||The present study established cobia preadipocytes culture system, and used the system to investigate the effects of dietary lipids or fatty acids on cobia preadipocytes proliferation, differentiation, lipid accumulation and adipogenesis genes expression. The aim was to explore the possibility modulate cobia lipid distribution and content through nutritional manipulation. Cobia is a warmwater finfish that accepts high lipid (>17%) diets and is well valued for its white muscle of high lipid levels. In the present study, in addition to optimizing the culture medium for the differentiation of preadipocytes model in Experiment I, several studies evaluating the effects of fatty acids were carried out, including: (Experiment II) comparisons of lipid accumulation and differentiation genes expression in adipocytes between in vivo and in vitro experimental settings, (Experiment III) the effects of single fatty acid as well as (Experiment IV) multiple fatty acids on cobia preadipocytes differentiation genes CCAAT/enhancer binding protein- β (C/EBPβ), peroxisome proliferator-activated receptors (PPARs), fatty acid binding protein1 (FABP1), fatty acid transport protein 2 (FATP2) and fatty acid synthase (FAS) expression.|
In the Experiment I, cobia preadipocytes cultured in L-15 medium with 10% FBS at 28 °C was found to have a high proliferation potential leading to a monolayer confluence by day 18. Oil Red O staining indicated numerous large cytoplasmic lipid droplets were formed and real-time PCR analyses showed increasing upregulations of FABP1, FATP2 and FAS as preadipocytes differentiated.
In the Experiment II, the expression levels of PPARs and FABP were compared between an in vivo and an in vitro experiments. The results of the in vitro and in vivo experiments were found to be compatible. Lipid accumulation was found to be greater in response to safflower oil, olive oil and palm oil treatments in both experiments than in fish oil and perilla oil treatments. At both molecular and cell levels, the effects of fatty acids on adipogenesis in vitro and in vivo systems showed similar trends.
In the Experiment III, palmitic acid (PA 16:0), stearic acid (SA 18:1 n-9), oleic acid (OA 18:1 -9), linoleic acid (LA 18:2 n-6), α-linolenic acid (LNA 18:3 n-3), eicosapentaenoic acid (EPA 20:5 n-3) or docosahexaenoic acid (DHA 22:6 n-3) were found to modulate differentially on cobia preadipocyte differentiation. C/EBPβ and PPARs expression increased during the early phase of differentiation and decreased at later stages of differentiation. On the other hand expressions of FABP1, FATP2 and FAS were increased throughout the differentiation process. The expression levels of C/EBPβ and PPARγ increased when the cells were exposed to OA, LA, EPA and DHA groups. OA and EPA increased the expression levels of FABP1, FATP2 and FAS. LNA and DHA led to a lower accumulation of triglycerides (TG) in mature adipocytes than OA.
In the Experiment IV, the synergistic or antagonistic effects of major fatty acids of palm oil, rapeseed oil, soybean oil, flaxseed oil, anchovy oil or cod liver oil on adipogenesis and adipocyte differentiation were investigated. The expression levels of C/EBPβ and PPARγ were increased when the adipocytes were exposed to OA, LA, EPA or DHA, indicating a synergistic effect. Transcription factor genes expression levels were reduced with the exposure to PA, SA and low levels of LNA. The expression level of FAS and TG accumulation were significantly higher for PA, OA and LA than for LNA, EPA and DHA. The amount of reactive oxygen species production increased in adipocytes with exposure to LNA, EPA and DHA.