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

Decoding the fish genome opens a new era in important trait research and molecular breeding in China

Aquaculture represents the fastest-growing global food production sector, as it has become an essential component of the global food supply. China has the world's largest aquaculture industry in terms of production volume. However, the sustainable development of fish culture is hindered by several concerns, including germplasm degradation and disease outbreaks. The practice of genomic breeding, which relies heavily on genome information and genotypephenotype relationships, has significant potential for increasing the efficiency of aquaculture production. In 2014, the completion of the genome sequencing and annotation of the Chinese tongue sole signified the beginning of the fish genomics era in China. Since then, domestic researchers have made dramatic progress in functional genomic studies. To date, the genomes of more than 60 species of fish in China have been assembled and annotated. Based on these reference genomes, evolutionary, comparative, and functional genomic studies have revolutionized our understanding of a wide range of biologically and economically important traits of fishes, including growth and development, sex determination, disease resistance, metamorphosis, and pigmentation. Furthermore, genomic tools and breeding techniques such as SNP arrays, genomic selection, and genome editing have greatly accelerated genetic improvement through the incorporation of functional genomic information into breeding activities. This review aims to summarize the current status, advances, and perspectives of the genome resources, genomic study of important traits, and genomic breeding techniques of fish in China. The review will provide aquaculture researchers, fish breeders, and farmers with updated information concerning fish genomic research and breeding technology. The summary will help to promote the genetic improvement of production traits and thus will support the sustainable development of fish aquaculture.

Hepatocyte vitamin D receptor functions as a nutrient sensor that regulates energy storage and tissue growth in zebrafish

Vitamin D receptor (VDR) has been implicated in fatty liver pathogenesis, but its role in the regulation of organismal energy usage remains unclear. Here, we illuminate the evolutionary function of VDR by demonstrating that zebrafish Vdr coordinates hepatic and organismal energy homeostasis through antagonistic regulation of nutrient storage and tissue growth. Hepatocyte-specific Vdr impairment increases hepatic lipid storage, partially through acsl4a induction, while simultaneously diminishing fatty acid oxidation and liver growth. Importantly, Vdr impairment exacerbates the starvation-induced hepatic storage of systemic fatty acids, indicating that loss of Vdr signaling elicits hepatocellular energy deficiency. Strikingly, hepatocyte Vdr impairment diminishes diet-induced systemic growth while increasing hepatic and visceral fat in adult fish, revealing that hepatic Vdr signaling is required for complete adaptation to food availability. These data establish hepatocyte Vdr as a regulator of organismal energy expenditure and define an evolutionary function for VDR as a transcriptional effector of environmental nutrient supply.

Association between maternal lipid profiles and vitamin D status in second trimester and risk of LGA or SGA: a retrospective study

Background

Accumulating evidence has linked dyslipidemia during pregnancy to the risk of delivering infants born either large for gestational age (LGA) or small for gestational age (SGA). However, the effects of the vitamin D status on these relationships require further investigation. This study investigated whether the relationship between lipid profiles and the risk of LGA or SGA was influenced by vitamin D levels during the second trimester.

Methods

Maternal lipid profile levels, including total cholesterol (TC), triglyceride (TG), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), and vitamin D levels, were measured in a cohort of 6,499 pregnant women during the second trimester. Multivariate regression models and subgroup analyses were employed to evaluate the potential associations between maternal lipid profiles, vitamin D levels, and the risk of LGA or SGA.

Results

The prevalence of SGA infants was 9.8% (n=635), whereas that of LGA infants was 6.9% (n=447). Maternal TG levels were found to be positively associated with the risk of LGA (odds ratio [OR] = 1.41, 95% confidence interval [CI]:1.17-1.70), whereas a negative association was observed between maternal TG, TC, LDL-C levels, and risk of SGA. Additionally, mothers with higher HDL-C levels were less likely to give birth to an LGA infant (OR=0.58, 95% CI:0.39-0.85). Importantly, associations between TG, TC, LDL-c, and SGA as well as between TG and LGA were primarily observed among pregnant women with insufficient vitamin D levels. As for HDL-C, the risk of LGA was lower in mothers with sufficient vitamin D (OR = 0.42, 95% CI:0.18-0.98) compared to those with insufficient vitamin D (OR = 0.65, 95% CI:0.42-0.99).

Conclusion

Vitamin D status during the second trimester exerts a modifying effect on the association between lipid profiles and the risk of LGA and SGA infants.

Sex-dependent regulation of vertebrate somatic growth and aging by germ cells

The function of germ cells in somatic growth and aging has been demonstrated in invertebrate models but remains unclear in vertebrates. We demonstrated sex-dependent somatic regulation by germ cells in the short-lived vertebrate model Nothobranchius furzeri. In females, germ cell removal shortened life span, decreased estrogen, and increased insulin-like growth factor 1 (IGF-1) signaling. In contrast, germ cell removal in males improved their health with increased vitamin D signaling. Body size increased in both sexes but was caused by different signaling pathways, i.e., IGF-1 and vitamin D in females and males, respectively. Thus, vertebrate germ cells regulate somatic growth and aging through different pathways of the endocrine system, depending on the sex, which may underlie the sexual difference in reproductive strategies.

Vitamin D3 Regulates Energy Homeostasis under Short-Term Fasting Condition in Zebrafish (Danio Rerio)

Vitamin D3 (VD3) is a steroid hormone that plays pivotal roles in pathophysiology, and 1,25(OH)2D3 is the most active form of VD3. In the current study, the crucial role of VD3 in maintaining energy homeostasis under short-term fasting conditions was investigated. Our results confirmed that glucose-depriving pathways were inhibited while glucose-producing pathways were strengthened in zebrafish after fasting for 24 or 48 h. Moreover, VD3 anabolism in zebrafish was significantly suppressed in a time-dependent manner under short-fasting conditions. After fasting for 24 or 48 h, zebrafish fed with VD3 displayed a higher gluconeogenesis level and lower glycolysis level in the liver, and the serum glucose was maintained at higher levels, compared to those fed without VD3. Additionally, VD3 augmented the expression of fatty acids (FAs) transporter cd36 and lipogenesis in the liver, while enhancing lipolysis in the dorsal muscle. Similar results were obtained in cyp2r1-/- zebrafish, in which VD3 metabolism is obstructed. Importantly, it was observed that VD3 induced the production of gut GLP-1, which is considered to possess a potent gluconeogenic function in zebrafish. Meanwhile, the gene expression of proprotein convertase subtilisin/kexin type 1 (pcsk1), a GLP-1 processing enzyme, was also induced in the intestine of short-term fasted zebrafish. Notably, gut microbiota and its metabolite acetate were involved in VD3-regulated pcsk1 expression and GLP-1 production under short-term fasting conditions. In summary, our study demonstrated that VD3 regulated GLP-1 production in zebrafish by influencing gut microbiota and its metabolite, contributing to energy homeostasis and ameliorating hypoglycemia under short-term fasting conditions.

Vitamin D promotes the folate transport and metabolism in zebrafish (Danio rerio)

Vitamin D (VD) is a fat-soluble sterol that possesses a wide range of physiological functions. The present study aimed to evaluate the effects of VD on folate metabolism in zebrafish and further investigated the underlying mechanism. Wild-type (WT) zebrafish were fed with a diet containing 0 IU/kg VD3 or 800 IU/kg VD3 for 3 wk. Meanwhile, cyp2r1 mutant zebrafish with impaired VD metabolism was used as another model of VD deficiency. Our results showed that VD deficiency in zebrafish suppressed the gene expression of folate transporters, including reduced folate carrier (RFC) and proton-coupled folate transporter (PCFT) in the intestine. Moreover, VD influenced the gene expression of several enzymes related to cellular folate metabolism in the intestine and liver of zebrafish. Importantly, VD-deficient zebrafish contained a remarkably lower level of folate content in the liver. Notably, VD was incapable of altering folate metabolism in zebrafish when gut microbiota was depleted by antibiotic treatment. Further studies proved that gut commensals from VD-deficient fish displayed a lower capacity to produce folate than those from WT fish. Our study revealed the potential correlation between VD and folate metabolism in zebrafish, and gut microbiota played a key role in VD-regulated folate metabolism in zebrafish.NEW & NOTEWORTHY Our study has identified that VD influences intestinal uptake and transport of folate in zebrafish while also altering hepatic folate metabolism and storage. Interestingly, the regulatory effects of VD on folate transport and metabolism diminished after the gut flora was interrupted by antibiotic treatment, suggesting that the regulatory effects of VD on folate metabolism in zebrafish are most likely dependent on the intestinal flora.

The interaction between lipid and vitamin D3 impacts lipid metabolism and innate immunity in Chinese mitten crabs Eriocheir sinensis

As a fat-soluble vitamin, vitamin D3 relies on fat to perform its biological function, affecting lipid metabolism and innate immunity. This study used different percentages of lipid and vitamin D3 diets to evaluate the synergistic effects on the growth, lipid metabolism and immunity of juvenile Eriocheir sinensis (5.83 ± 0.01 g) for 56 days, including low lipid (LL, 1.5%) and normal lipid (NL, 7.5%) and three levels of vitamin D3: low (LVD, 0 IU/kg), medium (MVD, 9000 IU/kg) and high (HVD, 27,000, IU/kg). The synergistic effect of lipid and vitamin D3 was not significant on growth but significant on ash content, total protein, hepatopancreas lipid content, hemolymph 1α,25-hydroxy vitamin D3 [1α,25(OH)2D3] content, hepatopancreas lipolysis and synthesis genes. Crabs fed normal lipid (7.5%) and medium vitamin D3 (9000 IU/kg) had the highest hepatopancreas index, hemolymph 1α,25(OH)2D3 content, antibacterial ability, immune-related genes and hepatopancreatic lipid synthesis genes expression, but down-regulated the lipolysis genes expression. In contrast, crabs fed diets with low lipid percentage (1.5%) had low growth performance, hemolymph 1α,25(OH)2D3, mRNA levels of lipid synthesis genes, antibacterial ability and immune-related gene expression. At the 1.5% lipid level, excessive or insufficient vitamin D3 supplementation led to the obstruction of ash and protein deposition, reduced growth and molting, aggravated the reduction in antioxidant capacity, hindered antimicrobial peptide gene expression and reduced innate immunity, and resulted in abnormal lipid accumulation and the risk of oxidative stress. This study suggests that diets' lipid and vitamin D3 percentage can enhance antioxidant capacity, lipid metabolism and innate immunity in E. sinensis. A low lipid diet can cause growth retardation, reduce antioxidant capacity and innate immunity, and enhance lipid metabolism disorder.

Vitamin D3 promotes fish oocyte development by directly regulating gonadal steroid hormone synthesis†

Vitamin D receptors and vitamin D3-metabolizing enzymes have been found to be highly expressed in the ovaries and spermatophores of fish. However, the role of vitamin D3 on fish gonadal development has rarely been reported. In this study, 2-month-old female zebrafish were fed with different concentrations of vitamin D3 diets (0, 700, 1400, and 11 200 IU/kg) to investigate the effects of vitamin D3 on ovarian development. The diet with 0 IU/kg vitamin D3 resulted in elevated interstitial spaces, follicular atresia, and reproductive toxicity in zebrafish ovaries. Supplementation with 700 and 1400 IU/kg of vitamin D3 significantly increased the oocyte maturation rate; upregulated ovarian gonadal steroid hormone synthesis capacity; and elevated plasma estradiol, testosterone, and ovarian vitellogenin levels. Furthermore, the current study identified a vitamin D response element in the cyp19a1a promoter and demonstrated that 1.25(OH)2D3-vitamin D response directly activated cyp19a1a production through activating the vitamin D response element. In conclusion, this study shows that an appropriate concentration of vitamin D3 can promote zebrafish ovarian development and affect vitellogenin synthesis through the vdr/cyp19a1a/er/vtg gene axis.

Vitamin D regulates glucose metabolism in zebrafish (Danio rerio) by maintaining intestinal homeostasis

Vitamin D (VD) is a steroid hormone that is widely known to play an important role in maintaining mineral homeostasis, and regulating various physiological functions. Our previous results demonstrated that the interruption of VD metabolism caused hyperglycemia in zebrafish. In the present study we further explored the mechanism that VD regulates glucose metabolism by maintaining intestinal homeostasis in zebrafish. Our results showed that the expression of several peptide hormones including gastric inhibitory peptide, peptide YY, and fibroblast growth factor 19 in the intestine decreased, while the expression of sodium glucose cotransporter-1 and gcg was increased in the intestine of the zebrafish fed with the VD3-deficient diet. Consistently, similar results were obtained in cyp2r1-/- zebrafish, in which endogenous VD metabolism is blocked. Furthermore, the results obtained from germ-free zebrafish exhibited that VD-regulated glucose metabolism was partly dependent on the microbiota in zebrafish. Importantly, the transplantation of gut microbiota collected from cyp2r1-/- zebrafish to germ-free zebrafish led to hyperglycemic symptoms in the fish, which were associated with the altered structure and functions of the microbiota in cyp2r1-/- zebrafish. Interestingly, the treatments with acetate or Cetobacterium somerae, a potent acetate producer, lowered the glucose contents whereas augmented insulin expression in zebrafish larvae. Notably, acetate supplementation alleviated hyperglycemia in cyp2r1-/- zebrafish and other diabetic zebrafish. In conclusion, our study has demonstrated that VD modulates the gut microbiota-SCFAs-gastrointestinal hormone axis, contributing to the maintenance of glucose homeostasis.

Corticotropin-Releasing Hormone: A Novel Stimulator of Somatolactin in Teleost Pituitary Cells

Corticotropin-releasing hormone (CRH) is known for its crucial role in the stress response system, which could induce pituitary adrenocorticotropic hormone (ACTH) secretion to promote glucocorticoid release in the adrenal gland. However, little is known about other pituitary actions of CRH in teleosts. Somatolactin is a fish-specific hormone released from the neurointermediate lobe (NIL) of the posterior pituitary. A previous study has reported that ACTH was also located in the pituitary NIL region. Interestingly, our present study found that CRH could significantly induce two somatolactin isoforms' (SLα and SLβ) secretion and synthesis in primary cultured grass carp pituitary cells. Pharmacological analysis further demonstrated that CRH-induced pituitary somatolactin expression was mediated by the AC/cAMP/PKA, PLC/IP3/PKC, and Ca2+/CaM/CaMK-II pathways. Finally, transcriptomic analysis showed that both SLα and SLβ should play an important role in the regulation of lipid metabolism in primary cultured hepatocytes. These results indicate that CRH is a novel stimulator of somatolactins in teleost pituitary cells, and somatolactins may participate in the stress response by regulating energy metabolism.

Vitamin D modulates disordered lipid metabolism in zebrafish (Danio rerio) liver caused by exposure to polystyrene nanoplastics

In this study, zebrafish (Danio rerio) were exposed to polystyrene nanoplastics (PS-NPs, 80 nm) at 0, 15, or 150 μg/L for 21 days and supplied with a low or high vitamin D (VD) diet (280 or 2800 IU/kg, respectively, indicated by - or +) to determine whether and how VD can regulate lipid metabolism disorder induced by PS-NPs. Six groups were created according to the PS-NP concentration and VD diet status: 0-, 0+, 15-, 15+,150-, and 150 +. Transmission electron microscopy showed that PS-NPs accumulated in the livers of zebrafish, which led to large numbers of vacuoles and lipid droplets in liver cell matrices; this accumulation was most prominent in the 150- group, wherein the number of lipid droplets increased significantly by 136.36%. However, the number of lipid droplets decreased significantly by 76.92% in the 150+ group compared with the 150- group. An examination of additional biochemical indicators showed that the high VD diet partially reversed the increases in the triglyceride and total cholesterol contents induced by PS-NPs (e.g., triglycerides decreased by 58.52% in the 150+ group, and total cholesterol decreased by 44.64% in the 15+ group), and regulated lipid metabolism disorder mainly by inhibiting lipid biosynthesis. Untargeted lipidomics analysis showed that exposure to PS-NPs was associated mainly with changes in the lipid molecular content related to cell membrane function and lipid biosynthesis and that the high VD diet reduced the content of lipid molecules related to lipid biosynthesis, effectively alleviating cell membrane damage and lipid accumulation. These findings highlight the potential of VD to alleviate lipid metabolism disorder caused by PS-NP exposure, thereby providing new insights into how the toxic effects of NPs on aquatic organisms could be reduced.

Implications of vitamin D for flesh quality of grass carp (Ctenopharyngodon idella): antioxidant ability, nutritional value, sensory quality, and myofiber characteristics

BACKGROUND

Muscle represents a unique and complex system with many components and comprises the major edible part of animals. Vitamin D is a critical nutrient for animals and is known to enhance calcium absorption and immune response. In recent years, dietary vitamin D supplementation in livestock has received increased attention due to biological responses including improving shear force in mammalian meat. However, the vitamin D acquisition and myofiber development processes in fish differ from those in mammals, and the effect of vitamin D on fish flesh quality is poorly understood. Here, the influence of dietary vitamin D on fillet quality, antioxidant ability, and myofiber development was examined in grass carp (Ctenopharyngodon idella).

METHODS

A total of 540 healthy grass carp, with an initial average body weight of 257.24 ± 0.63 g, were allotted in 6 experimental groups with 3 replicates each, and respectively fed corresponding diets with 15.2, 364.3, 782.5, 1,167.9, 1,573.8, and 1,980.1 IU/kg vitamin D for 70 d.

RESULTS

Supplementation with 1,167.9 IU/kg vitamin D significantly improved nutritional value and sensory quality of fillets, enhancing crude protein, free amino acid, lipid, and collagen contents; maintaining an ideal pH; and reducing lactate content, shear force, and cooking loss relative to respective values in the control (15.2 IU/kg) group. Average myofiber diameter and the frequency of myofibers > 50 μm in diameter increased under supplementation with 782.5-1,167.9 IU/kg vitamin D. Levels of oxidative damage biomarkers decreased, and the expression of antioxidant enzymes and nuclear factor erythroid 2-related factor 2 signaling molecules was upregulated in the 1,167.9 IU/kg vitamin D treatment compared to respective values in the control group. Furthermore, vitamin D supplementation activated cell differentiation by enhancing the expression of myogenic regulatory factors and myocyte enhancer factors compared to that in the control group. In addition, supplementation with 1,167.9 IU/kg vitamin D improved protein deposition associated with protein synthesis molecule (target of rapamycin) signaling and vitamin D receptor paralogs, along with inhibition of protein degradation (forkhead box protein 1) signaling.

CONCLUSIONS

Overall, the results demonstrated that vitamin D strengthened antioxidant ability and myofiber development, thereby enhancing nutritional value and sensory quality of fish flesh. These findings suggest that dietary vitamin D supplementation is conducive to the production of nutrient-rich, high quality aquaculture products.

Vitamin D Promotes Mucosal Barrier System of Fish Skin Infected with Aeromonas hydrophila through Multiple Modulation of Physical and Immune Protective Capacity

The vertebrate mucosal barrier comprises physical and immune elements, as well as bioactive molecules, that protect organisms from pathogens. Vitamin D is a vital nutrient for animals and is involved in immune responses against invading pathogens. However, the effect of vitamin D on the mucosal barrier system of fish, particularly in the skin, remains unclear. Here, we elucidated the effect of vitamin D supplementation (15.2, 364.3, 782.5, 1167.9, 1573.8, and 1980.1 IU/kg) on the mucosal barrier system in the skin of grass carp (Ctenopharyngodon idella) challenged with Aeromonas hydrophila. Dietary vitamin D supplementation (1) alleviated A. hydrophila-induced skin lesions and inhibited oxidative damage by reducing levels of reactive oxygen species, malondialdehyde, and protein carbonyl; (2) improved the activities and transcription levels of antioxidant-related parameters and nuclear factor erythroid 2-related factor 2 signaling; (3) attenuated cell apoptosis by decreasing the mRNA and protein levels of apoptosis factors involved death receptor and mitochondrial pathway processes related to p38 mitogen-activated protein kinase and c-Jun N-terminal kinase signaling; (4) improved tight junction protein expression by inhibiting myosin light-chain kinase signaling; and (5) enhanced immune barrier function by promoting antibacterial compound and immunoglobulin production, downregulating pro-inflammatory cytokine expression, and upregulating anti-inflammatory cytokines expression, which was correlated with nuclear factor kappa B and the target of rapamycin signaling pathways. Vitamin D intervention for mucosal barrier via multiple signaling correlated with vitamin D receptor a. Overall, these results indicate that vitamin D supplementation enhanced the skin mucosal barrier system against pathogen infection, improving the physical and immune barriers in fish. This finding highlights the viability of vitamin D in supporting sustainable aquaculture.

Attenuated glucose uptake promotes catabolic metabolism through activated AMPK signaling and impaired insulin signaling in zebrafish

Glucose metabolism in fish remains a controversial area of research as many fish species are traditionally considered glucose-intolerant. Although energy homeostasis remodeling has been observed in fish with inhibited fatty acid β-oxidation (FAO), the effects and mechanism of the remodeling caused by blocked glucose uptake remain poorly understood. In this study, we blocked glucose uptake by knocking out glut2 in zebrafish. Intriguingly, the complete lethality, found in Glut2-null mice, was not observed in glut2^-/- zebrafish. Approxiamately 30% of glut2^-/- fish survived to adulthood and could reproduce. The maternal zygotic mutant glut2 (MZglut2) fish exhibited growth retardation, decreased blood and tissue glucose levels, and low locomotion activity. The decreased pancreatic β-cell numbers and insulin expression, as well as liver insulin receptor a (insra), fatty acid synthesis (chrebp, srebf1, fasn, fads2, and scd), triglyceride synthesis (dgat1a), and muscle mechanistic target of rapamycin kinase (mtor) of MZglut2 zebrafish, suggest impaired insulin-dependent anabolic metabolism. Upregulated expression of lipolysis (atgl and lpl) and FAO genes (cpt1aa and cpt1ab) in the liver and proteolysis genes (bckdk, glud1b, and murf1a) in muscle were observed in the MZglut2 zebrafish, as well as elevated levels of P-AMPK proteins in both the liver and muscle, indicating enhanced catabolic metabolism associated with AMPK signaling. In addition, decreased amino acids and elevated carnitines of the MZglut2 zebrafish supported the decreased protein and lipid content of the whole fish. In summary, we found that blocked glucose uptake impaired insulin signaling-mediated anabolism via β-cell loss, while AMPK signaling-mediated catabolism was enhanced. These findings reveal the mechanism of energy homeostasis remodeling caused by blocked glucose uptake, which may be a potential strategy for adapting to low glucose levels.

Beneficial Effect of Vitamin D on Non-Alcoholic Fatty Liver Disease (NAFLD) Progression in the Zebrafish Model

A major cause of chronic liver disease, cirrhosis, and hepatocellular carcinoma, non-alcoholic fatty liver disease (NAFLD) results from excessive liver fat accumulation. Vitamin D (VitD) plays multiple important roles in diverse physiologic processes. Here, we describe the role of VitD in the complex pathogenesis of NAFLD and explore the possible therapeutic role of VitD supplementation in NAFLD therapy. To compare the effect of VitD to other interventions such as low-calorie diet, we induced NAFLD in young adult zebrafish (Danio rerio, AB strain) and monitored the effects of VitD supplementation on the disease course. The zebrafish administered with high-dose VitD (1.25 μg) had significantly reduced liver fat compared to those that received low-dose VitD (0.049 μg) or caloric restriction. Gene expression analysis revealed that VitD downregulated several pathways that may play a role in NAFLD etiology, which affected fatty acid metabolism, vitamins and their cofactors, ethanol oxidation, and glycolysis. The pathway analysis revealed that the cholesterol biosynthesis pathway and the isoprenoid biosynthetic process pathway were significantly upregulated whereas the small molecule catabolic process pathway significantly downregulated following the exposure of NAFLD zebrafish model to high VitD dose. Therefore, our findings suggest the association of novel biochemical pathways with NAFLD and highlight the potential of VitD supplementation to reverse the severity of NAFLD, especially in younger people.

Effects of Nutritionally Induced Obesity on Metabolic Pathways of Zebrafish

Human obesity has become a global epidemic that can lead to many metabolic diseases, including insulin resistance, type 2 diabetes, dyslipidemia, hypertension and nonalcoholic fatty liver. The development of obesity is closely associated with excess food intake and energy imbalance, family history, lifestyle, psychology and other factors, but molecular mechanisms underlying the induction and development of obesity remain to be intensively studied under a variety of internal and external pathogenesis conditions. In this study, we generated two obesity models of zebrafish that were treated with a high-fat diet (HFD) or an overfeeding diet (DIO). Both HFD and DIO zebrafish exhibited higher levels of lipid accumulation, fat distribution, microvascular steatosis and ectopic accumulation of lipid droplets in liver and muscle than normal diet (NOD) fish. The comparison of transcriptome sequencing data for the livers of HFD, DIO and NOD groups identified common and specific genes and signaling pathways that are potentially associated with zebrafish obesity induced by HFD and/or DIO. These findings provide clues for further understanding the mechanisms of obesity development and preventing nutritionally induced obesity through targeting the common signaling pathways and biological processes.

Vitamin D influences gut microbiota and acetate production in zebrafish (Danio rerio) to promote intestinal immunity against invading pathogens

Although evidence has shown that vitamin D (VD) influences gut homeostasis, limited knowledge is available how VD regulates intestinal immunity against bacterial infection. In the present study, cyp2r1 mutant zebrafish, lacking the capacity to metabolize VD, and zebrafish fed a diet devoid of VD, were utilized as VD-deficient animal models. Our results confirmed that the expression of antimicrobial peptides (AMPs) and IL-22 was restrained and the susceptibility to bacterial infection was increased in VD-deficient zebrafish. Furthermore, VD induced AMP expression in zebrafish intestine by activating IL-22 signaling, which was dependent on the microbiota. Further analysis uncovered that the abundance of the acetate-producer Cetobacterium in VD-deficient zebrafish was reduced compared to WT fish. Unexpectedly, VD promoted the growth and acetate production of Cetobacterium somerae under culture in vitro. Importantly, acetate treatment rescued the suppressed expression of β-defensins in VD-deficient zebrafish. Finally, neutrophils contributed to VD-induced AMP expression in zebrafish. In conclusion, our study elucidated that VD modulated gut microbiota composition and production of short-chain fatty acids (SCFAs) in zebrafish intestine, leading to enhanced immunity.

Vitamin D3 enhances the antibacterial ability in head-kidney macrophages of turbot (Scophthalmus maximus L.) through C-type lectin receptors

It has been known that vitamin D₃ (VD₃) not only plays an important role in regulating calcium and phosphorus metabolism in animals, but also has extensive effects on immune functions. In this study, the mechanism how VD₃ influences bactericidal ability in turbot was explored. The transcriptomic analysis identified that dietary VD₃ significantly upregulated the gene expression of C-type lectin receptors (CLRs), including mannose receptors (mrc1, mrc2, pla2r1) and collectins (collectin 11 and collectin 12) in turbot intestine. Further results obtained from in vitro experiments confirmed that the gene expression of mannose receptors and collectins in head-kidney macrophages (HKMs) of turbot was induced after the cells were incubated with different concentrations of VD₃ (0, 1, 10 nM) or 1,25(OH)₂D₃ (0, 10, 100 pM). Meanwhile, both phagocytosis and bactericidal functions of HKMs were significantly improved in VD₃ or 1,25(OH)₂D₃-incubated HKMs. Furthermore, phagocytosis and bacterial killing of HKMs decreased after collectin 11 was knocked down. Moreover, VD₃-enhanced antibacterial activities diminished in collectin 11-interfered cells. Interestingly, the evidence was provided in the present study that inactive VD₃ could be metabolized into active 1,25(OH)₂D₃ via hydroxylases encoded by cyp27a1 and cyp27b1 in fish macrophages. In conclusion, VD₃ could be metabolized to 1,25(OH)₂D₃ in HKMs, which promoted the expression of CLRs in macrophages, leading to enhanced bacterial clearance.

Enhanced insulin activity achieved in VDRa/b ablation zebrafish

INTRODUCTION

1α,25-dihydroxyvitamin D3 (1α,25[OH]₂VD₃) is a hormone known for its key roles in calcium absorption and nutrient metabolism. In teleost fishes, 1α,25(OH)₂VD₃ insufficiency causes impaired glucose metabolism and lipid oxidation. However, the cascade and mechanisms of 1α,25(OH)₂VD₃ and the vitamin d receptor (VDR) signaling are unclear.

RESULTS

In this study, two genes (vdra and vdrb) encoding paralogs of VDRs were genetically knocked out in zebrafish. Growth retardation and accumulated visceral adipose tissue have been observed in vdra ^-/-;vdrb ^-/- deficient line. In the liver elevated accumulation of triglycerides and suppressed lipid oxidation were detected. Morover significantly elevated 1α,25(OH)₂VD₃ levels were detected in vdra^-/-;vdrb^-/- zebrafish due to cyp24a1 transcription repression. Furthermore VDRs ablation Enhanced insulin signaling including elevated insulin/insra trancriptional levels, glycolysis, lipogenesis and promoted AKT/mTOR activity.

DISCUSSION

In conclusion, our present studies provides a zebrafish model with an elevated 1α,25(OH)₂VD₃ levels in vivo. The 1α,25(OH)₂VD₃/VDRs signaling promote lipid oxidation activity. However 1α,25(OH)₂VD₃ activity of regulation of glucose homeostasis through Insulin/Insr was independent of nuclear VDRs in teleosts.

Vitamin D impacts on the intestinal health, immune status and metabolism in turbot (Scophthalmus maximus L.)

Vitamin D (VD) plays a vital role in various physiological processes in addition to its classic functions on maintaining the balance of Ca and P metabolism. However, there still are gaps to understand in depth the issues on the precise requirement, metabolic processes and physiological functions of VD in fish. In this study, we investigated the effects of VD on the growth, intestinal health, host immunity and metabolism in turbot (Scophthalmus maximus L.), one important commercial carnivorous fish in aquaculture, through the supplementation of different doses of dietary VD3 (0, 200, 400, 800 and 1600 μg VD3/kg diet). According to our results, the optimal VD3 level in the feed for turbot growth was estimated to be around 400 IU/kg, whereas VD3 deficiency or overdose in diets induced the intestinal inflammation, lowered the diversity of gut microbiota and impaired the host resistance to bacterial infection in turbot. Moreover, the level of 1α,25(OH)2D3, the active metabolite of VD3, reached a peak value in the turbot serum in the 400 μg group, although the concentrations of Ca and phosphate in the turbot were stable in all groups. Finally, the deficiency of dietary VD3 disturbed the nutritional metabolism in turbot, especially the metabolism of lipids and glucose. In conclusion, this study evaluated the optimal dose of dietary VD3 for turbot and provided the evidence that VD has a significant impact on intestinal health, host immunity and nutritional metabolism in fish, which deepened our understanding on the physiological functions and metabolism of VD3 in fish.

Effects of dietary vitamin D3 supplementation on the growth performance, tissue Ca and P concentrations, antioxidant capacity, immune response and lipid metabolism in Litopenaeus vannamei larvae

An 8-week feeding trial was conducted to investigate the effects of dietary vitamin D3 supplementation on the growth performance, tissue Ca and P concentrations, antioxidant capacity, immune response and lipid metabolism in Litopenaeus vannamei larvae. A total of 720 shrimp (initial weight 0·50 ± 0·01 g) were randomly distributed into six treatments, each of which had three duplicates of forty shrimp per duplicate. Six isonitrogenous and isolipidic diets were formulated to contain graded vitamin D3 (0·18, 0·23, 0·27, 0·48, 0·57 and 0·98 mg/kg of vitamin D3, measured) supplementation levels. The results revealed that L. vannamei fed diet containing 0·48 mg/kg of vitamin D3 achieved the best growth performance. Compared with the control group, supplementing 0·48 mg/kg of vitamin D3 significantly increased (P < 0·05) the activities of catalase, total antioxidative capacity, alkaline phosphatase and acid phosphatase in serum and hepatopancreas. Expression levels of antioxidant and immune-related genes were synchronously increased (P < 0·05). Carapace P and Ca concentrations were increased (P < 0·05) with the increased vitamin D3 supplementation levels. Further analysis of lipid metabolism-related genes expression showed that shrimp fed 0·48 mg of vitamin D3 per kg diet showed the highest value in the expression of lipid synthesis-related genes, while shrimp fed 0·98 mg of vitamin D3 per kg diet showed the highest value in the expression of lipolysis-related genes. In conclusion, the results of present study indicated that dietary supplementation of 0·48 mg/kg of vitamin D3 could increase Ca and P concentrations, improve antioxidant capacity and immune response, and influence lipid metabolism in L. vannamei.

Effects of Dietary Vitamin D Deficiency on Markers of Skeletal Muscle Mitochondrial Biogenesis and Dynamics

We examined the effects of dietary vitamin D deficiency on markers of mitochondrial biogenesis and dynamics in rat soleus muscle. Male Wistar rats were fed a chow with no vitamin D (No-D; 0 IU/kg) or a moderate dose (Mod-D; 2,000 IU/kg) of vitamin D chow for 8 wk. Compared to the Mod-D group, at 8 wk the No-D group showed significantly lower serum 25(OH)D levels. Although vitamin D deficiency had no effect on body composition, the No-D rats showed significantly decreased levels of PGC-1α, a marker of skeletal muscle mitochondrial biogenesis, and DRP1, a marker of skeletal muscle mitochondrial fission. The change in the PGC-1α protein expression and the serum 25(OH)D concentrations were significantly correlated. The change in DRP1 protein expression and the serum 25(OH)D concentrations tended to be correlated. There was no significant between-group difference in markers of mitochondrial fusion (MFN2 and OPA1) and mitophagy (PARKIN) in soleus muscle, and no relationship with serum 25(OH)D concentrations. Collectively our findings suggest that dietary vitamin D deficiency decreased PGC-1α and DRP1 protein expression in rat soleus muscle.

Identification, conservation, and expression of tiered pharmacogenes in zebrafish

The number of adverse drug events in the United States is critically high, with annual rates exceeding 1 million cases over the last nine years. One cause of adverse drug events is the underlying genetic variation that can alter drug responses. Pharmacogenomics is a growing field that seeks to better understand the relationship between a patient’s genetics and drug efficacy. Currently, pharmacogenomics relies largely on human trials, as there is not a well-developed animal model for studying preventative measures and alternative treatments. Here, we analyzed pharmacogene expression at two developmental time points in zebrafish to demonstrate the potential of using this model organism for high-throughput pharmacogenomics research. We found that 76% of tiered human pharmacogenes have a zebrafish ortholog, and of these, many have highly conserved amino acid sequences. Additional gene ontology analysis was used to classify pharmacogenes and identify candidate pathways for future modeling in zebrafish. As precision medicine burgeons, adopting a high-throughput in vivo model such as the zebrafish could greatly increase our understanding of the molecular pathology underlying adverse drug events.

Recent insights into vitamin D, adipocyte, and adipose tissue biology

Several studies bring strong evidence for an active role of vitamin D and its metabolites in physiological adipocyte and adipose tissue processes in adulthood. This role includes effects of vitamin D on key adipose tissue and adipocyte biology parameters, including adipogenesis, energy metabolism, and inflammation. Interestingly, recent data also point to a role of maternal vitamin D deficiency in adipocyte and adipose tissue metabolic programming in offspring. This review summarizes the current state of knowledge on the biological effect of vitamin D on adipocyte/adipose tissue physiology.

Paricalcitol Attenuates Metabolic Syndrome-Associated Heart Failure through Enhanced Mitochondrial Fusion

Objectives

Transition from cardiac hypertrophy to failure involves adverse metabolic reprogramming involving mitochondrial dysfunction. We have earlier shown that vitamin D deficiency induces heart failure, at least in part, through insulin resistance. However, whether activation of vitamin D receptor (VDR) can attenuate heart failure and underlying metabolic phenotype requires investigation. Thus, we aimed to assess the cardioprotective potential of paricalcitol, a vitamin D receptor-activator, against cardiac hypertrophy and failure in high-fat high-fructose-fed rats.

Methods

Male Sprague Dawley rats were fed control (Con) or high-fat high-fructose (HFHFrD) diet for 20 weeks. After 12 weeks, rats from HFHFrD group were divided into the following: HFHFrD, HFHFrD+P (paricalcitol i.p. 0.08 μg/kg/day) and HFHFrD+E (enalapril maleate i.p. 10 mg/kg/day). Intraperitoneal glucose tolerance test, blood pressure measurement, and 2D echocardiography were performed. Cardiac fibrosis was assessed by Masson's trichrome staining of paraffin-embedded heart sections. Mitochondrial DNA and proteins, and citrate synthase activity were measured in rat hearts. VDR was silenced in H9c2 cardiomyoblasts, and immunoblotting was performed.

Results

Paricalcitol improved glucose tolerance, serum lipid profile, and blood pressure in high-fat high-fructose-fed rats. Paricalcitol reduced cardiac wall thickness and increased ejection fraction in high-fat high-fructose-fed rats but had no effect on perivascular fibrosis. PGC1-α was upregulated in the HFHFrD+P group compared to the HFHFrD group, but there was no significant difference in mitochondrial content. Citrate synthase activity was significantly higher in the HFHFrD+P group compared to the HFHFrD group. Rat hearts of the HFHFrD+P group had significantly higher expression of mitofusins. H9c2 cells with VDR knockdown showed significantly lower expression of Mfn2. Improvement in the HFHFrD+P group was comparable with that in the HFHFrD+E group.

Conclusions

Paricalcitol reverses cardiac dysfunction in rats with metabolic syndrome by enhancing mitochondrial fusion. We demonstrate repurposing potential of the drug currently used in end-stage kidney disease.

Vitamin D and Obesity/Adiposity—A Brief Overview of Recent Studies

Observational studies classically find an inverse relationship between human plasma 25-hydroxyvitamin D concentration and obesity. However, interventional and genetic studies have failed to provide clear conclusions on the causal effect of vitamin D on obesity/adiposity. Likewise, vitamin D supplementation in obese rodents has mostly failed to improve obesity parameters, whereas several lines of evidence in rodents and prospective studies in humans point to a preventive effect of vitamin D supplementation on the onset of obesity. Recent studies investigating the impact of maternal vitamin D deficiency in women and in rodent models on adipose tissue biology programming in offspring further support a preventive metabolically driven effect of vitamin D sufficiency. The aim of this review is to summarize the state of the knowledge on the relationship between vitamin D and obesity/adiposity in humans and in rodents and the impact of maternal vitamin D deficiency on the metabolic trajectory of the offspring.

Vitamin D regulates insulin pathway and glucose metabolism in zebrafish (Danio rerio)

1,25-dihydroxyvitamin D₃ [1,25(OH)₂ D₃ ], the most active vitamin D (VD) metabolite, is a steroid hormone playing an important role in many physiological functions in addition to maintaining mineral homeostasis. In this study, we explored the mechanism that the VD regulated insulin pathway and glucose metabolism in zebrafish in vitro and in vivo. Our results show that 1,25(OH)₂ D₃  significantly enhances the expression of insulin receptor a (insra), insulin receptor substrate 1 (irs1) and glucose transporter 2 (glut2), and promotes glycolysis and glycogenesis, while suppressing gluconeogenesis in zebrafish liver cell line (ZFL) under the condition of high glucose (20 mM), instead of the normal glucose (10 mM). Moreover, consistent results were obtained from the zebrafish fed with VD₃ -deficient diet, as well as the cyp2r1^-/- zebrafish, in which endogenous VD metabolism is blocked. Furthermore, results from dual-luciferase reporting system exhibited that 1,25(OH)₂ D₃ directly activated the transcription of insra, rather than insrb in zebrafish by binding to vitamin D response element (VDRE) located at -181 to -167 bp in the promoter region of insra. Importantly, the 1,25(OH)₂ D₃ treatment significantly alleviated the symptoms of hyperglycemia in diabetic zebrafish. In conclusion, our study demonstrated that VD activates VDRE located in the promoter area of insra in zebrafish to promote insulin/insra signaling pathway, thereby contributing to the maintenance of glucose homeostasis.

Fluorene-9-bisphenol exposure decreases locomotor activity and induces lipid-metabolism disorders by impairing fatty acid oxidation in zebrafish

AIMS

Fluorene-9-bisphenol (BHPF), as a substitute for bisphenol A, is used in many industries in daily life. Many studies have clarified its effects as an endocrine disruptor on organisms, but its effect on lipid metabolism of zebrafish larvae is not clear. Patients with non-alcoholic fatty liver disease (NAFLD) are more susceptible to external pollutants. It is not clear how BHPF perturbs lipid metabolism or promotes NAFLD progression.

MAIN METHODS

We explored the biological effects of BHPF on locomotor activity, inflammatory response, endoplasmic reticulum (ER) stress and lipid metabolism in zebrafish, especially in the mechanism of lipid homeostasis disorder. In addition, the role of BHPF in the progression of non-alcoholic fatty liver disease (NAFLD) was further explored.

KEY FINDINGS

We found that high concentration (100 nmol/L) BHPF caused retarded growth, mild lipid accumulation and reduced the locomotive activity of zebrafish larvae, accompanied by a decrease in endogenous cortisol level. At the same time, it caused the full activation of inflammation and ER stress. Rescue experiments by 25(OH)D₃ demonstrated that high concentration of BHPF caused defects in 1,25(OH)₂D₃ metabolic pathway through downregulation of cyp2r1, which further damaged pgc1a-mediated fatty acid oxidation and mitochondrial function, resulting in lipid accumulation. In summary, exposure to BHPF could damage lipid homeostasis and worsen the diet-induced NAFLD.

SIGNIFICANCE

Our findings provide new insights into the role of BHPF in development of overweight and obesity and also improve understanding of its toxicological mechanism. Our results play a warning role in the administration of environmental pollutants.

Andrographolide derivative as antagonist of vitamin D receptor to induce lipidation of microtubule associate protein 1 light chain 3 (LC3)

Lipidation of microtubule associated protein 1 light chain 3 (LC3) is the critical step in autophagosome formation, numerous efforts have been made to design and develop small molecules that trigger LC3 lipidation to activate autophagy. In this study, we discovered a series of andrographolide derivatives as potent antagonists of vitamin D receptor (VDR) by luciferase reporter assay. Structure-activity-relationship study revealed that andrographolide derivative ZAV-12 specifically inhibited VDR signaling but not NF-κB or STAT3 activation. Western blot analysis indicates that ZAV-12 markedly triggered lipidation of LC3 in MPP⁺-induced Parkinsonism in vitro in an mTOR-independent manner. The ZAV-12 triggered lipidation was mediated through SREBP2 activation instead of changing expression levels of lipid synthesis genes. Furthermore, ZAV-12 treatment increased the ratio of LC3-II/LC3-I and oligomerization of A53T α-synuclein (SNCA) in SNCA triggered neurotoxicity. Taken together, these results demonstrate the therapeutic potential of VDR antagonist as novel drug candidate for neurodegenerative diseases.

Impact of Dietary Vitamin D3 Supplementation on Growth, Molting, Antioxidant Capability, and Immunity of Juvenile Chinese Mitten Crabs (Eriocheir sinensis) by Metabolites and Vitamin D Receptor

Vitamin D₃ (vit-D₃), as an indispensable and fat-soluble nutrient, is associated with skeletal mineralization and health in mammals. However, such associations have not been well studied in economically important crustaceans. Six levels of vit-D₃ with isonitrogenous and isolipidic diets were used to feed Eriocheir sinensis. The range of optimal vit-D₃ requirements is 5685.43-10,000 IU/kg based on growth. The crabs fed 9000 IU/kg vit-D₃ showed the best growth performance. This vit-D₃ dose significantly increased antioxidant capacity in the hepatopancreas and intestine and was optimal for molting and innate immunity via quantitative polymerase chain reaction analysis. Transcriptomics analyses indicate that vit-D₃ could alter protein processing in the endoplasmic reticulum, steroid biosynthesis, and antigen processing and presentation. As shown by the enzyme-linked immunosorbent assay, vit-D₃ could improve vitamin D receptor, retinoic acid receptor, and C-type lectins concentrations. The 1α,25-dihydroxy vit-D₃ content in serum was significantly higher in 3000-9000 IU/kg vit-D₃. The study suggests that dietary vit-D₃ and its metabolites can regulate molting and innate immunity in crabs.

Vitamin D deficiency promotes accumulation of bioactive lipids and increased endocannabinoid tone in zebrafish

Vitamin D is well known for its traditional role in bone mineral homeostasis; however, recent evidence suggests that vitamin D also plays a significant role in metabolic control. This study served to investigate putative linkages between vitamin D deficiency (VDD) and metabolic disruption of bioactive lipids by MS imaging. Our approach employed infrared-matrix-assisted laser desorption electrospray ionization MS imaging for lipid metabolite profiling in 6-month-old zebrafish fed either a VDD or a vitamin D-sufficient (VDS) diet. Using a lipidomics pipeline, we found that VDD zebrafish had a greater abundance of bioactive lipids (N-acyls, endocannabinoids [ECs], diacylglycerols/triacylglycerols, bile acids/bile alcohols, and vitamin D derivatives) suggestive of increased EC tone compared with VDS zebrafish. Tandem MS was performed on several differentially expressed metabolites with sufficient ion abundances to aid in structural elucidation and provide additional support for MS annotations. To confirm activation of the EC pathways, we subsequently examined expression of genes involved in EC biosynthesis, metabolism, and receptor signaling in adipose tissue and liver from VDD and VDS zebrafish. Gene expression changes were congruent with increased EC tone, with VDD zebrafish demonstrating increased synthesis and metabolism of anandamide compared with VDS zebrafish. Taken together, our data suggest that VDD may promote accumulation of bioactive lipids and increased EC tone in zebrafish.

Comprehensive analysis of hub mRNA, lncRNA and miRNA, and associated ceRNA networks implicated in grass carp (Ctenopharyngodon idella) growth traits

Grass carp (Ctenopharyngodon idella) is the most productive freshwater aquaculture fish in worldwide. However, the molecular mechanism of its growth traits has not been fully elucidated. Whole transcriptome analysis of the brain and hepatopancreas of 29 six-month-old grass carp with different growth rates was performed. Weighted gene co-expression network analysis (WGCNA) was used to construct a weighted gene co-expression network of mRNA, miRNA and lncRNA separately. A total of 35 hub mRNAs, 47 hub lncRNAs and 33 hub miRNAs were identified from the brain, 37 hub mRNAs, 110 hub lncRNAs and 36 hub miRNAs were identified from the hepatopancreas. The ceRNA networks in the brain and hepatopancreas were involved in brain development and nutrient metabolism, respectively. Overall, this is the first investigation of the growth-related transcriptomic characteristics in the brain and hepatopancreas of grass carp, thus will help us to further explore the molecular mechanism of grass carp growth rate.

Functions of the Thyroid-Stimulating Hormone on Key Developmental Features Revealed in a Series of Zebrafish Dyshormonogenesis Models

The hypothalamic–pituitary–thyroid (HPT) axis regulates many critical features in vertebrates. Utilizing TALENs and CRISPR/Cas9 techniques, thyroid-stimulating hormone subunit beta a (tshba), thyroglobulin (tg), and solute carrier family 16 member 2 (slc16a2) mutant zebrafish lines were generated. Among the three mutants, the earliest time point for the significantly altered T3 contents was observed in tshba mutants, which resulted in the most severe defects, including typical defects such as the retardation of inflated anterior swimming bladder (aSB), proper formation of fin ray and posterior squamation (SP), the larval-to-juvenile transition (LTJT) process, juvenile growth retardation, and mating failure. In tg mutants, which are actually compensated with an alternative splicing form, growth retardation was observed in the juvenile stage without LTJT and reproductive defects. The evident goiter phenotype was only observed in tg- and slc16a2 mutants, but not in tshba mutants. Other than goiters being observed, no other significant developmental defects were found in the slc16a2 mutants. Regarding the reproductive defects observed in tshba mutants, the defective formation of the secondary sex characteristics (SSCs) was observed, while no obvious alterations during gonad development were found. Based on our analyses, zebrafish at the 6–12 mm standard length or 16–35 days post-fertilization (dpf) should be considered to be in their LTJT phase. Using a series of zebrafish dyshormonogenesis models, this study demonstrated that the TSH function is critical for the proper promotion of zebrafish LTJT and SSC formation. In addition, the elevation of TSH levels appears to be essential for goiter appearance in zebrafish.

A network-based approach to identify protein kinases critical for regulating srebf1 in lipid deposition causing obesity

Obesity is a rapidly growing health pandemic, underlying a wide variety of disease conditions leading to increases in global mortality. It is known that the phosphorylation of various proteins regulates sterol regulatory element-binding transcription factors 1 (srebf1), a key lipogenic transcription factor, to cause the development of obesity. To detect the key protein kinases for regulating srebf1 in lipid deposition, we established the srebf1 knockout model in zebrafish (KO, srebf1^-/-) by CRISPR/Cas9. The KO zebrafish exhibited a significant reduction of total free fatty acid content (fell 60.5%) and lipid deposition decrease compared with wild-type (WT) zebrafish. Meanwhile, srebf1 deletion in zebrafish eliminated lipid deposition induced by high-fat diet feeding. Compared with WT zebrafish, a total of 697 differentially expressed proteins and 316 differentially expressed phosphoproteins with 439 sites were identified in KO by differential proteomic and phosphoproteomic analyses. A significant number of proteins identified were involved in lipid and glucose metabolism. Moreover, some protein kinases critical for regulating srebf1 in lipid deposition, including Cdk2, Pkc, Prkceb, mTORC1, Mapk12, and Wnk1, were determined by network analyses. An in vitro study was performed to verify the network analysis results. Our findings provide potential targets (kinases) for human obesity treatments.

Polycyclic aromatic hydrocarbons modulate the activity of Atlantic cod (Gadus morhua) vitamin D receptor paralogs in vitro

Vitamin D receptor (VDR) mediates the biological function of the steroid hormone calcitriol, which is the metabolically active version of vitamin D. Calcitriol is important for a wide array of physiological functions, including calcium and phosphate homeostasis. In contrast to mammals, which harbor one VDR encoding gene, teleosts possess two orthologous vdr genes encoding Vdr alpha (Vdra) and Vdr beta (Vdrb). Genome mining identified the vdra and vdrb paralogs in the Atlantic cod (Gadus morhua) genome, which were further characterized regarding their phylogeny, tissue-specific expression, and transactivational properties induced by calcitriol. In addition, a selected set of polycyclic aromatic hydrocarbons (PAHs), including naphthalene, phenanthrene, fluorene, pyrene, chrysene, benzo[a]pyrene (BaP), and 7-methylbenzo[a]pyrene, were assessed for their ability to modulate the transcriptional activity of gmVdra and gmVdrb in vitro. Both gmVdra and gmVdrb were activated by calcitriol with similar potencies, but gmVdra produced significantly higher maximal fold activation. Notably, none of the tested PAHs showed agonistic properties towards the Atlantic cod Vdrs. However, binary exposures of calcitriol together with phenanthrene, fluorene, or pyrene, antagonized the activation of gmVdra, while chrysene and BaP significantly potentiated the calcitriol-mediated activity of both receptors. Homology modeling, solvent mapping, and docking analyses complemented the experimental data, and revealed a putative secondary binding site in addition to the canonical ligand-binding pocket (LBP). Calcitriol was predicted to interact with both binding sites, whereas PAHs docked primarily to the LBP. Importantly, our in vitro data suggest that PAHs can interact with the paralogous gmVdrs and interfere with their transcriptional activities, and thus potentially modulate the vitamin D signaling pathway and contribute to adverse effects of crude oil and PAH exposures on cardiac development and bone deformities in fish.

Cytochrome P450-dependent biotransformation capacities in embryonic, juvenile and adult stages of zebrafish (Danio rerio)-a state-of-the-art review

Given the strong trend to implement zebrafish (Danio rerio) embryos as translational model not only in ecotoxicological, but also toxicological testing strategies, there is an increasing need for a better understanding of their capacity for xenobiotic biotransformation. With respect to the extrapolation of toxicological data from zebrafish embryos to other life stages or even other organisms, qualitative and quantitative differences in biotransformation pathways, above all in cytochrome P450-dependent (CYP) phase I biotransformation, may lead to over- or underestimation of the hazard and risk certain xenobiotic compounds may pose to later developmental stages or other species. This review provides a comprehensive state-of-the-art overview of the scientific knowledge on the development of the CYP1-4 families and corresponding phase I biotransformation and bioactivation capacities in zebrafish. A total of 68 publications dealing with spatiotemporal CYP mRNA expression patterns, activities towards mammalian CYP-probe substrates, bioactivation and detoxification activities, as well as metabolite profiling were analyzed and included in this review. The main results allow for the following conclusions: (1) Extensive work has been done to document mRNA expression of CYP isoforms from earliest embryonic stages of zebrafish, but juvenile and adult zebrafish have been largely neglected so far. (2) There is insufficient understanding of how sex- and developmental stage-related differences in expression levels of certain CYP isoforms may impact biotransformation and bioactivation capacities in the respective sexes and in different developmental stages of zebrafish. (3) Albeit qualitatively often identical, many studies revealed quantitative differences in metabolic activities of zebrafish embryos and later developmental stages. However, the actual relevance of age-related differences on the outcome of toxicological studies still needs to be clarified. (4) With respect to current remaining gaps, there is still an urgent need for further studies systematically assessing metabolic profiles and capacities of CYP isoforms in zebrafish. Given the increasing importance of Adverse Outcome Pathway (AOP) concepts, an improved understanding of CYP capacities appears essential for the interpretation and outcome of (eco)toxicological studies.

Influences of dietary vitamin D3 on growth, antioxidant capacity, immunity and molting of Chinese mitten crab (Eriocheir sinensis) larvae

This study investigates the effects of vitamin D₃ (VD₃) on growth performance, antioxidant capacity, immunity and molting of larval Chinese mitten crab Eriocheir sinensis. A total of 6,000 larvae (7.52 ± 0.10 mg) were fed with six isonitrogenous and isolipidic experimental diets with different levels of dietary VD₃ (0, 3000, 6000, 9000, 12000 and 36000 IU/kg) respectively for 23 days. The highest survival and molting frequency were found in crabs fed 6000 IU/kg VD₃. Weight gain, specific growth rate, and carapace growth significantly increased in crabs fed 3000 and 6000 IU/kg VD₃ compared to the control. Broken-line analysis of molting frequency, weight gain and specific growth rate against dietary VD₃ levels indicates that the optimal VD₃ requirement for larval crabs is 4825-5918 IU/kg. The highest whole-body VD₃ content occurred in the 12000 IU/kg VD₃ group, and the 25-dihydroxy VD₃ content decreased with the increase of dietary VD₃. The malonaldehyde content was lower than the control. Moreover, the superoxide dismutase activity, glutathione peroxidase and total antioxidant capacity of crab fed 6000 IU/kg VD₃ were significantly higher than in control. Crabs fed 9000 IU/kg showed the highest survival after 120 h of salinity stress, and the relative mRNA expressions indicate vitamin D receptor (VDR) is the important regulatory element in molting and innate immunity. The molting-related gene expressions showed that the response of crab to salinity was self-protective. This study would contribute to a new understanding of the molecular basis underlying molting and innate immunity regulation by vitamin D₃ in E. sinensis.

Non-classical effects of vitamin D: Non-bone effects of vitamin D

Our understanding of vitamin D has improved considerably in recent years. The role of vitamin D in preventing osteoporotic fractures is now well-established. However, an important controversy has emerged in the last decade concerning the effects of the active form of vitamin D (1,25-dihydroxy-vitamin D) on tissues other than bone (non-classical effects). The demonstration that the vitamin D receptor (VDR) is ubiquitously, expressed combined with increasing observational data supporting a relationship between the level of 25-hydroxy-vitamin D in the serum and chronic metabolic disorders, cardiovascular disease and neoplasms, have led to its redefinition as a steroid hormone and the proposal of its use in preventing and/or treating those diseases. This article is an update on the different non-bone or non-classical effects of "vitamin-hormone D", and its potential preventive or therapeutic role in certain diseases, however, this review is not exhaustive. The different modalities of substitution or supplementation proposed in France by the Groupe de Recherche et d'Information sur les Ostéoporoses (GRIO) are also summarised.

Vitamin D deficiency serves as a precursor to stunted growth and central adiposity in zebrafish

Emerging evidence demonstrates the importance of sufficient vitamin D (1α, 25-dihydroxyvitamin D3) levels during early life stage development with deficiencies associated with long-term effects into adulthood. While vitamin D has traditionally been associated with mineral ion homeostasis, accumulating evidence suggests non-calcemic roles for vitamin D including metabolic homeostasis. In this study, we examined the hypothesis that vitamin D deficiency (VDD) during early life stage development precedes metabolic disruption. Three dietary cohorts of zebrafish were placed on engineered diets including a standard laboratory control diet, a vitamin D null diet, and a vitamin D enriched diet. Zebrafish grown on a vitamin D null diet between 2-12 months post fertilization (mpf) exhibited diminished somatic growth and enhanced central adiposity associated with accumulation and enlargement of visceral and subcutaneous adipose depots indicative of both adipocyte hypertrophy and hyperplasia. VDD zebrafish exhibited elevated hepatic triglycerides, attenuated plasma free fatty acids and attenuated lipoprotein lipase activity consistent with hallmarks of dyslipidemia. VDD induced dysregulation of gene networks associated with growth hormone and insulin signaling, including induction of suppressor of cytokine signaling. These findings indicate that early developmental VDD impacts metabolic health by disrupting the balance between somatic growth and adipose accumulation.

Mitochondrial Fatty Acid β-Oxidation Inhibition Promotes Glucose Utilization and Protein Deposition through Energy Homeostasis Remodeling in Fish

BACKGROUND

Fish cannot use carbohydrate efficiently and instead utilize protein for energy supply, thus limiting dietary protein storage. Protein deposition is dependent on protein turnover balance, which correlates tightly with cellular energy homeostasis. Mitochondrial fatty acid β-oxidation (FAO) plays a crucial role in energy metabolism. However, the effect of remodeled energy homeostasis caused by inhibited mitochondrial FAO on protein deposition in fish has not been intensively studied.

OBJECTIVES

This study aimed to identify the regulatory role of mitochondrial FAO in energy homeostasis maintenance and protein deposition by studying lipid, glucose, and protein metabolism in fish.

METHODS

Carnitine-depleted male Nile tilapia (initial weight: 4.29 ± 0.12 g; 3 mo old) were established by feeding them with mildronate diets (1000 mg/kg/d) for 6 wk. Zebrafish deficient in the carnitine palmitoyltransferase 1b gene (cpt1b) were produced by using CRISPR/Cas9 gene-editing technology, and their males (154 ± 3.52 mg; 3 mo old) were used for experiments. Normal Nile tilapia and wildtype zebrafish were used as controls. We assessed nutrient metabolism and energy homeostasis-related biochemical and molecular parameters, and performed 14C-labeled nutrient tracking and transcriptomic analyses.

RESULTS

The mitochondrial FAO decreased by 33.1-88.9% (liver) and 55.6-68.8% (muscle) in carnitine-depleted Nile tilapia and cpt1b-deficient zebrafish compared with their controls (P < 0.05). Notably, glucose oxidation and muscle protein deposition increased by 20.5-24.4% and 6.40-8.54%, respectively, in the 2 fish models compared with their corresponding controls (P < 0.05). Accordingly, the adenosine 5'-monophosphate-activated protein kinase/protein kinase B-mechanistic target of rapamycin (AMPK/AKT-mTOR) signaling was significantly activated in the 2 fish models with inhibited mitochondrial FAO (P < 0.05).

CONCLUSIONS

These data show that inhibited mitochondrial FAO in fish induces energy homeostasis remodeling and enhances glucose utilization and protein deposition. Therefore, fish with inhibited mitochondrial FAO could have high potential to utilize carbohydrate. Our results demonstrate a potentially new approach for increasing protein deposition through energy homeostasis regulation in cultured animals.

Inducibility of cytochrome P450-mediated 7-methoxycoumarin-O-demethylase activity in zebrafish (Danio rerio) embryos

The zebrafish (Danio rerio) embryo has increasingly been used as an alternative model in human and environmental toxicology. Since the cytochrome P450 (CYP) system is of fundamental importance for the understanding and correct interpretation of the outcome of toxicological studies, constitutive and xenobiotic-induced 7-methoxycoumarin-O-demethylase (MCOD), i.e. 'mammalian CYP2-like', activities were monitored in vivo in zebrafish embryos via confocal laser scanning microscopy. In order to elucidate molecular mechanisms underlying the MCOD induction, dose-dependent effects of the prototypical CYP inducers β-naphthoflavone (aryl hydrocarbon receptor (AhR) agonist), rifampicin (pregnane X receptor (PXR) agonist), carbamazepine and phenobarbital (constitutive androstane receptor (CAR) agonists) were analyzed in zebrafish embryos of varying age. Starting from 36 h of age, all embryonic stages of zebrafish could be shown to have constitutive MCOD activity, albeit with spatial variation and at distinct levels. Whereas carbamazepine, phenobarbital and rifampicin had no effect on in vivo MCOD activity in 96 h old zebrafish embryos, the model aryl hydrocarbon receptor agonist β-naphthoflavone significantly induced MCOD activity in 96 h old zebrafish embryos at 46-734 nM, however, without a clear concentration-effect relationship. Induction of MCOD activity by β-naphthoflavone gradually decreased with progression of embryonic development. By in vivo characterization of constitutive and xenobiotic-induced MCOD activity patterns in 36, 60, 84 and 108 h old zebrafish embryos, this decrease could primarily be attributed to an age-related decline in the induction of MCOD activity in the cardiovascular system. Results of this study provide novel insights into the mechanism and extent, by which specific CYP activities in early life-stages of zebrafish can be influenced by exposure to xenobiotics. The study thus lends further support to the view that zebrafish embryos- at least from an age of 36 h - have an elaborate and inducible biotransformation system.

fat-1 transgenic zebrafish are protected from abnormal lipid deposition induced by high-vegetable oil feeding

High dietary concentration of vegetable oil, particularly those rich in n-6 polyunsaturated fatty acids (PUFAs), can induce negative physiological effects including excessive lipid deposition in teleost fish. Omega-3 desaturase (Fat-1) of Caenorhabditis elegans is able to convert n-6 PUFAs to n-3 PUFAs and thus induces a low n-6/n-3 PUFAs ratio alleviating lipid deposition. In this study, we investigated the effects of dietary n-6 PUFAs on lipid metabolism of fat-1 transgenic zebrafish (Tg:fat-1), to explore the role of fat-1 in fish lipid metabolism. We first generated Tg:fat-1 zebrafish and assayed the effects of a low-fat diet (LFD) and a high-fat diet (HFD) prepared from soybean oil. Wild type zebrafish (WT) fed with HFD (HFD-WT) exhibited increased obesity and lipid deposition, especially in the abdominal cavity and liver. These defects were absent from HFD-Tg:fat-1. For each diet group, Tg:fat-1 exhibited significantly decreased levels of almost all hepatic lipid classes compared with WT. Expression levels of lipid synthesis-related genes and lipid deposition-related genes were markedly lower in the liver of HFD-Tg:fat-1 compared with HFD-WT. In contrast, the steatolysis-related genes significantly upregulated in HFD-Tg:fat-1. Then expression profiles of mitochondrial energy metabolism-related genes and ATP contents in the livers from LFD-WT, LFD-Tg:fat-1, HFD-WT, and HFD-Tg:fat-1 were determined. Our findings suggest that fat-1 protects fish from abnormal lipid deposition induced by high-vegetable oil feeding, through endogenously converting n-6 PUFAs to n-3 PUFAs. KEY POINTS: • fat-1 transgenic zebrafish (Tg:fat-1) can endogenously convert n-6 PUFAs to n-3 PUFAs. • Tg:fat-1 avoid serious abnormal lipid deposition induced by high-vegetable oil feeding. • fat-1 transgenosis effectively improved lipid metabolism and mitochondrial energy metabolism in zebrafish.

Feeding Faba Beans (Vicia faba L.) Reduces Myocyte Metabolic Activity in Grass Carp (Ctenopharyngodon idellus)

In this study, we aimed to explore the effects of faba bean (Vicia faba L.) on the energy metabolism of grass carp (Ctenopharyngodon idellus). A total of 180 fish (∼2900 g) were randomly assigned to six tanks (2.5 × 2.5 × 1.2 m; 30 individuals per tank) and fed either faba bean (Vicia faba L.) or a commercial diet for 120 days (3% body weight, twice per day). The results showed that faba bean-fed grass carp (FBFG) had significantly lower growth and higher fat accumulation in the mesenteric adipose tissue and hepatopancreas than commercial diet-fed grass carp (CDFG). Compared with CDFG, FBFG exhibited no significant difference in proximate composition of the muscle; however, an obvious decrease in muscle fiber size and significantly higher hardness, chewiness, and gumminess were observed. Transcriptome results showed that a total of 197 genes were differentially regulated in the dorsal muscle. Down-regulated genes included four genes annotated with myocyte development and 12 transcripts annotated with components of myofibrils. In addition, the FBFG group exhibited significantly lower expression of genes associated with oxygen transport, the mitochondrial respiratory chain, and creatine metabolism, suggesting reduced energy availability in the muscle of the FBFG. Moreover, using western-blotting and enzyme assays, we found decreased protein levels in the mitochondrial electron transport respiratory chain and creatine metabolism activities, as well as increased expression of autophagy marker protein levels, in the muscle of FBFG. Overall, our results suggest that an abnormal energy distribution may exist in grass carps after feeding with faba bean, which is reflected by a mass of fat deposition in the adipose tissue and hepatopancreas and subdued metabolic activity in the muscle.

Nutritional rickets: Historic overview and plan for worldwide eradication

Rickets was first described in great detail in the mid 17th century and was affecting a great number of children in major European cities. The disease, however, existed already in the Roman times. The etiology of this disease remained enigmatic until the 1920s when two different mechanisms, lack of exposure to sunlight and lack of a dietary factor were finally solved by the discovery of vitamin D and its dual origin. Soon thereafter, the implementation of vitamin D supplementation for all infants and small children largely eliminated nutritional rickets in Europe and North America. It took nearly a century to elucidate the complex chemistry, metabolism, mode and spectrum of activity of the vitamin D endocrine system. Nutritional rickets, whether due to simple vitamin D or calcium deficiency or both, remains widely ravaging many infants and children around the world. Asian countries and the Middle East are mainly confronted with vitamin D deficiency whereas many African and some Asian countries face calcium deficiency rickets. Immigrants and refugees or in general people with a darker skin living in moderate climate zone are also confronted with this disease. There is great consensus how this disease could be prevented or cured. In collaboration with most international professional societies, we prepare a memorandum, in line with the successful battle against iodine deficiency disorders, to convince the World Health Organization and its member states to start an implementation program to eradicate nutritional rickets by 2030.

Vitamin D Supplementation Improves Adipose Tissue Inflammation and Reduces Hepatic Steatosis in Obese C57BL/6J Mice

The beneficial effect of vitamin D (VD) supplementation on body weight gain limitation and inflammation has been highlighted in primary prevention mice models, but the long-term effect of VD supplementation in tertiary prevention has never been reported in obesity models. The curative effect of VD supplementation on obesity and associated disorders was evaluated in high-fat- and high-sucrose (HFS)-fed mice. Morphological, histological, and molecular phenotype were characterized. The increased body mass and adiposity caused by HFS diet as well as fat cell hypertrophy and glucose homeostasis were not improved by VD supplementation. However, VD supplementation led to a decrease of HFS-induced inflammation in inguinal adipose tissue, characterized by a decreased expression of chemokine mRNA levels. Moreover, a protective effect of VD on HFS-induced hepatic steatosis was highlighted by a decrease of lipid droplets and a reduction of triglyceride accumulation in the liver. This result was associated with a significant decrease of gene expression coding for key enzymes involved in hepatic de novo lipogenesis and fatty acid oxidation. Altogether, our results show that VD supplementation could be of interest to blunt the adipose tissue inflammation and hepatic steatosis and could represent an interesting nutritional strategy to fight obesity-associated comorbidities.

Fasting-Induced Transcription Factors Repress Vitamin D Bioactivation, a Mechanism for Vitamin D Deficiency in Diabetes

Low 25-hydroxyvitamin D levels correlate with the prevalence of diabetes; however, the mechanisms remain uncertain. Here, we show that nutritional deprivation-responsive mechanisms regulate vitamin D metabolism. Both fasting and diabetes suppressed hepatic cytochrome P450 (CYP) 2R1, the main vitamin D 25-hydroxylase responsible for the first bioactivation step. Overexpression of coactivator peroxisome proliferator-activated receptor γ coactivator 1-α (PGC-1α), induced physiologically by fasting and pathologically in diabetes, resulted in dramatic downregulation of CYP2R1 in mouse hepatocytes in an estrogen-related receptor α (ERRα)-dependent manner. However, PGC-1α knockout did not prevent fasting-induced suppression of CYP2R1 in the liver, indicating that additional factors contribute to the CYP2R1 repression. Furthermore, glucocorticoid receptor (GR) activation repressed the liver CYP2R1, suggesting GR involvement in the regulation of CYP2R1. GR antagonist mifepristone partially prevented CYP2R1 repression during fasting, suggesting that glucocorticoids and GR contribute to the CYP2R1 repression during fasting. Moreover, fasting upregulated the vitamin D catabolizing CYP24A1 in the kidney through the PGC-1α-ERRα pathway. Our study uncovers a molecular mechanism for vitamin D deficiency in diabetes and reveals a novel negative feedback mechanism that controls crosstalk between energy homeostasis and the vitamin D pathway.

Phenylephrine Alleviates 131I Radiation Damage in Submandibular Gland Through Maintaining Mitochondrial Homeostasis

PURPOSE

The impairment of the salivary glands is a permanent side effect of ¹³¹I ablation therapy for patients with differentiated thyroid cancer. Effective and safe treatments for protecting the salivary glands against ¹³¹I are currently not available. Mitochondria are susceptible to ionizing radiation, but alterations after ¹³¹I exposure are unknown. Here, we investigated the mechanisms of ¹³¹I damage in submandibular glands (SMGs) and evaluated the cytoprotective effect of phenylephrine (PE) against mitochondrial radiation damage.

METHODS AND MATERIALS

Rats were randomly divided into 4 groups: control, PE alone, ¹³¹I alone, and ¹³¹I with PE pretreatment. The mitochondrial structure of SMGs was observed under transmission electron microscopy. Apoptosis was detected using terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling. Cytochrome c, cleaved-caspase 3, SIRT1, NAMPT, and PGC-1α protein levels were determined with Western blot and immunohistochemistry. Levels of mitochondrial membrane potential, nicotinamide adenine dinucleotide (NAD), and adenosine triphosphate (ATP) were measured with relevant kits.

RESULTS

After exposing rat SMGs to ¹³¹I, the mitochondrial membrane structures were destroyed, the mitochondrial membrane potential decreased, the release of cytochrome c increased, and cleaved-caspase 3 and cell apoptosis were activated. Moreover, the expression of SIRT1, NAMPT, and PGC-1α was downregulated, and the levels of NAD and ATP decreased. In contrast, PE alleviated the ¹³¹I-induced mitochondrial damages and upregulated the expression of SIRT1/NAMPT/PGC-1α and the levels of NAD and ATP.

CONCLUSIONS

These findings demonstrate that ¹³¹I impairs the salivary glands via the downregulation of SIRT1/NAMPT/PGC-1α signal pathways, which disturbs mitochondrial homeostasis. PE alleviated the ¹³¹I damage in SMGs at the mitochondrial level, suggesting that PE could be used as a potential radioprotector for patients with differentiated thyroid cancer with radiation sialadenitis.

Maternal vitamin D deficiency and developmental origins of health and disease (DOHaD)

Vitamin D is an essential nutrient that is metabolized in the body to generate an active metabolite (1,25(OH)2D) with hormone-like activity and highly diverse roles in cellular function. Vitamin D deficiency (VDD) is a prevalent but easily preventable nutritional disturbance. Emerging evidence demonstrates the importance of sufficient vitamin D concentrations during fetal life with deficiencies leading to long-term effects into adulthood. Here, we provide a detailed review and perspective of evidence for the role of maternal VDD in offspring long term health, particularly as it relates to Developmental Origins of Health and Disease (DOHaD). We focus on roles in neurobehavioral and cardiometabolic disorders in humans and highlight recent findings from zebrafish and rodent models that probe potential mechanisms linking early life VDD to later life health outcomes. Moreover, we explore evidence implicating epigenetic mechanisms as a mediator of this link. Gaps in our current understanding of how maternal VDD might result in deleterious offspring outcomes later in life are also addressed.