Glycerolipid Synthesis and Lipid Droplet Formation in the Endoplasmic Reticulum

Untargeted metabolomics and transcriptomics joint analysis of the effects of polystyrene nanoplastics on lipid metabolism in the mouse liver

BACKGROUND

Micro/nanoplastics (MNPs), as emerging environmental pollutants, are widely present in environments that are essential for human survival. They exist in vast quantities and possess stable properties, making them challenging to manage. Some reports indicated that there is a positive correlation between the production of MNPs and the incidence of obesity. The liver serves as both the central hub for lipid metabolism and a prime target for MNPs toxicity. These studies revealed that MNPs can lead to increased hepatic lipid accumulation, suggesting that they may be potential obesogens. However, the specific metabolic changes and possible mechanisms involved remain to be elucidated.

METHODS

This study focuses on the impact of nanoplastics (NPs) on liver lipid metabolism, using C57BL/6J mice (hereinafter referred to as C57 mice) as the research subjects, and exposing them to 100 nm NPs at 1000 µg/L continuously for 12 weeks.

RESULTS

The study revealed that (1) NPs led to nondietary weight gain together with an increase in fat volume and mass in mice. (2) NPs significantly increased serum total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) levels, with notable differences between groups. Notably, NPs exposure induced opposing effects on serum lipid profiles, elevating high-density lipoprotein cholesterol (HDL-C) concentrations while suppressing triglyceride (TG) levels, though intergroup differences failed to reach statistical significance. (3) NPs caused multiple inflammatory responses in the liver, with significant lipid deposition. (4) Untargeted metabolomics analysis indicated that NPs exposure led to significant alterations in various lipid metabolites, particularly glycerophospholipids. Additionally, transcriptomics reveals that differentially expressed genes (DEGs) triggered by NPs exposure are predominantly involved in metabolic routes including lipid metabolism and cytochrome P450 (CYP). Taken together, these findings suggested that alterations in lipid metabolism resulting from NPs exposure may involve arachidonic acid metabolism. Phosphatidylcholine (PC) could be the key substance, and the CYP gene family (Cyp2c23, Cyp2c40) might be the critical genes regulating liver lipid metabolism during NPs exposure.

CONCLUSIONS

This study has demonstrated that NPs exposure induced obesity and hepatic lipid accumulation in male mice independently of food intake. The integrated omics data identified dysregulated PC metabolism and CYP gene family expression, suggesting their involvement in arachidonic acid-associated pathways. These findings provided preliminary mechanistic clues linking NP exposure to hepatic lipid metabolism dysregulation and helped to elucidate the adverse effects of NPs on liver lipid metabolism.

Machine Learning Based Early Diagnosis of ADHD with SHAP Value Interpretation: A Retrospective Observational Study

Background

Attention-Deficit/Hyperactivity Disorder (ADHD) is a common neurodevelopmental disorder in children, characterized by inattention, hyperactivity, and impulsivity. Current diagnostic methods for ADHD rely primarily on behavioral assessments, which can be challenging due to symptom overlap with other psychiatric disorders and significant inter-individual variability. Developing potential early diagnostic methods for ADHD is imperative to mitigate the risk of misdiagnosis and enhance the evaluation of treatment efficacy.

Methods

The study was conducted at the Department of Pediatrics, Affiliated Hospital of Jiangnan University, from November 2022 to January 2024. Clinical data, including complete blood count, liver and kidney function tests, blood glucose levels, serum electrolyte tests, and serum 25-dihydroxyvitamin D3 levels, were collected. Feature selection and model construction were performed using various machine learning algorithms.

Results

Our results indicated that the Gradient Boosting Machine algorithm is the optimal model.

Conclusion

Our machine learning analyses suggest that the Gradient Boosting Machine (GBM) model may be the optimal choice, highlighting blood beta-2 microglobulin levels, red blood cell distribution width, 25-dihydroxyvitamin D3, and the percentage of eosinophils as key predictors of ADHD risk, thereby aiding early diagnosis. Further large-scale studies are warranted to validate these findings and explore the underlying mechanisms.

ATP11B Modulates Microglial Lipid Metabolism and Alleviates Alzheimer's Disease Pathology

Abnormal lipid metabolism in microglia leads to the formation of pathological lipid droplets (LDs), a phenomenon also observed in neurodegenerative diseases such as Alzheimer's disease (AD). The abnormal accumulation of LDs disrupts normal cellular function and exacerbates the pathological process of AD. ATP11B is a P4-ATPase and the expression of Atp11b changes in the brain of patients with AD and diseases of lipid metabolism. The present study aimed to explore the regulatory role of ATP11B in microglial lipid metabolism and assess the potential of ATP11B as a therapeutic target for AD. Atp11b deficiency caused excessive fatty acid uptake and activated the PPAR signaling pathway, resulting in abnormal synthesis of neutral lipids and mitochondrial energy metabolism in microglia. Further results showed that Atp11b deficiency led to the accumulation of pathological LDs in microglia and AD mice. Conversely, overexpression of Atp11b alleviated exploratory behavior impairment, learning and memory impairment, LD accumulation, beta-amyloid (Aβ) deposition, and inflammatory response in the brain of AD mice. These findings provide important clues for a better understanding of the pathogenesis of AD and for developing novel therapeutic strategies.

Lipin1 ameliorates cognitive ability of diabetic encephalopathy via regulating Ca2+ transfer through mitochondria-associated endoplasmic reticulum membranes

Diabetic encephalopathy (DE) is a common central nervous system complication resulting from diabetes mellitus (DM). While the exact pathogenesis remains unclear, a homeostatic imbalance of mitochondria-associated endoplasmic reticulum (ER) membranes (MAMs) within neurons has been shown to be closely associated with the dysfunctional cognitive pathology of this condition. Our previous work has revealed that phosphatidate phosphatase Lipin1 plays a critical role in the cognitive processes of DE via regulating mitochondrial function. In this study, we reported that the integrity of neuronal MAMs was disrupted in DE mice, which was accompanied by a decrease in the expression of hippocampal Lipin1. With a knock-down of hippocampal Lipin1 in normal mice, ER stress was induced, MAMs structures were impaired and Ca2+ transfer was suppressed. Such effects resulted in mitochondrial dysfunction, synaptic plasticity impairments, and finally cognitive dysfunctions. In contrast, an up-regulation of hippocampal Lipin1 in the DE model partially alleviated these dysfunctions. These results suggest that Lipin1 may ameliorate the cognitive dysfunctions associated with DE via regulating Ca2+ transfers through MAMs. Therefore, targeting Lipin1 may serve as a therapeutic strategy for the clinical treatment of DE.

Acute diacylglycerol production activates critical membrane-shaping proteins leading to mitochondrial tubulation and fission

Mitochondrial dynamics are orchestrated by protein assemblies that directly remodel membrane structure, however the influence of specific lipids on these processes remains poorly understood. Here, using an inducible heterodimerization system to selectively modulate the lipid composition of the outer mitochondrial membrane (OMM), we show that local production of diacylglycerol (DAG) directly leads to transient tubulation and rapid fragmentation of the mitochondrial network, which are mediated by isoforms of endophilin B (EndoB) and dynamin-related protein 1 (Drp1), respectively. Reconstitution experiments on cardiolipin-containing membrane templates mimicking the planar and constricted OMM topologies reveal that DAG facilitates the membrane binding and remodeling activities of both EndoB and Drp1, thereby independently potentiating membrane tubulation and fission events. EndoB and Drp1 do not directly interact with each other, suggesting that DAG production activates multiple pathways for membrane remodeling in parallel. Together, our data emphasizes the importance of OMM lipid composition in regulating mitochondrial dynamics.

Incorporation of Triacylglycerol and Cholesteryl Ester Droplets in Phase-Separated Giant Unilamellar Vesicles

Cytoplasmic lipid droplets form from the endoplasmic reticulum (ER). Because the ER membrane can undergo phase separation, the interaction of lipid droplets with phase-separated bilayers is of significant interest. In this study, we used fluorescence microscopy to investigate the incorporation of droplets composed of triolein, trilinolein, trimyristolein, trieicosenoin, and cholesteryl arachidonate in the bilayers of giant unilamellar vesicles (GUVs) consisting of a mixture of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), and cholesterol. After the triacylglycerol droplets were incorporated, the DOPC/DPPC/cholesterol (3:3:2) GUVs, which exhibited liquid-disordered (Ld) and liquid-ordered (Lo) phase separation, retained their phase-separated state. The triacylglycerol droplets were predominantly partitioned in the Ld domains. To elucidate the basis of this preferential partitioning, we investigated the surface pressures of DOPC, DPPC, and cholesterol monolayers containing triolein at the air/water interface using a Langmuir trough. From these measurements, we determined the interfacial tension at the monolayer-covered triolein/water interface. The results showed that DOPC most effectively reduced the interfacial tension. Thus, the droplet sorting into the DOPC-enriched Ld domains likely arose from the difference in the abilities of the two phases to stabilize the droplet interface. In contrast, cholesteryl arachidonate had a profound effect on bilayer phase behavior. Fluorescence images of the DOPC/DPPC/cholesterol (3:3:2) GUVs showed that the domain structures disappeared after droplet incorporation. Additionally, surface pressure measurements of DOPC/DPPC/cholesterol (3:3:2) monolayers containing cholesteryl arachidonate at the air/water interface suggested that cholesteryl arachidonate weakened the lipid-lipid interaction. The results indicate that the cholesteryl arachidonate molecules diffused across the bilayer to hinder the bilayer phase separation.

CSN-CRL Complexes: New Regulators of Adipogenesis

Recent discoveries revealed mechanistic insights into the control of adipogenesis by the Constitutive Photomorphogenesis 9 Signalosome (CSN) and its variants, CSNCSN7A and CSNCSN7B, which differ in the paralog subunits, CSN7A and CSN7B. CSNCSN7A and CSNCSN7B variants form permanent complexes with cullin-RING-ubiquitin ligases 3 and 4A (CRL3 and CRL4A), respectively. These complexes can be found in most eukaryotic cells and represent a critical reservoir for cellular functions. In an early stage of adipogenesis, mitotic clonal expansion (MCE), CSN-CRL1, and CSNCSN7B-CRL4A are blocked to ubiquitinate the cell cycle inhibitor p27KIP, leading to cell cycle arrest. In addition, in MCE CSN-CRL complexes rearrange the cytoskeleton for adipogenic differentiation and CRL3KEAP1 ubiquitylates the inhibitor of adipogenesis C/EBP homologous protein (CHOP) for degradation by the 26S proteasome, an adipogenesis-specific proteolysis. During terminal adipocyte differentiation, the CSNCSN7A-CRL3 complex is recruited to a lipid droplet (LD) membrane by RAB18. Currently, the configuration of the substrate receptors of CSNCSN7A-CRL3 on LDs is unclear. CSNCSN7A-CRL3 is activated by neddylation on the LD membrane, an essential adipogenic step. Damage to CSN/CUL3/CUL4A genes is associated with diverse diseases, including obesity. Due to the tremendous impact of CSN-CRLs on adipogenesis, we need strategies for adequate treatment in the event of malfunctions.

Functional Specialization of S-Adenosylmethionine Synthases Links Phosphatidylcholine to Mitochondrial Function and Stress Survival

S-adenosylmethionine (SAM), produced by SAM synthases, is critical for various cellular regulatory pathways and the synthesis of diverse metabolites. Studies have often equated the effects of knocking down one synthase with broader SAM-dependent outcomes such as histone methylation or phosphatidylcholine (PC) production. Humans and many other organisms express multiple SAM synthases. Evidence in Caenorhabditis elegans , which possesses four SAM synthase genes, suggest that the enzymatic source of SAM impacts its function. For instance, loss of sams-1 leads to enhanced heat shock survival and increased lifespan, whereas reducing sams-4 adversely affects heat stress survival. Here, we show that SAMS-1 contributes to a variety of intermediary metabolic pathways, whereas SAMS-4 is more important to generate SAM for methylation reactions. We demonstrate that loss of sams-1 exerts age-dependent effects on nuclear-encoded mitochondrial gene expression, mitochondrial metabolites, and may induce mitophagy. We propose a mechanistic model where reduced SAM from SAMS-1 acts through PC to impact mitochondria, thereby enhancing survival during heat stress.

Food grade titanium dioxide induced endoplasmic reticulum stress in colon cells: Comparison between normal and colorectal carcinoma cells

BACKGROUND

Food-grade titanium dioxide (E171) has been under scrutiny in the last decade since its possible adverse effects; however, the cellular mechanisms underlying E171 toxicity have not been thoroughly described.

AIM

We aimed to compare the effects of E171 on endoplasmic reticulum (ER) homeostasis in normal and cancer colon cells.

EXPERIMENTAL DESIGN

We exposed normal, carcinoma, and adenocarcinoma cells to 0.1, 1, 10, 50 and 100 μg/cm2 of E171 for 24, 48 and 72 h, and we evaluated ER stress, cell viability, titanium uptake, intracellular calcium concentration, and gene expression related to unfolded protein response (UPR) and chaperone pathways.

RESULTS

Cell viability decreased only after 72 h of exposure to 100 μg/cm2 of E171. Adenocarcinoma cells internalized higher titanium amounts than normal and carcinoma cells, but the effects in ER distribution, intracellular calcium concentration, and gene expression were similar among the three cell lines. The expression of UPR and chaperone pathways were downregulated at the lowest concentrations but upregulated at the highest concentrations in the three cell lines.

CONCLUSION

E171 induces ER stress through alterations in ER distribution, intracellular calcium, and UPR and chaperone protein pathways.

Ramulus Mori (Sangzhi) alkaloids ameliorate high-fat diet induced obesity in rats by modulating gut microbiota and bile acid metabolism

Objective

The objective of this study is to investigate the ability of Ramulus Mori (Sangzhi) alkaloid tablets (SZ-A) to ameliorate obesity and lipid metabolism disorders in rats subjected to a high-fat diet (HFD) through metagenomics, untargeted lipidomics, targeted metabolism of bile acid (BA), and BA pathways, providing a novel perspective on the management of metabolic disorders.

Methods

In this research, HFD-fed rats were concurrently administered SZ-A orally. We measured changes in body weight (BW), blood lipid profiles, and liver function to assess therapeutic effects. Liver lipid status was visualized through H&E and Oil Red O. Gut microbiota composition was elucidated using metagenomics. The LC-MS-targeted metabolomics approach was utilized to define the fecal BA profiles. Furthermore, the lipid metabolomics of adipose tissue samples was investigated using an LC-MS analysis platform. The expression levels of the BA receptor were determined by western blotting. Additionally, serum insulin (INS), glucagon-like peptide-1 (GLP-1), and inflammatory cytokines were quantified using an ELISA kit. The integrity of the colonic epithelial barrier was assessed using immunofluorescence.

Results

SZ-A notably decreased BW and blood lipid levels in obese rats while also alleviating liver injury. Additionally, SZ-A reduced the serum levels of leptin (LEP), INS, and GLP-1, indicating its potential to modulate key metabolic hormones. Most notably, SZ-A substantially improved gut microbiota composition. Specifically, it reshaped the gut microbiota structure in HFD-fed rats by increasing the relative abundance of beneficial bacteria, such as Bacteroides, while decreasing the populations of potentially harmful bacteria, such as Dorea and Blautia. At the BA level, SZ-A decreased the levels of harmful BAs, including hyodeoxycholic acid (HDCA), deoxycholic acid (DCA), 12-keto lithocholic acid (12-KLCA), lithocholic acid (LCA), and muricholic acid (MDCA). Between the model group and SZ-A, 258 differentially abundant metabolites were detected, with 72 upregulated and 186 downregulated. Furthermore, these BAs are implicated in the activation of the FXR-FGF15 and TGR5-GLP-1 pathways in the intestine. This activation helps to alleviate HFD-fed intestinal inflammation and restore intestinal barrier damage by modulating inflammatory cytokines and bolstering the intestinal barrier's capabilities.

Conclusions

Our findings indicate that SZ-A effectively modulates BW, serum lipid profiles, and liver function in HFD-fed rats. Moreover, SZ-A exerts a positive influence on inflammatory cytokines, thereby mitigating inflammation and promoting the restoration of the intestinal barrier. Significantly, our research indicates that adjusting the gut microbiome and BA levels could serve as an effective approach for both preventing and treating obesity and related metabolic dyslipidemia.

Zebrafish are resilient to the loss of major diacylglycerol acyltransferase enzymes

In zebrafish, maternally deposited yolk is the source of nutrients for embryogenesis prior to digestive system maturation. Yolk nutrients are processed and secreted to the growing organism by an extra-embryonic tissue, the yolk syncytial layer (YSL). The export of lipids from the YSL occurs through the production of triacylglycerol-rich lipoproteins. Here we report that mutations in the triacylglycerol synthesis enzyme, diacylglycerol acyltransferase-2 (Dgat2), cause yolk sac opacity due to aberrant accumulation of cytoplasmic lipid droplets in the YSL. Although triacylglycerol synthesis continues, it is not properly coupled to lipoprotein production as dgat2 mutants produce fewer, smaller, ApoB-containing lipoproteins. Unlike DGAT2-null mice, which are lipopenic and die soon after birth, zebrafish dgat2 mutants are viable, fertile, and exhibit normal mass and adiposity. Residual Dgat activity cannot be explained by the activity of other known Dgat isoenzymes, as dgat1a;dgat1b;dgat2 triple mutants continue to produce YSL lipid droplets and remain viable as adults. Further, the newly identified diacylglycerol acyltransferase, Tmem68, is also not responsible for the residual triacylglycerol synthesis activity. Unlike overexpression of Dgat1a and Dgat1b, monoacylglycerol acyltransferase-3 (Mogat3b) overexpression does not rescue yolk opacity, suggesting it does not possess Dgat activity in the YSL. However, mogat3b;dgat2 double mutants exhibit increased yolk opacity and often have structural alterations of the yolk extension. Quadruple mogat3b;dgat1a;dgat1b;dgat2 mutants either have severely reduced viability and stunted growth or do not survive past 3 days post fertilization, depending on the dgat2 mutant allele present. Our study highlights the remarkable ability of vertebrates to synthesize triacylglycerol through multiple biosynthetic pathways.

FITM2 deficiency results in ER lipid accumulation, ER stress, and reduced apolipoprotein B lipidation and VLDL triglyceride secretion in vitro and in mouse liver

OBJECTIVE

Triglycerides (TGs) associate with apolipoprotein B100 (apoB100) to form very low density lipoproteins (VLDLs) in the liver. The repertoire of factors that facilitate this association is incompletely understood. FITM2, an integral endoplasmic reticulum (ER) protein, was originally discovered as a factor participating in cytosolic lipid droplet (LD) biogenesis in tissues that do not form VLDL. We hypothesized that in the liver, in addition to promoting cytosolic LD formation, FITM2 would also transfer TG from its site of synthesis in the ER membrane to nascent VLDL particles within the ER lumen.

METHODS

Experiments were conducted using a rat hepatic cell line (McArdle-RH7777, or McA cells), an established model of mammalian lipoprotein metabolism, and mice. FITM2 expression was reduced using siRNA in cells and by liver specific cre-recombinase mediated deletion of the Fitm2 gene in mice. Effects of FITM2 deficiency on VLDL assembly and secretion in vitro and in vivo were measured by multiple methods, including density gradient ultracentrifugation, chromatography, mass spectrometry, stimulated Raman scattering (SRS) microscopy, sub-cellular fractionation, immunoprecipitation, immunofluorescence, and electron microscopy.

MAIN FINDINGS

1) FITM2-deficient hepatic cells in vitro and in vivo secrete TG-depleted VLDL particles, but the number of particles is unchanged compared to controls; 2) FITM2 deficiency in mice on a high fat diet (HFD) results in decreased plasma TG levels. The number of apoB100-containing lipoproteins remains similar, but shift from VLDL to low density lipoprotein (LDL) density; 3) Both in vitro and in vivo, when TG synthesis is stimulated and FITM2 is deficient, TG accumulates in the ER, and despite its availability this pool is unable to fully lipidate apoB100 particles; 4) FITM2 deficiency disrupts ER morphology and results in ER stress.

CONCLUSION

The results suggest that FITM2 contributes to VLDL lipidation, especially when newly synthesized hepatic TG is in abundance. In addition to its fundamental importance in VLDL assembly, the results also suggest that under dysmetabolic conditions, FITM2 may be an important factor in the partitioning of TG between cytosolic LDs and VLDL particles.

Lipid Alterations in Chronic Nonspecific Low Back Pain in the Chinese Population: A Metabolomic and Lipidomic Study

Chronic nonspecific low back pain (cNLBP) accounts for approximately 90% of low back pain cases, affecting 65-80% of the population and significantly impacting life quality and productivity. This condition also leads to substantial financial burden. Although there have been advancements, a comprehensive understanding of the underlying etiology of cNLBP remains elusive, resulting in less than optimal treatment outcomes. This study aimed to examine the correlation between lipid variations and the development of cNLBP. The cohort consisted of 26 healthy volunteers (HV group) and 30 cNLBP patients, with an assessment of metabolites and lipid composition in both groups. Metabolomic results revealed significant alterations in lipid-associated metabolites between the HV and cNLBP groups. Subsequent lipid analysis revealed that monoacylglycerols (MAGs) increased approximately 1.2-fold (p = 0.016), diacylglycerols (DAGs) increased approximately 1.4-fold (p = 0.0003), and phosphatidylserine (PS) increased approximately 1.4-fold (p = 0.011). In contrast, triacylglycerol (TAG) decreased to about 0.7-fold (p = 0.035) in the cNLBP group compared to the HV group. The contrasting trends in MAG/DAG and TAG levels indicated that the imbalance between MAG/DAG and TAG may have an impact on the development of cNLBP. This study has provided new insights into the relationship between the progression of cNLBP and specific lipids, suggesting that these lipids could serve as therapeutic targets for cNLBP.

Excessive or sustained endoplasmic reticulum stress: one of the culprits of adipocyte dysfunction in obesity

As the prevalence of obesity continues to rise globally, the research on adipocytes has attracted more and more attention. In the presence of nutrient overload, adipocytes are exposed to pressures such as hypoxia, inflammation, mechanical stress, metabolite, and oxidative stress that can lead to organelle dysfunction. Endoplasmic reticulum (ER) is a vital organelle for sensing cellular pressure, and its homeostasis is essential for maintaining adipocyte function. Under conditions of excess nutrition, ER stress (ERS) will be triggered by the gathering of abnormally folded proteins in the ER lumen, resulting in the activation of a signaling response known as the unfolded protein responses (UPRs), which is a response system to relieve ERS and restore ER homeostasis. However, if the UPRs fail to rescue ER homeostasis, ERS will activate pathways to damage cells. Studies have shown a role for disturbed activation of adipocyte ERS in the pathophysiology of obesity and its complications. Prolonged or excessive ERS in adipocytes can aggravate lipolysis, insulin resistance, and apoptosis and affect the bioactive molecule production. In addition, ERS also impacts the expression of some important genes. In view of the fact that ERS influences adipocyte function through various mechanisms, targeting ERS may be a viable strategy to treat obesity. This article summarizes the effects of ERS on adipocytes during obesity.

Association of glycerolipid metabolism with gut microbiota disturbances in a hamster model of high-fat diet-induced hyperlipidemia

Background

High-fat diet (HFD)-induced hyperlipidemia, which is associated with gut microbiota disturbances, remains a major public health challenge. Glycerolipid metabolism is responsible for lipid synthesis and is thus involved in the development of hyperlipidemia. However, possible association between the HFD-modulated gut microbiome and the glycerolipid metabolism pathway remains unclear.

Methods

Hamsters were fed a HFD for 4 weeks to establish a hyperlipidemia model. Fecal, plasma and liver samples collected from hamsters fed a HFD or a normal chow diet (NCD) were used for integrative metagenomic and untargeted metabolomic analyses to explore changes in the composition and functions of the gut microbiota, and relevant metabolites. Spearman rank correlation analysis was used to explore correlations between gut microbes and circulating glycerolipid metabolites, gut microbes and lipids, and circulating glycerolipid metabolites and lipids.

Results

The gut microbial composition of HFD hamsters showed significant alterations at the phylum, genus, and species levels that were skewed toward metabolic disorders compared with that of NCD hamsters. Functional characterization by KEGG analysis identified enrichment of the glycerolipid metabolism pathway in the gut microbiome of HFD hamsters. Plasma and liver metabolomics further indicated the upregulation and enrichment of glycerolipid metabolites in HFD hamsters. The Faecalibaculum, Allobaculum, and Eubacterium genera were positively correlated with plasma glycerolipid metabolites and lipid indices.

Conclusion

The findings of this study suggest an association between glycerolipid metabolism and the HFD-modulated gut microbiome that is involved in the development of hyperlipidemia.

Long-term arsenic exposure decreases mice body weight and liver lipid droplets

Arsenic (As) is a widespread global pollutant, and there is significant controversy surrounding its complex relationship with obesity, primarily focused on short-term exposure. Recognizing the prolonged nature of dietary arsenic exposure, this study involved feeding mice with arsenic-contained food for 14 months. The results showed that mice exposed to arsenic developed a non-alcoholic fatty liver condition, characterized by a light-yellow hue on the liver surface and various pathological alterations in the liver cells, including enlarged nuclei, cellular necrosis, inflammatory infiltration, dysfunctional mitochondria, and endoplasmic reticulum disorganization. There were also disruptions in biochemistry indices, with a significant increase in total cholesterol (TC) level and a decrease in high-density lipoprotein (HDL) level. However, some contradictory observations occurred, such as a significant decrease in body weight, triglyceride (TG) level, and the numbers of lipid droplets. Several genes related to lipid metabolism were tested, and a model was used to explain these discrepancies. Besides, examinations of the colon revealed compromised intestinal barrier function and signs of inflammation. Fecal 16S rRNA sequencing and pseudo-targeted metabolomics revealed disruptions in internal homeostasis, such as modules, nodes, connections, and lipid-related KEGG pathways. Fecal targeted metabolomics analyses of short-chain fatty acids (SCFAs) and bile acids (BAs) demonstrated a significant upregulation in three primary bile acids (CA, CDCA, TCDCA), four secondary bile acids (TUDCA, DCA, LCA, GUDCA), and total SCFAs level. Oxidative stress and inflammation were also evident. Additionally, based on correlation analysis and mediation analysis, it was assumed that changes in the microbiota (e.g., Dubosiella) can impact the liver metabolites (e.g., TGs) through alterations in fecal metabolites (e.g., LPCs). These findings provide a theoretical reference for the long-term effect of arsenic exposure on liver lipid metabolism.

Tanshinone IIA Inhibits the Endoplasmic Reticulum Stress-Induced Unfolded Protein Response by Activating the PPARα/FGF21 Axis to Ameliorate Nonalcoholic Steatohepatitis

Nonalcoholic steatohepatitis (NASH) is a critical stage in the progression of nonalcoholic fatty liver disease (NAFLD). Tanshinone IIA (TIIA) is a tanshinone extracted from Salvia miltiorrhiza; due to its powerful anti-inflammatory and antioxidant biological activities, it is commonly used for treating cardiovascular and hepatic diseases. A NASH model was established by feeding mice a methionine and choline-deficient (MCD) diet. Liver surface microblood flow scanning, biochemical examination, histopathological examination, cytokine analysis through ELISA, lipidomic analysis, transcriptomic analysis, and Western blot analysis were used to evaluate the therapeutic effect and mechanism of TIIA on NASH. The results showed that TIIA effectively reduced lipid accumulation, fibrosis, and inflammation and alleviated endoplasmic reticulum (ER) stress. Lipidomic analysis revealed that TIIA normalized liver phospholipid metabolism in NASH mice. A KEGG analysis of the transcriptome revealed that TIIA exerted its effect by regulating the PPAR signalling pathway, protein processing in the ER, and the NOD-like receptor signalling pathway. These results suggest that TIIA alleviates NASH by activating the PPARα/FGF21 axis to negatively regulate the ER stress-induced unfolded protein response (UPR).

Lipid Quality Control and Ferroptosis: From Concept to Mechanism

Cellular quality control systems sense and mediate homeostatic responses to prevent the buildup of aberrant macromolecules, which arise from errors during biosynthesis, damage by environmental insults, or imbalances in enzymatic and metabolic activity. Lipids are structurally diverse macromolecules that have many important cellular functions, ranging from structural roles in membranes to functions as signaling and energy-storage molecules. As with other macromolecules, lipids can be damaged (e.g., oxidized), and cells require quality control systems to ensure that nonfunctional and potentially toxic lipids do not accumulate. Ferroptosis is a form of cell death that results from the failure of lipid quality control and the consequent accumulation of oxidatively damaged phospholipids. In this review, we describe a framework for lipid quality control, using ferroptosis as an illustrative example to highlight concepts related to lipid damage, membrane remodeling, and suppression or detoxification of lipid damage via preemptive and damage-repair lipid quality control pathways.

Enterocyte-specific FATP4 deficiency elevates blood lipids via a shift from polar to neutral lipids in distal intestine

Fatty acid transport protein (FATP)4 was thought to mediate intestinal lipid absorption, which was disputed by a study using keratinocyte-Fatp4-rescued Fatp4-/- mice. These knockouts when fed with a Western diet showed elevated intestinal triglyceride (TG) and fatty acid levels. To investigate a possible role of FATP4 on intestinal lipid processing, ent-Fatp4 (KO) mice were generated by Villin-Cre-specific inactivation of the Fatp4 gene. We aimed to measure circulating and intestinal lipids in control and KO mice after acute or chronic fat intake or during aging. Remarkably, ent-Fatp4 mice displayed an approximately 30% decrease in ileal behenic, lignoceric, and nervonic acids, ceramides containing these FA, as well as, ileal sphingomyelin, phosphatidylcholine, and phosphatidylinositol levels. Such decreases were concomitant with an increase in jejunal cholesterol ester. After a 2-wk recovery from high lipid overload by tyloxapol and oral-lipid treatment, ent-Fatp4 mice showed an increase in plasma TG and chylomicrons. Upon overnight fasting followed by an oral fat meal, ent-Fatp4 mice showed an increase in plasma TG-rich lipoproteins and the particle number of chylomicrons and very low-density lipoproteins. During aging or after feeding with a high-fat high-cholesterol (HFHC) diet, ent-Fatp4 mice showed an increase in plasma TG, fatty acids, glycerol, and lipoproteins as well as intestinal lipids. HFHC-fed KO mice displayed an increase in body weight, the number of lipid droplets with larger sizes in the ileum, concomitant with a decrease in ileal ceramides and phosphatidylcholine. Thus, enterocyte FATP4 deficiency led to a metabolic shift from polar to neutral lipids in distal intestine rendering an increase in plasma lipids and lipoproteins.NEW & NOTEWORTHY Enterocyte-specific Fatp4 deficiency in mice increased intestinal lipid absorption with elevation of blood lipids during fasting and aging, as well as after an acute oral fat-loading or chronic HFHC feeding. Lipidomics revealed that knockout mice displayed a shift from very long-chain to long-chain fatty acids, and from polar to neutral lipids, predominantly in the ileum. Thus, FATP4 may have a physiological function in the control of blood lipids via metabolic shifts in distal intestine.

Single-cell atlas of ABCA7 loss-of-function reveals impaired neuronal respiration via choline-dependent lipid imbalances

Loss-of-function (LoF) variants in the lipid transporter ABCA7 significantly increase the risk of Alzheimer's disease (odds ratio ∼2), yet the pathogenic mechanisms and the neural cell types affected by these variants remain largely unknown. Here, we performed single-nuclear RNA sequencing of 36 human post-mortem samples from the prefrontal cortex of 12 ABCA7 LoF carriers and 24 matched non-carrier control individuals. ABCA7 LoF was associated with gene expression changes in all major cell types. Excitatory neurons, which expressed the highest levels of ABCA7, showed transcriptional changes related to lipid metabolism, mitochondrial function, cell cycle-related pathways, and synaptic signaling. ABCA7 LoF-associated transcriptional changes in neurons were similarly perturbed in carriers of the common AD missense variant ABCA7 p.Ala1527Gly (n = 240 controls, 135 carriers), indicating that findings from our study may extend to large portions of the at-risk population. Consistent with ABCA7's function as a lipid exporter, lipidomic analysis of isogenic iPSC-derived neurons (iNs) revealed profound intracellular triglyceride accumulation in ABCA7 LoF, which was accompanied by a relative decrease in phosphatidylcholine abundance. Metabolomic and biochemical analyses of iNs further indicated that ABCA7 LoF was associated with disrupted mitochondrial bioenergetics that suggested impaired lipid breakdown by uncoupled respiration. Treatment of ABCA7 LoF iNs with CDP-choline (a rate-limiting precursor of phosphatidylcholine synthesis) reduced triglyceride accumulation and restored mitochondrial function, indicating that ABCA7 LoF-induced phosphatidylcholine dyshomeostasis may directly disrupt mitochondrial metabolism of lipids. Treatment with CDP-choline also rescued intracellular amyloid β -42 levels in ABCA7 LoF iNs, further suggesting a link between ABCA7 LoF metabolic disruptions in neurons and AD pathology. This study provides a detailed transcriptomic atlas of ABCA7 LoF in the human brain and mechanistically links ABCA7 LoF-induced lipid perturbations to neuronal energy dyshomeostasis. In line with a growing body of evidence, our study highlights the central role of lipid metabolism in the etiology of Alzheimer's disease.

Lipid Droplet-Mitochondria Contacts in Health and Disease

The orchestration of cellular metabolism and redox balance is a complex, multifaceted process crucial for maintaining cellular homeostasis. Lipid droplets (LDs), once considered inert storage depots for neutral lipids, are now recognized as dynamic organelles critical in lipid metabolism and energy regulation. Mitochondria, the powerhouses of the cell, play a central role in energy production, metabolic pathways, and redox signaling. The physical and functional contacts between LDs and mitochondria facilitate a direct transfer of lipids, primarily fatty acids, which are crucial for mitochondrial β-oxidation, thus influencing energy homeostasis and cellular health. This review highlights recent advances in understanding the mechanisms governing LD-mitochondria interactions and their regulation, drawing attention to proteins and pathways that mediate these contacts. We discuss the physiological relevance of these interactions, emphasizing their role in maintaining energy and redox balance within cells, and how these processes are critical in response to metabolic demands and stress conditions. Furthermore, we explore the pathological implications of dysregulated LD-mitochondria interactions, particularly in the context of metabolic diseases such as obesity, diabetes, and non-alcoholic fatty liver disease, and their potential links to cardiovascular and neurodegenerative diseases. Conclusively, this review provides a comprehensive overview of the current understanding of LD-mitochondria interactions, underscoring their significance in cellular metabolism and suggesting future research directions that could unveil novel therapeutic targets for metabolic and degenerative diseases.

Plasma membrane abundance dictates phagocytic capacity and functional cross-talk in myeloid cells

Professional phagocytes like neutrophils and macrophages tightly control what they consume, how much they consume, and when they move after cargo uptake. We show that plasma membrane abundance is a key arbiter of these cellular behaviors. Neutrophils and macrophages lacking the G protein subunit Gβ4 exhibited profound plasma membrane expansion, accompanied by marked reduction in plasma membrane tension. These biophysical changes promoted the phagocytosis of bacteria, fungus, apoptotic corpses, and cancer cells. We also found that Gβ4-deficient neutrophils are defective in the normal inhibition of migration following cargo uptake. Sphingolipid synthesis played a central role in these phenotypes by driving plasma membrane accumulation in cells lacking Gβ4. In Gβ4 knockout mice, neutrophils not only exhibited enhanced phagocytosis of inhaled fungal conidia in the lung but also increased trafficking of engulfed pathogens to other organs. Together, these results reveal an unexpected, biophysical control mechanism central to myeloid functional decision-making.

CIDE proteins and their regulatory mechanisms in lipid droplet fusion and growth

The cell death-inducing DFF45-like effector (CIDE) proteins, including Cidea, Cideb, and Cidec/Fsp27, regulate various aspects of lipid homeostasis, including lipid storage, lipolysis, and lipid secretion. This review focuses on the physiological roles of CIDE proteins based on studies on knockout mouse models and human patients bearing CIDE mutations. The primary cellular function of CIDE proteins is to localize to lipid droplets (LDs) and to control LD fusion and growth across different cell types. We propose a four-step process of LD fusion, characterized by (a) the recruitment of CIDE proteins to the LD surface and CIDE movement, (b) the enrichment and condensate formation of CIDE proteins to form LD fusion plates at LD-LD contact sites, (c) lipid transfer through lipid-permeable passageways within the fusion plates, and (d) the completion of LD fusion. Lastly, we outline CIDE-interacting proteins as regulatory factors, as well as their contribution in LD fusion.

A metabolically controlled contact site between vacuoles and lipid droplets in yeast

The lipid droplet (LD) organization proteins Ldo16 and Ldo45 affect multiple aspects of LD biology in yeast. They are linked to the LD biogenesis machinery seipin, and their loss causes defects in LD positioning, protein targeting, and breakdown. However, their molecular roles remained enigmatic. Here, we report that Ldo16/45 form a tether complex with Vac8 to create vacuole lipid droplet (vCLIP) contact sites, which can form in the absence of seipin. The phosphatidylinositol transfer protein (PITP) Pdr16 is a further vCLIP-resident recruited specifically by Ldo45. While only an LD subpopulation is engaged in vCLIPs at glucose-replete conditions, nutrient deprivation results in vCLIP expansion, and vCLIP defects impair lipophagy upon prolonged starvation. In summary, Ldo16/45 are multifunctional proteins that control the formation of a metabolically regulated contact site. Our studies suggest a link between LD biogenesis and breakdown and contribute to a deeper understanding of how lipid homeostasis is maintained during metabolic challenges.

Evaluation of Lipid Quality in Fruit: Utilizing Lipidomic Approaches for Assessing the Impact of Biotic Stress on Pecans (Carya illinoinensis)

There is a scarcity of data on how the lipid composition of oily seeds changes in response to biotic stress. Yellow peach moth (Conogethes punctiferalis) has caused massive economic losses on the pecan (Carya illinoinensis) industry. Lipidomics is used in this study to determine the lipid composition of pecan and how it changes in response to insect attack. Pecan had 167 lipids, including 34 glycerolipids (GL), 62 glycerophospholipids (GP), 17 fatty acyls (FA), 41 sphingolipids (SP), and 13 saccharolipids (SL). The effects of biotic stress on lipids, particularly GL and GP, were significant. Biotic stress significantly reduced the lipid content of chains longer than 48. Forty-four significantly different lipids were discovered as potential biomarkers for distinguishing non-infected pecans from infested pecans. In addition, we used bioinformatics to identify the five most important metabolic pathways in order to investigate the processes underlying the changes. Our discoveries may offer valuable insights for enhancing pecan production in the future and contribute novel perspectives towards enhancing the nutritional value of pecans.

Lipid droplets and cellular lipid flux

Lipid droplets are dynamic organelles that store neutral lipids, serve the metabolic needs of cells, and sequester lipids to prevent lipotoxicity and membrane damage. Here we review the current understanding of the mechanisms of lipid droplet biogenesis and turnover, the transfer of lipids and metabolites at membrane contact sites, and the role of lipid droplets in regulating fatty acid flux in lipotoxicity and cell death.

Dysregulated palmitic acid metabolism promotes the formation of renal calcium-oxalate stones through ferroptosis induced by polyunsaturated fatty acids/phosphatidic acid

The pathogenesis of renal calcium-oxalate (CaOx) stones is complex and influenced by various metabolic factors. In parallel, palmitic acid (PA) has been identified as an upregulated lipid metabolite in the urine and serum of patients with renal CaOx stones via untargeted metabolomics. Thus, this study aimed to mechanistically assess whether PA is involved in stone formation. Lipidomics analysis of PA-treated renal tubular epithelial cells compared with the control samples revealed that α-linoleic acid and α-linolenic acid were desaturated and elongated, resulting in the formation of downstream polyunsaturated fatty acids (PUFAs). In correlation, the levels of fatty acid desaturase 1 and 2 (FADS1 and FADS2) and peroxisome proliferator-activated receptor α (PPARα) in these cells treated with PA were increased relative to the control levels, suggesting that PA-induced upregulation of PPARα, which in turn upregulated these two enzymes, forming the observed PUFAs. Lipid peroxidation occurred in these downstream PUFAs under oxidative stress and Fenton Reaction. Furthermore, transcriptomics analysis revealed significant changes in the expression levels of ferroptosis-related genes in PA-treated renal tubular epithelial cells, induced by PUFA peroxides. In addition, phosphatidyl ethanolamine binding protein 1 (PEBP1) formed a complex with 15-lipoxygenase (15-LO) to exacerbate PUFA peroxidation under protein kinase C ζ (PKC ζ) phosphorylation, and PKC ζ was activated by phosphatidic acid derived from PA. In conclusion, this study found that the formation of renal CaOx stones is promoted by ferroptosis of renal tubular epithelial cells resulting from PA-induced dysregulation of PUFA and phosphatidic acid metabolism, and PA can promote the renal adhesion and deposition of CaOx crystals by injuring renal tubular epithelial cells, consequently upregulating adhesion molecules. Accordingly, this study provides a new theoretical basis for understanding the correlation between fatty acid metabolism and the formation of renal CaOx stones, offering potential targets for clinical applications.

ER-LD Membrane Contact Sites: A Budding Area in the Pathogen Survival Strategy

The endoplasmic reticulum (ER) and lipid droplets (LDs) are essential organelles involved in lipid synthesis, storage, and transport. Physical membrane contacts between the ER and LDs facilitate lipid and protein exchange and thus play a critical role in regulating cellular lipid homeostasis. Recent research has revealed that ER-LD membrane contact sites are targeted by pathogens seeking to exploit host lipid metabolic processes. Both viruses and bacteria manipulate ER-LD membrane contact sites to enhance their replication and survival within the host. This review discusses the research advancements elucidating the mechanisms by which pathogens manipulate the ER-LD contacts through protein molecular mimicry and host cell protein manipulation, thereby hijacking host lipid metabolic processes to facilitate pathogenesis. Understanding the crosstalk between ER and LDs during infection provides deeper insight into host lipid regulation and uncovers potential therapeutic targets for treating infectious diseases.

FITM2 deficiency results in ER lipid accumulation, ER stress, reduced apolipoprotein B lipidation, and VLDL triglyceride secretion in vitro and in mouse liver

Objectives

Triglyceride (TG) association with apolipoprotein B100 (apoB100) serves to form very low density lipoproteins (VLDL) in the liver. The repertoire of factors that facilitate this association is incompletely defined. FITM2, an integral endoplasmic reticulum (ER) protein, was originally discovered as a factor participating in cytoplasmic lipid droplets (LDs) in tissues that do not form VLDL. We hypothesized that in the liver, in addition to promoting cytosolic LD formation, FITM2 would also transfer TG from its site of synthesis in the ER membrane to nascent VLDL particles within the ER lumen.

Methods

Experiments were conducted using a rat hepatic cell line (McArdle-RH7777, or McA cells), an established model of mammalian lipoprotein metabolism, and mice. FITM2 expression was reduced using siRNA in cells and by liver specific cre-recombinase mediated deletion of the Fitm2 gene in mice. Effects of FITM2 deficiency on VLDL assembly and secretion in vitro and in vivo were measured by multiple methods, including density gradient ultracentrifugation, chromatography, mass spectrometry, simulated Raman spectroscopy (SRS) microscopy, sub-cellular fractionation, immunoprecipitation, immunofluorescence, and electron microscopy.

Main findings

1) FITM2-deficient hepatic cells in vitro and in vivo secrete TG-depleted VLDL particles, but the number of particles is unchanged compared to controls; 2) FITM2 deficiency in mice on a high fat diet (HFD) results in decreased plasma TG levels. The number of apoB100-containing lipoproteins remains similar, but shift from VLDL to LDL density; 3) Both in vitro and in vivo , when TG synthesis is stimulated and FITM2 is deficient, TG accumulates in the ER, and despite its availability this pool is unable to fully lipidate apoB100 particles; 4) FITM2 deficiency disrupts ER morphology and results in ER stress.

Principal conclusions

The results suggest that FITM2 contributes to VLDL lipidation, especially when newly synthesized hepatic TG is in abundance. In addition to its fundamental importance in VLDL assembly, the results also suggest that under dysmetabolic conditions, FITM2 may be a limiting factor that ultimately contributes to non-alcoholic fatty liver disease (NAFLD) and steatohepatitis (NASH).

Lipid compartments and lipid metabolism as therapeutic targets against coronavirus

Lipids perform a series of cellular functions, establishing cell and organelles' boundaries, organizing signaling platforms, and creating compartments where specific reactions occur. Moreover, lipids store energy and act as secondary messengers whose distribution is tightly regulated. Disruption of lipid metabolism is associated with many diseases, including those caused by viruses. In this scenario, lipids can favor virus replication and are not solely used as pathogens' energy source. In contrast, cells can counteract viruses using lipids as weapons. In this review, we discuss the available data on how coronaviruses profit from cellular lipid compartments and why targeting lipid metabolism may be a powerful strategy to fight these cellular parasites. We also provide a formidable collection of data on the pharmacological approaches targeting lipid metabolism to impair and treat coronavirus infection.

Lipid droplet-specific near-infrared fluorescent probe for discriminating cancer and normal cells and diagnosing fatty liver

Lipid droplets (LDs) is a newly essential organelle, which participates in carious physiological and pathological processes. LDs are considered as potential markers for disease diagnosis. Specific imaging of LDs is useful to understand their basic biological function and to diagnose diseases. Here we designed and synthesized two fluorescent probes based on the low polarity and high viscosity in LDs. The terminal probe ZH-2 exhibits lipophilicity, NIR emission, viscosity sensitivity, and LDs specificity. The probe has been successfully used for visualizing LDs metabolism, discriminating between normal and cancerous cells, and diagnosing fatty liver disease.

Visualization of accessible cholesterol using a GRAM domain-based biosensor

Cholesterol is important for membrane integrity and cell signaling, and dysregulation of the distribution of cellular cholesterol is associated with numerous diseases, including neurodegenerative disorders. While regulated transport of a specific pool of cholesterol, known as "accessible cholesterol", contributes to the maintenance of cellular cholesterol distribution and homeostasis, tools to monitor accessible cholesterol in live cells remain limited. Here, we engineer a highly sensitive accessible cholesterol biosensor by taking advantage of the cholesterol-sensing element (the GRAM domain) of an evolutionarily conserved lipid transfer protein, GRAMD1b. Using this cholesterol biosensor, which we call GRAM-W, we successfully visualize in real time the distribution of accessible cholesterol in many different cell types, including human keratinocytes and iPSC-derived neurons, and show differential dependencies on cholesterol biosynthesis and uptake for maintaining levels of accessible cholesterol. Furthermore, we combine GRAM-W with a dimerization-dependent fluorescent protein (ddFP) and establish a strategy for the ultrasensitive detection of accessible plasma membrane cholesterol. These tools will allow us to obtain important insights into the molecular mechanisms by which the distribution of cellular cholesterol is regulated.