Fatty Acid Oxidation in Zebrafish Adipose Tissue Is Promoted by 1α,25(OH) 2 D 3

Vitamin D Stimulates Cardiomyocyte Proliferation and Controls Organ Size and Regeneration in Zebrafish

Attaining proper organ size during development and regeneration hinges on the activity of mitogenic factors. Here, we performed a large-scale chemical screen in embryonic zebrafish to identify cardiomyocyte mitogens. Although commonly considered anti-proliferative, vitamin D analogs like alfacalcidol had rapid, potent mitogenic effects on embryonic and adult cardiomyocytes in vivo. Moreover, pharmacologic or genetic manipulation of vitamin D signaling controlled proliferation in multiple adult cell types and dictated growth rates in embryonic and juvenile zebrafish. Tissue-specific modulation of vitamin D receptor (VDR) signaling had organ-restricted effects, with cardiac VDR activation causing cardiomegaly. Alfacalcidol enhanced the regenerative response of injured zebrafish hearts, whereas VDR blockade inhibited regeneration. Alfacalcidol activated cardiac expression of genes associated with ErbB2 signaling, while ErbB2 inhibition blunted its effects on cell proliferation. Our findings identify vitamin D as mitogenic for cardiomyocytes and other cell types in zebrafish and indicate a mechanism to regulate organ size and regeneration.

Dissecting metabolism using zebrafish models of disease

Zebrafish (Danio rerio) are becoming an increasingly powerful model organism to study the role of metabolism in disease. Since its inception, the zebrafish model has relied on unique attributes such as the transparency of embryos, high fecundity and conservation with higher vertebrates, to perform phenotype-driven chemical and genetic screens. In this review, we describe how zebrafish have been used to reveal novel mechanisms by which metabolism regulates embryonic development, obesity, fatty liver disease and cancer. In addition, we will highlight how new approaches in advanced microscopy, transcriptomics and metabolomics using zebrafish as a model system have yielded fundamental insights into the mechanistic underpinnings of disease.

Obese zebrafish: A small fish for a major human health condition

Obesity is becoming a silent worldwide epidemic, with a steady increase in both adults and children. To date, even though several drugs have been licensed for long-term obesity treatment, none of them are yet used in routine clinical practice. So far the only successful intervention has been behavioral therapy. A suitable and economic experimental model mimicking the human condition would therefore be extremely useful to evaluate preventive measures and novel treatments. Zebrafish are emerging as an important model system to study obesity and related metabolic disease. Remarkable similarities have been reported in lipid metabolism and the adipogenic pathway between zebrafish and mammals. Moreover, the zebrafish possesses a number of features-the relative inexpensiveness of animal husbandry, its optical transparency and the ability to produce a large number of offspring at low cost-that make it ideal for large-scale screening and for testing drugs and intervention. In this review, we summarize recent progress in using zebrafish as a model system to study obesity and obesity-related metabolic disorders. We describe several zebrafish models (in both larvae and adult animals) that develop obesity and non-alcoholic fatty liver disease (NAFLD) using different approaches, including gene manipulation, diet manipulation and modification of microbiota composition. For these models, we have outlined the specific aspects related to obesity and its development and we have summarized their advantages and limitations.

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.

Chronic glucocorticoid treatment induced circadian clock disorder leads to lipid metabolism and gut microbiota alterations in rats

AIM

Glucocorticoids (GCs), steroid hormones synthetized by the adrenal gland, are regulated by circadian cycles, and dysregulation of GC signaling can lead to the development of metabolic syndrome. The effects and potential mechanism of GCs in physiology were investigated in the present study.

MAIN METHODS

Male Wistar rats were orally administered dexamethasone sodium phosphate (DEX, 0.01 and 0.05mg/kg body weight per day) for 7weeks.

KEY FINDING

DEX treatment attenuated body weight gain and reduced food intake, whereas it induced the accumulation of fat. Administration of DEX induced dysregulation of the expression of lipogenic genes in both fat and liver. Moreover, the mRNA levels of genes related to mitochondrial biogenesis and function were significantly downregulated in the liver and fat of DEX-treated rats. Furthermore, DEX treatment caused a significant reduction in the richness and diversity of the microbiota in the colon, as assessed using high-throughput sequencing of the 16s rRNA gene V3-V4 region, an increase in inflammatory cell infiltration, and a decrease in mucus secretion in the colon. Additionally, DEX administration induced phase shift or loss of circadian rhythmicity of clock-related genes in peripheral tissues. These results were associated with higher serum corticosterone levels and upregulation of GC receptor (GR) expression in peripheral tissues.

SIGNIFICANCE

Our findings indicate that long-term administration of GC caused lipid accumulation, changes in the structure of the intestinal flora, and reduced colonic mucus secretion in vivo. The mechanism of these physiological changes may involve a circadian rhythm disorder and dysregulation of GR expression.