FoxO1 in Micropterus salmoides: Molecular characterization and its roles in glucose metabolism by glucose or insulin-glucose loading

Molecular characterization and function of sodium-dependent glucose transporter 1 in postprandial glucose homeostasis in Macrobrachium rosenbergii

Aquatic animals often exhibit glucose intolerance following a glucose load, and understanding the mechanisms of glucose uptake is crucial for elucidating the underlying processes. Sodium-dependent glucose transporter 1 (SGLT1) plays a crucial role in the process of intestinal glucose absorption and transport in vertebrates, but there is limited information about its function in crustaceans. This study identified the SGLT1 gene (named MrSGLT1) from Macrobrachium rosenbergii. The full cDNA sequence is 3764 bp, encoding 903 amino acids. Unlike SGLT1 in most teleost fish, which have 14 transmembrane domains, MrSGLT1 protein has only 12. MrSGLT1 was predominantly expressed in the intestine, with its expression increasing after feeding. This was accompanied by elevated levels of glucose and trehalose in the hemolymph, and increased glycogen levels in the hepatopancreas. Silencing MrSGLT1 in vivo resulted in decreased glucose and trehalose levels in the hemolymph and reduced glycogen levels in the hepatopancreas, although muscle glycogen levels were unaffected. Moreover, knockdown of MrSGLT1 led to increased expression of genes involved in glycogenolysis and decreased expression of genes associated with glycogenesis, inhibiting postprandial glycogen accumulation in the hepatopancreas. Feeding-induced glycolysis was also inhibited following MrSGLT1 silencing, while no significant changes were observed in gluconeogenesis-related genes. These findings highlight the critical role of MrSGLT1 in regulating postprandial glucose homeostasis in crustaceans.

AKT-FoxO1-PCK/ChREBP signaling pathway regulates metabolic liver disease induced by high glucose in largemouth bass

Starch is widely used in aquaculture because of its low price and the advantages for processing expanded feed. Largemouth bass are naturally type 2 diabetic and intolerant to dietary carbohydrates. In this study, we found that the phosphorylation of AKT and FoxO1 were down-regulated in the fish suffering from metabolic liver disease (MLD). High glucose (25 mM) stimulation in hepatocytes significantly reduced AKT and FoxO1 phosphorylation level, while enhancing glycolysis and gluconeogenesis enzyme activities, leading to acute glucose metabolism disorder. However, after treatment of insulin or FoxO1 inhibitor, the related parameters returned to control level. The mRNA levels of ChREBP and lipid synthesis genes were increased after high glucose stimulation, and then decreased after adding FoxO1 inhibitor, accompanied by a reduction of TG content. Furtherly, plasmid transfection, dual-luciferase reporter assay experiments and EMSA proved that AKT positively regulated the phosphorylation of FoxO1 and FoxO1 positively regulated the promoter activities of PCK and ChREBP, and the transcription factor binding sites were found. In summary, these results support a critical role of AKT-FoxO1-PCK/ChREBP signaling pathway in regulating the occurrence of MLD in largemouth bass. Moreover, we identified a novel FoxO1-mediated gene regulation mechanism, revealing a previously unrecognized cross-talk between FoxO1 and ChREBP.

PI3KR1 and AKT1 in largemouth bass (Micropterus salmoides): molecular cloning, characterization, and its involvement in the alleviation of hepatic glycogen deposition caused by insulin inclusion in vitro

In this study, the full-length cDNA sequences of the phosphatidylinositol-3-kinase p85 alpha (PI3KR1) and serine/threonine kinase 1 (AKT1) genes in largemouth bass (Micropterus salmoides) were obtained using the rapid amplification of cDNA ends (RACE) method. Sequence analysis revealed that the cloned sequences of PI3KR1 and AKT1 are 4170 bp and 3672 bp in length, with open reading frames (ORFs) of 1389 bp and 1422 bp encoding 462 and 473 amino acids, respectively. Sequence alignment and evolutionary tree analysis indicated their close relationship to other teleosts, especially those with similar feeding habits. Tissue distribution demonstrated widespread distribution of both genes in various tissues, with the highest abundance in the liver. Further results found that the upregulation of the expression of p-PI3KR1, p-AKT1, p-FoxO1, and GLUT2 proteins by insulin, while suppressing the expression of the total FoxO1 protein, effectively triggers a significant activation of the PI3KR1-AKT1 insulin signaling pathway. Meanwhile, the mRNA levels of the key glycolytic genes, including glucokinase (gk), pyruvate kinase (pk), and phosphofructokinase liver type (pfkl), have been enhanced evidently. In contrast, the expression of gluconeogenic genes such as phosphoenolpyruvate carboxykinase (pepck), glucose-6-phosphatase catalytic subunit (g6pc), and fructose-1,6-bisphosphatase-1 (fbp1) has been notably down-regulated. In addition, insulin treatment promoted the phosphorylation of glycogen phosphorylase (PYGL) and the dephosphorylation of glycogen synthase (GS), and the glycogen content in the insulin-treated group was remarkably reduced compared to the control group. Overall, our study indicates that the activation of PI3KR1-AKT1 insulin signaling pathway represses the hepatic glycogen deposition via the regulation of glycolysis and gluconeogenesis, which provides some new insights into nutritional strategy to effectively regulate the glucose metabolism in carnivorous fish.

Astaxanthin attenuates glucose-induced liver injury in largemouth bass: role of p38MAPK and PI3K/Akt signaling pathways

BACKGROUND

Astaxanthin (ASX) has been documented to exert beneficial influence on various processes in fish. Largemouth bass (Micropterus salmoides) serves as a common model for studying glucose-induced liver disease, making it imperative to investigate the regulatory mechanisms underlying its liver health.

METHODS

Largemouth bass were fed with a control diet (CON), a high carbohydrate diet (HC), or a HC diet supplemented astaxanthin (HCA) for 8-weeks, followed by the glucose tolerance test (GTT). Primary hepatocytes were treated with low glucose and high glucose combined with different concentrations of astaxanthin for 48 h. The histopathology, enzymology, transcriptomics, molecular biology and cell biology were combined to investigate the mechanism of liver injury.

RESULTS

This study provides evidence for the protective effects of ASX against growth performance reduction and hepatic liver injure in largemouth bass fed HC diet. In GTT, HCA diet exhibited an improvement in glucose tolerance following glucose loading. Although HCA diet did not restore the expression of insulin resistance-related genes in livers at different time during the GTT, the addition of ASX in the long-term HC diet did improve the insulin resistance pathway by regulating the PTP1B/PI3K/Akt signaling pathway. Hepatic transcriptome analyses showed that ASX plays an essential role in the modulation of glucose homeostasis in response to treated with HC diet. In in vitro study, ASX treatment resulted in an exaltation in cell viability and a reduction in the rate of cell apoptosis and reactive oxygen species (ROS). Additionally, astaxanthin was observed to improve apoptosis induced by high-glucose via p38MAPK/bcl-2/caspase-3 signaling pathway.

CONCLUSIONS

Astaxanthin exhibited a protective effect against apoptosis by regulating p38MAPK/bcl-2/caspase-3 pathway, and ameliorated insulin resistance by activating the PTP1B/PI3K/Akt pathway. This study elucidated the mechanism of astaxanthin in the liver injury of largemouth bass from a new perspective and provided a new target for the treatment of insulin resistance.

Advancing insights into microgravity induced muscle changes using Caenorhabditis elegans as a model organism

Spaceflight presents significant challenges to the physiological state of living organisms. This can be due to the microgravity environment experienced during long-term space missions, resulting in alterations in muscle structure and function, such as atrophy. However, a comprehensive understanding of the adaptive mechanisms of biological systems is required to devise potential solutions and therapeutic approaches for adapting to spaceflight conditions. This review examines the current understanding of the challenges posed by spaceflight on physiological changes, alterations in metabolism, dysregulation of pathways and the suitability and advantages of using the model organism Caenorhabditis elegans nematodes to study the effects of spaceflight. Research has shown that changes in the gene and protein composition of nematodes significantly occur across various larval stages and rearing environments, including both microgravity and Earth gravity settings, often mirroring changes observed in astronauts. Additionally, the review explores significant insights into the fundamental metabolic changes associated with muscle atrophy and growth, which could lead to the development of diagnostic biomarkers and innovative techniques to prevent and counteract muscle atrophy. These insights not only advance our understanding of microgravity-induced muscle atrophy but also lay the groundwork for the development of targeted interventions to mitigate its effects in the future.

Dietary inclusion of Clostridium butyricum cultures alleviated impacts of high-carbohydrate diets in largemouth bass (Micropterus salmoides)

A 60-d feeding trial was conducted to explore the potential regulatory effects of dietary Clostridium butyricum cultures (CBC) supplementation in high-carbohydrate diet (HCD) on carbohydrate utilisation, antioxidant capacity and intestinal microbiota of largemouth bass. Triplicate groups of largemouth bass (average weight 35·03 ± 0·04 g), with a destiny of twenty-eight individuals per tank, were fed low-carbohydrate diet and HCD supplemented with different concentration of CBC (0 %, 0·25 %, 0·50 % and 1·00 %). The results showed that dietary CBC inclusion alleviated the hepatic glycogen accumulation induced by HCD intake. Additionally, the expression of hepatic ampkα1 and insulin signaling pathway-related genes (ira, irb, irs, p13kr1 and akt1) increased linearly with dietary CBC inclusion, which might be associated with the activation of glycolysis-related genes (gk, pfkl and pk). Meanwhile, the expression of intestinal SCFA transport-related genes (ffar3 and mct1) was significantly increased with dietary CBC inclusion. In addition, the hepatic antioxidant capacity was improved with dietary CBC supplementation, as evidenced by linear decrease in malondialdehyde concentration and expression of keap1, and linear increase in antioxidant enzyme activities (total antioxidative capacity, total superoxide dismutase and catalase) and expression of antioxidant enzyme-related genes (nrf2, sod1, sod2 and cat). The analysis of bacterial 16S rRNA V3-4 region indicated that dietary CBC inclusion significantly reduced the enrichment of Firmicutes and potential pathogenic bacteria genus Mycoplasma but significantly elevated the relative abundance of Fusobacteria and Cetobacterium. In summary, dietary CBC inclusion improved carbohydrate utilization, antioxidant capacity and intestinal microbiota of largemouth bass fed HCD.

High dietary wheat starch negatively regulated growth performance, glucose and lipid metabolisms, liver and intestinal health of juvenile largemouth bass, Micropterus salmoides

Largemouth bass (Micropterus salmoides) were fed with three diets containing 6%, 12%, and 18% wheat starch for 70 days to examine their impacts on growth performance, glucose and lipid metabolisms, and liver and intestinal health. The results suggested that the 18% starch group inhibited the growth, and improved the hepatic glycogen content compared with the 6% and 12% starch groups (P < 0.05). High starch significantly improved the activities of glycolysis-related enzymes, hexokinase (HK), glucokinase (GK), phosphofructokinase (PFK), and pyruvate kinase (PK) (P < 0.05); promoted the mRNA expression of glycolysis-related phosphofructokinase (pfk); decreased the activities of gluconeogenesis-related enzymes, pyruvate carboxylase (PC), and phosphoenolpyruvate carboxykinase (PEPCK); and reduced the mRNA expression of gluconeogenesis-related fructose-1,6-bisphosphatase-1(fbp1) (P < 0.05). High starch reduced the hepatic mRNA expressions of bile acid metabolism-related cholesterol hydroxylase (cyp7a1) and small heterodimer partner (shp) (P < 0.05), increased the activity of hepatic fatty acid synthase (FAS) (P < 0.05), and reduced the hepatic mRNA expressions of lipid metabolism-related peroxisome proliferator-activated receptor α (ppar-α) and carnitine palmitoyltransferase 1α (cpt-1α) (P < 0.05). High starch promoted inflammation; significantly reduced the mRNA expressions of anti-inflammatory cytokines transforming growth factor-β1 (tgf-β1), interleukin-10 (il-10), and interleukin-11β (il-11β); and increased the mRNA expressions of pro-inflammatory cytokine tumor necrosis factor-α (tnf-α), interleukin-1β (il-1β), and interleukin-8 (il-8) in the liver and intestinal tract (P < 0.05). Additionally, high starch negatively influenced the intestinal microbiota, with the reduced relative abundance of Trichotes and Actinobacteria and the increased relative abundance of Firmicutes and Proteobacteria. In conclusion, low dietary wheat starch level (6%) was more profitable to the growth and health of M. salmoides, while high dietary starch level (12% and 18%) could regulate the glucose and lipid metabolisms, impair the liver and intestinal health, and thus decrease the growth performance of M. salmoides.

Molecular cloning and tissue distribution of glucokinase and glucose-6-phosphatase catalytic subunit paralogs in largemouth bass Micropterus salmoides: Regulation by dietary starch levels and a glucose load

The dysregulation of glucose-G6P (glucose-6-phosphate) interconversion is thought to be one of the main reasons for the low glucose disposal of carnivorous fish, but is not yet well understood in largemouth bass Micropterus salmoides (LMB). In this study, the full length cDNA sequences of genes encoding glucokinase (Gck, catalyzing glucose phosphorylation) and glucose-6-phosphatase catalytic subunit (G6pc, catalyzing glucose dephosphorylation) were cloned by the RACE method from the liver of LMB. Subsequently, the distribution of g6pc and gck as well as their transcriptional regulation by dietary starch levels and a glucose load were investigated. Only one gck gene was identified, while the tandem duplication of g6pca.1 gene was named as g6pca.2 in LMB. The full cDNA sequences of g6pca.1, g6pca.2 and gck in LMB were 1585, 1813 and 2115 bp in length, encoding 478, 352 and 359 amino acids, respectively. Gck was predicted to contain two hexokinase domains, an ATP-binding domain and multiple functional sites, while G6pca.1 and G6pca.2 contained nine transmembrane helices, a PAP2 (type-2 phosphatidic acid phosphatase) domain and multiple functional amino acid sites. Both g6pca.1 and g6pca.2 were predominantly distributed in the liver and to some extent in the intraperitoneal fat, intestine and pyloric caeca, while gck was mainly transcribed in the liver and to some extent in the heart, intestine and brain. Both feeding a high starch diet and a glucose load stimulated the mRNA expression of gck in the liver of LMB. An increase of dietary starch from 9% to 14% down-regulated the transcription of g6pca.1 in the liver of LMB. However, both the mRNA levels of hepatic g6pca.1 and g6pca.2 were sharply up-regulated in LMB during 1-3 h after a glucose load. Overall, the results of this study suggested that the functions of G6pc (G6pca.1 and G6pca.2) and Gck in LMB were highly conserved in evolution. Though hepatic glucose-G6P interconversion was well regulated at the transcript level in LMB fed high starch diets, a futile cycle between glucose and G6P was induced in the liver after a glucose load.

Gut bacterium promotes host fitness in special ecological niche by affecting sugar metabolism in Drosophila suzukii

As an important fruit pest of global significance, Drosophila suzukii occupies a special ecological niche, with the characteristics of high sugar and low protein contents. This niche differs from those occupied by other fruit-damaging Drosophila species. Gut bacteria substantially impact the physiology and ecology of insects. However, the contribution of gut microbes to the fitness of D. suzukii in their special ecological niche remains unclear. In this study, the effect of Klebsiella oxytoca on the development of D. suzukii was examined at physiological and molecular levels. The results showed that, after the removal of gut microbiota, the survival rate and longevity of axenic D. suzukii decreased significantly. Reintroduction of K. oxytoca to the midgut of D. suzukii advanced the development level of D. suzukii. The differentially expressed genes and metabolites between axenic and K. oxytoca-reintroduced D. suzukii were enriched in the pathways of carbohydrate metabolism. This advancement was achieved through an increased glycolysis rate and the regulation of the transcript level of key genes in the glycolysis/gluconeogenesis pathway. Klebsiella oxytoca is likely to play an important role in increasing host fitness in their high-sugar ecological niche by stimulating the glycolysis/gluconeogenesis pathway. As a protein source, bacteria can also provide direct nutrition for D. suzukii, which depends on the quantity or biomass of K. oxytoca. This result may provide a new target for controlling D. suzukii by inhibiting sugar metabolism through eliminating the effect of K. oxytoca and thus disrupting the balance of gut microbial communities.

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.

Sodium oxamate reduces lactate production to improve the glucose homeostasis of Micropterus salmoides fed high-carbohydrate diets

The study was performed to evaluate the effects of the reduced lactate production by sodium oxamate (SO) on growth performance, lactate and glucose and lipid metabolism, and glucose tolerance of Micropterus salmoides fed high-carbohydrate (CHO) diets. In in vitro study, primary hepatocytes were incubated for 48 h in a control medium (5.5 mM glucose), a high-glucose medium (25 mM glucose, HG), or a SO-containing high-glucose medium (25 mM glucose + 50 mM SO, HG-SO). Results indicated lactate and triglyceride (TG) levels, and lactate dehydrogenase a (LDH-a) expression in the HG-SO group were remarkably lower than those of the HG group. In in vivo study, M. salmoides (5.23 ± 0.03 g) were fed four diets containing a control diet (10% CHO, C) and three SO contents [0 (HC), 100 (HC-SO1), and 200 (HC-SO2) mg·kg^-1, respectively] of high-CHO diets (20% CHO) for 11 wk. High-CHO diets significantly reduced weight gain rate (WGR), specific growth rate (SGR), p-AMPK-to-t-AMPK ratio, and expression of insulin receptor substrate 1 (IRS1), insulin-like growth factor I (IGF-I), insulin-like growth factor I receptor (IGF-IR), fructose-1,6-biphosphatase (FBPase), peroxisome proliferator-activated receptor α (PPARα), and carnitine palmitoyl transferase 1α (CPT1α) compared with the C group, whereas the opposite was true for plasma levels of glucose, TG, lactate, tissue glycogen, and lipid contents, and expression of LDH-a, monocarboxylate transporter 1 and 4 (MCT1 and MCT4), insulin, glucokinase (GK), pyruvate dehydrogenase E1 subunit (PDH), sterol-regulatory element-binding protein 1 (SREBP1), fatty acid synthase (FAS). The HC-SO2 diets remarkably increased WGR, SGR, p-AMPK-to-t-AMPK ratio, and expression of IRS1, IGF-I, IGF-IR, GK, PDHα, PDHβ, FAS, acetyl-CoA carboxylase 1 (ACC1), PPARα, and CPT1α compared with the HC group. Besides, HC-SO2 diets also enhanced glucose tolerance of fish after a glucose loading. Overall, the reduced lactate production by SO benefits growth performance and glucose homeostasis of high-CHO-fed M. salmoides through the enhancement of glycolysis, lipogenesis, and fatty acid β-oxidation coupled with the suppression of glycogenesis and gluconeogenesis.

Proteomic analysis of hepatic fibrosis induced by a high starch diet in largemouth bass (Micropterus salmoides)

Largemouth bass is sensitive to the dietary starch level and excess starch can induce metabolic liver diseases (MLD). Hepatic fibrosis is a typical pathological phenotype of MLD in largemouth bass, but the molecular basis underlying is largely unclear. This study fed fish with a low or high starch diet for 4 weeks. Liver tissues with or without fibrotic symptoms were recognized through histopathological and molecular markers analysis of hepatic fibrosis, following TMT Quantitative proteomics and conducted Parallel Reaction Monitoring (PRM) analyses. 2455 differentially expressed proteins with 1618 up-regulated and 837 down-regulated were identified in this study. In GO terms, up-regulated proteins were correlated with cytoskeleton organization, supramolecular fiber, cytoskeleton protein binding, and actin-binding, while down-regulated proteins were involved in mainly metabolism-related processes, and molecular binding activity. Down-regulated proteins were enriched in 63 KEGG pathways and concentrated in metabolism-related pathways, especially glucose, lipid, and amino acid metabolism. 70 KEGG pathways of up-regulated proteins mainly included immunity and inflammation-related pathways. The expression trends of 11 differentially expressed proteins were consistent with proteome results by PRM analysis. In conclusion, the development of hepatic fibrosis induced by high starch may be related to multi-signaling pathways, metabolism processes, and targets, which provides important data for further study on revealing the molecular mechanism of hepatic fibrosis.

Effects of Dietary Phospholipids on Growth Performance, Digestive Enzymes Activity and Intestinal Health of Largemouth Bass (Micropterus salmoides) Larvae

While the beneficial roles of dietary phospholipids on health status and overall performances of fish larvae have been well demonstrated, the underlying mechanisms remain unclear. To address this gap, the present study was conducted to investigate the effects of dietary phospholipids on growth performance, intestinal development, immune response and microbiota of larval largemouth bass (Micropterus salmoides). Five isonitrogenous and isolipidic micro-diets were formulated to contain graded inclusion levels of phospholipids (1.69, 3.11, 5.23, 7.43 and 9.29%). Results showed that the supplementation of dietary phospholipids linearly improved the growth performance of largemouth bass larvae. The inclusion of dietary phospholipids increased the activity of digestive enzymes, such as lipase, trypsin and alkaline phosphatase, and promoted the expression of tight junction proteins including ZO-1, claudin-4 and claudin-5. Additionally, dietary phospholipids inclusion alleviated the accumulation of intestinal triacylglycerols, and further elevated the activity of lysozyme. Dietary phospholipids inhibited the transcription of some pro-inflammatory cytokines, including il-1β, and tnf-α, but promoted the expression of anti-inflammatory cytokines tgf-β, with these modifications being suggested to be mediated by the p38MAPK/Nf-κB pathway. The analysis of bacterial 16S rRNA V3-4 region indicated that the intestinal microbiota profile was significantly altered at the genus level with dietary phospholipids inclusion, including a decreased richness of pathogenic bacteria genera Klebsiella in larval intestine. In summary, it was showed that largemouth bass larvae have a specific requirement for dietary phospholipids, and this study provided novel insights on how dietary phospholipids supplementation contributes to improving the growth performance, digestive tract development and intestinal health.