Cytosolic lipolysis and lipophagy: two sides of the same coin

Diacylglycerol Kinases and Its Role in Lipid Metabolism and Related Diseases

Lipids are essential components of eukaryotic membranes, playing crucial roles in membrane structure, energy storage, and signaling. They are predominantly synthesized in the endoplasmic reticulum (ER) and subsequently transported to other organelles. Diacylglycerol kinases (DGKs) are a conserved enzyme family that phosphorylate diacylglycerol (DAG) to produce phosphatidic acid (PA), both of which are key intermediates in lipid metabolism and second messengers involved in numerous cellular processes. Dysregulation of DGK activity is associated with several diseases, including cancer and metabolic disorders. In this review, we provide a comprehensive overview of DGK types, functions, cellular localization, and their potential as therapeutic targets. We also discuss DGKs' roles in lipid metabolism and their physiological functions and related diseases.

Molting of laying hens can activate AMPK- lipophagy - lipid metabolism pathway and improve intestinal digestion and absorption

Poultry molting is a natural phenomenon, and process that improves the physiological function of laying hens. In this study, artificial intervention was used to induced molting (IM) in aged hens and improve their egg- laying performance. Jejunal lipophagy and lipid metabolism data were analyzed to elucidate the regulatory mechanisms by which the intestine affects egg production performance, particularly through the lens of digestion and absorption processes. Molting process in laying hens facilitated the regeneration of small intestinal villi following damage and shedding, while also reducing excess lipid accumulation within the intestine. Analyses of lipophagy and lipid metabolism-related factors revealed, increased the expression levels of genes and proteins, such as AMPK, FOXO1, TFEB, TFE3, PGC-1α and PPAR-α (P<0.05, P<0.01 and P<0.001). Serological analysis and detection of enzymes involved in digestion and absorption, showed upregulated expression of GLUT2, FABP (P<0.05 and P<0.001) and CD36 (P<0.01), and the activities of amylase, chymotrypsin and Lipase also increased significantly (P<0.05, P<0.01 and P<0.001). In conclusion, artificially IM activates the AMPK-lipophagy-lipid metabolism pathway to enhance intestinal digestion and absorption in laying hens. Our findings offer a theoretical framework for the intentional use of IM to promote a healthy state of digestion and absorption.

The TFEB activator clomiphene citrate ameliorates lipid metabolic syndrome pathology by activating lipophagy and lipolysis

The balance between lipid synthesis and lipid catabolism is critical to maintain energy homeostasis. Lipophagy and lipolysis are two important pathways for lipid selective catabolism. Defects in lipophagy and lipolysis are linked to lipid metabolic diseases. Transcription factor EB (TFEB) is a master regulator of autophagy and lysosome biogenesis, as well as lipid metabolism by promoting expression of genes encoding fat catabolic lipases. Therefore, targeting TFEB provides a novel potential strategy for the treatment of lipid metabolic diseases. In this study, we showed that the TFEB activator clomiphene citrate (CC) activated the autophagy-lysosome and lipolysis pathways, and promoted degradation of lipid droplets induced by the free fatty acids oleate and palmitate in HepG2 cells. Moreover, CC treatment promoted lipid catabolism and attenuated obesity, restored lipid levels, blood glucose levels and insulin resistance, hepatocellular injury and hepatic steatosis, as well as liver inflammation in the HFD fed mice. In addition, we found that En-CC, a trans-isomer of CC, displayed less toxicity and more efficient activation of TFEB. Consistent with CC, En-CC treatment improved lipid metabolic syndrome pathology. These findings demonstrate that CC promotes clearance of lipids and ameliorates HFD-induced lipid metabolic syndrome pathology through activating TFEB-mediated lipophagy and lipolysis, indicating that CC has the potential to be used to treat lipid metabolic diseases.

Size of lipid emulsion droplets influences metabolism in human CD4+ T cells

SCOPE

Triglyceride-based lipid emulsions are critical for total parenteral nutrition (TPN), but their long-term use has adverse effects, such as severe liver dysfunction necessitating improved formulations. This study compares the uptake mechanism and intracellular fate of novel glycerol-stabilized nano-sized lipid emulsions with conventional emulsions in CD4+ T cells, focusing on their impact on cellular metabolism.

METHODS AND RESULTS

Nanoemulsions were formulated with increased glycerol content. Uptake of emulsions in primary human CD4+ T cells was investigated using different endocytic blockers, then quantified by flow cytometry, and visualized by confocal microscopy. To investigate emulsion intracellular fate, fatty acids in membrane phospholipids were quantified by GC-MS/MS and cellular metabolism was assessed by Seahorse technology. Results show T cells internalize both conventional and nano-sized emulsions using macropinocytosis. Fatty acids from emulsions are stored as neutral lipids in intracellular vesicles and are incorporated into phospholipids of cellular membranes. However, only nanoemulsions additionally use clathrin-mediated endocytosis and deliver fatty acids to mitochondria for increased β-oxidation.

CONCLUSIONS

Size of lipid emulsion droplets significantly influences their uptake and subsequent metabolism in CD4+ T cells. Our results highlight the potential for improved nutrient utilization with nanoemulsions in TPN formulations possibly leading to less adverse effects.

Analysis of Lipid Metabolism in Adipose Tissue and Liver of Chinese Soft-Shelled Turtle Pelodiscus sinensis During Hibernation

Hibernation serves as an energy-conserving strategy that enables animals to withstand harsh environments by reducing their metabolic rate significantly. However, the mechanisms underlying energy adaptation in hibernating ectotherms, such as Pelodiscus sinensis, remain contentious. This paper first reports the decrease in lipid levels and the expression of metabolism-related genes in P. sinensis during hibernation. The results of physiological and biochemical analysis showed that adipocyte cell size was reduced and liver lipid droplet (LD) contents were decreased during hibernation in P. sinensis. Concurrently, serum levels of triglycerides (TGs), total cholesterol (TC), non-esterified fatty acids (NEFAs), high-density lipoprotein cholesterol (HDLC), and low-density lipoprotein cholesterol (LDLC) were diminished (n = 8, p < 0.01), while an increase in serum glucose (Glu) (n = 8, p < 0.01) was noted among hibernating P. sinensis. These observations suggest a shift in energy metabolism during hibernation. To gain insights into the molecular mechanisms, we performed integrated transcriptomic and lipidomic analyses of adipose tissue and livers from summer-active versus overwintering P. sinensis, which revealed downregulation of free fatty acids (FFAs), triglycerides (TGs), diglycerides (DGs), and ceramides (Cers) during hibernation. The results of GSEA analysis showed that metabolic pathways associated with lipid metabolism, including glycerolipid metabolism and regulation of lipolysis in adipocytes, were suppressed significantly. Notably, acute cold exposure induced significant downregulation of genes related to lipolysis such as PNPLA2, ABHD5, LPL, CPT1A, and PPARα. The results indicate that lipolysis is suppressed during hibernation in P. sinensis. Collectively, these findings deepen our understanding of survival mechanisms and elucidate the unique energy adaptation strategies employed by hibernating ectotherms. Future research should explore the implications of these findings for the conservation of ectotherms and the applications for artificially inducing hibernation.

Targeting selective autophagy and beyond: From underlying mechanisms to potential therapies

BACKGROUND

Autophagy is an evolutionarily conserved turnover process for intracellular substances in eukaryotes, relying on lysosomal (in animals) or vacuolar (in yeast and plants) mechanisms. In the past two decades, emerging evidence suggests that, under specific conditions, autophagy can target particular macromolecules or organelles for degradation, a process termed selective autophagy. Recently, accumulating studies have demonstrated that the abnormality of selective autophagy is closely associated with the occurrence and progression of many human diseases, including neurodegenerative diseases, cancers, metabolic diseases, and cardiovascular diseases.

AIM OF REVIEW

This review aims at systematically and comprehensively introducing selective autophagy and its role in various diseases, while unravelling the molecular mechanisms of selective autophagy. By providing a theoretical basis for the development of related small-molecule drugs as well as treating related human diseases, this review seeks to contribute to the understanding of selective autophagy and its therapeutic potential.

KEY SCIENTIFIC CONCEPTS OF REVIEW

In this review, we systematically introduce and dissect the major categories of selective autophagy that have been discovered. We also focus on recent advances in understanding the molecular mechanisms underlying both classical and non-classical selective autophagy. Moreover, the current situation of small-molecule drugs targeting different types of selective autophagy is further summarized, providing valuable insights into the discovery of more candidate small-molecule drugs targeting selective autophagy in the future. On the other hand, we also reveal clinically relevant implementations that are potentially related to selective autophagy, such as predictive approaches and treatments tailored to individual patients.

Lipid Dynamics in Pancreatic β-Cells: Linking Physiology to Diabetes Onset

Significance: Glucose-induced lipid metabolism is essential for preserving functional β-cells, and its disruption is linked to type 2 diabetes (T2D) development. Lipids are an integral part of the cells playing an indispensable role as structural components, energy storage molecules, and signals. Recent Advances: Glucose presence significantly impacts lipid metabolism in β-cells, where fatty acids are primarily synthesized de novo and/or are transported from the bloodstream. This process is regulated by the glycerolipid/free fatty acid cycle, which includes lipogenic and lipolytic reactions producing metabolic coupling factors crucial for insulin secretion. Disrupted lipid metabolism involving oxidative stress and inflammation is a hallmark of T2D. Critical Issues: Lipid metabolism in β-cells is complex involving multiple simultaneous processes. Exact compartmentalization and quantification of lipid metabolism and its intermediates, especially in response to glucose or chronic hyperglycemia, are essential. Current research often uses non-physiological conditions, which may not accurately reflect in vivo situations. Future Directions: Identifying and quantifying individual steps and their signaling, including redox, within the complex fatty acid and lipid metabolic pathways as well as the metabolites formed during acute versus chronic glucose stimulation, will uncover the detailed mechanisms of glucose-stimulated insulin secretion. This knowledge is crucial for understanding T2D pathogenesis and identifying pharmacological targets to prevent this disease. Antioxid. Redox Signal. 41, 865-889.

Spatial Transcriptomic Study Reveals Heterogeneous Metabolic Adaptation and a Role of Pericentral PPARα/CAR/Ces2a Axis During Fasting in Mouse Liver

Spatial heterogeneity and plasticity of the mammalian liver are critical for systemic metabolic homeostasis in response to fluctuating nutritional conditions. Here, a spatially resolved transcriptomic landscape of mouse livers across fed, fasted and refed states using spatial transcriptomics is generated. This approach elucidated dynamic temporal-spatial gene cascades and how liver zonation-both expression levels and patterns-adapts to shifts in nutritional status. Importantly, the pericentral nuclear receptor Nr1i3 (CAR) as a pivotal regulator of triglyceride metabolism is pinpointed. It is showed that the activation of CAR in the pericentral region is transcriptionally governed by Pparα. During fasting, CAR activation enhances lipolysis by upregulating carboxylesterase 2a, playing a crucial role in maintaining triglyceride homeostasis. These findings lay the foundation for future mechanistic studies of liver metabolic heterogeneity and plasticity in response to nutritional status changes, offering insights into the zonated pathology that emerge during liver disease progression linked to nutritional imbalances.

Pyruvate dehydrogenase kinase 1 controls triacylglycerol hydrolysis in cardiomyocytes

Pyruvate dehydrogenase kinase (PDK) 1 is one of four isozymes that inhibit the oxidative decarboxylation of pyruvate to acetyl-CoA via pyruvate dehydrogenase. PDK activity is elevated in fasting or starvation conditions to conserve carbohydrate reserves. PDK has also been shown to increase mitochondrial fatty acid utilization. In cardiomyocytes, metabolic flexibility is crucial for the fulfillment of high energy requirements. The PDK1 isoform is abundant in cardiomyocytes, but its specific contribution to cardiomyocyte metabolism is unclear. Here we show that PDK1 regulates cardiomyocyte fuel preference by mediating triacylglycerol turnover in differentiated H9c2 myoblasts using lentiviral shRNA to knockdown Pdk1. Somewhat surprisingly, PDK1 loss did not affect overall PDH activity, basal glycolysis, or glucose oxidation revealed by oxygen consumption rate experiments and 13C6 glucose labelling. On the other hand, we observed decreased triacylglycerol turnover in H9c2 cells with PDK1 knockdown, which was accompanied by decreased mitochondrial fatty acid utilization following nutrient deprivation. 13C16 palmitate tracing of uniformly labelled acyl chains revealed minimal acyl chain shuffling within triacylglycerol, indicating that the triacylglycerol hydrolysis, and not re-esterification, was dysfunctional in PDK1 suppressed cells. Importantly, PDK1 loss did not significantly impact the cellular lipidome or triacylglycerol accumulation following palmitic acid treatment, suggesting that effects of PDK1 on lipid metabolism were specific to the nutrient-deprived state. We validated that PDK1 loss decreased triacylglycerol turnover in Pdk1 knockout mice. Together, these findings implicate a novel role for PDK1 in lipid metabolism in cardiomyocytes, independent of its canonical roles in glucose metabolism.

De novo lipid synthesis and polarized prenylation drive cell invasion through basement membrane

To breach the basement membrane, cells in development and cancer use large, transient, specialized lipid-rich membrane protrusions. Using live imaging, endogenous protein tagging, and cell-specific RNAi during Caenorhabditis elegans anchor cell (AC) invasion, we demonstrate that the lipogenic SREBP transcription factor SBP-1 drives the expression of the fatty acid synthesis enzymes POD-2 and FASN-1 prior to invasion. We show that phospholipid-producing LPIN-1 and sphingomyelin synthase SMS-1, which use fatty acids as substrates, produce lysosome stores that build the AC's invasive protrusion, and that SMS-1 also promotes protrusion localization of the lipid raft partitioning ZMP-1 matrix metalloproteinase. Finally, we discover that HMG-CoA reductase HMGR-1, which generates isoprenoids for prenylation, localizes to the ER and enriches in peroxisomes at the AC invasive front, and that the final transmembrane prenylation enzyme, ICMT-1, localizes to endoplasmic reticulum exit sites that dynamically polarize to deliver prenylated GTPases for protrusion formation. Together, these results reveal a collaboration between lipogenesis and a polarized lipid prenylation system that drives invasive protrusion formation.

Astragaloside I Promotes Lipophagy and Mitochondrial Biogenesis to Improve Hyperlipidemia by Regulating Akt/mTOR/TFEB Pathway

The simultaneous enhancement of lipophagy and mitochondrial biogenesis has emerged as a promising strategy for lipid lowering. The transcription factor EB (TFEB) exhibits a dual role, whereby it facilitates the degradation of lipid droplets (LDs) through the process of lipophagy while simultaneously stimulating mitochondrial biogenesis to support the utilization of lipophagy products. The purpose of this study was to explore the effect of astragaloside I (AS I) on hyperlipidemia and elucidate its underlying mechanism. AS I improved serum total cholesterol and triglyceride levels and reduced hepatic steatosis and lipid accumulation in db/db mice. AS I enhanced the fluorescence colocalization of LDs and autophagosomes and promoted the proteins and genes related to the autolysosome. Moreover, AS I increased the expression of mitochondrial biogenesis-related proteins and genes, indicating that AS I promoted lipophagy and mitochondrial biogenesis. Mechanistically, AS I inhibits the protein level of p-TFEB (ser211) expression and promotes TFEB nuclear translocation. The activation of TFEB by AS I was impeded upon the introduction of the mammalian target of rapamycin (mTOR) agonist MHY1485. The inhibition of p-mTOR by AS I and the activation of TFEB were no longer observed after administration of the Akt agonist SC-79, which indicated that AS I activated TFEB to promote lipophagy-dependent on the Akt/mTOR pathway and may be a potentially effective pharmaceutical and food additive for the treatment of hyperlipidemia.

Role of lipid droplets in neurodegenerative diseases: From pathogenesis to therapeutics

Neurodegenerative diseases (NDDs) are a series of disorders characterized by the progressive loss of specific neurons, leading to cognitive and locomotor impairment. NDDs affect millions of patients worldwide but lack effective treatments. Dysregulation of lipids, particularly the accumulation of lipid droplets (LDs), is strongly implicated in the pathogenesis of NDDs. How LDs contribute to the occurrence and development of NDDs, and their potential as therapeutic targets remain to be addressed. In present review, we first introduce the processes of LDs formation, transportation and degradation. We then highlight how the accumulation of LDs contributes to the pathogenesis of NDDs in a cell type-specific manner. Moreover, we discuss currently available methods for detecting LDs and elaborate on LDs-based therapeutic strategies for NDDs. Lastly, we identify gaps that need to be filled to better leverage LD-based theranostics in NDDs and other diseases. We hope this review could shed light on the role of LDs in NDDs and facilitate the development of novel therapeutic strategies for NDDs.

Mechanisms of lipid droplet degradation

Lipid droplets (LDs) are subcellular organelles that play an integral role in lipid metabolism by regulating the storage and release of fatty acids, which are essential for energy production and various cellular processes. Lipolysis and lipophagy are the two major LD degradation pathways that mediate the utilization of lipids stored in these organelles. Recent studies have further uncovered alternative pathways, including direct lysosomal LD degradation and LD exocytosis. Here, we highlight recent findings that dissect the molecular basis of these diverse LD degradation pathways. Then, we discuss speculations on the crosstalk among these pathways and the potential unconventional roles of LD degradation.

Emerging role of natural lipophagy modulators in metabolic dysfunction-associated steatotic liver disease

Metabolic dysfunction-associated steatotic liver disease (MASLD), previously known as non-alcoholic fatty liver disease (NAFLD), is a seriously increasing liver disorder affecting nearly 32% of adults globally. Hepatic triglycerides (TG) accumulation is the hallmark of MASLD, which results from dysregulated lipid and fatty acid uptake, increased de novo lipogenesis (DNL), and decreased lipid removal. More recently, selective autophagy of lipid droplets (LDs), termed lipophagy, has emerged to be closely associated with disrupted hepatic lipid homeostasis. Recent studies have indicated that a series of natural products have shown promise as an alternative approach in attenuating MASLD via regulating lipophagy in vivo and in vitro. Therefore, lipophagy could be a new approach for natural products to be used to improve MASLD. This article aims to provide a comprehensive overview on the interrelationship between dysregulated lipid metabolism, lipophagy, and MASLD pathogenesis. In addition, the role of some natural products as lipophagy modulators and their impact on MASLD will be discussed.

The novel TFEB agonist desloratadine ameliorates hepatic steatosis by activating the autophagy-lysosome pathway

The autophagy-lysosome pathway plays an essential role in promoting lipid catabolism and preventing hepatic steatosis in non-alcoholic fatty liver disease (NAFLD). Transcription factor EB (TFEB) enhances the autophagy-lysosome pathway by regulating the expression of genes related to autophagy and lysosome biogenesis. Therefore, targeting TFEB provides a novel strategy for the treatment of lipid metabolic diseases. In this study, the antiallergic drug desloratadine was screened and identified as a novel TFEB agonist. Desloratadine effectively induced translocation of TFEB to the nucleus and promoted autophagy and lysosome biogenesis. Desloratadine-induced TFEB activation was dependent on AMPK rather than mTORC1. Moreover, desloratadine treatment enhanced clearance of lipid droplets in cells induced by fatty acids oleate and palmitate. Furthermore, high-fat diet (HFD) induced obesity mouse model experiments indicated treatment with desloratadine markedly reduced the body weight of HFD-fed mice, as well as the levels of hepatic triglycerides and total cholesterol, serum glutamic pyruvic transaminase and glutamic-oxaloacetic transaminase. Oil red O staining showed the liver fat was significantly reduced after desloratadine treatment, and H&E staining analysis demonstrated hepatocellular ballooning was improved. In addition, autophagy and lysosomal biogenesis was stimulated in the liver of desloratadine treated mice. Altogether, these findings demonstrate desloratadine ameliorates hepatic steatosis through activating the TFEB-mediated autophagy-lysosome pathway, thus desloratadine has an exciting potential to be used to treat fatty liver disease.

Targeting lipid droplets and lipid droplet-associated proteins: a new perspective on natural compounds against metabolic diseases

BACKGROUND

Lipid droplet (LD) is a metabolically active organelle, which changes dynamically with the metabolic state and energy requirements of cells. Proteins that either insert into the LD phospholipid monolayer or are present in the cytoplasm, playing a crucial role in lipid homeostasis and signaling regulation, are known as LD-associated proteins.

METHODS

The keywords "lipid droplets" and "metabolic diseases" were used to obtain literature on LD metabolism and pathological mechanism. After searching databases including Scopus, OVID, Web of Science, and PubMed from 2013 to 2024 using terms like "lipid droplets", "lipid droplet-associated proteins", "fatty liver disease", "diabetes", "diabetic kidney disease", "obesity", "atherosclerosis", "hyperlipidemia", "natural drug monomers" and "natural compounds", the most common natural compounds were identified in about 954 articles. Eventually, a total of 91 studies of 10 natural compounds reporting in vitro or in vivo studies were refined and summarized.

RESULTS

The most frequently used natural compounds include Berberine, Mangostin, Capsaicin, Caffeine, Genistein, Epigallocatechin-3-gallate, Chlorogenic acid, Betaine, Ginsenoside, Resveratrol. These natural compounds interact with LD-associated proteins and help ameliorate abnormal LDs in various metabolic diseases.

CONCLUSION

Natural compounds involved in the regulation of LDs and LD-associated proteins hold promise for treating metabolic diseases. Further research into these interactions may lead to new therapeutic applications.

Triiodothyronine (T3) promotes browning of white adipose through inhibition of the PI3K/AKT signalling pathway

Obesity arises from an imbalance between energy consumption and energy expenditure, and thyroid hormone levels serve as a determinant of energy expenditure. We conducted experiments at the animal and cellular levels and combined those findings with clinical data to elucidate the role of triiodothyronine (T3) in facilitating the browning of white adipose tissue (WAT) and its underlying mechanism. The results showed (i) the impaired metabolic function of local WAT and the compensatory elevation of systemic thermogenesis in obesity; (ii) T3 treatment of white adipocytes in vitro and local WAT in vivo induced a shift towards a morphologically "brown" phenotype, accompanied by upregulation of mRNA and protein expression of browning-related and mitochondrial function markers, which suggest that T3 intervention promotes the browning of WAT; and (iii) the aforementioned processes could be modulated through inhibition of the PI3K/AKT signalling pathway; however, whether T3 affects the PI3K/AKT signalling pathway by affecting insulin signalling remains to be studied and clarified. The results of our study indicate that T3 treatment promotes browning of WAT through inhibition of the PI3K/AKT signalling pathway; these findings offer novel perspectives regarding the potential of localised therapies for addressing WAT volume in individuals with obesity.

Tetrahydrocurcumin ameliorates hepatic steatosis by restoring hepatocytes lipophagy through mTORC1-TFEB pathway in nonalcoholic steatohepatitis

PURPOSE

To investigate the therapeutic effect and underlying mechanism of tetrahydrocurcumin (THC) on nonalcoholic steatohepatitis (NASH) induced by high-fat diet (HFD).

METHODS

NASH rat model was established through long-term feeding HFD, and the steatosis cell model was stimulated via palmitate acid (PA). The therapeutic effect of THC was evaluated in terms of liver function, lipid metabolism, liver pathophysiology, inflammation and oxidative stress in vivo, and lipid accumulation in vitro. The alteration in lipophagy was identified by using western blot and immunofluorescence. mTORC1-TFEB signaling pathway was measured by qRT-PCR, western blot and protein-ligand docking. In addition, chloroquine and MHY1485 were further introduced to validate the effect of THC on lipophagy and mTORC1-TFEB signaling pathway, respectively.

RESULTS

THC effectively improved hepatic steatosis, inflammation and oxidative stress in NASH rats, and reduced lipid accumulation in steatosis L02 cells and Hep G2 cells. THC promoted lipophagy with increasing LC3B-II as well as decreasing P62 expression via lysosomal biogenesis upregulation, which was greatly weakened after chloroquine intervention. mTORC1-TFEB is a critical pathway for regulating lysosome in autophagy, THC treatment induced TFEB nucleus translocation via inhibiting mTORC1 to upregulate lysosomal biogenesis. However, these effects were partly eliminated by mTORC1 activator MHY1485.

CONCLUSION

THC restored lipophagy to reduce lipid accumulation by regulating mTORC1-TFEB pathway in NASH rats and steatosis hepatocytes. These findings suggested that THC represents a therapeutic candidate for NASH treatment.

Overview of a novel osmotin abolishes abnormal metabolic-associated adiponectin mechanism in Alzheimer's disease: Peripheral and CNS insights

Alzheimer's disease (AD) is a degenerative brain disease that affects millions of people worldwide. It is caused by abnormalities in cholinergic neurons, oxidative stress, and inflammatory cascades. The illness is accompanied by personality changes, memory issues, and dementia. Metabolic signaling pathways help with fundamental processes like DNA replication and RNA transcription. Being adaptable is essential for both surviving and treating illness. The body's metabolic signaling depends on adipokines, including adiponectin (APN) and other adipokines secreted by adipose tissues. Energy homeostasis is balanced by adipokines, and nutrients. Overconsumption of nutrients messes with irregular signaling of adipokines, such as APN in both peripheral and brain which leads to neurodegeneration, such as AD. Despite the failure of traditional treatments like memantine and cholinesterase inhibitors, natural plant bioactive substances like Osmotin (OSM) have been given a focus as potential therapeutics due to their antioxidant properties, better blood brain barrier (BBB) permeability, excellent cell viability, and especially nanoparticle approaches. The review highlights the published preclinical literature regarding the role of OSM in AD pathology while there is a need for more research to investigate the hidden therapeutic potential of OSM which may open a new gateway and further strengthen its healing role in the pathogenesis of neurodegeneration, especially AD.

Effects of Exogenous Regulation of PPARγ on Ovine Oocyte Maturation and Embryonic Development In Vitro

Lactating oocytes consume a lot of energy during maturation, a large part of which comes from lipid metabolism. PPARγ is a key regulator of lipid metabolism. In this study, rosiglitazone (RSG), an activator of PPARγ, was added to a mature medium to investigate its effects on the levels of spindle and the chromosome arrangement, lipid deposition, reactive oxygen species (ROS), and glutathione (GSH) levels, oocyte secretion factors, apoptosis and lipid metabolism-related gene expression, and subsequent embryonic development during the maturation of sheep oocytes. The oocyte secretion factor affects gene expression related to apoptosis and lipid metabolism and subsequent embryonic development. The results showed that the proportion of spindle and normal chromosome arrangements increased in the 5 μM RSG treatment group, the lipid content increased after cell maturation, the ROS level decreased, and the GSH level increased. The expressions of oocyte secretion factor (GDF9 and BMP15), anti-apoptosis gene (BCL2), and lipid metabolism-related genes (ACAA1, CPT1A, PLIN2) were increased in the 5 μM treatment group. Finally, the development of blastocysts was examined. After the oocytes were treated with 5 μM RSG, the blastocyst rate and the gene expression of the totipotency gene (OCT4) were increased. It was concluded that increasing PPARγ activity during ovine oocyte maturation could promote lipid metabolism, reduce oxidative stress, and improve the ovine oocyte maturation rate and subsequent embryo development.

Interplay of FXN expression and lipolysis in white adipocytes plays a critical role in insulin sensitivity in Friedreich's ataxia mouse model

Frataxin (FXN) is required for iron-sulfur cluster biogenesis, and its loss causes the early-onset neurodegenerative disease Friedreich ataxia (FRDA). Loss of FXN is a susceptibility factor in the development of diabetes, a common metabolic complication after myocardial hypertrophy in patients with FRDA. The underlying mechanism of FXN deficient-induced hyperglycemia in FRDA is, however, poorly understood. In this study, we confirmed that the FXN deficiency mouse model YG8R develops insulin resistance in elder individuals by disturbing lipid metabolic homeostasis in adipose tissues. Evaluation of lipolysis, lipogenesis, and fatty acid β-oxidation showed that lipolysis is most severely affected in white adipose tissues. Consistently, FXN deficiency significantly decreased expression of lipolytic genes encoding adipose triglyceride lipase (Atgl) and hormone-sensitive lipase (Hsl) resulting in adipocyte enlargement and inflammation. Lipolysis induction by fasting or cold exposure remarkably upregulated FXN expression, though FXN deficiency lessened the competency of lipolysis compared with the control or wild type mice. Moreover, we found that the impairment of lipolysis was present at a young age, a few months earlier than hyperglycemia and insulin resistance. Forskolin, an activator of lipolysis, or pioglitazone, an agonist of PPARγ, improved insulin sensitivity in FXN-deficient adipocytes or mice. We uncovered the interplay between FXN expression and lipolysis and found that impairment of lipolysis, particularly the white adipocytes, is an early event, likely, as a primary cause for insulin resistance in FRDA patients at later age.

Lipases are differentially regulated by hormones to maintain free fatty acid homeostasis for insect brain development

BACKGROUND

Free fatty acids (FFAs) play vital roles as energy sources and substrates in organisms; however, the molecular mechanism regulating the homeostasis of FFA levels in various circumstances, such as feeding and nonfeeding stages, is not fully clarified. Holometabolous insects digest dietary triglycerides (TAGs) during larval feeding stages and degrade stored TAGs in the fat body during metamorphosis after feeding cessation, which presents a suitable model for this study.

RESULTS

This study reported that two lipases are differentially regulated by hormones to maintain the homeostasis of FFA levels during the feeding and nonfeeding stages using the lepidopteran insect cotton bollworm Helicoverpa armigera as a model. Lipase member H-A-like (Lha-like), related to human pancreatic lipase (PTL), was abundantly expressed in the midgut during the feeding stage, while the monoacylglycerol lipase ABHD12-like (Abhd12-like), related to human monoacylglycerol lipase (MGL), was abundantly expressed in the fat body during the nonfeeding stage. Lha-like was upregulated by juvenile hormone (JH) via the JH intracellular receptor methoprene-tolerant 1 (MET1), and Abhd12-like was upregulated by 20-hydroxyecdysone (20E) via forkhead box O (FOXO) transcription factor. Knockdown of Lha-like decreased FFA levels in the hemolymph and reduced TAG levels in the fat body. Moreover, lipid droplets (LDs) were small, the brain morphology was abnormal, the size of the brain was small, and the larvae showed the phenotype of delayed pupation, small pupae, and delayed tissue remodeling. Knockdown of Abhd12-like decreased FFA levels in the hemolymph; however, TAG levels increased in the fat body, and LDs remained large. The development of the brain was arrested at the larval stage, and the larvae showed a delayed pupation phenotype and delayed tissue remodeling.

CONCLUSIONS

The differential regulation of lipases expression by different hormones determines FFAs homeostasis and different TAG levels in the fat body during the feeding larval growth and nonfeeding stages of metamorphosis in the insect. The homeostasis of FFAs supports insect growth, brain development, and metamorphosis.

The pivotal role of dysregulated autophagy in the progression of non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is a clinicopathologic syndrome characterized by excessive fat deposition in hepatocytes and a major cause of end-stage liver disease. Autophagy is a metabolic pathway responsible for degrading cytoplasmic products and damaged organelles, playing a pivotal role in maintaining the homeostasis and functionality of hepatocytes. Recent studies have shown that pharmacological intervention to activate or restore autophagy provides benefits for liver function recovery by promoting the clearance of lipid droplets (LDs) in hepatocytes, decreasing the production of pro-inflammatory factors, and inhibiting activated hepatic stellate cells (HSCs), thus improving liver fibrosis and slowing down the progression of NAFLD. This article summarizes the physiological process of autophagy, elucidates the close relationship between NAFLD and autophagy, and discusses the effects of drugs on autophagy and signaling pathways from the perspectives of hepatocytes, kupffer cells (KCs), and HSCs to provide assistance in the clinical management of NAFLD.

A promising anti-tumor targeting on ERMMDs mediated abnormal lipid metabolism in tumor cells

The investigation of aberrations in lipid metabolism within tumor has become a burgeoning field of study that has garnered significant attention in recent years. Lipids can serve as a potent source of highly energetic fuel to support the rapid growth of neoplasia, in where the ER-mitochondrial membrane domains (ERMMDs) provide an interactive network for facilitating communication between ER and mitochondria as well as their intermembrane space and adjunctive proteins. In this review, we discuss fatty acids (FAs) anabolic and catabolic metabolism, as well as how CPT1A-VDAC-ACSL clusters on ERMMDs participate in FAs transport, with a major focus on ERMMDs mediated collaborative loop of FAO, Ca2+ transmission in TCA cycle and OXPHOS process. Here, we present a comprehensive perspective on the regulation of aberrant lipid metabolism through ERMMDs conducted tumor physiology might be a promising and potential target for tumor starvation therapy.

S-acylation of ATGL is required for lipid droplet homoeostasis in hepatocytes

Lipid droplets (LDs) are organelles specialized in the storage of neutral lipids, cholesterol esters and triglycerides, thereby protecting cells from the toxicity of excess lipids while allowing for the mobilization of lipids in times of nutrient deprivation. Defects in LD function are associated with many diseases. S-acylation mediated by zDHHC acyltransferases modifies thousands of proteins, yet the physiological impact of this post-translational modification on individual proteins is poorly understood. Here, we show that zDHHC11 regulates LD catabolism by modifying adipose triacylglyceride lipase (ATGL), the rate-limiting enzyme of lipolysis, both in hepatocyte cultures and in mice. zDHHC11 S-acylates ATGL at cysteine 15. Preventing the S-acylation of ATGL renders it catalytically inactive despite proper localization. Overexpression of zDHHC11 reduces LD size, whereas its elimination enlarges LDs. Mutating ATGL cysteine 15 phenocopies zDHHC11 loss, causing LD accumulation, defective lipolysis and lipophagy. Our results reveal S-acylation as a mode of regulation of ATGL function and LD homoeostasis. Modulating this pathway may offer therapeutic potential for treating diseases linked to defective lipolysis, such as fatty liver disease.

ACADM inhibits AMPK activation to modulate PEDV-induced lipophagy and β-oxidation for impairing viral replication

Porcine epidemic diarrhea virus (PEDV) belongs to the Alphacoronavirus genus within the Coronavirus family, causing severe watery diarrhea in piglets and resulting in significant economic losses. Medium-chain acyl-CoA dehydrogenase (ACADM) is an enzyme participating in lipid metabolism associated with metabolic diseases and pathogen infections. Nonetheless, the precise role of ACADM in regulating PEDV replication remains uncertain. In this study, we identified ACADM as the host binding partner of NSP4 via immunoprecipitation-mass spectrometry analysis. The interaction between ACADM and NSP4 was subsequently corroborated through coimmunoprecipitation and laser confocal microscopy. Following this, a notable upsurge in ACADM expression was observed during PEDV infection. ACADM overexpression effectively inhibited virus replication, whereas ACADM knockdown facilitated virus replication, suggesting ACADM has negative regulation effect on PEDV infection. Furthermore, we demonstrated fatty acid β-oxidation affected PEDV replication for the first time, inhibition of fatty acid β-oxidation reduced PEDV replication. ACADM decreased PEDV-induced β-oxidation to suppress PEDV replication. Mechanistically, ACADM reduced cellular free fatty acid levels and subsequent β-oxidation by hindering AMPK-mediated lipophagy. In summary, our results reveal that ACADM plays a negative regulatory role in PEDV replication by regulating lipid metabolism. The present study introduces a novel approach for the prevention and control of PEDV infection.

Role of hypoxia-inducible-factor-1α (HIF-1α) in ferroptosis of adipose tissue during ketosis

Postpartum cows experience lipolysis in adipose tissue due to negative energy balance (NEB), and accumulation of free fatty acids (FFA) leads to metabolic stress in adipose tissue. Ferroptosis is a type of cell death triggered by excessive buildup of iron-dependent lipid peroxides, which is involved in the occurrence and development of various metabolic diseases in nonruminants. However, it is still unclear whether ferroptosis occurs in the adipose tissue of ketotic cows and the regulatory mechanisms behind ferroptosis. Despite multiple studies demonstrating the significant involvement of hypoxia-inducible-factor-1α (HIF-1α) in regulating cellular dysfunction, its specific function in adipose tissue of ketotic dairy cows remains uncertain, particularly its regulation of oxidative stress and ferroptosis. The study aimed to explore the impact of HIF-1α on oxidative stress and ferroptosis in bovine subcutaneous adipose tissue and isolated adipocytes. The adipose tissue of clinical ketosis cows (n = 15) with a serum BHB concentration of 3.13 mM (interquartile range = 0.14) and healthy cows (n = 15) with a serum BHB concentration of and 0.58 mM (interquartile range = 0.13) was collected. The results showed that the concentrations of lipid peroxidation malondialdehyde (MDA), reactive oxygen species (ROS), Fe2+ and total iron were increased in adipose tissue of cows with ketosis, while the contents of glutathione (GSH) were reduced. Furthermore, the protein levels of HIF-1α, heme oxygenase 1 (HMOX1), catalase (CAT), superoxide dismutase 1 (SOD1), acyl-CoA synthetase 4 (ACSL4), and nuclear factor erythroid-derived 2-like 2 (NFE2L2) exhibited higher abundance in adipose tissue obtained from cows with ketosis, whereas the protein abundance of solute carrier family 7 member 11 (SLC7A11), glutamate cysteine ligase catalytic subunit (GCLC), kelch-like ECH-associated protein 1 (KEAP1), glutamate cysteine ligase regulatory subunit (GCLM) and glutathione peroxidase 4 (GPX4) were lower. To simulate the ferroptosis state of adipose tissue in ketotic cows, primary bovine adipocytes were isolated from the adipose tissue of healthy cows and cultured with erastin to construct ferroptosis model. Adipocytes were cultured with either an adenovirus overexpressing HIF-1α or small interfering RNA targeting HIF-for 48 h, followed by exposure to erastin (1 μM) for 24 h. Treatment with erastin led to higher protein abundance of CAT, SOD1, NFE2L2 and HMOX1, while it inhibited the protein expression levels of GCLC, SLC7A11, GCLM, GPX4 and KEAP1. Furthermore, erastin treatment elevated the levels of ROS, MDA, Fe2+, total iron and reduced the content of GSH. The overexpression of HIF-1α reversed the erastin-induced decreases in the protein abundance of GPX4 and SLC7A11, as well as the levels of MDA, ROS, Fe2+ and total iron, while significantly increasing protein abundance and content of CAT, SOD1, NFE2L2, HMOX1, GCLC, GCLM, GPX4, SLC7A11 and GSH. Conversely, the silencing of HIF-1α further exacerbated the erastin-induced levels of MDA, ROS, Fe2+ and total iron, while inhibiting the upregulation of SOD1, CAT, NFE2L2 and HMOX1. Collectively, these findings suggest that activation of HIF-1α may function as an adaptive mechanism to mitigate ferroptosis and alleviate oxidative stress in adipose tissue.

Pro-survival signaling regulates lipophagy essential for multiple myeloma resistance to stress-induced death

Pro-survival metabolic adaptations to stress in tumorigenesis remain less well defined. We find that multiple myeloma (MM) is unexpectedly dependent on beta-oxidation of long-chain fatty acids (FAs) for survival under both basal and stress conditions. However, under stress conditions, a second pro-survival signal is required to sustain FA oxidation (FAO). We previously found that CD28 is expressed on MM cells and transduces a significant pro-survival/chemotherapy resistance signal. We now find that CD28 signaling regulates autophagy/lipophagy that involves activation of the Ca2+→AMPK→ULK1 axis and regulates the translation of ATG5 through HuR, resulting in sustained lipophagy, increased FAO, and enhanced MM survival. Conversely, blocking autophagy/lipophagy sensitizes MM to chemotherapy in vivo. Our findings link a pro-survival signal to FA availability needed to sustain the FAO required for cancer cell survival under stress conditions and identify lipophagy as a therapeutic target to overcome treatment resistance in MM.

TNKS1BP1 facilitates ubiquitination of CNOT4 by TRIM21 to promote hepatocellular carcinoma progression and immune evasion

Immune checkpoint inhibitors, particularly PD-1/PD-L1 blockades, have been approved for unresectable hepatocellular carcinoma (HCC). However, high resistance rates still limit their efficacy, highlighting the urgent need to understand the underlying mechanisms and develop strategies for overcoming the resistance. In this study, tankyrasel binding protein 1 (TNKS1BP1) was found to interact with tripartite motif containing 21 (TRIM21) and mediated the ubiquitination of CCR4-NOT transcription complex subunit 4 (CNOT4) at the K239 residue via K48 and K6 linkage, which was essential for its tumorigenesis function. Autophagy and lipid reprogramming were identified as two possible mechanisms underlying the pro-tumor effect of TNKS1BP1. Upregulated TNKS1BP1 inhibited autophagy while induced lipid accumulation by inhibiting the JAK2/STAT3 pathway upon the degradation of CNOT4 in HCC. Importantly, knocking down TNKS1BP1 synergized with anti-PD-L1 treatment by upregulating PD-L1 expression on tumor cells via the JAK2/STAT3 pathway, and remodeling the tumor microenvironment by increasing infiltration of tumor-infiltrating lymphocytes as well as augmenting the effect of cytotoxic T lymphocytes. In conclusion, this study identified TNKS1BP1 as a predictive biomarker for patient prognosis and a promising therapeutic target to overcome anti-PD-L1 resistance in HCC.

Autophagy counters inflammation-driven glycolytic impairment in aging hematopoietic stem cells

Autophagy is central to the benefits of longevity signaling programs and to hematopoietic stem cell (HSC) response to nutrient stress. With age, a subset of HSCs increases autophagy flux and preserves regenerative capacity, but the signals triggering autophagy and maintaining the functionality of autophagy-activated old HSCs (oHSCs) remain unknown. Here, we demonstrate that autophagy is an adaptive cytoprotective response to chronic inflammation in the aging murine bone marrow (BM) niche. We find that inflammation impairs glucose uptake and suppresses glycolysis in oHSCs through Socs3-mediated inhibition of AKT/FoxO-dependent signaling, with inflammation-mediated autophagy engagement preserving functional quiescence by enabling metabolic adaptation to glycolytic impairment. Moreover, we show that transient autophagy induction via a short-term fasting/refeeding paradigm normalizes glycolytic flux and significantly boosts oHSC regenerative potential. Our results identify inflammation-driven glucose hypometabolism as a key driver of HSC dysfunction with age and establish autophagy as a targetable node to reset oHSC regenerative capacity.

General autophagy-dependent and -independent lipophagic processes collaborate to regulate the overall level of lipophagy in yeast

ABBREVIATION

AP: autophagosome; ATG: autophagy related; CMA: chaperone-mediated autophagy; ESCRT: endosomal sorting complex required for transport; FA: fatty acid; LD: lipid droplet; Ld microdomains: liquid-disordered microdomains; NL: neutral lipid.

Role of diacylglycerol O-acyltransferase 1 (DGAT1) in lipolysis and autophagy of adipose tissue from ketotic dairy cows

High-yielding dairy cows in early lactation often encounter difficulties in meeting the energy requirements essential for maintaining milk production. This is primarily attributed to insufficient dry matter intake, which consequently leads to sustained lipolysis of adipose tissue. Fatty acids released by lipolysis can disrupt metabolic homeostasis. Autophagy, an adaptive response to intracellular environmental changes, is considered a crucial mechanism for regulating lipid metabolism and maintaining a proper cellular energy status. Despite its close relationship with aberrant lipid metabolism and cytolipotoxicity in animal models of metabolic disorders, the precise function of diacylglycerol o-acyltransferase 1 (DGAT1) in bovine adipose tissue during periods of negative energy balance is not fully understood, particularly regarding its involvement in lipolysis and autophagy. The objective of the present study was to assess the effect of DGAT1 on both lipolysis and autophagy in bovine adipose tissue and isolated adipocytes. Adipose tissue and blood samples were collected from cows diagnosed as clinically ketotic (n = 15) or healthy (n = 15) following a veterinary evaluation based on clinical symptoms and serum concentrations of BHB, which were 3.19 mM (interquartile range = 0.20) and 0.50 mM (interquartile range = 0.06), respectively. Protein abundance of DGAT1 and phosphorylation levels of unc-51-like kinase 1 (ULK1), were greater in adipose tissue from cows with ketosis, whereas phosphorylation levels of phosphoinositide 3-kinase (PI3K), protein kinase B (AKT), and mammalian target of rapamycin (mTOR) were lower. Furthermore, when adipocytes isolated from the harvested adipose tissue of 15 healthy cows were transfected with DGAT1 overexpression adenovirus or DGAT1 small interfering RNA followed by exposure to epinephrine (EPI), it led to greater ratios and protein abundance of phosphorylated hormone-sensitive triglyceride lipase (LIPE) to total LIPE and adipose triglyceride lipase (ATGL), while inhibiting the protein phosphorylation levels of ULK1, PI3K, AKT, and mTOR. Overexpression of DGAT1 in EPI-treated adipocytes reduced lipolysis and autophagy, whereas silencing DGAT1 further exacerbated EPI-induced lipolysis and autophagy. Taken together, these findings indicate that upregulation of DGAT1 may function as an adaptive response to suppress adipocytes lipolysis, highlighting the significance of maintaining metabolic homeostasis in dairy cows during periods of negative energy balance.

Review article: Hepatic steatosis and its associations with acute and chronic liver diseases

BACKGROUND

Hepatic steatosis is a common finding in liver histopathology and the hallmark of metabolic dysfunction-associated steatotic liver disease (MASLD), formerly known as non-alcoholic fatty liver disease (NAFLD), whose global prevalence is rising.

AIMS

To review the histopathology of hepatic steatosis and its mechanisms of development and to identify common and rare disease associations.

METHODS

We reviewed literature on the basic science of lipid droplet (LD) biology and clinical research on acute and chronic liver diseases associated with hepatic steatosis using the PubMed database.

RESULTS

A variety of genetic and environmental factors contribute to the development of chronic hepatic steatosis or steatotic liver disease, which typically appears macrovesicular. Microvesicular steatosis is associated with acute mitochondrial dysfunction and liver failure. Fat metabolic processes in hepatocytes whose dysregulation leads to the development of steatosis include secretion of lipoprotein particles, uptake of remnant lipoprotein particles or free fatty acids from blood, de novo lipogenesis, oxidation of fatty acids, lipolysis and lipophagy. Hepatic insulin resistance is a key feature of MASLD. Seipin is a polyfunctional protein that facilitates LD biogenesis. Assembly of hepatitis C virus takes place on LD surfaces. LDs make important, functional contact with the endoplasmic reticulum and other organelles.

CONCLUSIONS

Diverse liver pathologies are associated with hepatic steatosis, with MASLD being the most important contributor. The biogenesis and dynamics of LDs in hepatocytes are complex and warrant further investigation. Organellar interfaces permit co-regulation of lipid metabolism to match generation of potentially toxic lipid species with their LD depot storage.

13C-metabolic flux analysis reveals metabolic rewiring in HL-60 neutrophil-like cells through differentiation and immune stimulation

Neutrophils are innate immune cells and the first line of defense for the maintenance of homeostasis. However, our knowledge of the metabolic rewiring associated with their differentiation and immune stimulation is limited. Here, quantitative 13C-metabolic flux analysis was performed using HL-60 cells as the neutrophil model. A metabolic model for 13C-metabolic flux analysis of neutrophils was developed based on the accumulation of 13C in intracellular metabolites derived from 13C-labeled extracellular carbon sources and intracellular macromolecules. Aspartate and glutamate in the medium were identified as carbon sources that enter central carbon metabolism. Furthermore, the breakdown of macromolecules, estimated to be fatty acids and nucleic acids, was observed. Based on these results, a modified metabolic model was used for 13C-metabolic flux analysis of undifferentiated, differentiated, and lipopolysaccharide (LPS)-activated HL-60 cells. The glucose uptake rate and glycolytic flux decreased with differentiation, whereas the tricarboxylic acid (TCA) cycle flux remained constant. The addition of LPS to differentiated HL-60 cells activated the glucose uptake rate and pentose phosphate pathway (PPP) flux levels, resulting in an increased rate of total NADPH regeneration, which could be used to generate reactive oxygen species. The flux levels of fatty acid degradation and synthesis were also increased in LPS-activated HL-60 cells. Overall, this study highlights the quantitative metabolic alterations in multiple pathways via the differentiation and activation of HL-60 cells using 13C-metabolic flux analysis.

Effect of MEHP on testosterone synthesis via Sirt1/Foxo1/Rab7 signaling pathway inhibition of lipophagy in TM3 cells

Mono-2-ethylhexyl phthalic acid (MEHP) is the most toxic metabolite of the plasticizer di-2-ethylhexyl phthalic acid (DEHP), and studies have shown that MEHP causes serious reproductive effects. However, its exact mechanisms of action remain elusive. In this study, we aimed to investigate the reproductive effects of MEHP and preliminarily explore its underlying molecular mechanisms. We found that TM3 cells gradually secreted less testosterone and intracellular free cholesterol with increasing MEHP exposure. MEHP exposure inhibited lipophagy and the Sirt1/Foxo1/Rab7 signaling pathway in TM3 cells, causing aberrant accumulation of intracellular lipid droplets. Addition of the Sirt1 agonist SRT1720 and Rab7 agonist ML-098 alleviated the inhibition of lipophagy and increased free cholesterol and testosterone contents in TM3 cells. SRT1720 alleviated the inhibitory effect of MEHP on the Sirt1/Foxo1/Rab7 signaling pathway, whereas ML-098 only alleviated the inhibition of Rab7 protein expression by MEHP and had no effect on Sirt1 and Foxo1 protein expression. This suggests that MEHP inhibits lipophagy in TM3 cells by suppressing the Sirt1/Foxo1/Rab7 signaling pathway, ultimately leading to a further decrease in cellular testosterone secretion. This study improves our current understanding of the toxicity and molecular mechanisms of action of MEHP and provides new insights into the reproductive effects of phthalic acid esters.

Inflammation-mediated metabolic regulation in adipose tissue

Chronic inflammation of adipose tissue is a prominent characteristic of many metabolic diseases. Lipid metabolism in adipose tissue is consistently dysregulated during inflammation, which is characterized by substantial infiltration by proinflammatory cells and high cytokine concentrations. Adipose tissue inflammation is caused by a variety of endogenous factors, such as mitochondrial dysfunction, reactive oxygen species (ROS) production, endoplasmic reticulum (ER) stress, cellular senescence, ceramides biosynthesis and mediators of lipopolysaccharides (LPS) signaling. Additionally, the gut microbiota also plays a crucial role in regulating adipose tissue inflammation. Essentially, adipose tissue inflammation arises from an imbalance in adipocyte metabolism and the regulation of immune cells. Specific inflammatory signals, including nuclear factor-κB (NF-κB) signaling, inflammasome signaling and inflammation-mediated autophagy, have been shown to be involved in the metabolic regulation. The pathogenesis of metabolic diseases characterized by chronic inflammation (obesity, insulin resistance, atherosclerosis and nonalcoholic fatty liver disease [NAFLD]) and recent research regarding potential therapeutic targets for these conditions are also discussed in this review.

The role of lymphatic endothelial cell metabolism in lymphangiogenesis and disease

Lymphatic endothelial cells (LECs) line lymphatic vessels, which play an important role in the transport of lymph fluid throughout the human body. An organized lymphatic network develops via a process termed "lymphangiogenesis." During development, LECs respond to growth factor signaling to initiate the formation of a primary lymphatic vascular network. These LECs display a unique metabolic profile, preferring to undergo glycolysis even in the presence of oxygen. In addition to their reliance on glycolysis, LECs utilize other metabolic pathways such as fatty acid β-oxidation, ketone body oxidation, mitochondrial respiration, and lipid droplet autophagy to support lymphangiogenesis. This review summarizes the current understanding of metabolic regulation of lymphangiogenesis. Moreover, it highlights how LEC metabolism is implicated in various pathological conditions.

Vine tea total flavonoids activate the AMPK/mTOR pathway to amelioration hepatic steatosis in mice fed a high-fat diet

Vine tea (Ampelopsis grossedentata), a traditional Chinese tea, is rich in flavonoids with various biological activities. Our study found that Vine tea total flavonoids (TFs) treatment reduced the body mass and blood lipid levels and improved the hepatic tissue morphology in mice fed the high-fat diet (HFD). In vivo, TF treatment activated the hepatic adenosine monophosphate-activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR) pathway, initiated autophagy, and regulated the expression levels of proteins for lipid metabolism in those HFD-fed mice. In vitro, TF treatment dramatically reduced the lipid droplets and triacylglycerol content in HepG2 and L02 cells treated with oleic acid (OA). These were associated with the activation of the AMPK/mTOR pathway and autophagy initiation in OA-treated hepatocytes. This phenotype was abolished in the presence of 3-methyladenine, an autophagy inhibitor. Our results indicated that the TF activation of AMPK/mTOR leads to the stimulation of autophagy and a decrease in the buildup of intracellular lipids in hepatocytes, showing the potential of TF as a therapeutic agent for nonalcoholic fatty liver disease. PRACTICAL APPLICATION: Vine tea, a tea drink, has been consumed by Chinese folk for over a thousand years. The result of this study will provide evidence that vine tea total flavonoids have potential use as a functional material for the prevention and amelioration of nonalcoholic fatty liver disease.

Lipid droplets provide metabolic flexibility for cancer progression

A hallmark of cancer cells is their remarkable ability to efficiently adapt to favorable and hostile environments. Due to a unique metabolic flexibility, tumor cells can grow even in the absence of extracellular nutrients or in stressful scenarios. To achieve this, cancer cells need large amounts of lipids to build membranes, synthesize lipid-derived molecules, and generate metabolic energy in the absence of other nutrients. Tumor cells potentiate strategies to obtain lipids from other cells, metabolic pathways to synthesize new lipids, and mechanisms for efficient storage, mobilization, and utilization of these lipids. Lipid droplets (LDs) are the organelles that collect and supply lipids in eukaryotes and it is increasingly recognized that the accumulation of LDs is a new hallmark of cancer cells. Furthermore, an active role of LD proteins in processes underlying tumorigenesis has been proposed. Here, by focusing on three major classes of LD-resident proteins (perilipins, lipases, and acyl-CoA synthetases), we provide an overview of the contribution of LDs to cancer progression and discuss the role of LD proteins during the proliferation, invasion, metastasis, apoptosis, and stemness of cancer cells.

The ubiquitous role of ubiquitination in lipid metabolism

Lipids are essential molecules that play key roles in cell physiology by serving as structural components, for storage of energy, and in signal transduction. Hence, efficient regulation and maintenance of lipid homeostasis are crucial for normal cellular and tissue function. In the past decade, increasing research has shown the importance of ubiquitination in regulating the stability of key players in different aspects of lipid metabolism. This review describes recent insights into the regulation of lipid metabolism by ubiquitin signaling, discusses how ubiquitination can be targeted in diseases characterized by lipid dysregulation, and identifies areas that require further research.

Modulation of adipose tissue metabolism by exosomes in obesity

Obesity and its related metabolic complications represent a significant global health challenge. Central to this is the dysregulation of glucolipid metabolism, with a predominant focus on glucose metabolic dysfunction in the current research, whereas adipose metabolism impairment garners less attention. Exosomes (EXs), small extracellular vesicles (EVs) secreted by various cells, have emerged as important mediators of intercellular communication and have the potential to be biomarkers, targets, and therapeutic tools for diverse diseases. In particular, EXs have been found to play a role in adipose metabolism by transporting cargoes such as noncoding RNAs (ncRNA), proteins, and other factors. This review article summarizes the current understanding of the role of EXs in mediating adipose metabolism disorders in obesity. It highlights their roles in adipogenesis (encompassing adipogenic differentiation and lipid synthesis), lipid catabolism, lipid transport, and white adipose browning. The insights provided by this review offer new avenues for developing exosome-based therapies to treat obesity and its associated comorbidities.

Sea Cucumber Plasmalogen Regulates the Lipid Profile in High-Fat Diet Mouse Liver via Lipophagy

The sea cucumber plasmalogen PlsEtn has been shown to be associated with various chronic diseases related to lipid metabolism. However, the mechanism is unclear. Therefore, the present study used the sea cucumber plasmanylcholine PakCho as a structural contrast to PlsEtn and assessed its effect in 8 week high-fat diet (HFD)-fed mice. The lipidomic approach based on high-resolution mass spectrometry combined with molecular biology techniques was used to evaluate the mechanism of PlsEtn. The results showed that both PlsEtn and PakCho significantly inhibited an increase in mouse body weight and liver total triglyceride and total cholesterol levels caused by HFD. In addition, oil red O staining demonstrated that lipid droplets stored in the liver were degraded. Meanwhile, untargeted lipidomic experiments revealed that total lipids (increased by 42.8 mmol/mg prot; p < 0.05), triglycerides (increased by 38.9 mmol/mg prot; p < 0.01), sphingolipids (increased by 1.5 mmol/mg prot; p < 0.0001), and phospholipids (increased by 2.5 mmol/mg prot; p < 0.05) were all significantly elevated under HFD. PlsEtn resolved lipid metabolism disorders by alleviating the abnormal expression of lipid subclasses. In addition, five lipid molecular species, PE (18:1/20:4), PE (18:1/20:3), PE (18:1/18:3), TG (16:0/16:0/17:0), and TG (15:0/16:0/18:1), were identified as the biomarkers of HFD-induced lipid metabolism disorders. Finally, lipophagy-associated protein expression analysis showed that HFD abnormally activated lipophagy via ULK1 phosphorylation and PlsEtn alleviated lipophagy disorder through lysosomal function promotion. In addition, PlsEtn performed better than PakCho. Taken together, the current study results unraveled the mechanism of PlsEtn in alleviating lipid metabolism disorder and offered a new theoretical foundation for the high-value development of sea cucumber.

In the fed state, autophagy plays a crucial role in assisting the insect vector Rhodnius prolixus mobilize TAG reserves under forced flight activity

Autophagy is a cellular degradation pathway mediated by highly conserved autophagy-related genes (Atgs). In our previous work, we showed that inhibiting autophagy under starvation conditions leads to significant physiological changes in the insect vector of Chagas disease Rhodnius prolixus; these changes include triacylglycerol (TAG) retention in the fat body, reduced survival and impaired locomotion and flight capabilities. Herein, because it is known that autophagy can be modulated in response to various stimuli, we further investigated the role of autophagy in the fed state, following blood feeding. Interestingly, the primary indicator for the presence of autophagosomes, the lipidated form of Atg8 (Atg8-II), displayed 20%-50% higher autophagic activation in the first 2 weeks after feeding compared to the third week when digestion was complete. Despite the elevated detection of autophagosomes, RNAi-mediated suppression of RpAtg6 and RpAtg8 did not cause substantial changes in TAG or protein levels in the fat body or the flight muscle during blood digestion. We also found that knockdown of RpAtg6 and RpAtg8 led to modest modulations in the gene expression of essential enzymes involved in lipid metabolism and did not significantly stimulate the expression of the chaperones BiP and PDI, which are the main effectors of the unfolded protein response. These findings indicate that impaired autophagy leads to slight disturbances in lipid metabolism and general cell proteostasis. However, the ability of insects to fly during forced flight until exhaustion was reduced by 60% after knockdown of RpAtg6 and RpAtg8. This change was accompanied by TAG and protein increases as well as decreased ATP levels in the fat body and flight muscle, indicating that autophagy during digestion, i.e., under fed conditions, is necessary to sustain high-performance activity.

2-Bromopalmitate depletes lipid droplets to inhibit viral replication

The global impact of emerging viral infections emphasizes the urgent need for effective broad-spectrum antivirals. The cellular organelle, lipid droplet (LD), is utilized by many types of viruses for replication, but its reduction does not affect cell survival. Therefore, LD is a potential target for developing broad-spectrum antivirals. In this study, we found that 2-bromopalmitate (2 BP), a previously defined palmitoylation inhibitor, depletes LD across all studied cell lines and exerts remarkable antiviral effects on different coronaviruses. We comprehensively utilized 2 BP, alongside other palmitoylation inhibitors such as cerulenin and 2-fluoro palmitic acid (2-FPA), as well as the enhancer palmostatin B and evaluated their impact on LD and the replication of human coronaviruses (hCoV-229E, hCoV-Oc43) and murine hepatitis virus (MHV-A59) at non-cytotoxic concentrations. While cerulenin and 2-FPA exhibited moderate inhibition of viral replication, 2 BP exhibited a much stronger suppressive effect on MHV-A59 replication, although they share similar inhibitory effects on palmitoylation. As expected, palmostatin B significantly enhanced viral replication, it failed to rescue the inhibitory effects of 2 BP, whereas it effectively counteracted the effects of cerulenin and 2-FPA. This suggests that the mechanism that 2 BP used to inhibit viral replication is beyond palmitoylation inhibition. Further investigations unveil that 2 BP uniquely depletes LDs, a phenomenon not exhibited by 2-FPA and cerulenin. Importantly, the depletion of LDs was closely associated with the inhibition of viral replication because the addition of oleic acid to 2 BP significantly rescued LD depletion and its inhibitory effects on MHV-A59. Our findings indicate that the inhibitory effects of 2 BP on viral replication primarily stem from LD disruption rather than palmitoylation inhibition. Intriguingly, fatty acid (FA) assays demonstrated that 2 BP reduces the FA level in mitochondria while concurrently increasing FA levels in the cytoplasm. These results highlight the crucial role of LDs in viral replication and uncover a novel biological activity of 2 BP. These insights contribute to the development of broad-spectrum antiviral strategies.

IMPORTANCE

In our study, we conducted a comparative investigation into the antiviral effects of palmitoylation inhibitors including 2-bromopalmitate (2-BP), 2-fluoro palmitic acid (2-FPA), and cerulenin. Surprisingly, we discovered that 2-BP has superior inhibitory effects on viral replication compared to 2-FPA and cerulenin. However, their inhibitory effects on palmitoylation were the same. Intrigued by this finding, we delved deeper into the underlying mechanism of 2-BP's potent antiviral activity, and we unveiled a novel biological activity of 2-BP: depletion of lipid droplets (LDs). Importantly, we also highlighted the crucial role of LDs in viral replication. Our insights shed new light on the antiviral mechanism of LD depletion paving the way for the development of broad-spectrum antiviral strategies by targeting LDs.

Regional Differences in the Small Intestinal Proteome of Control Mice and of Mice Lacking Lysosomal Acid Lipase

The metabolic contribution of the small intestine (SI) is still unclear despite recent studies investigating the involvement of single cells in regional differences. Using untargeted proteomics, we identified regional characteristics of the three intestinal tracts of C57BL/6J mice and found that proteins abundant in the mouse ileum correlated with the high ileal expression of the corresponding genes in humans. In the SI of C57BL/6J mice, we also detected an increasing abundance of lysosomal acid lipase (LAL), which is responsible for degrading triacylglycerols and cholesteryl esters within the lysosome. LAL deficiency in patients and mice leads to lipid accumulation, gastrointestinal disturbances, and malabsorption. We previously demonstrated that macrophages massively infiltrated the SI of Lal-deficient (KO) mice, especially in the duodenum. Using untargeted proteomics (ProteomeXchange repository, data identifier PXD048378), we revealed a general inflammatory response and a common lipid-associated macrophage phenotype in all three intestinal segments of Lal KO mice, accompanied by a higher expression of GPNMB and concentrations of circulating sTREM2. However, only duodenal macrophages activated a metabolic switch from lipids to other pathways, which were downregulated in the jejunum and ileum of Lal KO mice. Our results provide new insights into the process of absorption in control mice and possible novel markers of LAL-D and/or systemic inflammation in LAL-D.

Di (2-ethylhexyl) phthalate induced lipophagy-related renal ferroptosis in quail (Coturnix japonica)

Di(2-ethylhexyl) phthalate (DEHP) is a synthetic chemical applied as a plasticizer. As an environmental toxicant, DEHP poses a serious health threat. Many studies have revealed that DEHP can cause lead to various degrees of damage to the kidney. However, the evidence of DEHP-induced renal ferroptosis has not been reported. The purpose of this work was to probe the specific role of lipophagy in DEHP-induced renal injury and to investigate the relationship between lipophagy and ferroptosis. Quail were treated with DEHP (250 mg/kg BW/day, 500 mg/kg BW/day and 750 mg/kg BW/day) for 45 days. Microstructural and ultrastructural observations showed that DEHP caused damage to glomerular and tubular cells, and autophagy with multilayer structures were observed, suggesting that DEHP can induce lipophagy. The results indicated that the iron homeostasis was abnormal and the lipid peroxidation was increased. SLC7A11 and SLC3A2 were down-regulated. PTGS2, ACSL4 and LPCAT3 were elevated. In conclusion, DEHP could induce lipid peroxidation, lead to ferroptosis, and damage renal cells. Therefore, the relationship between lipophagy and ferroptosis was elucidated, which provided a new basis for intervention and prevention of DEHP increased diseases.

Glucose controls lipolysis through Golgi PtdIns4P-mediated regulation of ATGL

Metabolic crosstalk of the major nutrients glucose, amino acids and fatty acids (FAs) ensures systemic metabolic homeostasis. The coordination between the supply of glucose and FAs to meet various physiological demands is especially important as improper nutrient levels lead to metabolic disorders, such as diabetes and metabolic dysfunction-associated steatohepatitis (MASH). In response to the oscillations in blood glucose levels, lipolysis is thought to be mainly regulated hormonally to control FA liberation from lipid droplets by insulin, catecholamine and glucagon. However, whether general cell-intrinsic mechanisms exist to directly modulate lipolysis via glucose sensing remains largely unknown. Here we report the identification of such an intrinsic mechanism, which involves Golgi PtdIns4P-mediated regulation of adipose triglyceride lipase (ATGL)-driven lipolysis via intracellular glucose sensing. Mechanistically, depletion of intracellular glucose results in lower Golgi PtdIns4P levels, and thus reduced assembly of the E3 ligase complex CUL7FBXW8 in the Golgi apparatus. Decreased levels of the E3 ligase complex lead to reduced polyubiquitylation of ATGL in the Golgi and enhancement of ATGL-driven lipolysis. This cell-intrinsic mechanism regulates both the pool of intracellular FAs and their extracellular release to meet physiological demands during fasting and glucose deprivation. Moreover, genetic and pharmacological manipulation of the Golgi PtdIns4P-CUL7FBXW8-ATGL axis in mouse models of simple hepatic steatosis and MASH, as well as during ex vivo perfusion of a human steatotic liver graft leads to the amelioration of steatosis, suggesting that this pathway might be a promising target for metabolic dysfunction-associated steatotic liver disease and possibly MASH.

Lipid Droplets: Formation, Degradation, and Their Role in Cellular Responses to Flavivirus Infections

Lipid droplets (LDs) are cellular organelles derived from the endoplasmic reticulum (ER), serving as lipid storage sites crucial for maintaining cellular lipid homeostasis. Recent attention has been drawn to their roles in viral replication and their interactions with viruses. However, the precise biological functions of LDs in viral replication and pathogenesis remain incompletely understood. To elucidate the interaction between LDs and viruses, it is imperative to comprehend the biogenesis of LDs and their dynamic interactions with other organelles. In this review, we explore the intricate pathways involved in LD biogenies within the cytoplasm, encompassing the uptake of fatty acid from nutrients facilitated by CD36-mediated membranous protein (FABP/FATP)-FA complexes, and FA synthesis via glycolysis in the cytoplasm and the TCL cycle in mitochondria. While LD biogenesis primarily occurs in the ER, matured LDs are intricately linked to multiple organelles. Viral infections can lead to diverse consequences in terms of LD status within cells post-infection, potentially involving the breakdown of LDs through the activation of lipophagy. However, the exact mechanisms underlying LD destruction or accumulation by viruses remain elusive. The significance of LDs in viral replication renders them effective targets for developing broad-spectrum antivirals. Moreover, considering that reducing neutral lipids in LDs is a strategy for anti-obesity treatment, LD depletion may not pose harm to cells. This presents LDs as promising antiviral targets for developing therapeutics that are minimally or non-toxic to the host.

FOXO3/Rab7-Mediated Lipophagy and Its Role in Zn-Induced Lipid Metabolism in Yellow Catfish (Pelteobagrus fulvidraco)

Lipophagy is a selective autophagy that regulates lipid metabolism and reduces hepatic lipid deposition. However, the underlying mechanism has not been understood in fish. In this study, we used micronutrient zinc (Zn) as a regulator of autophagy and lipid metabolism and found that Ras-related protein 7 (rab7) was involved in Zn-induced lipophagy in hepatocytes of yellow catfish Pelteobagrus pelteobagrus. We then characterized the rab7 promoter and identified binding sites for a series of transcription factors, including Forkhead box O3 (FOXO3). Site mutation experiments showed that the -1358/-1369 bp FOXO3 binding site was responsible for Zn-induced transcriptional activation of rab7. Further studies showed that inhibition of rab7 significantly inhibited Zn-induced lipid degradation by lipophagy. Moreover, rab7 inhibitor also mitigated the Zn-induced increase of cpt1α and acadm expression. Our results suggested that Zn exerts its lipid-lowering effect partly through rab7-mediated lipophagy and FA β-oxidation in hepatocytes. Overall, our findings provide novel insights into the FOXO3/rab7 axis in lipophagy regulation and enhance the understanding of lipid metabolism by micronutrient Zn, which may help to reduce excessive lipid accumulation in fish.