Docosahexaenoic acid increases accumulation of adipocyte triacylglycerol through up-regulation of lipogenic gene expression in pigs

Co-administration of oleic and docosahexaenoic acids enhances glucose uptake rather than lipolysis in mature 3T3-L1 adipocytes cell culture

This study investigated the effect of different types of long-chain fatty acids and their combination on the triglyceride accumulation, glucose utilisation, and lipolysis in already obese adipocytes. 3T3-L1 MBX cells were first differentiated into mature adipocytes using adipogenic inducers (3-isobutyl-1-methylxanthine, dexamethasone, indomethacin, insulin, and high glucose), then 100 µM 0.1% ethanol extracts of palmitic (PA), oleic (OA), or docosahexaenoic acid (DHA) were applied for nine days. Unsaturated fatty acids decreased the intracellular lipid accumulation while maintaining glucose utilisation levels. However, unlike OA, self-administration of DHA only intensified lipolysis by 25% vs induced untreated control (IC), which may have a direct detrimental impact on the whole body’s metabolic state. DHA applied in equal proportion with PA elevated triglyceride accumulation by 10% compared to IC, but applied with OA, enhanced glucose uptake without any significant changes in the lipogenic drive and the lipolytic rate, suggesting that this unsaturated fatty acids combination may offer a considerable advantage in amelioration of obesity-related disorders.

Docosahexaenoic Acid Suppresses Expression of Adipogenic Tetranectin through Sterol Regulatory Element-Binding Protein and Forkhead Box O Protein in Pigs

Tetranectin (TN), a plasminogen-binding protein originally involved in fibrinolysis and bone formation, was later identified as a secreted adipokine from human and rat adipocytes and positively correlated with adipogenesis and lipid metabolism in adipocytes. To elucidate the nutritional regulation of adipogenic TN from diets containing different sources of fatty acids (saturated, n-6, n-3) in adipocytes, we cloned the coding region of porcine TN from a cDNA library and analyzed tissue expressions in weaned piglets fed with 2% soybean oil (SB, enriched in n-6 fatty acids), docosahexaenoic acid oil (DHA, an n-3 fatty acid) or beef tallow (BT, enriched in saturated and n-9 fatty acids) for 30 d. Compared with tissues in the BT- or SB-fed group, expression of TN was reduced in the adipose, liver and lung tissues from the DHA-fed group, accompanied with lowered plasma levels of triglycerides and cholesterols. This in vivo reduction was also confirmed in porcine primary differentiated adipocytes supplemented with DHA in vitro. Then, promoter analysis was performed. A 1956-bp putative porcine TN promoter was cloned and transcription binding sites for sterol regulatory-element binding protein (SREBP)-1c or forkhead box O proteins (FoxO) were predicted on the TN promoter. Mutating binding sites on porcine TN promoters showed that transcriptional suppression of TN by DHA on promoter activity was dependent on specific response elements for SREBP-1c or FoxO. The inhibited luciferase promoter activity by DHA on the TN promoter coincides with reduced gene expression of TN, SREBP-1c, and FoxO1 in human embryonic kidney HEK293T cells supplemented with DHA. To conclude, our current study demonstrated that the adipogenic TN was negatively regulated by nutritional modulation of DHA both in pigs in vivo and in humans/pigs in vitro. The transcriptional suppression by DHA on TN expression was partly through SREBP-1c or FoxO. Therefore, down-regulation of adipogenic tetranectin associated with fibrinolysis and adipogenesis may contribute to the beneficial effects of DHA on ameliorating obesity-induced metabolic syndromes such as atherosclerosis and adipose dysfunctions.

Dietary fat content and adipose triglyceride lipase and hormone-sensitive lipase gene expressions in adults' subcutaneous and visceral fat tissues

INTRODUCTION

We examined the association of adipose triglyceride lipase (ATGL) and hormone-sensitive lipase (HSL) gene expressions, as the key regulators of lipolysis, with dietary fat quantity and composition in subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT).

METHODS

In this observational study, samples were collected from patients undergoing elective abdominal surgery. Participants were categorized into two groups based on their body mass index (BMI) status. Dietary, anthropometric, and biochemical data were collected before surgery. Linear regression was performed to determine the association of dietary fat content with ATGL and HSL gene expressions in SAT and VAT.

RESULTS

152 individuals with a mean ± SD age of 40.7 ± 13.2 years and a median (inter-quartile range) BMI of 39.4 (26.5-45.3 kg/m²) participated in this study, of whom 54 were non-obese (BMI<30 kg/m²), and 98 were obese (BMI≥30 kg/m²). Among non-obese participants, positive associations were observed between ATGL mRNA expression and reported intakes of total fatty acids (TFA) (β=0.306, P = 0.025), myristic (β=0.285, P = 0.038), palmitic (β=0.417, P = 0.002), oleic (β=0.333, P = 0.017), dairy trans (β=0.374, P = 0.006), and other trans FAs (β=0.369, P = 0.006) in SAT. In contrast, inverse associations between HSL mRNA expression and reported intakes of TFAs (β=-0.377, P = 0.005), myristic (β=-0.282, P = 0.039), palmitic (β=-0.372, P = 0.006), stearic (β=-0.314, P = 0.020), and oleic acid (β=-0.372, P = 0.007) were observed in SAT. No associations were observed among obese participants, nor in VAT among non-obese individuals.

CONCLUSION

ATGL and HSL mRNA expressions in SAT were associated with dietary fat quantity and composition among non-obese adults.

Overexpression of Adiponectin Receptor 1 Inhibits Brown and Beige Adipose Tissue Activity in Mice

Adult humans and mice possess significant classical brown adipose tissues (BAT) and, upon cold-induction, acquire brown-like adipocytes in certain depots of white adipose tissues (WAT), known as beige adipose tissues or WAT browning/beiging. Activating thermogenic classical BAT or WAT beiging to generate heat limits diet-induced obesity or type-2 diabetes in mice. Adiponectin is a beneficial adipokine resisting diabetes, and causing “healthy obese” by increasing WAT expansion to limit lipotoxicity in other metabolic tissues during high-fat feeding. However, the role of its receptors, especially adiponectin receptor 1 (AdipoR1), on cold-induced thermogenesis in vivo in BAT and in WAT beiging is still elusive. Here, we established a cold-induction procedure in transgenic mice over-expressing AdipoR1 and applied a live 3-D [¹⁸F] fluorodeoxyglucose-PET/CT (¹⁸F-FDG PET/CT) scanning to measure BAT activity by determining glucose uptake in cold-acclimated transgenic mice. Results showed that cold-acclimated mice over-expressing AdipoR1 had diminished cold-induced glucose uptake, enlarged adipocyte size in BAT and in browned WAT, and reduced surface BAT/body temperature in vivo. Furthermore, decreased gene expression, related to thermogenic Ucp1, BAT-specific markers, BAT-enriched mitochondrial markers, lipolysis and fatty acid oxidation, and increased expression of whitening genes in BAT or in browned subcutaneous inguinal WAT of AdipoR1 mice are congruent with results of PET/CT scanning and surface body temperature in vivo. Moreover, differentiated brown-like beige adipocytes isolated from pre-adipocytes in subcutaneous WAT of transgenic AdipoR1 mice also had similar effects of lowered expression of thermogenic Ucp1, BAT selective markers, and BAT mitochondrial markers. Therefore, this study combines in vitro and in vivo results with live 3-D scanning and reveals one of the many facets of the adiponectin receptors in regulating energy homeostasis, especially in the involvement of cold-induced thermogenesis.

Short-Term Effects of Early Menopause on Adiposity, Fatty Acids Profile and Insulin Sensitivity of a Swine Model of Female Obesity

Menopause strongly increases incidence and consequences of obesity and non-communicable diseases in women, with recent research suggesting a very early onset of changes in lipid accumulation, dyslipidemia, and insulin resistance. However, there is a lack of adequate preclinical models for its study. The present trial evaluated the usefulness of an alternative method to surgical ovariectomy, the administration of two doses of a GnRH analogue-protein conjugate (Vacsincel^®), for inducing ovarian inactivity in sows used as preclinical models of obesity and menopause. All the sows treated with the compound developed ovarian stoppage after the second dose and, when exposed to obesogenic diets during the following three months, showed changes in the patterns of fat deposition, in the fatty acids profiles at the different tissues and in the plasma concentrations of fructosamine, urea, β-hydroxibutirate, and haptoglobin when compared to obese fed with the same diet but maintaining ovarian activity. Altogether, these results indicate that menopause early augments the deleterious effects induced by overfeeding and obesity on metabolic traits, paving the way for future research on physiopathology of these conditions and possible therapeutic targets using the swine model.

Changes in the diet composition of fatty acids and fiber affect the lower gastrointestinal motility but have no impact on cardiovascular parameters: In vivo and in vitro studies

BACKGROUND

Food and diet are central issues for proper functioning of the cardiovascular (CV) system and gastrointestinal (GI) tract. We hypothesize that different types of dietary FAs affect CV parameters as well as GI motor function and visceral sensitivity.

METHODS

Male Wistar rats were fed with control diet (CTRL), diet supplemented with 7% soybean oil (SOY), SOY + 3.5% virgin coconut oil (COCO), and SOY + 3.5% evening primrose oil (EP) for 4 weeks. The content of insoluble fiber in CTRL was higher than in SOY, COCO, or EP. Body weight gain and food/water intake were measured. At day 28, biometric, biochemical, CV parameters, GI motor function (X-ray and colon bead expulsion test), and visceral sensitivity were evaluated. Changes in propulsive colonic activity were determined in vitro. The colon and adipose tissue were histologically studied; the number of mast cells (MCs) in the colon was calculated.

RESULTS

SOY, COCO, and EP had increased body weight gain but decreased food intake vs CTRL. Water consumption, biometric, biochemical, and CV parameters were comparable between groups. SOY increased the sensitivity to colonic distention. All groups maintained regular propulsive neurogenic contractions; EP delayed colonic motility (P < 0.01). SOY, COCO, and EP displayed decreased size of the cecum, lower number and size of fecal pellets, and higher infiltration of MCs to the colon (P < 0.001).

CONCLUSIONS AND INFERENCES

Dietary FAs supplementation and lower intake of insoluble fiber can induce changes in the motility of the lower GI tract, in vivo and in vitro, but CV function and visceral sensitivity are not generally affected.

Effect of diets supplemented with linseed alone or combined with vitamin E and selenium or with plant extracts, on Longissimus thoracis transcriptome in growing-finishing Italian Large White pigs

Background

Supplementing farm animals diet with functional ingredients may improve the nutritional quality of meat products. Diet composition has been also demonstrated to influence the gene expression with effect on biological processes and pathways. However, the knowledge on the effect of nutrients at the molecular level is scant. In particular, studies on the effects of antioxidants and polyphenols dietary supplementation have been investigated mainly in rodents, and only scarcely in farm animals so far. RNA-Seq with next-generation sequencing is increasingly the method of choice for studying changes in the transcriptome and it has been recently employed also in pig nutrigenomics studies to identify diet-induced changes in gene expression. The present study aimed to investigate the effect of diets enriched with functional ingredients (linseed, vitamin E and plant extracts) on the transcriptome of pig Longissimus thoracis to elucidate the role of these compounds in influencing genes involved in muscle physiology and metabolism compared to a standard diet.

Results

Eight hundred ninety-three significant differentially expressed genes (DEGs) (FDR adjusted P-value ≤ 0.05) were detected by RNA-Seq analysis in the three diet comparisons (D2-D1, D3-D1, D4-D1). The functional analysis of DEGs showed that the diet enriched with n-3 PUFA from linseed (D2) mostly downregulated genes in pathways and biological processes (BPs) related to muscle development, contraction, and glycogen metabolism compared to the standard diet. The diet supplemented with linseed and vitamin E/Selenium (D3) showed to mostly downregulate genes linked to oxidative phosphorylation. Only few genes involved in extracellular matrix (ECM) organization were upregulated by the D3. Finally, the comparison D4-D1 showed that the diet supplemented with linseed and plant extracts (D4) upregulated the majority of genes compared to D1 that were involved in a complex network of pathways and BPs all connected by hub genes. In particular, IGF2 was a hub gene connecting protein metabolism, ECM organization, immune system and lipid biosynthesis pathways.

Conclusion

The supplementation of pig diet with n-3 PUFA from linseed, antioxidants and plant-derived polyphenols can influence the expression of a relevant number of genes in Longissimus thoracis muscle that are involved in a variety of biochemical pathways linked to muscle function and metabolism.

Effect of dietary polyunsaturated fatty acid and antioxidant supplementation on the transcriptional level of genes involved in lipid and energy metabolism in swine

Porcine fat traits depend mostly on the interaction between nutritional and genetic factors. However, the pathways and biological processes influenced by this interaction are still poorly known in pigs, although they can have a huge impact on meat quality traits. The present research provides new knowledge insight into the effect of four diets (D1 = standard diet; D2 = linseed supplementation; D3 = linseed, vitamin E and selenium supplementation; D4 = linseed and plant-derived polyphenols supplementation) on the expression of 24 candidate genes selected for their role in lipid and energy metabolism. The data indicated that 10 out of 24 genes were differentially expressed among diets, namely ACACA, ADIPOQ, ADIPOR1, CHREBP (MLXPL), ELOVL6, FASN, G6PD, PLIN2, RXRA and SCD. Results from the univariate analysis displayed an increased expression of ACACA, ADIPOQ, ADIPOR1, CHREBP, ELOVL6, FASN, PLIN2, RXRA and SCD in D4 compared to D2. Similarly, ACACA, ADIPOQ, ADIPOR1, ELOVL6 and SCD were highly expressed in D4 compared to D3, while no differences were observed in D2-D3 comparison. Moreover, an increased expression of G6PD and ELOVL6 genes in D4 compared to D1 was observed. Results from the multivariate analysis confirmed that D2 was not different from D3 and that ACACA, SCD and FASN expression made D4 different from D2 and D3. Comparing D4 and D1, the expression levels of ELOVL6 and ACACA were the most influenced. This research provides evidence that the addition of both n-3 PUFA and polyphenols, derived from linseed, grape-skin and oregano supplementation in the diets, stimulates the expression of genes involved in lipogenesis and in oxidative processes. Results evidenced a greater effect on gene expression of the diet added with both plant extracts and n-3 PUFA, resulting in an increased expression of genes coding for fatty acid synthesis, desaturation and elongation in pig Longissimus thoracis muscle.

Docosahexaenoic Acid (DHA) Induced Morphological Differentiation of Astrocytes Is Associated with Transcriptional Upregulation and Endocytosis of β2-AR

Docosahexaenoic acid (DHA), an important ω-3 fatty acid, is abundantly present in the central nervous system and is important in every step of brain development. Much of this knowledge has been based on studies of the role of DHA in the function of the neurons, and reports on its effect on the glial cells are few and far between. We have previously reported that DHA facilitates astrocyte differentiation in primary culture. We have further explored the signaling mechanism associated with this event. It was observed that a sustained activation of the extracellular signal-regulated kinase (ERK) appeared to be critical for DHA-induced differentiation of the cultured astrocytes. Prior exposure to different endocytic inhibitors blocked both ERK activation and differentiation of the astrocytes during DHA treatment suggesting that the observed induction of ERK-2 was purely endosomal. Unlike the β₁-adrenergic receptor (β₁-AR) antagonist, atenolol, pre-treatment of the cells with the β₂-adrenergic receptor (β₂-AR) antagonist, ICI-118,551 inhibited the DHA-induced differentiation process, indicating a downstream involvement of β₂-AR in the differentiation process. qRT-PCR and western blot analysis demonstrated a significant induction in the mRNA and protein expression of β₂-AR at 18-24 h of DHA treatment, suggesting that the induction of β₂-AR may be due to transcriptional upregulation. Moreover, DHA caused activation of PKA at 6 h, followed by activation of downstream cAMP response element-binding protein, a known transcription factor for β₂-AR. Altogether, the observations suggest that DHA upregulates β₂-AR in astrocytes, which undergo endocytosis and signals for sustained endosomal ERK activation to drive the differentiation process.

Effect of Eicosapentaenoic Acid and Docosahexaenoic Acid on Myogenesis and Mitochondrial Biosynthesis during Murine Skeletal Muscle Cell Differentiation

Polyunsaturated fatty acids are important nutrients for human health, especially omega-3 fatty acids such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which have been found to play positive roles in the prevention of various diseases. However, previous studies have reported that excessive omega-3 fatty acids supplement during pregnancy caused side effects such as slower neural transmission times and postnatal growth restriction. In this study, we investigated the effect of EPA and DHA on mitochondrial function and gene expression in C2C12 myoblasts during skeletal muscle differentiation. C2C12 myoblasts were cultured to confluency and then treated with differentiation medium that contained fatty acids (50-µM EPA and DHA). After 72 h of myogenic differentiation, mRNA was collected, and gene expression was analyzed by real-time PCR. Microscopy was used to examine cell morphology following treatment with fatty acids. The effect of EPA and DHA on cellular oxygen consumption was measured using a Seahorse XF24 Analyzer. Cells treated with fatty acids had fewer myotubes formed (P ≤ 0.05) compared with control cells. The expression of the genes related to myogenesis was significantly lower (P ≤ 0.05) in cells treated with fatty acids, compared with control cells. Genes associated with adipogenesis had higher (P ≤ 0.05) expression after treatment with fatty acids. Also, the mitochondrial biogenesis decreased with lower (P ≤ 0.05) gene expression and lower (P ≤ 0.05) mtDNA/nDNA ratio in cells treated with fatty acids compared with control cells. However, the expression of genes related to peroxisome biosynthesis was higher (P ≤ 0.05) in cells treated with fatty acids. Moreover, fatty-acid treatment reduced (P ≤ 0.05) oxygen consumption rate under oligomycin-inhibited (reflecting proton leak) and uncoupled conditions. Our data imply that fatty acids might reduce myogenesis and increase adipogenesis in myotube formation. Fatty acids may also decrease cell metabolism by reducing mitochondrial biogenesis as well as respiration rate. This study suggests that the maternal overdosage of EPA and DHA may influence fetal muscle development, increase intramuscular adipose tissue deposition in offspring, and have a long-term effect on the development of metabolic diseases such as obesity and diabetes in adult offspring.

Omega-3 fatty acids and adipose tissue biology

This review provides evidence for the importance of white and brown adipose tissue (i.e. WAT and BAT) function for the maintenance of healthy metabolic phenotype and its preservation in response to omega-3 polyunsaturated fatty acids (omega-3 PUFA), namely in the context of diseased states linked to aberrant accumulation of body fat, systemic low-grade inflammation, dyslipidemia and insulin resistance. More specifically, the review deals with (i) the concept of immunometabolism, i.e. how adipose-resident immune cells and adipocytes affect each other and define the immune-metabolic interface; and (ii) the characteristic features of "healthy adipocytes" in WAT, which are relatively small fat cells endowed with a high capacity for mitochondrial oxidative phosphorylation, triacylglycerol/fatty acid (TAG/FA) cycling and de novo lipogenesis (DNL). The intrinsic metabolic features of WAT and their flexible regulations, reflecting the presence of "healthy adipocytes", provide beneficial local and systemic effects, including (i) protection against in situ endoplasmic reticulum stress and related inflammatory response during activation of adipocyte lipolysis; (ii) prevention of ectopic fat accumulation and dyslipidemia caused by increased hepatic VLDL synthesis, as well as prevention of lipotoxic damage of insulin signaling in extra-adipose tissues; and also (iii) increased synthesis of anti-inflammatory and insulin-sensitizing lipid mediators with pro-resolving properties, including the branched fatty acid esters of hydroxy fatty acids (FAHFAs), also depending on the activity of DNL in WAT. The "healthy adipocytes" phenotype can be induced in WAT of obese mice in response to various stimuli including dietary omega-3 PUFA, especially when combined with moderate calorie restriction, and possibly also with other life style (e.g. physical activity) or pharmacological (e.g. thiazolidinediones) interventions. While omega-3 PUFA could exert beneficial systemic effects by improving immunometabolism of WAT without a concomitant induction of BAT, it is currently not clear whether the metabolic effects of the combined intervention using omega-3 PUFA and calorie restriction or thiazolidinediones depend also on the activation of BAT function and/or the induction of brite/beige adipocytes in WAT. It remains to be established why omega-3 PUFA intervention in type 2 diabetic subjects does not improve insulin sensitivity and glucose homeostasis despite inducing various anti-inflammatory mediators in WAT, including the recently discovered docosahexaenoyl esters of hydroxy linoleic acid, the lipokines from the FAHFA family, as well as several endocannabinoid-related anti-inflammatory lipids. To answer the question whether and to which extent omega-3 PUFA supplementation could promote the formation of "healthy adipocytes" in WAT of human subjects, namely in the obese insulin-resistant patients, represents a challenging task that is of great importance for the treatment of some serious non-communicable diseases.