Fish Oil Suppresses Body Fat Accumulation in Zebrafish

Stripe pattern differences can be used to distinguish individual adult zebrafish

Adult zebrafish are commonly used as disease models in biomedical research, but unlike in other model organisms such as rodents, there is no simple method for distinguishing individuals, even though the importance of individual differences is recognized in such research. We developed a side viewing device that can be used to capture images of stripe patterns and identified eight distinct components of stripe patterns on the caudal and anal fins that allowed us to distinguish individual fish. We found that the stripe patterns were consistent for at least 8 weeks in males and females of two lines of wild-type zebrafish. These results suggest that individual adult zebrafish can be distinguished in an easy and non-invasive manner, allowing researchers to incorporate individual differences in biomedical research as in rodent models.

The effects of isocaloric diets derived from different lipid sources on zebrafish

Characterizing the effects of saturated fat intake on metabolic health and its changes remains a major challenge. Lipid diets, from different sources, vary widely in their physiological effects on health; therefore, it is important to consider the specific lipid source consumed. The objective of the study was to evaluate the effect of the imposition of isocaloric diets with different lipid sources in zebrafish (fish oil/pork lard). Depicting how metabolic, morphological and behavioral parameters might express themselves in these fishes. Forty adult female fishes were used for the experiment. The animals were divided into a control group (C), fed with unsaturated fatty acid diet, and a saturated fatty acid group (Sat). They received food three times a day, during the 11-week period. The results showed that animals in the Sat group had increased body weight, with a difference relative to the C group, from the third week of diet until the end of the experiment. At the end of the last week, the Sat group had a body weight 32% higher (P=0.0182) than the body weight of the control group. The consumption of a diet rich in saturated fatty acids did not generate signs related to stress and anxiety in zebrafish. There was an increase in glycemia at T60 and T120, with a statistically significant difference between the two moments. Animals in the Sat group showed an increase (P=0.0086) in hepatic steatosis compared to animals in the control group. The results obtained on the relationship between diet and metabolic changes are fundamental to ensure the understanding and appropriate treatment of these problems.

The zebrafish model system for dyslipidemia and atherosclerosis research: Focus on environmental/exposome factors and genetic mechanisms

Dyslipidemias and atherosclerosis play a pivotal role in cardiovascular risk and disease. Although some pathophysiological mechanisms underlying these conditions have been unveiled, several knowledge gaps still remain. Experimental models, both in vitro and in vivo, have been instrumental to our better understanding of such complex processes. The latter have often been based on rodent species, either wild-type or, in several instances, genetically modified. In this context, the zebrafish may represent an additional very useful in vivo experimental model for dyslipidemia and atherosclerosis. Interestingly, the lipid metabolism of zebrafish shares several features with that present in humans, recapitulating some molecular features and pathophysiological aspects in a better way than that of rodents. The zebrafish model may be of help to address questions related to exposome factors as well as to genetic features, aiming to dissect selected aspects of the more complex scenario observed in humans. Indeed, exposome-related dyslipidemia/atherosclerosis research in zebrafish may target different scientific questions, related to nutrition, microbiota, temperature, light exposure at the larval stage, exposure to chemicals and epigenetic consequences of such external factors. Addressing genetic features related to dyslipidemia/atherosclerosis using the zebrafish model is already a reality and active research is now ongoing in this promising area. Novel technologies (gene and genome editing) may help to identify new candidate genes involved in dyslipidemia and dyslipidemia-related diseases. Based on these considerations, the zebrafish experimental model appears highly suitable for the study of exposome factors, genes and molecules involved in the development of atherosclerosis-related disease as well as for the validation of novel potential treatment options.

DHA Suppresses Hepatic Lipid Accumulation via Cyclin D1 in Zebrafish

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.

High-fat diet impairs cognitive function of zebrafish

An unhealthy diet with excessive fat intake has often been claimed to induce not only obesity but also cognitive dysfunction in mammals; however, it is not known whether this is the case in zebrafish. Here, we investigated the effect of excessive fat in the diet on cognitive function and on gene expression in the telencephalon of zebrafish. Cognitive function, as measured by active avoidance test, was impaired by feeding of a high-fat diet compared with a control diet. In RNA sequencing analysis of the telencephalon, 97 genes were identified with a fold change in expression greater than 2 and a p-value less than 0.05 between the two diets. In quantitative real-time PCR analysis of the telencephalon, genes related to neuronal activity, anti-oxidative stress, blood–brain barrier function and amyloid-β degradation were found to be downregulated, whereas genes related to apoptosis and amyloid-β production were found to be upregulated, in the high-fat diet group, which are changes known to occur in mammals fed a high-fat diet. Collectively, these results are similar to those found in mammals, suggesting that zebrafish can serve as a suitable animal model in research into cognitive impairment induced by excessive fat in the diet.

Zebrafish as a Model for Obesity and Diabetes

Obesity and diabetes now considered global epidemics. The prevalence rates of diabetes are increasing in parallel with the rates of obesity and the strong connection between these two diseases has been coined as “diabesity.” The health risks of overweight or obesity include Type 2 diabetes mellitus (T2DM), coronary heart disease and cancer of numerous organs. Both obesity and diabetes are complex diseases that involve the interaction of genetics and environmental factors. The underlying pathogenesis of obesity and diabetes are not well understood and further research is needed for pharmacological and surgical management. Consequently, the use of animal models of obesity and/or diabetes is important for both improving the understanding of these diseases and to identify and develop effective treatments. Zebrafish is an attractive model system for studying metabolic diseases because of the functional conservation in lipid metabolism, adipose biology, pancreas structure, and glucose homeostasis. It is also suited for identification of novel targets associated with the risk and treatment of obesity and diabetes in humans. In this review, we highlight studies using zebrafish to model metabolic diseases, and discuss the advantages and disadvantages of studying pathologies associated with obesity and diabetes in zebrafish.