Adipose triglyceride lipase and the lipolytic catabolism of cellular fat stores

Decoding the connection between lncRNA and obesity: Perspective from humans and Drosophila

Background

Obesity is a burgeoning global health problem with an escalating prevalence and severe implications for public health. New evidence indicates that long non-coding RNAs (lncRNAs) may play a pivotal role in regulating adipose tissue function and energy homeostasis across various species. However, the molecular mechanisms underlying obesity remain elusive.

Scope of review

This review discusses obesity and fat metabolism in general, highlighting the emerging importance of lncRNAs in modulating adipogenesis. It describes the regulatory networks, latest tools, techniques, and approaches to enhance our understanding of obesity and its lncRNA-mediated epigenetic regulation in humans and Drosophila.

Major conclusions

This review analyses large datasets of human and Drosophila lncRNAs from published databases and literature with experimental evidence supporting lncRNAs role in fat metabolism. It concludes that lncRNAs play a crucial role in obesity-related metabolism. Cross-species comparisons highlight the relevance of Drosophila findings to human obesity, emphasizing their potential role in adipose tissue biology. Furthermore, it discusses how recent technological advancements and multi-omics data integration enhance our capacity to characterize lncRNAs and their function. Additionally, this review briefly touches upon innovative methodologies like experimental evolution and advanced sequencing technologies for identifying novel genes and lncRNA regulators in Drosophila, which can potentially contribute to obesity research.

Nano-drug delivery systems (NDDS) in metabolic dysfunction-associated steatotic liver disease (MASLD): current status, prospects and challenges

About one-third of the global population suffers from metabolic dysfunction-associated steatotic liver disease (MASLD), but specific treatments for MASLD have long been lacking, primarily due to the unclear etiology of the disease. In addition to lifestyle modifications and weight loss surgery, pharmacotherapy is the most common treatment among MASLD patients, and these drugs typically target the pathogenic factors of MASLD. However, bioavailability, efficacy, and side effects all limit the maximum therapeutic potential of the drugs. With the development of nanomedicine, recent years have seen attempts to combine MASLD pharmacotherapy with nanomaterials, such as liposomes, polymer nanoparticles, micelles, and cocrystals, which effectively improves the water solubility and targeting of the drugs, thereby enhancing therapeutic efficacy and reducing toxic side effects, offering new perspectives and futures for the treatment of MASLD.

Evaluation of carcass traits, meat quality and the expression of lipid metabolism-related genes in different slaughter ages and muscles of Taihang black goats

OBJECTIVE

This study was conducted to investigate the effect of slaughter age on carcass traits, meat quality, and the relative mRNA levels of lipid metabolism-related genes in different muscles of Taihang black goats.

METHODS

In this study, the triceps brachii (TB), longissimus dorsi (LD) and gluteus (GL) muscles of 15 grazing Taihang black goats slaughtered at the age of 2, 3, and 4 (designated as 2-year-old, 3-year-old, and 4-year-old, respectively) were collected. The differences in carcass shape, meat quality, amino acid composition and lipid metabolism gene expression among Taihang black goats of different ages and from different plant parts were compared.

RESULTS

Compared with goats at other ages, goats slaughtered at the age of 4 had greater live and carcass weights, meat weights, bone weights and skin areas (p<0.05). LD in the 4-years-old had the lowest cooking loss and moisture content. The crude protein content in the LD of 2-year-old was significantly greater than that in the other age group, and at the age of 2, the LD had the highest crude protein content than TB and GL. The highest fat content was in LD, followed by TB, for goats slaughtered at the age of 4. Eight out of 9 essential amino acids had higher content in the TB compared with other muscles, regardless of age. The total essential amino acid content was highest in the 4-year-old and lowest in the GL muscle at the age of 3. The sterol regulatory element-binding protein-1c (SREBP-1c) and adipose triglyceride lipase (ATGL) genes were significantly more abundant in the TB muscle than in the other muscles for goats slaughtered at the age of 2. At the age of 4, the ATGL and peroxisome proliferator-activated receptor γ (PPARγ) genes were significantly more abundant in the GL than in the LD, while the fatty acid synthase (FAS) genes were significantly less abundant in the GL than in the other muscles. Similarly, compared with those in goats of other ages, the relative mRNA expression levels of the FAS and heart-type fatty acid binding protein (H-FABP) genes in goats slaughtered at the age of 4 were the highest, and the relative mRNA expression of the PPARγ gene was the lowest (p<0.05). The relative mRNA expression of the H-FABP and FAS genes was positively correlated with the intramuscular fat (IMF) content, while the relative mRNA expression levels of the PPARγ and ATGL genes was negatively correlated with the IMF content.

CONCLUSION

Overall, a better nutritional value was obtained for TB from 4-year-old goats, in which the total essential amino acid and fat contents were greater than those of other muscles. The comprehensive action of lipid metabolism genes was consistent with that of the IMF content, among which the FAS, H-FABP, PPARγ, and ATGL genes had positive and negative effects on the process of IMF deposition in Taihang black goats.

Untargeted metabolomic insights into plastisphere communities in European rivers

Every year, rivers introduce a staggering amount of hundred kilotons of plastic into the Oceans. This plastic is inhabited by microorganisms known as the plastisphere, which can be transferred between different ecosystems through the transport of microplastics. Here, we simulated the microbial colonization of polyethylene-based plastic pellets that are classically used to manufacture large-scale plastic products. The pellets were immersed for 1 month in four to five sampling stations along the river-to-sea continuum of nine of the major European rivers. This study presents the first untargeted metabolomics analysis of the plastisphere, by using ultra high-performance liquid chromatography coupled to high-resolution mass spectrometry (UHPLC-HRMS). The plastisphere metabolomes were similar in the Rhine and Rhone rivers, while being different from the Tiber and Loire rivers, which showed greater similarity to the Thames and Seine rivers. Interestingly, we found a clear distinction between plastisphere metabolomes from freshwater and marine water in most of the river-to-sea continuum, thus suggesting a complete segregation in plastisphere metabolites that is not consistent with a major transfer of microorganisms between the two contrasted ecosystems. Putative annotations of 189 discriminating metabolites suggested that lipid metabolism was significantly modulated. These results enlightened the relevance of using environmental metabolomic as complementary analysis to the current OMICs analysis.

Exosomal miRNA 16-5p/29a-3p from pancreatic cancer induce adipose atrophy by inhibiting adipogenesis and promoting lipolysis

Over 80% of the patients with pancreatic ductal adenocarcinoma (PDAC) have cachexia/wasting syndrome. Cachexia is associated with reduced survival, decreased quality of life, and higher metastasis rates. Here, we demonstrate that fat loss is the earliest feature of PDAC-exosome-induced cachexia. MicroRNA sequencing of exosomal components from normal and cancer-derived exosomes revealed enrichment of miR-16-5p, miR-21-5p, miR-29a-3p, and miR-125b-5p in serum exosomes of mice harboring PDAC and patients with PDAC. Further, miR-16-5p and miR-29a-3p inhibited adipogenesis through decreasing Erlin2 and Cmpk1 expression which downregulates C/EBPβ and PPARγ. Synergistically, miR-29a-3p promotes lipolysis through increasing ATGL expression by suppressing MCT1 expression. Furthermore, PDAC-exosomes deprived of miR-16-5p and miR-29a-3p fail to induce fat loss. Hence, miR-16-5p and miR-29a-3p exosomal miRs are essential for PDAC-induced fat loss. Thus, we unravel that PDAC induces adipose atrophy via exosomal miRs. This knowledge may provide new diagnostic and therapeutic strategies for PDAC-induced cachexia.

Potential of Chlorogenic Acid in the Management of Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD): Animal Studies and Clinical Trials-A Narrative Review

Chlorogenic acid (CGA) is a natural polyphenol found in coffee, tea, vegetables, and fruits. It exhibits strong antioxidant activity and possesses several other biological properties, including anti-inflammatory effects, antimicrobial activity, and insulin-sensitizing properties. Moreover, it may improve lipid and glucose metabolism. This review summarizes the available information on the therapeutic effect of CGA in metabolic dysfunction-associated steatotic liver disease (MASLD). As the literature search engine, the browsers in the PubMed, Scopus, Web of Science databases, and ClinicalTrials.gov register were used. Animal trials and clinical studies suggest that CGA has promising therapeutic potential in treating MASLD and hepatic steatosis. Its mechanisms of action include antioxidant, anti-inflammatory, and anti-apoptotic effects via the activation of the Nrf2 signaling pathway and the inhibition of the TLR4/NF-κB signaling cascade. Furthermore, the alleviation of liver disease by CGA also involves other important molecules such as AMPK and important physiological processes such as the intestinal barrier and gut microbiota. Nevertheless, the specific target cell and key molecule to which CGA is directed remain unidentified and require further study.

PNPLA3 is a triglyceride lipase that mobilizes polyunsaturated fatty acids to facilitate hepatic secretion of large-sized very low-density lipoprotein

The I148M variant of PNPLA3 is closely associated with hepatic steatosis. Recent evidence indicates that the I148M mutant functions as an inhibitor of PNPLA2/ATGL-mediated lipolysis, leaving the role of wild-type PNPLA3 undefined. Despite showing a triglyceride hydrolase activity in vitro, PNPLA3 has yet to be established as a lipase in vivo. Here, we show that PNPLA3 preferentially hydrolyzes polyunsaturated triglycerides, mobilizing polyunsaturated fatty acids for phospholipid desaturation and enhancing hepatic secretion of triglyceride-rich lipoproteins. Under lipogenic conditions, mice with liver-specific knockout or acute knockdown of PNPLA3 exhibit aggravated liver steatosis and reduced plasma VLDL-triglyceride levels. Similarly, I148M-knockin mice show decreased hepatic triglyceride secretion during lipogenic stimulation. Our results highlight a specific context whereby the wild-type PNPLA3 facilitates the balance between hepatic triglyceride storage and secretion, and suggest the potential contribution of a loss-of-function by the I148M variant to the development of fatty liver disease in humans.

Perilipins: A family of five fat-droplet storing proteins that play a significant role in fat homeostasis

Lipid droplets are organelles with unique spherical structures. They consist of a hydrophobic neutral lipid core that varies depending on the cell type and tissue. These droplets are surrounded by phospholipid monolayers, along with heterogeneous proteins responsible for neutral lipid synthesis and metabolism. Additionally, there are specialized lipid droplet-associated surface proteins. Recent evidence suggests that proteins from the perilipin family (PLIN) are associated with the surface of lipid droplets and are involved in their formation. These proteins have specific roles in hepatic lipid droplet metabolism, such as protecting the lipid droplets from lipase action and maintaining a balance between lipid storage and utilization in specific cells. Metabolic dysfunction-associated steatotic liver disease (MASLD) is characterized by the accumulation of lipid droplets in more than 5% of the hepatocytes. This accumulation can progress into metabolic dysfunction-associated steatohepatitis, fibrosis, cirrhosis, and hepatocellular carcinoma. The accumulation of hepatic lipid droplets in the liver is associated with the progression of MASLD and other diseases such as sarcopenic obesity. Therefore, it is crucial to understand the role of perilipins in this accumulation, as these proteins are key targets for developing novel therapeutic strategies. This comprehensive review aims to summarize the structure and characteristics of PLIN proteins, as well as their pathogenic role in the development of hepatic steatosis and fatty liver diseases.

Codonopsis pilosula-derived glycopeptide dCP1 promotes the polarization of tumor-associated macrophage from M2-like to M1 phenotype

The majority of the immune cell population in the tumor microenvironment (TME) consists of tumor-associated macrophages (TAM), which are the main players in coordinating tumor-associated inflammation. TAM has a high plasticity and is divided into two main phenotypes, pro-inflammatory M1 type and anti-inflammatory M2 type, with tumor-suppressive and tumor-promoting functions, respectively. Considering the beneficial effects of M1 macrophages for anti-tumor and the high plasticity of macrophages, the conversion of M2 TAM to M1 TAM is feasible and positive for tumor treatment. This study sought to evaluate whether the glycopeptide derived from simulated digested Codonopsis pilosula extracts could regulate the polarization of M2-like TAM toward the M1 phenotype and the potential regulatory mechanisms. The results showed that after glycopeptide dCP1 treatment, the mRNA relative expression levels of some M2 phenotype marker genes in M2-like TAM in simulated TME were reduced, and the relative expression levels of M1 phenotype marker genes and inflammatory factor genes were increased. Analysis of RNA-Seq of M2-like TAM after glycopeptide dCP1 intervention showed that the gene sets such as glycolysis, which is associated with macrophage polarization in the M1 phenotype, were significantly up-regulated, whereas those of gene sets such as IL-6-JAK-STAT3 pathway, which is associated with polarization in the M2 phenotype, were significantly down-regulated. Moreover, PCA analysis and Pearson's correlation also indicated that M2-like TAM polarized toward the M1 phenotype at the transcriptional level after treatment with the glycopeptide dCP1. Lipid metabolomics was used to further explore the efficacy of the glycopeptide dCP1 in regulating the polarization of M2-like TAM to the M1 phenotype. It was found that the lipid metabolite profiles in dCP1-treated M2-like TAM showed M1 phenotype macrophage lipid metabolism profiles compared with blank M2-like TAM. Analysis of the key differential lipid metabolites revealed that the interconversion between phosphatidylcholine (PC) and diacylglycerol (DG) metabolites may be the central reaction of the glycopeptide dCP1 in regulating the conversion of M2-like TAM to the M1 phenotype. The above results suggest that the glycopeptide dCP1 has the efficacy to regulate the polarization of M2-like TAM to M1 phenotype in simulated TME.

Adipose tissue in cortisol excess: What Cushing's syndrome can teach us?

Endogenous Cushing's syndrome (CS) is a rare condition due to prolonged exposure to elevated circulating cortisol levels that features its typical phenotype characterised by moon face, proximal myopathy, easy bruising, hirsutism in females and a centripetal distribution of body fat. Given the direct and indirect effects of hypercortisolism, CS is a severe disease burdened by increased cardio-metabolic morbidity and mortality in which visceral adiposity plays a leading role. Although not commonly found in clinical setting, endogenous CS is definitely underestimated leading to delayed diagnosis with consequent increased rate of complications and reduced likelihood of their reversal after disease control. Most of all, CS is a unique model for systemic impairment induced by exogenous glucocorticoid therapy that is commonly prescribed for a number of chronic conditions in a relevant proportion of the worldwide population. In this review we aim to summarise on one side, the mechanisms behind visceral adiposity and lipid metabolism impairment in CS during active disease and after remission and on the other explore the potential role of cortisol in promoting adipose tissue accumulation.

Human recombinant relaxin-2 (serelaxin) regulates the proteome, lipidome, lipid metabolism and inflammatory profile of rat visceral adipose tissue

Recombinant human relaxin-2 (serelaxin) has been widely proven as a novel drug with myriad effects at different cardiovascular levels, which support its potential therapeutic efficacy in several cardiovascular diseases (CVD). Considering these effects, together with the influence of relaxin-2 on adipocyte physiology and adipokine secretion, and the connection between visceral adipose tissue (VAT) dysfunction and the development of CVD, we could hypothesize that relaxin-2 may regulate VAT metabolism. Our objective was to evaluate the impact of a 2-week serelaxin treatment on the proteome and lipidome of VAT from Sprague-Dawley rats. We found that serelaxin increased 1 polyunsaturated fatty acid and 6 lysophosphatidylcholines and decreased 4 triglycerides in VAT employing ultra-high performance liquid chromatography-mass spectrometry (UHPLC-MS) based platforms, and that regulates 47 phosphoproteins using SWATH/MS analysis. Through RT-PCR, we found that serelaxin treatment also caused an effect on VAT lipolysis through an increase in the mRNA expression of hormone-sensitive lipase (HSL) and a decrease in the expression of adipose triglyceride lipase (ATGL), together with a reduction in the VAT expression of the fatty acid transporter cluster of differentiation 36 (Cd36). Serelaxin also caused an anti-inflammatory effect in VAT by the decrease in the mRNA expression of tumor necrosis factor α (TNFα), interleukin-1β (IL-1β), chemerin, and its receptor. In conclusion, our results highlight the regulatory role of serelaxin in the VAT proteome and lipidome, lipolytic function, and inflammatory profile, suggesting the implication of several mechanisms supporting the potential benefit of serelaxin for the prevention of obesity and metabolic disorders.

Futile lipid cycling: from biochemistry to physiology

In the healthy state, the fat stored in our body isn't just inert. Rather, it is dynamically mobilized to maintain an adequate concentration of fatty acids (FAs) in our bloodstream. Our body tends to produce excess FAs to ensure that the FA availability is not limiting. The surplus FAs are actively re-esterified into glycerides, initiating a cycle of breakdown and resynthesis of glycerides. This cycle consumes energy without generating a new product and is commonly referred to as the 'futile lipid cycle' or the glyceride/FA cycle. Contrary to the notion that it's a wasteful process, it turns out this cycle is crucial for systemic metabolic homeostasis. It acts as a control point in intra-adipocyte and inter-organ cross-talk, a metabolic rheostat, an energy sensor and a lipid diversifying mechanism. In this Review, we discuss the metabolic regulation and physiological implications of the glyceride/FA cycle and its mechanistic underpinnings.

Lacticaseibacillus rhamnosus HF01 fermented yogurt alleviated high-fat diet-induced obesity and hepatic steatosis via the gut microbiota-butyric acid-hepatic lipid metabolism axis

The objective of this study was to investigate the anti-obesity effects and underlying mechanism of Lacticaseibacillus rhamnosus HF01 fermented yogurt (HF01-Y). Herein, obesity was induced in mice through a high-fat diet and the changes in the gut microbiota were evaluated using 16S rRNA gene sequencing, combined with the expression levels of the liver AMPK signaling pathway to analyze the potential relationship between HF01-Y-mediated gut microbiota and obesity. The results showed that supplementation with HF01-Y improved obesity-related phenotypes in mice, including reduced body weight, improved serum lipid profiles, and decreased hepatic lipid droplet formation. In addition, HF01-Y altered the composition of the gut microbiota in obese mice, significantly upregulated norank_f__Muribaculaceae, unclassified_c__Clostridia, Blautia, unclassified_o__Bacteroidales, and Rikenellaceae_RC9_gut_group, while downregulating unclassified_f__Desulfovibrionaceae, Colidextribacter, and unclassified_f__Oscillospiraceae. These alterations led to an increase of the cecum butyric acid content, which in turn indirectly promoted the activation of the AMPK signaling pathway, subsequently, inhibited fat synthesis, and promoted fatty acid oxidation related gene expression. Therefore, HF01-Y was likely to alleviate hepatic fat and relieve obesity by modulating the gut microbiota-butyric acid-hepatic lipid metabolism axis, ultimately promoting host health.

All-trans retinoic acid induces lipophagy through the activation of the AMPK-Beclin1 signaling pathway and reduces Rubicon expression in adipocytes

Lipophagy is defined as a lipolysis pathway that degrades lipid droplet (LD) via autophagy. All-trans retinoic acid (atRA), a metabolite of vitamin A, stimulates lipolysis through hormone-sensitive lipase and β-oxidation. However, the regulation of lipolysis by atRA-induced autophagy in adipocytes remains unclear. In this study, we investigated the effect of atRA on autophagy in epididymal fat of mice and the molecular mechanisms of autophagy in 3T3-L1 adipocytes. Western blotting showed that atRA decreased the expression of p62, a cargo receptor for autophagic degradation, and increased the expression of the lipidated LC3B (LC3B-II), an autophagy marker, in epididymal fat. Next, we confirmed that atRA increased autophagic flux in differentiated 3T3-L1 cells using the GFP-LC3-RFP-LC3ΔG probe. Immunofluorescent staining revealed that the colocalization of LC3B with perilipin increased in differentiated 3T3-L1 cells treated with atRA. The knockdown of Atg5, an essential gene in autophagy induction, partly suppressed the atRA-induced release of non-esterified fatty acid (NEFA) from LDs in differentiated 3T3-L1 cells. atRA time-dependently elicited the phosphorylation of AMPK and Beclin1, autophagy-inducing factors, in mature 3T3-L1 adipocytes. Inversely, atRA decreased the protein expression of Rubicon, an autophagy repressor, in differentiated 3T3-L1 cells and epididymal fat. Interestingly, the expression of ALDH1A1, atRA-synthesizing enzymes, increased in epididymal fat with decreased protein expression of Rubicon in aged mice. These results suggest that atRA may partially induce lipolysis through lipophagy by activating the AMPK-Beclin1 signaling pathway in the adipocytes and increased atRA levels may contribute to decreased Rubicon expression in the epididymal fat of aged mice. (248/250 words).

Vascular ATGL-dependent lipolysis and the activation of cPLA2-PGI2 pathway protect against postprandial endothelial dysfunction

Adipose triglyceride lipase (ATGL) is involved in lipolysis and displays a detrimental pathophysiological role in cardio-metabolic diseases. However, the organo-protective effects of ATGL-induced lipolysis were also suggested. The aim of this work was to characterize the function of lipid droplets (LDs) and ATGL-induced lipolysis in the regulation of endothelial function. ATGL-dependent LDs hydrolysis and cytosolic phospholipase A2 (cPLA2)-derived eicosanoids production were studied in the aorta, endothelial and smooth muscle cells exposed to exogenous oleic acid (OA) or arachidonic acid (AA). Functional effects of ATGL-dependent lipolysis and subsequent activation of cPLA2/PGI2 pathway were also studied in vivo in relation to postprandial endothelial dysfunction.The formation of LDs was invariably associated with elevated production of endogenous AA-derived prostacyclin (PGI2). In the presence of the inhibitor of ATGL or the inhibitor of cytosolic phospholipase A2, the production of eicosanoids was reduced, with a concomitant increase in the number of LDs. OA administration impaired endothelial barrier integrity in vitro that was further impaired if OA was given together with ATGL inhibitor. Importantly, in vivo, olive oil induced postprandial endothelial dysfunction that was significantly deteriorated by ATGL inhibition, cPLA2 inhibition or by prostacyclin (IP) receptor blockade.In summary, vascular LDs formation induced by exogenous AA or OA was associated with ATGL- and cPLA2-dependent PGI2 production from endogenous AA. The inhibition of ATGL resulted in an impairment of endothelial barrier function in vitro. The inhibition of ATGL-cPLA2-PGI2 dependent pathway resulted in the deterioration of endothelial function upon exposure to olive oil in vivo. In conclusion, vascular ATGL-cPLA2-PGI2 dependent pathway activated by lipid overload and linked to LDs formation in endothelium and smooth muscle cells has a vasoprotective role by counterbalancing detrimental effects of lipid overload on endothelial function.

Exercise ameliorates lipid droplet metabolism disorder by the PLIN2-LIPA axis-mediated lipophagy in mouse model of non-alcoholic fatty liver disease

Excessive hepatic lipid droplets (LDs) accumulation-induced lipid metabolism disorder contributes to the development of non-alcoholic fatty liver disease (NAFLD). Exercise is a promising therapeutic strategy for NAFLD. However, the mechanism by which exercise ameliorates NAFLD through regulating the catabolism of hepatic LDs remains unclear. In the present study, we investigated the effect of perilipin2 (PLIN2)-lysosomal acid lipase (LIPA) axis mediating exercise-triggered lipophagy in a high-fat diet (HFD)-induced NAFLD mouse model. Our results showed that exercise could reduce HFD-induced hepatic LDs accumulation and change the expression of lipolysis-related enzymes. Moreover, exercise upregulated the expression of microtubule associated protein 1 light chain 3 (LC3) and autophagy-related proteins, and downregulated sequestosome 1 (P62) expression and promoted autophagosomes formation. Interestingly, exercise downregulated PLIN2 expression, upregulated LIPA expression, and increased the activity of hepatic LIPA and serum levels of LIPA in the NAFLD mouse model. Further mechanistic studies demonstrated that adenosine monophosphate-activated protein kinase (AMPK) activator-5-Aminoimidazole-4-carboxamide ribonucleoside (AICAr) treatment significantly increased mRNA levels and protein expression of LIPA and LC3II and decreased levels of PLIN2 and P62 in palmitic acid (PA)-treated HepG2 cells. PLIN2 silencing and LIPA overexpression notably increased the mRNA level and protein expression of LC3II and decreased the mRNA level and protein expression of p62, respectively. In summary, our findings reveal novel insights into the effect of exercise on improving lipid droplet metabolism disorder in NAFLD. Enhancing the PLIN2-LIPA axis-mediated lipophagy may be one of the key mechanisms involved in NAFLD alleviation by exercise.

Leveraging inter-individual transcriptional correlation structure to infer discrete signaling mechanisms across metabolic tissues

Inter-organ communication is a vital process to maintain physiologic homeostasis, and its dysregulation contributes to many human diseases. Given that circulating bioactive factors are stable in serum, occur naturally, and are easily assayed from blood, they present obvious focal molecules for therapeutic intervention and biomarker development. Recently, studies have shown that secreted proteins mediating inter-tissue signaling could be identified by 'brute force' surveys of all genes within RNA-sequencing measures across tissues within a population. Expanding on this intuition, we reasoned that parallel strategies could be used to understand how individual genes mediate signaling across metabolic tissues through correlative analyses of gene variation between individuals. Thus, comparison of quantitative levels of gene expression relationships between organs in a population could aid in understanding cross-organ signaling. Here, we surveyed gene-gene correlation structure across 18 metabolic tissues in 310 human individuals and 7 tissues in 103 diverse strains of mice fed a normal chow or high-fat/high-sucrose (HFHS) diet. Variation of genes such as FGF21, ADIPOQ, GCG, and IL6 showed enrichments which recapitulate experimental observations. Further, similar analyses were applied to explore both within-tissue signaling mechanisms (liver PCSK9) and genes encoding enzymes producing metabolites (adipose PNPLA2), where inter-individual correlation structure aligned with known roles for these critical metabolic pathways. Examination of sex hormone receptor correlations in mice highlighted the difference of tissue-specific variation in relationships with metabolic traits. We refer to this resource as gene-derived correlations across tissues (GD-CAT) where all tools and data are built into a web portal enabling users to perform these analyses without a single line of code (gdcat.org). This resource enables querying of any gene in any tissue to find correlated patterns of genes, cell types, pathways, and network architectures across metabolic organs.

Reactivity of metal-oxo clusters towards biomolecules: from discrete polyoxometalates to metal-organic frameworks

Metal-oxo clusters hold great potential in several fields such as catalysis, materials science, energy storage, medicine, and biotechnology. These nanoclusters of transition metals with oxygen-based ligands have also shown promising reactivity towards several classes of biomolecules, including proteins, nucleic acids, nucleotides, sugars, and lipids. This reactivity can be leveraged to address some of the most pressing challenges we face today, from fighting various diseases, such as cancer and viral infections, to the development of sustainable and environmentally friendly energy sources. For instance, metal-oxo clusters and related materials have been shown to be effective catalysts for biomass conversion into renewable fuels and platform chemicals. Furthermore, their reactivity towards biomolecules has also attracted interest in the development of inorganic drugs and bioanalytical tools. Additionally, the structural versatility of metal-oxo clusters allows for the efficiency and selectivity of the biomolecular reactions they promote to be readily tuned, thereby providing a pathway towards reaction optimization. The properties of the catalyst can also be improved through incorporation into solid supports or by linking metal-oxo clusters together to form Metal-Organic Frameworks (MOFs), which have been demonstrated to be powerful heterogeneous catalysts. Therefore, this review aims to provide a comprehensive and critical analysis of the state of the art on biomolecular transformations promoted by metal-oxo clusters and their applications, with a particular focus on structure-activity relationships.

Differential expression of brummer and levels of TAG in different developmental stages Aedes aegypti (Diptera: Culicidae), including fasted adults

Lipid storage in the form of triacylglycerol (TAG) is essential for insect life, as it enables flight, development, and reproduction. The activity of the lipase brummer (bmm) has been shown to be essential to insects' homeostasis. The objective of this study was to evaluate how bmm expression occurs in Aedes aegypti larvae and adults, and to observe TAG levels during fasting in adult females. The bmm sequence was identified in A. aegypti and exhibited a patatin-like phospholipase domain reinforced by the presence of a catalytic dyad with serine and aspartate residues, revealing a high degree of similarity with other organisms. Bmm expression was differentiated in the larvae and adult fat body (FB) following TAG reserve dynamics. Bmm was expressed three times in larval stages L3, L4, and pupae compared with L1 and L2, which could indicate its role in the maturation of these insects. In the postemergence (PE) and post-blood meal (PBM) FB of adult insects, bmm expression varied over several days. PE adults showed a pronounced bmm increase from the third day onward compared with those not subjected to fasting. This was accompanied by a decrease in TAG from the third day onward, suggesting the participation of bmm. Six hours after blood feeding, TAG levels increased in mosquitos reared in the absence of sucrose, suggesting lipid accumulation to guarantee reproduction. Bmm responded positively to fasting, followed by TAG mobilization in adult FB. During the previtellogenic period, bmm levels responded to low TAG levels, unlike the PBM period.

Association of Aquaporin 7 and 9 with Obesity and Fatty Liver in db/db Mice

Aquaporin (AQP) 7 and AQP9 are membrane channel proteins called aquaglyceroporins and are related to glucose and lipid metabolism. AQP7 is mainly expressed in white adipose tissue (WAT) and is involved in releasing glycerol into the bloodstream. AQP9 is the glycerol channel in the liver that supplies glycerol to the hepatic cells. In this study, we investigated the relationship between the expression of aquaglyceroporins and lifestyle-related diseases, such as obesity and fatty liver, using 22-week-old db/db mice. Body weight, WAT, and liver weight showed increases in db/db mice. The levels of liver lipids, plasma lipids, insulin, and leptin were also increased in db/db mice. Gene expression related to fatty acid and triglyceride synthesis in the liver was enhanced in db/db mice. In addition, gene and protein expression of gluconeogenesis-related enzymes was increased. Conversely, lipolysis-related gene expression in WAT was reduced. In the db/db mice, AQP9 expression in the liver was raised; however, AQP7 expression in WAT was reduced. These results suggest that in db/db mice, enhanced hepatic AQP9 expression increased the supply of glycerol to the liver and induced fatty liver and hyperglycemia. Additionally, reduced AQP7 expression in WAT is associated with excessive lipid accumulation in adipocytes. Aquaglyceroporins are essential molecules for glucose and lipid metabolism, and may be potential target molecules for the treatment of obesity and lifestyle-related diseases.

Overexpression of ATGL impairs lipid droplet accumulation by accelerating lipolysis in goat mammary epithelial cells

Adipose triglyceride lipase (ATGL) is the key enzyme for the degradation of triacylglycerols (TAGs). It functions in concert with other enzymes to mobilize TAG and supply fatty acids (FAs) for energy production. Dysregulated lipolysis leads to excess concentrations of circulating FAs, which may lead to destructive and lipotoxic effects to the organism. To understand the role of ATGL in mammary lipid metabolism, ATGL was overexpressed in goat mammary epithelial cells (GMECs) by using a recombinant adenovirus system. ATGL overexpression decreased lipid droplet (LD) accumulation and cellular TG content (p < 0.05) along with a decrease in the expression of the key enzyme that catalyzes the final step of TG synthesis (DGAT). Significant increases were observed in the expression of genes related to lipolysis (hormone-sensitive lipase [HSL]) and FA desaturation (SCD) by ATGL overexpression. Genes responsible for FA oxidation (PPARα), LD formation and secretion (ADRP and BTN1A1), and long-chain FA uptake (CD36) were all decreased by ATGL overexpression (p < 0.05). The primary products of TAG lipolysis, free FAs (FFAs), were notably increased in the ATGL-overexpressing cells. Taken together, our results demonstrated that ATGL activation impairs lipid formation partially through accelerating lipolysis in GMECs.

Lipid droplets modulate proteostasis, SQST-1/SQSTM1 dynamics, and lifespan in C. elegans

In several long-lived Caenorhabditis elegans strains, such as insulin/IGF-1 receptor daf-2 mutants, enhanced proteostatic mechanisms are accompanied by elevated intestinal lipid stores, but their role in longevity is unclear. Here, while determining the regulatory network of the selective autophagy receptor SQST-1/SQSTM1, we uncovered an important role for lipid droplets in proteostasis and longevity. Using genome-wide RNAi screening, we identified several SQST-1 modulators, including lipid droplets-associated and aggregation-prone proteins. Expansion of intestinal lipid droplets by silencing the conserved cytosolic triacylglycerol lipase gene atgl-1/ATGL enhanced autophagy, and extended lifespan. Notably, a substantial amount of ubiquitinated proteins were found on lipid droplets. Reducing lipid droplet levels exacerbated the proteostatic collapse when autophagy or proteasome function was compromised, and significantly reduced the lifespan of long-lived daf-2 animals. Altogether, our study uncovered a key role for lipid droplets in C. elegans as a proteostatic mediator that modulates ubiquitinated protein accumulation, facilitates autophagy, and promotes longevity.

Leveraging inter-individual transcriptional correlation structure to infer discrete signaling mechanisms across metabolic tissues

Inter-organ communication is a vital process to maintain physiologic homeostasis, and its dysregulation contributes to many human diseases. Beginning with the discovery of insulin over a century ago, characterization of molecules responsible for signal between tissues has required careful and elegant experimentation where these observations have been integral to deciphering physiology and disease. Given that circulating bioactive factors are stable in serum, occur naturally, and are easily assayed from blood, they present obvious focal molecules for therapeutic intervention and biomarker development. For example, physiologic dissection of the actions of soluble proteins such as proprotein convertase subtilisin/kexin type 9 (PCSK9) and glucagon-like peptide 1 (GLP1) have yielded among the most promising therapeutics to treat cardiovascular disease and obesity, respectively1–4. A major obstacle in the characterization of such soluble factors is that defining their tissues and pathways of action requires extensive experimental testing in cells and animal models. Recently, studies have shown that secreted proteins mediating inter-tissue signaling could be identified by “brute-force” surveys of all genes within RNA-sequencing measures across tissues within a population5–9. Expanding on this intuition, we reasoned that parallel strategies could be used to understand how individual genes mediate signaling across metabolic tissues through correlative analyses of gene variation between individuals. Thus, comparison of quantitative levels of gene expression relationships between organs in a population could aid in understanding cross-organ signaling. Here, we surveyed gene-gene correlation structure across 18 metabolic tissues in 310 human individuals and 7 tissues in 103 diverse strains of mice fed a normal chow or HFHS diet. Variation of genes such asFGF21, ADIPOQ, GCGandIL6showed enrichments which recapitulate experimental observations. Further, similar analyses were applied to explore both within-tissue signaling mechanisms (liverPCSK9) as well as genes encoding enzymes producing metabolites (adiposePNPLA2), where inter-individual correlation structure aligned with known roles for these critical metabolic pathways. Examination of sex hormone receptor correlations in mice highlighted the difference of tissue-specific variation in relationships with metabolic traits. We refer to this resource asGene-DerivedCorrelationsAcrossTissues (GD-CAT) where all tools and data are built into a web portal enabling users to perform these analyses without a single line of code (gdcat.org). This resource enables querying of any gene in any tissue to find correlated patterns of genes, cell types, pathways and network architectures across metabolic organs.

High Gamma-Aminobutyric Acid (GABA) Oolong Tea Alleviates High-Fat Diet-Induced Metabolic Disorders in Mice

Obesity and overweight are associated with an increasing risk of developing health conditions and chronic non-communicable diseases, including cardiovascular diseases, cancer, musculoskeletal problems, respiratory problems, and mental health, and its prevalence is rising. Diet is one of three primary lifestyle interventions. Many bioactive components in tea especially oolong tea, including flavonoids, gamma-aminobutyric acid (GABA), and caffeine were reported to show related effects in reducing the risk of obesity. However, the effects of GABA oolong tea extracts (OTEs) on high-fat diet (HFD)-induced obesity are still unclear. Therefore, this study aims to explore whether the intervention of GABA OTEs can prevent HFD-induced obesity and decipher its underlying mechanisms using male C57BL/6 J mice. The result indicated that GABA OTEs reduced leptin expression in epididymal adipose tissue and showed a protective effect on nonalcoholic fatty liver disease. It promoted thermogenesis-related protein of uncoupling protein-1 and peroxisome proliferator-activated receptor-gamma coactivator (PGC-1α), boosted lipid metabolism, and promoted fatty acid oxidation. It also reduced lipogenesis-related protein levels of sterol regulatory element binding protein, acetyl-CoA carboxylase, and fatty acid synthase and inhibited hepatic triglyceride (TG) levels. These data suggest that regular drinking of GABA oolong tea has the potential to reduce the risk of being overweight, preventing obesity development through thermogenesis, lipogenesis, and lipolysis.

Relationships among body weight, lipids and bone mass in elderly individuals with fractures: A case-control study

BACKGROUND

The prevalence of osteoporosis and low bone mass is steadily rising each year. Low body weight is commonly linked to diminished bone mass and serves as a robust predictor of osteoporosis. Nonetheless, the connection between body mass index (BMI), bone mineral density, and lipid profiles among the elderly remains elusive.

AIM

To examine the association between BMI and bone mass, explore the correlation between lipid profiles and bone mass, and delve into the interplay between lipid metabolism and bone health.

METHODS

The study included 520 patients aged ≥ 65 years (178 men and 342 women). Age, sex, weight, and height were recorded. Femoral neck bone mineral density and T scores were determined using a dual-energy X-ray absorptiometry scanner. Blood calcium (Ca), phosphorus (P), albumin (ALB), alkaline phosphatase (ALP), aspartate aminotransferase, alanine aminotransferase, triglyceride (TG), total cholesterol (TC), high-density lipoprotein (HDL) and low-density lipoprotein (LDL) levels were measured. Patients were classified by sex (male and female), age (65-79 years and ≥ 80 years), and T score (normal bone mineral density, osteopenia and osteoporosis).

RESULTS

Age, sex, BMI, and ALP and TG levels were independent risk factors for osteoporosis. For the 65-79- and ≥ 80-year-old groups, females presented lower T scores than males. Ca, P, ALB, ALP, TC, HDL and LDL levels were significantly different between men and women in the 65-79-year-old group. In addition, BMI and TG levels were significantly decreased in osteoporotic patients compared with patients with normal bone mass. TC levels declined in 65- to 79-year-old male and female osteoporosis patients. In the group of women aged ≥ 80 years, osteoporotic patients showed significantly increased ALP levels. Furthermore, we found positive correlations between BMI and TG levels in the male and female patient groups. However, we found no significant differences in ALB, Ca, P, HDL and LDL levels in osteoporotic patients compared to patients with normal bone mass.

CONCLUSION

Osteoporotic patients showed significantly decreased BMI and TG levels compared with those with normal bone mass. BMI showed positive correlations with TG levels in male and female patients. These results indicate correlations between BMI and bone mass and between lipid profiles and bone mass.

Substrate-Specific Function of PNPLA3 Facilitates Hepatic VLDL-Triglyceride Secretion During Stimulated Lipogenesis

The I148M variant of PNPLA3 is strongly linked to hepatic steatosis. Evidence suggests a gain-of-function role for the I148M mutant as an ATGL inhibitor, leaving the physiological relevance of wild-type PNPLA3 undefined. Here we show that PNPLA3 selectively degrades triglycerides (TGs) enriched in polyunsaturated fatty acids (PUFAs) independently of ATGL in cultured cells and mice. Lipidomics and metabolite tracing analyses demonstrated that PNPLA3 mobilizes PUFAs from intracellular TGs for phospholipid desaturation, supporting hepatic secretion of TG-rich lipoproteins. Consequently, mice with liver-specific knockout or acute knockdown of PNPLA3 both exhibited aggravated liver steatosis and concomitant decreases in plasma VLDL-TG, phenotypes that manifest only under lipogenic conditions. I148M-knockin mice similarly displayed impaired hepatic TG secretion during lipogenic stimulation. Our results highlight a specific context whereby PNPLA3 facilitates the balance between hepatic TG storage and secretion and suggest the potential contributions of I148M variant loss-of-function to the development of hepatic steatosis in humans.

Summary Statement

We define the physiological role of wild type PNPLA3 in maintaining hepatic VLDL-TG secretion.

Dingkun pill alleviates metabolic abnormalities in polycystic ovary syndrome through brown adipose tissue activation

BACKGROUND

Traditional Chinese medicine has been used for a long time to treat a variety of gynecological diseases. Among various traditional Chinese medicine, Dingkun Pill (DK) has been used for the treatment of female gynecological diseases. However, DK therapeutic effect on PCOS and the target tissue for its potential effect need to be explored. This study aims to explore the therapeutic effect of DK for PCOS in mice from three aspects: metabolism, endocrine and fertility, and determine whether the brown adipose tissue is the target organ to alleviate the PCOS phenotype.

METHODS

PCOS mouse model was constructed by subcutaneous injection of DHEA. The estrous cycle, ovulation, and pregnancy outcome was examined in mice. The level of hormone including the LH, FSH, estrogen and testosterone in the serum were measured by ELISA. Both the glucose sensitivity and insulin sensitivity were determined in mice with different treatment. The histomorphology and lipid contents in the brown adipose tissue were analyzed. RNA-Seq was conducted for the brown adipose tissue and different expression of critical metabolism marker genes was confirmed by real-time PCR.

RESULTS

The data showed that the fertility in PCOS mice with DK treatment was significantly increased, and the metabolic disorder was partially restored. Both the whiten of brown adipose tissue and reduced UCP1 expression induced by DHEA was rescued by the DK. The RNA-Seq data further demonstrated both the DHEA induced downregulation of lipolysis genes and oxidative phosphorylation genes were at least partially rescued by DK in the brown adipose tissue.

CONCLUSIONS

DK has therapeutic effect on PCOS in DHEA treated mice and the brown adipose tissue is at least one critical target organ to alleviate the PCOS. This is achieved by not only regulating the lipid mobilization of brown adipose, but also restoring its thermogenic function.

Pharmacological inhibition of lipolysis prevents adverse metabolic outcomes during glucocorticoid administration

OBJECTIVE

Glucocorticoids are one of the most commonly prescribed classes of anti-inflammatory drugs; however, chronic treatment promotes iatrogenic (drug-induced) diabetes. As part of their physiological role, glucocorticoids stimulate lipolysis to spare glucose. We hypothesized that persistent stimulation of lipolysis during glucocorticoid therapy plays a causative role in the development of iatrogenic diabetes.

METHODS

Male C57BL/6J mice were given 100 μg/mL corticosterone (Cort) in the drinking water for two weeks and were fed either normal chow (TekLad 8640) or the same diet supplemented with an adipose triglyceride lipase inhibitor (Atglistatin - 2  g/kg diet) to inhibit the first step of lipolysis.

RESULTS

Herein, we report for the first time that glucocorticoid administration promotes a unique state of substrate excess and energetic overload in skeletal muscle that primarily results from the rampant mobilization of endogenous fuels. Inhibiting lipolysis protected mice from Cort-induced gains in fat mass, excess ectopic lipid accrual, hyperinsulinemia, and hyperglycemia. The role lipolysis plays in Cort-mediated pathology appears to differ between tissues. Within skeletal muscle, Cort-induced lipolysis facilitated diversion of glucose-derived carbons toward the pentose phosphate and hexosamine biosynthesis pathways but contributed to <3% of the Cort-induced genomic adaptations. In contrast, Cort stimulation of lipolysis accounted for ∼35% of the genomic changes in the liver but had minimal impact on hepatic metabolites reported.

CONCLUSIONS

These data support the idea that activation of lipolysis plays a causal role in the progression toward iatrogenic diabetes during glucocorticoid therapy with differential impact on skeletal muscle and liver.

Respiratory issues in patients with multiple sclerosis as a risk factor during SARS-CoV-2 infection: a potential role for exercise

Coronavirus disease-2019 (COVID-19) is associated with cytokine storm and is characterized by acute respiratory distress syndrome (ARDS) and pneumonia problems. The respiratory system is a place of inappropriate activation of the immune system in people with multiple sclerosis (MS), and this may cause damage to the lung and worsen both MS and infections.The concerns for patients with multiple sclerosis are because of an enhance risk of infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The MS patients pose challenges in this pandemic situation, because of the regulatory defect of autoreactivity of the immune system and neurological and respiratory tract symptoms. In this review, we first indicate respiratory issues associated with both diseases. Then, the main mechanisms inducing lung damages and also impairing the respiratory muscles in individuals with both diseases is discussed. At the end, the leading role of physical exercise on mitigating respiratory issues inducing mechanisms is meticulously evaluated.

The PNPLA family of enzymes: characterisation and biological role

This paper brings a brief review of the human patatin-like phospholipase domain-containing protein (PNPLA) family. Even though it consists of only nine members, their physiological roles and mechanisms of their catalytic activity are not fully understood. However, the results of a number of knock-out and gain- or loss-of-function research models suggest that these enzymes have an important role in maintaining the homeostasis and integrity of organelle membranes, in cell growth, signalling, cell death, and the metabolism of lipids such as triacylglycerol, phospholipids, ceramides, and retinyl esters. Research has also revealed a connection between PNPLA family member mutations or irregular catalytic activity and the development of various diseases. Here we summarise important findings published so far and discuss their structure, localisation in the cell, distribution in the tissues, specificity for substrates, and their potential physiological role, especially in view of their potential as drug targets.

Recombinant PNPLA1 catalyzes the synthesis of acylceramides and acyl acids with selective incorporation of linoleic acid

Loss-of-function mutations in patatin-like phospholipase domain-containing protein 1 (PNPLA1) cause autosomal recessive congenital ichthyosis, and altered PNPLA1 activity is implicated in the pathogenesis of atopic dermatitis and other common skin diseases. To examine the hypothesis that PNPLA1 catalyzes the synthesis of acylceramides and acyl acids, we expressed and partially purified a soluble, truncated form of PNPLA1 in Escherichia coli, (PNPLA1trun) along with the related protein PNPLA2 (ATGL, adipose triglyceride lipase) and coactivator CGI-58. Liposomal substrates were incubated with recombinant enzymes for 0.5-24 h and products analyzed by HPLC-UV and LC-MS. Using trilinolein or dilinolein substrates, PNPLA1trun, like ATGLtrun, catalyzed lipolysis and acyltransferase reactions with 2-30% conversion into linoleic acid, monolinolein, and trilinolein. CGI-58 enhanced ATGL-catalyzed lipolysis as previously reported, but transacylase activity was not enhanced with ATGL or PNPLA1. In matching the proposed activity in vivo, PNPLA1 catalyzed acyl transfer from trilinolein and dilinolein donors to omega-hydroxy ceramide, omega-hydroxy glucosylceramide, and omega-hydroxy acid acceptors to form acylceramide, glucosyl-acylceramide, and acyl acid, respectively, albeit with only ∼0.05% conversion of the substrates. Notably, in experiments comparing dilinolein vs. diolein acyl donors, PNPLA1 transferred linoleate with 3:1 selectivity over oleate into acylceramide. These results support the role for PNPLA1 in the synthesis of acylceramides and acyl acids in epidermis and suggest that the enrichment of these lipids with linoleic acid could result from the substrate selectivity of PNPLA1.

The lipase cofactor CGI58 controls placental lipolysis

In eutherians, the placenta plays a critical role in the uptake, storage, and metabolism of lipids. These processes govern the availability of fatty acids to the developing fetus, where inadequate supply has been associated with substandard fetal growth. Whereas lipid droplets are essential for the storage of neutral lipids in the placenta and many other tissues, the processes that regulate placental lipid droplet lipolysis remain largely unknown. To assess the role of triglyceride lipases and their cofactors in determining placental lipid droplet and lipid accumulation, we assessed the role of patatin like phospholipase domain containing 2 (PNPLA2) and comparative gene identification-58 (CGI58) in lipid droplet dynamics in the human and mouse placenta. While both proteins are expressed in the placenta, the absence of CGI58, not PNPLA2, markedly increased placental lipid and lipid droplet accumulation. These changes were reversed upon restoration of CGI58 levels selectively in the CGI58-deficient mouse placenta. Using co-immunoprecipitation, we found that, in addition to PNPLA2, PNPLA9 interacts with CGI58. PNPLA9 was dispensable for lipolysis in the mouse placenta yet contributed to lipolysis in human placental trophoblasts. Our findings establish a crucial role for CGI58 in placental lipid droplet dynamics and, by extension, in nutrient supply to the developing fetus.

Sudachitin and Nobiletin Stimulate Lipolysis via Activation of the cAMP/PKA/HSL Pathway in 3T3-L1 Adipocytes

Polymethoxyflavones are flavonoids that are abundant in citrus fruit peels and have beneficial effects on human health. Previous studies have demonstrated that the polymethoxyflavones, namely sudachitin and nobiletin, ameliorate obesity and diabetes in humans and rodents. Although nobiletin induces lipolysis in adipocytes, lipolytic pathway activation by sudachitin has not been clarified in adipocytes. In this study, the effect of sudachitin on lipolysis was elucidated in murine 3T3-L1 adipocytes. Glycerol release into the medium and activation of the cyclic AMP (cAMP)/protein kinase A (PKA)/hormone-sensitive lipase (HSL) pathway was evaluated in 3T3-L1-differentiated adipocytes. Treatment with sudachitin and nobiletin for 24 and 48 h did not induce cytotoxicity at concentrations of up to 50 μM. Sudachitin and nobiletin at concentrations of 30 and 50 μM increased intracellular cAMP and medium glycerol levels in 3T3-L1 adipocytes. Western blotting revealed that sudachitin and nobiletin dose-dependently increased protein levels of phosphorylated PKA substrates and phosphorylated HSL. Sudachitin- and nobiletin-induced glycerol release, phosphorylation of PKA substrates, and HSL phosphorylation were suppressed by pharmacological inhibition of adenylate cyclase and PKA. These findings indicated that sudachitin, similar to nobiletin, exerts anti-obesogenic effects, at least in part through the induction of lipolysis in adipocytes.

Adipose Tissue Macrophage-Mediated Inflammation in Obesity: A Link to Posttranslational Modification

Adipose tissue macrophages (ATM) are an essential type of immune cells in adipose tissue. Obesity induces the inflammation of adipose tissues, as expressed by ATM accumulation, that is more likely to become a source of systemic metabolic diseases, including insulin resistance. The process is characterized by the transcriptional regulation of inflammatory pathways by virtue of signaling molecules such as cytokines and free fatty acids. Notably, posttranslational modification (PTM) is a key link for these signaling molecules to trigger the proinflammatory or anti-inflammatory phenotype of ATMs. This review focuses on summarizing the functions and molecular mechanisms of ATMs regulating inflammation in obese adipose tissue. Furthermore, the role of PTM is elaborated, hoping to identify new horizons of treatment and prevention for obesity-mediated metabolic disease.

Inhibiting degradation of 2-arachidonoylglycerol as a therapeutic strategy for neurodegenerative diseases

Endocannabinoids are endogenous lipid signaling mediators that participate in a variety of physiological and pathological processes. 2-Arachidonoylglycerol (2-AG) is the most abundant endocannabinoid and is a full agonist of G-protein-coupled cannabinoid receptors (CB1R and CB2R), which are targets of Δ⁹-tetrahydrocannabinol (Δ⁹-THC), the main psychoactive ingredient in cannabis. While 2-AG has been well recognized as a retrograde messenger modulating synaptic transmission and plasticity at both inhibitory GABAergic and excitatory glutamatergic synapses in the brain, growing evidence suggests that 2-AG also functions as an endogenous terminator of neuroinflammation in response to harmful insults, thus maintaining brain homeostasis. Monoacylglycerol lipase (MAGL) is the key enzyme that degrades 2-AG in the brain. The immediate metabolite of 2-AG is arachidonic acid (AA), a precursor of prostaglandins (PGs) and leukotrienes. Several lines of evidence indicate that pharmacological or genetic inactivation of MAGL, which boosts 2-AG levels and reduces its hydrolytic metabolites, resolves neuroinflammation, mitigates neuropathology, and improves synaptic and cognitive functions in animal models of neurodegenerative diseases, including Alzheimer's disease (AD), multiple sclerosis (MS), Parkinson's disease (PD), and traumatic brain injury (TBI)-induced neurodegenerative disease. Thus, it has been proposed that MAGL is a potential therapeutic target for treatment of neurodegenerative diseases. As the main enzyme hydrolyzing 2-AG, several MAGL inhibitors have been identified and developed. However, our understanding of the mechanisms by which inactivation of MAGL produces neuroprotective effects in neurodegenerative diseases remains limited. A recent finding that inhibition of 2-AG metabolism in astrocytes, but not in neurons, protects the brain from TBI-induced neuropathology might shed some light on this unsolved issue. This review provides an overview of MAGL as a potential therapeutic target for neurodegenerative diseases and discusses possible mechanisms underlying the neuroprotective effects of restraining degradation of 2-AG in the brain.

The lipidomic and inflammatory profiles of visceral and subcutaneous adipose tissues are distinctly regulated by the SGLT2 inhibitor empagliflozin in Zucker diabetic fatty rats

The pharmacological inhibition of sodium-glucose cotransporter 2 (SGLT2) has emerged as a treatment for patients with type 2 diabetes mellitus (T2DM), cardiovascular disease and/or other metabolic disturbances, although some of the mechanisms implicated in their beneficial effects are unknown. The SGLT2 inhibitor (SGLT2i) empagliflozin has been suggested as a regulator of adiposity, energy metabolism, and systemic inflammation in adipose tissue. The aim of our study was to evaluate the impact of a 6-week-empagliflozin treatment on the lipidome of visceral (VAT) and subcutaneous adipose tissue (SAT) from diabetic obese Zucker Diabetic Fatty (ZDF) rats using an untargeted metabolomics approach. We found that empagliflozin increases the content of diglycerides and oxidized fatty acids (FA) in VAT, while in SAT, it decreases the levels of several lysophospholipids and increases 2 phosphatidylcholines. Empagliflozin also reduces the expression of the cytokines interleukin-1 beta (IL-1β), IL-6, tumor necrosis factor-alpha (TNFα), monocyte-chemotactic protein-1 (MCP-1) and IL-10, and of Cd86 and Cd163 M1 and M2 macrophage markers in VAT, with no changes in SAT, except for a decrease in IL-1β. Empagliflozin treatment also shows an effect on lipolysis increasing the expression of hormone-sensitive lipase (HSL) in SAT and VAT and of adipose triglyceride lipase (ATGL) in VAT, together with a decrease in the adipose content of the FA transporter cluster of differentiation 36 (CD36). In conclusion, our data highlighted differences in the VAT and SAT lipidomes, inflammatory profiles and lipolytic function, which suggest a distinct metabolism of these two white adipose tissue depots after the empagliflozin treatment.

Adipose triglyceride lipase: the first transacylase for FAHFAs

In a recent article published in Nature, Patel et al. identified adipose triglyceride lipase (ATGL, also known as patatin-like phospholipase domain containing 2) as the first biosynthetic enzyme of fatty acid esters of hydroxy fatty acids (FAHFAs), further expanding the knowledge on bioactive lipid research and being a potential paradigm shift for ATGL studies.

Metabolic Role of Autophagy in the Pathogenesis and Development of NAFLD

Non-alcoholic fatty liver disease (NAFLD) is a spectrum of liver disease, ranging from simple steatosis to hepatitis, fibrosis, cirrhosis, and hepatocellular carcinoma (HCC). Liver fibrosis, which portends a poor prognosis in NAFLD, is characterized by the excessive accumulation of extracellular matrix (ECM) proteins resulting from abnormal wound repair response and metabolic disorders. Various metabolic factors play crucial roles in the progression of NAFLD, including abnormal lipid, bile acid, and endotoxin metabolism, leading to chronic inflammation and hepatic stellate cell (HSC) activation. Autophagy is a conserved process within cells that removes unnecessary or dysfunctional components through a lysosome-dependent regulated mechanism. Accumulating evidence has shown the importance of autophagy in NAFLD and its close relation to NAFLD progression. Thus, regulation of autophagy appears to be beneficial in treating NAFLD and could become an important therapeutic target.

Caveolae-associated protein 3 promotes adipogenic differentiation of porcine preadipocytes by promoting extracellular signal-regulated kinase phosphorylation

Fat deposition is one of the key factors affecting the economic development of pig husbandry. The aim of this study was to investigate the expression characteristics of caveolae-associated protein 3 (CAVIN3) and to elucidate its effect and mechanism on adipogenic differentiation of porcine preadipocytes. Cell transfection, quantitative reverse transcription polymerase chain reaction (qRT-PCR), western blot, and oil red O staining were used to detect the effect of CAVIN3 on the differentiation of porcine preadipocytes. The results showed that CAVIN3 was expressed in various tissues, with higher expression in adipose tissue, differentially expressed during cell adipogenic differentiation, and mainly distributed in the cytoplasm. Functional studies showed that, after CAVIN3 interference in preadipocytes, the expression of adipogenic factors and the content of lipid droplets were significantly decreased (p < 0.05). The results were reversed after CAVIN3 was overexpressed. The mechanism research showed that LY3214996 inhibited the extracellular signal-regulated kinase (ERK) phosphorylation and further inhibited lipogenic factors expression. Overexpression of CAVIN3 attenuates the inhibitory effect of LY3214996 on ERK phosphorylation and attenuates its inhibitory effect on adipogenic differentiation. Therefore, this study demonstrated that CAVIN3 promotes the differentiation of porcine preadipocytes by promoting ERK phosphorylation. The present study can lay a theoretical foundation for further studying the molecular mechanism of porcine fat deposition.

Recent insights into the molecular mechanisms of simultaneous fatty acid oxidation and synthesis in brown adipocytes

Brown adipocytes is a specialized fat cell that dissipates nutrient-derived chemical energy in the form of heat, instead of ATP synthesis. This unique feature provides a marked capacity for brown adipocyte mitochondria to oxidize substrates independent of ADP availability. Upon cold exposure, brown adipocytes preferentially oxidize free fatty acids (FFA) liberated from triacylglycerol (TAG) in lipid droplets to support thermogenesis. In addition, brown adipocytes take up large amounts of circulating glucose, concurrently increasing glycolysis and de novo FA synthesis from glucose. Given that FA oxidation and glucose-derived FA synthesis are two antagonistic mitochondrial processes in the same cell, it has long been questioned how brown adipocytes run FA oxidation and FA synthesis simultaneously. In this review, I summarize mechanisms regulating mitochondrial substrate selection and describe recent findings of two distinct populations of brown adipocyte mitochondria with different substrate preferences. I further discuss how these mechanisms may permit a concurrent increase in glycolysis, FA synthesis, and FA oxidation in brown adipocytes.

Comprehensive sequence and structure analysis of algal lipid catabolic enzyme Triacylglycerol lipase: an in silico study to vitalize the development of optimum engineered strains with high lipid productivity

Microalgae as an alternative renewable resource for biofuel production have captured much significance. Nonetheless, its economic viability is a field of major concern for researchers. Unraveling the lipid catabolic pathway and gaining insights into the sequence-structural features of its primary functioning enzyme, Triacylglycerol lipase, will impart valuable information to target microalgae for augmented lipid content. In the present study, a genome-wide comparative study on putative Triacylglycerol lipase (TAGL) enzyme from algal species belonging to varied phylogenetic lineages was performed. The comprehensive sequence analysis revealed that TAGL comprises of three distinct conserved domains, such as, Patatin, Class III Lipase, and Abhydro_lipase, and also confirmed the ubiquitous presence of GXSXG motif in the sequences analyzed. In the absence of a crystal structure of algal TAGL till date, we developed the first 3D model of patatin domain of TAGL from an oleaginous microalga, Phaedactylum tricornutum, employing homology modeling, docking and molecular dynamic simulations methods. The domain-substrate complex having the low-ranking docking score revealed the binding of palmitic acid to the TAGL patatin domain surface with strong hydrogen bond interactions. The simulation results implied that the substrate-complexed patatin domain and the free enzyme adopted a more stable conformation after 40 ns. This is the first ever attempt to provide in-silico insights into the structural and dynamical insights on catalytic mechanism of the TAGL patatin domain. Subsequently, these findings aided our understanding on their structural stability, folding mechanism and protein-substrate interactions, which could be further utilized to design site-specific mutagenic experiments for engineering microalgal strains.Communicated by Ramaswamy H. Sarma.

Identification of motifs and mechanisms for lipid droplet targeting of the lipolytic inhibitors G0S2 and HIG2

G0S2 and HIG2 are two selective inhibitors of ATGL (also known as PNPLA2), the key enzyme for intracellular lipolysis. Whereas G0S2 regulates triglyceride (TG) mobilization in adipocytes and hepatocytes, HIG2 functions to enhance intracellular TG accumulation under hypoxic conditions. A homologous hydrophobic domain (HD) is shared by G0S2 and HIG2 (also known as HILPDA) for binding to ATGL. However, the determinants of their lipid droplet (LD) localization are unknown. Here, we study how G0S2 and HIG2 are targeted to LDs, and identify both ATGL-independent and -dependent mechanisms. Structural prediction and studies in cells reveal that ATGL-independent localization of G0S2 to both the endoplasmic reticulum (ER) and LDs is mediated by a hairpin structure consisting of two hydrophobic sequences. Positively charged residues in the hinge region play a crucial role in sorting G0S2, which initially localizes to ER, to LDs. Interestingly, the role of these positive charges becomes dispensable when ATGL is co-expressed. In comparison, HIG2, which lacks a similar hairpin structure, is dependent on ATGL for its full LD targeting. Thus, our studies identify specific structural features and mechanisms for mediating accumulation of these two ATGL inhibitors on LDs.

An Overview of Hormone-Sensitive Lipase (HSL)

Hormone-sensitive lipase (HSL) is a pivotal enzyme that mediates triglyceride hydrolysis to provide free fatty acids and glycerol in adipocytes in a hormonally controlled lipolysis process. Elevated plasma-free fatty acids were accompanied by insulin resistance, type-2 diabetes, and obesity. Inhibition of lipolysis through HSL inhibition may provide a mechanism to prevent the accumulation of free fatty acids and to improve the affectability of insulin and blood glucose handling in type II diabetes. The published studies that examine the structure, regulation, and function of HSL and major inhibitors were reviewed in this paper.

Non-Alcoholic Fatty Liver Disease (NAFLD) Pathogenesis and Natural Products for Prevention and Treatment

Non-alcoholic fatty liver disease (NAFLD) is the most prevalent chronic liver disease, affecting approximately one-quarter of the global population, and has become a world public health issue. NAFLD is a clinicopathological syndrome characterized by hepatic steatosis, excluding ethanol and other definite liver damage factors. Recent studies have shown that the development of NAFLD is associated with lipid accumulation, oxidative stress, endoplasmic reticulum stress, and lipotoxicity. A range of natural products have been reported as regulators of NAFLD in vivo and in vitro. This paper reviews the pathogenesis of NAFLD and some natural products that have been shown to have therapeutic effects on NAFLD. Our work shows that natural products can be a potential therapeutic option for NAFLD.

Lipid-laden lung mesenchymal cells foster breast cancer metastasis via metabolic reprogramming of tumor cells and natural killer cells

While the distant organ environment is known to support metastasis of primary tumors, its metabolic roles in this process remain underdetermined. Here, in breast cancer models, we found lung-resident mesenchymal cells (MCs) accumulating neutral lipids at the pre-metastatic stage. This was partially mediated by interleukin-1β (IL-1β)-induced hypoxia-inducible lipid droplet-associated (HILPDA) that subsequently represses adipose triglyceride lipase (ATGL) activity in lung MCs. MC-specific ablation of the ATGL or HILPDA genes in mice reinforced and reduced lung metastasis of breast cancer respectively, suggesting a metastasis-promoting effect of lipid-laden MCs. Mechanistically, lipid-laden MCs transported their lipids to tumor cells and natural killer (NK) cells via exosome-like vesicles, leading to heightened tumor cell survival and proliferation and NK cell dysfunction. Blockage of IL-1β, which was effective singly, improved the efficacy of adoptive NK cell immunotherapy in mitigating lung metastasis. Collectively, lung MCs metabolically regulate tumor cells and anti-tumor immunity to facilitate breast cancer lung metastasis.

Flow-Induced Secretion of Endothelial Heparanase Regulates Cardiac Lipoprotein Lipase and Changes Following Diabetes

Background Lipoprotein lipase (LPL)-derived fatty acid is a major source of energy for cardiac contraction. Synthesized in cardiomyocytes, LPL requires translocation to the vascular lumen for hydrolysis of lipoprotein triglyceride, an action mediated by endothelial cell (EC) release of heparanase. We determined whether flow-mediated biophysical forces can cause ECs to secrete heparanase and thus regulate cardiac metabolism. Methods and Results Isolated hearts were retrogradely perfused. Confluent rat aortic ECs were exposed to laminar flow using an orbital shaker. Cathepsin L activity was determined using gelatin-zymography. Diabetes was induced in rats with streptozotocin. Despite the abundance of enzymatically active heparanase in the heart, it was the enzymatically inactive, latent heparanase that was exceptionally responsive to flow-induced release. EC exposed to orbital rotation exhibited a similar pattern of heparanase secretion, an effect that was reproduced by activation of the mechanosensor, Piezo1. The laminar flow-mediated release of heparanase from EC required activation of both the purinergic receptor and protein kinase D, a kinase that assists in vesicular transport of proteins. Heparanase influenced cardiac metabolism by increasing cardiomyocyte LPL displacement along with subsequent replenishment. The flow-induced heparanase secretion was augmented following diabetes and could explain the increased heparin-releasable pool of LPL at the coronary lumen in these diabetic hearts. Conclusions ECs sense fluid shear-stress and communicate this information to subjacent cardiomyocytes with the help of heparanase. This flow-induced mechanosensing and its dynamic control of cardiac metabolism to generate ATP, using LPL-derived fatty acid, is exquisitely adapted to respond to disease conditions, like diabetes.

Postbiotics Prepared Using Lactobacillus paracasei CCFM1224 Prevent Nonalcoholic Fatty Liver Disease by Modulating the Gut Microbiota and Liver Metabolism

Postbiotics are rich in a variety of bioactive components, which may have beneficial effects in inhibiting hepatic lipid accumulation. In this study, we investigated the preventive effects of postbiotics (POST) prepared from Lactobacillus paracasei on non-alcoholic fatty liver disease (NAFLD). Our results showed that when mice ingested a high-fat diet (HFD) and POST simultaneously, weight gain was slowed, epididymal white fat hypertrophy and insulin resistance were suppressed, serum biochemical indicators related to blood lipid metabolism were improved, and hepatic steatosis and liver inflammation decreased. Bacterial sequencing showed that POST modulated the gut microbiota in HFD mice, increasing the relative abundance of Akkermansia and reducing the relative abundance of Lachnospiraceae NK4A136 group, Ruminiclostridium and Bilophila. Spearman’s correlation analysis revealed significant correlations between lipid metabolism parameters and gut microbes. Functional prediction results showed that the regulation of gut microbiota was associated with the improvement of metabolic status. The metabolomic analysis of the liver revealed that POST-regulated liver metabolic pathways, such as glycerophospholipid and ether lipid metabolism, pantothenate and CoA biosynthesis, some parts of amino acid metabolism, and other metabolic pathways. In addition, POST regulated the gene expression in hepatocytes at the mRNA level, thereby regulating lipid metabolism. These findings suggest that POST plays a protective role against NAFLD and may exert its efficacy by modulating the gut microbiota and liver metabolism, and these findings may be applied to related functional foods.

Lipid metabolism in sarcopenia

Sarcopenia is an age-related disease associated with loss of muscle mass and strength. This geriatric syndrome predisposes elderly individuals to a disability, falls, fractures, and death. Fat infiltration in muscle is one of the hallmarks of sarcopenia and aging. Alterations in fatty acid (FA) metabolism are evident in aging, type 2 diabetes, and obesity, with the accumulation of lipids inside muscle cells contributing to muscle insulin resistance and ceramide accumulation. These lipids include diacylglycerol, lipid droplets, intramyocellular lipids, intramuscular triglycerides, and polyunsaturated fatty acids (PUFAs). In this review, we examine the regulation of lipid metabolism in skeletal muscle, including lipid metabolization and storage, intervention, and the types of lipases expressed in skeletal muscle responsible for the breakdown of adipose triglyceride fats. In addition, we address the role of FAs in sarcopenia and the potential benefits of PUFAs.

Approaches to Measuring the Activity of Major Lipolytic and Lipogenic Enzymes In Vitro and Ex Vivo

Since the 1950s, one of the goals of adipose tissue research has been to determine lipolytic and lipogenic activity as the primary metabolic pathways affecting adipocyte health and size and thus representing potential therapeutic targets for the treatment of obesity and associated diseases. Nowadays, there is a relatively large number of methods to measure the activity of these pathways and involved enzymes, but their applicability to different biological samples is variable. Here, we review the characteristics of mean lipogenic and lipolytic enzymes, their inhibitors, and available methodologies for assessing their activity, and comment on the advantages and disadvantages of these methodologies and their applicability in vivo, ex vivo, and in vitro, i.e., in cells, organs and their respective extracts, with the emphasis on adipocytes and adipose tissue.