Dietary Glucose Increases Glucose Absorption and Lipid Deposition via SGLT1/2 Signaling and Acetylated ChREBP in the Intestine and Isolated Intestinal Epithelial Cells of Yellow Catfish

Effects of Commonly used Surfactants, Poloxamer 188 and Tween 80, on the Drug Transport Capacity of Intestinal Glucose Transporters

Some glycoside drugs can be transported through intestinal glucose transporters (IGTs). The surfactants used in oral drug preparations can affect the function of transporter proteins. This study aimed to investigate the effect of commonly used surfactants, Poloxamer 188 and Tween 80, on the drug transport capacity of IGTs. Previous studies have shown that gastrodin is the optimal drug substrate for IGTs. Gastrodin was used as a probe drug to evaluate the effect of these two surfactants on intestinal absorption in SD rats through pharmacokinetic and in situ single-pass intestinal perfusion. Then, the effects of the two surfactants on the expression of glucose transporters and tight-junction proteins were examined using RT-PCR and western blotting. Additionally, the effect of surfactants on intestinal permeability was evaluated through hematoxylin-eosin staining. The results found that all experimental for Poloxamer 188 (0.5%, 2.0% and 8.0%) and Tween 80 (0.1% and 2.0%) were not significantly different from those of the blank group. However, the AUC(0-∞) of gastrodin increased by approximately 32% when 0.5% Tween 80 was used. The changes in IGT expression correlated with the intestinal absorption of gastrodin. A significant increase in the expression of IGTs was observed at 0.5% Tween 80. In conclusion, Poloxamer 188 had minimal effect on the drug transport capacity of IGTs within the recommended limits of use. However, the expression of IGTs increased in response to 0.5% Tween 80, which significantly enhanced the drug transport capacity of IGTs. However, 0.1% and 2.0% Tween 80 had no significant effect.

Characterization and expression analysis of seven lipid metabolism-related genes in yellow catfish Pelteobagrus fulvidraco fed high fat and bile acid diet

SREBPs, such as SREBP1 and SREBP2, were the key transcriptional factors regulating lipid metabolism. The processing of SREBPs involved many genes, such as scap, s1p, s2p, cideb. Here, we deciphered the full-length cDNA sequences of scap, srebp1, srebp2, s1p, s2p, cideb and cidec from yellow catfish Pelteobagrus fulvidraco. Their full-length cDNA sequences ranged from 1587 to 3884 bp, and their ORF length from 1191 to 2979 bp, encoding 396-992 amino acids. Some conservative domains were predicted, including the multiple transmembrane domains in SCAP, the bHLH-ZIP domain in SREBP1 and SREBP2, the ApoB binding region, ER targeting region and LD targeting region in CIDEb, the LD targeting region in the CIDEc, the conserved catalytic site and processing site in S1P, and the transmembrane helix domain in S2P. Their mRNA expression could be observed in the heart, spleen, liver, kidney, brain, muscle, intestine and adipose, but varied with tissues. The changes of their mRNA expression in responses to high-fat (HFD) and bile acid (BA) diets were also investigated in the brain, heart, intestine, kidney and spleen tissues. In the brain, HFD significantly increased the mRNA expression of seven genes (scap, srebp1, srebp2, s1p, s2p, cideb and cidec), and the BA attenuated the increase of scap, srebp1, srebp2, s1p, s2p, cideb and cidec mRNA expression induced by HFD. In the heart, HFD significantly increased the mRNA abundances of six genes (srebp1, srebp2, scap, s2p, cideb and cidec), and BA attenuated the increase of their mRNA abundances induced by HFD. In the intestine, HFD increased the cideb, s1p and s2p mRNA abundances, and BA attenuated the HFD-induced increment of their mRNA abundances. In the kidney, HFD significantly increased the scap, cidec and s1p mRNA expression, and BA diet attenuated the increment of their mRNA expression. In the spleen, HFD treatment increased the scap, srebp2, s1p and s2p mRNA expression, and BA diet attenuated HFD-induced increment of their mRNA expression. Taken together, our study elucidated the characterization, expression profiles and transcriptional response of seven lipid metabolic genes, which would serve as the good basis for the further exploration into their function and regulatory mechanism in fish.

Choline-mediated hepatic lipid homoeostasis in yellow catfish: unravelling choline's lipotropic and methyl donor functions and significance of ire-1α signalling pathway

Choline plays a crucial role in hepatic lipid homeostasis by acting as a major methyl-group donor. However, despite this well-accepted fact, no study has yet explored how choline's methyl-donor function contributes to preventing hepatic lipid dysregulation. Moreover, the potential regulatory role of Ire-1α, an ER-transmembrane transducer for the unfolded protein response (UPRer), in choline-mediated hepatic lipid homeostasis remains unexplored. Thus, this study investigated the mechanism by which choline prevents hepatic lipid dysregulation, focusing on its role as a methyl-donor and the involvement of Ire-1α in this process. To this end, a model animal for lipid metabolism, yellow catfish (Pelteobagrus fulvidraco) were fed two different diets (adequate or deficient choline diets) in vivo for 10 weeks. The key findings of studies are as follows: 1. Dietary choline, upregulated selected lipolytic and fatty acid β-oxidation transcripts promoting hepatic lipid homeostasis. 2. Dietary choline ameliorated UPRer and prevented hepatic lipid dysregulation mainly through ire-1α signalling, not perk or atf-6α signalling. 3. Choline inhibited the transcriptional expression level of ire-1α by activating site-specific DNA methylations in the promoter of ire-1α. 4. Choline-mediated ire-1α methylations reduced Ire-1α/Fas interactions, thereby further inhibiting Fas activity and reducing lipid droplet deposition. These results offer a novel insight into the direct and indirect regulation of choline on lipid metabolism genes and suggests a potential crosstalk between ire-1α signalling and choline-deficiency-induced hepatic lipid dysregulation, highlighting the critical contribution of choline as a methyl-donor in maintaining hepatic lipid homeostasis.

Sequential Activations of ChREBP and SREBP1 Signals Regulate the High-Carbohydrate Diet-Induced Hepatic Lipid Deposition in Gibel Carp (Carassius gibelio)

The present study investigated the sequential regulation signals of high-carbohydrate diet (HCD)-induced hepatic lipid deposition in gibel carp (Carassius gibelio). Two isonitrogenous and isolipidic diets, containing 25% (normal carbohydrate diet, NCD) and 45% (HCD) corn starch, were formulated to feed gibel carp (14.82 ± 0.04 g) for 8 weeks. The experimental fish were sampled at 2^nd, 4^th, 6^th, and 8^th week. In HCD group, the hyperlipidemia and significant hepatic lipid deposition (oil red O area and triglyceride content) was found at 4^th, 6^th, and 8^th week, while the significant hyperglycemia was found at 2^nd, 4^th, and 8^th week, compared to NCD group (P < 0.05). HCD induced hepatic lipid deposition via increased hepatic lipogenesis (acc, fasn, and acly) but not decreased hepatic lipolysis (hsl and cpt1a). When compared with NCD group, HCD significantly elevated the hepatic sterol regulatory element binding proteins 1 (SREBP1) signals (positive hepatocytes and fluorescence intensity) at 4^th, 6^th, and 8^th week (P < 0.05). The hepatic SREBP1 signals increased from 2^nd to 6^th week, but decreased at 8^th week due to substantiated insulin resistance (plasma insulin levels, plasma glucose levels, and P-AKT^Ser473 levels) in HCD group. Importantly, the hepatic carbohydrate response element binding protein (ChREBP) signals (positive hepatocytes, fluorescence intensity, and expression levels) were all significantly elevated by HCD-induced glucose-6-phosphate (G6P) accumulation at 2^nd, 4^th, 6^th, and 8^th week (P < 0.05). Compared to 2^nd and 4^th week, the hepatic ChREBP signals and G6P contents was significantly increased by HCD at 6^th and 8^th week (P < 0.05). The HCD-induced G6P accumulation was caused by the significantly increased expression of hepatic gck, pklr, and glut2 (P < 0.05) but not 6pfk at 4^th, 6^th, and 8^th week, compared to NCD group. These results suggested that the HCD-induced hepatic lipid deposition was mainly promoted by SREBP1 in earlier stage and by ChREBP in later stage for gibel carp. This study revealed the sequential regulation pathways of the conversion from feed carbohydrate to body lipid in fish.

Phosphorus Overload Promotes Hepatic Lipolysis by Suppressing GSK3β-Dependent Phosphorylation of PPARα at Ser84 and Thr265 in a Freshwater Teleost

Excessive phosphorus (Pi) contributes to eutrophication in an aquatic environment, which threatens human and fish health. However, the mechanisms by which Pi overload influences aquatic animals remain largely unexplored. In the present study, Pi supplementation increased the Pi content, inhibited lipid accumulation and lipogenesis, and stimulated lipolysis in the liver. Pi supplementation increased the phosphorylation of glycogen synthase kinase-3 β (GSK3β) at serine 9 (S9) but inhibited the phosphorylation of GSK3α at tyrosine 279 (Y279), GSK3β at tyrosine 216 (Y216), and peroxisome proliferator-activated receptor α (PPARα) at serine 84 (S84) and threonine 265 (T265). Pi supplementation also upregulated PPARα protein expression and stimulated its transcriptional activity, thereby inducing lipolysis. Pi suppressed GSK3β activity and prevented GSK3β, but not GSK3α, from interacting with PPARα, which in turn alleviated PPARα phosphorylation. GSK3β-induced phosphorylation of PPARα was dependent on GSK3β S9 dephosphorylation rather than Y216 phosphorylation. Mechanistically, underphosphorylation of PPARα mediated Pi-induced lipid degradation through transcriptionally activating adipose triglyceride lipase (atgl) and very long-chain-specific acyl-CoA dehydrogenase (acadvl). Collectively, our findings uncovered a new mechanism by which Pi facilitates lipolysis via the GSK3β-PPARα pathway and highlighted the importance of S84 and T265 phosphorylation in PPARα action.

Metabolic adaptation to high-starch diet in largemouth bass (Micropterus salmoides) was associated with the restoration of metabolic functions via inflammation, bile acid synthesis and energy metabolism

A short-term 2-week (2w) and long-term 8-week (8w) feeding trial was conducted to investigate the effects of low-starch (LS) and high-starch (HS) diets on the growth performance, metabolism and liver health of largemouth bass (Micropterus salmoides). Two isonitrogenous and isolipidic diets containing two levels of starch (LS, 9·06 %; HS, 13·56 %) were fed to largemouth bass. The results indicated that HS diet had no significant effects on specific growth rate during 2w, whereas significantly lowered specific growth rate at 8w. HS diet significantly increased hepatic glycolysis and gluconeogenesis at postprandial 24 h in 2w. The hepatosomatic index, plasma alkaline phosphatase, total bile acid (TBA) levels, and hepatic glycogen, TAG, total cholesterol, TBA, and NEFA contents were significantly increased in the HS group at 2w. Moreover, HS diet up-regulated fatty acid and TAG synthesis-related genes and down-regulated TAG hydrolysis and β-oxidation-related genes. Therefore, the glucolipid metabolism disorders resulted in metabolic liver disease induced by HS diet at 2w. However, the up-regulation of bile acid synthesis, inflammation and energy metabolism-related genes in 2w indicated that largemouth bass was still in a state of 'self-repair' response. Interestingly, all the metabolic parameters were returned to homoeostasis, with up-regulation of intestinal glucose uptake and transport-related genes, even hepatic histopathological analysis showed no obvious abnormality in the HS group in 8w. In conclusion, HS feed induced short-term acute metabolic disorder, but long-term metabolic adaptation to HS diet was related to repairing metabolism disorders via improving inflammatory responses, bile acid synthesis and energy metabolism. These results strongly indicated that the largemouth bass owned certain adaptability to HS diet.

Dietary Choline Mitigates High-Fat Diet-Impaired Chylomicrons Assembly via UPRer Modulated by perk DNA Methylation

High-fat diets (HFD) lead to impairment of chylomicrons (CMs) assembly and adversely influence intestinal lipid homeostasis. However, the mechanisms of HFD impairing CMs assembly have yet to be fully understood. Additionally, although choline, as a lipid-lowering agent, has been widely used and its deficiency has been closely linked to non-alcoholic steatohepatitis (NASH), the contribution of choline by functioning as a methyl donor in alleviating HFD-induced intestinal lipid deposition is unknown. Thus, this study was conducted to determine the mechanism of HFD impairing CMs assembly and also tested the effect of choline acting as a methyl donor in this process. To this end, in this study, four diets (control, HFD, choline and HFD + choline diet) were fed to yellow catfish for 10 weeks in vivo and their intestinal epithelial cells were isolated and incubated for 36 h in fatty acids (FA) with or without choline solution combining si-perk transfection in vitro. The key findings from this study as follows: (1) HFD caused impairment of CMs assembly main by unfolded protein response (UPRer). HFD activated perk and then induced UPRer, which led to endoplasmic reticulum dysfunction and further impaired CMs assembly via protein-protein interactions between Perk and Apob48. (2) Choline inhibited the transcriptional expression level of perk via activating the -211 CpG methylation site, which initiated the subsequent ameliorating effect on HFD-impaired CMs assembly and intestinal lipid dysfunction. These results provide a new insight into direct crosstalk between UPRer and CMs assembly, and also emphasize the critical contribution of choline acting as a methyl donor and shed new light on choline-deficient diet-induced NASH.

Dietary berberine alleviates high carbohydrate diet-induced intestinal damages and improves lipid metabolism in largemouth bass (Micropterus salmoides)

High carbohydrate diet (HCD) causes metabolism disorder and intestinal damages in aquaculture fish. Berberine has been applied to improve obesity, diabetes and NAFLD. However, whether berberine contributes to the alleviation of HCD-induced intestinal damages in aquaculture fish is still unclear. Here we investigated the effects and mechanism of berberine on HCD-induced intestinal damages in largemouth bass (Micropterus salmoides). We found dietary berberine (50 mg/kg) improved the physical indexes (VSI and HSI) without affecting the growth performance and survival rate of largemouth bass. Importantly, the results showed that dietary berberine reduced the HCD-induced tissue damages and repaired the barrier in the intestine of largemouth bass. We observed dietary berberine significantly suppressed HCD-induced intestinal apoptosis rate (from 31.21 to 8.35%) and the activity level of Caspase3/9 (P < 0.05) by alleviating the inflammation (il1β, il8, tgfβ, and IL-6, P < 0.05) and ER stress (atf6, xbp1, perk, eif2α, chopa, chopb, and BIP, P < 0.05) in largemouth bass. Further results showed that dietary berberine declined the HCD-induced excessive lipogenesis (oil red O area, TG content, acaca, fasn, scd, pparγ, and srebp1, P < 0.05) and promoted the lipolysis (hsl, lpl, cpt1a, and cpt2, P < 0.05) via activating adenosine monophosphate-activated protein kinase (AMPK, P < 0.05) and inhibiting sterol regulatory element-binding protein 1 (SREBP1, P < 0.05) in the intestine of largemouth bass. Besides, we also found that dietary berberine significantly promoted the hepatic lipid catabolism (hsl, lpl, cpt1a, and cpt2, P < 0.05) and glycolysis (pk and ira, P < 0.05) to reduce the systematic lipid deposition in largemouth bass fed with HCD. Therefore, we elucidated that 50 mg/kg dietary berberine alleviated HCD-induced intestinal damages and improved AMPK/SREBP1-mediated lipid metabolism in largemouth bass, and evaluated the feasibility for berberine as an aquafeed additive to enhance the intestinal function of aquaculture species.

SGLT1/2 as the potential biomarkers of renal damage under Apoe−/− and chronic stress via the BP neural network model and support vector machine

Background

Chronic stress (CS) could produce negative emotions. The molecular mechanism of SGLT1 and SGLT2 in kidney injury caused by chronic stress combined with atherosclerosis remains unclear.

Methods

In total, 60 C57BL/6J mice were randomly divided into four groups, namely, control (CON, n = 15), control diet + chronic stress (CON+CS, n = 15), high-fat diet + Apoe−/− (HF + Apoe−/−, n = 15), and high-fat diet + Apoe−/− + chronic stress (HF+Apoe−/− + CS, n = 15) groups. The elevated plus maze and open field tests were performed to examine the effect of chronic stress. The expression of SGLT1 and SGLT2 in the kidney was detected. The support vector machine (SVM) and back propagation (BP) neural network model were constructed to explore the predictive value of the expression of SGLT1/2 on the renal pathological changes. The receiver operating characteristic (ROC) curve analysis was used.

Results

A chronic stress model and atherosclerosis model were constructed successfully. Edema, broken reticular fiber, and increased glycogen in the kidney would be obvious in the HF + Apoe−/− + CS group. Compared with the CON group, the expression of SGLT1/2 in the kidney was upregulated in the HF + Apoe−/− + CS group (P &lt; 0.05). There existed positive correlations among edema, glycogen, reticular fiber, expression of SGLT1/2 in the kidney. There were higher sensitivity and specificity of diagnosis of SGLT1/2 for edema, reticular fiber, and glycogen in the kidney. The result of the SVM and BP neural network model showed better predictive values of SGLT1 and SGLT2 for edema and glycogen in the kidney.

Conclusion

In conclusion, SGLT1/2 might be potential biomarkers of renal damage under Apoe−/− and chronic stress, which provided a potential research direction for future related explorations into this mechanism.

Sirt3-Sod2-mROS-Mediated Manganese Triggered Hepatic Mitochondrial Dysfunction and Lipotoxicity in a Freshwater Teleost

Exposure to excessive manganese (Mn) is toxic to humans and animals. However, the toxic effects and mechanisms of excessive Mn influencing the vertebrates have been highly overlooked. In the present study, dietary Mn overload significantly increased hepatic lipid and Mn contents, decreased superoxide dismutase 2 (Sod2) activity, increased the Sod2 acetylation level, and induced mitochondrial dysfunction; Mn induced mitochondrial dysfunction through Mtf1/sirtuin 3 (Sirt3)-mediated acetylation of Sod2 at the sites K55 and K70. Meanwhile, mitochondrial oxidative stress was involved in Mn-induced lipotoxicity. Mechanistically, Mn-induced lipotoxicity was via oxidative stress-induced Hsf1 nucleus translocation and its DNA binding capacity to the regions of a peroxisome proliferator-activated receptor g (pparg) promoter, which in turn induced the transcription of lipogenic-related target genes. For the first time, our study demonstrated that Mn-induced hepatic lipotoxicity via a mitochondrial oxidative stress-dependent Hsf1/Pparg pathway and Mtf1/sirt3-mediated Sod2 acetylation participated in mitochondrial dysfunction. Considering that lipid metabolism and lipotoxicity are widely used as the biomarkers for environmental assessments of pollutants, our study provided innovative and important insights into Mn toxicological and environmental evaluation in aquatic environments.

Dietary amylose and amylopectin ratio changes starch digestion and intestinal microbiota diversity in goslings

1. Research has confirmed that amylopectin (AP) is more easily digested than amylose (AM) because AP polymers have more intramolecular hydrogen bonds and less surface area. Studying the relationship between the amylose:amylopectin (AM:AP) ratio and intestine digestion in goslings can provide useful information for effective utilisation of starch.2. A total of 288 healthy male Jiangnan White Goslings, aged three days old, were randomly allotted to four groups, which included six pen replicates per treatment with 12 goslings per replicate. Four diets were formulated with maize, long-grained rice and glutinous rice as starch sources, with AM:AP ratios of 0.12, 0.23, 0.34, and 0.45. In vitro starch digestion of the four diets was measured, as well as the effect of AM:AP ratio on growth performance, serum amino-acid concentration and intestinal microbiota diversity of goslings.3. In terms of in vitro starch digestion, the increase in dietary AM:AP ratio resulted in a decrease followed by an increase in both rapidly and slowly digestible starch. The glucose release rate at an AM:AP ratio of 0.34 showed a steady upward trend.4. The in vivo study showed that increasing the AM:AP ratio resulted in a quadratic increase in body weight (BW) and average daily feed intake (ADFI; P<0.05). Goslings fed diets with an AM:AP ratio of 0.34 had lower (P<0.05) histidine and valine serum concentrations compared with the other three starch sources. Higher AM was beneficial to jejunal microbial and diversity. The species colonisation level of the jejunum microbiota samples at an AM:AP ratio of 0.34 was higher than that in the other groups.5. The results indicated that diets with an AM:AP ratio of 0.34 improved the growth performance and intestinal microbiota diversity of goslings. This may have been due to the higher level of resistant starch in amylose, which resulted in a slow release of intestinal glucose that acted as a substrate for the microbial species, thus providing conditions that were more conducive to growth.

Molecular identification and post-prandial regulation of glucose carrier proteins in the hindgut of Pacific hagfish, Eptatretus stoutii

Hagfish are an excellent model species in which to draw inferences on the evolution of transport systems in early-vertebrates owing to their basal position in vertebrate phylogeny. Glucose is a ubiquitous cellular energy source that is transported into cells via two classes of carrier proteins: sodium-glucose linked transporters (Sglt; Slc5a) and glucose transporters (Glut; Slc2a). While previous pharmacological evidence has suggested the presence of both sodium-dependent and -independent transport mechanisms in the hagfish, the molecular identities were heretofore unconfirmed. We have identified and phylogenetically characterized both a Slc5a1-like and Slc2a-like gene in the Pacific hagfish (Eptatretus stoutii); the latter sharing common ancestry with other glucose-transporting isoforms of the Slc2a family. To assess the potential post-prandial regulation of these glucose transporters, we examined the abundance and localization of these transporters with qPCR and immunohistochemistry alongside functional studies using radiolabeled ¹⁴C-_D-glucose. The effects of glucose- or insulin-injection on glucose transport rate and transporter expression were also examined to determine their potential role(s) in the regulation of intestinal glucose carrier proteins. Feeding prompted an increase in glucose uptake across the hindgut at both 0.5 mM (~84%) and 1 mM (~183%) concentrations. Concomitant increases were observed in hindgut Slc5a1 protein expression. These effects were not observed following either of glucose- or insulin-injection, indicating these post-prandial factors are not the driving force for transporter regulation over this timeframe. We conclude that Pacific hagfish utilize evolutionarily-conserved mechanisms of glucose uptake and so represent a useful model to understand early vertebrate evolution of glucose uptake and regulation.

Phospholipase C signal mediated the glucose-induced changes of glucose absorption and lipid accumulation in the intestinal epithelial cells of yellow catfish Pelteobagrus fulvidraco

In present study, we explored the effects and the underlying mechanisms of phospholipase C (PLC) mediating glucose-induced changes in intestinal glucose transport and lipid metabolism by using U-73122 (a PLC inhibitor). We found that glucose incubation activated the PLC signal and U-73122 pre-incubation alleviated the glucose-induced increase in plcb2, plce1 and plcg1 mRNA expression. Meanwhile, U-73122 pre-treatment blunted the glucose-induced increase in sodium/glucose co-transporters 1/2 mRNA and protein expressions. U-73122 pre-treatment alleviated the glucose-induced increase in TAG content, BODIPY 493/503 fluorescence intensity, lipogenic enzymes (glucose 6-phospate dehydrogenase (G6PD), 6-phosphogluconate dehydrogenase (6PGD), malic enzyme and fatty acid synthase (FAS)) activity and the mRNA expressions of lipogenic genes and related transcription factors (6pgd, g6pd, fas, acca, srebp1 and carbohydrate response element-binding protein (chrebp)) in intestinal epithelial cells of yellow catfish. Further research found that U-73122 pre-incubation mitigated the glucose-induced increase in the ChREBP protein expression and the acetylation level of ChREBP in HEK293T cells. Taken together, these data demonstrated that the PLC played a major role in the glucose-induced changes of glucose transport and lipid metabolism and provide a new perspective for revealing the molecular mechanism of glucose-induced changes of intestinal glucose absorption, lipid deposition and metabolism.

Molecular characterization and nutritional regulation of sodium-dependent glucose cotransporter 1 (Sglt1) in blunt snout bream (Megalobrama amblycephala)

Fish has poor utilization capacity for glucose metabolism. The possible reasons are related to the core regulatory elements of glucose metabolism: transport proteins. Studies on the species and functions of Sglt1 in aquatic animals are scarce, therefore further studies are needed. In this study, the full length of blunt snout bream (Megalobrama amblycephala) sglt1 (Masglt1) was 2965 bp including 5′-UTR region of 168 bp and a 3′-UTR region of 820 bp. Masglt1 have a highest sequence homology in Cypriniformes fish. MaSglt1 protein was identified as a transmembrane protein with 14 α-helix structures locating plasma membrane by the methods of predicted tertiary structure and immunohistochemical staining. MaSglt1 protein has a hollow channel forms which could be specifically coupled with two Na⁺ ions to recognize glucose and carry out transmembrane transport. High sglt1 mRNA was found in the intestine and kidney. The mRNA levels of intestinal sglt1 had a positive correlation with dietary starch levels at 3 h after feeding, and the mRNA was significantly higher than that at 24 h, however, the mRNA levels of renal sglt1 presented results opposite to those of intestinal sglt1. The mRNA levels of renal sglt1 had a positive correlation with dietary starch levels at 24 h after feeding, and the expression was significantly higher than that at 3 h. These results confirmed that Masglt11 was mainly found in the intestine and kidney and was located in the cell membrane, playing a role in glucose homeostasis.

Methionine-chelated Zn promotes anabolism by integrating mTOR signal and autophagy pathway in juvenile yellow catfish

BACKGROUND

Amino acid-chelated zinc (Zn) can increase anabolism of animals. However, the underlying mechanisms are unclear. We aimed to examine how autophagy impact anabolism following a diet containing methionine-chelated Zn (ZnMet) compared with inorganic Zn (ZnSO₄).

METHODS

Yellow catfish (weight: 4.02 ± 0.08 g) were fed two diets containing ZnSO₄ or ZnMet for 8 wk. The differences in transcriptional responses and corresponding biological profiles were compared between the livers of fish fed the two Zn sources of diets. Hepatocytes of yellow catfish were incubated for 48 h in medium containing ZnSO₄ (10 μM ZnSO₄) or ZnMet (10 μM ZnMet) after 2 h pretreated with or without pathway inhibitors. Intracellular Zn, TG and protein contents, lipid droplet and autophagic vesicles were detected. Ultrastructural observation, enzymatic activities, qPCR assays, western blot and immunofluorescence analysis were conducted.

RESULTS

ZnMet up-regulated the expression of genes associated with anabolism and autophagy. The differentially expressed genes (DEG) analysis indicated that both mTOR and autophagy pathways were activated. ZnMet-induced activation of autophagy was mTOR-independent. In this process, forkhead box class O was deacetylated and activated, and induced autophagy, which provided substrates for energy generation.

CONCLUSIONS

ZnMet increased anabolism through integrating mTOR signal and autophagy pathway in yellow catfish. The present study unravels a novel mechanism for amino acid-chelated minerals improving anabolism.

Gut bacterial communities in the freshwater snail Planorbella trivolvis and their modification by a non-herbivorous diet

The freshwater pulmonate snail Planorbella trivolvis is a common species in various bodies of water but is not native to China. Planorbella trivolvis usually live on diets with high fiber content, such as water grasses, algae and fallen leaves. These snails can attach to the wall of a water tank or to water grass and can be transported overseas to China through the ornamental fish trade. There are few studies investigating the intestinal microbiota of freshwater snails. In this study, using culture-independent molecular analysis, we assessed for the first time the complexity of bacterial communities in the intestines of reared snails. The intestinal microbiota in the snails fed different diets, that is, herbivorous feed (HV) with high cellulose and non-herbivorous feed (NHV) with low cellulose, were analyzed by Illumina sequencing. The results showed that the NHV-based diet significantly increased the body mass, shell diameter and specific growth rate of the snails after 60 days of rearing (P < 0.05). Histological experiments showed that the fat droplets in the epithelium columnar cells of the intestines of the NHV snails increased, and the cilia on these cells fell off. The sequencing results identified 486 and 195 OTUs in HV and NHV, respectively. Lots of bacteria were not reported previously in snails. The intestinal microbiota diversity index (Shannon, Simpson, Ace and Chao) in the NHV snails was significantly lower than that in the HV snails. The gut microbiota in the HV snails were predominantly Proteobacteria (52.97%) and Bacteroidetes (28.75%), while the gut microbiota in NHV snails were predominantly Proteobacteria (95.23%). At the genus level, Cloacibacterium (24.60%), Pseudomonas (4.47%), OM6ON (6.12%), and Rhodobacter (5.79%) were observed to be abundant in HV snails. However, Aeromonas (85.4%) was determined to be predominant in NHV snails. Functional prediction of the gut microbiome in snails by PICRUSt demonstrated a significant difference between the two groups, and the HV snails exhibited higher lignocellulose enzyme activity than did the NHV snails. This study represents a first step in characterizing the gut microbiota of the freshwater snail. Most of these microbes can process plant biomass and digest cellulose and lignocellulose, and the enzymes of these bacteria may have potential biotechnological applications in a variety of industrial processes.

Effects of dietary carbohydrate sources on lipid metabolism and SUMOylation modification in the liver tissues of yellow catfish

Dysregulation in hepatic lipid synthesis by excess dietary carbohydrate intake is often relevant with the occurrence of fatty liver; therefore, the thorough understanding of the regulation of lipid deposition and metabolism seems crucial to search for potential regulatory targets. In the present study, we examined TAG accumulation, lipid metabolism-related gene expression, the enzyme activities of lipogenesis-related enzymes, the protein levels of transcription factors or genes involving lipogenesis in the livers of yellow catfish fed five dietary carbohydrate sources, such as glucose, maize starch, sucrose, potato starch and dextrin, respectively. Generally speaking, compared with other carbohydrate sources, dietary glucose promoted TAG accumulation, up-regulated lipogenic enzyme activities and gene expressions, and down-regulated mRNA expression of genes involved in lipolysis and small ubiquitin-related modifier (SUMO) modification pathways. Further studies found that sterol regulatory element binding protein 1 (SREBP1), a key transcriptional factor relevant to lipogenic regulation, was modified by SUMO1. Mutational analyses found two important sites for SUMOylation modification (K254R and K264R) in SREBP1. Mutant SREBP lacking lysine 264 up-regulated the transactivation capacity on an SREBP-responsive promoter. Glucose reduced the SUMOylation level of SREBP1 and promoted the protein expression of SREBP1 and its target gene stearoyl-CoA desaturase 1 (SCD1), indicating that SUMOylation of SREBP1 mediated glucose-induced hepatic lipid metabolism. Our study elucidated the molecular mechanism of dietary glucose increasing hepatic lipid deposition and found that the SREBP-dependent transactivation was regulated by SUMO1 modification, which served as a new target for the transcriptional programmes governing lipid metabolism.