Fang Qiao

Systemic adaptation of lipid metabolism in response to low- and high-fat diet in Nile tilapia (Oreochromis niloticus).

Natural selection endows animals with the abilities to store lipid when food is abundant and to synthesize lipid when it is limited. However, the relevant adaptive strategy of lipid metabolism has not been clearly elucidated in fish. This study examined the systemic metabolic strategies of Nile tilapia to maintain lipid homeostasis when fed with low‐ or high‐fat diets. Three diets with different lipid contents (1%, 7%, and 13%) were formulated and fed to tilapias for 10 weeks. At the end of the feeding trial, the growth rate, hepatic somatic index, and the triglyceride (TG) contents of serum, liver, muscle, and adipose tissue were comparable among three groups, whereas the total body lipid contents and the mass of adipose tissue increased with the increased dietary lipid levels. Overall quantitative PCR, western blotting and transcriptomic assays indicated that the liver was the primary responding organ to low‐fat (LF) diet feeding, and the elevated glycolysis and accelerated biosynthesis of fatty acids (FA) in the liver is likely to be the main strategies of tilapia toward LF intake. In contrast, excess ingested lipid was preferentially stored in adipose tissue through increasing the capability of FA uptake and TG synthesis. Increasing numbers, but not enlarging size, of adipocytes may be the main strategy of Nile tilapia responding to continuous high‐fat (HF) diet feeding. This is the first study illuminating the systemic adaptation of lipid metabolism responding to LF or HF diet in fish, and our results shed new light on fish physiology.

Symbiotic Bacteria in Gills and Guts of Chinese Mitten Crab (Eriocheir sinensis) Differ from the Free-Living Bacteria in Water

Aquatic animals have a close relationship with water, but differences in their symbiotic bacteria and the bacterial composition in water remains unclear. Wild or domestic Chinese mitten crabs (Eriocheir sinensis) and the water in which they live were collected from four sampling sites in Jiangsu and Shanghai, China. Bacterial composition in water, gills or guts of E. sinensis, were compared by high-throughput sequencing using 16S rRNA genes. Analysis of >660,000 sequences indicated that bacterial diversity was higher in water than in gills or guts. Tenericutes and Proteobacteria were dominant phyla in guts, while Actinobacteria, Proteobacteria and Bacteroidetes were dominant in gills and water. Non-metric multidimensional scaling analysis indicated that microbiota from gills, guts or water clearly separated into three groups, suggesting that crabs harbor a more specific microbial community than the water in which they live. The dominant OTUs in crab gut were related to Mycoplasmataceae, which were low in abundance in gills, showing that, like mammals, crabs have body-site specific microbiota. OTUs related to Ilumatobacter and Albimonas, which are commonly present in sediment and seawater, were dominant in gills but almost absent from the sampled water. Considering E. sinensis are bottom-dwelling crustacean and they mate in saline water or seawater, behavior and life cycle of crabs may play an important role in shaping the symbiotic bacterial pattern. This study revealed the relationship between the symbiotic bacteria of Chinese mitten crab and their habitat, affording information on the assembly factors of commensal bacteria in aquatic animals.

Nutritional background changes the hypolipidemic effects of fenofibrate in Nile tilapia ( Oreochromis niloticus )

Peroxisome proliferation activated receptor α (PPARα) is an important transcriptional regulator of lipid metabolism and is activated by high-fat diet (HFD) and fibrates in mammals. However, whether nutritional background affects PPARα activation and the hypolipidemic effects of PPARα ligands have not been investigated in fish. In the present two-phase study of Nile tilapia (Oreochromis niloticus), fish were first fed a HFD (13% fat) or low-fat diet (LFD; 1% fat) diet for 10 weeks, and then fish from the first phase were fed the HFD or LFD supplemented with 200 mg/kg body weight fenofibrate for 4 weeks. The results indicated that the HFD did not activate PPARα or other lipid catabolism-related genes. Hepatic fatty acid β-oxidation increased significantly in the HFD and LFD groups after the fenofibrate treatment, when exogenous substrates were sufficiently provided. Only in the HFD group, fenofibrate significantly increased hepatic PPARα mRNA and protein expression, and decreased liver and plasma triglyceride concentrations. This is the first study to show that body fat deposition and dietary lipid content affects PPARα activation and the hypolipidemic effects of fenofibrate in fish, and this could be due to differences in substrate availability for lipid catabolism in fish fed with different diets.

Influence of Endogenous and Exogenous Estrogenic Endocrine on Intestinal Microbiota in Zebrafish

Gender is one of the factors influencing the intestinal microbial composition in mammals, but whether fish also have gender-specific intestinal microbial patterns remains unknown. In this decade, endocrine disrupting chemicals in surface and ground water of many areas and increasing observation of freshwater male fish displaying female sexual characteristics have been reported. Here we identified the difference in intestinal microbiota between male and female zebrafish, and revealed the influence of endocrine disrupting chemicals on zebrafish intestinal microbiota by using high-throughput sequencing. The results indicated that Fusobacteria, Bacteroidetes and Proteobacteria were dominant in the gut of zebrafish and there were no obvious gender-specific intestinal microbial patterns. Two endocrine disrupting chemicals, Estradiol (E2) and Bisphenol A (BPA), were selected to treat male zebrafish for 5 weeks. E2 and BPA increased vitellogenin expression in the liver of male zebrafish and altered the intestinal microbial composition with the abundance of the phylum CKC4 increased significantly. Our results suggested that because of the developmental character and living environment, gender did not influence the assembly of intestinal microbiota in zebrafish as it does in mammals, but exposure extra to endocrine disrupting chemicals disturbed the intestinal microbial composition, which may be related to changes in host physiological metabolism.

Environmental concentrations of antibiotics impair zebrafish gut health

Antibiotics have been widely used in human and veterinary medicine to both treat and prevent disease. Due to their high water solubility and low bioavailability, many antibiotic residues have been found in aquatic environments. Fish are an indispensable link between the environmental pollution and human health. However, the chronic effects of environmental concentrations of antibiotics in fish have not been thoroughly investigated. Sulfamethoxazole (SMX) and oxytetracycline (OTC) are frequently detected in aquatic environments. In this study, zebrafish were exposed to SMX (260 ng/L) and OTC (420 ng/L) for a six-week period. Results indicated that exposure to antibiotics did not influence weight gain of fish but increased the metabolic rate and caused higher mortality when treated fish were challenged with Aeromonas hydrophila. Furthermore, exposure to antibiotics in water resulted in a significant decrease in intestinal goblet cell numbers, alkaline phosphatase (AKP), acid phosphatase (ACP) activities, and the anti-oxidant response while there was a significant increase in expression of inflammatory factors. Antibiotic exposure also disturbed the intestinal microbiota in the OTC-exposed group. Our results indicated that environmental antibiotic concentrations can impair the gut health of zebrafish. The potential health risk of antibiotic residues in water should be evaluated in the future.

Physiological and metabolic differences between visceral and subcutaneous adipose tissues in Nile tilapia (Oreochromis niloticus)

Visceral adipose tissue (VAT) and subcutaneous adipose tissue (SCAT) have different structures and metabolic functions and play different roles in the regulation of the mammal endocrine system. However, little is known about morphology and physiological and metabolic functions between VAT and SCAT in fish. We compared the morphological, physiological, and biochemical characteristics of VAT and SCAT in Nile tilapia and measured their functions in energy intake flux, lipolytic ability, and gene expression patterns. SCAT contained more large adipocytes and nonadipocytes than VAT in Nile tilapia. VAT had higher lipid content and was the primary site for lipid deposition. Conversely, SCAT had higher hormone-induced lipolytic activity. Furthermore, SCAT had a higher percentage of monounsaturated and lower polyunsaturated fatty acids than VAT. SCAT had higher mitochondrial DNA, gene expression for fatty acid β-oxidation, adipogenesis, and brown adipose tissue characteristics, but it also had a lower gene expression for inflammation and adipocyte differentiation than VAT. SCAT and VAT have different morphological structures, as well as physiological and metabolic functions in fish. VAT is the preferable lipid deposition tissue, whereas SCAT exhibits higher lipid catabolic activity than VAT. The physiological functions of SCAT in fish are commonly overlooked. The present study indicates that SCAT has specific metabolic characteristics that differ from VAT. The differences between VAT and SCAT should be considered in future metabolism studies using fish as models, either in biomedical or aquaculture studies.

The Presence or Absence of Intestinal Microbiota Affects Lipid Deposition and Related Genes Expression in Zebrafish (Danio rerio)

Understanding how intestinal microbiota alters energy homeostasis and lipid metabolism is a critical process in energy balance and health. However, the exact role of intestinal microbiota in the regulation of lipid metabolism in fish remains unclear. Here, we used two zebrafish models (germ-free and antibiotics-treated zebrafish) to identify the role of intestinal microbiota in lipid metabolism. Conventional and germ-free zebrafish larvae were fed with egg yolk. Transmission electron microscopy was used to detect the presence of lipid droplets in the intestinal epithelium. The results showed that, microbiota increased lipid accumulation in the intestinal epithelium. The mRNA sequencing technology was used to assess genes expression level. We found majority of the differentially expressed genes were related to lipid metabolism. Due to the limitation of germ-free zebrafish larvae, antibiotics-treated zebrafish were also used to identify the relationship between the gut microbiota and the host lipid metabolism. Oil-red staining showed antibiotics-treated zebrafish had less intestinal lipid accumulation than control group. The mRNA expression of genes related to lipid metabolism in liver and intestine was also quantified by using real-time PCR. The results indicated that apoa4, hsl, cox15, slc2a1a, and lss were more related to intestinal bacteria in fish, while the influence of intestinal microbiota on the activity of fabp6, acsl5, cd36, and gpat2 was different between the liver and intestine. This study identified several genes regulated by intestinal microbiota. Furthermore, the advantages and disadvantages of each model have been discussed. This study provides valuable information for exploring host-microbiota interactions in zebrafish in future.