Triglyceride Storage Research Articles

Hypoxia-Inducible Lipid Droplet-Associated Interacts with DGAT1 to Promote Lipid Storage in Hepatocytes

Lipid droplets (LD) are dynamic organelles that can expand and shrink, driven by fluctuations in the rate of triglyceride synthesis and degradation. Triglyceride synthesis, storage in LD, and degradation are governed by a complex set of LD-associated proteins. One of these LD-associated proteins, hypoxia-inducible lipid droplet-associated (HILPDA), was found to impair LD breakdown by inhibiting adipose triglyceride lipase. Here we characterized the physiological role and mechanism of action of HILPDA in hepatocytes. Expression of HILPDA was induced by fatty acids in several hepatoma cell lines. Fluorescence microscopy showed that HILPDA partly colocalizes with LD and with the endoplasmic reticulum, is especially abundant in perinuclear areas, and mainly associates with newly added fatty acids. Real-time fluorescence live-cell imaging revealed that HILPDA preferentially localizes to LD that are being remodelled. Deficiency of HILPDA in mouse precision-cut liver slices and primary hepatocytes reduced lipid storage and accumulation of fluorescently-labelled fatty acids in LD, respectively, which was independent of adipose triglyceride lipase. Confocal microscopy and Forster resonance energy transfer-fluorescence lifetime imaging microscopy analysis indicated that HILPDA colocalizes and physically interacts with DGAT1. In human hepatoma HepG2 cells, HILPDA overexpression increased lipid storage concomitant with an increase in DGAT activity and DGAT1 protein levels. Finally, hepatocyte-specific deficiency of HILPDA in mice modestly but significantly reduced hepatic triglyceride and plasma alanine aminotransferase levels in mice with non-alcoholic fatty liver disease. Overall, our data indicate that HILPDA physically interacts with DGAT1 and increases DGAT activity and DGAT1 protein levels. These findings suggest a novel mechanism in hepatocytes that links elevated fatty acid levels to stimulation of triglyceride synthesis and storage.

Sex-specific metabolic responses to 6 hours of fasting during the active phase in young mice.

Night time/active phase food restriction for 6 h impaired glucose intolerance in young male and female mice. Females displayed increased capacity for lipogenesis and triglyceride storage in response to a short daily fast. Females had lower fasting insulin levels and an increased potential for utilizing fat for energy through β-oxidation compared to males. The need for the inclusion of both sexes, and the treatment of sex as an independent variable, is emphasized within the context of this fasting regime. There is growing interest in understanding the mechanistic significance and benefits of fasting physiology in combating obesity. Increasing the fasting phase of a normal day can promote restoration and repair mechanisms that occur during the post-absorptive period. Most studies exploring the effect of restricting food access on mitigating obesity have done so with a large bias towards the use of male mice. Here, we disentangle the roles of sex, food intake and food withdrawal in the response to a short-term daily fasting intervention, in which food was removed for 6h in the dark/active phase of young, 8-week-old mice. We showed that the removal of food during the dark phase impaired glucose tolerance in males and females, possibly due to the circadian disruption induced by this feeding protocol. Although both sexes demonstrated similar patterns of food intake, body composition and various metabolic markers, there were clear sex differences in the magnitude and extent of these responses. While females displayed enhanced capacity for lipogenesis and triglyceride storage, they also had low fasting insulin levels and an increased potential for utilizing available energy sources such as fat for energy through β-oxidation. Our results highlight the intrinsic biological and metabolic disparities between male and female mice, emphasizing the growing need for the inclusion of both sexes in scientific research. Furthermore, our results illustrate sex-specific metabolic pathways that regulate lipogenesis, obesity and overall metabolic health.

The immune system of adipose tissue: obesity-associated inflammation

Adipose tissue is an important endocrine organ. Via its secretion products, it cross-talks with other organs of the body and communicates the filling state of its triglyceride stores. Obesity is characterized by the excessive accumulation of body fat and leads to the infiltration and accumulation of immune cells in white adipose tissue. In this review article we introduce the various immune cell populations of adipose tissue and discuss their local and systemic influence.

Ecklonia stolonifera Extract Suppresses Lipid Accumulation by Promoting Lipolysis and Adipose Browning in High-Fat Diet-Induced Obese Male Mice.

Obesity develops due to an energy imbalance and manifests as the storage of excess triglyceride (TG) in white adipose tissue (WAT). Recent studies have determined that edible natural materials can reduce lipid accumulation and promote browning in WAT. We aimed to determine whether Ecklonia stolonifera extract (ESE) would increase the energy expenditure in high-fat diet (HFD)-induced obese mice and 3T3-L1 cells by upregulating lipolysis and browning. ESE is an edible brown marine alga that belongs to the family Laminariaceae and contains dieckol, a phlorotannin. We report that ESE inhibits body mass gain by regulating the expression of proteins involved in adipogenesis and lipogenesis. In addition, ESE activates protein kinase A (PKA) and increases the expression of lipolytic enzymes including adipose triglyceride lipase (ATGL), phosphorylated hormone-sensitive lipase (p-HSL), and monoacylglycerol lipase (MGL) and also thermogenic genes, such as carnitine palmitoyltransferase 1 (CPT1), PR domain-containing 16 (PRDM16), and uncoupling protein 1 (UCP1). These findings indicate that ESE may represent a promising natural means of preventing obesity and obesity-related metabolic diseases.

Weight Cycling Creates an Obesogenic Memory in Adipose Tissue Which Exacerbates the Inflammatory Response to Obesity

The obesity pandemic has continued to grow over the past few years, with over 44% of the adult world population estimated to be overweight. Energy expenditure through physical activity and dieting promotes weight loss which can lead to beneficial adaptations that promote healthy metabolism. However, few patients successfully manage to include physical activity in their daily routine and tend to weight cycle. The purpose of this study was to evaluate the inflammatory status of mice undergoing weight cycling. Male C57BL/6 mice were randomized into four groups: low fat diet for 32 weeks (LFD) (n=10), high fat diet for 32 weeks (HFD) (n=10), low fat diet for 28 weeks then changed to high fat for 4 weeks (LFD‐>H) (n=10), high fat diet for 21 weeks then changed to low fat for 7 weeks and then changed back to high fat for 4 weeks (HFD‐>L‐>H) (n=10). LFD‐>H and HFD‐>L‐>H mice did not significantly differ in body weight, body fat weight, or body fat percentage, but were significantly higher than LFD mice (p<0.05) while remaining lower than HFD mice (p<0.05) at the conclusion of the study. We measured the average adipocyte size of the epididymal fat pad and found that HFD‐>L‐>H mice had smaller adipocytes compared to HFD and LFD‐>H mice which both had significantly larger adipocytes (p<0.05) compared to LFD. Frequency analysis of adipocyte size revealed that LFD and HFD‐>L‐>H mice had significantly more small adipocytes (p<0.05) compared to HFD and LFD‐H mice. TNFa and IFNg were significantly higher (p<0.05) in the epididymal fat pad of HFD‐>L‐>H mice compared to LFD and LFD‐>H mice. However, MCP1 was significantly lower (p<0.05) in HFD‐>L‐>H mice compared to LFD‐>H. These trends in cytokines were complemented by more M1‐type macrophages (p<0.05) and cytotoxic T‐cells (p<0.05) in the epididymal fat as indicated by ITGAX and CD8a gene expression, respectively. Interestingly, there was no difference in total macrophages between LFD‐>H and HFD‐>L‐>H mice as indicated by EMR1 expression. Liver histopathological analysis revealed HFD‐>L‐>H mice had greater NASH (p<0.05) and NAS (p<0.05) scores compared to LFD controls, whereas LFD‐>H mice did not show any differences compared to LFD controls. Liver protein analysis showed increased total STAT3 (p<0.05) and NF‐kB (p<0.05) in HFD‐>L‐>H compared to LFD controls. Further, p‐AMPK (T172) was significantly increased (p<0.05) in all groups compared to LFD controls indicating metabolic stress was present in the livers, however there was no difference between LFD‐>H and HFD‐>L‐>H mice. Taken together, we have shown that weight cycling can lead to aberrations in the storage of triglycerides when challenged with an increased caloric intake. This is further supported by an increase in M1 type pro‐inflammatory macrophages in the epididymal fat tissue in weight cycling mice which is likely contributing to the observed obesogenic memory phenotype.

Ablation of uncoupling protein 1 causes opposing changes of glucose uptake in brown and brite fat compatible with regulation of Glut 4 gene expression

BackgroundRecruitment and activation of uncoupling protein 1 – dependent thermogenesis in brown and brite fat is a candidate mechanism to promote negative energy balance and improve systemic glucose homeostasis. Non‐shivering thermogenesis mediated by UCP1 is mainly sustained by fatty acid oxidation and to lesser extent by glucose. Glucose supply, however, is essential to run serial and parallel metabolic pathways involved in thermogenesis, including glycolysis, glyceroneogenesis, anabolic bolstering of the citric acid cycle and de novo lipogenesis. Norepinephrine release in the cold stimulates glucose uptake via GLUT1 to support thermogenesis, while insulin stimulates uptake via GLUT4 for the storage of glycogen and triglyceride. It is unclear, however, whether glucose uptake depends on the presence of UCP1.ObjectiveWe aimed to quantify the effect of UCP1 ablation on insulin sensitivity, glucose tolerance and glucose uptake in brown and brite adipose tissues of mice fed either low, intermediate or high fat diets.MethodsWe assessed insulin sensitivity and oral glucose tolerance, and measured 2‐deoxyglucose uptake in different brown and white fat depots of UCP1‐KO and WT mice (B6 and 129 background) housed at thermoneutral temperature. Mice were fed low, intermediate and high fat diets. Transcriptomes of interscapular brown fat and inguinal brite fat were sequenced (RNA‐SEQ) and subjected to bioinformatic analysis.Results and DiscussionIn UCP1‐KO mice fed intermediate and high fat diets, body weight trajectories and body fat mass were rather unchanged or decreased. They rather showed reduced metabolic efficiency when fed the high fat diet, thus challenging a role of UCP1‐dependent thermogenesis in diet‐induced obesity resistance. Oral glucose tolerance, when analyzed as incremental area under the curve, was robustly impaired in UCP1‐KO mice fed intermediate and high fat diets, whereas insulin sensitivity was unchanged. In WT mice, brown fat showed the highest mass‐specific glucose uptake, with total uptake in the interscapular brown fat depot attaining up to 70% of the amount of glucose uptake measured in liver. Glucose uptake in UCP1‐KO mice was reduced in different brown fat depots, irrespective of diet. In contrast, glucose uptake was increased in inguinal brite fat of UCP1‐KO mice fed low fat diet. This increase was attenuated in mice fed intermediate or high fat diets. These differential genotype effects on glucose uptake in brown and brite fat were strongly associated with corresponding changes in Glut4 expression. Our results demonstrate a role of UCP1 in post‐prandial glucose homeostasis, most likely due to the reduced uptake into brown fat. Increased glucose uptake in inguinal brite fat of UCP1‐KO further corroborates the recruitment of alternative UCP1‐independent thermogenic capacity. We conclude that UCP1 is a modulator of adipose tissue glucose uptake and systemic glucose homeostasis.Support or Funding InformationThis work was supported by the EU FP7 project DIABAT (HEALTH‐F2‐2011‐278373), the Deutsche Forschungsgemeinschaft (KL973/13‐1, NUTRIBRITE) and the Else Kröner‐Fresenius Stiftung (EKFS).

Pansteatitis in the Nile Crocodile: A Glimpse into the Pathophysiology using RNA‐Seq and bioinformatics

Concerted efforts to identify the pathogenesis and mechanism(s) involved in pansteatitis, that was attributed to the recent crocodile die off in the Kruger National Park, South Africa have been in the forefront of investigation in recent time. As part of the efforts, molecular characterization of healthy and pansteatitis adipose tissue was carried out by RNA sequencing (RNA‐Seq) using Next Generation Sequencing (NGS) and de novo assembly of the adipose transcriptome, followed by differential gene expression analysis.Healthy adipose tissue consisting of fifty samples was collected from the subcutaneous, visceral, intermuscular adipose tissues and the abdominal fat body of ten 4 years old juvenile crocodiles from a local crocodile farm in Pretoria, South Africa. Ten pansteatitis samples were collected from visceral and intermuscular adipose tissues of five crocodiles that were dying of pansteatitis.Seventy genes were differentially expressed in pansteatitis. They include genes coding for extracellular matrix (ECM) signaling ligands, inflammatory cytokines and tumour necrosis factor alpha (TNFα) receptors, fatty acid synthase and fatty acid binding proteins, peroxisome proliferator‐activated receptor gamma (PPARγ), nuclear factor and apoptosis signaling ligands, and mitogen activated protein kinase enzymes among others. Majority (88.6%) of the upregulated genes were found to be involved in hypoxia inducible pathways for activation of NFkβ and inflammation, apoptosis, Toll‐like receptor pathway and PPARγ. Bicaudal homologous 2 Drosophila gene (BICD2) associated with spinal and lower extremity muscle atrophy was also upregulated in pansteatitis while Sphingosine‐1‐phosphate phosphatase 2 (SGPP2) involved in Sphingosine‐1‐phosphate metabolism was downregulated. Futhermore, Doublesex –mab‐related transcription factor 1 (DMRT1) responsible for sex gonad development and germ cell differentiation was also downregulated.Thus, from the present study, based on differentially expressed genes in pansteatitis, affected Nile crocodiles might have died partly due to their inability to utilize stored triglycerides as a result of inflammation induced insulin resistance, leading to starvation in the midst of plenty. Affected animals may have also suffered muscular atrophy of the lower extremities and poor fertility.

Intestinal gluconeogenesis prevents obesity-linked liver steatosis and non-alcoholic fatty liver disease

ObjectiveHepatic steatosis accompanying obesity is a major health concern, since it may initiate non-alcoholic fatty liver disease (NAFLD) and associated complications like cirrhosis or cancer. Intestinal gluconeogenesis (IGN) is a...

Drosophila estrogen-related receptor directs a transcriptional switch that supports adult glycolysis and lipogenesis.

Metabolism and development must be closely coupled to meet the changing physiological needs of each stage in the life cycle. The molecular mechanisms that link these pathways, however, remain poorly understood. Here we show that the Drosophila estrogen-related receptor (dERR) directs a transcriptional switch in mid-pupae that promotes glucose oxidation and lipogenesis in young adults. dERR mutant adults are viable but display reduced locomotor activity, susceptibility to starvation, elevated glucose, and an almost complete lack of stored triglycerides. Molecular profiling by RNA-seq, ChIP-seq, and metabolomics revealed that glycolytic and pentose phosphate pathway genes are induced by dERR, and their reduced expression in mutants is accompanied by elevated glycolytic intermediates, reduced TCA cycle intermediates, and reduced levels of long chain fatty acids. Unexpectedly, we found that the central pathways of energy metabolism, including glycolysis, the tricarboxylic acid cycle, and electron transport chain, are coordinately induced at the transcriptional level in mid-pupae and maintained into adulthood, and this response is partially dependent on dERR, leading to the metabolic defects observed in mutants. Our data support the model that dERR contributes to a transcriptional switch during pupal development that establishes the metabolic state of the adult fly.

ATP7B knockout disturbs copper and lipid metabolism in Caco-2 cells.

Intestinal cells control delivery of lipids to the body by adsorption, storage and secretion. Copper (Cu) is an important trace element and has been shown to modulate lipid metabolism. Mutation of the liver Cu exporter ATP7B is the cause of Wilson disease and is associated with Cu accumulation in different tissues. To determine the relationship of Cu and lipid homeostasis in intestinal cells, a CRISPR/Cas9 knockout of ATP7B (KO) was introduced in Caco-2 cells. KO cells showed increased sensitivity to Cu, elevated intracellular Cu storage, and induction of genes regulating oxidative stress. Chylomicron structural protein ApoB48 was significantly downregulated in KO cells by Cu. Apolipoproteins ApoA1, ApoC3 and ApoE were constitutively induced by loss of ATP7B. Formation of small sized lipid droplets (LDs) was enhanced by Cu, whereas large sized LDs were reduced. Cu reduced triglyceride (TG) storage and secretion. Exposure of KO cells to oleic acid (OA) resulted in enhanced TG storage. The findings suggest that Cu represses intestinal TG lipogenesis, while loss of ATP7B results in OA-induced TG storage.

Exon 9-deleted CETP inhibits full length-CETP synthesis and promotes cellular triglyceride storage

Cholesteryl ester transfer protein (CETP) exists as full-length (FL) and exon 9 (E9)-deleted isoforms. The function of E9-deleted CETP is poorly understood. Here, we investigated the role of E9-deleted CETP in regulating the secretion of FL-CETP by cells and explored its possible role in intracellular lipid metabolism. CETP overexpression in cells that naturally express CETP confirmed that E9-deleted CETP is not secreted, and showed that cellular FL- and E9-deleted CETP form an isolatable complex. Coexpression of CETP isoforms lowered cellular levels of both proteins and impaired FL-CETP secretion. These effects were due to reduced synthesis of both isoforms; however, the predominate consequence of FL- and E9-deleted CETP coexpression is impaired FL-CETP synthesis. We reported previously that reducing both CETP isoforms or overexpressing FL-CETP impairs cellular triglyceride (TG) storage. To investigate this further, E9-deleted CETP was expressed in SW872 cells that naturally synthesize CETP and in mouse 3T3-L1 cells that do not. E9-deleted CETP overexpression stimulated SW872 triglyceride synthesis and increased stored TG 2-fold. Expression of E9-deleted CETP in mouse 3T3-L1 cells produced a similar lipid phenotype. In vitro, FL-CETP promotes the transfer of TG from ER-enriched membranes to lipid droplets. E9-deleted CETP also promoted this transfer, although less effectively, and it inhibited the transfer driven by FL-CETP. We conclude that FL- and E9-deleted CETP isoforms interact to mutually decrease their intracellular levels and impair FL-CETP secretion by reducing CETP biosynthesis. E9-deleted CETP, like FL-CETP, alters cellular TG metabolism and storage but in a contrary manner.

Circulating and tissue specific transcription of angiopoietin-like protein 4 in human Type 2 diabetes

AimsObesity is associated with adipose tissue (AT) dysfunction marked by cellular hypertrophy, inflammation, hypoxia and fibrosis. Angiopoietin-like protein 4 (ANGPTL4) inhibits lipoprotein lipase which regulates triglyceride storage. Recently, inhibition of ANGPTL4 has been suggested as potential treatment for type 2 diabetes. Here we evaluate ANGPTL4's role in diabetes and examine ANGPTL4 in relation to markers of AT dysfunction and fatty liver disease. Materials & methodsWe obtained a unique set of paired samples from subjects undergoing weight loss surgery including subcutaneous AT (SCAT), omental AT (OMAT), liver, thigh muscle biopsies and serum including a post-surgical SCAT biopsy after 9 months. ResultsSCAT ANGPTL4 expression and circulating protein levels were higher in people with diabetes and correlated with glucose levels and HOMA-IR but not BMI. At post-surgical follow up, SCAT ANGPTL4 declined in subjects with diabetes to levels of those without diabetes. ANGPTL4 expression correlated with HIF1A and inflammation (MCP-1, IL-6). ConclusionsWe found that SCAT ANGPTL4 was closely linked with the expression of ANGPTL4 in the liver and represented a good proxy for liver steatosis. We suggest the elevation of ANGPTL4 levels in diabetes and the association with inflammation and hypoxia is due to a compensatory mechanism to limit further AT dysfunction. A reduction of ANGPTL4 for the treatment of T2DM as previously suggested is thus unlikely to be of further benefit.

Transcriptome profiling reveals multiple pathways responsible for the beneficial metabolic effects of Smilax glabra flavonoids in mouse 3T3-L1 adipocytes

Smilax glabra Roxb. (SG) is a well-known traditional Chinese medicine that has been extensively used as both food and folk medicine in many countries. Although many beneficial health effects of SG and its primary components have been reported, their action on adipocyte function remains unknown. In the present study, we investigated the effects of the total flavonoids from Smilax glabra Roxb. (SGF) on lipid accumulation in mouse 3T3-L1 adipocytes and further elucidated its potential mechanism using RNA-Seq transcriptome technique. Our results showed that SGF exposure significantly decreased the lipid droplet size and the levels of cellular free fatty acids, while triglyceride accumulation was not affected by SGF. Transcriptome analysis revealed that SGF induced the expression of genes involved in triglyceride storage, fatty acid β-oxidation and mitochondrial biogenesis. Furthermore, we also observed an increased cellular ATP level and mitochondrial mass after SGF exposure, indicating that SGF enhanced mitochondrial function. The other relevant transcriptional changes appeared to be involved in AMPK/PGC-1α signaling, inflammatory response, as well as PI3K/AKT and calcium signaling pathways, which might contribute to the beneficial metabolic effects of SGF on adipocyte function. The results of Western blotting confirmed that SGF could increase the phosphorylation of AMPK while decrease the phosphorylation of AKT in adipocytes. Altogether, our results provided novel information about the molecular mechanism responsible for the effects of SGF on fat storage in adipocytes and highlights the potential metabolic benefits of SGF on human obesity and its related chronic diseases.

Proprotein convertase 7 (PCSK7) reduces apoA-V levels.

The locus of the human proprotein convertase subtilisin-kexin type-7 (PC7) gene (PCSK7) is on chromosome 11q23.3 close to the gene cluster APOA5/APOA4/APOC3/APOA1, a region implicated in the regulation of lipoprotein metabolism. A GWAS reported the association of PCSK7 SNPs with plasma triglyceride(TG), and exome sequencing of African Americans revealed the association of a low-frequency coding variant of PC7 (R504H; SNP rs142953140) with a ~30% TG reduction. Another PCSK7 SNP rs508487 is in linkage disequilibrium with a promoter variant of the liver-derived apolipoprotein A-V (apoA-V), an indirect activator of the lipoprotein lipase (LpL), and is associated with elevated TG levels. We thus hypothesized that PC7 regulates the levels/activity of apoA-V. Studies in the human hepatic cell line HuH7 revealed that wild-type (WT) PC7 and its endoplasmic reticulum (ER)-retained forms bind to and enhance the degradation of human apoA-V in acidic lysosomes in a nonenzymatic fashion. PC7-induced degradation of apoA-V is inhibited by bafilomycin A1 and the alkalinizing agents: chloroquine and NH4 Cl. Thus, the PC7-induced apoA-V degradation implicates an ER-lysosomal communication inhibited by bafilomycin A1. Invitro, the natural R504H mutant enhances PC7 Ser505 phosphorylation at the structurally exposed Ser-X-Glu507 motif recognized by the secretory kinase Fam20C. Co-expression of the phosphomimetic PC7-S505E with apoA-V resulted in lower degradation compared to WT, suggesting that Ser505 phosphorylation of PC7 lowers TG levels via reduced apoA-V degradation. In agreement, in Pcsk7-/- mice fed high-fat diet, plasma apoA-V levels and adipocyte LpL activity are increased, providing an invivo mechanistic link for a role of liver PC7 in enhanced TG storage in adipocytes.

The role of the heterogeneous nuclear ribonucleoprotein (hnRNP) Hrb27C in regulating lipid storage in the Drosophila fat body

The storage of excess nutrients as triglycerides is essential for all organisms to survive when food is scarce; however, the mechanisms by which triglycerides are stored are not completely understood. Genome-wide RNAi screens in Drosophila cells have identified genes involved in mRNA splicing that are important in the regulation of triglyceride storage. Our lab has identified a number of splicing factors important for regulating lipid metabolism; however, the full complement of splicing proteins involved in achieving metabolic homeostasis is unknown. Heterogeneous nuclear ribonucleoproteins (hnRNPs), RNA binding proteins that inhibit the splicing of introns by preventing the assembly of splicing complexes, have no established metabolic functions. To assess any metabolic functions of hnRNPs, we used the GAL4/UAS system to induce RNAi to six hnRNP’s: hnRNP-K, rumpelstiltskin (rump), smooth (sm), Hrb27C (also referred to as Hrp48), Hrb98DE, and Hrb87F in the Drosophila fat body. Decreasing the levels of hnRNP-K and rump resulted in a decrease in triglyceride storage, whereas decreasing the levels of sm, Hrb27C, and Hrb98DE resulted in an increase in triglyceride storage. The excess triglyceride phenotype in Hrb27C-RNAi flies resulted from both an increase in the number of fat body cells and the amount of fat stored per cell. In addition, both the splicing of the β-oxidation gene, CPT1, and the expression of the lipase brummer (bmm) was altered in flies with decreased Hrb27C, providing insight into the lipid storage phenotype in these flies. Together, these results suggest that the hnRNP family of splicing factors have varying metabolic functions and may act on specific metabolic genes to control their expression and processing.

A role for triglyceride lipase brummer in the regulation of sex differences in Drosophila fat storage and breakdown.

Triglycerides are the major form of stored fat in all animals. One important determinant of whole-body fat storage is whether an animal is male or female. Here, we use Drosophila, an established model for studies on triglyceride metabolism, to gain insight into the genes and physiological mechanisms that contribute to sex differences in fat storage. Our analysis of triglyceride storage and breakdown in both sexes identified a role for triglyceride lipase brummer (bmm) in the regulation of sex differences in triglyceride homeostasis. Normally, male flies have higher levels of bmm mRNA both under normal culture conditions and in response to starvation, a lipolytic stimulus. We find that loss of bmm largely eliminates the sex difference in triglyceride storage and abolishes the sex difference in triglyceride breakdown via strongly male-biased effects. Although we show that bmm function in the fat body affects whole-body triglyceride levels in both sexes, in males, we identify an additional role for bmm function in the somatic cells of the gonad and in neurons in the regulation of whole-body triglyceride homeostasis. Furthermore, we demonstrate that lipid droplets are normally present in both the somatic cells of the male gonad and in neurons, revealing a previously unrecognized role for bmm function, and possibly lipid droplets, in these cell types in the regulation of whole-body triglyceride homeostasis. Taken together, our data reveal a role for bmm function in the somatic cells of the gonad and in neurons in the regulation of male–female differences in fat storage and breakdown and identify bmm as a link between the regulation of triglyceride homeostasis and biological sex.

Comparative transcriptome analysis of adipose tissues from bactrian camel

The purpose of this study was to reveal the molecular mechanism that regulates fat metabolism in hump of Bactrian camel. The subcutaneous fat (SF), greater omentum (GOM) and hump fat (HF) of Bactrian camel were sequenced by RNA sequencing, and the differentially expressed genes of fat tissue in 3 different parts at transcriptome level were obtained by paired comparison. Genes related to fat metabolism were screened out, among which HF vs. GOM group had the largest number of different genes related to fat metabolism. Some genes such as SCD, FASN, ACACA, ADIPOQ, PLIN1, PLIN4, LPL and HSL were highly expressed in HF. These genes may play an important role in maintaining the energy homeostasis of Bactrian camels in the absence of food. Signaling pathway analysis revealed a number of pathways involved in fat metabolism including AMPK signaling pathway, PPAR signaling pathway, Adipocytokine signaling pathway, ECM-receptor interaction and regulation of lipolysis in adipocytes. These data suggests HF has a greater capacity to modulate the release and storage of triglycerides in adipocytes than GOM.

The regulation of triglyceride storage by ornithine decarboxylase (Odc1) in Drosophila

Polyamines are low molecular weight, organic cations that play a critical role in many major cellular processes including cell cycle regulation and apoptosis, cellular division, tissue proliferation, and cellular differentiation; however, the functions of polyamines in regulating the storage of metabolic fuels such as triglycerides and glycogen is poorly understood. To address this question, we focused on the Drosophila homolog of ornithine decarboxylase (Odc1), the first rate-limiting enzyme in the synthesis of polyamines. Mutants in Odc1 are lethal, but heterozygotes were viable to adulthood. Odc1 heterozygotes appeared larger than their genetic background control flies and consistent with this observation, weighed more than the controls. However, the increased weight was not due to increased food consumption as heterozygotes ate less than the controls. Interestingly, Odc1 heterozygous flies had augmented triglyceride storage, and this lipid phenotype was due to increased triglyceride storage per cell and an increase in the number of fat cells produced. Odc1 heterozygous flies also displayed increased expression of the lipid synthesis genes fatty acid synthase (FASN) and acetyl-CoA carboxylase (ACC), suggesting increased lipid synthesis was the cause of the augmented triglyceride phenotype. These results provide a link between the expression of Odc1 and triglyceride storage suggesting that the polyamine pathway plays a role in regulating lipid metabolism.

Saccharomyces boulardii Tht 500101 changes gut microbiota and ameliorates hyperglycaemia, dyslipidaemia, and liver inflammation in streptozotocin-diabetic mice.

Type 1 diabetes mellitus (T1DM) is a disorder resulting from chronic autoimmune destruction of insulin-producing pancreatic β-cells, lack of insulin production and hyperglycaemia. The aim of this study was to evaluate the hypothesis that streptozotocin-diabetic mice treated with Saccharomyces boulardii THT 500101 strain present improvement of glucose and triglycerides metabolism, reduction of liver inflammation concomitant with a beneficial impact in the gut microbiota profile. C57BL/6 male mice were randomly assigned into three groups: Control, Diabetes, Diabetes+Probiotic, and were euthanised 8 weeks after probiotic chronic administration. Mice submitted to treatment presented reduced glycemia in comparison with the diabetic group, which was correlated with an increase in C-peptide level and in hepatic glycogen content. Fat metabolism was significantly altered in streptozotocin-induced diabetic group, and S. boulardii treatment regulated it, leading to a decrease in serum triglycerides secretion, increase in hepatic triglycerides storage and modulation of inflammatory profile. The phenotypic changes seen from chronic S. boulardii treatment were found to be broadly associated with the changes in microbioma of diabetic animals, with increased proportion in Bacteroidetes, Firmicutes and Deferribacteres, and a decreased proportion of Proteobacteria and Verrucomicrobia phylum. Thus, the data presented here show up a novel potential therapeutic role of S. boulardii for the treatment and attenuation of diabetes-induced complications.

Long Term Ovariectomy-Induced Osteoporosis is Associated with High Stearoyl-CoA Desaturase Indexes in Rat Femur.

Osteoporosis is characterized by a bone loss associated to an increased bone marrow adiposity; however, it is still unclear what kind of lipids are involved. Therefore, the main purpose of this study was to see if there is any local bone lipid changes related to osteoporosis, by using the ovariectomy-induced osteoporosis (OVX) rat model. Female SD rats (operated at 6months of age for skeletal maturity) were divided in control SHAM and OVX groups (n = 6/group) and maintained for 9month post-surgery. Lipids were analyzed in two compartments of femoral diaphyses: bone marrow (BM) and mineralized tissue (MT), by chromatographic methods. As expected, osteoporotic femurs had a larger BM mass associated with a two-fold increase of lipid content. The MT had a similar lipid enrichment, indicating that adiposity affected the mineral part as well. The main lipids concerned were triglycerides, sphingomyelin, phosphatidylcholine and phosphatidylserine in BM, and triglycerides and cholesterol esters in MT. The increase of both energy-storage and membrane-associated lipids in BM suggested that cell number and/or size was enhanced to allow more triglyceride storage. Interestingly, in MT of osteoporotic femurs, sphingomyelin was decreased, suggesting that its catabolism could be linked to osteoporosis. In both femoral compartments, fatty acid profiles were enriched in 14:0 and 16:1, lowered in 18:0 and 20:4 n-6, and two-fold higher stearoyl-CoA desaturase indexes (16:1/16:0 and 18:1/18:0 ratios), suggesting an increased de novo lipogenesis in osteoporotic femurs. Thus, the present study is first to report local changes of individual lipids in rat osteoporotic femurs and suggests that osteoporosis is a pathologic condition associated with an enhanced de novo lipogenesis. Further studies will be needed to better understand the consequences of these lipid changes in osteoporotic bones.