22:6n-3, DHA), have positive effects on multiple biologic and pathologic processes. Fish are the major dietary source of n-3 LC-PUFA for humans. Growing evidence supports acyl-coenzyme A (acyl-CoA) synthetase 6 (acsl6) being involved in cellular DHA uptake and lipogenesis in mammals, while its molecular function and regulatory mechanism remain unknown in fish. The present study focused on investigating the molecular characterization and transcription regulation of the acsl6 gene in the freshwater teleost common carp (Cyprinus carpio). First, the full length of acsl6 cDNA contained a coding region of 2148 bp for 715 amino acids, which possessed all characteristic features of the acyl-CoA synthetase (ACSL) family. Its mRNA expression was the highest in the brain, followed by in the heart, liver, kidney, muscle, and eyes, but little expression was detected in the ovary and gills. Additionally, a candidate acsl6 promoter region of 2058 bp was cloned, and the sequence from −758 bp to −198 bp was determined as core a promoter by equal progressive deletion and electrophoretic mobility shift assay. The binding sites for important transcription factors (TFs), including stimulatory protein 1 (SP1), CCAAT enhancer-binding protein (C/EBPα), sterol-regulatory element binding protein 1c (SREBP1c), peroxisome proliferator activated receptor α (PPARα), and PPARγ were identified in the core promoter by site-directed mutation and functional assays. Furthermore, the intraperitoneal injection of PPARγ agonists (balaglitazone) increased the expression of acsl6 mRNA, coupling with an increased proportion of DHA in the muscle, while opposite results were obtained in the injection of the SREBP1c antagonist (betulin). However, the expression of acsl6 and DHA content in muscle were largely unchanged by PPARα agonist (fenofibrate) treatment. These results indicated that acsl6 may play an important role for the muscular DHA uptake and deposition in common carp, and PPARγ and SREBP-1c are the potential TFs involved in the transcriptional regulation of acsl6 gene. To our knowledge, this is the first report of the characterization of acsl6 gene and its promoter in teleosts.
Highlights
Omega-3 long chain polyunsaturated fatty acids (n-3 LC-PUFAs), eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acids (22:6n-3, DHA), have positive effects on multiple biologic and pathologic processes including metabolic disorders, cardiovascular and neurological diseases, cancer, inflammation, and pain [1,2,3,4,5]
Several members of the ACSL family catalyze a wide range of fatty acids to form acyl-CoAs with some substrate preferences toward different FA metabolic fates [16]
ACSL1, ACSL3, and ACSL4 have well been identified in numerous species, while acsl6 has only been identified in rat, human, and mouse [16,28,29,30]
Summary
Omega-3 long chain polyunsaturated fatty acids (n-3 LC-PUFAs), eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acids (22:6n-3, DHA), have positive effects on multiple biologic and pathologic processes including metabolic disorders, cardiovascular and neurological diseases, cancer, inflammation, and pain [1,2,3,4,5]. It is well known that the benefits of food fish are to provide n-3 LC-PUFAs in diets, while with wild fish resources declining, the major source of n-3 LC-PUFAs has turned to cultured fish [7]. To efficiently use plant-based alternatives and to maximize endogenous n-3 LC-PUFA biosynthesis, much attention has been focused on illuminating the regulation mechanisms of LC-PUFA biosynthesis in teleosts [9,10,11,12]. It is still unclear about the n-3 LC-PUFA deposition process and its regulatory mechanism in fish muscle
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