Hepatic lipid droplet homeostasis and fatty liver disease

Ablation of Hepatic Asah1 Gene Disrupts Hepatic Lipid Homeostasis and Promotes Fibrotic Nonalcoholic Steatohepatitis in Mice

Nonalcoholic fatty liver disease (NAFLD) encompasses a spectrum of chronic liver conditions, ranging from simple steatosis to nonalcoholic steatohepatitis, which may progress to fibrosis/cirrhosis. Here, the GSE163211 data set was analyzed, and Asah1 (encoding acid ceramidase) was identified as a crucial lysosomal gene that positively correlated with NAFLD stages in obese patients. To evaluate the role of Asah1 in the progression of NAFLD, Asah1fl/fl/Albcre mice (hepatocyte-specific deletion of Asah1) and Asah1 floxed (Asah1fl/fl/wild-type) mice were fed with either a normal diet or a high-fat, high-cholesterol paigen diet (PD) for 20 weeks. The results showed that hepatocyte-specific Asah1 ablation markedly aggravated PD-induced hepatic steatosis, hepatitis, and apoptosis, and resulted in marked fibrotic changes. In addition, Asah1 gene ablation exacerbated PD-induced portal venous hemodynamic abnormality. In cultured hepatocytes, Asah1 gene knockdown resulted in increased ceramide and cholesterol levels but did not affect triglyceride level. Knocking down Asah1 gene also exhibited broad impacts on lipid homeostasis pathways, including lipogenesis, fatty acid uptake, fatty acid oxidation, and lipid transport. Furthermore, Asah1 knockdown resulted in increased endoplasmic reticulum stress and lipid droplet biogenesis. Last, Asah1 gene knockdown impaired chaperone-mediated autophagy. In conclusion, these results suggest that Asah1 functions as an important regulator of hepatic lipid homeostasis, and its deficiency exacerbates hepatocyte lipotoxicity and injury, and promotes the development of fibrotic nonalcoholic steatohepatitis.

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.

Bisphenol A induces lipid metabolism disorder and impairs hepatopancreas of Sesarmops sinensis

Bisphenol A (BPA) is a chemical that disrupts the endocrine system and may have negative implications on the lipid metabolism of organisms. To ascertain BPA implications on lipid metabolism in the hepatopancreas of Sesarmops sinensis, we exposed S. sinensis to different concentrations of BPA for 14 days. The outcomes manifested that BPA may stimulate hepatopancreas injury and lipid deposition in the hepatopancreas of S. sinensis and lead to the increase of hepatosomatic index (HSI). Transcriptome analysis showed that lipid metabolism-related pathways were significantly enriched in KEGG pathways. BPA exposure also caused disorders in lipid metabolism by altering fatty acid composition and lipid metabolites. The up-regulation of lipid synthesis genes and the alteration of lipid transport genes may be important reasons for the disorder of lipid metabolism. Furthermore, these outcomes provide a fresh point of reference for comprehending the ecotoxicological impacts of BPA on aquatic organisms.

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.

Recent advances in fluorescent probes for fatty liver imaging by detecting lipid droplets

Fatty liver, a major health problem worldwide, is closely associated with aberrant accumulation and alteration of energy storage organelles, lipid droplets (LDs), in the disease process. Fluorescent probes with excellent optical performance, high sensitivity/selectivity and real-time monitoring have emerged as an attractive tool for the detection of LDs used in the diagnosis of fatty liver. In this review, we summarize various probes based on different response mechanisms to image LDs in the fatty liver process using different excitation imaging modes and emission wavelengths, including the visible to the near-infrared, two/three-photon, and the second near-infrared region. The perspectives and barriers associated with the reported lipid droplet (LD) probes for future development are also discussed.

LncRNA lncLLM Facilitates Lipid Deposition by Promoting the Ubiquitination of MYH9 in Chicken LMH Cells

The liver plays an important role in regulating lipid metabolism in animals. This study investigated the function and mechanism of lncLLM in liver lipid metabolism in hens at the peak of egg production. The effect of lncLLM on intracellular lipid content in LMH cells was evaluated by qPCR, Oil Red O staining, and detection of triglyceride (TG) and cholesterol (TC) content. The interaction between lncLLM and MYH9 was confirmed by RNA purification chromatin fractionation (CHIRP) and RNA immunoprecipitation (RIP) analysis. The results showed that lncLLM increased the intracellular content of TG and TC and promoted the expression of genes related to lipid synthesis. It was further found that lncLLM had a negative regulatory effect on the expression level of MYH9 protein in LMH cells. The intracellular TG and TC content of MYH9 knockdown cells increased, and the expression of genes related to lipid decomposition was significantly reduced. In addition, this study confirmed that the role of lncLLM is at least partly through mediating the ubiquitination of MYH9 protein to accelerate the degradation of MYH9 protein. This discovery provides a new molecular target for improving egg-laying performance in hens and treating fatty liver disease in humans.

Progress in the Study of Animal Models of Metabolic Dysfunction-Associated Steatotic Liver Disease

Metabolic dysfunction-associated steatotic liver disease (MASLD) has recently been proposed as an alternative term to NAFLD. MASLD is a globally recognized chronic liver disease that poses significant health concerns and is frequently associated with obesity, insulin resistance, and hyperlipidemia. To better understand its pathogenesis and to develop effective treatments, it is essential to establish suitable animal models. Therefore, attempts have been made to establish modelling approaches that are highly similar to human diet, physiology, and pathology to better replicate disease progression. Here, we reviewed the pathogenesis of MASLD disease and summarised the used animal models of MASLD in the last 7 years through the PubMed database. In addition, we have summarised the commonly used animal models of MASLD and describe the advantages and disadvantages of various models of MASLD induction, including genetic models, diet, and chemically induced models, to provide directions for research on the pathogenesis and treatment of MASLD.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Salvianolic acid A attenuates non-alcoholic fatty liver disease by regulating the AMPK-IGFBP1 pathway

Non-alcoholic fatty liver disease (NAFLD) affects approximately a quarter of the population and, to date, there is no approved drug therapy for this condition. Individuals with type 2 diabetes mellitus (T2DM) are at a significantly elevated risk of developing NAFLD, underscoring the urgency of identifying effective NAFLD treatments for T2DM patients. Salvianolic acid A (SAA) is a naturally occurring phenolic acid that is an important component of the water-soluble constituents isolated from the roots of Salvia miltiorrhiza Bunge. SAA has been demonstrated to possess anti-inflammatory and antioxidant stress properties. Nevertheless, its potential in ameliorating diabetes-associated NAFLD has not yet been fully elucidated. In this study, diabetic ApoE-/- mice were employed to establish a NAFLD model via a Western diet. Following this, they were treated with different doses of SAA (10 mg/kg, 20 mg/kg) via gavage. The study demonstrated a marked improvement in liver injury, lipid accumulation, inflammation, and the pro-fibrotic phenotype after the administration of SAA. Additionally, RNA-seq analysis indicated that the primary pathway by which SAA alleviates diabetes-induced NAFLD involves the cascade pathways of lipid metabolism. Furthermore, SAA was found to be effective in the inhibition of lipid accumulation, mitochondrial dysfunction and ferroptosis. A functional enrichment analysis of RNA-seq data revealed that SAA treatment modulates the AMPK pathway and IGFBP-1. Further experimental results demonstrated that SAA is capable of inhibiting lipid accumulation through the activation of the AMPK pathway and IGFBP-1.

Green Tea Polyphenol (-)-Epicatechin Pretreatment Mitigates Hepatic Steatosis in an In Vitro MASLD Model

Metabolic dysfunction-associated steatotic liver disease (MASLD), previously known as non-alcoholic fatty liver disease (NAFLD), is becoming more prominent globally due to an increase in the prevalence of obesity, dyslipidemia, and type 2 diabetes. A great deal of studies have proposed potential treatments for MASLD, with few of them demonstrating promising results. The aim of this study was to investigate the potential effects of (-)-epicatechin (EPI) on the development of MASLD in an in vitro model using the HepG2 cell line by determining the metabolic viability of the cells and the levels of PPARα, PPARγ, and GSH. HepG2 cells were pretreated with 10, 30, 50, and 100 μM EPI for 4 h to assess the potential effects of EPI on lipid metabolism. A MASLD cell culture model was established using HepG2 hepatocytes which were exposed to 1.5 mM oleic acid (OA) for 24 h. Moreover, colorimetric MTS assay was used in order to determine the metabolic viability of the cells, PPARα and PPARγ protein levels were determined using enzyme-linked immunosorbent assay (ELISA), and lipid accumulation was visualized using the Oil Red O Staining method. Also, the levels of intracellular glutathione (GSH) were measured to determine the level of oxidative stress. EPI was shown to increase the metabolic viability of the cells treated with OA. The metabolic viability of HepG2 cells, after 24 h incubation with OA, was significantly decreased, with a metabolic viability of 71%, compared to the cells pretreated with EPI, where the metabolic viability was 74-86% with respect to the concentration of EPI used in the experiment. Furthermore, the levels of PPARα, PPARγ, and GSH exhibited a decrease in response to increasing EPI concentrations. Pretreatment with EPI has demonstrated a great effect on the levels of PPARα, PPARγ, and GSH in vitro. Therefore, considering that EPI mediates lipid metabolism in MASLD, it should be considered a promising hepatoprotective agent in future research.

Overexpression of METTL14 mediates steatohepatitis and insulin resistance in mice

Background

Lipid accumulation and redox imbalance, resulting from dysregulation of hepatic fatty acids oxidation, contribute to the development of steatohepatitis and insulin resistance. Recently, dysregulated RNA N6-methyladenosine (m6A) methylation modification has been found involving fatty liver. However, the role of methyltransferase-like 14 (METTL14), the core component of m6A methylation, in the development of steatohepatitis is unknown. Herein, we aimed to explore the role of METTL14 on steatohepatitis and insulin resistance in mice with metabolic dysfunction-associated steatotic liver disease (MASLD).

Methods

The liver tissues of mice and patients with MASLD were collected to detect the expression of METTL14. METTL14 overexpression and METTL14 silence were used to investigate the effect of METTL14 on lipid metabolism disorder in vivo and in vitro. Knockout of METTL14 in primary hepatocytes was used to investigate the role of Sirtuin 1 (SIRT1) on lipid accumulation induced by METTL14.

Results

METTL14 was dramatically up-regulated in the livers of db/db mice, high-fat diet (HFD)-fed mice, and patients with MASLD. METTL14 overexpression exacerbated MASLD and promoted lipid metabolism disorder and insulin resistance in mice. Conversely, METTL14 knockout ameliorated lipid deposition and insulin resistance in HFD-fed mice. Furthermore, METTL14 overexpression facilitated lipid accumulation, while METTL14 knockout reduced lipid accumulation in HepG2 cells and primary hepatocytes. In addition, METTL14 lost up-regulated SIRT1 expression in hepatocytes. SIRT1 deficiency abrogated the ameliorating effects of METTL14 downregulation in MASLD mice.

Conclusions

These findings suggest that dysfunction of the METTL14-SIRT1 pathway might promote hepatic steatosis and insulin resistance.

Synthesis and preclinical testing of a selective beta-subtype agonist of thyroid hormone receptor ZTA-261

BACKGROUND

Thyroid hormones (TH) regulate the basal metabolic rate through their receptors THRα and THRβ. TH activates lipid metabolism via THRβ, however, an excess amount of TH can lead to tachycardia, bone loss, and muscle wasting through THRα. In recent years, TH analogs that selectively bind to THRβ have gained attention as new agents for treating dyslipidemia and obesity, which continue to pose major challenges to public health worldwide.

METHODS

We developed a TH analog, ZTA-261, by modifying the existing THRβ-selective agonists GC-1 and GC-24. To determine the THRβ-selectivity of ZTA-261, an in vitro radiolabeled TH displacement assay was conducted. ZTA-261 was intraperitoneally injected into a mouse model of high-fat diet-induced obesity, and its effectiveness in reducing body weight and visceral fat, and improving lipid metabolism was assessed. In addition, its toxicity in the liver, heart, and bone was evaluated.

RESULTS

ZTA-261 is more selective towards THRβ than GC-1. Although ZTA-261 is less effective in reducing body weight and visceral fat than GC-1, it is as effective as GC-1 in reducing the levels of serum and liver lipids. These effects are mediated by the same pathway as that of T3, a natural TH, as evidenced by similar changes in the expression of TH-induced and lipid metabolism-related genes. The bone, cardiac, and hepatotoxicity of ZTA-261 are significantly lower than those of GC-1.

CONCLUSIONS

ZTA-261, a highly selective and less toxic THRβ agonist, has the potential to be used as a drug for treating diseases related to lipid metabolism.

Assessment of the disruption effects of tetrabromobisphenol A and its analogues on lipid metabolism using multiple in vitro models

Tetrabromobisphenol A (TBBPA), a widely-used brominated flame retardant, has been revealed to exert endocrine disrupting effects and induce adipogenesis. Given the high structural similarities of TBBPA analogues and their increasing exposure risks, their effects on lipid metabolism are necessary to be explored. Herein, 9 representative TBBPA analogues were screened for their interference on 3T3-L1 preadipocyte adipogenesis, differentiation of C3H10T1/2 mesenchymal stem cells (MSCs) to brown adipocytes, and lipid accumulation of HepG2 cells. TBBPA bis(2-hydroxyethyl ether) (TBBPA-BHEE), TBBPA mono(2-hydroxyethyl ether) (TBBPA-MHEE), TBBPA bis(glycidyl ether) (TBBPA-BGE), and TBBPA mono(glycidyl ether) (TBBPA-MGE) were found to induce adipogenesis in 3T3-L1 preadipocytes to different extends, as evidenced by the upregulated intracellular lipid generation and expressions of adipogenesis-related biomarkers. TBBPA-BHEE exhibited a stronger obesogenic effect than did TBBPA. In contrast, the test chemicals had a weak impact on the differentiation process of C3H10T1/2 MSCs to brown adipocytes. As for hepatic lipid formation test, only TBBPA mono(allyl ether) (TBBPA-MAE) was found to significantly promote triglyceride (TG) accumulation in HepG2 cells, and the effective exposure concentration of the chemical under oleic acid (OA) co-exposure was lower than that without OA co-exposure. Collectively, TBBPA analogues may perturb lipid metabolism in multiple tissues, which varies with the test tissues. The findings highlight the potential health risks of this kind of emerging chemicals in inducing obesity, non-alcoholic fatty liver disease (NAFLD) and other lipid metabolism disorders, especially under the conditions in conjunction with high-fat diets.

Review: Mechanism of herbivores synergistically metabolizing toxic plants through liver and intestinal microbiota

Interspecific interactions are central to ecological research. Plants produce toxic plant secondary metabolites (PSMs) as a defense mechanism against herbivore overgrazing, prompting their gradual adaptation to toxic substances for tolerance or detoxification. P450 enzymes in herbivore livers bind to PSMs, whereas UDP-glucuronosyltransferase and glutathione S-transferase increase the hydrophobicity of the bound PSMs for detoxification. Intestinal microorganisms such as Bacteroidetes metabolize cellulase and other macromolecules to break down toxic components. However, detoxification is an overall response of the animal body, necessitating coordination among various organs to detoxify ingested PSMs. PSMs undergo detoxification metabolism through the liver and gut microbiota, evidenced by increased signaling processes of bile acids, inflammatory signaling molecules, and aromatic hydrocarbon receptors. In this context, we offer a succinct overview of how metabolites from the liver and gut microbiota of herbivores contribute to enhancing metabolic PSMs. We focused mainly on elucidating the molecular communication between the liver and gut microbiota involving endocrine, immune, and metabolic processes in detoxification. We have also discussed the potential for future alterations in the gut of herbivores to enhance the metabolic effects of the liver and boost the detoxification and metabolic abilities of PSMs.

Life cycle assessment of hepatotoxicity induced by cyhalofop-butyl in environmental concentrations on zebrafish in light of gut-liver axis

Cyhalofop-butyl (CB) poses a significant threat to aquatic organisms, but there is a discrepancy in evidence about hepatotoxicity after prolonged exposure to environmental levels. The aim of this study was to investigate long-term hepatotoxicity and its effects on the gut-liver axis through the exposure of zebrafish to environmental concentrations of CB (0.1,1,10 μg/L) throughout their life cycle. Zebrafish experienced abnormal obesity symptoms and organ index after a prolonged exposure of 120 days. The gut-liver axis was found to be damaged both morphologically and functionally through an analysis of histology, electron microscopy subcellular structure, and liver function. The disruption of the gut-liver axis inflammatory process by CB is suggested by the rise in inflammatory factors and the alteration of inflammatory genes. Furthermore, there was a noticeable alteration in the blood and gut-liver axis biochemical parameters as well as gene expression linked to lipid metabolism, which may led to an imbalance in the gut flora. In conclusion, the connection between the gut-liver axis, intestinal microbiota, and liver leads to the metabolic dysfunction of zebrafish exposed to long-term ambient concentrations of CB, and damaged immune system and liver lipid metabolism. This study gives another knowledge into the hepatotoxicity component of long haul openness to ecological centralization of CB, and might be useful to assess the potential natural and wellbeing dangers of aryloxyphenoxypropionate herbicides.

Tomato genotype but not crop water deficit matters for tomato health benefits in diet-induced obesity of C57BL/6JRj male mice

Several studies have linked the intake of lycopene and/or tomato products with improved metabolic health under obesogenic regime. The aim was to evaluate the differential impact of supplementations with several tomato genotypes differing in carotenoid content and subjected to different irrigation levels on obesity-associated disorders in mice. In this study, 80 male C57BL/6JRj mice were assigned into 8 groups to receive: control diet, high fat diet, high fat diet supplemented at 5 % w/w with 4 tomato powders originating from different tomato genotypes cultivated under control irrigation: H1311, M82, IL6-2, IL12-4. Among the 4 genotypes, 2 were also cultivated under deficit irrigation, reducing the irrigation water supply by 50 % from anthesis to fruit harvest. In controlled irrigation treatment, all genotypes significantly improved fasting glycemia and three of them significantly lowered liver lipids content after 12 weeks of supplementation. In addition, IL6-2 genotype, rich in β-carotene, significantly limited animal adiposity, body weight gain and improved glucose homeostasis as highlighted in glucose and insulin tolerance tests. No consistent beneficial or detrimental impact of deficit irrigation to tomato promoting health benefits was found. These findings imply that the choice of tomato genotype can significantly alter the composition of fruit carotenoids and phytochemicals, thereby influencing the anti-obesogenic effects of the fruit. In contrast, deficit irrigation appears to have an overall insignificant impact on enhancing the health benefits of tomato powder in this context, particularly when compared to the genotype-related variations in carotenoid content.

A fluorescent perilipin 2 knock-in mouse model reveals a high abundance of lipid droplets in the developing and adult brain

Lipid droplets (LDs) are dynamic lipid storage organelles. They are tightly linked to metabolism and can exert protective functions, making them important players in health and disease. Most LD studies in vivo rely on staining methods, providing only a snapshot. We therefore developed a LD-reporter mouse by labelling the endogenous LD coat protein perilipin 2 (PLIN2) with tdTomato, enabling staining-free fluorescent LD visualisation in living and fixed tissues and cells. Here we validate this model under standard and high-fat diet conditions and demonstrate that LDs are highly abundant in various cell types in the healthy brain, including neurons, astrocytes, ependymal cells, neural stem/progenitor cells and microglia. Furthermore, we also show that LDs are abundant during brain development and can be visualized using live imaging of embryonic slices. Taken together, our tdTom-Plin2 mouse serves as a novel tool to study LDs and their dynamics under both physiological and diseased conditions in all tissues expressing Plin2.

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.

Oligonucleotide therapies for nonalcoholic steatohepatitis

Nonalcoholic steatohepatitis (NASH) represents a severe disease subtype of nonalcoholic fatty liver disease (NAFLD) that is thought to be highly associated with systemic metabolic abnormalities. It is characterized by a series of substantial liver damage, including hepatocellular steatosis, inflammation, and fibrosis. The end stage of NASH, in some cases, may result in cirrhosis and hepatocellular carcinoma (HCC). Nowadays a large number of investigations are actively under way to test various therapeutic strategies, including emerging oligonucleotide drugs (e.g., antisense oligonucleotide, small interfering RNA, microRNA, mimic/inhibitor RNA, and small activating RNA) that have shown high potential in treating this fatal liver disease. This article systematically reviews the pathogenesis of NASH/NAFLD, the promising druggable targets proven by current studies in chemical compounds or biological drug development, and the feasibility and limitations of oligonucleotide-based therapeutic approaches under clinical or pre-clinical studies.

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

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

The switch triggering the invasion process: Lipid metabolism in the metastasis of hepatocellular carcinoma

ABSTRACT

In humans, the liver is a central metabolic organ with a complex and unique histological microenvironment. Hepatocellular carcinoma (HCC), which is a highly aggressive disease with a poor prognosis, accounts for most cases of primary liver cancer. As an emerging hallmark of cancers, metabolic reprogramming acts as a runaway mechanism that disrupts homeostasis of the affected organs, including the liver. Specifically, rewiring of the liver metabolic microenvironment, including lipid metabolism, is driven by HCC cells, propelling the phenotypes of HCC cells, including dissemination, invasion, and even metastasis in return. The resulting formation of this vicious loop facilitates various malignant behaviors of HCC further. However, few articles have comprehensively summarized lipid reprogramming in HCC metastasis. Here, we have reviewed the general situation of the liver microenvironment and the physiological lipid metabolism in the liver, and highlighted the effects of different aspects of lipid metabolism on HCC metastasis to explore the underlying mechanisms. In addition, we have recapitulated promising therapeutic strategies targeting lipid metabolism and the effects of lipid metabolic reprogramming on the efficacy of HCC systematical therapy, aiming to offer new perspectives for targeted therapy.

Effect of globin peptide on female fertility in aging granulosa cell-specific Nrg1 knockout mice

Ovarian fibrosis contributes to age-related ovarian dysfunction. In our previous study, we observed ovarian fibrosis in both obese and aging mice with intracellular lipid droplets in the fibrotic ovaries. Although the importance of mitochondria in ovarian fibrosis has been recognized in pharmacological studies, their role in lipid metabolism remains unclear. Globin peptide (GP), derived from hemoglobin, enhances lipid metabolism in obese mice. This study aimed to elucidate the importance of lipid metabolism in ovarian fibrosis by using GP. Treatment of ovarian stromal cells with GP increased mitochondrial oxygen consumption during β-oxidation. Lipid accumulation was also observed in the ovaries of granulosa cell-specific Nrg1 knockout mice (gcNrg1KO), and the administration of GP to gcNrg1KO mice for two months reduced ovarian lipid accumulation and fibrosis in addition to restoring the estrous cycle. GP holds promise for mitigating lipid-related ovarian issues and provides a novel approach to safeguarding ovarian health by regulating fibrosis via lipid pathways.

Exacerbated ischemia-reperfusion injury in fatty livers is mediated by lipid peroxidation stress and ferroptosis

BACKGROUND

Ischemia-reperfusion injury is a common problem in liver surgery and transplantation. Although ischemia-reperfusion injury is known to be more pronounced in fatty livers, the underlying mechanisms for this difference remain poorly understood. We hypothesized that ferroptosis plays a significant role in fatty liver ischemia-reperfusion injury due to increased lipid peroxidation in the presence of stored iron in the fatty liver. To test this hypothesis, the ferroptosis pathway was evaluated in a murine fatty liver ischemia-reperfusion injury model.

METHODS

C57BL6 mice were fed with a normal diet or a high fat, high sucrose diet for 12 weeks. At 22 weeks of age, liver ischemia-reperfusion injury was induced through partial (70%) hepatic pedicle clamping for 60 minutes, followed by 24 hours of reperfusion before tissue harvest. Acyl-coenzyme A synthetase long-chain family member 4 and 4-hydroxynonenal were quantified in the liver tissues. In separate experiments, liproxstatin-1 or vehicle control was administered for 7 consecutive days before liver ischemia-reperfusion injury.

RESULTS

Exacerbated ischemia-reperfusion injury was observed in the livers of high fat, high sucrose diet fed mice. High fat, high sucrose diet + ischemia-reperfusion injury (HDF+IRI) livers had a significantly greater abundance of acyl-coenzyme A synthetase long-chain family member 4 and 4-hydroxynonenal compared with normal diet + ischemia-reperfusion injury (ND+IRI) livers or sham fatty livers, which indicated an increase of ferroptosis. HFD fed animals receiving liproxstatin-1 injections had a significant reduction in serum aspartate transaminase and alanine transaminase after ischemia-reperfusion injury, consistent with attenuation of ischemia-reperfusion injury in the liver.

CONCLUSION

Ferroptosis plays a significant role in ischemia-reperfusion injury in fatty livers. Inhibiting ferroptotic pathways in the liver may serve as a novel therapeutic strategy to protect the fatty liver in the setting of ischemia-reperfusion injury.

Impact of Seipin in cholesterol mediated lipid droplet maturation; status of endoplasmic reticulum stress and lipophagy

The global prevalence of nonalcoholic fatty liver disease (NAFLD) defined by the increased number of lipid droplets (LDs) in hepatocytes, have risen continuously in parallel with the obesity. LDs and related proteins are known to affect cellular metabolism and signaling. Seipin, one of the most important LD-related proteins, plays a critical role in LD biogenesis. Although the role of adipose tissue-specific Seipin silencing is known, hepatocyte-specific silencing upon cholesterol-mediated lipid accumulation has not been investigated. In our study, we investigated the effect of Seipin on endoplasmic reticulum (ER) stress and lipophagy in cholesterol accumulated mouse hepatocyte cells. In this direction, cholesterol accumulation was induced by cholesterol-containing liposome, while Seipin mRNA and protein levels were reduced by siRNA. Our findings show that cholesterol containing liposome administration in hepatocytes increases both Seipin protein and number of large LDs. However Seipin silencing reduced the increase of cholesterol mediated large LDs and Glucose-regulated protein 78 (GRP78) mRNA. Additionally, lysosome-LD colocalization increased only in cells treated with cholesterol containing liposome, while the siRNA against Seipin did not lead any significant difference. According to our findings, we hypothesize that Seipin silencing in hepatocytes reduced cholesterol mediated LD maturation as well as GRP78 levels, but not lipophagy.

Essential phospholipids impact cytokine secretion and alter lipid-metabolizing enzymes in human hepatocyte cell lines

BACKGROUND

Essential phospholipids (EPL) are hepatoprotective.

METHODS

The effects on interleukin (IL)-6 and -8 secretion and on certain lipid-metabolizing enzymes of non-cytotoxic concentrations of EPL (0.1 and 0.25 mg/ml), polyenylphosphatidylcholine (PPC), and phosphatidylinositol (PtdIns) (both at 0.1 and 1 mg/ml), compared with untreated controls, were assessed in human hepatocyte cell lines (HepG2, HepaRG, and steatotic HepaRG).

RESULTS

Lipopolysaccharide (LPS)-induced IL-6 secretion was significantly decreased in HepaRG cells by most phospholipids, and significantly increased in steatotic HepaRG cells with at least one concentration of EPL and PtdIns. LPS-induced IL-8 secretion was significantly increased in HepaRG and steatotic HepaRG cells with all phospholipids. All phospholipids significantly decreased amounts of fatty acid synthase in steatotic HepaRG cells and the amounts of acyl-CoA oxidase in HepaRG cells. Amounts of lecithin cholesterol acyltransferase were significantly decreased in HepG2 and HepaRG cells by most phospholipids, and significantly increased with 0.1 mg/ml PPC (HepaRG cells) and 1 mg/ml PtdIns (steatotic HepaRG cells). Glucose-6-phosphate dehydrogenase activity was unaffected by any phospholipid in any cell line.

CONCLUSIONS

EPL, PPC, and PtdIns impacted the secretion of pro-inflammatory cytokines and affected amounts of several key lipid-metabolizing enzymes in human hepatocyte cell lines. Such changes may help liver function improvement, and provide further insights into the EPL's mechanism of action.

Inhibition of Drp1-Filamin Protein Complex Prevents Hepatic Lipid Droplet Accumulation by Increasing Mitochondria-Lipid Droplet Contact

Lipid droplet (LD) accumulation in hepatocytes is one of the major symptoms associated with fatty liver disease. Mitochondria play a key role in catabolizing fatty acids for energy production through β-oxidation. The interplay between mitochondria and LD assumes a crucial role in lipid metabolism, while it is obscure how mitochondrial morphology affects systemic lipid metabolism in the liver. We previously reported that cilnidipine, an already existing anti-hypertensive drug, can prevent pathological mitochondrial fission by inhibiting protein-protein interaction between dynamin-related protein 1 (Drp1) and filamin, an actin-binding protein. Here, we found that cilnidipine and its new dihydropyridine (DHP) derivative, 1,4-DHP, which lacks Ca2+ channel-blocking action of cilnidipine, prevent the palmitic acid-induced Drp1-filamin interaction, LD accumulation and cytotoxicity of human hepatic HepG2 cells. Cilnidipine and 1,4-DHP also suppressed the LD accumulation accompanied by reducing mitochondrial contact with LD in obese model and high-fat diet-fed mouse livers. These results propose that targeting the Drp1-filamin interaction become a new strategy for the prevention or treatment of fatty liver disease.

Exploring the impact of lipid droplets on the evolution and progress of hepatocarcinoma

Over the past 10 years, the biological role of lipid droplets (LDs) has gained significant attention in the context of both physiological and pathological conditions. Considerable progress has been made in elucidating key aspects of these organelles, yet much remains to be accomplished to fully comprehend the myriad functions they serve in the progression of hepatic tumors. Our current perception is that LDs are complex and active structures managed by a distinct set of cellular processes. This understanding represents a significant paradigm shift from earlier perspectives. In this review, we aim to recapitulate the function of LDs within the liver, highlighting their pivotal role in the pathogenesis of metabolic dysfunction-associated steatotic liver disease (MASLD) (Hsu and Loomba, 2024) and their contribution to the progression towards more advanced pathological stages up to hepatocellular carcinoma (HC) (Farese and Walther, 2009). We are aware of the molecular complexity and changes occurring in the neoplastic evolution of the liver. Our attempt, however, is to summarize the most important and recent roles of LDs across both healthy and all pathological liver states, up to hepatocarcinoma. For more detailed insights, we direct readers to some of the many excellent reviews already available in the literature (Gluchowski et al., 2017; Hu et al., 2020; Seebacher et al., 2020; Paul et al., 2022).

Unveiling the role of disulfidptosis-related genes in the pathogenesis of non-alcoholic fatty liver disease

Backgrounds

Non-alcoholic fatty liver disease (NAFLD) presents as a common liver disease characterized by an indistinct pathogenesis. Disulfidptosis is a recently identified mode of cell death. This study aimed to investigate the potential role of disulfidptosis-related genes (DRGs) in the pathogenesis of NAFLD.

Methods

Gene expression profiles were obtained from the bulk RNA dataset GSE126848 and the single-cell RNA dataset GSE136103, both associated with NAFLD. Our study assessed the expression of DRGs in NAFLD and normal tissues. Weighted gene co-expression network analysis (WGCNA) and differential expression analysis were employed to identify the key NAFLD-specific differentially expressed DRGs (DE-DRGs). To explore the biological functions and immune regulatory roles of these key DE-DRGs, we conducted immune infiltration analysis, functional enrichment analysis, consensus clustering analysis, and single-cell differential state analysis. Finally, we validated the expression and biological functions of DRGs in NAFLD patients using histology and RNA-sequencing transcriptomic assays with human liver tissue samples.

Results

Through the intersection of WGCNA, differentially expressed genes, and DRGs, two key DE-DRGs (DSTN and MYL6) were identified. Immune infiltration analysis indicated a higher proportion of macrophages, T cells, and resting dendritic cells in NAFLD compared to control liver samples. Based on the key DE-DRGs, Two disulfidptosis clusters were defined in GSE126848. Cluster 1, with higher expression of the key DE-DRGs, exhibited increased immune infiltration abundance and was closely associated with oxidative stress and immune regulation compared to cluster 2. High-resolution analysis of mononuclear phagocytes highlighted the potential role of MYL6 in intrahepatic M1 phenotype Kupffer cells in NAFLD patients. Our transcriptome data revealed that the expression levels of the majority of DRGs were significantly increased in NAFLD patients. NAFLD patients exhibit elevated MYL6 correlating with inflammation, oxidative stress, and disease severity, offering promising diagnostic specificity.

Conclusion

This comprehensive study provides evidence for the association between NAFLD and disulfidptosis, identifying potential target genes and pathways in NAFLD. The identification of MYL6 as a possible treatment target for NAFLD provided a novel understanding of the disease's development.

Molecular dynamics simulations of intracellular lipid droplets: a new tool in the toolbox

Lipid droplets (LDs) are ubiquitous intracellular organelles with a central role in multiple lipid metabolic pathways. However, identifying correlations between their structural properties and their biological activity has proved challenging, owing to their unique physicochemical properties as compared with other cellular membranes. In recent years, molecular dynamics (MD) simulations, a computational methodology allowing the accurate description of molecular assemblies down to their individual components, have been demonstrated to be a useful and powerful approach for studying LD structural and dynamical properties. In this short review, we attempt to highlight, as comprehensively as possible, how MD simulations have contributed to our current understanding of multiple molecular mechanisms involved in LD biology.

O-GlcNAcylation regulates long-chain fatty acid metabolism by inhibiting ACOX1 ubiquitination-dependent degradation

BACKGROUND

Cold as a common environmental stress, causes increased heat production, accelerated metabolism and even affects its production performance. How to improve the adaptability of the animal organism to cold has been an urgent problem. As a key hub of lipid metabolism, the liver can regulate lipid metabolism to maintain energy balance, and O-GlcNAcylation is a kind of important PTMs, which participates in a variety of signaling and mechanism regulation, and at the same time, is very sensitive to changes in stress and nutritional levels, and is the body's "stress receptors" and "nutrient receptors". Therefore, the aim of this experiment was to investigate the effect of cold-induced O-GlcNAcylation on hepatic lipid metabolism, and to explore the potential connection between O-GlcNAcylation and hepatic lipid metabolism.

METHODS

To investigate the loss of O-linked N-acetylglucosamine (O-GlcNAc) transferase (OGT) and the precise impacts of additional cold-induced circumstances on liver mass, shape, and metabolic profile, C57 mice were used as an animal model. Using the protein interactions approach, the mechanism of O-GlcNAcylation, as well as the degradation pathway of acyl-Coenzyme A oxidase 1 (ACOX1), were clarified. Additional in vitro analyses of oleic acid (OA) and OGT inhibitor tetraoxan (Alloxan) (Sigma, 2244-11-3) on lipid breakdown in AML-12 cells.

RESULTS

In C57BL/6 mice, deletion of O-GlcNAcylation disrupted lipid metabolism, caused hepatic edema and fibrosis, and altered mitochondrial apoptosis. This group of modifications was made worse by cold induction. The accumulation of medium- and long-chain fatty acids is a hallmark of lipolysis, which is accelerated by the deletion of O-GlcNAcylation, whereas lipid synthesis is slowed down. The association between ACOX1 and OGT at the K48 gene precludes ubiquitinated degradation.

Sea Buckthorn Polyphenols Alleviate High-Fat-Diet-Induced Metabolic Disorders in Mice via Reprograming Hepatic Lipid Homeostasis Owing to Directly Targeting Fatty Acid Synthase

Our previous studies found that Sea Buckthorn polyphenols (SBP) extract inhibits fatty acid synthase (FAS) in vitro. Thus, we continued to explore possible effects and underlying mechanisms of SBP on complicated metabolic disorders in long-term high-fat-diet (HFD)-fed mice. To reveal that, an integrated approach was developed in this study. Targeted quantitative lipidomics with a total of 904 unique lipids mapping contributes to profiling the comprehensive features of disarranged hepatic lipid homeostasis and discovering a set of newfound lipid-based biomarkers to predict the occurrence and indicate the progression of metabolic disorders beyond current indicators. On the other hand, technologies of intermolecular interactions characterization, especially surface plasmon resonance (SPR) assay, contribute to recognizing targeted bioactive constituents present in SBP. Our findings highlight hepatic lipid homeostasis maintenance and constituent-FAS enzyme interactions, to provide new insights that SBP as a functional food alleviates HFD-induced metabolic disorders in mice via reprograming hepatic lipid homeostasis caused by targeting FAS, owing to four polyphenols directly interacting with FAS and cinaroside binding to FAS with good affinity.

Metabolic dysfunction-associated fatty liver disease: current therapeutic strategies

The definition of "Metabolic Associated Fatty Liver Disease - MAFLD" has replaced the previous definition of Nonalcoholic Fatty Liver Disease (NAFLD), because cardiometabolic criteria have been added for the prevention of cardiological risk in these patients. This definition leads to an in-depth study of the bidirectional relationships between hepatic steatosis, Type 2 Diabetes Mellitus (T2DM), Cardiovascular Disease (CVD) and/or their complications. Lifestyle modification, which includes correct nutrition combined with regular physical activity, represents the therapeutic cornerstone of MAFLD. When therapy is required, there is not clear accord on how to proceed in an optimal way with nutraceutical or pharmacological therapy. Numerous studies have attempted to identify nutraceuticals with a significant benefit on metabolic alterations and which contribute to the improvement of hepatic steatosis. Several evidences are supporting the use of silymarin, berberine, curcumin, Nigella sativa, Ascophyllum nodosum, and Fucus vesiculosus, vitamin E, coenzyme Q10 and Omega-3. However, more evidence regarding the long-term efficacy and safety of these compounds are required. There is numerous evidence that highlights the use of therapies such as incretins or the use of Proprotein Convertase Subtilisin/Kexin type 9 (PCSK9) inhibitors or other similar therapies which, by assisting existing therapies for pathologies such as diabetes, hypertension, insulin resistance, have given a breakthrough in prevention and the reduction of cardiometabolic risk. This review gave an overview of the current therapeutic strategies that are expected to aid in the treatment and prevention of MAFLD.

A lipid index for risk of hyperlipidemia caused by anti-retroviral drugs

HIV-associated lipodystrophy has been reported in people taking anti-retroviral therapy (ART). Lipodystrophy can cause cardiovascular diseases, affecting the quality of life of HIV-infected individuals. In this study, we propose a pharmacological lipid index to estimate the risk of hyperlipidemia caused by anti-retroviral drugs. Lipid droplets were stained in cells treated with anti-retroviral drugs and cyclosporin A. Signal intensities of lipid droplets were plotted against the drug concentrations to obtain an isodose of 10 μM of cyclosporin A, which we call the Pharmacological Lipid Index (PLI). The PLI was then normalized by EC50. PLI/EC50 values were low in early proteinase inhibitors and the nucleoside reverse transcriptase inhibitor, d4T, indicating high risk of hyperlipidemia, which is consistent with previous findings of hyperlipidemia. In contrast, there are few reports of hyperlipidemia for drugs with high PLI/EC50 scores. Data suggests that PLI/EC50 is a useful index for estimating the risk of hyperlipidemia.

VLDL Biogenesis and Secretion: It Takes a Village

The production and secretion of VLDLs (very-low-density lipoproteins) by hepatocytes has a direct impact on liver fat content, as well as the concentrations of cholesterol and triglycerides in the circulation and thus affects both liver and cardiovascular health, respectively. Importantly, insulin resistance, excess caloric intake, and lack of physical activity are associated with overproduction of VLDL, hepatic steatosis, and increased plasma levels of atherogenic lipoproteins. Cholesterol and triglycerides in remnant particles generated by VLDL lipolysis are risk factors for atherosclerotic cardiovascular disease and have garnered increasing attention over the last few decades. Presently, however, increased risk of atherosclerosis is not the only concern when considering today's cardiometabolic patients, as they often also experience hepatic steatosis, a prevalent disorder that can progress to steatohepatitis and cirrhosis. This duality of metabolic risk highlights the importance of understanding the molecular regulation of the biogenesis of VLDL, the lipoprotein that transports triglycerides and cholesterol out of the liver. Fortunately, there has been a resurgence of interest in the intracellular assembly, trafficking, degradation, and secretion of VLDL by hepatocytes, which has led to many exciting new molecular insights that are the topic of this review. Increasing our understanding of the biology of this pathway will aid to the identification of novel therapeutic targets to improve both the cardiovascular and the hepatic health of cardiometabolic patients. This review focuses, for the first time, on this duality.

Par3L, a polarity protein, promotes M1 macrophage polarization and aggravates atherosclerosis in mice via p65 and ERK activation

Proinflammatory M1 macrophages are critical for the progression of atherosclerosis. The Par3-like protein (Par3L) is a homolog of the Par3 family involved in cell polarity establishment. Par3L has been shown to maintain the stemness of mammary stem cells and promote the survival of colorectal cancer cells. In this study, we investigated the roles of the polar protein Par3L in M1 macrophage polarization and atherosclerosis. To induce atherosclerosis, Apoe-/- mice were fed with an atherosclerotic Western diet for 8 or 16 weeks. We showed that Par3L expression was significantly increased in human and mouse atherosclerotic plaques. In primary mouse macrophages, oxidized low-density lipoprotein (oxLDL, 50 μg/mL) time-dependently increased Par3L expression. In Apoe-/- mice, adenovirus-mediated Par3L overexpression aggravated atherosclerotic plaque formation accompanied by increased M1 macrophages in atherosclerotic plaques and bone marrow. In mouse bone marrow-derived macrophages (BMDMs) or peritoneal macrophages (PMs), we revealed that Par3L overexpression promoted LPS and IFNγ-induced M1 macrophage polarization by activating p65 and extracellular signal-regulated kinase (ERK) rather than p38 and JNK signaling. Our results uncover a previously unidentified role for the polarity protein Par3L in aggravating atherosclerosis and favoring M1 macrophage polarization, suggesting that Par3L may serve as a potential therapeutic target for atherosclerosis.

Altered hepatic lipid droplet morphology and lipid metabolism in fasted Plin2-null mice

Perilipin 2 (Plin2) binds to the surface of hepatic lipid droplets (LDs) with expression levels that correlate with triacylglyceride (TAG) content. We investigated if Plin2 is important for hepatic LD storage in fasted or high-fat diet-induced obese Plin2+/+ and Plin2-/- mice. Plin2-/- mice had comparable body weights, metabolic phenotype, glucose tolerance, and circulating TAG and total cholesterol levels compared with Plin2+/+ mice, regardless of the dietary regime. Both fasted and high-fat fed Plin2-/- mice stored reduced levels of hepatic TAG compared with Plin2+/+ mice. Fasted Plin2-/- mice stored fewer but larger hepatic LDs compared with Plin2+/+ mice. Detailed hepatic lipid analysis showed substantial reductions in accumulated TAG species in fasted Plin2-/- mice compared with Plin2+/+ mice, whereas cholesteryl esters and phosphatidylcholines were increased. RNA-Seq revealed minor differences in hepatic gene expression between fed Plin2+/+ and Plin2-/- mice, in contrast to marked differences in gene expression between fasted Plin2+/+ and Plin2-/- mice. Our findings demonstrate that Plin2 is required to regulate hepatic LD size and storage of neutral lipid species in the fasted state, while its role in obesity-induced steatosis is less clear.

Loss of carnitine palmitoyltransferase 1a reduces docosahexaenoic acid-containing phospholipids and drives sexually dimorphic liver disease in mice

BACKGROUND AND AIMS

Genome and epigenome wide association studies identified variants in carnitine palmitoyltransferase 1a (CPT1a) that associate with lipid traits. The goal of this study was to determine the role of liver-specific CPT1a on hepatic lipid metabolism.

APPROACH AND RESULTS

Male and female liver-specific knockout (LKO) and littermate controls were placed on a low-fat or high-fat diet (60% kcal fat) for 15 weeks. Mice were necropsied after a 16 h fast, and tissues were collected for lipidomics, matrix-assisted laser desorption ionization mass spectrometry imaging, kinome analysis, RNA-sequencing, and protein expression by immunoblotting. Female LKO mice had increased serum alanine aminotransferase levels which were associated with greater deposition of hepatic lipids, while male mice were not affected by CPT1a deletion relative to male control mice. Mice with CPT1a deletion had reductions in DHA-containing phospholipids at the expense of monounsaturated fatty acids (MUFA)-containing phospholipids in whole liver and at the level of the lipid droplet (LD). Male and female LKO mice increased RNA levels of genes involved in LD lipolysis (Plin2, Cidec, G0S2) and in polyunsaturated fatty acid metabolism (Elovl5, Fads1, Elovl2), while only female LKO mice increased genes involved in inflammation (Ly6d, Mmp12, Cxcl2). Kinase profiling showed decreased protein kinase A activity, which coincided with increased PLIN2, PLIN5, and G0S2 protein levels and decreased triglyceride hydrolysis in LKO mice.

CONCLUSIONS

Liver-specific deletion of CPT1a promotes sexually dimorphic steatotic liver disease (SLD) in mice, and here we have identified new mechanisms by which females are protected from HFD-induced liver injury.

A comprehensive review of the family of very-long-chain fatty acid elongases: structure, function, and implications in physiology and pathology

BACKGROUND

The very-long-chain fatty acid elongase (ELOVL) family plays essential roles in lipid metabolism and cellular functions. This comprehensive review explores the structural characteristics, functional properties, and physiological significance of individual ELOVL isoforms, providing insights into lipid biosynthesis, cell membrane dynamics, and signaling pathways.

AIM OF REVIEW

This review aims to highlight the significance of the ELOVL family in normal physiology and disease development. By synthesizing current knowledge, we underscore the relevance of ELOVLs as potential therapeutic targets.

KEY SCIENTIFIC CONCEPTS OF REVIEW

We emphasize the association between dysregulated ELOVL expression and diseases, including metabolic disorders, skin diseases, neurodegenerative conditions, and cancer. The intricate involvement of ELOVLs in cancer biology, from tumor initiation to metastasis, highlights their potential as targets for anticancer therapies. Additionally, we discuss the prospects of using isoform-specific inhibitors and activators for metabolic disorders and cancer treatment. The identification of ELOVL-based biomarkers may advance diagnostics and personalized medicine.

CONCLUSION

The ELOVL family's multifaceted roles in lipid metabolism and cellular physiology underscore its importance in health and disease. Understanding their functions offers potential therapeutic avenues and personalized treatments.

Polyenylphosphatidylcholine as bioactive excipient in tablets for the treatment of liver fibrosis

Liver fibrosis is a condition characterized by the accumulation of extracellular matrix (ECM) arising from the myofibroblastic transdifferentiation of hepatic stellate cells (HSCs) occurring as the natural response to liver damage. To date, no pharmacological treatments have been specifically approved for liver fibrosis. We recently reported a beneficial effect of polyenylphosphatidylcholines (PPCs)-rich formulations in reverting fibrogenic features of HSCs. However, unsaturated phospholipids' properties pose a constant challenge to the development of tablets as preferred patient-centric dosage form. Profiting from the advantageous physical properties of the PPCs-rich Soluthin® S 80 M, we developed a tablet formulation incorporating 70% w/w of this bioactive lipid. Tablets were characterized via X-ray powder diffraction, thermogravimetry, and Raman confocal imaging, and passed the major compendial requirements. To mimic physiological absorption after oral intake, phospholipids extracted from tablets were reconstituted as protein-free chylomicron (PFC)-like emulsions and tested on the fibrogenic human HSC line LX-2 and on primary cirrhotic rat hepatic stellate cells (PRHSC). Lipids extracted from tablets and reconstituted in buffer or as PFC-like emulsions exerted the same antifibrotic effect on both activated LX-2 and PRHSCs as observed with plain S 80 M liposomes, showing that the manufacturing process did not interfere with the bioactivity of PPCs.

A lipidomic approach to bisphenol F-induced non-alcoholic fatty liver disease-like changes: altered lipid components in a murine model

Bisphenol A (BPA), a typical environmental endocrine disruptor, is an "obesogen" that can induce lipid accumulation in the liver. Highly similar in structure to BPA, bisphenol F (BPF) is becoming the dominant BPA substitute on the market, which attracts more and more attention due to its potential adverse effects. Recently, BPF exposure is found to cause non-alcoholic fatty liver disease (NAFLD)-like changes; however, the underlying toxic effects remain poorly understood. Therefore, in the current study, we focused on BPF-mediated lipid homeostasis, especially the alterations of lipid components and metabolism. In human serum, the BPF levels in healthy controls and NAFLD patients were assessed by ELISA, and BPF-induced disturbance of lipid metabolism was evaluated in mouse model via non-targeted lipomic methods with ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry. It suggested that BPF exposure was positively correlated with NAFLD severity and triglyceride level in patients. Based on the relationships, lipid metabolites were assessed in mouse livers between control and BPF-treated group, and it revealed that twenty-six lipid metabolites (including phospholipids, sphingolipids, and glycerides) were significantly changed in mouse livers. Phosphatidylcholine, phosphatidylethanolamine, and diglyceryl ester levels were lower than those in the control mice; hexose ceramide content in sphingolipids markedly increased in BPF-treated mouse livers. Noteworthily, the glycerophospholipid metabolic pathway was found to be the most pronounced in BPF-induced disturbance of lipid metabolism. Therefore, the current study, for the first time, is deciphering the BPF-induced lipid metabolic disturbance, which may provide novel intervention strategies for BPF-induced NAFLD-like changes.

MnO2 nanoparticles and MnSO4 differentially affected hepatic lipid metabolism through miR-92a/acsl3-dependent de novo lipogenesis in yellow catfish Pelteobagrusfulvidraco

With the increasing production and use of MnO2 NPs and MnSO4 in various fields, their discharge into the aquatic environment is inevitable, which poses potential threats to aquatic organisms and humans. However, to date, few studies have been conducted to investigate the potential mechanism of the toxicity of MnO2 NPs, and a comprehensive understanding of the differences between this mechanism and the toxicity mechanism of inorganic Mn (MnSO4) is still lacking. Since lipid metabolism-relevant parameters have been widely recognized as novel biomarkers for risk assessment of environmental contaminants, the present study investigated the differential mechanisms of how MnO2 NPs and MnSO4 affect hepatic lipid metabolism in a freshwater fish yellow catfish. Compared to MnSO4, dietary MnO2 NPs caused liver injury, increased hepatic lipid accumulation and induced lipotoxicity, and up-regulated mRNA expression of de novo lipogenic genes. Moreover, MnO2 NPs downregulated the expression of miR-92a and miR-92b-3p, microRNAs involved in regulation of lipid metabolism, in the liver. Mechanistically, we found that acls3, an acetyl-coenzyme A synthetase, is target gene of miR-92a, and miR-92a-acsl3-dependent de novo lipogenesis contributes to lipid accumulation and lipotoxicity induced by MnO2 NPs. Collectively, these findings provided novel insights into mechanism whereby miRNAs mediate nanoparticles- and inorganic Mn-induced hepatic lipotoxicity and changes of lipid metabolism in vertebrates. Our findings also shed new perspective for ecotoxicity and ecological risk of MnO2 NPs and MnSO4 in aquatic environment.

Oridonin restores hepatic lipid homeostasis in an LXRα-ATGL/EPT1 axis-dependent manner

Hepatosteatosis is characterized by abnormal accumulation of triglycerides (TG), leading to prolonged and chronic inflammatory infiltration. To date, there is still a lack of effective and economical therapies for hepatosteatosis. Oridonin (ORI) is a major bioactive component extracted from the traditional Chinese medicinal herb Rabdosia rubescens. In this paper, we showed that ORI exerted significant protective effects against hepatic steatosis, inflammation and fibrosis, which was dependent on LXRα signaling. It is reported that LXRα regulated lipid homeostasis between triglyceride (TG) and phosphatidylethanolamine (PE) by promoting ATGL and EPT1 expression. Therefore, we implemented the lipidomic strategy and luciferase reporter assay to verify that ORI contributed to the homeostasis of lipids via the regulation of the ATGL gene associated with TG hydrolysis and the EPT1 gene related to PE synthesis in a LXRα-dependent manner, and the results showed the TG reduction and PE elevation. In detail, hepatic TG overload and lipotoxicity were reversed after ORI treatment by modulating the ATGL and EPT1 genes, respectively. Taken together, the data provide mechanistic insights to explain the bioactivity of ORI in attenuating TG accumulation and cytotoxicity and introduce exciting opportunities for developing novel natural activators of the LXRα-ATGL/EPT1 axis for pharmacologically treating hepatosteatosis and metabolic disorders.

Effect of natural polysaccharides on alcoholic liver disease: A review

In this study, we systematically collected relevant literature in the past five years on the intervention of natural polysaccharides in alcoholic liver disease (ALD) and reviewed the pharmacological activities and potential mechanisms of action. Natural polysaccharides are effective in preventing liver tissue degeneration, inhibiting the alcohol-induced expression of inflammatory factors, inactivation of antioxidant enzymes, and abnormal hepatic lipid deposition. Natural polysaccharides regulate the expression of proteins, such as tight junction proteins, production of small molecule metabolites, and balance of intestinal flora in the intestinal tract to alleviate ALD. Natural polysaccharides also exert therapeutic effects by modulating inflammatory, oxidative, lipid metabolism, and other pathways in the liver. Natural polysaccharides also inhibit alcohol-induced intestinal abnormalities by regulating intestinal flora and feeding back into the liver via the gut-liver axis. However, existing research on natural polysaccharides has many shortcomings: for example, most of the natural polysaccharides for testing are total polysaccharides or crude polysaccharides, progress in research on in vivo metabolic processes and mechanisms is slow, and the degree of industrialisation is insufficient. Finally, we discuss the difficulties in studying natural polysaccharides and future directions to provide a theoretical basis for their development and application.

Single-cell metabolic profiling reveals subgroups of primary human hepatocytes with heterogeneous responses to drug challenge

BACKGROUND

Xenobiotics are primarily metabolized by hepatocytes in the liver, and primary human hepatocytes are the gold standard model for the assessment of drug efficacy, safety, and toxicity in the early phases of drug development. Recent advances in single-cell genomics demonstrate liver zonation and ploidy as main drivers of cellular heterogeneity. However, little is known about the impact of hepatocyte specialization on liver function upon metabolic challenge, including hepatic metabolism, detoxification, and protein synthesis.

RESULTS

Here, we investigate the metabolic capacity of individual human hepatocytes in vitro. We assess how chronic accumulation of lipids enhances cellular heterogeneity and impairs the metabolisms of drugs. Using a phenotyping five-probe cocktail, we identify four functional subgroups of hepatocytes responding differently to drug challenge and fatty acid accumulation. These four subgroups display differential gene expression profiles upon cocktail treatment and xenobiotic metabolism-related specialization. Notably, intracellular fat accumulation leads to increased transcriptional variability and diminishes the drug-related metabolic capacity of hepatocytes.

CONCLUSIONS

Our results demonstrate that, upon a metabolic challenge such as exposure to drugs or intracellular fat accumulation, hepatocyte subgroups display different and heterogeneous transcriptional responses.

Polarity-Sensitive Probe for Two-Photon Fluorescence Lifetime Imaging of Lipid Droplets In Vitro and In Vivo

Lipid droplets (LDs) are crucial organelles used to store lipids and participate in lipid metabolism in cells. The abnormal aggregation and polarity change of LDs are associated with the occurrence of diseases, such as steatosis. Herein, the polarity-sensitive probe TBPCPP with a donor-acceptor-π-acceptor (D-A-π-A) structure was designed and synthesized. The TBPCPP has a large Stokes shift (∼220 nm), excellent photostability, high LD targeting, and considerable two-photon absorption (TPA) cross-section (∼226 GM), enabling deep two-photon imaging (∼360 μm). In addition, the fluorescence lifetime of TBPCPP decreases linearly with increasing solvent polarity. Therefore, with the assistance of two-photon fluorescence lifetime imaging microscopy (TP-FLIM), TBPCPP has successfully achieved not only the visualization of polarity changes caused by LD accumulation in HepG-2 cells but also lipid-specific imaging and visualization of different polarities in lipid-rich regions in zebrafish for the first time. Furthermore, TP-FLIM revealed that the polarity gradually decreases during steatosis in HepG-2 cells, which provided new insights into the diagnosis of steatosis.

Preferential lipolysis of DGAT1 over DGAT2 generated triacylglycerol in Huh7 hepatocytes

Two distinct diacylglycerol acyltransferases (DGAT1 and DGAT2) catalyze the final committed step of triacylglycerol (TG) synthesis in hepatocytes. After its synthesis in the endoplasmic reticulum (ER) TG is either stored in cytosolic lipid droplets (LDs) or is assembled into very low-density lipoproteins in the ER lumen. TG stored in cytosolic LDs is hydrolyzed by adipose triglyceride lipase (ATGL) and the released fatty acids are converted to energy by oxidation in mitochondria. We hypothesized that targeting/association of ATGL to LDs would differ depending on whether the TG stores were generated through DGAT1 or DGAT2 activities. Individual inhibition of DGAT1 or DGAT2 in Huh7 hepatocytes incubated with oleic acid did not yield differences in TG accretion while combined inhibition of both DGATs completely prevented TG synthesis suggesting that either DGAT can efficiently esterify exogenously supplied fatty acid. DGAT2-made TG was stored in larger LDs, whereas TG formed by DGAT1 accumulated in smaller LDs. Inactivation of DGAT1 or DGAT2 did not alter expression (mRNA or protein) of ATGL, the ATGL activator ABHD5/CGI-58, or LD coat proteins PLIN2 or PLIN5, but inactivation of both DGATs increased PLIN2 abundance despite a dramatic reduction in the number of LDs. ATGL was found to preferentially target to LDs generated by DGAT1 and fatty acids released from TG in these LDs were also preferentially used for fatty acid oxidation. Combined inhibition of DGAT2 and ATGL resulted in larger LDs, suggesting that the smaller size of DGAT1-generated LDs is the result of increased lipolysis of TG in these LDs.

Pelargonic acid vanillylamide alleviates hepatic autophagy and ER stress in hepatic steatosis model

Pelargonic acid vanillylamide (PAVA) has been shown to reduce hepatic lipid accumulation in an obese rat model, however the underlying mechanism responsible for regulating lipid metabolism remains unclear. This study investigated the molecular mechanisms invoked by PAVA in regulating lipogenesis, autophagy, and endoplasmic reticulum (ER) stress in obese rats. Male Sprague-Dawley rats were fed on a diet consisting of 65.26% fat (16 weeks) and HepG2 cells were incubated with 200 μM oleic acid (OA) plus 100 μM palmitic acid (PA) for 48 h. These treatments resulted in a steatosis model. PAVA was shown to reduce fat deposition in hepatocytes in HepG2 by reducing lipotoxicity, the triglyceride content, the expression of sterol regulatory element binding protein 1c (SREBP-1c) and fatty acid synthase (FASN). PAVA also significantly reduced the calcium level and the expression of calpain 2 and upregulated the expression of Atg7 in comparison to the HFD group. In addition, PAVA was shown to significantly decrease the expression of autophagy pathway-related proteins including LC3 and p62. Treatment with PAVA (1 mg/day) reduced the expressions of ER stress markers Bip, ATF6 (p50), p-IRE1/IRE1, p-eIF2α/eIF2α, pJNK, CHOP and cleaved CASP12. In conclusion, PAVA ameliorated obesity induced hepatic steatosis by attenuating defective autophagy and ER stress pathways.

Metabolic characteristics of voriconazole - Induced liver injury in rats

Voriconazole (VOR) - induced liver injury is a common adverse reaction, and can lead to serious clinical outcomes. It is of great significance to describe the metabolic characteristics of VOR - induced liver injury and to elucidate the potential mechanisms. This study investigated the changes of plasma metabolic profiles in a rat model of VOR - induced liver injury by non - targeted metabolomics. Correlation analysis was performed between differentially expressed metabolites and plasma liver function indexes. The metabolites with strong correlation were determined for their predictive performance for liver injury using receiver operating characteristic (ROC) curve analysis. Potential biomarkers were then screened combined with liver pathological scores. Finally, the expression level of genes that involved in lipid metabolism were determined in rat liver to verify the mechanism of VOR - induced liver injury we proposed. VOR - induced liver injury in rats was characterized by plasma alanine aminotransferase (ALT) and aspartate aminotransferase (AST) elevation, the lipid droplets accumulation in liver, as well as inflammation and fibrosis. Significant changes of plasma metabolites were observed, with a decrease in lipid metabolites accounting for over 50% of all changed metabolites, and alterations of cholesterol and bile acids metabolites. The decrease of 3 phosphatidylcholine (PC) in plasma could indicate the occurrence of VOR - induced liver injury. Decreased fatty acids (FA) oxidation and bile acid excretion might be the potential mechanisms of VOR - induced liver injury. This study provided new insights into the molecular characterization of VOR - induced liver injury.

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

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

Summary Statement

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

Loss of Carnitine Palmitoyltransferase 1a Reduces Docosahexaenoic Acid-Containing Phospholipids and Drives Sexually Dimorphic Liver Disease in Mice

Background and Aims

Genome and epigenome wide association studies identified variants in carnitine palmitoyltransferase 1a (CPT1a) that associate with lipid traits. The goal of this study was to determine the impact by which liver-specific CPT1a deletion impacts hepatic lipid metabolism.

Approach and Results

Six-to-eight-week old male and female liver-specific knockout (LKO) and littermate controls were placed on a low-fat or high-fat diet (HFD; 60% kcal fat) for 15 weeks. Mice were necropsied after a 16 hour fast, and tissues were collected for lipidomics, matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI), kinome analysis, RNA-sequencing, and protein expression by immunoblotting. Female LKO mice had increased serum alanine aminotransferase (ALT) levels which were associated with greater deposition of hepatic lipids, while male mice were not affected by CPT1a deletion relative to male control mice. Mice with CPT1a deletion had reductions in DHA-containing phospholipids at the expense of monounsaturated fatty acids (MUFA)-containing phospholipids in both whole liver and at the level of the lipid droplet (LD). Male and female LKO mice increased RNA levels of genes involved in LD lipolysis ( Plin2 , Cidec , G0S2 ) and in polyunsaturated fatty acid (PUFA) metabolism ( Elovl5, Fads1, Elovl2 ), while only female LKO mice increased genes involved in inflammation ( Ly6d, Mmp12, Cxcl2 ). Kinase profiling showed decreased protein kinase A (PKA) activity, which coincided with increased PLIN2, PLIN5, and G0S2 protein levels and decreased triglyceride hydrolysis in LKO mice.

Conclusions

Liver-specific deletion of CPT1a promotes sexually dimorphic steatotic liver disease (SLD) in mice, and here we have identified new mechanisms by which females are protected from HFD-induced liver injury.

Graphical Summary