The effect of insulin, TNFα and DHA on the proliferation, differentiation and lipolysis of preadipocytes isolated from large yellow croaker (Pseudosciaena Crocea R.)

lpla (lipoprotein lipase a) is a marker of early adipogenesis rather than late adipogenesis in grass carp (Ctenopharyngodon idellus)

Lipoprotein lipase (LPL) functions as a marker of adipocyte differentiation in mammals, but little is known about its role in fish adipogenesis. The aim of this research is to investigate the function of Lpl in adipocyte differentiation in fish. In this paper, we isolated and characterized lipoprotein lipase a (lpla) and lipoprotein lipase b (lplb) from grass carp (Ctenopharyngodon idellus). The complete coding sequence of lpla and lplb was 1524 bp and 1503 bp in length, coding for 507 amino acids and 500 amino acids, respectively. Both lpla and lplb mRNA were expressed in a great number of tissues. During adipogenesis, the level of lpla mRNA reached its maximum at day 2 and then dropped gradually, while the level of lplb mRNA had no significant changes, indicating that lpla and lplb may have different function in the differentiation of grass carp adipocyte. Furthermore, inhibition of lpla by inhibitor of LPL(GSK264220A) at early time points most clearly reduced adipogenesis, whereas these effects were less pronounced at later stages, suggesting that lpla predominantly affects early adipogenesis rather than late adipogenesis. Based on these findings, it can be inferred that lpla and lplb in grass carp may have distinct roles in the differentiation of grass carp adipocyte, and lpla may play an important role in the early adipogenesis rather than late adipogenesis in grass carp.

Discovery, characterization, and adipocyte differentiation regulation in perirenal adipose tissue of large yellow croaker (Larimichthys crocea)

Adipose tissue is an essential tissue for lipid deposition in fish and is associated with excess lipid accumulation in aquaculture. However, the knowledge of the distribution and characterization of adipose tissue in fish still needs further investigation. This study for the first time discovered perirenal adipose tissue (PAT) in large yellow croaker by MRI and CT technologies. Then, the morphological and cytological characteristics of PAT were observed, showing a typical characteristic of white adipose tissue. Meanwhile, the mRNA expression of marker genes of white adipose tissue was highly expressed in PAT compared with the liver and muscle in large yellow croaker. Moreover, based on the discovery of PAT, preadipocytes from PAT were isolated, and the differentiation system of preadipocytes was established. The lipid droplet and TG content of cell were gradually increased during adipocyte differentiation. In addition, mRNA expressions of lipoprotein lipase, adipose triglyceride lipase, and transcription factors related to adipogenesis (cebpα, srebp1, pparα, and pparγ) were quantified to explain the regulation mechanism during the differentiation process. In summary, the present study first discovered perirenal adipose tissue in fish, then explored the characterization of PAT, and revealed the regulation of adipocyte differentiation. These results could advance the understanding of adipose tissue in fish and provide a novel idea for the study of the mechanism of lipid accumulation.

Tissue-like cultured fish fillets through a synthetic food pipeline

Tissue-like cultured meats of some livestock have successfully been established by different approaches. However, the production of a structure similar to fish fillets is still challenging. Here, we develop tissue-like cultured fish fillets by assembly of large yellow croaker muscle fibers and adipocytes with 3D-printed gel. Inhibition of Tgf-β and Notch signals significantly promoted myogenic differentiation of piscine satellite cells (PSCs). The mixture of fish gelatin and sodium alginate combined with a p53 inhibitor and a Yap activator supported PSC viability and proliferation. Based on the texture of fish muscle tissue, a 3D scaffold was constructed by gelatin-based gel mixed with PSCs. After proliferation and differentiation, the muscle scaffold was filled with cultured piscine adipocytes. Finally, tissue-like fish fillets with 20 × 12 × 4 mm were formed, consisting of 5.67 × 10⁷ muscles and 4.02 × 10⁷ adipocytes. The biomanufacture of tissue-like cultured fish fillet here could be a promising technology to customize meat production with high fidelity.

Differentiation and Maturation of Muscle and Fat Cells in Cultivated Seafood: Lessons from Developmental Biology

Cultivated meat, also known as cultured or cell-based meat, is meat produced directly from cultured animal cells rather than from a whole animal. Cultivated meat and seafood have been proposed as a means of mitigating the substantial harms associated with current production methods, including damage to the environment, antibiotic resistance, food security challenges, poor animal welfare, and-in the case of seafood-overfishing and ecological damage associated with fishing and aquaculture. Because biomedical tissue engineering research, from which cultivated meat draws a great deal of inspiration, has thus far been conducted almost exclusively in mammals, cultivated seafood suffers from a lack of established protocols for producing complex tissues in vitro. At the same time, fish such as the zebrafish Danio rerio have been widely used as model organisms in developmental biology. Therefore, many of the mechanisms and signaling pathways involved in the formation of muscle, fat, and other relevant tissue are relatively well understood for this species. The same processes are understood to a lesser degree in aquatic invertebrates. This review discusses the differentiation and maturation of meat-relevant cell types in aquatic species and makes recommendations for future research aimed at recapitulating these processes to produce cultivated fish and shellfish.

Recent advances in the crosstalk between adipose, muscle and bone tissues in fish

Control of tissue metabolism and growth involves interactions between organs, tissues, and cell types, mediated by cytokines or direct communication through cellular exchanges. Indeed, over the past decades, many peptides produced by adipose tissue, skeletal muscle and bone named adipokines, myokines and osteokines respectively, have been identified in mammals playing key roles in organ/tissue development and function. Some of them are released into the circulation acting as classical hormones, but they can also act locally showing autocrine/paracrine effects. In recent years, some of these cytokines have been identified in fish models of biomedical or agronomic interest. In this review, we will present their state of the art focusing on local actions and inter-tissue effects. Adipokines reported in fish adipocytes include adiponectin and leptin among others. We will focus on their structure characteristics, gene expression, receptors, and effects, in the adipose tissue itself, mainly regulating cell differentiation and metabolism, but in muscle and bone as target tissues too. Moreover, lipid metabolites, named lipokines, can also act as signaling molecules regulating metabolic homeostasis. Regarding myokines, the best documented in fish are myostatin and the insulin-like growth factors. This review summarizes their characteristics at a molecular level, and describes both, autocrine effects and interactions with adipose tissue and bone. Nonetheless, our understanding of the functions and mechanisms of action of many of these cytokines is still largely incomplete in fish, especially concerning osteokines (i.e., osteocalcin), whose potential cross talking roles remain to be elucidated. Furthermore, by using selective breeding or genetic tools, the formation of a specific tissue can be altered, highlighting the consequences on other tissues, and allowing the identification of communication signals. The specific effects of identified cytokines validated through in vitro models or in vivo trials will be described. Moreover, future scientific fronts (i.e., exosomes) and tools (i.e., co-cultures, organoids) for a better understanding of inter-organ crosstalk in fish will also be presented. As a final consideration, further identification of molecules involved in inter-tissue communication will open new avenues of knowledge in the control of fish homeostasis, as well as possible strategies to be applied in aquaculture or biomedicine.

Effects of PLIN1 Gene Knockout on the Proliferation, Apoptosis, Differentiation and Lipolysis of Chicken Preadipocytes

Perilipin 1 (PLIN1) is one of the most abundant lipid droplet-related proteins on the surface of adipocytes. Our previous results showed that PLIN1 plays an important role in chicken lipid metabolism. To further reveal the role of PLIN1 in the growth and development of adipocytes, a chicken preadipocyte line with a PLIN1 gene knockout was established by the CRISPR/Cas9 gene editing technique, and the effects of the PLIN1 gene on the proliferation, apoptosis, differentiation and lipolysis of chicken preadipocytes were detected. The results showed that the CRISPR/Cas9 system effectively mediated knockout of the PLIN1 gene. After the deletion of PLIN1, the differentiation ability and early apoptotic activity of chicken preadipocytes decreased, and their proliferation ability increased. Moreover, knockout of PLIN1 promoted chicken preadipocyte lipolysis under basal conditions and inhibited chicken preadipocyte lipolysis under hormone stimulation. Taken together, our results inferred that PLIN1 plays a regulatory role in the process of proliferation, apoptosis, differentiation and lipolysis of chicken preadipocytes.

Medium-chain fatty acids enhance expression and histone acetylation of genes related to lipid metabolism in insulin-resistant adipocytes

Background

The expressions of genes related to lipid metabolism are decreased in adipocytes with insulin resistance. In this study, we examined the effects of fatty acids on the reduced expressions and histone acetylation of lipid metabolism-related genes in 3T3-L1 adipocytes treated with insulin resistance induced by tumor necrosis factor (TNF)-α.

Methods

Short-, medium-, and long-chain fatty acid were co-administered with TNF-α in 3T3-L1 adipocytes. Then, mRNA expressions and histone acetylation of genes involved in lipid metabolism were determined using mRNA microarrays, qRT-PCR, and chromatin immunoprecipitation assays.

Results

We found in microarray and subsequent qRT-PCR analyses that the expression levels of several lipid metabolism-related genes, including Gpd1, Cidec, and Cyp4b1, were reduced by TNF-α treatment and restored by co-treatment with a short-chain fatty acid (C4: butyric acid) and medium-chain fatty acids (C8: caprylic acid and C10: capric acid). The pathway analysis of the microarray showed that capric acid enhanced mRNA levels of genes in the PPAR signaling pathway and adipogenesis genes in the TNF-α-treated adipocytes. Histone acetylation around Cidec and Gpd1 genes were also reduced by TNF-α treatment and recovered by co-administration with short- and medium-chain fatty acids.

General significance

Medium- and short-chain fatty acids induce the expressions of Cidec and Gpd1, which are lipid metabolism-related genes in insulin-resistant adipocytes, by promoting histone acetylation around these genes.

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Expressions of lipid metabolism genes are reduced in insulin-resistant adipocytes.

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Short- and medium-chain fatty acids inhibit lipid metabolism gene downregulation.

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Capric acid enhances expressions of PPAR signaling and adipogenesis genes.

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This mechanism involves recovery of histone acetylation in lipid metabolism genes.

A Study on the Therapeutic Efficacy of San Zi Yang Qin Decoction for Non-Alcoholic Fatty Liver Disease and the Underlying Mechanism Based on Network Pharmacology

OBJECTIVE

This study aims to explore the therapeutic efficacy of San Zi Yang Qin Decoction (SZ) and its potential mechanism in the treatment of non-alcoholic fatty liver disease (NAFLD) based on network pharmacology and in vivo experiments.

METHODS

Effective chemicals and targets of SZ were searched in online databases, according to the drug-likeness of compounds and the binomial distribution of targets. A disease-target-chemical network was established using NAFLD-associated genes screened through GeneCards database, Gene Ontology (GO) terms, and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. Furthermore, animal experiments were conducted to verify the efficacy and mechanism of SZ predicted by network pharmacology. The NAFLD mouse model was established with C57BL/6J mice fed with a high-fat diet for 22 weeks. The mice in the control group were fed with a chow diet. From the 23rd week, the NAFLD mice were treated with intragastric SZ or normal saline for 8 weeks. After the glucose tolerance was measured, the mice were sacrificed, followed by the collection of serum and liver tissues. Pathological changes in liver tissues were examined by H&E staining. Additionally, alanine aminotransferase (ALT), aspartate aminotransferase (AST), serum fast blood glucose, and insulin levels were detected. Expression levels of TNF-α of serum and liver tissues were determined by ELISA and qRT-PCR, respectively. Western blot was used to detect the activation of AKT in liver tissues.

RESULTS

A total of 27 effective compounds and 20 targets of SZ were screened. GO analysis uncovered a significant correlation between the targets of SZ and those of NAFLD. KEGG analysis presented the signaling pathways enriched in SZ and NAFLD, including NAFLD, TNF-α, and apoptosis pathways. The area under the curve of major GO and KEGG pathways indicated the potential role of SZ in improving NAFLD. In vivo experiments demonstrated that SZ significantly alleviated hepatosteatosis and inflammatory cell infiltration in liver tissues, reduced serum transaminases, and improved insulin resistance and glucose tolerance of NAFLD mice. The protein level of phospho-AKT was upregulated by SZ. Additionally, SZ treatment obviously impaired the TNF-α level in the serum and liver tissue of NAFLD mice.

CONCLUSIONS

According to the network pharmacology analysis and in vivo experiments, SZ could have therapeutic efficacy for NALFD. The mechanism mainly involves pathways relative to insulin resistance, TNF-α, and apoptosis. Our results provide a scientific basis for SZ in the clinical treatment of NAFLD.

Lipopolysaccharide promoted proliferation and adipogenesis of preadipocytes through JAK/STAT and AMPK-regulated cPLA2 expression

The proliferation and adipogenesis of preadipocytes played important roles in the development of adipose tissue and contributed much to the processes of obesity. On the other hand, lipopolysaccharide (LPS), also known as endotoxin, is a key outer membrane component of gram-negative bacteria in the gut microbiota, and has a dominant role in linking inflammation to high-fat diet-induced metabolic syndrome. Studies suggested the potential roles of LPS in hepatic steatosis and in obese mice models. However, the molecular mechanisms underlying LPS-regulated obesity remained largely unknown. Here we reported that LPS stimulated expression of cyosolic phospholipase A2 (cPLA2), one of inflammation regulators of obesity, in the preadipocytes. Pretreatment the inhibitors of JAK2, STAT3, STAT5 or AMPK significantly reduced LPS-increased mRNA and protein expression of cPLA2 together with phosphorylation of JAK2, STAT3, STAT5 and AMPK, separately. Similarly, transfection of siRNA against JAK2 or AMPK abolished expression of cPLA2 and phosphorylation of JAK2 or AMPK together with downregulated expression of JAK2 and AMPK protein. LPS enhanced activation of STAT3 and STAT5 via JAK2-dependent manner in the preadipocytes. Transfection of JAK2 or AMPK siRNA further proofed the independence of JAK2 and AMPK in LPS-treated preadipocytes. In addition, LPS-increased DNA synthesis, cell numbers and cell viability of preadipocytes were attenuated by AACOCF3, AG490, BML-275, cPLA2 siRNA, JAK2 siRNA or AMPK siRNA. Attenuation JAK2/STAT or AMPK-dependent cPLA2 expression reduced LPS-mediated adipogenesis of preadipocytes. Stimulation of arachidonic acid or AMPK activator, A-769662, increased cell numbers and cell viability and promoted differentiation of preadipocytes. Collectively, these results indicated that LPS increased preadipocytes proliferation and adipogenesis via JAK/STAT and AMPK-dependent cPLA2 expression. The mechanisms of LPS-stimulated cPLA2 expression may be a link between bacteria and obesity and provides the molecular basis for preventing metabolic syndrome or hyperplasic obesity.

Molecular cloning of adipose triglyceride lipase (ATGL) gene from blunt snout bream and its expression after LPS-induced TNF-α factor

The aims of the present study were to clone the full-length cDNA of adipose triglyceridelipase (ATGL) and to analyze its expression after lipopolysaccharide (LPS)-induced tumor necrosis factor alpha (TNF-α). The cDNA obtained covered 1801 bp with an open reading frame of 1500 bp encoding 499 amino acids. Sequence alignment and phylogenetic analysis show the best identity with Cyprinus carpio (86%). The ATGL protein shared a highly conserved 169-amino acid patatin domain, containing a glycine-rich motif, an active serine hydrolase motif, and an aspartic active site. The highest ATGL expression was observed in the liver followed by muscle, whereas relatively low values were detected in the brain and adipose. TNF-α is regarded as an important factor in regulating fat metabolism. Here, LPS was used to induce TNF-α in vivo to verify whether TNF-α can affect ATGL expression. TNF-α expression in liver and muscle is increased and remains unchanged in adipose tissue and brain. The variation of ATGL activity is consistent with that of TNF-α gene expression. Next, we explored the mechanism by which LPS-induced TNF-α mediates the mRNA expression of ATGL in the liver and muscle. For liver, the mRNA levels of c-Jun N-terminal kinase (JNK), nuclear factor kappa B (NF-κB), Sirtuin 1 (SIRT1), and AMP-activated protein kinase (AMPK) were increased by LPS-induced TNF-α. Differencing from the situation in the liver, there was a near-significant decrease trend in the expression of SIRT1 in muscle. Those results indicated that the ATGL gene of blunt snout bream shared a high similarity with the other vertebrates. The expression level of ATGL in tissues with high-fat content was intended to be high. LPS can induce ATGL expression perhaps related to TNF-α.

Adipogenesis in fish

White adipose tissue (AT) is the main lipid storage depot in vertebrates. Initially considered to be a simple lipid store, AT has recently been recognized as playing a role as an endocrine organ that is implicated in processes such as energy homeostasis and as a rich source of stem cells. Interest in adipogenesis has increased not only because of the prevalence of obesity, metabolic syndrome and type 2 diabetes in humans, but also in aquaculture because of the excessive fat deposition experienced in some cultured fish species, which may compromise both their welfare and their final product quality. Adipocyte development is well conserved among vertebrates, and this conservation has facilitated the rapid characterization of several adipogenesis models in fish. This Review presents the main findings of adipogenesis research based in primary cultures of the preadipocytes of farmed fish species. Zebrafish has emerged as an excellent model for studying the early stages of adipocyte fish development in vivo. Nevertheless, larger fish species are more suitable for the isolation of preadipocytes from visceral AT and for studies in which preadipocytes are differentiated in vitro to form mature adipocytes. Differentiated adipocytes contain lipid droplets and express adipocyte marker genes such as those encoding the peroxisome proliferator activated receptor γ (pparγ), CCAAT-enhancer-binding protein α (c/ebpα), lipoprotein lipase (lpl), fatty acid synthase (fas), fatty acid binding protein 11 (fabp11), fatty acid transporter protein1 (fatp1), adiponectin and leptin. Differentiated adipocytes also have elevated glycerol 3-phosphate (G3P) dehydrogenase (GPDH) activity. To better understand fish adipocyte development and regulation, different adipokines, fatty acids, growth factors and PPAR agonists have been studied, providing relevant insights into which factors affect these processes and counterbalance AT dysregulation.

Dietary docosahexaenoic acid decreased lipid accumulation via inducing adipocytes apoptosis of grass carp, Ctenopharygodon idella

The purpose of this study was to explore the mechanism of by which docosahexaenoic acid (DHA) inhibit the accumulation of adipose tissue lipid in grass carp (Ctenopharyngodon idella). We therefore designed two semi-purified diets, namely DHA-free (control) and DHA-supplemented, and fed them to grass carp (22.19 ± 1.76 g) for 3 and 6 weeks. DHA supplementation led to a significantly lower intraperitoneal fat index (IPFI) than that in the control group by reducing the number of adipocytes but significantly higher adipocyte size (P < 0.05). In the intraperitoneal adipose tissue, the DHA-fed group showed significantly higher peroxisome proliferator-activated receptor (PPAR)γ, CCAAT enhancer-binding protein (C/EBP)α, and sterol regulatory element-binding protein (SREBP)1c mRNA expression levels at both 3 and 6 weeks (P < 0.05). However, the ratio of the expression levels of B cell leukemia 2 (Bcl-2) and Bcl-2-associated X protein (Bax) was significantly lower in the DHA-fed group than in the control group (P < 0.05), and the protein expression levels of the apoptosis-related proteins caspase 3, caspase 8, and caspase 9 were also significantly higher (P < 0.05). Overall, although DHA promotes lipid synthesis, it is more likely that DHA could suppress the lipid accumulation in adipocytes of grass carp by inducing adipocyte apoptosis.

PAM, OLA, and LNA are Differentially Taken Up and Trafficked Via Different Metabolic Pathways in Porcine Adipocytes

Dietary fatty acids have different effects on fat deposition in pigs. To clarify the underlying mechanisms of this difference, we compared the metabolism of palmitic (PAM, saturated), oleic (OLA, monounsaturated) and linoleic acid (LNA, polyunsaturated) in porcine adipocytes treated with 100 μM PAM, OLA or LNA. We observed that the adipocytes incubated with LNA accumulated more lipids compared with those treated with PAM and OLA. We then probed the metabolism of these fatty acids in porcine adipocytes by using isotope-labelled fatty acids. The results showed that 42% of the [1-¹⁴C] LNA, 34% of the [1-¹⁴C] PAM and 28% of the [1-¹⁴C] OLA were recovered in the cellular lipids. The gene expression analyses showed that LNA significantly increased the expression of adipogenesis- and oxidation-related genes including PPARγ, C/EBPα, ap2 and NRF1. In addition, the cells incubated with LNA showed a decreased Ser¹¹² phosphorylation in PPARγ compared to those incubated with PAM and OLA. Furthermore, when PPARγ Ser¹¹² phosphorylation was inhibited, no significant difference in the triacylglycerol contents in the adipocytes was observed. These results showed the dietary fatty acids had different metabolism pathways in porcine adipocytes, and LNA significantly promoted lipid accumulation, probably by regulating PPARγ phosphorylation in adipocytes.

Suppression of adipocyte differentiation and lipid accumulation by stearidonic acid (SDA) in 3T3-L1 cells

Background

Increased consumption of omega-3 (ω-3) fatty acids found in cold-water fish and fish oil has been reported to protect against obesity. A potential mechanism may be through reduction in adipocyte differentiation. Stearidonic acid (SDA), a plant-based ω-3 fatty acid, has been targeted as a potential surrogate for fish-based fatty acids; however, its role in adipocyte differentiation is unknown. This study was designed to evaluate the effects of SDA on adipocyte differentiation in 3T3-L1 cells.

Methods

3T3-L1 preadipocytes were differentiated in the presence of SDA or vehicle-control. Cell viability assay was conducted to determine potential toxicity of SDA. Lipid accumulation was measured by Oil Red O staining and triglyceride (TG) quantification in differentiated 3T3-L1 adipocytes. Adipocyte differentiation was evaluated by adipogenic transcription factors and lipid accumulation gene expression by quantitative real-time polymerase chain reaction (qRT-PCR). Fatty acid analysis was conducted by liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS).

Results

3T3-L1 cells treated with SDA were viable at concentrations used for all studies. SDA treatment reduced lipid accumulation in 3T3-L1 adipocytes. This anti-adipogenic effect by SDA was a result of down-regulation of mRNA levels of the adipogenic transcription factors CCAAT/enhancer-binding proteins alpha and beta (C/EBPα, C/EBPβ), peroxisome proliferator-activated receptor gamma (PPARγ), and sterol-regulatory element binding protein-1c (SREBP-1c). SDA treatment resulted in decreased expression of the lipid accumulation genes adipocyte fatty-acid binding protein (AP2), fatty acid synthase (FAS), stearoyl-CoA desaturase (SCD-1), lipoprotein lipase (LPL), glucose transporter 4 (GLUT4) and phosphoenolpyruvate carboxykinase (PEPCK). The transcriptional activity of PPARγ was found to be decreased with SDA treatment. SDA treatment led to significant EPA enrichment in 3T3-L1 adipocytes compared to vehicle-control.

Conclusion

These results demonstrated that SDA can suppress adipocyte differentiation and lipid accumulation in 3T3-L1 cells through down-regulation of adipogenic transcription factors and genes associated with lipid accumulation. This study suggests the use of SDA as a dietary treatment for obesity.

Electronic supplementary material

The online version of this article (10.1186/s12944-017-0574-7) contains supplementary material, which is available to authorized users.

The Role of Peroxisome Proliferator-Activated Receptor Gamma (PPARG) in Adipogenesis: Applying Knowledge from the Fish Aquaculture Industry to Biomedical Research

The tropical freshwater zebrafish has recently emerged as a valuable model organism for the study of adipose tissue biology and obesity-related disease. The strengths of the zebrafish model system are its wealth of genetic mutants, transgenic tools, and amenability to high-resolution imaging of cell dynamics within live animals. However, zebrafish adipose research is at a nascent stage and many gaps exist in our understanding of zebrafish adipose physiology and metabolism. By contrast, adipose research within other, closely related, teleost species has a rich and extensive history, owing to the economic importance of these fish as a food source. Here, we compare and contrast knowledge on peroxisome proliferator-activated receptor gamma (PPARG)-mediated adipogenesis derived from both biomedical and aquaculture literatures. We first concentrate on the biomedical literature to (i) briefly review PPARG-mediated adipogenesis in mammals, before (ii) reviewing Pparg-mediated adipogenesis in zebrafish. Finally, we (iii) mine the aquaculture literature to compare and contrast Pparg-mediated adipogenesis in aquaculturally relevant teleosts. Our goal is to highlight evolutionary similarities and differences in adipose biology that will inform our understanding of the role of adipose tissue in obesity and related disease.

Adipogenic Gene Expression in Gilthead Sea Bream Mesenchymal Stem Cells from Different Origin

During the last decades, adipogenesis has become an emerging field of study in aquaculture due to the relevance of the adipose tissue in many physiological processes and its connection with the endocrine system. In this sense, recent studies have translated into the establishment of preadipocyte culture models from several fish species, sometimes lacking information on the mRNA levels of adipogenic genes. Thus, the aim of this study was to determine the gene expression profile of gilthead sea bream (Sparus aurata) primary cultured mesenchymal stem cells (MSCs) from different origin (adipose tissue and vertebra bone) during adipogenesis. Both cell types differentiated into adipocyte-like cells, accumulating lipids inside their cytoplasm. Adipocyte differentiation of MSCs from adipose tissue resulted in downregulation of several adipocyte-related genes (such as lpl, hsl, pparα, pparγ and gapdh2) at day 4, gapdh1 at day 8, and fas and pparβ at day 12. In contrast, differences in lxrα mRNA expression were not observed, while g6pdh levels increased during adipocyte maturation. Gapdh and Pparγ protein levels were also detected in preadipocyte cultures; however, only the former increased its expression during adipogenesis. Moreover, differentiation of bone-derived cells into adipocytes also resulted in the downregulation of several adipocyte gene markers, such as fas and g6pdh at day 10 and hsl, pparβ, and lxrα at day 15. On the other hand, the osteogenic genes fib1a, mgp, and op remained stable, but an increase in runx2 expression at day 20 was observed. In summary, the present study demonstrates that gilthead sea bream MSCs, from both adipose tissue and bone, differentiate into adipocyte-like cells, although revealed some kind of species- and cell lineage-specific regulation with regards to gene expression. Present data also provide novel insights into some of the potential key genes controlling adipogenesis in gilthead sea bream that can help to better understand the regulation of lipid storage in fish.

Protein Profiles for Muscle Development and Intramuscular Fat Accumulation at Different Post-Hatching Ages in Chickens

Muscle development and growth influences the efficiency of poultry meat production, and is closely related to deposition of intramuscular fat (IMF), which is crucial in meat quality. To clarify the molecular mechanisms underlying muscle development and IMF deposition in chickens, protein expression profiles were examined in the breast muscle of Beijing-You chickens at ages 1, 56, 98 and 140 days, using isobaric tags for relative and absolute quantification (iTRAQ). Two hundred and four of 494 proteins were expressed differentially. The expression profile at day 1 differed greatly from those at day 56, 98 and 140. KEGG pathway analysis of differential protein expression from pair-wise comparisons (day 1 vs. 56; 56 vs. 98; 98 vs. 140), showed that the fatty acid degradation pathway was more active during the stage from day 1 to 56 than at other periods. This was consistent with the change in IMF content, which was highest at day 1 and declined dramatically thereafter. When muscle growth was most rapid (days 56-98), pathways involved in muscle development were dominant, including hypertrophic cardiomyopathy, dilated cardiomyopathy, cardiac muscle contraction, tight junctions and focal adhesion. In contrast with hatchlings, the fatty acid degradation pathway was downregulated from day 98 to 140, which was consistent with the period for IMF deposition following rapid muscle growth. Changes in some key specific proteins, including fast skeletal muscle troponin T isoform, aldehyde dehydrogenase 1A1 and apolipoprotein A1, were verified by Western blotting, and could be potential biomarkers for IMF deposition in chickens. Protein-protein interaction networks showed that ribosome-related functional modules were clustered in all three stages. However, the functional module involved in the metabolic pathway was only clustered in the first stage (day 1 vs. 56). This study improves our understanding of the molecular mechanisms underlying muscle development and IMF deposition in chickens.

Identification of informative genes and pathways using an improved penalized support vector machine with a weighting scheme

Incorporation of pathway knowledge into microarray analysis has brought better biological interpretation of the analysis outcome. However, most pathway data are manually curated without specific biological context. Non-informative genes could be included when the pathway data is used for analysis of context specific data like cancer microarray data. Therefore, efficient identification of informative genes is inevitable. Embedded methods like penalized classifiers have been used for microarray analysis due to their embedded gene selection. This paper proposes an improved penalized support vector machine with absolute t-test weighting scheme to identify informative genes and pathways. Experiments are done on four microarray data sets. The results are compared with previous methods using 10-fold cross validation in terms of accuracy, sensitivity, specificity and F-score. Our method shows consistent improvement over the previous methods and biological validation has been done to elucidate the relation of the selected genes and pathway with the phenotype under study.

GSK-3b participates in the regulation of hepatic lipid deposition in large yellow croaker (Larmichthys crocea)

In this study, the participation of glycogen synthase kinase-3β (GSK-3β) in the lipid deposition was investigated in the liver of large yellow croaker (Larmichthys crocea) by LiCl treatment. It was found that the expression of GSK-3β and peroxisome proliferator-activated receptor-γ (PPARγ) was inhibited, but the expression of β-catenin was induced by LiCl treatment. Furthermore, the gene expression and activity of fatty acid synthetase (FAS) and lipoprotein lipase (LPL) in the liver was inhibited by LiCl treatment. The content of total cholesterol (TC), triglyceride (TG), and non-estesterified fatty acid in the liver, as well as TC, TG, and low-density lipoprotein cholesterol in plasma, was decreased by LiCl treatment. However, high-density lipoprotein cholesterol in plasma was increased, and the number of lipid droplets in the liver was decreased by LiCl treatment. The results indicate that GSK-3β/β-catenin may participate in regulating LPL and FAS through PPARγ in the liver of large yellow croaker, which will lead to the inhibition of hepatic lipid deposition.

Ontogenetic development of adipose tissue in grass carp (Ctenopharyngodon idellus)

To investigate the adipose tissue development process during the early stages of grass carp (Ctenopharyngodon idellus) development, samples were collected from fertilized eggs to 30 days post-fertilization (dpf) of fish. Paraffin and frozen sections were taken to observe the characteristics of adipocytes in vivo by different staining methods, including hematoxylin and eosin (H&E), Oil red O, and BODIPY. The expression of lipogenesis-related genes of the samples at different time points was detected by real-time qPCR. In addition, protein expression level of peroxisome proliferator-activated receptors γ (PPAR γ) was detected by immunohistochemistry. The results showed that the neutral lipid droplets accumulated first in the hepatocytes of 14-dpf fish larvae, and visceral adipocytes appeared around the hepatopancreas on 16 dpf. As grass carp grew, the adipocytes increased in number and spread to other tissues. In 20-dpf fish larvae, the intestine was observed to be covered by adipose tissue. However, there was no significant change in the average size (30.40-40.01 μm) of adipocytes during this period. Accordingly, the gene expression level of PPAR γ and CCAAT/enhancer-binding proteins α (C/EBP α) was significantly elevated after fertilization for 12 days (p < 0.05), but C/EBP α declined at 20 dpf. Expression of lipoprotein lipase (LPL) increased from 2 to 16 dpf and then declined. In addition, immunoreaction of PPAR γ was positive on hepatocytes after fertilization for 15 days. These results implied that the early developmental stage of adipose tissue is caused by active recruitment of adipocytes as opposed to hypertrophy of the cell. In addition, our study indicated that lipogenesis-related genes might regulate the ongoing development of adipose tissue.

Roles of leptin and ghrelin in adipogenesis and lipid metabolism of rainbow trout adipocytes in vitro

Leptin and ghrelin are important regulators of energy homeostasis in mammals, whereas their physiological roles in fish have not been fully elucidated. In the present study, the effects of leptin and ghrelin on adipogenesis, lipolysis and on expression of lipid metabolism-related genes were examined in rainbow trout adipocytes in vitro. Leptin expression and release increased from preadipocytes to mature adipocytes in culture, but did not affect the process of adipogenesis. While ghrelin and its receptor were identified in cultured differentiated adipocytes, ghrelin did not influence either preadipocyte proliferation or differentiation, indicating that it may have other adipose-related roles. Leptin and ghrelin increased lipolysis in mature freshly isolated adipocytes, but mRNA expression of lipolysis markers was not significantly modified. Leptin significantly suppressed the fatty acid transporter-1 expression, suggesting a decrease in fatty acid uptake and storage, but did not affect expression of any of the lipogenesis or β-oxidation genes studied. Ghrelin significantly increased the mRNA levels of lipoprotein lipase, fatty acid synthase and peroxisome proliferator-activated receptor-β, and thus appears to stimulate synthesis of triglycerides as well as their mobilization. Overall, the study indicates that ghrelin, but not leptin seems to be an enhancer of lipid turn-over in adipose tissue of rainbow trout, and this regulation may at least partly be mediated through autocrine/paracrine mechanisms. The mode of action of both hormones needs to be further explored to better understand their roles in regulating adiposity in fish.

Alterations in oral [1-(14)C] 18:1n-9 distribution in lean wild-type and genetically obese (ob/ob) mice

Obesity may result from altered fatty acid (FA) disposal. Altered FA distribution in obese individuals is poorly understood. Lean wild-type C57BL/6J and obese C57BL/6Job/ob mice received an oral dose of [1-(14)C]18:1n-9 (oleic acid), and the radioactivity in tissues was evaluated at various time points. The (14)C concentration decreased rapidly in gastrointestinal tract but gradually increased and peaked at 96 h in adipose tissue, muscle and skin in lean mice. The (14)C concentration was constant in adipose tissue and muscle of obese mice from 4 h to 168 h. (14)C-label content in adipose tissue was significantly affected by genotype, whereas muscle (14)C-label content was affected by genotype, time and the interaction between genotype and time. There was higher total (14)C retention (47.7%) in obese mice than in lean mice (9.0%) at 168 h (P<0.05). The (14)C concentrations in the soleus and gastrocnemius muscle were higher in obese mice than in lean mice (P<0.05). Perirenal adipose tissue contained the highest (14)C content in lean mice, whereas subcutaneous adipose tissue (SAT) had the highest (14)C content and accounted for the largest proportion of total radioactivity among fat depots in obese mice. More lipid radioactivity was recovered as TAG in SAT from obese mice than from lean mice (P<0.05). Gene expression suggested acyl CoA binding protein and fatty acid binding protein are important for FA distribution in adipose tissue and muscle. The FA distribution in major tissues was altered in ob/ob mice, perhaps contributing to obesity. Understanding the disparity in FA disposal between lean and obese mice may reveal novel targets for the treatment and prevention of obesity.

mRNA m⁶A methylation downregulates adipogenesis in porcine adipocytes

Fat Mass and Obesity-associated protein (FTO), associated with obesity, is proved to demethylate N6-methyladenosine (m(6)A), which raises questions regarding whether m(6)A plays vital roles in adipogenesis. To prove this, overexpression and knockdown of FTO and METTL3, as well as the chemical treatment in procine adipocytes were conducted. The results showed FTO negatively regulated m(6)A levels and positively regulated adipogenesis, while METTL3 positively correlated with m(6)A levels and negatively with adipogenesis. To remove the potential effect of FTO and METTL3 gene, chemical reagents of methylation inhibitor cycloleucine and methyl donor betaine were used to test the regulation effect of m(6)A on adipogenesis. The results showed the inverse effect of m(6)A on lipid accumulation in porcine adipocytes. These findings provide compelling evidence that m(6)A plays a critical role in the regulation of adipogenesis.

Extract of Ginkgo Biloba Ameliorates Streptozotocin-Induced Type 1 Diabetes Mellitus and High-Fat Diet-Induced Type 2 Diabetes Mellitus in Mice

Diabetes mellitus (DM) is caused by either destruction of pancreatic β-cells (type 1 DM) or unresponsiveness to insulin (type 2 DM). Conventional therapies for diabetes mellitus have been developed but still needs improvement. Many diabetic patients have complemented conventional therapy with alternative methods including oral supplementation of natural products. In this study, we assessed whether Ginkgo biloba extract (EGb) 761 could provide beneficial effects in the streptozotocin-induced type 1 DM and high-fat diet-induced type 2 DM murine model system. For the type 1 DM model, streptozotocin-induced mice were orally administered EGb 761 for 10 days prior to streptozotocin injection and then again administered EGb 761 for an additional 10 days. Streptozotocin-treated mice administered EGb 761 exhibited lower blood triglyceride levels, lower blood glucose levels and higher blood insulin levels compared to streptozotocin-treated mice. Furthermore, liver LPL and liver PPAR-α were increased whereas IL-1β and TNF-α were decreased in streptozotocin-injected mice treated with EGb 761 compared to mice injected with streptozotocin alone. For the type 2 DM model, mice were given high-fat diet for 60 days and then orally administered EGb 761 every other day for 80 days. We found that mice given a high-fat diet and EGb 761 showed decreased blood triglyceride levels, increased liver LPL, increased liver PPAR-α and decreased body weight compared to mice given high-fat diet alone. These results suggest that EGb 761 can exert protective effects in both type 1 and type 2 DM murine models.

Regulation of adipocytes lipolysis by n-3 HUFA in grass carp (Ctenopharyngodon idellus) in vitro and in vivo

N-3 highly unsaturated fatty acids (n-3 HUFA) have been shown to inhibit body fat accumulation in animals. To clarify the mechanism of this fat-lowering effect of n-3 HUFA in grass carp (Ctenopharyngodon idellus), two experiments were conducted. In experiment 1, isolated grass carp mature adipocytes were incubated with docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) at different concentrations for 6 h. The release of glycerol to the medium was detected, and the expression of the lipolysis-related genes was analyzed. In experiment 2, a 95-day feeding trial was conducted with two diets formulated with either lard oil (as control) or fish oil (supplying n-3 HUFA as treatment) as the main lipid source. The glycerol and free fatty acid (FFA) released from the isolated adipocytes of both groups were detected after the feeding period. The expression of select lipolysis-related genes in adipose tissue was also analyzed. The results from experiment 1 showed that the release of glycerol was significantly increased by DHA and EPA (P < 0.05). Moreover, the expression of lipolysis-related genes, such as adipose triglyceride lipase (ATGL), hormone-sensitive lipase (HSL), tumor necrosis factor α (TNFα) and leptin, was also significantly elevated in the treatment group (P < 0.05). Experiment 2 demonstrated that glycerol and FFA release from the isolated adipocytes were significantly higher in the treatment group compared to the control group (P < 0.05). The expression level of ATGL, HSL, TNFα and leptin in the treatment group was significantly higher than in the control group (P < 0.05). The present results provide novel evidence that n-3 HUFAs could regulate grass carp adipocyte lipolysis in vitro or in vivo, and the effect might be in part associated with their influence on the expression of lipolysis-related genes and lipolysis-related adipokines genes.

In vitro and in vivo enhancement of adipogenesis by Italian ryegrass (Lolium multiflorum) in 3T3-L1 cells and mice

Adipogenesis is very much important in improving the quality of meat in animals. The aim of the present study was to investigate the in vitro and in vivo adipogenesis regulation properties of Lolium multiflorum on 3T3-L1 pre-adipocytes and mice. Chemical composition of petroleum ether extract of L. multiflorum (PET-LM) confirmed the presence of fatty acids, such as α-linolenic acid, docosahexaenoic acid, oleic acid, docosatetraenoic acid, and caprylic acid, as the major compounds. PET-LM treatment increased viability, lipid accumulation, lipolysis, cell cycle progression, and DNA synthesis in the cells. PET-LM treatment also augmented peroxysome proliferator activated receptor (PPAR)-γ2, CCAAT/enhancer binding protein-α, adiponectin, adipocyte binding protein, glucose transporter-4, fatty acid synthase, and sterol regulatory element binding protein-1 expression at mRNA and protein levels in differentiated adipocytes. In addition, mice administered with 200 mg/kg body weight PET-LM for 8 weeks showed greater body weight than control mice. These findings suggest that PET-LM facilitates adipogenesis by stimulating PPARγ-mediated signaling cascades in adipocytes which could be useful for quality meat development in animals.

Characterization and endocrine regulation of proliferation and differentiation of primary cultured preadipocytes from gilthead sea bream (Sparus aurata)

A preadipocyte primary cell culture was established to gain knowledge about adipose tissue development in gilthead sea bream (Sparus aurata), one of the most extensively produced marine aquaculture species in the Mediterranean. The preadipocytes obtained from the stromal-vascular cell fraction of adipose tissue proliferated in culture, reaching confluence around day 8. At that time, the addition of an adipogenic medium promoted differentiation of the cells into mature adipocytes, which showed an enlarged cytoplasm filled with lipid droplets. First, cell proliferation and differentiation were analyzed under control and adipogenic conditions during culture development. Next, the effects of insulin, GH, and IGF-I on cell proliferation were evaluated at day 8. All peptides significantly stimulated proliferation of the cells after 48 h of incubation (P < 0.002 for GH and IGF-I and P < 0.05 for insulin), despite no differences were observed between the different doses tested. Subsequently, the effects of insulin and IGF-I maintaining differentiation when added to growth medium were studied at day 11, after 3 d of induction with adipogenic medium. The results showed that IGF-I is more potent than insulin enhancing differentiation (P < 0.01 for IGF-I compared with the control). In summary, a primary culture of gilthead sea bream preadipocytes has been characterized and the effects of several regulators of growth and development have been evaluated. This cellular system can be a good model to study the process of adipogenesis in fish, which may help improve the quality of the product in aquaculture.