Lipid droplets and cellular lipid metabolism

Cytoskeleton regulates lipid droplet fusion and lipid storage by controlling lipid droplet movement

Lipid droplets (LDs) are highly dynamic organelles that maintain cellular lipid homeostasis through size and number control. In adipose tissue, CIDEC plays a crucial role in LD fusion and lipid homeostasis. However, the regulatory factors and mechanisms of LD fusion remain largely unknown. Here, we established a high-throughput LD phenotypic screen on a compound library consisting of 2010 small molecules, and identified 11 cytoskeleton inhibitors that negatively regulate LD size. Using specific inhibitors against each of the three types of cytoskeleton, our data showed that the disruption of microtubules and microfilaments but not intermediate filaments limits CIDEC-mediated LD fusion and growth by reducing LD movement and LD-LD contact. The collective effect of microtubule inhibitors results in a small LD phenotype which favors lipolysis upon activation of cAMP-PKA pathway in adipocytes. Our findings demonstrate that cytoskeleton is involved in the process of LD fusion and growth, indicating their role in lipid storage metabolism. One-Sentence Summary: Cytoskeleton regulates lipid droplet fusion and lipid storage.

Radiolabeling lipoproteins to study and manage disease

PURPOSE

Lipoproteins are endogenous nanoparticles with essential roles in lipid transport and inflammation. Lipoproteins are also valuable in diagnosing and treating disease. For instance, certain lipoproteins are overexpressed in patients with atherosclerotic cardiovascular disease, and reconstituted lipoproteins have been extensively used for drug delivery. Radiolabeling has proven an especially powerful approach for studying and therapeutically exploiting lipoproteins. This review details how radiochemistry and nuclear imaging can facilitate the study of lipoproteins in health and disease. Among other topics, we discuss approaches for radiolabeling lipoproteins and detail how these have helped advance our understanding of lipoprotein biology and the diagnosis and treatment of diseases, including atherosclerosis, cancer, and hypercholesteremia.

METHODS

We performed an extensive literature search on all peer-reviewed studies involving radiolabeled lipoproteins and selected representative examples to provide a high-level overview of the most important discoveries and technological advancements.

RESULTS

More than 200 peer-reviewed papers involved radiolabeled lipoproteins, spanning mechanistic, diagnostic, and therapeutic studies across a wide range of diseases.

CONCLUSION

Radiolabeling has been critical in advancing our understanding of lipoprotein biology and leveraging these nanomaterials for diagnosing and treating disease.

Nuclear receptor signaling regulates compartmentalized phosphatidylcholine remodeling to facilitate thermosensitive lipid droplet fusion

Lipid droplet (LD) fusion plays a key role in cellular fat storage. How the phospholipid monolayer membrane of LD functions in fusion, however, is poorly understood. In Caenorhabditis elegans, loss of cytochrome P450 protein CYP-37A1 causes de-repression of nuclear receptor DAF-12, promoting thermosensitive LD fusion. Here, we report that in cyp-37A1 mutants, DAF-12 up-regulates the transcription and LD localization of seven fatty acid desaturases (FAT-1 to FAT-7) and a lysophosphatidylcholine acyltransferase 3 (LPCAT3) homolog MBOA-6. LD-targeting of these enzymes increases phosphatidylcholine (PC) containing ω-3 C20 polyunsaturated fatty acids, which are essential for thermosensitive fusion. ω-3 C20-PC increase LD membrane fluidity, as does high ambient temperature. Lowering LD membrane fluidity by a chemical membrane rigidifier attenuates thermosensitive fusion; ectopic targeting of ω3 desaturase FAT-1 or MBOA-6 to LDs increases fusion kinetics and thermosensitivity. Furthermore, human LPCAT3 localizes to LDs, positively regulates LD size in human cells and facilitates thermosensitive fusion in C. elegans. These results demonstrate that DAF-12 signaling regulates compartmentalized membrane remodeling and fluidization to facilitate conserved thermosensitive LD fusion.

Probiotics for the treatment of hyperlipidemia: Focus on gut-liver axis and lipid metabolism

Hyperlipidemia, a metabolic disorder marked by dysregulated lipid metabolism, is a key contributor to the onset and progression of various chronic diseases. Maintaining normal lipid metabolism is critical for health, as disruptions lead to dyslipidemia. The gut and liver play central roles in lipid homeostasis, with their bidirectional communication, known as the gut-liver axis, modulated by bile acids (BAs), gut microbiota, and their metabolites. BAs are essential for regulating their own synthesis, lipid metabolism, and anti-inflammatory responses, primarily through the farnesoid X receptor (FXR) and Takeda G protein-coupled receptor 5 (TGR5). Available evidence suggests that high-fat diet-induced the gut microbiota dysbiosis can induce "leaky gut," allowing toxic microbial metabolites to enter the liver via portal circulation, triggering liver inflammation and lipid metabolism disturbances, ultimately leading to hyperlipidemia. Extensive studies have highlighted the roles of probiotics and Traditional Chinese Medicine (TCM) in restoring gut-liver axis balance and modulating lipid metabolism through regulating the levels of lipopolysaccharides, short-chain fatty acids, and BAs. However, the therapeutic potential of probiotics and TCM for hyperlipidemia remains unclear. Here, firstly, we explore the intricate interplay among gut microbiota and metabolites, lipid metabolism, gut-liver axis, and hyperlipidemia. Secondly, we summarize the mechanisms by which probiotics and TCM can alleviate hyperlipidemia by altering the composition of gut microbiota and regulating lipid metabolism via the gut-liver axis. Finally, we emphasize that more clinical trials of probiotics and TCM are necessary to examine their effects on lipid metabolism and hyperlipidemia.

Application of humanized mice to toxicology studies: properties of chimeric mice with humanized liver (PXB-mice) for hepatotoxicity

Chimeric mice with humanized liver are considered a useful tool to predict drug pharmacokinetics and in vivo toxicity in humans. The PXB-mouse is one of such chimeric (humanized) mouse models with more than 70% of human hepatocytes in their liver, which can produce human albumin with human-type bile secretion and express human xenobiotic metabolizing enzymes. However, data are limited regarding the properties of such humanized mice in hepatotoxicity studies. This study aimed to explore the distinctive characteristics of chimeric PXB-mice with humanized liver that can influence susceptibility to hepatotoxicity. Morphologically, the PXB-mice have a diffuse hepatic macrovesicular and microvesicular steatosis in the transplanted human hepatocytes, which can be suppressed after human growth hormone treatment. The humanized liver of the PXB-mice has a metabolic zonation of glutamine synthetase, cytochrome P450 2E1, and argininosuccinate synthase 1, similar to normal liver in rodents and humans. The transplanted human hepatocytes in the PXB liver have a markedly decreased N-cadherin expression compared with normal human liver. Scanning electron microscopy revealed formation of septum-like structures encircling the transplanted human hepatocytes in the PXB liver, which consists of an accumulation of fibers in the space of Disse under transmission electron microscopy and is immunolabeled for laminin. Overall, the present report demonstrated the morphological and immunohistochemical characteristics of the PXB-mice with humanized liver along with some abnormalities in the cell adhesion of the transplanted human hepatocytes. These findings would be useful for hepatotoxicity studies using humanized animal models.

Proteome of granulosa cells lipid droplets reveals mechanisms regulating lipid metabolism at hierarchical and pre-hierarchical follicle in goose

Avian hierarchical follicles are formed by selection and dominance of pre-hierarchical follicles, and lipid metabolism plays a pivotal role in this process. The amount of lipid in goose follicular granulosa cells increases with the increase of culture time, and the neutral lipid in the cells is stored in the form of lipid droplets (LDs). LD-associated proteins (LDAPs) collaborate with LDs to regulate intracellular lipid homeostasis, which subsequently influences avian follicle development. The mechanism by which LDAPs regulate lipid metabolism in goose granulosa cells at different developmental stages is unclear. Therefore, using BODIPY staining, we found that at five time points during in vitro culture, the LD content in hierarchical granulosa cells was significantly higher than that in pre-hierarchical granulosa cells in this study (p < 0.001). Next, we identified LDAPs in both hierarchical and pre-hierarchical granulosa cells, and screened out 1,180, 922, 907, 663, and 1,313 differentially expressed proteins (DEPs) at the respective time points. Subsequently, by performing Clusters of Orthologous Groups (COGs) classification on the DEPs, we identified a large number of proteins related to lipid transport and metabolism. Following this, the potential functions of these DEPs were investigated through Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) functional enrichment analysis. Finally, the important pathway of fatty acid degradation and the key protein ACSL3 were screened out using Short Time-series Expression Miner (STEM) and Protein-Protein Interaction (PPI) analysis methods. It is hypothesized that ACSL3 may potentially modulate lipid metabolism through the fatty acid degradation pathway, thereby contributing to the difference in lipid content between hierarchical and pre-hierarchical granulosa cells. These findings will provide a theoretical foundation for further studies on the role of LDs and LDAPs in avian follicle development.

Factorial-Design-Based Optimization of a Commercial MALDI-2 timsTOF Mass Spectrometer for Lipid Analysis

Matrix-assisted laser desorption/ionization mass spectrometry with laser postionization (MALDI-2 MS) has become an important technique for the analysis of a wide range of biomolecules. It has traditionally been limited to custom lab-built setups until the recent introduction of a commercial timsTOF fleX MALDI-2 system. A comprehensive optimization of the timsTOF fleX system for lipid analysis was performed using a factorial design of experiments (DOE). By examining 13 instrumental parameters across three full factorial DOEs, we performed over 1500 individual runs to assess the impact and cross interactions of these parameters on the lipid signal intensity. We found optimal values for both ion transmission and MALDI-2 parameters to maximize the signals within the lipid region. These results show that laser shot frequency, collision RF, and pre pulse storage were essential for enhancing lipid ion transmission, resulting in a nearly 5-fold increase in signal intensity compared to default parameters. For MALDI-2 optimization, positive and negative modes showed similar optimized values, with TIMS In pressure and laser power being crucial. Overall, optimization of ion optics and MALDI-2 resulted in signal enhancements of nearly 2 orders of magnitude for certain lipid species.

Protein kinase-mediated inhibition of autophagy by palmitic acid in hepatocytes

Steatosis is characterized by an increase in free fatty acids, such as palmitic acid (PA), in hepatocytes and the accumulation of triglycerides in the liver. However, the role of intracellular autophagy in PA accumulation-induced hepatotoxicity is not clearly understood. Therefore, in this study, we investigated the effects of PA on autophagy in hepatocytes and its underlying mechanism of action. Treatment of HepG2 cells with PA induced a significant increase in intracellular p62 and LC3-II levels, suggesting inhibition of autophagy. Furthermore, PA inhibited autophagic flux in HepG2 cells, as monitored using GFP-RFP-LC3. Mechanistically, PA increased the phosphorylation of the Ser12 and Thr29 residues of LC3, which are autophagy inhibition markers, through protein kinase A (PKA) and protein kinase C (PKC) signaling. Finally, PKA and PKC inhibitors restored PA-induced autophagic flux inhibition, reduced intracellular lipid accumulation, and rescued the altered expression of lipogenic genes, such as SREBP-1c, in HepG2 cells. Thus, our study demonstrates the mechanism of autophagy inhibition by PA in hepatocytes and provides a potential therapeutic approach for preventing and treating hepatic steatosis.

Mitochondria associated membranes in dilated cardiomyopathy: connecting pathogenesis and cellular dysfunction

Dilated cardiomyopathy (DCM) is a leading cause of heart failure, yet therapeutic options remain limited. While traditional research has focused on mechanisms such as energy deficits and calcium dysregulation, increasing evidence suggests that mitochondria-associated membranes (MAMs) could provide new insights into understanding and treating DCM. In this narrative review, we summarize the key role of MAMs, crucial endoplasmic reticulum (ER)-mitochondria interfaces, in regulating cellular processes such as calcium homeostasis, lipid metabolism, and mitochondrial dynamics. Disruption of MAMs function may initiate pathological cascades, including ER stress, inflammation, and cell death. These disruptions in MAM function lead to further destabilization of cellular homeostasis. Identifying MAMs as key modulators of cardiac health may provide novel insights for early diagnosis and targeted therapies in DCM.

The role of Perilipin 5 in pathological myocardial remodeling

Pathological cardiac remodeling (REM), caused by various pathological factors and characterized by changes in cardiac structure and geometry, is strongly associated with heart failure (HF). It damages cardiac tissue, alters energy metabolism, increases oxidative stress, and cause matrix metalloproteinase activation, cardiomyocyte hypertrophy, and interstitial fibrosis, leading to HF. REM determines the outcome of cardiovascular disease. Current treatments have limitations. REM is associated with cardiac energetic remodeling, and modulation of metabolic substrates may slow down the disease. Perilipin 5 (Plin5), positioned as a structural protein located on the surface of lipid droplets (LDs), is abundant in tissues and cells that rely on mitochondrial β-oxidation for energy production. It is the most recently identified member of the perilipin protein (PAT) family, with a notable enrichment in the cardiac muscle. Emerging evidence highlights the critical role of intracellular LD in the regulation of energy metabolism, with metabolic disruptions of LD being directly correlated with the incidence of metabolic disease. As a key barrier to LD, Plin5 is instrumental in controlling the catabolism of LD and regulating the metabolism and transport of fatty acids (FAs). As a protectant against excessive β-oxidation of free fatty acids (FFAs), Plin5 acts to isolate and neutralize overly oxidized fatty acids, thereby shielding the heart from myocardial remodeling instigated by a variety of etiological factors. This protective mechanism helps to ameliorate the progression of persistent and detrimental myocardial remodeling, which can otherwise lead to the development of severe heart failure. This systematic review attempts to delineate the metabolic disorders associated with pathological cardiac remodeling, focusing on the properties and regulatory mechanisms of Plin5. By synthesising current literature, it investigates the pivotal role of Plin5 in modulating the distinctive attributes, initiating factors, and molecular signaling networks underpinning pathological cardiac remodeling.

A single fluorescent probe for dual-color imaging and polarity precise analysis in lipid droplets and endoplasmic reticulum

BACKGROUND

Elaborating the subcellular polarity is pivotal for pathophysiological research and early disease diagnosis. Despite its significance, achieving simultaneous two-color fluorescence imaging and quantitative analysis of polarity across multiple organelles remains challenging. This limitation primarily stems from the lack of single fluorescent (SF) probes capable of such precise and multifaceted functionality.

RESULTS

We introduce a novel SF probe LE-TPA, designed for concurrent dual-color imaging and precise polarity determination in lipid droplets (LDs) and the endoplasmic reticulum (ER) under a single excitation. LE-TPA adopts a D-π-A-π-D configuration, which demonstrates highly selective and sensitive fluorescence response to polarity variations in Oleic acid-THF or THF-water mixtures, accompanied with an exceptional linearity (R2 > 0.99) between the max λem and polarity parameter Δf, paving the way for quantitative polarity analysis in live samples. Furthermore, LE-TPA enables simultaneous, real-time imaging of these organelles due to their different water contents, and provides compelling evidence for supporting the hypothesis that LDs derive from the ER. Importantly, LE-TPA effectively identifies polarity differences between healthy and cancerous cells at the subcellular level and allows precise polarity mapping of non-alcoholic fatty liver disease (NAFLD) tissues at different pathological stages.

SIGNIFICANCE

These findings highlight the versatility of probe LE-TPA as a powerful tool for subcellular polarity studies and related disease diagnosis.

An endoplasmic reticulum and lipid droplets dual-localized strategy to develop small molecular photosensitizers that induce ferroptosis during photodynamic therapy

Organelle-localized photosensitizers have been well-developed to enhance the photodynamic therapy (PDT) efficacy through triggering given cell death. The endoplasmic reticulum (ER) and lipid droplets (LDs) are two key organelles mutually regulating ferroptosis. Thus, in this study, small molecular photosensitizer CAR PSs were developed through fragment integration strategy and the heavy-atom modification. It was showed that the integration strategy did not affect the organelle localization and CAR PSs successfully achieved ER/LDs dual location. Besides, the heavy-atom modification help CAR PSs display good ROS generation efficiency. Importantly, ER/LDs dual-localized CAR PSs exhibited superior photo-toxicity and lower dark-toxicity against multiple breast cancer cell lines than the only ER-targeting Ce6, which further explained the superposition effect of dual organelle targeting. Preliminary studies revealed that CAR PSs induced enhanced ferroptosis via simultaneously triggering the ER stress and lipid peroxidation during PDT. Moreover, CAR-2 demonstrated significant in vivo PDT activity to suppress the tumor growth in 4T1 tumor bearing mice. These findings not only provide a promising photosensitizer CAR-2 exerting excellent in vitro and in vivo PDT effect through stimulating ferroptosis, but also propose a design strategy for the development of ER/LDs dual localized PSs.

Arsenic exposure induces neural cells senescence and abnormal lipid droplet accumulation leading to social memory impairment in mice

The long-term harmful effects of arsenic exposure remain one of the important public health issues. The effects of arsenic exposure on the central nervous system, particularly concerning brain structure and function, have been garnering increasing attention. Hence, the aim of this study was to investigate the impact of chronic low-dose arsenic exposure on murine social memory and to elucidate the underlying molecular mechanisms. Male C57BL/6 mice at six months of age were randomly assigned to a control group and three treatment groups with different arsenic concentrations (50, 100, and 200 μg/L), with exposure durations of 30, 90, 180, and 360 days. The five-social memory test and three-chamber social memory test results indicated that chronic low-dose arsenic exposure disrupted social memory in mice. Further analysis revealed that arsenic exposure led to degeneration of neurons within the dorsal CA2 of the hippocampus (dCA2) and the lateral entorhinal cortex (LEC), which are pivotal for the modulation of social memory, and dCA2 neurons demonstrated structural disruptions and cytoplasmic fragmentation. In addition, arsenic exposure induced neurons and glial cells senescence in both dCA2 and LEC, with a particularly pronounced effect in microglia, and worse with dosage increasing of arsenic exposure, correlating with elevated expression levels of p16INK4A, ferritin light chain and the senescence-associated secretory factors TNF-α and IL-1β, and reduced expression of Lamin B1. Moreover, arsenic exposure triggered substantial cytoplasmic lipid droplets accumulation in neurons, astrocytes and microglia, with an upregulation of PLIN2 expression, a protein associated with lipid droplet formation in astrocytes. At the same time, the aberrant accumulation of lipid droplets further aggravated the astrocytes and microglia aging, especially microglia. Additionally, correlation analysis revealed that social memory impairment was negatively correlated with nerve cell senescence and lipid accumulation. Our findings suggest that arsenic exposure induced cellular functional abnormalities by triggering cellular senescence and the accumulation of lipid droplets, thereby exacerbated neuronal degeneration and result in impaired social memory in mice.

Intestinal human carboxylesterase 2 (CES2) expression rescues drug metabolism and most metabolic syndrome phenotypes in global Ces2 cluster knockout mice

Carboxylesterase 2 (CES2) is expressed mainly in liver and intestine, but most abundantly in intestine. It hydrolyzes carboxylester, thioester, and amide bonds in many exogenous and endogenous compounds, including lipids. CES2 therefore not only plays an important role in the metabolism of many (pro-)drugs, toxins and pesticides, directly influencing pharmacology and toxicology in humans, but it is also involved in energy homeostasis, affecting lipid and glucose metabolism. In this study we investigated the pharmacological and physiological functions of CES2. We constructed Ces2 cluster knockout mice lacking all eight Ces2 genes (Ces2-/- strain) as well as humanized hepatic or intestinal CES2 transgenic strains in this Ces2-/- background. We showed that oral availability and tissue disposition of capecitabine were drastically increased in Ces2-/- mice, and tissue-specifically decreased by intestinal and hepatic human CES2 (hCES2) activity. The metabolism of the chemotherapeutic agent vinorelbine was strongly reduced in Ces2-/- mice, but only marginally rescued by hCES2 expression. On the other hand, Ces2-/- mice exhibited fatty liver, adipositis, hypercholesterolemia and diminished glucose tolerance and insulin sensitivity, but without body mass changes. Paradoxically, hepatic hCES2 expression rescued these metabolic phenotypes but increased liver size, adipose tissue mass and overall body weight, suggesting a "healthy" obesity phenotype. In contrast, intestinal hCES2 expression efficiently rescued all phenotypes, and even improved some parameters, including body weight, relative to the wild-type baseline values. Our results suggest that the induction of intestinal hCES2 may combat most, if not all, of the adverse effects of metabolic syndrome. These CES2 mouse models will provide powerful preclinical tools to enhance drug development, increase physiological insights, and explore potential solutions for metabolic syndrome-associated disorders.

Stearoyl-coenzyme A desaturase enhances cell survival in human uterine leiomyoma

OBJECTIVE

Stearoyl-CoA desaturase (SCD1) is an enzyme that catalyzes the conversion of saturated delta-9 fatty acids to monounsaturated fatty acids. SCD1 is highly expressed in various cancers and facilitates cancer cell survival, tumor growth, and metastasis. This study aimed to assess SCD1 expression and function in uterine leiomyoma and matched myometrial tissue and evaluate the impact of SCD1 inhibition on leiomyoma cell viability and apoptosis.

DESIGN

Gene set enrichment analysis was performed to determine whether lipid metabolism pathways are dysregulated in leiomyoma. To assess the function of SCD1, primary leiomyoma and myometrial cells, as well as a CRISPR-engineered leiomyoma-relevant MED12 mutant human uterine smooth muscle (UtSM) cell line, were treated with SCD1 small interfering RNA or a small molecule inhibitor of SCD1, CAY10566. Cell viability and apoptosis assays, real-time quantitative polymerase chain reaction, and immunoblot analyses were performed to evaluate cell function in response to treatment.

SUBJECTS

Leiomyoma and myometrial tissues were obtained from premenopausal individuals designated female at birth (n = 30) undergoing myomectomy or hysterectomy.

EXPOSURES

SCD1 inhibition by small interfering RNA and CAY10566 treatment.

MAIN OUTCOME MEASURES

Messenger RNA (mRNA) and protein levels and cell viability and apoptosis.

RESULTS

Gene set enrichment analysis revealed that the cholesterol homeostasis pathway was significantly different in leiomyoma vs. adjacent myometrial tissues. Among the genes in this pathway, SCD1 mRNA levels were found to be significantly higher in leiomyoma than in matched myometrium. SCD1 inhibition by small interfering RNA or CAY10566 decreased antiapoptotic BCL2 mRNA and protein levels and cell viability in primary leiomyoma but not myometrial cells. SCD1 protein levels were significantly higher in the mutant MED12 UtSM cell line than in the wild-type MED12 UtSM cell line. CAY10566 treatment specifically decreased cell viability and increased apoptosis in mutant MED12 UtSM cells, with increased protein levels of cleaved caspase 3, cleaved PARP, and DDIT3 in mutant MED12 UtSM but not in wild-type MED12 UtSM cells.

CONCLUSION

SCD1, an enzyme involved in lipid homeostasis, may play an important role in promoting leiomyoma growth and represents a novel target for the treatment of leiomyoma.

Identification of the LCOR-PLCL1 pathway that restrains lipid accumulation and tumor progression in clear cell renal cell carcinoma

Clear cell renal cell carcinoma (ccRCC) is the typical pathological subtype of renal cell carcinoma (RCC), representing about 80% of RCC. Reprogramming of lipid metabolism is one of the nonnegligible pathogeneses in ccRCC. Currently, the underlying regulatory mechanisms of lipid metabolism in ccRCC remain inadequately understood. In this study, we performed bioinformatics analyses and experiments both in vivo and in vitro to explore the biological functions and specific mechanisms of the ligand dependent nuclear receptor corepressor LCOR in ccRCC. Mechanistically, RUNX1 was a transcriptional suppressor of PLCL1, LCOR could interact with RUNX1 to relieve RUNX1-mediated repression of PLCL1, leading to increased PLCL1 expression, which, in turn, inhibited the tumor progression and lipid accumulation in ccRCC. Furthermore, PLCL1 decreased lipid accumulation through UCP1-mediated lipid browning and facilitated tumor apoptosis by activating p38 phosphorylation. In conclusion, the LCOR-RUNX1-PLCL1 axis provides a novel molecular mechanism underlying the progression and lipid storage of ccRCC. LCOR modulation represents a potential therapeutic strategy for the treatment in ccRCC.

The Interplay Between Immunity, Inflammation and Endothelial Dysfunction

The endothelium is pivotal in multiple physiological processes, such as maintaining vascular homeostasis, metabolism, platelet function, and oxidative stress. Emerging evidence in the past decade highlighted the immunomodulatory function of endothelium, serving as a link between innate, adaptive immunity and inflammation. This review examines the regulation of the immune-inflammatory axis by the endothelium, discusses physiological immune functions, and explores pathophysiological processes leading to endothelial dysfunction in various metabolic disturbances, including hyperglycemia, obesity, hypertension, and dyslipidaemia. The final section focuses on the novel, repurposed, and emerging therapeutic targets that address the immune-inflammatory axis in endothelial dysfunction.

Metabolic profiling of two white-rot fungi during 4-hydroxybenzoate conversion reveals biotechnologically relevant biosynthetic pathways

White-rot fungi are efficient organisms for the mineralization of lignin and polysaccharides into CO2 and H2O. Despite their biotechnological potential, WRF metabolism remains underexplored. Building on recent findings regarding the utilization of lignin-related aromatic compounds as carbon sources by WRF, we aimed to gain further insights into these catabolic processes. For this purpose, Trametes versicolor and Gelatoporia subvermispora were incubated in varying conditions - in static and agitation modes and different antioxidant levels - during the conversion of 4-hydroxybenzoic acid (a lignin-related compound) and cellobiose. Their metabolic responses were assessed via transcriptomics, proteomics, lipidomics, metabolomics, and microscopy analyses. These analyses reveal the significant impact of cultivation conditions on sugar and aromatic catabolic pathways, as well as lipid composition of the fungal mycelia. Additionally, this study identifies biosynthetic pathways for the production of extracellular fatty acids and phenylpropanoids - both products with relevance in biotechnological applications - and provides insights into carbon fate in nature.

Pathology-specific lipid alterations with triacylglycerol as a potential biomarker in Focal cortical dysplasia (FCD) and Mesial Temporal Lobe Epilepsy with Hippocampal Sclerosis (MTLE-HS)

Focal Cortical Dysplasia (FCD) & Mesial Temporal Lobe Epilepsy-Hippocampal Sclerosis (MTLE-HS) are two common pathologies of drug-resistant focal epilepsy (DRE). Inappropriate localization of the epileptogenic zones (EZs) in FCD is a significant contributing factor to the unsatisfactory surgical results observed in FCD cases. Currently, no molecular or cellular indicators are available which can aid in identifying the epileptogenic zones (EZs) in FCD. Phospholipid modifications in healthy and malignant tumour tissues have been documented and used to demarcate tumour boundaries. The objective of this research was to analyze and evaluate the lipid profiles in a manner that takes into account the specific disease and subtype. The technique of liquid chromatography and tandem mass spectrometry was utilized to detect changes in lipids in surgically resected brain samples from patients with FCD and MTLE-HS, in comparison to non-epileptic controls. Significant upregulation of TAGs was seen in both FCD and MTLE-HS. Additionally, the levels of triglycerides in the plasma of peripheral blood were measured in patients with FCD, MTLE-HS, and healthy individuals as controls. These findings suggest that employing distinct lipid mass spectra could be an effective method for identifying the EZs in FCD. The unique lipid mass spectra of cortical tissues from patients with FCD can be utilized for real-time surgical guidance. Additionally, the plasma triglyceride (TAG) level has the potential to act as a biomarker once validated on a larger cohort.

Wash-free fluorescent tools based on organic molecules: Design principles and biomedical applications

Fluorescence-assisted tools based on organic molecules have been extensively applied to interrogate complex biological processes in a non-invasive manner with good sensitivity, high resolution, and rich contrast. However, the signal-to-noise ratio is an essential factor to be reckoned with during collecting images for high fidelity. In view of this, the wash-free strategy is proven as a promising and important approach to improve the signal-to-noise ratio, thus a thorough introduction is presented in the current review about wash-free fluorescent tools based on organic molecules. Firstly, generalization and summarization of the principles for designing wash-free molecular fluorescent tools (WFTs) are made. Subsequently, to make the thought of molecule design more legible, a wash-free strategy is highlighted in recent studies from four diverse but tightly binding aspects: (1) special chemical structures, (2) molecular interactions, (3) bio-orthogonal reactions, (4) abiotic reactions. Meanwhile, biomedical applications including bioimaging, biodetection, and therapy, are ready to be accompanied by. Finally, the prospects for WFTs are elaborated and discussed. This review is a timely conclusion about wash-free strategy in the fluorescence-guided biomedical applications, which may bring WFTs to the forefront and accelerate their extensive applications in biology and medicine.

Lipid-laden uterus: Investigating uterine fibroids and lipid association

Uterine Fibroids (UF) are the most common (about 70 % cases) benign gynecological smooth muscle tumors of the uterus in women of reproductive age, characterized by abnormal cholesterol, lipoproteins, and triglyceride levels, and are a major public health concern. Despite its high prevalence, this condition remains complex and poorly understood. These tumors are hormone-dependent and hormones and lipid levels are inversely related. This review delves into the existing literature and critically evaluates studies that explore the potential relationship between lipids in the pathogenesis of uterine fibroids. This review concludes by critically appraising the research gaps in the involvement of lipids and signaling pathways in the pathogenesis of uterine fibroids and future directions for investigating this intriguing biological connection. By elucidating the potential link between uterine fibroids and lipids, this review paves the way for an improved understanding of fibroid pathogenesis, personalized risk assessment, and novel lipid-lowering therapeutic strategies.

WDR36 Regulates Trophectoderm Differentiation During Human Preimplantation Embryonic Development Through Glycolytic Metabolism

Mammalian pre-implantation development is a complex process involving sophisticated regulatory dynamics. WD repeat domain 36 (WDR36) is known to play a critical role in mouse early embryonic development, but its regulatory function in human embryogenesis is still elusive due to limited access to human embryos. The human pluripotent stem cell-derived blastocyst-like structure, termed a blastoid, offers an alternative means to study human development in a dish. In this study, after verifying that WDR36 inhibition disrupted polarization in mouse early embryos, it is further demonstrated that WDR36 interference can block human blastoid formation, dominantly hindering the trophectoderm lineage commitment. Both transcriptomics and targeted metabolomics analyses revealed that WDR36 interference downregulated glucose metabolism. WDR36 can interact with glycolytic metabolic protein lactate dehydrogenase A (LDHA), thereby positively regulating glycolysis during the late stage of human blastoid formation. Taken together, the study has established a mechanistic connection between WDR36, glucose metabolism, and cell fate determination during early embryonic lineage commitment, which may provide potential insights into novel therapeutic targets for early adverse pregnancy interventions.

Sesamol Ameliorates Lipid Deposition by Maintaining the Integrity of the Lipid Droplet-Mitochondria Connection in Diabetic Nephropathy

Diabetic nephropathy (DN) is a serious complication of diabetes mellitus and an important cause of end-stage renal disease (ESRD). However, there is still a lack of effective prevention and treatment strategies in clinical practice. As a metabolic disease, DN is accompanied by renal ectopic lipid deposition, and the deposited lipids further aggravate kidney injury. However, the molecular mechanism of renal ectopic lipid deposition is currently unknown. In this study, we observed changes in lipid droplet (LD)-mitochondria connections in the kidney for the first time. Destruction of LD-mitochondria connection was involved in renal lipid deposition in the kidneys of patients and mice with DN or in high-glucose-treated HK-2 cells. Furthermore, sesamol treatment significantly increased the integrity of the LD-mitochondria connection and ameliorated renal lipotoxicity. Finally, we demonstrated that sesamol maintains the integrity of the LD-mitochondria connection by activating the peroxisome proliferator-activated receptor α (PPARα)/perilipin 5 (PLIN5) signaling pathway. Our study is the first to show that the LD-mitochondria connection may be a target for ameliorating lipid deposition in diabetic kidneys.

Live cell imaging of lipid droplets: fluorescent chalcones as probes for lipophagy and lipid-mitochondria interactions

Lipid droplets are crucial organelles involved in cellular energy storage and metabolism, which is key in maintaining energy homeostasis through lipophagy. In this work, we successfully synthesized donor-acceptor chalcone derivatives (M1-M3) with improved photophysical characteristics, such as significant Stokes shifts and strong emission features. DFT and TDDFT calculations have been employed to evaluate the structure-property relationship of the chalcone derivatives. The molecules show excellent selectivity in staining lipid droplets in COS-7 cells and other cell lines. The molecule M1 was also further utilized to monitor verapamil-induced lipophagy. Using M1, we also demonstrate the link between lipid droplets and mitochondria during stress, emphasizing the significance of lipophagy in cellular energy balance and metabolism. These results not only shed light on the lipid metabolism but also have profound implications for researching and potentially treating metabolic diseases, underscoring the importance of our work in the field.

Nanomaterial-enabled metabolic reprogramming strategies for boosting antitumor immunity

Immunotherapy has become a crucial strategy in cancer treatment, but its effectiveness is often constrained. Most cancer immunotherapies focus on stimulating T-cell-mediated immunity by driving the cancer-immunity cycle, which includes tumor antigen release, antigen presentation, T cell activation, infiltration, and tumor cell killing. However, metabolism reprogramming in the tumor microenvironment (TME) supports the viability of cancer cells and inhibits the function of immune cells within this cycle, presenting clinical challenges. The distinct metabolic needs of tumor cells and immune cells require precise and selective metabolic interventions to maximize therapeutic outcomes while minimizing adverse effects. Recent advances in nanotherapeutics offer a promising approach to target tumor metabolism reprogramming and enhance the cancer-immunity cycle through tailored metabolic modulation. In this review, we explore cutting-edge nanomaterial strategies for modulating tumor metabolism to improve therapeutic outcomes. We review the design principles of nanoplatforms for immunometabolic modulation, key metabolic pathways and their regulation, recent advances in targeting these pathways for the cancer-immunity cycle enhancement, and future prospects for next-generation metabolic nanomodulators in cancer immunotherapy. We expect that emerging immunometabolic modulatory nanotechnology will establish a new frontier in cancer immunotherapy in the near future.

Biallelic variants in SREBF2 cause autosomal recessive spastic paraplegia

Hereditary spastic paraplegias (HSPs) refer to a genetically and clinically heterogeneous group of neurodegenerative disorders characterized by the degeneration of motor neurons. To date, a significant number of patients still have not received a definite genetic diagnosis. Therefore, identifying unreported causative genes continues to be of great importance. Here, we perform whole exome sequencing in a cohort of Chinese HSP patients. Three homozygous variants (p.L604W, p.S517F, and p.T984A) within the sterol regulatory element-binding factor 2 (SREBF2) gene are identified in one autosomal recessive family and two sporadic patients, respectively. Co-segregation is confirmed by Sanger sequencing in all available members. The three variants are rare in the public or in-house database and are predicted to be damaging. The biological impacts of variants in SREBF2 are examined by functional experiments in patient-derived fibroblasts and Drosophila. We find that the variants upregulate cellular cholesterol due to the overactivation of SREBP2, eventually impairing the autophagosomal and lysosomal functions. The overexpression of the mature form of SREBP2 leads to locomotion defects in Drosophila. Our findings identify SREBF2 as a causative gene for HSP and highlight the impairment of cholesterol as a critical pathway for HSP.

Lipid droplets in central nervous system and functional profiles of brain cells containing lipid droplets in various diseases

Lipid droplets (LDs), serving as the convergence point of energy metabolism and multiple signaling pathways, have garnered increasing attention in recent years. Different cell types within the central nervous system (CNS) can regulate energy metabolism to generate or degrade LDs in response to diverse pathological stimuli. This article provides a comprehensive review on the composition of LDs in CNS, their generation and degradation processes, their interaction mechanisms with mitochondria, the distribution among different cell types, and the roles played by these cells-particularly microglia and astrocytes-in various prevalent neurological disorders. Additionally, we also emphasize the paradoxical role of LDs in post-cerebral ischemia inflammation and explore potential underlying mechanisms, aiming to identify novel therapeutic targets for this disease.

Single-base m6A epitranscriptomics reveals novel HIV-1 host interaction targets in primary CD4+ T cells

N 6-methyladenosine (m6A) is the most prevalent cellular mRNA modification and plays a critical role in regulating RNA stability, localization, and gene expression. m6A modification plays a vital role in modulating the expression of viral and cellular genes during HIV-1 infection. HIV-1 infection increases cellular RNA m6A levels in many cell types, which facilitates HIV-1 replication and infectivity in target cells. However, the function of m6A modification in regulating HIV-1 infection of primary CD4+ T cells remains unclear. Here, we demonstrate that HIV-1 infection of Jurkat CD4+ T cells and primary CD4+ T cells promotes the interaction between the m6A writer complex subunits methyltransferase-like 3 and 14 (METTL3/METTL14). Using single-base m6A-specific RNA sequencing, we identified several differentially m6A-modified cellular mRNAs, including perilipin 3 (PLIN3), during HIV-1 infection in primary CD4+ T cells. Interestingly, HIV-1 infection increased PLIN3 mRNA level by enhancing its stability, but PLIN3 protein level was decreased. Knocking down PLIN3 in primary CD4+ T cells reduced HIV-1 production but enhanced virion infectivity. In contrast, in Jurkat cells, PLIN3 mRNA and protein expression levels were unaffected by HIV-1 infection, and knocking out PLIN3 did not impact HIV-1 production or infectivity. These results indicate that the interplay between HIV-1 and PLIN3 is cell-type specific and only observed in primary CD4+ T cells. Overall, our results highlight the importance of m6A RNA modification in HIV-1-infected primary CD4+ T cells and suggest its significance as a regulatory mechanism in HIV-1 infection.

Impaired suppression of fatty acid release by insulin is a strong predictor of reduced whole-body insulin-mediated glucose uptake and skeletal muscle insulin receptor activation

AIM

To examine factors underlying why most, but not all, adults with obesity exhibit impaired insulin-mediated glucose uptake, we compared: (1) adipose tissue fatty acid (FA) release, (2) skeletal muscle lipid droplet (LD) characteristics, and (3) insulin signalling events, in skeletal muscle of adults with obesity with relatively high versus low insulin-mediated glucose uptake.

METHODS

Seventeen adults with obesity (BMI: 36 ± 3 kg/m2) completed a 2 h hyperinsulinemic-euglycemic clamp with stable isotope tracer infusions to measure glucose rate of disappearance (glucose Rd) and FA rate of appearance (FA Ra). Skeletal muscle biopsies were collected at baseline and 30 min into the insulin infusion. Participants were stratified into HIGH (n = 7) and LOW (n = 10) insulin sensitivity cohorts by their glucose Rd during the hyperinsulinemic clamp (LOW< 400; HIGH >550 nmol/kgFFM/min/[μU/mL]).

RESULTS

Insulin-mediated suppression of FA Ra was lower in LOW compared with HIGH (p < 0.01). In skeletal muscle, total intramyocellular lipid content did not differ between cohorts. However, the size of LDs in the subsarcolemmal region (SS) of type II muscle fibres was larger in LOW compared with HIGH (p = 0.01). Additionally, insulin receptor-β (IRβ) interactions with regulatory proteins CD36 and Fyn were lower in LOW versus HIGH (p < 0.01), which aligned with attenuated insulin-mediated Tyr phosphorylation of IRβ and downstream insulin-signalling proteins in LOW.

CONCLUSION

Collectively, reduced ability for insulin to suppress FA mobilization, with accompanying modifications in intramyocellular LD size and distribution, and diminished IRβ interaction with key regulatory proteins may be key contributors to impaired insulin-mediated glucose uptake commonly found in adults with obesity.

Encapsulation of paclitaxel into date palm lipid droplets for enhanced brain cancer therapy

Paclitaxel, a powerful anticancer drug, is limited by its poor water solubility and systemic toxicity, which hinder its effectiveness against aggressive brain tumors. This study aims to overcome these challenges by exploring novel intranasal delivery methods using lipid droplets (LDs) derived from date palm seeds (DPLDs) and mouse liver (MLLDs). The anticancer efficacy of PTX was evaluated using a comparative intranasal delivery approach. The lipid droplets were fractionated, and their physicochemical and biochemical properties were assessed. Our results showed that both DPLDs and MLLDs were spherical, with average diameters of 257 ± 36 nm and 416 ± 83 nm, respectively, and contained oil-rich cores of 392.5 and 612.4 mg mL-1. The MLLDs displayed a distinct lipid profile with low triglyceride content and high monoglyceride and diglyceride content. Conversely, the DPLDs primarily consisted of triglycerides, with stable granularity at around 83% and 79% for MLLDs and DPLDs, respectively. Both lipid droplets showed high encapsulation efficiencies, reaching 48.6 ± 3.2% and 45.4 ± 2.4% for MLLDs and DPLDs, respectively, after 4 h of incubation. The bio-distribution kinetics of paclitaxel post-intranasal administration demonstrated lower plasma paclitaxel levels in formulations compared to free paclitaxel. Notably, the accumulation of paclitaxel in the brain was significantly higher for paclitaxel-DPLD at early time points, with 1.527 ± 0.1% ID g-1 and 2.4 ± 0.16% ID g-1 at 5 and 30 min, respectively, compared to paclitaxel-MLLD and free paclitaxel. In Conclusion, the study highlights the potential of intranasal DPLD and MLLD formulations for enhanced brain targeting in brain tumor therapy, offering improved paclitaxel delivery and overcoming solubility and toxicity challenges.

Exploiting lipid droplet metabolic pathway to foster lipid production: oleosin in focus

In the past decade, there has been an emerging gap between the demand and supply of vegetable oils globally for both edible and industrial use. Lipids are important biomolecules with enormous applications in the industrial sector and a major source of energy for animals and plants. Hence, to elevate the lipid content through metabolic engineering, new strategies have come up for triacylglycerol (TAG) accumulation and in raising the lipid or oil yield in crop plants. Increased levels of energy density can be achieved by single and multiple gene strategies that re-orient the carbon flux into TAG. Transcription factors and enzymes of the metabolic pathways have been targeted to foster lipid production. Oleosin, a structural protein of the lipid droplet plays a vital role in its stabilization and subsequently in its mobilization for seed germination and seedling growth. Maintenance of increased lipid content with optimal composition is a major target. Knowledge gained from genetic engineering strategies suggests that oleosin co-expression can result in a significant shift in carbon allocation to LDs. In this review, we present a detailed analysis of the recent advancements in metabolic engineering of plant lipids with emphasis on oleosin with its distinct patterns and functions in plants.

SWATH-MS insights on sodium butyrate effect on mAbs production and redox homeostasis in CHO cells

Sodium butyrate (NaBu), well-known as a histone deacetylase inhibitor and for its capacity to impede cell growth, can enhance the production of a specific protein, such as an antibody, in recombinant Chinese hamster ovary (CHO) cell cultures. In this study, two CHO cell lines, namely K1 and DG44, along with their corresponding mAb-producing lines, K1-Pr and DG44-Pr, were cultivated with or without NaBu. A SWATH-based profiling method was employed to analyze the proteome. Cells cultured in the presence of NaBu exhibited a reduction in mitosis and gene expression, supported by their culture data demonstrating growth inhibition. The presence of NaBu corresponded to upregulation of intracellular trafficking and secretion pathways, aligned with an observed increase in mAb production, and was associated with an elevated glycosylation pathway and a slight alteration in the glycosylation profile of the mAbs. Increased fatty acid oxidation, redox interactions, and lipid biosynthesis were also observed and are likely attributable to the metabolism of NaBu. A comprehensive understanding of the systemic effects of NaBu will facilitate the discovery of strategies to enhance or prolong the productivity of CHO cells.

Engineered Strategies for Lipid Droplets-Targeted AIEgens Based on Tetraphenylethene

Lipid droplets (LDs), once regarded as inert fat particles, have been ignored by scientific researchers for a long time. Now, studies have shown that LDs are dynamic organelles used to store neutral lipids in cells and maintain cell stability. The abnormality of intracellular LDs usually causes metabolic disorders in the body, such as obesity, atherosclerosis, diabetes, and cancer, so the LDs have attracted wide attention. The traditional small molecules used for LDs recognition seriously affect the imaging effect due to their poor photo-stability, low signal-to-noise ratios, and aggregation-induced quenching (ACQ). In contrast to ACQ, aggregation-induced emission (AIE) materials, with structural modifiability, can make up for the aforementioned deficiencies in the field of fluorescence imaging and have attracted much attention. In this review, the importance of LDs in vivo, the design principles for LDs recognition, and the recent research progress of AIE compounds with tetraphenylethene (TPE) structure in LDs targets are reviewed. We expect this review to further provide researchers with feasible methods and protocols for expanding LDs identification, imaging, and other applications.

Heightened cholesterol 25-hydroxylase expression in aged lung during Streptococcus pneumoniae

Introduction

Alveolar macrophages (AM) are critical effectors of the immune response and are essential for host responses to Streptococcus pneumoniae. Changes in lipid metabolism in AM can alter cellular function and biology. Impaired metabolism can contribute to excessive lipid accumulation and pro-inflammatory signaling. Our current study was designed to examine the role of cholesterol 25-hydroxylase (Ch25h), a redox enzyme that catalyzes the oxidation of cholesterol to 25-hydroxycholesterol (25-HC), in modulating AM responses in the aged lung during S. pneumoniae infection.

Methods

To observe the impact of aging on Ch25h expression in AM during infection, in vitro and in vivo murine models of S. pneumoniae were used.

Results

At baseline and in response to infection, cholesterol metabolism significantly altered in aged AM, which corresponded with increased lipid droplet formation. In vitro, treatment of aged macrophages with Ch25 h-specific siRNA improved S. pneumoniae clearance and enhanced phagocytic receptor expression. In vivo siRNA targeting significantly reduced Ch25h expression in aged lungs and improved clinical parameters during S. pneumoniae infection. Reduction of Ch25h was associated with changes in phagocytosis and antibacterial signaling, correlated with changes in cholesterol metabolism, and increased S. pneumoniae clearance.

Discussion

The results of our current study demonstrate that Ch25h plays an essential role in modulating aged AM responses to S. pneumoniae.

Clog P-Guided Development of Multi-Colored Buffering Fluorescent Probes for Super-Resolution Imaging of Lipid Droplet Dynamics

Super-resolution fluorescence imaging of live cells increasingly demands fluorescent probes capable of multi-color and long-term dynamic imaging. Understanding the mechanisms of probe-target recognition is essential for the engineered development of such probes. In this study, it is discovered that the molecular lipid solubility parameter, Clog P, determines the staining performance of fluorescent dyes on lipid droplets (LDs). Fluorescent dyes with Clog P values between 2.5 and 4 can form buffering pools outside LDs, replacing photobleached dyes within LDs to maintain constant fluorescence intensity in LDs, thereby enabling dynamic super-resolution imaging of LDs. Guided by Clog P, four different colored buffering LD probes spanning the visible light spectrum have been developed. Using Structured Illumination Microscopy (SIM), the role of LD dynamics have been tracked during cellular ferroptosis with the secretion, storage, and degradation of overexpressed ACSL3 proteins. It is found that LDs serve as storage sites for these proteins through membrane fusion, and further degrade overexpressed proteins via interactions with organelles like lysosomes or through lipophagy, thereby maintaining cellular homeostasis.

Ether-Linked Glycerophospholipids Are Potential Chemo-Desensitisers and Are Associated With Overall Survival in Carcinoma Patients

Lipid reprogramming in carcinoma is reported to have a role in carcinogenesis, prognosis and therapy response. The lipid reprogramming could be contributed by either autonomous or nonautonomous resources. Since the nonautonomous lipid resources contributed by lipoproteins and their receptors have been reported in epithelial ovarian cancer (EOC), the impact of autonomous lipid metabolites was unknown. This report revealed a unique lipid class, ether-linked phosphatidyl-ethanolamine (PE O-), which enhances chemo-insensitivity and progression in EOC and potentially cross carcinomas. Analysis of CCLEC/GDSCC database and in-house cell line lipidomes identified PE O- as the major lipid associated with cisplatin/paclitaxel sensitivity. In the testing of PE O- effect on cancer phenotypes, it enhanced cell growth, migratory activities and promoted cisplatin/paclitaxel insensitivity. In addition, treating AGPS inhibitor-sensitised chemo-cytotoxic upon cisplatin/paclitaxel treatments. Treating PE O- could reverse AGPS inhibitor chemosensitisation effect on EOC cells. At last, using TCGA-EOC transcriptome database, the PE O- related gene expressions were positive correlated with patient prognosis in general, or in whom were treated with platin- or taxel-based chemotherapies. The expressions of genes for the synthesis of PE O- aggravates therapy response in EOC patients. PE O- facilitates human carcinoma cell line growth, mobility and chemo-insensitivity.

Cytoplasmic nucleoporin assemblage: the cellular artwork in physiology and disease

Nucleoporins, essential proteins building the nuclear pore, are pivotal for ensuring nucleocytoplasmic transport. While traditionally confined to the nuclear envelope, emerging evidence indicates their presence in various cytoplasmic structures, suggesting potential non-transport-related roles. This review consolidates findings on cytoplasmic nucleoporin assemblies across different states, including normal physiological conditions, stress, and pathology, exploring their structural organization, formation dynamics, and functional implications. We summarize the current knowledge and the latest concepts on the regulation of nucleoporin homeostasis, aiming to enhance our understanding of their unexpected roles in physiological and pathological processes.

Persistent organic pollutants and metabolic diseases: From the perspective of lipid droplets

The characteristic of semi-volatility enables persistent organic pollutants (POPs) almost ubiquitous in the environment. There is increasing concern about the potential risks of exposure to POPs due to their lipophilicity and readily bioaccumulation. Lipid droplets (LDs) are highly dynamic lipid storage organelles, alterations of intracellular LDs play a vital role in the progression of many prevalent metabolic diseases, such as type 2 diabetes (T2D) and nonalcoholic fatty liver disease (NAFLD). This article systematically reviewed the biological processes involved in LDs metabolism, the role of LDs proteins and LDs in metabolic diseases, and summarized updating researches on involvement of POPs in the progression of LDs-related metabolic diseases and potential mechanisms. POPs might change the physiological functions of LDs, also interfere the processes of adipogenesis and lipolysis by altering LDs synthesis, decomposition and function. However, further studies are still needed to explore the underlying mechanism of POPs-induced metabolic diseases, which can offer scientific evidences for metabolic disease prevention.

Real-Time Analysis of Lipid Droplet Morpho-Chemical Dynamics in Living Human Hepatocytes via Phase-Guided Raman Sampling

Lipid droplets (LDs) are highly dynamic organelles, undertaking many important functions such as maintaining lipid metabolism and cellular homeostasis. Traditional methods to analyze LD dynamics focus on morphological changes, while chemical dynamics cannot be easily probed with traditional analytical chemistry techniques. To overcome this challenge, we show here how our phase-guided Raman sampling method, where high-resolution phase microscopy images direct a Raman sampling beam, can perform label-free, multimodal characterization of LD dynamics in living cells at both the single-cell and single-LD levels with submicron accuracy and high temporal resolution. We demonstrate the study of the morphological-compositional dynamics of human hepatocellular carcinoma cells (PLC cells) under different environmental conditions and with and without fatty acid supplementation, providing insight into LD heterogeneity and heterogeneity of response. Finally, we introduce a measurement method for the dynamics of cell-average LD composition, which can quickly and accurately characterize the lipid dynamics at the single-cell level with <30 s temporal resolution. The results here show the promise of the phase-guided Raman sampling method for dynamic morpho-chemical profiling of organelle populations.

Inhibiting lipid droplet biogenesis enhances host protection against hypervirulent Klebsiella pneumoniae infections

Hypervirulent Klebsiella pneumoniae (hvKp), an emerging Kp subtype, has become a serious global pathogen. However, the information regarding host interactions and innate immune responses during hvKp infection is limited. Here, we found that hvKp clinical strains increased triacylglycerol synthesis, resulting in lipid droplets (LDs) formation via the mammalian target of rapamycin signaling pathway in RAW264.7 cells. Treatment with rapamycin, an inhibitor of this pathway, affected LDs formation and antimicrobial responses against clinical hvKp infections. In accordance with the role of LDs in modulating inflammation, the pharmacological inhibition of lipogenesis reduced proinflammatory cytokine expression during hvKp infections. In addition, inhibition of LDs formation using pharmacological inhibitors and knockdown of lipogenesis regulators decreased the intracellular survival of hvKp in macrophages. Moreover, inhibiting LDs biogenesis reduced mortality, weight loss, and bacterial loads in hvKp-infected mice. Collectively, these data suggest that LDs biogenesis is crucial in linking host immune responses to clinical hvKp infections.

Alarmin-loaded extracellular lipid droplets induce airway neutrophil infiltration during type 2 inflammation

Group 2 innate lymphoid cells (ILC2s) play a crucial role in allergic diseases by coordinating a complex network of various effector cell lineages involved in type 2 inflammation. However, their function in regulating airway neutrophil infiltration, a deleterious symptom of severe asthma, remains unknown. Here, we observed ILC2-dependent neutrophil accumulation in the bronchoalveolar lavage fluid (BALF) of allergic mouse models. Chromatography followed by proteomics analysis identified the alarmin high mobility group box-1 (HMGB1) in the supernatant of lung ILC2s initiated neutrophil chemotaxis. Genetic perturbation of Hmgb1 in ILC2s reduced BALF neutrophil numbers and alleviated airway inflammation. HMGB1 was loaded onto the membrane of lipid droplets (LDs) released from activated lung ILC2s. Genetic inhibition of LD accumulation in ILC2s significantly decreased extracellular HMGB1 abundance and BALF neutrophil infiltration. These findings unveil a previously uncharacterized extracellular LD-mediated immune signaling delivery pathway by which ILC2s regulate airway neutrophil infiltration during allergic inflammation.

A polar viscosity-sensitive fluorescent probe with large Stokes shifts for simultaneous imaging of lipid droplets and lysosomes in tobacco leaf vein cells and biological systems

Lipid droplets (LDs) and lysosomes were dynamic organelles present in most eukaryotic cells that were interconnected and worked closely together to ensure the smooth physiological activities of organisms. The interaction between lipid droplets and lysosomes was thought to play a role in the development of certain diseases. In this paper we designed and synthesised a lipid droplet lysosomal probe. The Nap-Lyso-Ph-OH probe was constructed according to the ICT mechanism and exhibited sensitivity to both polarity and viscosity. The probe exhibited low cytotoxicity, a large Stokes shift, excellent selectivity and photostability. The probe was successfully used for labelling and imaging of lipid droplets and lysosomes in cells and zebrafish. Interestingly, we used tobacco seedling cells to explore the ability of Nap-Lyso-Ph-OH for imaging lipid droplet labelling in plant cells.

Optimized methods to image hepatic lipid droplets in zebrafish larvae

The optical transparency of zebrafish larvae enables visualization of subcellular structures in intact organs, and these vertebrates are widely used to study lipid biology and liver disease. Lipid droplet (LD) presence is a prevalent feature of healthy cells, but, under conditions such as nutrient excess, toxicant exposure or metabolic imbalance, LD accumulation in hepatocytes can be a harbinger of more severe forms of liver disease. We undertook a comprehensive analysis of approaches useful to investigate LD distribution and dynamics in physiological and pathological conditions in the liver of zebrafish larvae. This comparative analysis of the lipid dyes Oil Red O, Nile Red, LipidTox and LipidSpot, as well as transgenic LD reporters that rely on EGFP fusions of the LD-decorating protein perilipin 2 (PLIN2), demonstrates the strengths and limitations of each approach. These protocols are amenable to detection methods ranging from low-resolution stereomicroscopy to confocal imaging, which enables measurements of hepatic LD size, number and dynamics at cellular resolution in live and fixed animals. This resource will benefit investigators studying LD biology in zebrafish disease models.

Heightened TPD52 linked to metabolic dysfunction and associated abnormalities in zebrafish

The tumor protein D52 (TPD52) gene encodes a proto-oncogene protein associated with various medical conditions, including breast and prostate cancers. It plays a role in multiple biological pathways such as cell growth, differentiation, and apoptosis. The function of TPD52 in lipid droplet biosynthesis has been investigated in vitro. However, its precise role in lipid metabolism in animal models is not fully understood. To investigate the functions of TPD52 in vivo, we performed a conditional TPD52 protein expression analysis using a Tet-off transgenic system to establish conditionally expressed Tpd52 transgenic zebrafish. The effect of Tpd52 on lipogenesis was assessed using various methods, including whole-mount Oil Red O staining, histological examination, and measurement of inflammatory markers and potential targets using real-time quantitative polymerase chain reaction and immunoblotting in Tpd52 fish. Zebrafish with increased Tpd52 levels exhibited notable weight gain and the enlargement of fat deposits, which were mainly attributed to an increase in the volume of adipocytes. Moreover, Tpd52 overexpression was correlated with the triggering of the adipocyte differentiation signaling pathway. During adipocytic differentiation in response to nutrient status, our observations revealed adipogenesis, nonalcoholic fatty liver disease, and metabolic cardiomyopathy (MCM) in Tpd52 transgenic zebrafish. To gain a deeper understanding of the contribution of these proteins to the regulation of cellular growth, we investigated the expression of their corresponding genes and proteins in zebrafish. In the present study, the activated protein kinase pathway was identified as the primary target of TPD52. Adult Tpd52 zebrafish showed increased lipid accumulation, resulting in the development of visceral obesity, nonalcoholic fatty liver disease, and MCM. These findings strongly suggest that TPD52 actively contributes to adipose tissue expansion and its subsequent effects. This investigation provides compelling evidence that Tpd52 facilitates adipocyte development and related metabolic comorbidities in zebrafish.

Intramolecular Charge Transfer Inhibition Strategy toward a Desired Solvatochromic Fluorescent Platform: Visualization of Duple Organelles and Detection of Carbon Dioxide

Solvatochromic fluorescent probes are crucial molecular tools to investigate and aggregate proteins' fold, visualize fine structures in biomembranes, and label different organelles in dual emission colors. However, solvatochromic fluorogens often displayed a weak emission at high polarity, hindering their bioimaging applications. To resolve this problem, herein, we propose an intramolecular charge transfer (ICT) inhibition strategy. The probe was designed with a single electronic donor and two acceptors in order to split and inhibit the ICT procedure. As a result, the probe displayed an intense emission at both low and high polarities and showed a large emission shift (84 nm) upon polarity change. Using the probe, we successfully imaged lipid droplets and the endoplasmic reticulum in different fluorescence colors. Moreover, the different degrees of lipid accumulation by oleic acid, stearic acid, and cholesterol (oleic acid > stearic acid > cholesterol) have been revealed. The lipid accumulation induced by the three lipids could be rapidly consumed under lipid-less conditions, and the lipids with stearic acid were the most difficult to be consumed. The biological results could facilitate the understanding and treatment of lipid accumulation and obesity. Furthermore, utilizing the polarity increase of diethylamine after the reaction with CO2, the ratiometric detection of CO2 has been achieved for the first time with the probe.

Modification of an AIE Fluorescent Probe for Monitoring the Polarity of Lipid Droplets Based on a Series of Synthesized Aryl Naphthalizes

Lipid droplets (LDs) are subcellular organelles that are dynamic and play a central role in energy homeostasis and lipid metabolism. They also contribute to the transport and maturation of cellular proteins and are closely associated with several diseases. The important role of the cellular microenvironment in maintaining cellular homeostasis. Changes in cell polarity, particularly in organelles, have been found to be strongly linked to inflammation, Alzheimer's disease, cancer, and other illnesses. It is essential to check the polarity of the LDs. A series of arylated naphthalimide derivatives were synthesized using the Suzuki reaction. Modification of synthesized aryl naphthalimides using oligomeric PEG based on intramolecular charge transfer (ICT) mechanism. A series of fluorescent probes were designed to target LDs and detect their polarity. Nap-TPA-PEG3 probe exhibited high sensitivity to polarity. The addition of oligomeric polyethylene glycol (PEG) to the probe not only significantly improved its solubility in water, but also effectively reduced its cytotoxicity. In addition, the probe exhibited excellent aggregation-induced luminescence (AIE) properties and solvent discolouration effects. Nap-TPA-PEG3 probe exhibited high Pearson correlation coefficient (0.957163) in lipid droplet co-localization in cells. Nap-TPA-PEG3 could be used as an effective hand tool to monitor cell polarity.

Super-Resolution Microscopic Imaging of Lipid Droplets in Living Cells via Carbonized Polymer Dot-Based Polarity-Responsive Nanoprobe

Lipid droplets (LDs) are dynamic subcellular organelles that participate in various physiological processes, and their abnormality can also lead to various diseases. Tracing the dynamics of LDs in living cells will be valuable for understanding cell physiological states. Here, we employed a structured light illumination super-resolution imaging assisted with a carbonized polymer dot (CPD)-based fluorescence nanoprobe to track the travel paths of LDs and other organelles. The CPDs we developed are highly biocompatible with living cells and exhibit a highly sensitive response to solvent polarity, allowing for high specificity in staining LDs in living cells. Aided by these nanoprobes, we successfully observed many real-time LD-involved dynamics in living cells, such as intracellular LD interactions, communications with other organelles, and dynamic behaviors under external stimuli (oxidative stress inducer). These studies deepen our comprehension of the physiological role of LDs and drive the advancement of super-resolution fluorescent probes.

Hyperproduction of 7-dehydrocholesterol by rewiring the post-squalene module in lipid droplets of Saccharomyces cerevisiae

Lipid droplets (LDs) are specialized organelles that store neutral lipids to reduce the negative effects of lipotoxicity on cells. However, many neutral lipids are precursors for the synthesis of sterols and complex terpenoids, and this sequestration often greatly limits the efficient biosynthesis of sterols and complex terpenoids. In this study, taking 7-dehydrocholesterol (7-DHC) synthesis in Saccharomyces cerevisiae as an example, we revealed the blocking mechanism of LD sequestration on the efficient synthesis of metabolic products and found that LDs can sequester a significant amount of squalene, the precursor of 7-DHC, effectively preventing it from being directed toward the post-squalene pathway. Based on this, a post-squalene pathway was reconstructed on LDs, which resulted in a 28.7% increase in the 7-DHC titer, reaching 684.1 mg/L, whereas the squalene titer was reduced by approximately 97%. Subsequently, the triacylglycerol degradation pathway was weakened to release the storage space in LDs, and the esterification pathway was concurrently strengthened to guide 7-DHC storage within LDs, which further increased 7-DHC production, reaching 792.9 mg/L. Finally, by reducing the NADH/NAD + ratio to alleviate the redox imbalance, the 7-DHC titer reached 867.6 mg/L in shake flask and 5.1 g/L in a 3-L bioreactor, which is the highest reported titer to date. In summary, this study provides new insights into the important role of LDs in sterol synthesis and offers a novel strategy for constructing cell factories for the efficient synthesis of sterol compounds.

Lipase activated endocytosis-like behavior of oil-in-water emulsion

Oil-in-water emulsion is a system with extensive applications in foods, cosmetics and coating industries, and it could also be designed into an artificial lipid droplet in recent works. However, the insights into the biophysical dynamic behaviors of such artificial lipid droplets are lacking. Here, we reveal an enzymatic reaction triggered endocytosis-like behavior in the oil-in-water emulsion lipid droplets. A thermodynamically favored recruitment of lipases onto the membrane of the droplets is demonstrated. We confirm that the hydrolysis of tributyrin by lipases can decrease the interfacial tension and increase the compressive force on the membrane, which are the two main driving forces for triggering the endocytosis-like behavior. The endocytosis-like behavior induced various emerging functionalities of the lipid droplets, including proteins, DNA or inorganic particles being efficiently sequestered into the oil droplet with reversible release as well as enhanced cascade enzymatic reaction. Overall, our studies are expected to open up a way to functionalize oil-in-water emulsions capable of life-inspired behaviors and tackle emerging challenges in bottom-up synthetic biology, revealing the unknown dynamic behaviors of lipid droplets in living organisms.

A fluorescence lifetime-based novel method for accurate lipid quantification of BODIPY vital-stained C. elegans

Lipid droplets (LDs) are organelles associated with lipid storage and energy metabolism, thus, their morphology and quantity are of significant research interest. While commercially available BODIPY dye effectively labels LDs in various cell types, it also labels lysosome-related organelles (LROs) in C. elegans, leading to non-specific LD quantification. Here, we report that the fluorescent signals of BODIPY exhibit distinct fluorescence lifetime patterns for LROs and LDs, which can be captured, visualized, and filtered by fluorescence lifetime imaging microscopy. Furthermore, we proposed and validated a method based on fluorescence lifetime that can improve the accuracy of fat storage quantification in BODIPY vital-staining worms, which holds broad applications, including rapid and accurate LD quantification in forward genetic screening. Additionally, our method enables observing dynamic LD-LRO interactions in living worms, a unique capability of BODIPY vital staining. Our findings highlight distinct BODIPY fluorescence lifetime characteristics of LDs and LROs, providing a valuable tool for future research on LDs, LROs, or their interactions.