DHA Suppresses Hepatic Lipid Accumulation via Cyclin D1 in Zebrafish

Abstract

With the widespread use of high-fat diets (HFDs) in aquaculture, fatty livers are frequently observed in many fish species. The aim of this study was to investigate if docosahexaenoic acid (DHA) could be used to reduce the fatty liver in zebrafish generated by a 16% soybean oil-HFD over 2 weeks of feeding. The DHA was added to iso-lipidic HFD at 0.5, 1.0, and 2.0% of diet. Supplementation of DHA reduced growth and feed efficiency in a dose dependent manner being lowest in the HFDHA2.0 group. Hepatic triglyceride (TG) in zebrafish fed 0.5% DHA-supplemented HFD (HFDHA0.5) was significantly lower than in the HFD control. Transcriptional analyses of hepatic genes showed that lipid synthesis was reduced, while fatty acid β-oxidation was increased in the HFDHA0.5 group. Furthermore, the expression of Cyclin D1 in liver of zebrafish fed HFDHA0.5 was significantly reduced compared to that in fish fed HFD. In zebrafish liver cells, Cyclin D1 knockdown and blocking of Cyclin D1-CDK4 signal led to inhibited lipid biosynthesis and elevated lipid β-oxidation. Besides, DHA-supplemented diet resulted in a rich of Proteobacteria and Actinobacteriota in gut microbiota, which promoted lipid β-oxidation but did not alter the expression of Cyclin D1 in germ-free zebrafish model. In conclusion, DHA not only inhibits hepatic lipid synthesis and promotes lipid β-oxidation via Cyclin D1 inhibition, but also facilitates lipid β-oxidation via gut microbiota. This study reveals the lipid-lowering effects of DHA and highlights the importance of fatty acid composition when formulating fish HFD.

Excess DHA Induces Liver Injury via Lipid Peroxidation and Gut Microbiota-Derived Lipopolysaccharide in Zebrafish

“…The health-promoting effects of DHA, such as alleviating hyperglycemia, insulin resistance, and lipid metabolism abnormalities, are partly mediated by the modulation of gut microbiome and bacterial metabolites ( 21 – 23 ). The previous works in zebrafish also observed a similar phenomenon ( 24 , 25 ). However, in the case of high dietary DHA, the available information is scarce both in mammals and fish.…”

“…The feed formulation is presented in Table 1 . The feeds were prepared as described in previous work ( 24 ). Casein, soybean oil, and wheat flour were used as dietary protein, lipid, and carbohydrate sources, respectively.…”

“…During the feeding, healthy, uniformly sized 1-month-old zebrafish (1.57 ± 0.011 g/20 fish) were divided into four groups at random and fed with the LFD, 2.0% DHA oil-supplemented LFD (LFDHA2.0), HFD, or 2.0% DHA oil-supplemented HFD (HFDHA2.0) ( Table 1 ). The fatty acid compositions of diets have been described in previous work ( 24 ). The feeding amount was at 6% of body weight, twice a day at 9:00 and 16:00.…”

“…A histological analysis of livers was conducted as described in a previous study ( 24 ). In brief, the livers of zebrafish were rinsed with sterilized phosphate buffer solution (PBS), fixed in 4% formalin solution, and embedded in paraffin.…”

“…Moreover, the tissue deposition of DHA and oxidative stress induced by dietary DHA have been observed in zebrafish ( 31 ). A previous study has suggested that short-term (2 weeks) and medium-term (4 weeks) intakes of low level of DHA (0.5% of diet) are beneficial for reducing hepatic lipid accumulation induced by HFD, however, as the inclusion of DHA increased to 2.0% of diet, this lipid-lowering effect was abolished ( 24 ). Thus, in this study, the effects of high dietary DHA (2.0% of diet) on liver health as well as hepatic oxidative stress were studied.…”